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1

FDM Simulation of an Anomalous Later Phase from the Japan Trench Subduction Zone Earthquakes  

NASA Astrophysics Data System (ADS)

We investigated the development of a distinct later phase observed at stations near the Japan Trench associated with shallow, outer-rise earthquakes off the coast of Sanriku, northern Japan based on the analysis of three-component broadband seismograms and FDM simulations of seismic wave propagation using a heterogeneous structural model of the Japan Trench subduction zone. Snapshots of seismic wave propagation obtained through these simulations clearly demonstrate the complicated seismic wavefield constructed by a coupling of the ocean acoustic waves and the Rayleigh waves propagating within seawater and below the sea bottom by multiple reflections associated with shallow subduction zone earthquakes. We demonstrated that the conversion to the Rayleigh wave from the coupled ocean acoustic waves and the Rayleigh wave as they propagate upward along the slope of seafloor near the coast is the primary cause of the arrival of the distinct later phase at the station near the coast. Through a sequence of simulations using different structural models of the Japan Trench subduction zone, we determined that the thick layer of seawater along the trench and the suddenly rising sea bottom onshore of the Japanese island are the major causes of the distinct later phase. The results of the present study indicate that for realistic modeling of seismic wave propagation from the subduction zone earthquakes, a high-resolution bathymetry model is very crucial, although most current simulations do not include a water column in their simulation models.

Noguchi, Shinako; Maeda, Takuto; Furumura, Takashi

2013-01-01

2

Seismic Structure of the Middle Japan Trench Subduction Zone by Airgun-OBS Experiment  

Microsoft Academic Search

In the middle part of the Japan trench subduction zone, the off-Miyagi area, large interplate earthquakes with M>7 is known to regularly recur with about 40 years interval. The most recent event occurred 25 years ago (the 1978 Miyagi-Oki earthquake M7.4) and the Japanese government evaluated that the next large earthquake may occur within 20 years from now with over

R. Hino; M. Nishino; K. Mochizuki; K. Uehira; T. Sato; M. Nakamura; S. Nakata; M. Shinohara; J. Kasahara

2003-01-01

3

Erosional Subduction Zone in the Northern Japan Trench: Review of Submersible Dive Reports  

Microsoft Academic Search

\\u000a Submersible studies of the oceanward and landward slopes of the northern Japan trench are reviewed, and the typical erosional\\u000a features of this subduction zone are discussed. On the oceanward slope, normal faults with tension cracks have created horst\\u000a and graben structures, forming a series of steps. On the landward slope, brecciated Miocene sedimentary rocks with calcite\\u000a veins and cement are

Yujiro Ogawa

4

Water supplement by silica diagenesis in cold subduction zone: an implication for the Japan Trench  

NASA Astrophysics Data System (ADS)

The fluid existing at plate interfaces in subduction zone makes a strong effect on seismicity and fault slip of the plate boundary megathrusts. As a source of the fluid, pore fluid included in subducting sedimentsand dehydration reaction of clay minerals have been discussed in detail, however, dewatering from siliceous sediments such as diatom and radiolarian ooze are poorly investigated in spite of their major occurrence in old oceanic plate. Silica in the siliceous sediment is transformed from amorphous silica into quartz via cristobalite phase (Opal A ? Opal CT ? Quartz) releasing structured water. In this study, we evaluate the amount of dehydration from siliceous sediment in subducting plate. Silica diagenesis and dehydration are calculated quantitatively introducing reaction kinetics (Mizutani, 1970) and temperature profile models of the Japan Trench, a cold type subduction zone where the siliceous sediments subduct in (Peacock and Wang, 1999; Wang and Suyehiro, 1999; Wada and Wang, 2009; Kimura et al., submitted). As a result, through this diagenetic conversion, structured water of silica minerals is released as much as 140g/m^2/year at shallow plate boundary (~13km depth below the sea floor), where the temperature is about ~100 -~120°C. This water should generate an excess pore pressure which drops effective stress and rock strength along the décollement. Dehydration of silica can play an important role in slip propagation to shallow portion of plate boundary as the Grate Tohoku Earthquake (9 March 2011).

Hina, S.; Hamada, Y.; Kameda, J.; Yamaguchi, A.; Kimura, G.

2011-12-01

5

Along-trench structural variation and seismic coupling in the northern Japan subduction zone  

NASA Astrophysics Data System (ADS)

Large destructive interplate earthquakes, such as the 2011 Mw 9.0 Tohoku-oki earthquake, have occurred repeatedly in the northern Japan subduction zone. The spatial distribution of large interplate earthquakes shows distinct along-trench variations, implying regional variations in interplate coupling. We conducted an extensive wide-angle seismic survey to elucidate the along-trench variation in the seismic structure of the forearc and to examine structural factors affecting the interplate coupling beneath the forearc mantle wedge. Seismic structure models derived from wide-angle traveltimes showed significant along-trench variation within the overlying plate. In a weakly coupled segment, (i) the sediment layer was thick and flat, (ii) the forearc upper crust was extremely thin, (iii) the forearc Moho was remarkably shallow (about 5 km), and (iv) the P-wave velocity within the forearc mantle wedge was low, whereas in the strongly coupled segments, opposite conditions were found. The good correlation between the seismic structure and the segmentation of the interplate coupling implies that variations in the forearc structure are closely related to those in the interplate coupling.

Fujie, G.; Miura, S.; Kodaira, S.; Kaneda, Y.; Shinohara, M.; Mochizuki, K.; Kanazawa, T.; Murai, Y.; Hino, R.; Sato, T.; Uehira, K.

2013-02-01

6

Geochemical and biogeochemical observations on the biological communities associated with fluid venting in Nankai Trough and Japan Trench subduction zones  

NASA Astrophysics Data System (ADS)

We have studied the compositions and structure of the lamellibranchia Calyptogena sp associated with fluid venting in subduction zones off Japan. The gills of the Calyptogena are the habitat of symbiotic bacteria which develop owing to chemoautotrophy. They most probably assimilate hydrogen sulfide, methane and/or carbon dioxide and reduce nitrogen. The isotopic budget of methane uptake enables to establish the thermal diagenetic origin of the light hydrocarbons brought by the upwelling fluids. The microscopic examination of thin sections of the bacteria enables to establish that their membranes are compatible with uptake of inorganic nutrients and to establish relations with the metabolism of archeobacteria.

Boulègue, J.; Benedetti, E. L.; Dron, D.; Mariotti, A.; Létolle, R.

1987-05-01

7

High-resolution seismic imaging in the Japan Trench axis area off Miyagi, northeastern Japan  

NASA Astrophysics Data System (ADS)

obtained high-resolution seismic data reveal the detailed structure of the Japan Trench axis off Miyagi, Japan, in the region of large shallow slip during the 11 March 2011 M9 Tohoku earthquake. Correlation of seismic images with previous drilling results identifies a possible basal chert-rich layer and hemipelagic/pelagic mudstones overlying igneous Pacific crust. Mapping of acoustic basement depicts the subduction of horst-and-graben topography. The basement and basal chert are subducted beneath a seismically chaotic frontal prism, but the majority of overlying hemipelagic mudstones is offscraped and imbricated at the trench axis as a result of plate boundary compression. A possible décollement is imaged as a seaward dipping reflection at landward part of the trench graben and was likely generated by loading and failure of underthrust sediments. Collectively, these analyses provide a structural framework for understanding sedimentary inputs and the localization of shallow plate boundary slip at the Japan Trench.

Nakamura, Yasuyuki; Kodaira, Shuichi; Miura, Seiichi; Regalla, Christine; Takahashi, Narumi

2013-05-01

8

A subduction zone reference frame based on slab geometry and subduction partitioning of plate motion and trench migration  

NASA Astrophysics Data System (ADS)

The geometry of subducted slabs that interact with the transition zone depends critically on the partitioning of the subduction velocity (vS$\\perp$) at the surface into its subducting plate motion component (vSP$\\perp$) and trench migration component (vT$\\perp$). Geodynamic models of progressive subduction demonstrate such dependence with five distinct slab geometries and corresponding partitioning ratios (vSP$\\perp$/vS$\\perp$): slab draping (vSP$\\perp$/vS$\\perp$ ? 0.5), slab draping with recumbent folds (0.5 < vSP$\\perp$/vS$\\perp$ < ˜0.8), slab piling (˜0.8 ? vSP$\\perp$/vS$\\perp$ ? ˜1.2), slab roll-over with recumbent folds (˜1.2 < vSP$\\perp$/vS$\\perp$ < ˜1.5) and slab roll-over (vSP$\\perp$/vS$\\perp$ ? ˜1.5). The model findings have been applied to subduction zones in nature with well-resolved slab geometries, for which subduction partitioning ratios have been calculated during the last 20 million years in two global reference frames: the Indo-Atlantic and Pacific hotspot reference frames. The model-nature comparison determines in which reference frame subduction partitioning ratios are most in agreement with observed slab geometries. In the Indo-Atlantic frame, five (out of five) selected subduction zone segments with well-resolved slab geometries, plate velocities and trench velocities (Japan, Izu-Bonin, Mariana, Tonga, Kermadec) agree with the geodynamic model predictions, as calculated subduction partitioning ratios match the observed slab geometries. In the Pacific frame the partitioning ratio of only one subduction zone segment (Izu-Bonin) matches observations. It is thus concluded that the Indo-Atlantic hotspot reference frame is preferred over the Pacific one as a subduction zone reference frame in which to describe plate motions, subduction kinematics and mantle flow.

Schellart, W. P.

2011-08-01

9

Oblique convergence and deformation along the Kuril and Japan trenches  

Microsoft Academic Search

The hypothesis that present-day deformation within the southern Kuril forearc is driven by oblique subduction of the Pacific plate is tested using 397 horizontal slip directions derived from shallow-thrust earthquakes from the Kuril and Japan trenches for the period 1963-1991. A simple two-plate model fits the 397 slip vectors significantly worse than a model that permits strike-slip motion of the

Charles Demets

1992-01-01

10

Oblique convergence and deformation along the Kuril and Japan trenches  

NASA Astrophysics Data System (ADS)

The hypothesis that present-day deformation within the southern Kuril forearc is driven by oblique subduction of the Pacific plate is tested using 397 horizontal slip directions derived from shallow-thrust earthquakes from the Kuril and Japan trenches for the period 1963-1991. A simple two-plate model fits the 397 slip vectors significantly worse than a model that permits strike-slip motion of the southern Kuril forearc relative to the overlying plate. Weighted, mean slip directions along the southern Kuril trench are systematically rotated toward the direction orthogonal to the trench, which implies that the net convergence is partitioned into less oblique subduction and trench-parallel displacement of the southern Kuril forearc. The angular discrepancy between the observed slip direction and the direction predicted by the NUVEL-1 Pacific-North America Euler vector implies that the southern Kuril forearc translates 6-11 mm/yr to the southwest relative to the overlying North American plate. These results are consistent with geologically, geodetically, and seismologically observed convergence at the leading edge of the forearc sliver in southern Kokkaido and with previously inferred extension at the trailing edge of the sliver, which is located at the Bussol Strait at 46 deg N.

Demets, Charles

1992-11-01

11

Rapid Weakening of Subducting Plates From Trench-Parallel Estimates of Flexural Rigidity  

NASA Astrophysics Data System (ADS)

The percentage of slab pull force transmitted from the slab to the subducting plate depends on the slab strength (e.g., Conrad and Hager, 2001). Slab strength has been studied in the context of plate bending within subduction zones for a wide range of rheologies (i.e., perfectly elastic, perfectly viscous, perfectly plastic, layered brittle-ductile layered), but applicability of these rheologic models cannot be distinguished based on trench-perpendicular plate bending models alone (Forsyth, 1980). Consequently, a method was developed to directly measure variations in plate strength with distance from the trench and has found significant plate weakening within 100 km of the Kermadec trench (Billen and Gurnis, 2005). Using the same method we show that rapid plate weakening trenchward of the forebulge also exists at the Tonga and Japan-Izu-Bonin subduction zones within 100 km of the trench. The observed plate weakening provides further evidence for a plate rheology that leads to significant lithospheric-scale yielding (loss of elastic strength and reduction in effective viscosity) within the bending region of the subducting plate. This rapid weakening within the shallow, low curvature, region of the plate may significantly decrease energy dissipation related to plate bending compared to past calculations that assume constant strength, plate thickness and plate curvature. While a decrease in bending energy dissipation would provide more energy for slab pull, lithospheric plate weakening may decrease transmission to the subducting plate. Additionally, the high degree of lithospheric weakening suggests that plate age has a weaker influence on slab strength and energy dissipation then previously believed, as very old oceanic lithosphere weakens to effective elastic thickness predicted for relatively young plates. Billen, M. I., Gurnis, H.A., 2005. Constraints on subducting plate strength within the Kermadec trench. J. Geophys. Res. 110, B05407, doi:10.1029/2004JB003308. Conrad, C.P., Hager, B.H., 2001. Mantle convection with strong subduction zones. Geophys. J. Int. 144 (2), 271-288. Forsyth, D.W., 1980. Comparison of mechanical models of oceanic lithosphere. J. Geophys. Res. 85, 6364-6368.

Arredondo, K.; Billen, M. I.

2011-12-01

12

En echelon patterns of Calyptogena colonies in the Japan Trench  

NASA Astrophysics Data System (ADS)

The distribution of Calyptogena phaseoliformis colonies in right-stepping en echelon patterns was observed by the Japanese submersible Shinkai 6500 at the foot of the landward escarpment of the northern Japan Trench at around 6437 6274 m depth. The north-south trending Sanriku Escarpment has a thrust origin and is subparallel to the trench axis along which the Pacific plate is being subducted beneath the North America or Okhotsk plate at about 300° at a rate of about 7.8 to 8.3 cm/yr. The trends of colonies are concentrated at 250°, 300°, and 330°: each trend matches either an antithetic riedel shear, extension fracture, or synthetic riedel shear, respectively, within a left-lateral shear regime caused by the oblique subduction. Methane- and hydrogen sulfide bearing fluid advection from depth occurs essentially along the thrust fault, but finally seeps along the fractures at the sea floor. This supplies energy to the food chain through bacteria utilizing hydrogen sulfide, then eventually sustains the Calyptogena colonies. Because the clams select the best places to survive, the geometric arrangement of the clam colonies provides a kinematic indicator of relative plate motions.

Ogawa, Yujiro; Fujioka, Kantaro; Fujikura, Katsunori; Iwabuchi, Yo

1996-09-01

13

Morphology of the distorted subducted Pacific slab beneath the Hokkaido corner, Japan  

Microsoft Academic Search

The intersection of the Japan and Kurile arcs is expressed as a cuspate feature at the trench, a bend in the Japanese islands, and a complex lithospheric structure and is known as the Hokkaido corner. The Pacific plate is subducting beneath the two arcs in the northwest Pacific at different velocities, which has resulted in an arc–arc collision and distortion

M. S. Miller; B. L. N. Kennett; A. Gorbatov

2006-01-01

14

Two-dimensional viscosity structure of the northeastern Japan islands arc-trench system  

NASA Astrophysics Data System (ADS)

Two-dimensional viscosity profiles were constructed for the northeastern Japan islands arc-trench system covering the source area of the 2011 Tohoku-Oki earthquake. From seismologically determined models of lithospheric structure, experimentally derived constitutive laws of various rocks, and densely measured geothermal gradient data, we have predicted the steady state effective viscosity across the subduction zone. The profile reveals strong lateral viscosity gradients both parallel and normal to the trench axis. The detailed viscosity structures presented here contribute to accurate evaluation of viscoelastic relaxation components when modeling geodetically measured postseismic deformation at high spatial and temporal resolution.

Muto, Jun; Shibazaki, Bunichiro; Ito, Yoshihiro; Iinuma, Takeshi; Ohzono, Mako; Matsumoto, Takumi; Okada, Tomomi

2013-09-01

15

Heat-flow determination in three DSDP boreholes near the Japan trench  

SciTech Connect

The first deep borehole determinations of temperature gradients and heat flow of the landward wall of the Japan Trench and forearc were made on IPOD DSDP leg 57. These heat flow values are based on temperature logs corrected to equilibrium, using a detailed model of the drilling disturbance. Heat flow values on a deeply submerged terrace, landward of the trench slope break are 28 and 32 mW m/sup -2/. A measurement in the midslope terrace basin on the landward wall of the trench yielded a value of 22 mW m/sup -2/. The results are in good agreement with earlier seafloor measurements and indicate that most of the forearc area is characterized by heat flow about one half of that over oceanic lithosphere seaward of the trench. Our observations indicate only a small increase of heat flow from the trench to the volcanic arc, in agreement with thermal models, which suggests that the subduction of the relatively cold oceanic plate continues to dominate the temperature structure for distances of up to 250 km landward of the trench. The temperature profile in the borehole on the midslope terrace indicates possible vertical flow of pore waters. Hundreds of conductivity determinations were made using a new technique.

Burch, T.K.; Langseth, M.G.

1981-10-10

16

Heat-flow determination in three DSDP boreholes near the Japan Trench  

NASA Astrophysics Data System (ADS)

The first deep borehole determinations of temperature gradients and heat flow on the landward wall of the Japan Trench and forearc were made on IPOD DSDP leg 57. These heat flow values are based on temperature logs corrected to equilibrium, using a detailed model of the drilling disturbance. Heat flow values on a deeply submerged marine terrace, landward of the trench slope break are 28 and 32 mW m-2. A measurement in the midslope terrace basin on the landward wall of the trench yielded a value of 22 mW m-2. The results are in good agreement with earlier seafloor measurements and indicate that most of the forearc area is characterized by heat flow about one half of that over oceanic lithosphere seaward of the trench. Our observations indicate only a small increase of heat flow from the trench to the volcanic arc, in agreement with thermal models, which suggests that the subduction of the relatively cold oceanic plate continues to dominate the temperature structure for distances of up to 250 km landward of the trench. The temperature profile in the borehole on the midslope terrace indicates possible vertical flow of pore waters. Hundreds of conductivity determinations were made using a new technique.

Burch, Thomas K.; Langseth, Marcus G.

1981-10-01

17

Seamount subduction changes hydrogeology to form chemosynthetic community-Finding of a huge community at the Cadet seamount, Kuril Trench-  

NASA Astrophysics Data System (ADS)

Huge chemosynthetic animal communities with carbonate chimneys and bacterial mats were found on the southern slope of the Cadet Seamount, a subducted seamount which was found in 1984 by the SeaBeam mapping at the southern end of the Kuril Trench forearc. We had three dives at depth range from 5340m to 4050m by submersible Shinkai 6500 in June 2002. Multi-channel Seismic profile line HK103 across the Erimo and Cadet seamounts indicate two strong and two weak landward dipping steep reflectors along the southern slope of the Cadet seamount. Two strong reflectors may correspond to sandy layer or highly deformed mud layers with large shear zone. However another line 101 across the normal Kuril Trench shows monotonous seaward dipping reflectors just like Japan Trench forearc. Chemosynthetic communities exist at depths from 5275m to 4490m with barren interval from 5200m to 4983m. Dense distribution of clam communities is existed at the depths about 5275m and 4675m. Sediments we observed along the dive tracks were highly deformed mudstone partly coarse sandstone with intercalated ash layers. They show the perfect EW trending stratification with about 20 degree landward dipping. Distribution of clams and stratification of sandstones and mudstones are well correlated to the seismic profile record across the Cadet seamount. We propose here the following model for the distribution of animal community. About 300,000 years ago Cadet seamount reached the Kuril Trench then started to subduct. Permeable layers in the front of the seamount pushed up gradually to form steep layers with deformation. The origin of fluid to sustain the community is estimated to be the interstitial water in the permeable layers. So the seamount subduction may change the hydrogeology of the tow area to offer the best place for chemosynthetic animal community.

Fujioka, K.; Sato, T.; Miwa, T.; Tsuru, T.; Kido, Y.; Nakanishi, A.; Kato, C.

2002-12-01

18

Examining Stress Changes Due to Subducting Topography and Variable Rheology in the Middle America Trench at Nicoya Gulf, Costa Rica  

Microsoft Academic Search

Offshore of the Nicoya Gulf at the Middle America Trench, the Cocos Plate is subducting beneath the Caribbean plate at about 84 mm per year. A line of seamounts are entering the trench in this region, causing dramatic deformation of the seafloor landward of the thrust. It has been suggested that these seamounts are being subducted, causing coastal uplift and

C. E. Elliott; S. L. Bilek; C. Lithgow-Bertelloni

2007-01-01

19

Trench-parallel flow and seismic anisotropy in the Mariana and Andean subduction systems.  

PubMed

Shear-wave splitting measurements above the mantle wedge of the Mariana and southern Andean subduction zones show trench-parallel seismically fast directions close to the trench and abrupt rotations to trench-perpendicular anisotropy in the back arc. These patterns of seismic anisotropy may be caused by three-dimensional flow associated with along-strike variations in slab geometry. The Mariana and Andean subduction systems are associated with the largest along-strike variations of slab geometry observed on Earth and are ideal for testing the link between slab geometry and solid-state creep processes in the mantle. Here we show, with fully three-dimensional non-newtonian subduction zone models, that the strong curvature of the Mariana slab and the transition to shallow slab dip in the Southern Andes give rise to strong trench-parallel stretching in the warm-arc and warm-back-arc mantle and to abrupt rotations in stretching directions that are accompanied by strong trench-parallel stretching. These models show that the patterns of shear-wave splitting observed in the Mariana and southern Andean systems may be caused by significant three-dimensional flow induced by along-strike variations in slab geometry. PMID:18097407

Kneller, Erik A; van Keken, Peter E

2007-12-20

20

A New View on the Space-Time Pattern of Great or Large Earthquakes along the Northern Japan to Southern Kurile Trenches  

Microsoft Academic Search

The northern Japan to southern Kurile trenches have been regarded as a typical subduction zone with spatially and temporally regular recurrence of great interplate earthquakes. The source regions had been divided into six segments, named A to F from SW to NE (Utsu, 1972; 1984), on the basis of great interplate events during an active period from 1952 to 1973.

T. Harada; K. Satake; K. Ishibashi

2010-01-01

21

Upper plate controls on deep subduction, trench migrations and deformations at convergent margins  

NASA Astrophysics Data System (ADS)

Thus far, relatively simplistic models of free subduction, in which the trench and plate motions are emergent features completely driven by the negative buoyancy of the slab, have investigated the dynamics of a single, isolated subducting plate. Here we extend such models to incorporate an overriding plate and present the results of how such an overriding plate feedbacks into the dynamics of free subduction. In this study, we address three fundamental aspects of these dynamics: 1) how does the presence of an overriding plate change the force balance at the convergent margins? 2) How are the forces from deep subduction propagated to the surface? And 3) what controls the stress regime in a system of coupled upper and subducting plates and how is it expressed in the deformations and plate motions? In general, we find that the evolution of subduction zones is strongly controlled by both the interactions between the slab and the upper-lower mantle discontinuity as well as the strength of the upper plate. When either the subducting or upper plates are unable to move, subduction motions are steady-state and partitioned entirely into either slab rollback or plate advance, respectively. When conditions favour a quasi-stationary trench, subducted lithosphere can form into a pile with multiple recumbent folds of slab material atop the lower mantle. Alternating between forwards- and backwards-draping slab, the corresponding horizontal trench motions at the surface are frontward and rearward, respectively, resulting in either a compressive or extensional regime in the back-arc. Time-dependent forcing arising from the slab piling behaviour can have a feedback with upper plate and produce strongly non-steady state, intermittent phases of upper plate deformation as those commonly observed on Earth. Two types of discontinuous back-arc strain evolution are identified: (1) periodic, when recurrent phases of strain over finite durations are accommodated by (viscous) stretching/thickening of the plate, and (2) episodic, when upper plate deformation localizes (plastic strain) and allows for punctuated episodes. These phases can include extension, quiescence, and compression, giving rise to a large variety of possible tectonic evolutions. The models presented here provide insight into the dynamics behind the non-steady state evolution of subduction, which can help unravel seemingly erratic motions of major convergent margins and back-arc deformations around the Pacific and Indian Oceans during the Cenozoic.

Sharples, W.; Capitanio, F. A.; Stegman, D.; Moresi, L. N.

2009-12-01

22

Effects of mantle and subduction-interface rheologies on slab stagnation and trench rollback  

NASA Astrophysics Data System (ADS)

Trench rollback has been a widely discussed phenomenon in recent years, and multiple studies have concentrated on various parameters that may influence trench migration and related aspects of slab deformation in the (upper) mantle. Here we concentrate on the effects of rheological description (yield stress, lower-mantle viscosity, viscosity of crust) in controlling the rollback and associated stagnation of slabs in the transition zone (410–660 km depth). We perform numerical simulations of slab evolution in a 2D Cartesian model with strongly nonlinear rheology combining diffusion creep, dislocation creep and a power-law stress limiter. We demonstrate that trench retreat develops in most models considered, regardless of the subducting plate age or prescribed strength. Rollback then mostly produces slabs that are horizontally deflected at the 660-km phase boundary and remain subhorizontal at the bottom of the transition zone. Slab morphologies are in agreement with stagnant, horizontally deflected structures reported in the transition zone by seismic tomography. Furthermore, if the strength of the slab is limited to less than 0.5 GPa, the slab experiences a significant amount of horizontal buckling. The amplitude of the rollback velocity is sensitive to several model parameters. As one might expect, it increases with the age of the subducting plate, thus reflecting its increasingly negative buoyancy. On the other hand, rollback velocity decreases if we increase the viscosity of the crust and thereby strengthen the coupling between the subducting and overriding plates. High friction on the contact between the subducting and overriding plates may even result in slabs penetrating into the lower mantle after a period of temporary stagnation. Also, reducing the additional negative buoyancy imparted by the 410-km exothermic phase transition suppresses trench rollback. Interpretation of the controls on slab rollback and stagnation may be rather complex in strongly nonlinear rheological models, where, for example, buoyancy effects may be counteracted by associated yield-stress weakening.

?ížková, Hana; Bina, Craig R.

2013-10-01

23

Neogene evolution of lower trench-slope basins and wedge development in the central Hikurangi subduction margin, New Zealand  

NASA Astrophysics Data System (ADS)

Detailed analysis of the stratigraphic architecture and deformation of lower trench-slope sedimentary basins permits the tectonic evolution of subduction margins to be constrained. This study utilises offshore seismic reflection profiles and onshore outcrop data to examine the entire lower trench-slope of the Hikurangi subduction margin in the eastern North Island, New Zealand. Our results constrain the main spatial and temporal changes of facies and sedimentary units since about 25 Ma. We demonstrate that the geometries and locations of Miocene to Quaternary sedimentary basins are controlled by tectonic activity and reflect stages of subduction wedge development.

Bailleul, Julien; Chanier, Frank; Ferrière, Jacky; Robin, Cécile; Nicol, Andrew; Mahieux, Geoffroy; Gorini, Christian; Caron, Vincent

2013-04-01

24

Alteration of the subducting oceanic lithosphere at the southern central Chile trench-outer rise  

NASA Astrophysics Data System (ADS)

Hydrothermal circulation and brittle faulting processes affecting the oceanic lithosphere are usually confined to the upper crust for oceanic lithosphere created at intermediate to fast spreading rates. Lower crust and mantle rocks are therefore relatively dry and undeformed. However, recent studies at subduction zones suggest that hydration of the oceanic plate is most vigorous at the trench-outer rise, where extensional bending-related faulting affects the hydrogeology of the oceanic crust and mantle. To understand the degree of hydration, we studied the seismic velocity structure of the incoming Nazca plate offshore of southern central Chile (˜43°S); here the deep-sea trench is heavily filled with up to 2 km of sediments. Seismic refraction and wide-angle data, complemented by seismic reflection imaging of sediments, are used to derive a two-dimensional velocity model using joint refraction and reflection traveltime tomography. The seismic profile runs perpendicular to the spreading ridge and trench axes. The velocity model derived from the tomography inversion consists of a ˜5.3-km-thick oceanic crust and shows P wave velocities typical for mature fast spreading crust in the seaward section of the profile, with uppermost mantle velocities as fast as ˜8.3 km/s. Approaching the Chile trench, seismic velocities are significantly reduced, however, suggesting that the structures of both the oceanic crust and uppermost mantle have been altered, possibly due to a certain degree of fracturing and hydration. The decrease of the velocities roughly starts at the outer rise, ˜120 km from the deformation front, and continues into the trench. Even though the trench is filled with sediment, basement outcrops in the outer rise frequently pierce the sedimentary blanket. Anomalously low heat flow values near outcropping basement highs indicate an efficient inflow of cold seawater into the oceanic crust. Hydration and crustal cracks activated by extensional bending-related faulting are suggested to govern the reduced velocities in the vicinity of the trench. Considering typical flow distances of 50 km, water might be redistributed over most of the trench-outer rise area. Where trapped in faults, seawater may migrate down to mantle depth, causing up to ˜9% of serpentinization in at least the uppermost ˜2 km of the mantle between the outer rise and the trench axis.

Contreras-Reyes, Eduardo; Grevemeyer, Ingo; Flueh, Ernst R.; Scherwath, Martin; Heesemann, Martin

2007-07-01

25

Tectonic Settings of Great Outer-Rise\\/Outer-Trench-Slope (OR\\/OTS) Earthquakes in the Instrumental Record  

Microsoft Academic Search

Great off-trench earthquakes in subduction zones are rare in the instrumental seismic record. Only five, or possibly six such events are presently known or suspected (2 May 1917 in vicinity of Kermadec Trench; 26 June 1917 in vicinity of Tonga Trench; 2 March 1933 in Sanriku, Japan under outer-trench slope; 19 August 1977 near the Sunda Trench off Sumbawa Island,

S. H. Kirby; R. Hino; E. L. Geist; D. J. Wright; E. Okal; J. M. Wartman

2009-01-01

26

Nonvolcanic Deep Tremor Associated with Subduction in Southwest Japan  

Microsoft Academic Search

Deep long-period tremors were recognized and located in a nonvolcanic region in southwest Japan. Epicenters of the tremors were distributed along the strike of the subducting Philippine Sea plate over a length of 600 kilometers. The depth of the tremors averaged about 30 kilometers, near the Mohorovic discontinuity. Each tremor lasted for at most a few weeks. The location of

Kazushige Obara

2002-01-01

27

Crustal structure and deformation associated with seamount subduction at the north Manila Trench represented by analog and gravity modeling  

NASA Astrophysics Data System (ADS)

We investigated the deformation in the accretionary wedge associated with subducted seamounts in the northern Manila Trench by combining observations from seismic profiles and results from laboratory sandbox experiments. From three seismic reflection profiles oriented approximately perpendicular to the trench, we observed apparent variations in structural deformation along the trench. A number of back-thrust faults were formed in the accretionary wedge where subducted seamounts were identified. In contrast, observable back-thrusts were quite rare along the profile without seamounts, indicating that seamount subduction played an important role in deformation of the accretionary wedge. We then conducted laboratory sandbox experiments to investigate the effects of subducted seamounts on the structural deformation of the accretionary wedge. From the analog modeling results we found that seamount subduction could cause well-developed back-thrusts, gravitational collapse, and micro-fractures in the wedge. We also found that a seamount may induce normal faults in the wedge and that normal faults may be eroded by subsequent seamount subduction. In addition, we constrained the crustal structure of the South China Sea plate from modeling free-air gravity data. The dip angle of the subducting plate, which was constrained by hypocenters of available earthquakes, increased from south to north in the northern Manila Trench. We found a laterally heterogeneous density distribution of the oceanic crust according to the gravity data. The density of subducted crust is ~2.92 g/cm3, larger than that of the South China Sea crust (2.88 g/cm3).

Li, Fucheng; Sun, Zhen; Hu, Dengke; Wang, Zhangwen

2013-09-01

28

Relationship between subduction and seismicity in the Mexican part of the Middle America trench  

NASA Astrophysics Data System (ADS)

Two catalogs of earthquakes in the Mexican part of the Middle America trench are analyzed to elucidate principal relations between structure of the subducting Cocos plate and seismicity. A catalog of historical events that have occurred during the last two centuries with large magnitudes (M(sub s) greater than 6.0) is used to obtain cumulative seismic moment (M(sub 0) and seismic moment release rate (dot-M(sub 0)) distributions along the Mexican subduction zone. The catalog of instrumentally observed earthquakes from 1963 to 1990 (International Seismological Center and U.S. Geological Survey) with 4.5 less than or equal to M(sub b) less than 6.0 is applied to investigate background seismicity for the region. The strength of coupling between the Cocos and North American plates would be expected to grow gradually from the southeast to the northwest according to the variation of convergence rate (V) and age (A) of the Cocos plate. This correlates in general with a steady reduction in background seismicity and a slight average increase of M(sub 0) and seismic energy release rate (dot-W). At sites where the main fracture zones of the Cocos plate; Tehuantepec, O'Gorman, Orozco and Rivera, undergo the subduction the general correlation breaks down. The background seismicity increases at fracture zones while M(sub 0) and (dot-M(sub 0)) decrease significantly. This feature is interpreted as a drop of the coupling at the areas where transform faults are being subducted. Seismic slip rates along the trench obtained from M(sub 0) are lower than the values of plate convergence rates but the avarage seismic slip is in agreement with the estimates from the V model (interaction between lithospheric plates at convergent zones through the viscous layer of subducted sediments). Variability of (dot M(sub 0))and seismic slip rate in relation with tectonics should be taken into account when the seismic gap model is being used for the prediction of strong earthquakes. An examination of space-time plots for the historical catalogs supposes a probable tendency of northwest migration of strong events with a rate of approximately equals 10 km/yr.

Kostoglodov, Vladimir; Ponce, Lautaro

1994-01-01

29

The potential influence of subduction zone polarity on overriding plate deformation, trench migration and slab dip angle  

NASA Astrophysics Data System (ADS)

A geodynamic model exists, the westward lithospheric drift model, in which the variety of overriding plate deformation, trench migration and slab dip angles is explained by the polarity of subduction zones. The model predicts overriding plate extension, a fixed trench and a steep slab dip for westward-dipping subduction zones (e.g. Mariana) and predicts overriding plate shortening, oceanward trench retreat and a gentle slab dip for east to northeastward-dipping subduction zones (e.g. Chile). This paper investigates these predictions quantitatively with a global subduction zone analysis. The results show overriding plate extension for all dip directions (azimuth ? = - 180° to 180°) and overriding plate shortening for dip directions with ? = - 90° to 110°. The wide scatter in data negate any obvious trend and only local mean values in overriding plate deformation rate indicate that overriding plate extension is somewhat more prevalent for west-dipping slabs. West-dipping subduction zones are never fixed, irrespective of the choice of reference frame, while east to northeast-dipping subduction zones are both retreating and advancing in five out of seven global reference frames. In addition, westward-dipping subduction zones have a range in trench-migration velocities that is twice the magnitude of that for east to northeastward-dipping slabs. Finally, there is no recognizable correlation between slab dip direction and slab dip angle. East to northeast-dipping slabs (? = 30° to 120°) have shallow (0 125 km) slab dip angles in the range 10 60° and deep (125 670 km) slab dip angles in the range 40 82°, while west-dipping slabs (? = - 60° to - 120°) have shallow slab dip angles in the range 19 50° and deep slab dip angles in the range 25 86°. Local mean deep slab dip angles are nearly identical for east and west-dipping slabs, while local mean shallow slab dip angles are lower by only 4.7 8.1° for east to northeast-dipping slabs. It is thus concluded that overall, there is no observational basis to support the three predictions made by the westward drift model, and for some sub-predictions the observational basis is very weak at most. Alternative models, which incorporate and underline the importance of slab buoyancy-driven trench migration, slab width and overriding plate motion, are better candidates to explain the complexity of subduction zones, including the variety in trench-migration velocities, overriding plate deformation and slab dip angles.

Schellart, W. P.

2007-12-01

30

Pore pressure evolution at the plate interface along the Cascadia subduction zone from the trench to the ETS transition zone  

Microsoft Academic Search

Pore fluid pressures in subduction zones are a primary control on fault strength and slip dynamics. Numerous studies document elevated pore pressures in the outer wedge along several margins. Seismic observations and the occurrence of non-volcanic tremor provide additional evidence for the presence of near-lithostatic pore pressures at the plate interface far down-dip from the trench (~35 km depth). Here

R. M. Skarbek; A. W. Rempel; D. A. Schmidt

2010-01-01

31

Supercycles along the Japan Trench and Foreseeability of the 2011 Tohoku Earthquake  

NASA Astrophysics Data System (ADS)

The devastating Tohoku earthquake of magnitude (M) 9.0 occurred on 11 March 2011 UTC along the Japan trench, where the Pacific plate is subducting beneath the Tohoku district. The national program of seismic hazard assessment, which was initiated by the Japanese government after the 1995 Kobe earthquake, failed to foresee this earthquake, because no supercycle of megathrust events had been identified along the Japan trench. For example, the program identified a regular cycle of six M7 to 8 characteristic earthquakes in the land side of the Miyagi-oki region, and only reported the high probability of having another M7 earthquake there. The Japanese government also built nation-wide dense arrays of seismometers and GPS receivers after the Kobe earthquake. Nishimura et al. recovered annual rates of back slip, which is the drag of the overriding plate by interplate coupling, using GPS data during a calm period before the Tohoku earthquake. We then recovered coseismic slips through a joint inversion of ground motion and GPS data during the earthquake. The distributions of recovered coseismic slips and back slip rates bear a close resemblance to each other. An area of large back slip rate was previously thought to be related to a regular cycle of characteristic earthquakes. However, our result demonstrates that the area is related to a supercycle of megathrust earthquakes. From the coseismic slips and back slip rates in the Miyagi-oki region, we calculated the coseismic moment release and moment accumulation rate of the Tohoku earthquake to be 143 x 10**20 Nm and 0.434 x 10**20 Nm/year, respectively. Since characteristic earthquakes occasionally release some part of accumulated seismic moment, those in the Miyagi-oki region were compiled. We then calculated the moment releases by them to be 47 x 10**20 Nm. These moment releases and accumulation rate lead to a supercycle period of 438 years. However, this period is too short, if the 869 Jogan earthquake is the only documented event to have occurred with a possible magnitude and location similar to that of the Tohoku earthquake. Within the compilation, the 1611 Keicho earthquake can be a hidden candidate between the 869 Jogan and 2011 Tohoku earthquakes. Extensive tsunami damage caused by this earthquake was documented over the Tohoku district. The time series, which was drawn using the moment releases and accumulation rate, is mostly controlled by the moment releases of megathrust earthquakes. Supercycles were found in the Mentawai region along the Sunda trench, but the rupture pattern of two large earthquakes in 2007 does not completely coincide with the back slip distribution. Similar disagreement was also found for the 2010 Maule earthquake in the Chilean subduction zone. These imply that they are not megathrust earthquakes of supercycles. Therefore, we cannot foresee characteristic earthquakes in regular cycles using a back slip distribution, but the 2011 Tohoku earthquake could be foreseen with respect to at least its location and extent, if we monitored GPS array data considering their relation to megathrust earthquakes of supercycles.

Koketsu, K.; Yokota, Y.

2011-12-01

32

Subduction of the South China Sea ridge along the Manila trench : implication for the localisation of the Philippine Fault in north Luzon, Philippines  

Microsoft Academic Search

The Philippine Sea Plate is converging obliquely towards the Sunda block along the Philippine archipelago. In the central and southern Philippines, this motion is mainly absorbed along the Philippine trench to the east and the left-lateral Philippine Fault. Further north, the convergence is transferred to the west to the Manila trench, along which the South China Sea is subducted. The

A. Loevenbruck; X. Le Pichon; M. Pubellier

2003-01-01

33

Shear strength of sediments approaching subduction in the Nankai Trough, Japan as constraints on forearc mechanics  

NASA Astrophysics Data System (ADS)

The mechanical behavior of the plate boundary fault zone is of paramount importance in subduction zones, because it controls megathrust earthquake nucleation and propagation as well as the structural style of the forearc. In the Nankai area along the NanTroSEIZE (Kumano) drilling transect offshore SW Japan, a heterogeneous sedimentary sequence overlying the oceanic crust enters the subduction zone. In order to predict how variations in lithology, and thus mechanical properties, affect the formation and evolution of the plate boundary fault, we conducted laboratory tests measuring the shear strengths of sediments approaching the trench covering each major lithological sedimentary unit. We observe that shear strength increases nonlinearly with depth, such that the (apparent) coefficient of friction decreases. In combination with a critical taper analysis, the results imply that the plate boundary position is located on the main frontal thrust. Further landward, the plate boundary is expected to step down into progressively lower stratigraphic units, assisted by moderately elevated pore pressures. As seismogenic depths are approached, the décollement may further step down to lower volcaniclastic or pelagic strata but this requires specific overpressure conditions. High-taper angle and elevated strengths in the toe region may be local features restricted to the Kumano transect.

Ikari, Matt J.; Hüpers, Andre; Kopf, Achim J.

2013-08-01

34

Improvement of the GPS/A system for extensive observation along subduction zones around Japan  

NASA Astrophysics Data System (ADS)

The M9.0 earthquake in March 2011 along the Japan Trench off Tohoku has elucidated that it is crucial to geodetically observe seismic coupling on the subduction plate boundary, and that the most important observation that should be strengthened is seafloor geodetic observation, especially on the deep seafloor near the trench axis. Repeated observation of GPS/Acoustic (GPS/A) seafloor positioning is the most probable way to cope with the requirement. The observation is urgent along the Japan Trench to analyze how the stress was accumulated that caused the giant earthquake. It is also important along the Nankai Trough off southwestern Japan where another giant earthquake can be being prepared. These surveys will aim at mapping of seismic coupling, and GPS/A observation points should be extended to be arrays in focused areas. On the other hand, ship time for the surveys will remain limited. Extensive geodetic observation along the subduction zones around Japan will not be attained without improvement in GPS/A observation systems. The first step that we are planning is common use of seafloor instruments. In Japan, mainly three groups are engaged in seafloor geodetic measurement by means of GPS/Acoustic technique with their own type of instruments. This has prevented us to conduct mutual surveys to each other, which would become crucial when number of survey sites increases in the future. A precision acoustic transponder (PXP) is a mirror transponder, which returns a received signal without any change after a fixed delay. Considering that different PXPs have intrinsically similar operational principle, we plan to develop PXPs which can be used in common. Then there will be more chance of repeated observations and evaluation of the observed results. A joint observation will An AUV (autonomous underwater vehicle) or an auto-navigation buoy can be an alternative of a survey ship. Asada and Ura (2005) have investigated a GPS/A observation system by using an AUV. Extending surveys into the deeper ocean to cover the wide range of possible rupture area is another important item to be carried out. Our current sites lie on the seafloor shallower than 3500 m. However, the 2011 Tohoku-oki earthquake revealed that the rupture area extended close to the trench, where depth ranges 5000 to 7000 m. Observation of tectonic motion of the incoming plate which is under deep sea is another target of seafloor geodesy. GPS/A observation on such a deep seafloor was technically confirmed (Osada et al., 2003, EPS), but there has been no report on repeated seafloor positioning. We plan to extend the depth range of GPS/A observation by optimizing threshold of responding level of the PXPs as well as increasing its power. Assessment of the application needs careful offshore test.

Fujimoto, H.; Kido, M.; Tadokoro, K.; Sato, M.; Ishikawa, T.; Asada, A.; Mochizuki, M.

2011-12-01

35

Coseismic Slip Distributions of Great or Large Earthquakes in the Northern Japan to Kurile Subduction Zone  

NASA Astrophysics Data System (ADS)

Slip distributions of great and large earthquakes since 1963 along the northern Japan and Kuril trenches are examined to study the recurrence of interplate, intraslab and outer-rise earthquakes. The main findings are that the large earthquakes in 1991 and 1995 reruptured the 1963 great Urup earthquake source, and the 2006, 2007 and 2009 Simshir earthquakes were all different types. We also identify three seismic gaps. The northern Japan to southern Kurile trenches have been regarded as a typical subduction zone with spatially and temporally regular recurrence of great (M>8) interplate earthquakes. The source regions were grouped into six segments by Utsu (1972; 1984). The Headquarters for Earthquake Research Promotion of the Japanese government (2004) divided the southern Kurile subduction zone into four regions and evaluated future probabilities of great interplate earthquakes. Besides great interplate events, however, many large (M>7) interplate, intraslab, outer-rise and tsunami earthquakes have also occurred in this region. Harada, Ishibashi, and Satake (2010, 2011) depicted the space-time pattern of M>7 earthquakes along the northern Japan to Kuril trench, based on the relocated mainshock-aftershock distributions of all types of earthquakes occurred since 1913. The space-time pattern is more complex than that had been considered conventionally. Each region has been ruptured by a M8-class interplate earthquake or by multiple M7-class events. In this study, in order to examine more detail space pattern, or rupture areas, of M>7 earthquakes since 1963 (WWSSN waveform data have been available since this year), we estimated cosiesmic slip distributions by the Kikuchi and Kanamori's (2003) teleseismic body wave inversion method. The WWSSN waveform data were used for earthquakes before 1990, and digital teleseismic waveform data compiled by the IRIS were used for events after 1990. Main-shock hypocenters that had been relocated by our previous study were used as initial rupture points. Some preliminary results are as follows. Offshore Urup Is. is source region of the 1963 Urup earthquake (M 8.5). Large interplate earthquakes occurred in the eastern and western part of the 1963 source region in 1991 (M 7.6) and 1995 (M 7.9), respectively. Their aftershock areas almost re-occupied the 1963 aftershock area. The 1963, 1991, and 1995 coseismic slip distributions show that the southwestern asperity of the 1963 event seems to be re-ruptured by the 1995 earthquake. The 2009 Simushir earthquake (M 7.4) with reverse faulting occurred within the aftershock area of the 2007 great outer-rise event (M 8.1). The 2007 and 2009 coseismic slip distributions show that the 2007 normal faulting occurred in the shallower part of the Pacific plate and the 2009 reverse intraplate faulting occurred in the deeper part. Giant (the 2011 Tohoku earthquake of M 9.0), great and large interplate earthquakes occurred in the Kurile to Japan subduction zone after 1990s successively. The aftershock areas and coseismic slip distributions clearly show that only three seismic gaps (offshore Aomori pref., offshore eastern Hokkaido to Etorofu Is., and offshore between Urup and Simushir Is.) have remained in this region.

Harada, T.; Satake, K.; Ishibashi, K.

2011-12-01

36

Seismic consequences of warm versus cool subduction metamorphism: examples from southwest and northeast japan  

PubMed

Warm and cool subduction zones exhibit differences in seismicity, seismic structure, and arc magmatism, which reflect differences in metamorphic reactions occurring in subducting oceanic crust. In southwest Japan, arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth; in northeast Japan, arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth. Thermal-petrologic models predict that oceanic crust subducting beneath southwest Japan is 300 degrees to 500 degrees C warmer than beneath northeast Japan, resulting in shallower eclogite transformation and slab dehydration reactions, and possible slab melting. PMID:10542143

Peacock; Wang

1999-10-29

37

Deformation Patterns and Subduction Behavior of Continental Lithosphere Entering a Trench  

Microsoft Academic Search

We perform 2-D numerical simulations of continental lithosphere entering a subduction zone, to better understand deformation patterns resulting from subduction of a continental margin. The model consists of a subduction zone in which an attached slab drives subduction of a passive continental margin beneath an oceanic plate. A particle-based 2-D visco-elasto-plastic thermo-mechanical finite element code is employed to study the

C. E. Steedman; B. J. Kaus; T. W. Becker; D. Okaya

2007-01-01

38

Influence of trench width on subduction hinge retreat rates in 3-D models of slab rollback  

Microsoft Academic Search

Subduction of tectonic plates limited in lateral extent and with a free-trailing tail, i.e., “free subduction,” is modeled in a three-dimensional (3-D) geometry. The models use a nonlinear viscoplastic rheology for the subducting plate and exhibit a wide range of behaviors depending on such plate characteristics as strength, width, and thickness. We investigate the time evolution of this progressive rollback

D. R. Stegman; J. Freeman; W. P. Schellart; L. Moresi; D. May

2006-01-01

39

From subduction to transform motion: a seabeam survey of the Hellenic trench system  

Microsoft Academic Search

Preliminary results of a multi-narrow beam survey of the Hellenic trench system, in the Eastern Mediterranean, are presented. The southwestern Ionian branch is divided in small basins, partly filled with Pleistocene sediments. The morphology suggests that the basins are deformed by a compressional stress acting roughly perpendicularly to the trench along N50°E. This direction is the direction of the regional

Xavier Le Pichon; Jacques Angelier; Jean Aubouin; Nicolas Lyberis; Serge Monti; Vincent Renard; Henri Got; Ken Hsü; Yossi Mart; Jean Mascle; Drummond Matthews; Dimitri Mitropoulos; Pandelis Tsoflias; Georges Chronis

1979-01-01

40

Autocorrelation analysis of ambient noise in northeastern Japan subduction zone  

NASA Astrophysics Data System (ADS)

We obtained ambient seismic noise interferograms as seismic reflection images using autocorrelation functions (ACFs) in the northeastern Japan subduction zone. The ACFs with a time window length of 120 s were calculated from the continuous seismic records obtained at each seismic station over an analysis period of 300 days. These ACFs show some distinct signals with relatively large amplitude without any significant temporal variations during the analysis period. The signals, which are stable, appear at both small lag times of less than 10 s and large lag times of 20-50 s during the analysis period. The lag time of 10 s corresponds to the travel time of the PP reflection arrival from the continental Mohorovi?i? discontinuity. The signals with the large lag times between 30 and 50 s correspond to the back-scattered signals from the mantle wedge or the plate boundary; these signals are identified clearly at the stations located on the back-arc side. In the ACFs calculated from the records obtained from the fore-arc side stations, weak signals (interpreted as the reflection from the plate boundary) with a lag time range of 20 to 30 s are observed. We constructed depth-migrated images using the ACFs to obtain the reflectivity profile by assuming that the ACFs represent Green's functions composed of a random wavefield excited by stochastic sources or scatterers distributed in the vertical or near-vertical direction from the stations. Further, we assumed that the ACFs can be treated as zero-offset seismic traces recorded at each of the stations. The depth-migrated images show a relatively seismically transparent structure within the subducting Pacific slab and a reflective structure within the mantle wedge; this reflective structure is characterized by low-velocity zones corresponding to the wedge flow imaged by 3-D seismic velocity tomography.

Ito, Yoshihiro; Shiomi, Katsuhiko; Nakajima, Junichi; Hino, Ryota

2012-10-01

41

Trench-parallel flow in the southern Ryukyu subduction system: Effects of progressive rifting of the overriding plate  

NASA Astrophysics Data System (ADS)

AbstractThe Okinawa trough in the Ryukyu <span class="hlt">subduction</span> system is one of a few actively extending back arc basins within the continental lithosphere. Recent shear-wave splitting measurements show variable fast directions along the trough suggesting a complex three-dimensional mantle flow field. In this study we use numerical <span class="hlt">subduction</span> models to demonstrate that the thickness variations of the continental lithosphere bounding the edge of a <span class="hlt">subduction</span> zone can result in complicated mantle circulation and regional dynamics. The model results for the southern Ryukyu show a combination of two effects: Along the Okinawa trough, the increasing thickness of the overriding Eurasian plate toward Taiwan due to a gradually diminishing rifting induces pressure gradients that drive <span class="hlt">trench</span>-parallel flow to the edge in the shallow portion of the mantle wedge, and the thick Eurasian lithosphere to the west effectively blocks and diverts this along-arc flow and limits the toroidal flow around the slab edge below it. The toroidal flow thus enters the mantle wedge at depths of more than about 100 km, opposite in direction with and largely below the along-arc flow. These combined geometry effects of the Eurasian lithosphere create an intricate three-dimensional flow structure at the southern edge of the Ryukyu <span class="hlt">subduction</span> zone. Model predictions for lattice preferred orientations of olivine aggregates show rotation patterns that agree with the observed shear-wave splitting patterns. This three-dimensional scenario echoes the geochemical and seismological evidence worldwide that indicates complex, depth-varying mantle circulations in <span class="hlt">subduction</span> systems.</p> <div class="credits"> <p class="dwt_author">Lin, Shu-Chuan; Kuo, Ban-Yuan</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">42</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EGUGA..14.9357K"> <span id="translatedtitle">Identification and simulation of seismic supercycles along the <span class="hlt">Japan</span> <span class="hlt">Trench</span> including the 2011 Tohoku earthquake</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The devastating Tohoku earthquake of magnitude (M) 9.0 occurred on 11 March 2011 UTC along the <span class="hlt">Japan</span> <span class="hlt">Trench</span>, where the Pacific plate is <span class="hlt">subducting</span> beneath the Tohoku district. The national program of seismic hazard assessment, which was initiated by the Japanese government after the 1995 Kobe earthquake, failed to foresee this earthquake, because no supercycle of megathrust events had been identified along the <span class="hlt">Japan</span> <span class="hlt">Trench</span>. For example, the program identified a normal cycle of six M7 to 8 earthquakes in the land side of the Miyagi-oki region, and only reported the high probability of having another M7 earthquake there. The Japanese government also built nation-wide dense arrays of seismometers and GPS receivers after the Kobe earthquake. We have recovered annual rates of back slip, which is the drag of the overriding plate by interplate coupling, using GPS data during a calm period before the Tohoku earthquake. We then recovered coseismic slips through a inversion of GPS data during the earthquake. The distributions of recovered coseismic slips and back slip rates bear a close resemblance to each other. An area of large back slip rate was previously thought to be related to a normal cycle of M7 to 8 earthquakes. However, our result demonstrates that the area is related to a supercycle of megathrust earthquakes. From the coseismic slips and back slip rates in the Miyagi-oki region, we calculated the coseismic moment release and moment accumulation rate of the Tohoku earthquake to 15 x 10**21 Nm and 0.04 x 10**21 Nm/year, respectively. Since normal earthquakes occasionally release some part of accumulated seismic moment, those in the Miyagi-oki region were compiled. We then calculated the moment releases by them to be 5 x 10**21 Nm. These moment releases and accumulation rate lead to a supercycle period of about 500 years. However, this period is too short, if the 869 Jogan earthquake is the only documented event to have occurred with a possible magnitude and location similar to that of the Tohoku earthquake. Within the compilation, the 1611 Keicho earthquake can be a hidden candidate between the 869 Jogan and 2011 Tohoku earthquakes. Extensive tsunami damage caused by this earthquake was documented over the Tohoku district. The time series, which was drawn using the moment releases and accumulation rate, is mostly controlled by the moment releases of megathrust earthquakes. We next conducted a numerical simulation of the seismic supercycles and normal earthquake cycles identified above. A strong patch (asperity) with higher effective normal stress and a large value of characteristic slip distance is assumed at a shallower part of the plate interface. This strong patch controls the occurrence of megathrust earthquakes that broke the entire seismogenic plate interface with recurrence intervals of several hundred years. The present model explains coseismic slips at a shallower part of the Tohoku earthquake and back slip rates at deeper parts, where normal events repeatedly occurred before the earthquake.</p> <div class="credits"> <p class="dwt_author">Koketsu, K.; Yokota, Y.; Kato, N.; Kato, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">43</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011E%26PSL.303..108V"> <span id="translatedtitle">Kinematic links between <span class="hlt">subduction</span> along the Hellenic <span class="hlt">trench</span> and extension in the Gulf of Corinth, Greece: A multidisciplinary analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Rapid northeast-vergent <span class="hlt">subduction</span> along the Hellenic <span class="hlt">trench</span>, at ~ 35 mm/yr, exists in concert with widespread extensional and strike-slip faulting within the upper plate lithosphere of western Greece. Integration of regional geomorphic, geologic, seismic, GPS, remote sensing and field data demonstrates that young and active deformation in the area, extending from the Hellenic <span class="hlt">subduction</span> boundary near Kephalonia to the Gulf of Corinth, consists of an interconnected network containing highly localized zones of deformation. These bound a series of crustal fragments with relatively little internal deformation. These deformation zones merge to form triple junction-like features at the western end of the Gulf of Corinth and in the Amvrakikos Gulf. At the western end of the Corinth Gulf, most of its 14 ± 2 mm/yr of extension is relayed to the northwest along a prominent zone of left-slip and extension through Lake Trichonis and the Amphilochia fault zone (11 ± 2 mm/yr). The remaining displacement across the western Gulf of Corinth is relayed into 7 ± 2 mm/yr of right-slip on the southwest-striking Achaia fault zone, which traverses the northwestern margin of the Peloponnesus. A second triple-junction like feature occurs in the Amvrakikos Basin, where the left-slip Amphilochia fault zone, the right-slip Kephalonia transform fault (15 ± 2 mm/yr) and the convergent thrust front of northern Hellenides (4 ± 2 mm/yr) are joined. Thus the extensional deformation in the Gulf of Corinth can be shown to be connected to convergence and <span class="hlt">subduction</span> along the Hellenic <span class="hlt">trench</span> through a series of discrete deformation zones that are not dissimilar from those observed in the global plate tectonic system.</p> <div class="credits"> <p class="dwt_author">Vassilakis, E.; Royden, L.; Papanikolaou, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">44</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000JGR...105.8355B"> <span id="translatedtitle">Glacial-interglacial <span class="hlt">trench</span> supply variation, spreading-ridge <span class="hlt">subduction</span>, and feedback controls on the Andean margin development at the Chile triple junction area (45-48°S)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">During the Chile triple junction (CTJ) cruise (March-April 1997), EM12 bathymetry and seismic reflection data were collected in the vicinity of the Chile triple junction (45-480S), where an active spreading ridge is being <span class="hlt">subducted</span> beneath the Andean continental margin. Results show a continental margin development shaped by tectonic processes spanning a spectrum from <span class="hlt">subduction</span>-erosion to <span class="hlt">subduction</span>-accretion. The Andean continental margin and the Chile <span class="hlt">trench</span> exhibit a strong segmentation which reflects the slab segmentation and the Chile triple junction migration. Three segments were identified along the Andean continental margin: the presubduction, the synsubduction, and the postsubduction segments, from north to south. Both climate-induced variations of the sediment supply to the <span class="hlt">trench</span> and the tectonic reorganization at the Nazca-Antarctica plate boundary involving postsubduction ridge jump are the two main factors that control the tectonic regime of this continental margin. Along the survey area we infer the succession of two different periods during the last glacial-interglacial cycle: a glacial period with ice-rafted detrital discharges restricted to the shoreline area and low river output and a warmer period during which the Andean ice cap retreat allowed the Andes to be drained off. During these warm periods, rapid increase in <span class="hlt">trench</span> deposition caused the margin to switch from subductionerosion or nonaccretion to <span class="hlt">subduction</span>-accretion: (1) along the presubduction segment after the last deglaciation and (2) along the postsubduction segment after the interglacial episode at 130-117 ka. Conversely, a nonaccretion or <span class="hlt">subduction</span>-érosion mode characterized the presubduction and postsubduction segments during glacial maximums. The major effects of <span class="hlt">subduction</span> of the buoyant Chile ridge include a shallow <span class="hlt">trench</span> which diverts <span class="hlt">trench</span> sediment supply and tectonic instabilities at the Nazca-Antarctica plate boundary. We suggest that a postsubduction westward jump of the Chile ridge occurred during the past 780 kyr. It produced slab fragmentation and individualization of an ephemeral microplate north of the Taitao fracture zone: the Chonos microplate. In 780 kyr, two episodes of <span class="hlt">subduction</span>-accretion separated by an episode of <span class="hlt">subduction</span>-erosion occurred in relation with the Chonos microplate individualization and <span class="hlt">subduction</span>. The current northward migration of the triple junction along the Chonos microplate-South America plate boundary introduces a sharp change in the tectonic mode from <span class="hlt">subduction</span>-erosion to the north to <span class="hlt">subduction</span>-accretion to the south. The data collected along the Taitao ridge have revealed the complex three-dimensional structure of an accretionary wedge which includes a midslope thrust sheet exhibiting the characteristics of an ophiolite: the Taitao Ridge ophiolite. No connection exists between the Taitao Ridge ophiolite and the Bahia Barrientos ophiolite cropping out onland in the Taitao peninsula.</p> <div class="credits"> <p class="dwt_author">Bourgois, Jacques; Guivel, Christele; Lagabrielle, Yves; Calmus, Thierry; BoulèGue, Jacques; Daux, ValéRie</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">45</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.T13A2158S"> <span id="translatedtitle">Pore pressure evolution at the plate interface along the Cascadia <span class="hlt">subduction</span> zone from the <span class="hlt">trench</span> to the ETS transition zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Pore fluid pressures in <span class="hlt">subduction</span> zones are a primary control on fault strength and slip dynamics. Numerous studies document elevated pore pressures in the outer wedge along several margins. Seismic observations and the occurrence of non-volcanic tremor provide additional evidence for the presence of near-lithostatic pore pressures at the plate interface far down-dip from the <span class="hlt">trench</span> (~35 km depth). Here we use numerical models in one and two dimensions to evaluate the pore pressure and compaction state of sediments on the <span class="hlt">subducting</span> Juan de Fuca plate in Cascadia from the <span class="hlt">trench</span> to the ETS zone. 2-D models allow pressure to diffuse vertically and also laterally normal to strike of the megathrust; 1-D models simulate only vertical diffusion. Model parameters are chosen with reference to two strike-normal profiles: one through central Oregon and one through the Olympic Peninsula of Washington. We examine temporal variations in sediment input to the <span class="hlt">trench</span> and consider implications for fault strength and permeability as well as the down-dip extent to which compactive dewatering can be considered a significant fluid source. In 1-D, we use a general and fully nonlinear model of sediment compaction derived without making any assumptions regarding stress-strain or porosity-permeability relations and allowing finite strains. In contrast, most previous models of fluid flow in <span class="hlt">subduction</span> zones have used linear models of diffusion that rely on assumptions of constant sediment permeability and infinitesimal strains for their formulation. Our nonlinear finite-strain model remains valid at greater depths, where stresses and strains are large. Boundary conditions in 1-D are constrained by pore pressure estimates along the megathrust fault that are based on seismic velocities (e.g. Tobin and Saffer, 2010) and data from consolidation tests conducted on sediments gathered during ODP Leg 204 (Tan, 2001). Initial conditions rely on input sediment thickness; while sediment thickness at the <span class="hlt">trench</span> in Cascadia is fairly well constrained (~1-3 km) by seismic studies, it is less clear how much of the section is frontally accreted and how much is <span class="hlt">subducted</span> with the downgoing plate. Along the Washington profile, Batt et al. (2001) estimated that 80-100% of the incoming sediment is frontally accreted, based on comparisons between accretionary flux at the <span class="hlt">trench</span> and erosional flux in the Olympic Mountains. We assume that similar values hold for the Oregon profile as well. Values of permeability along the plate interface are extracted from 1-D models and used to parameterize 2-D models. 2-D modeling is motivated by the need to examine time dependency of sediment influx, as well as the influence of splay faults within the accretionary wedge. Preliminary results indicate that fluid flux resulting from sediment compaction is complete well up-dip of the ETS zone, where the magnitude of fluid flux associated with mineral dehydration reactions becomes more significant. Ongoing work is centered on incorporating the effects of dehydration fluid sources within our models of pore pressure evolution and examining the implications of our results on the dynamics of slow slip events.</p> <div class="credits"> <p class="dwt_author">Skarbek, R. M.; Rempel, A. W.; Schmidt, D. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">46</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40122275"> <span id="translatedtitle">Enrichment of adsorbed methane in authigenic carbonate concretions of the <span class="hlt">Japan</span> <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Substantial amounts of adsorbed methane were detected in authigenic carbonate concretions recovered from sedimentary layers\\u000a from depths between 245 and 1,108 m below seafloor during Ocean Drilling Program Leg 186 to ODP sites 1150 and 1151 on the\\u000a deep-sea terrace of the <span class="hlt">Japan</span> <span class="hlt">Trench</span>. Methane contents were almost two orders of magnitude higher in the concretions (291–4,528\\u000a nmol\\/g wet wt)</p> <div class="credits"> <p class="dwt_author">Akira Ijiri; Urumu Tsunogai; Toshitaka Gamo; Fumiko Nakagawa; Tatsuhiko Sakamoto; Saneatsu Saito</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">47</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41986571"> <span id="translatedtitle">Deep structure of <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone as derived from local, regional, and teleseismic events</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We have determined a detailed three-dimensional P wave velocity structure of the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone to 500-km depth by inverting local, regional, and teleseismic data simultaneously. We used 45,318 P wave arrivals from 1241 shallow and deep earthquakes which occurred in and around the <span class="hlt">Japan</span> Islands. The arrival times are recorded by the <span class="hlt">Japan</span> University Seismic Network which covers the</p> <div class="credits"> <p class="dwt_author">Dapeng Zhao; Akira Hasegawa; Hiroo Kanamori</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">48</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007JAESc..30..666O"> <span id="translatedtitle">Geology of the Gorny Altai <span class="hlt">subduction</span> accretion complex, southern Siberia: Tectonic evolution of an Ediacaran Cambrian intra-oceanic arc-<span class="hlt">trench</span> system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Gorny Altai region in southern Siberia is one of the key areas in reconstructing the tectonic evolution of the western segment of the Central Asian Orogenic Belt (CAOB). This region features various orogenic elements of Late Neoproterozoic Early Paleozoic age, such as an accretionary complex (AC), high-P/T metamorphic (HP) rocks, and ophiolite (OP), all formed by ancient <span class="hlt">subduction</span> accretion processes. This study investigated the detailed geology of the Upper Neoproterozoic to Lower Paleozoic rocks in a traverse between Gorno-Altaisk city and Lake Teletskoy in the northern part of the region, and in the Kurai to Chagan-Uzun area in the southern part. The tectonic units of the studied areas consist of (1) the Ediacaran (=Vendian) Early Cambrian AC, (2) ca. 630 Ma HP complex, (3) the Ediacaran Early Cambrian OP complex, (4) the Cryogenian Cambrian island arc complex, and (5) the Middle Paleozoic fore-arc sedimentary rocks. The AC consists mostly of paleo-atoll limestone and underlying oceanic island basalt with minor amount of chert and serpentinite. The basaltic lavas show petrochemistry similar to modern oceanic plateau basalt. The 630 Ma HP complex records a maximum peak metamorphism at 660 °C and 2.0 GPa that corresponds to 60 km-deep burial in a <span class="hlt">subduction</span> zone, and exhumation at ca. 570 Ma. The Cryogenian island arc complex includes boninitic rocks that suggest an incipient stage of arc development. The Upper Neoproterozoic Lower Paleozoic complexes in the Gorno-Altaisk city to Lake Teletskoy and the Kurai to Chagan-Uzun areas are totally involved in a subhorizontal piled-nappe structure, and overprinted by Late Paleozoic strike-slip faulting. The HP complex occurs as a nappe tectonically sandwiched between the non- to weakly metamorphosed AC and the OP complex. These lithologic assemblages and geologic structure newly documented in the Gorny Altai region are essentially similar to those of the circum-Pacific (Miyashiro-type) orogenic belts, such as the <span class="hlt">Japan</span> Islands in East Asia and the Cordillera in western North America. The Cryogenian boninite-bearing arc volcanism indicates that the initial stage of arc development occurred in a transient setting from a transform zone to an incipient <span class="hlt">subduction</span> zone. The less abundant of terrigenous clastics from mature continental crust and thick deep-sea chert in the Ediacaran Early Cambrian AC may suggest that the southern Gorny Altai region evolved in an intra-oceanic arc-<span class="hlt">trench</span> setting like the modern Mariana arc, rather than along the continental arc of a major continental margin. Based on geological, petrochemical, and geochronological data, we synthesize the Late Neoproterozoic to Early Paleozoic tectonic history of the Gorny Altai region in the western CAOB.</p> <div class="credits"> <p class="dwt_author">Ota, Tsutomu; Utsunomiya, Atsushi; Uchio, Yuko; Isozaki, Yukio; Buslov, Mikhail M.; Ishikawa, Akira; Maruyama, Shigenori; Kitajima, Koki; Kaneko, Yoshiyuki; Yamamoto, Hiroshi; Katayama, Ikuo</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">49</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007Tecto..26.3005P"> <span id="translatedtitle">Tectonic accretion versus erosion along the southern Chile <span class="hlt">trench</span>: Oblique <span class="hlt">subduction</span> and margin segmentation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The southernmost tip of South America is an active continental margin where oblique convergence between plates, transcurrent motion, and tectonic rotation on land make the geodynamic setting more complex than that of the central Andes. A multichannel seismic data set has been used in conjunction with multibeam and altimetry data to clarify the regional architecture of the continental margin from 50°S to 57°S. Despite the thick sedimentary section in the <span class="hlt">trench</span> and the slow plate convergence rate peculiar of typical accretionary margins, seismic reflection profiles image widely varying frontal wedge morphologies, different rates of accretion, a high degree of structural diversity, and different modes of continental building (offscraping, underplating, tectonic erosion). Correlation between structural parameters (depth of the décollement level, width of the wedge, accretionary rates, Moho depth) suggests large-scale structural control on margin geometry and structural diversity. The transition from tectonic accretion to erosion and general structural variations do not show any gradual trend, but rather, they occur along oblique structural trends that produce a tectonic segmentation of the margin. This is mainly related to tectonic processes on the overriding plate (block rotations along strike-slip faults), while local disturbances on the incoming plate (seamounts, fracture zones, and oceanic fabric relative orientation) add further structural complexity. Altimetry data, in conjunction with structural analysis, suggest that large-scale tectonic variations and structural development are related to <span class="hlt">trench</span>-parallel gravity anomaly variations and, ultimately, to basal friction on the plate interface. Strong negative gravity anomalies are associated with sedimentary basins, wide wedges, and accretionary domains, while positive gravity anomalies mainly refer to transverse structural highs and narrow wedges.</p> <div class="credits"> <p class="dwt_author">Polonia, A.; Torelli, L.; Brancolini, G.; Loreto, M.-F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">50</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.U53A0047S"> <span id="translatedtitle">Permeability anisotropy in marine mudstones in the Nankai Trough, SW <span class="hlt">Japan</span>: Implications for hypothesized lateral fluid flow and chemical transport outboard of the <span class="hlt">trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Characterizing dewatering pathways and chemical fluxes near and outboard of <span class="hlt">subduction</span> <span class="hlt">trenches</span> is important toward understanding early sediment dewatering and devolatilization. Quantifying fluid flow rates also constrains the hydraulic gradients driving flow, and thus ultimately hold implications for pore pressure distribution and fault mechanical strength. We focus on the well-studied Nankai Trough offshore SW <span class="hlt">Japan</span>, where drilling has sampled the sedimentary section at several boreholes from ~11 km outboard of the <span class="hlt">trench</span> to 3 km landward. At these drillsites, &?37Cl data and correlation of distinct extrema in downhole chloride profiles have been interpreted to reflect substantial horizontal fluid flow to >10 km outboard of the <span class="hlt">trench</span> within the ~400 m-thick, homogeneous Lower Shikoku Basin (LSB) facies mudstone. The estimated horizontal velocities are 13 ± 5 cm yr-1; the flow is presumably driven by loading during <span class="hlt">subduction</span>, and mediated by either permeable conduits or strong anisotropy in permeability. However, the pressure gradients and sediment permeabilities necessary for such flow have not been quantified. Here, we address this problem by combining (1) laboratory measurement of horizontal and vertical sediment permeability from a combination of constant rate of strain (CRS) consolidation tests and flow-through measurements on core samples; and (2) numerical models of fluid flow within a cross section perpendicular to the <span class="hlt">trench</span>. In our models, we assign hydrostatic pressure at the top and seaward edges, a no-flow condition at the base of the sediments, and pore pressures ranging from 40%-100% of lithostatic at the arcward model boundary. We assign sediment permeability on the basis of our laboratory measurements, and evaluate the possible role of thin permeable conduits as well as strong anisotropy in the incoming section. Our laboratory results define a systematic log-linear relationship between sediment permeability and porosity within the LSB mudstones. The overall variation in permeability for our suite of samples is ~1 order of magnitude. Notably, horizontal permeabilities fall within the range of measured vertical permeabilities, and indicate no significant anisotropy. Using laboratory-derived permeability values, simulated horizontal flow rates range from 10-4 to 10-1 cm yr-1, and decrease dramatically with distance seaward of the <span class="hlt">trench</span>. With permeability anisotropy of 1000x (i.e. kh = 1000kv), simulated flow rates peak at 3 cm yr-1 at the <span class="hlt">trench</span>, and decrease to 3x10-1 cm yr-1 by 10 km seaward. These flow rates are substantially lower than those inferred from the geochemical data and also lower than the plate convergence rate of 4 cm yr-1, such that net transport of fluids out of the <span class="hlt">subduction</span> zone is not likely. If discrete conduits are included in our models, permeabilities of ~10-114m2 are required to sustain the inferred flow rates. However, no potential conduits in the LSB were observed by coring or logging- while-drilling. In contrast, net egress of fluids - and associated chemical transport and pressure translation - are plausible at margins where continuous permeable strata are <span class="hlt">subducting</span>. Overall, our results highlight a major discrepancy between constraints on fluid flow derived from physical hydrogeology and inferences from geochemical data. In this case, we suggest that the chemical signals may be affected by other processes such as in situ clay dehydration and down-section chemical variations.</p> <div class="credits"> <p class="dwt_author">Saffer, D. M.; McKiernan, A. W.; Skarbek, R. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">51</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFMOS43A0527C"> <span id="translatedtitle">Microbial Community Structure of the <span class="hlt">Japan</span> <span class="hlt">Trench</span> Cold Seeps Sediment Determined by Phospholipid Analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Seafloor cold seeps support some of the most prolific and diverse ecosystems on Earth. A multitude of microbial habitats are associated with cold seeps. The seeping fluids are enriched in reduced chemical species such as sulfide and methane. These reduced species are utilized by microorganisms to gain energy from the reduction of sulfate and oxidation of methane, the so-called anaerobic oxidation of methane. The <span class="hlt">Japan</span> <span class="hlt">Trench</span> is characterized by abundant chemosynthesis-based communities associated with cold seeps. Chemosynthetic communities of Maorithyas hadalis and Calyptogena phaseoliformis have been discovered at depths of over 7,000 m. In this project, sediment samples were collected from communities dominated by thyasirid bivalve Maorithyas hadalis and the vesicomyid clam Calyptogena phaseoliformis and analyzed for phospholipid fatty acids (PLFA). Our objectives were to determine and compare the microbial biomass and community structure of the two sites with different megafaunal species. Result showed the average estimated microbial biomass was 2.97*109 and 4.78*109 cells (g dry wt)-1 for Calyptogena and Maorithyas sediment, respectively. Fatty acids ranging from 12 to 22 carbons were detected. The PLFA profiles suggest the presence of methanotrophic bacteria, sulfur-oxidizing bacteria as well as sulfate-reducers. The polyunsaturated fatty acids (C 18:2 and C20:5) also allow us to trace the possible source of the sediment to the piezophilic bacteria. The assemblage of fatty acids indicates the presence of complex microbial communities in the cold seeps sediments of the <span class="hlt">Japan</span> <span class="hlt">Trench</span>.</p> <div class="credits"> <p class="dwt_author">Chan, O.; Fang, J.; Kato, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">52</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/g23t2jn034470308.pdf"> <span id="translatedtitle">Imaging Interseismic Locking at the Nankai <span class="hlt">Subduction</span> Zone, Southwest <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Recent geodetic and seismological observations have revealed that brittle-plastic transition zones at <span class="hlt">subduction</span> zone interfaces\\u000a are loci of slow slip episodes and nonvolcanic harmonic tremors. It is therefore important to estimate the depth range of\\u000a brittle-plastic transition zones and how interplate locking changes with space and time within the brittle-plastic transition\\u000a zone, not only for understanding the interseismic stress accumulation</p> <div class="credits"> <p class="dwt_author">Yosuke Aoki; Christopher H. Scholz</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">53</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002AGUFM.V61D..09V"> <span id="translatedtitle">The Hf-Nd isotopic fingerprint of <span class="hlt">subducting</span> sediments --A tale of two <span class="hlt">trenches</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report Lu-Hf and Sm-Nd isotopic data for sediments from two DSDP cores from the Pacific (Aleutian site 183 and Tonga sites 595/6) in order to determine the isotopic fingerprint of <span class="hlt">subducting</span> sediments and whether Hf-Nd can serve as a tracer as sediments make their way through the <span class="hlt">subduction</span> zone. These sections appear to represent near end-member types in terms of Lu-Hf-Sm-Nd isotopic systematics. The Aleutian section is 516 meters thick, is composed dominantly of clastic turbidites and diatomaceous oozes and has an overall Hf-Nd isotopic composition similar to continental sediments. The Aleutian section has crustal Lu/Hf ratios (wtd. avg. 176Lu/177Hf = 0.017) and Hf-Nd isotopic compositions that lie within the Hf-Nd array (wtd. avg. ?Nd =-0.6; ?Hf =+5.5). The ~90 meter Tonga section, in contrast, is composed almost entirely of slowly accumulating metalliferous clays and is unique in two regards. First, it has highly radiogenic Hf (?Hf=+7.5) relative to Nd (?Nd =-5.6) such that it plots well above the terrestrial array. More significantly, perhaps, the Tonga sediments are also characterized by extremely high 176Lu/177Hf (0.107) and Nd/Hf (42) ratios which have two important effects. First, high Lu/Hf ratios cause the Tonga compositions to evolve quickly toward highly radiogenic Hf. Second, a simple batch mixing model between Tonga sediment and depleted mantle compositions form a highly curved hyperbolic trend. This curve diverges from mantle compositions toward -?Nd values, leveraged by the high Nd/Hf ratios in these sediments, and should be recognizable with as little as a 1% sediment contribution [1]. This mixing line falls along a trend recognized in Tonga arc lavas by Pearce et al. [2] clearly indicating the contribution of the Tonga pelagic sediments in the source of these arc magmas. The anomalous Lu-Hf-Nd signatures in the Tonga sediments appear to result from decoupling of Hf and Nd sources in these sediments: Nd is derived from REE scavenging from seawater and is ultimately of continental origin whereas Hf is dominated by hydrothermal inputs with a mantle isotopic signature. [1] Vervoort et al., 2002, GCA: 66:A806. [2] Pearce et al., 2002, GCA, 66:A584.</p> <div class="credits"> <p class="dwt_author">Vervoort, J. D.; Plank, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">54</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/19583499"> <span id="translatedtitle">Discovery of dense aggregations of stalked crinoids in Izu-Ogasawara <span class="hlt">trench</span>, <span class="hlt">Japan</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Stalked crinoids are recognized as living fossils that typically inhabit modern deep-water environments exceeding 100 m. Previous records of stalked crinoids from hadal depths (exceeding 6000 m) are extremely rare, and no in-situ information has been available. We show here that stalked crinoids live densely on rocky substrates at depths over 9000 m in the Izu-Ogasawara <span class="hlt">Trench</span> off the eastern coast of <span class="hlt">Japan</span>, evidenced by underwater photos and videos taken by a remotely operated vehicle. This is the deepest in-situ observation of stalked crinoids and demonstrates that crinoid meadows can exist at hadal depths close to the deepest ocean floor, in a fashion quite similar to populations observed in shallower depths. PMID:19583499</p> <div class="credits"> <p class="dwt_author">Oji, Tatsuo; Ogawa, Yujiro; Hunter, Aaron W; Kitazawa, Kota</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">55</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40848393"> <span id="translatedtitle">A detailed receiver function image of the upper mantle discontinuities in the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We have imaged the upper mantle discontinuities in a 30×20° large region at the active continental margin of the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone and neighboring areas, using P-to-S converted phases from teleseismic records of permanent broadband stations. The 410 km discontinuity is detected within ±10 km of its global average position. An interesting exception in its observation is a gap near</p> <div class="credits"> <p class="dwt_author">X. Li; S. V. Sobolev; R. Kind; X. Yuan; Ch. Estabrook</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">56</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003JGRB..108.2345G"> <span id="translatedtitle">Very shallow melting of oceanic crust during spreading ridge <span class="hlt">subduction</span>: Origin of near-<span class="hlt">trench</span> Quaternary volcanism at the Chile Triple Junction</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent dacites and basaltic andesites carrying a <span class="hlt">subduction</span>-related geochemical imprint were dredged within the active Chile <span class="hlt">Trench</span> off the Taitao Peninsula, where the Chile Ridge is being <span class="hlt">subducted</span> beneath the South America Plate. Their maximal Ar/Ar ages range from 70-127 ka to 2 Ma. The basaltic andesites, which have a predominantly mantle-derived geochemical signature are thought to result from the mixing of dacitic magmas with MORB-type liquids derived from the buried spreading ridge. Two groups are distinguished among the dacites: the low-Si group has the chemical characteristics of adakitic slab melts, with depleted heavy rare earth element (HREE) abundances suggesting the occurrence of residual garnet in their source. The high-Si group has less depleted HREE contents. The Sr, Nd, and O isotopic signatures of both groups are ?Sr = -14.9 to +0.8, ?Nd = +2.9 to +3.8, and ?18O values = +6.4 to +6.9‰ respectively, consistent with mixed magma sources that include a MORB-type component and sediments. We propose that the high-Si dacites are derived from the hydrous melting of a mixture of MORB and sediments at high temperatures (800°-900°C) under low pressures (<0.8 GPa). The low-Si dacites originate from the melting of a similar source under higher pressures consistent with depths of 25-45 km. Two scenarios accounting for the near-<span class="hlt">trench</span> position of these latter rocks are envisioned. The first invokes rapid tectonic erosion and changes in sedimentary wedge geometry. The second one postulates that parts of the slab are <span class="hlt">subducted</span> rapidly to depths of 20-30 km right under the <span class="hlt">trench</span>.</p> <div class="credits"> <p class="dwt_author">Guivel, ChristèLe; Lagabrielle, Yves; Bourgois, Jacques; Martin, Hervé; Arnaud, Nicolas; Fourcade, Serge; Cotten, Joseph; Maury, René C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">57</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AGUFM.T23C0505T"> <span id="translatedtitle">Three Dimensional Seismic Velocity Structure of the <span class="hlt">Subducted</span> Pacific Slab Beneath NE <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The occurrence of earthquakes in the <span class="hlt">subducting</span> slab is an enigma because the fact that lithostatic pressure at such depths appears to be too high for any brittle fracture. Dehydration embrittlement has been proposed as a possible mechanism for triggering intraslab earthquakes. It is accepted that the slab is hydrated prior to <span class="hlt">subduction</span> principally through infiltration of seawater via normal or transform faulting [e.g. Kirby et al., 1996] and/or through hot-spot magmatism [Seno and Yamanaka, 1996]. During <span class="hlt">subduction</span>, the fluids released by dehydration reactions induce in situ mechanical instability and brittle deformation by increasing pore pressure. Mishra and Zhao [2004] revealed the existence of low-velocity zone around the hypocenter of the 2003 Miyagi- Oki intraslab earthquake (M7.1). Nakajima and Hasegawa [2006] detected a linear alignment of seismicity and a narrow low-velocity zone along it within the Pacific slab beneath Kanto, <span class="hlt">Japan</span>. These results suggest that the occurrence of intraslab earthquakes is closely associated with the heterogeneous structure in the <span class="hlt">subducted</span> slab. This study is the first attempt to investigate 3D seismic velocity structure in the <span class="hlt">subducted</span> Pacific slab for the entire NE <span class="hlt">Japan</span>. A detailed investigation of heterogeneous structure is essential to understand the mechanism for triggering intraslab earthquake. We apply the Double-Difference Tomogaphy method (Zhang and Thurber, 2003) to arrival-time data of 208,026 and 142,259 P and S waves, respectively, obtained from 3131 earthquakes that occurred from October 1997 to March 2006. The total number of stations used in this study is 206. We adopted a grid spacing of 10km-40km in the horizontal direction and 5-30km in the vertical direction. At the first inversion, we used only absolute travel-time data and determine large scale velocity structure, and then differential travel-time data were added to the absolute data to investigate slab structure in detail. The obtained results show that the <span class="hlt">subducted</span> Pacific plate is generally imaged as a high-velocity anomaly. However, a low-velocity zone exists along the upper plane seismicity of the double seismic zone [e.g. Hasegawa et al. 1987], which probably corresponds to the <span class="hlt">subducted</span> oceanic crust. The lower plane of the double seismic zone exhibits a low Vp/Vs ratio where a sllightly low-Vp anomaly is observed. This feature is pointed out by Zhang et al. [2004]. A prominant low-velocity zone is imaged around the hypocenter of the 2003 Miyagi-oki intraslab earthquake. These observations strongly suggest the relationship between the occurrence of intraslab earthquakes and heterogeneous structure in the <span class="hlt">subducted</span> slab.</p> <div class="credits"> <p class="dwt_author">Tsuji, Y.; Nakajima, J.; Okada, T.; Matsuzawa, T.; Hasegawa, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">58</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.S34A..02K"> <span id="translatedtitle">Peeling off of the uppermost crustal layer from the <span class="hlt">subducting</span> plate at deep extensions of the <span class="hlt">subduction</span> zone in <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Determination of the fine structure at the <span class="hlt">subduction</span> zones is essential to reveal the generation mechanisms of interplate phenomena, including megathrust earthquakes. The peeling off of the uppermost layer from a <span class="hlt">subducting</span> plate and accretion to the bottom of the overlying plate is called underplating. Underplating at deep region has been inferred from exhumed metamorphic rocks and deep seismic imaging. However, its details, such as behavior at shorter time scale than the geologic time scale, remain unresolved. In this study, we succeed to detect active deep underplating based on the detailed relation between small repeating earthquakes, which can be regarded as an indicator of plate motion, and the deep seismic imaging. It is usually difficult to do such comparisons with high accuracy, however, we resolved this problem by a series of relative comparisons. Off the Kanto region, central <span class="hlt">Japan</span>, the Philippine Sea plate (PHS) <span class="hlt">subducts</span> causing various interplate phenomena, including megathrust earthquakes (e.g., the largest aftershock (Mw7.5) of the 1923 Kanto earthquake (Mw7.9)), slow slip events (SSEs), and small repeating earthquakes, whose areas are distributed in order. The uppermost layer of the PHS consists of unconsolidated sediments and the underlying volcaniclastic and volcanic rock layer (hereinafter, VCR layer). While the sediments are fully scraped off at the entrance of <span class="hlt">subduction</span>, the VCR layer <span class="hlt">subducts</span>. Processing of seismic reflection data just above the repeating earthquake region revealed the VCR layer of 3.1 - 3.6 km thickness, on the top of the PHS. Strong reflectors at the top and the bottom of the VCR layer show large velocity contrasts. At such boundaries, seismic waves are likely to be converted. We studied seismograms of ~2000 earthquakes that occurred from 1979 to 2003, based on the seismic database maintained by NIED, and found clear phases between the direct P and S waves in the radial components for earthquakes occurring below the repeating earthquakes. Analyses of traveltime and polarity indicate that this phase was converted from P to S at the bottom of the VCR layer. Traveltime of converted waves can be used to determine the relative location between earthquake hypocenters and the conversion plane. We used traveltime differences between the P-to-S converted wave and the direct S wave to cancel out the effects of paths through complex surface structures. Combination of traveltime analyses and high-precision hypocenters determined by the Double Difference method using waveform cross-correlations revealed that repeating earthquakes are distributed along the bottom of the VCR layer with 1.6 km depth uncertainty. Because repeating earthquakes are indicators of the plate motion, our result implies that the VCR layer is now being peeled off from the <span class="hlt">subducting</span> PHS and accreted to the overlying plate. This is an active, deep underplating process. The underplating region coincides with the source region of the SSE. The SSE off Kanto repeats every ~6 years with almost the same size. This SSE activity indicates that deep underplating occurs intermittently.</p> <div class="credits"> <p class="dwt_author">Kimura, H.; Takeda, T.; Obara, K.; Kasahara, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">59</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JSAES..45...24L"> <span id="translatedtitle">Middle Miocene near <span class="hlt">trench</span> volcanism in northern Colombia: A record of slab tearing due to the simultaneous <span class="hlt">subduction</span> of the Caribbean Plate under South and Central America?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Field, geochemical, geochronological, biostratigraphical and sedimentary provenance results of basaltic and associated sediments northern Colombia reveal the existence of Middle Miocene (13-14 Ma) mafic volcanism within a continental margin setting usually considered as amagmatic. This basaltic volcanism is characterized by relatively high Al2O3 and Na2O values (>15%), a High-K calc-alkaline affinity, large ion lithophile enrichment and associated Nb, Ta and Ti negative anomalies which resemble High Al basalts formed by low degree of asthenospheric melting at shallow depths mixed with some additional slab input. The presence of pre-Cretaceous detrital zircons, tourmaline and rutile as well as biostratigraphic results suggest that the host sedimentary rocks were deposited in a platform setting within the South American margin. New results of P-wave residuals from northern Colombia reinforce the view of a Caribbean slab <span class="hlt">subducting</span> under the South American margin.The absence of a mantle wedge, the upper plate setting, and proximity of this magmatism to the <span class="hlt">trench</span>, together with geodynamic constraints suggest that the <span class="hlt">subducted</span> Caribbean oceanic plate was fractured and a slab tear was formed within the oceanic plate. Oceanic plate fracturing is related to the splitting of the <span class="hlt">subducting</span> Caribbean Plate due to simultaneous <span class="hlt">subduction</span> under the Panama-Choco block and northwestern South America, and the fast overthrusting of the later onto the Caribbean oceanic plate.</p> <div class="credits"> <p class="dwt_author">Lara, M.; Cardona, A.; Monsalve, G.; Yarce, J.; Montes, C.; Valencia, V.; Weber, M.; De La Parra, F.; Espitia, D.; López-Martínez, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">60</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.S13A1028N"> <span id="translatedtitle">A zone of anomalously low b-values within the <span class="hlt">subducting</span> slab prior to the September 26, 2003 Tokachi-oki, <span class="hlt">Japan</span>, earthquake (M=8.0)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The M=8.0 26 September 2003 Tokachi-oki earthquake occurred in the southern Kuril <span class="hlt">Trench</span> southeast of Hokkaido, <span class="hlt">Japan</span>, close to the epicentre of the another very large earthquake in 1952 (M=8.1) [Yamanaka and Kikuchi, 2003]. The coseismic rupture process during each of the two earthquakes has been analysed using seismic and geodetic data, for the 2003 event [e.g., Yamanaka and Kikuchi, 2003; Koketsu et al., 2004; Yagi, 2004], and tsunami data, for the 1952 event [e.g., Hirata et al., 2003], and the spatial distribution of asperities within the <span class="hlt">subduction</span> zone has also been estimated. The b-value of an earthquake catalogue, defined as the slope of the Gutenberg-Richter frequency-magnitude relationship, log N = a - bM, is typically found to be ˜1 in a variety of tectonic situations. However, several factors appear to influence b locally [e.g., Mogi, 1962; Scholz, 1968; Warren and Latham, 1970; Wyss, 1973; Urbancic et al., 1992; Wiemer and Wyss, 1997; Enescu and Ito, 2002]. In the basis of the investigations of previous researchers, observations of relatively low b-values may reflect locally elevated shear or effective stresses. It is widely accepted that the bulk of the coseismic moment release during interplate earthquakes occurs recurrently near one or more large asperities at which shear stress is concentrated by incremental <span class="hlt">subduction</span> [e.g., Tanioka and Ruff, 1996; Nagai et al., 2001; Iio et al., 2003; Igarashi et al., 2003; Uchida et al., 2003]. Our analysis of seismicity data from the <span class="hlt">subducting</span> slab along the Kuril <span class="hlt">Trench</span> reveals a zone of anomalously low b-values near the hypocenter of the 26 September 2003 Tokachi-oki earthquake (M=8.0). The b-value time-series shows that b-values decreased from initial values of ~0.8 to values as low as 0.4 during the three years prior to the mainshock. Here we show that the anomalously low b-value in the <span class="hlt">subducting</span> slab prior to the mainshock provide seismological evidence for high stress concentrations associated with interseismic strain accumulation. Changes in b-value may provide a means of monitoring future stress changes at shallow depths ( ˜140 km) within the <span class="hlt">subducting</span> slab.</p> <div class="credits"> <p class="dwt_author">Nakaya, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_2");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> 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showDiv("page_5");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">61</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40845632"> <span id="translatedtitle">Normal faulting of the Daiichi-Kashima Seamount in the <span class="hlt">Japan</span> <span class="hlt">Trench</span> revealed by the Kaiko I cruise, Leg 3</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern <span class="hlt">Japan</span> <span class="hlt">Trench</span>, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2-4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and</p> <div class="credits"> <p class="dwt_author">Kazuo Kobayashi; Jean-Paul Cadet; Jean Aubouin; Jacques Boulègue; Jacques Dubois; Roland von Huene; Laurent Jolivet; Toshihiko Kanazawa; Junzo Kasahara; Kin-Ichiro Koizumi; Serge Lallemand; Yasuo Nakamura; Guy Pautot; Kiyoshi Suyehiro; Shin Tani; Hidekazu Tokuyama; Toshitsugu Yamazaki</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">62</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.V53F..02H"> <span id="translatedtitle">Earthquakes in <span class="hlt">Japan</span>: A vital role of geofluids in earthquake generation in <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent seismic observations based on a dense nationwide seismic network in <span class="hlt">Japan</span> have shown that generations of all the three main types of earthquakes in this <span class="hlt">subduction</span> zone (except for deep earthquakes) are closely related with geofluids. Studies on spatial distribution of earthquakes and seismic velocity structure within the <span class="hlt">subducted</span> slab provide evidence which strongly supports the dehydration embrittlement hypothesis for generation of intermediate-depth intraslab earthquakes. Detailed imagings of seismic velocity structure in and around the plate boundary zones suggest that interplate coupling is mainly controlled by fluid overpressure there. Seismic tomography studies have shown the existence of inclined sheet-like seismic low-velocity zones in the mantle wedge not only in Tohoku but also in other areas in <span class="hlt">Japan</span>, which perhaps correspond to the upwelling flow of the <span class="hlt">subduction</span>-induced convection system. These upwelling flows reach the Moho right beneath the volcanic areas, suggesting that those volcanic areas are formed by the upwelling flows. Aqueous fluids derived from the slab are probably transported upward through the upwelling flows to reach the arc crust, where they might work to weaken the surrounding crustal rocks and finally cause shallow inland earthquakes. Generations of the 2011 M9.0 great Tohoku earthquake and earthquake activities induced by it also seem to be closely related with geofluids. Observed temporal change in stress field near the source area after the earthquake shows nearly complete stress drop by the earthquake, which suggests the plate interface is weak. Temporal change in stress field after the Tohoku earthquake is also observed for inland areas far from the source, suggesting that faults for shallow inland earthquakes are weak as well. These weak faults are inferred to be caused by overpressured fluids. Detailed imagings in the source area of a large (M7.1) intermediate-depth intraslab earthquake that occurred about one month after the Tohoku earthquake provide evidence for reactivation of a buried hydrated fault ,caused by the Tohoku earthquake, in the <span class="hlt">subducted</span> Pacific slab. All these observations suggest that geofluids expelled from the <span class="hlt">subducting</span> slab play an important role in the generation of earthquakes in <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Hasegawa, A.; Nakajima, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">63</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56121945"> <span id="translatedtitle">3-D simulation of temporal change in tectonic deformation pattern and evolution of the plate boundary around the Kanto Region of <span class="hlt">Japan</span> due to the collision of the Izu-Bonin Arc</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Kanto region of <span class="hlt">Japan</span> is in a highly complex tectonic setting with four plates interacting with each other: beneath Kanto, situated on the Eurasian and North American plates, the Philippine sea plate <span class="hlt">subducts</span> and the Pacific plate further descends beneath the North American and Philippine sea plates, forming the unique <span class="hlt">trench-trench-trench</span> triple junction on the earth. In addition, the</p> <div class="credits"> <p class="dwt_author">A. Hashima; T. Sato; T. Ito; T. Miyauchi; H. Furuya; N. Tsumura; K. Kameo; S. Yamamoto</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">64</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GeoRL..39.8304Y"> <span id="translatedtitle">Small repeating earthquake activity, interplate quasi-static slip, and interplate coupling in the Hyuga-nada, southwestern <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Small repeating earthquake (RE) analysis is a useful method for estimating interplate quasi-static slip, which is a good indicator of interplate coupling. We detected 170 continual-type interplate RE groups and then estimated the spatial variation in quasi-static slip in the Hyuga-nada over the past 17 years. The RE activity in this region has different characteristics compared with that in the northeast <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone, presumably reflecting differences in the <span class="hlt">subduction</span> properties. Our results revealed that interplate coupling spatially changes along the <span class="hlt">trench</span>-axis and dip-direction—a phenomenon that cannot be resolved by land-based Global Positioning System (GPS) analysis. By comparing seismicity, the low-slip-rate areas correspond with the location of hypocenters and asperities for large- and moderate-sized interplate earthquakes, suggesting strong interplate coupling at these sites. These results indicate that the slip rate distribution estimated from RE activity is reliable and useful for assessing the potential of future large earthquakes.</p> <div class="credits"> <p class="dwt_author">Yamashita, Yusuke; Shimizu, Hiroshi; Goto, Kazuhiko</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">65</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T23B1901G"> <span id="translatedtitle">Micro-seismicity survey of a seismic gap caused by the <span class="hlt">subduction</span> of the Louisville seamount chain in the Tonga <span class="hlt">trench</span>, 25°30’S to 28°S</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The distribution of teleseismically recorded earthquakes in the Kermadec-Tonga <span class="hlt">subduction</span> zone reveals a major seismic gap centered roughly at 26°S. The gap parallels the <span class="hlt">trench</span> axis and stretches for approximately 250 km. The seismic gap coincides with the area, where the Louisville hotspot chain enters the Tonga <span class="hlt">trench</span>. <span class="hlt">Subducting</span> seamounts may therefore control seismic coupling and hence define seismogenic asperities in <span class="hlt">subduction</span> zones. Louisville seamounts rise 3 to 4 km above the regional seafloor. Seamounts and guyots are between 10 to 40 km in diameter and hence smaller than the width of the seismic gap, suggesting that other features - like the hotspot swell, crustal underplating or the flexural may contribute or control seismic locking. We deployed a network of 21 ocean-bottom-seismometers (OBS) and 2 ocean-bottom-hydrophones (OBH), including 9 broadband OBS with Guralp CMG-40T sensors. The network covered the southern portion of the seismic gap and the transition zone to “normal” seismic behavior. The ocean bottom seismic stations provided data from July 9, 2007 to December 31, 2007. For the earthquake location procedure we derived a minimum 1-D velocity model from active seismic wide-angle profiling in the uppermost 6 km of the fore-arc crust and earthquake arrival time data at greater depths. In total 1523 local and regional earthquake could be located. Within the network, 383 events have been recorded with a gap of <230 degree at 4 stations, and 160 events with a gap of <180 degree at 6 stations. It is interesting to note that local earthquakes (M < 4) did not mimic the teleseismic gap. Overall, seismicity seems to be randomly distributed within the network. Furthermore, in contrast to other <span class="hlt">subduction</span> zones, where earthquakes occur predominantly along the <span class="hlt">subduction</span> megathrust fault, we observed only a few events along the plate boundary. Thus, most local earthquakes occur in the uppermost mantle, perhaps caused by extension related to the slab-pull force of the down-going Pacific lithosphere. However, events that were related to the <span class="hlt">subduction</span> thrust generally occur in small clusters with 10-20 sub-events, while earthquakes in the mantle of the lower plate were single events. One cluster has been observed in the outer rise seaward of the <span class="hlt">trench</span> axis. Fife events of this cluster were also reported in the NEIC/PDE catalogue and the largest earthquake was reported as a tensional event in Lamont’s global CMT catalogue. During the time of network operation we recorded in total 15 events that have been reported in the NEIC/PDE catalogue. Earthquake in the global catalogue were biased with respect to the epicenters from the local network. In general, events were mislocated by 40-60 km in east-west direction. In latitude the error was generally in the order of <10 km.</p> <div class="credits"> <p class="dwt_author">Grevemeyer, I.; Dannowski, A.; Flueh, E. R.; Moeller, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">66</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/16445179"> <span id="translatedtitle">Dynamic changes in environment condition and microbial community structure in <span class="hlt">trench</span> and flat seabed sediments of Tokyo Bay, <span class="hlt">Japan</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Dynamic changes in the chemical environment in the bottom of overlying water and microbial community structure in <span class="hlt">trench</span> and flat seabed sediments were evaluated during summer and autumn in Tokyo Bay, <span class="hlt">Japan</span>, to elucidate the response of microbial community changes as a consequence of dredging activity. Quinone profile analysis was performed to evaluate the changes in microbial community structure in the sediments. Bottom shape and location of each station affected the chemical environment of the overlying water. The <span class="hlt">trench</span> bottom shape had longer anoxic conditions than the flat bottom shape. Nitrogen and phosphorus concentrations affected the microbial density in the sediment. During anoxic conditions, the ubiquinone/menaquinone ratio (UQ/MK) was less than unity and increased with rising dissolved oxygen (DO) concentrations. The dominant quinone species in the <span class="hlt">trench</span> and flat seabed sediments were MK with 6 and 7 isoprene units (MK-6 and MK-7) and UQ with 8 and 9 isoprene units (UQ-8 and UQ-9). MK-6 and UQ-8 containing bacteria might have a great influence on the sulfur cycle of the aquatic ecosystem. While, MK-7 and UQ-9 containing bacteria correlated with the deposition of phototropic bacteria cells onto the seabed sediment. The <span class="hlt">trench</span> bottom shape contained higher concentrations of MK-6, MK-7, UQ-8 and UQ-9, especially during summer. PMID:16445179</p> <div class="credits"> <p class="dwt_author">Hasanudin, U; Fujita, M; Koibuchi, Y; Fujie, K</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">67</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFMDI13A1853W"> <span id="translatedtitle">Seismic anisotropy beneath the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone from teleseismic receiver functions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A complete characterization of seismic anisotropy can yield powerful constraints on mantle flow and deformation. This is particularly important for the mantle wedge above <span class="hlt">subducting</span> slabs, where the geometry of mantle flow remains poorly understood. In this study we attempt to better characterize the geometry and strength of anisotropy in the mantle wedge beneath northern Honshu and Hokkaido, which overlie the <span class="hlt">subducting</span> Pacific plate. Our previous shear wave splitting measurements indicate that anisotropy in the mantle wedge beneath the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone is highly complex, with splitting patterns that exhibit both dramatic spatial variations and a strong dependence on frequency (Wirth and Long, 2010). In order to complement the splitting data set and characterize these lateral variations in anisotropy more completely, we are currently analyzing teleseismic receiver functions (RFs) from a subset of broadband F-net stations in northern Honshu and Hokkaido using the multitaper correlation receiver function estimator (Park and Levin, 2000). Observations of coherent P-to-SV converted energy at time delays of ~8 sec are consistent with conversions originating at the top of the slab. We also observe significant spatial variations in the character of transverse RFs which are consistent with lateral variations in structure. In northern Honshu, P-to-SH converted energy originating from sharp gradients in structure just above the <span class="hlt">subducting</span> slab show a strong sin(2?) amplitude pattern with backazimuth, providing clear evidence for the presence of anisotropy. Based on our receiver function analysis and in conjunction with forward modeling of synthetic seismograms, we are currently developing models for the depths, thicknesses, and strengths of the anisotropic layers in the mantle wedge beneath northern Honshu.</p> <div class="credits"> <p class="dwt_author">Wirth, E. A.; Long, M. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">68</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.T23A1989K"> <span id="translatedtitle">Can Interseismic Geodetic Observations Resolve Persistent Rupture Asperities? A study of the <span class="hlt">Japan</span> <span class="hlt">trench</span> off Tohoku.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In the last century, several large (M > 7) earthquakes have occured on the megathrust interface along the <span class="hlt">Japan</span> <span class="hlt">Trench</span>, offshore of <span class="hlt">Japan</span>'s Tohoku region. Published earthquake source inversions based on seismological data suggest that some of these earthquakes have repeatedly ruptured the same region of the fault (i.e., asperities), while others have ruptured closely clustered asperities (e.g., Yamanaka and Kikuchi, 2004). For instance, the 1978, M 7.4 and the 2005, M 7.2 Miyagi-oki events are inferred to have ruptured the same asperity, while the 1968, M 7.9 Tokachi-oki event, and the 1994, M 7.5 Sanriku-oki event ruptured distinct asperities that are close to each other. In contrast, inversions of geodetic data from interseismic periods produce models that are locked over more spatially extensive regions (e.g., Suwa et al, 2003). These broad and smooth regions are in contrast to the smaller discrete asperities indicated by earthquake source studies, and may be a consequence of lack of model resolution and a resulting need for regularization that is inherent to the use of onshore geodetic data. Alternatively, the differences may imply the potential for a large earthquake in the future. Thus, the different levels of apparent coupling implied by these two classes of models have very different implications for regional seismic hazard. Here, we test the hypothesis that mechanical coupling on inferred asperities alone is sufficient to explain available geodetic observations or alternatively, that these data require additional regions on the megathrust to be coupled. To address this question, we use a 3-D mechanical model of stress-dependent interseismic creep along the megathrust, that is consistent with a given frictional rheology and the known spatio-temporal distribution of large earthquakes. These mechanical models predict that asperities are surrounded by a "halo" of very low creep-rates (a "stress-shadow" effect) late in the seismic cycle, which also results in a relatively smooth and long wavelength surface velocity field (see poster by Hetland et al. in this session). We test if this "physical" smoothing preserves any signature of the original asperities, in comparison to the artificial smoothing produced by model regularization in inversions of interseismic geodetic data. Underlying this analysis is the assumption that known asperities persist across multiple earthquake cycles.</p> <div class="credits"> <p class="dwt_author">Kanda, R. V.; Hetland, E. A.; Simons, M.; Owen, S. E.; Webb, F. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">69</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.S41A2179I"> <span id="translatedtitle">Investigation of P- and S-wave Anisotropy beneath the <span class="hlt">Japan</span> <span class="hlt">Subduction</span> Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">To understand the dynamics of the <span class="hlt">subduction</span> zone, we investigated P- and S-wave seismic anisotropy beneath the <span class="hlt">Japan</span> islands through travel-time and receiver function analyses. Assuming weakly anisotropic media with horizontal symmetry axes, we resolved the three-dimensional P-wave anisotropic structure (with heterogeneity and azimuthal anisotropy described by the fast propagation direction and the strength of anisotropy) beneath the <span class="hlt">Japan</span> islands. The P-wave tomography manifested the crust anisotropy with the fast direction parallel to the trend of large-scale geological structures, the mantle anisotropy parallel/sub-parallel to the direction of the present-day absolute plate motions, and the frozen slab anisotropy within the old Pacific slab. Furthermore, the young Philippine Sea slab showed anisotropy that reflects the present-day tectonic condition. In addition, we measured splitting for some clear Ps phases identified on receiver functions to investigate the S-wave anisotropy. The preliminary measurements revealed a crust anisotropy that polarizes the fast S-wave in the same direction as the P-wave crust anisotropy. Unfortunately, however, S-wave anisotropy in the mantle region including slabs remains unsolved, because anisotropy in the uppermost layer has a significant effect on all Ps phases. To understand the <span class="hlt">subduction</span> system, consideration of the characteristics of both P- and S-anisotropy is required. In particular, mantle anisotropy is an essential factor. Accordingly, to resolve the three-dimensional S-wave anisotropic velocity structure of the <span class="hlt">Japan</span> islands, we are working on a tomographic study using S-wave travel time under the same conditions as described for the P-wave.</p> <div class="credits"> <p class="dwt_author">Ishise, M.; Watanabe, M.; Oda, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">70</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.6401P"> <span id="translatedtitle">Spatial variation of attenuation factor in <span class="hlt">subduction</span> zone of Philippine Sea slab around Kyushu Island <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Kyushu Island, in south-western part of <span class="hlt">Japan</span> is characterized by <span class="hlt">subduction</span> from Philippine Sea Slab and Eurasian Plate (Amurian); volcanic front seen in islands arcs runs through the central part of Kyushu Island. In Kyushu, shallow and intermediate-depth earthquakes occur robustly through a depth of about 200 km. We estimated attenuation structure beneath Southern Part of <span class="hlt">Japan</span>, at <span class="hlt">subduction</span> zone of Philippine Sea Slab by applying modified coda normalization method (Eq.1) proposed by Parithusta, et.al. (2008*). The method estimates relative source spectra by taking spectral ratio in coda waves between two events at first. From a lot of the spectral data, those can be estimated with higher stability through singular value decomposition. After that, the relative source effect between event pair can be eliminated by the solution from ratios between direct wave spectra for many event pairs. We confirmed the estimation of source factor by assessment with empirical method, the result show that estimates of source factor almost satisfy empirical relation between magnitude and energy relation. The attenuation factor can be obtained from a relation below; ( ) Edij(tij,?-)- -1 dn = ln Edi'j(ti'j,?) = - ?Q(?) (tij - ti'j)+ const.... (1) Where: Ed denotes Direct S-wave power spectrum and Q is attenuation factor at target area; t is lapse time from origin time. Subscript i,jdenote identification number for event and station, respectively. Q-1 factor can be estimated from decay with ?tii'j(= tij - ti'j). By using this method, we obtained frequency dependent Q-1 value with smaller estimation error than previous study carried by Matsumoto et.al (2007). We used waveform data from earthquakes occurred in Philippine Sea Slab, recorded by Hi-net and Kyushu University seismic networks. Window length adopted here is 2.5 seconds for taking spectrum. The results shows the Q-1 values around Bungo-Suido area, northern part of Kyushu. Q-1 values are plotted in seven depth ranges as a function of frequency. The Q-1 values are obtained in a range from 10-4 to 10-1. This range is similar to that estimated in other studies. These results suggest that attenuation at depths 30-60 km is high but decreases markedly within 75 km depth, high attenuation is also observed at depth greater than 90 km. We found that Q-1 value in this study has frequency dependency, which decrease gradually with frequency. Keywords: Attenuation, Coda, Philippine Sea Slab, <span class="hlt">Subduction</span>, Kyushu Island. *Presented on <span class="hlt">Japan</span> Geosciences Union Makuhari -May 2008</p> <div class="credits"> <p class="dwt_author">Parithusta, Rizkita; Matsumoto, Satoshi; Shimizu, Hiroshi</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">71</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMOS13B1517G"> <span id="translatedtitle">The Mariana <span class="hlt">Trench</span>: A new view based on multibeam echosounding</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The entire Mariana <span class="hlt">Trench</span>, from its northern end at Dutton Ridge to the southwestern terminus at the Yap <span class="hlt">Trench</span>, was mapped in 2010 using a Kongsberg EM122 12-kHz multibeam echosounder. The region ranges in depths from the shoreline at Guam to almost 11,000 m at the Challenger Deep. The northern part of the <span class="hlt">trench</span> is receiving seamounts and guyots of the Magellan Seamount chain, whereas the southern section is receiving seafloor that carries the Caroline Ridge to the <span class="hlt">trench</span>. The area immediately seaward of the <span class="hlt">trench</span> where the Pacific Plate has bent downward toward the <span class="hlt">subduction</span> zone has been broken by a series of subparallel horst and graben structures generated by extension on the bending upper surface of the Pacific Plate. Four bathymetric "bridges" span across the <span class="hlt">trench</span> axis and extend from the Pacific Plate to the inner wall of the <span class="hlt">trench</span>. The bridges stand as much as 2500 m above the <span class="hlt">trench</span> axis and are composed of Latest Jurassic to Early Cretaceous accreted seamounts and guyots of the Magellan Seamount chain that are in the process of breaking up and being <span class="hlt">subducted</span> beneath the Philippine Plate. Only two seamounts of the Caroline Ridge are in the vicinity of the <span class="hlt">trench</span> and they both presently reside on the outer <span class="hlt">trench</span> wall. The faults of the horsts and grabens have fractured the seamounts and guyots within the <span class="hlt">trench</span> depression seaward from the axis outward for about 80 km, but within ~5 km of the <span class="hlt">trench</span> axis the faults have reactivated to compressional thrust faults. The faults tend to parallel the axis of the <span class="hlt">trench</span> until the immediate vicinity of an accreting seamount or guyot where the faults bend inward toward the <span class="hlt">trench</span> axis, as has been observed in many other <span class="hlt">trenches</span>. Most of the accreted seamounts and guyots are not associated with embayments or reentrants on the inner <span class="hlt">trench</span> wall, as has been documented in the Middle America and <span class="hlt">Japan</span> <span class="hlt">Trenches</span>, perhaps because there is not a large accretionary prism that extends seaward of the forearc. The one exception is a large seamount of the Caroline Ridge that has been fractured into several sections, some of which appear to be mostly <span class="hlt">subducted</span>, that are associated with a 30 km embayment landward from the <span class="hlt">trench</span> axis. However, there are reentrants along the inner <span class="hlt">trench</span> wall but without bathymetric expression of an associated <span class="hlt">subducting</span> seamount or guyot. These reentrants may mark zones where seamounts and guyots have been completely consumed into the <span class="hlt">trench</span>. There is no evidence from the acoustic backscatter of sediment filling by debris flows and other failure deposits along the entire <span class="hlt">trench</span> axis, although the inner <span class="hlt">trench</span> wall has numerous scarps from wall failures. The forearc area has numerous features that resemble diapirs with what appears from the acoustic backscatter to be ponded sediment in bathymetric lows that are surrounded by diapirs. An analysis of the individual soundings within Challenger Deep shows the deepest depth of the Mariana <span class="hlt">Trench</span> is 10,994 m (2? ±40 m), based on numerous soundings and sound-speed profiles collected during the cruise in the immediate area. The location of the deepest depth does not coincide exactly with published claims of the deepest depth, although many of the claims are within a few kilometers of the 10,944 m depth.</p> <div class="credits"> <p class="dwt_author">Gardner, J. V.; Armstrong, A. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">72</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51810466"> <span id="translatedtitle">Amount of Sediment-Derived Fluid in Mantle Wedge Beneath Northeast <span class="hlt">Japan</span> Arc: Comparison Between B and Other Element Contents in <span class="hlt">Japan</span> <span class="hlt">Trench</span> Sediments and Those in Iwate Lavas</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">From the <span class="hlt">Japan</span> <span class="hlt">Trench</span>, the Pacific Plate descends to the deep mantle. Parts of the plate, the altered oceanic crust (AOC) and overlying sediments, release hydrous fluids at the deep mantle, and these slab-derived fluids would be added to the mantle wedge beneath Northeast <span class="hlt">Japan</span> arc. In order to estimate the weight percent of the fluid in the mantle wedge,</p> <div class="credits"> <p class="dwt_author">T. Sano; T. Hasenaka; T. Fukuoka</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">73</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.5679Y"> <span id="translatedtitle">Numerical simulations of temperature distributions associated with <span class="hlt">subduction</span> of the Philippine Sea plate, southwest <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Large megathrust earthquakes have occurred repeatedly along the Nankai Trough with recurrence interval of about 90 to 150 years, which have been caused by plate motion of the Philippine Sea (PHS) plate in the NW direction <span class="hlt">subducting</span> beneath southwest <span class="hlt">Japan</span>. Deep low-frequency earthquakes have occurred beneath Shikoku and the Kii Peninsula. These earthquakes that have occurred in the convergent plate boundary have close relation to thermal state produced by plate <span class="hlt">subduction</span>. The PHS plate embraces the Shikoku Basin in its northern part. The Kinan seamount chain is located in the central part of the Shikoku Basin. This is the fossil ridge which had been spreading in the ENE-WSW direction. The fossil ridge and its surrounding region are subducing along the Nankai Trough, and the direction of the plate motion of the PHS plate is considered to be changed to the current direction at about 3 Ma (Takahashi, 2004). We constructed a 2-D thermal convection model to simulate temperature field associated with <span class="hlt">subduction</span> of the PHS plate along the Nankai Trough. Then, we evaluated the reliability of the calculated temperature field, by comparing it with observed heat flow data. In this study, we constructed the numerical model, taking account of spatio-temporal change of the age of the PHS plate, kinematics of the past and present plate motion of the PHS plate, and the up-to-date shape of the upper surface of the PHS plate. We calculated temperature distribution and heat flow along three profiles passing through northern Kyushu, Shikoku, and the Kii Peninsula, and compared these results with the observed heat flow data. We used Hi-net heat flow data (Matsumoto, 2009) as well as borehole and heat probe (Tanaka et al., 2004) and BSR (Ashi et al., 1999, 2002) data. The calculated heat flow fits well with the observation for all the three profiles within the range of horizontal distance of about 100km landward from the trough axis. But the observation values increased gradually at about 100km, and decreased at more landward. On the other hand, the calculated results tended to decrease gradually toward just above the mantle wedge when we only considered the effect of plate <span class="hlt">subduction</span>. To explain high heat flow values obtained by Hi-net, we took into account the effect of large-scale hot plume in our model, which was indicated by seismic tomography results. We also incorporated the effect of yield stress and thinner conductive continental plate into our model. The calculated results showed higher heat flow values with short wavelength, which was consistent with the observation. This suggests that high heat flow values observed by Hi-net may be explained by the existence of large-scale hot plume reaching shallow depths in addition to plate <span class="hlt">subduction</span>.</p> <div class="credits"> <p class="dwt_author">Yoshioka, Shoichi; Suminokura, Yoichiro; Matsumoto, Takumi; Nakajima, Junichi</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">74</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T11C1833O"> <span id="translatedtitle">Precise hypocenter distribution of deep low-frequency earthquakes and its relationship to the local geometry of the <span class="hlt">subducting</span> plate in Nankai <span class="hlt">subduction</span> zone, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent studies have shown that deep low frequency tremor in the western Shikoku is a swarm activity of low-frequency earthquakes (LFEs) that occur as shear slips on the plate interface. Tremor is also observed in other regions in Nankai <span class="hlt">subduction</span> zone, such as Tokai, Kii peninsula, Shikoku, and Bungo strait, but hypocenters in the catalog of <span class="hlt">Japan</span> Meteorological Agency (JMA) have wide depth distribution and it is not obvious if they are slips on the plate interface. This is because of large noise, which also yields large errors when we apply a hypocenter determination method using cross-correlation for each station. To overcome this problem, we developed a new robust hypocenter determination method (Ohta and Ide, EPS, 2008) using the summed waveform cross-correlation coefficient over many stations, termed a network correlation coefficient (NCC). In this study, we apply this method to more than 1500 LFEs in JMA catalog which occur from 2002 to 2008 along Nankai trough. Relocated hypocenters construct plane surfaces in every region, which suggests that LFEs in Nankai <span class="hlt">subduction</span> zone occur on the plate boundary as demonstrated in the western Shikoku. Precise LFE distribution is consistent with the geometry of the <span class="hlt">subducting</span> Philippine Sea plate estimated by receiver function analysis (Shiomi et al., 2008). It also suggests the possibility that precise locations of the plate boundary are estimated by the tremor locations.</p> <div class="credits"> <p class="dwt_author">Ohta, K.; Ide, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">75</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.5708S"> <span id="translatedtitle">Deep seismic reflection profiling of the <span class="hlt">subduction</span> megathrust across the Sagimi trough and Tokyo bay, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Beneath the metropolitan Tokyo, the Philippine Sea plate, in particular the fore arc portion of the Izu-Bonin island arc, has been <span class="hlt">subducted</span>. <span class="hlt">Subduction</span> megathrust beneath Tokyo generated M-8 class earthquakes, such as the 1923 Kanto (M7.9) and 1703 Genroku (M8.0) earthquakes. Due to the buyant <span class="hlt">subduction</span> of the Izu-Bonin arc, the megathrust lies very shallow part of the crust. The Kozu-Matsuda fault, probable spray fault from the megathrust, emerged at the surface. In 2009, we acquired the deep seismic reflection data across the toe of the thrust system to reveal the connectivity of the probable spray fault to the megathrust. Together with the deep seismic section acquired in 2003, we show a 120-km-long deep seismic reflection profile from the front to 30 km in depth and discuss the geometry and characteristics of the thrust system. We performed deep seismic profiling across the Sagami trough for a 70-km-long seismic line in September 2009, using two ships for offshore seismic data acquisition: a gun-ship with a 3020 cu. inch air-gun and a cable-ship with a 2-km-long, streamer cable and a 480 cu. inch air-gun. The seismic signals were recorded at Miura and Izu peninsulas located both ends of the seismic line. At both sides of the onshore line, off-line recorders were deployed along total 20-km-long seismic lines at a 50m interval. Seismic reflection data were acquired by different offset of ships making large-offset gathers. The northeast end of the seismic line connected with the 2003 Tokyo bay seismic line (Sato et al., 2005: Science). The obtained seismic sections portray the detailed geometry of the spray faults, suggesting an emergent thrust with 4 km thick landward dipping strata. It merges to the megathrust at 6-7 sec (TWT). Judging from the geometry of fault-related fold in the trough fill sediments, the tip of the megathrust is located at 3 sec (TWT) beneath the trough axis. According to the co-seismic crustal deformation, the slip of the 1923 Kanto earthquake occurred along the main megathrust. According to the paleoseismic <span class="hlt">trenching</span> survey of the spray fault (the Kozu-Matsuda fault, KMF), KMF displaced from AD 1100 to 1350 (Kanagawa Pref., 2005). Shimazaki et al. (2009: JpGU meeting) found the tsunami sediments correlatable to the 1923 Kanto, the 1703 Genroku and 1293 seismic event. Judging from the connectivity of KMF to the megathrust, the seismic event of AD 1293 was caused by displacement of the megathrust and out-of-sequence spay fault (KMF). From the coseismic crustal deformation and seismic waveforms of the 1923 Kanto earthquake, the locations of asperities were well determined (Sato et al., 2005). The distribution of slip deficit on the plate interface determined by GPS (Sagiya and Sato, 2005: Seismol. Soc. Jpn. meeting) accords well to the estimated asperity zone. On the seismic reflection profile, the asperity zone (stack plate interface) is marked by poor reflection from the fault surface and the plate interface is clearly identified as strong reflectors at the deeper steady creeping zone.</p> <div class="credits"> <p class="dwt_author">Sato, Hiroshi; Iwasaki, Takaya; Abe, Susumu; Saito, Hideo; Kawanaka, Taku; Hirata, Naoshi</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">76</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40844564"> <span id="translatedtitle">A triple-planed structure of seismicity and earthquake mechanisms at the <span class="hlt">subduction</span> zone off Miyagi Prefecture, northern Honshu, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A detailed cross-section of seismicity combined with types of earthquake mechanisms was constructed for the <span class="hlt">subduction</span> zone off Miyagi Prefecture, northern Honshu, <span class="hlt">Japan</span>, where a large Ms = 7.5 earthquake occurred on June 12, 1978. Nodal-plane solutions were determined for fourteen earthquakes with body wave magnitudes >=5.4 using data recorded at WWSSN and Japanese stations. For smaller-magnitude events, the types</p> <div class="credits"> <p class="dwt_author">Tetsuzo Seno; Bubpha Pongsawat</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">77</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51924620"> <span id="translatedtitle">Mega-thrust and Intra-slab Earthquakes beneath Tokyo Metropolitan Area around <span class="hlt">subduction</span> and collision zones in <span class="hlt">JAPAN</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In central <span class="hlt">Japan</span> the Philippine Sea plate (PSP) <span class="hlt">subducts</span> beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9). The vertical proximity of this down going lithospheric plate is of concern because the greater Tokyo urban region has a population of 42 million and</p> <div class="credits"> <p class="dwt_author">N. Hirata; K. Kasahara; H. Hagiwara; H. Satow; K. Shimazaki; K. Koketsu; F. Wu; D. Okaya</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">78</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55651539"> <span id="translatedtitle">Mega-thrust and Intra-slab Earthquakes beneath Tokyo Metropolitan Area around <span class="hlt">subduction</span> and collision zones in <span class="hlt">JAPAN</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In central <span class="hlt">Japan</span> the Philippine Sea plate (PSP) <span class="hlt">subducts</span> beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9). The vertical proximity of this down going lithospheric plate is of concern because the greater Tokyo urban region has a population of 42 million and</p> <div class="credits"> <p class="dwt_author">N. Hirata; K. Kasahara; H. Hagiwara; H. Satow; K. Shimazaki; K. Koketsu; F. Wu; D. Okaya</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">79</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.S23B2275S"> <span id="translatedtitle">3D array observation of the low frequency earthquakes in Tokai <span class="hlt">subduction</span> zone, central <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Tokai area is the eastern side of Southwest <span class="hlt">Japan</span> <span class="hlt">subduction</span> where great earthquakes and deep low-frequency earthquakes (LFEs) occur along the convergent plate boundary. Researching the relationship between the great interplate earthquakes and activity of LFEs, Tono Research Institute of Earthquake Science (TRIES) installed two seismic arrays at Shimoyama in Tokai area. The first was a small-aperture array (six stations in the area of 120m diameter) with short-period velocity type seismographs. The second was a middle-aperture array (four stations in the area of 4 km diameter) with high-sensitive acceleration type seismographs. Geological Survey of <span class="hlt">Japan</span> (AIST) also installed a seismic array of three borehole-type instruments with high-sensitive seismographs at three depths of 50m, 200m, and 600m at Shimoyama. We used seismic data of those three arrays and SMYH station of Hi-net array of National Research Institute of Earth Science and Disaster Prevention (NIED) as 3D array data for investigating LFEs. Using the 3D array (total 14 stations), we observed a remarkable activity of LFEs occurring in Tokai area in November 10-30, 2010. We analyzed the 3D array data to pick out direct P and S-waves propagating from LFE origins by using the semblance method (Neidel and Tarner, 1971). Assuming a homogeneous half space model with Vp=4.5 km/s and Vs=2.2 km/s, we obtained a semblance distribution for each component depending on the three factors of time, back-azimuth and incident angle of seismic waves. The maximum semblance point in each component shows a direct P-wave in UD, and S-wave in NS and EW, respectively. Incident angles and back-azimuths are compared with theoretical ones calculated by using JMA hypocenter data.</p> <div class="credits"> <p class="dwt_author">Suzuki, S.; Okubo, M.; Imanishi, K.; Kitagawa, Y.; Takeda, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">80</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T21C1822S"> <span id="translatedtitle">Numerical simulations of temperature distributions associated with <span class="hlt">subduction</span> of the Philippine Sea plate in southwest <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Large megathrust earthquakes have occurred repeatedly along the Nankai Trough with recurrence interval of about 90 to 150 years, which have been caused by plate motion of the Philippine Sea (PHS) plate in the NW direction <span class="hlt">subducting</span> beneath southwest <span class="hlt">Japan</span>. Deep low-frequency earthquakes have occurred beneath Shikoku and the Kii Peninsula. These earthquakes that have occurred in the convergent plate boundary have close relation to thermal state produced by plate <span class="hlt">subduction</span>. The PHS plate embraces the Shikoku Basin in its northern part. The Kinan seamount chain is located in the central part of the Shikoku Basin. This is the fossil ridge which had been spreading in the ENE-WSW direction. The fossil ridge and its surrounding region are subducing along the Nankai Trough, and the direction of the plate motion of the PHS plate is considered to be changed to the current direction at about 3 Ma (Takahashi, 2004). We constructed a 2-D thermal convection model to simulate temperature field associated with <span class="hlt">subduction</span> of the PHS plate along the Nankai Trough (Torii and Yoshioka, 2007). Then, we evaluated the reliability of the calculated temperature field, by comparing it with observed heat flow data. In this study, we constructed the numerical model, taking account of spatio-temporal change of the age of the PHS plate, kinematics of the past and present plate motion of the PHS plate, and the up-to-date shape of the upper surface of the PHS plate. We calculated temperature distribution and heat flow along three profiles passing through northern Kyushu, Shikoku, and the Kii Peninsula, and compared these results with the observed heat flow data. We used Hi-net heat flow data (Matsumoto, 2007) as well as borehole and heat probe (Tanaka et al., 2004) and BSR (Ashi et al., 1999, 2002) data. The calculated heat flow fit well with the observation for all the three profiles within the range of horizontal distance of about 100km landward from the trough axis. But the observation value increased gradually at about 100km, and decreased at more landward. On the other hand, the calculated results tended to decrease gradually toward just above the mantle wedge associated with <span class="hlt">subduction</span> of the slab. The observed heat flow increased and decreased from fore arc to back arc along the profile passing through northern Kyushu. The calculated results in northern Kyushu had a tendency that was similar to that in Shikoku and the Kii Peninsula. In addition, the calculated values for all the three profiles were less than those of the observed Hi-net heat flow data. More detailed analyses and examinations of the observed data are necessary to explain the high heat flow obtained by Hi-net. There may be effective heat transport and/or internal heating which are not considered in our model. We will mention such models in our presentation.</p> <div class="credits"> <p class="dwt_author">Suminokura, Y.; Yoshioka, S.; Matsumoto, T.; Nakajima, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_3");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a 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<img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">81</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUFM.T11A0349O"> <span id="translatedtitle">What controls the earthquake and tsunami sources in <span class="hlt">subduction</span> zone? MCS profiles across the Tokachi-oki earthquake sources along the Kuril <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">High-resolution multi-channel seismic profiles show a contrast in active geologic structure in forearc slopes of the Kuril <span class="hlt">subduction</span> zone, which reflects the mechanical processes along the plate boundary and the source regions of the recent earthquakes and tsunamis. Structural and tectonic patterns are different to the east and west of Kushiro submarine canyon along the southwestern Kuril <span class="hlt">trench</span>, where recurrence of large (Msim8) earthquakes have been documented in the last 200 years. The source regions of recent earthquakes and tsunamis, 2003, 1952 and 1843, seem to be variable. The most recent two events, 1952 and 2003, shared the same asperity beneath the forearc slope to the west of Kushiro Submarine Canyon, according to seismological analysis (Yamanaka and Kikuchi, 2003). However, their tsunami sources were different; the 1952 tsunami source extended to the lower slope east of the canyon, according the inversion of tide gauge records (Hirata et al., 2003). While the data were limited, the tsunami height distribution of the 1843 earthquake was similar to that of the 1952 event. We performed high-resolution multi-channel seismic surveys on both upper and lower forearc slopes of southwestern Kuril <span class="hlt">Trench</span>. The upper slope was surveyed during 2002-2004 R/V Hakurei cruises, while the lower slope was covered during JAMSTEC's R/V Kairei cruise in 2005. These profiles indicate a subsiding forearc basin covered by > 3 km thick Neogene sediments around the Tokachi-oki asperity. A gentle structural high bounds the seaward edge of both basin and asperity, suggesting that they are closely related. The structural high continues to the east and becomes a clear topographic ridge beyond the Kushiro submarine canyon. The seaward slope of the ridge shows seaward-dipping, discontinuous obscure reflections, indicating that the slope is a frontal accretionary prism. The 1952 tsunami source is located in the prism, which is probably uplifting. No indication of large-scale landslide indicates that the extended tsunami source in 1952 is due to tectonic origin.</p> <div class="credits"> <p class="dwt_author">Okamura, Y.; Tsujino, T.; Arai, K.; Satake, K.; Sasaki, T.; Ikehara, K.; Noda, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">82</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51362614"> <span id="translatedtitle">Deep seismic reflection profiling of the <span class="hlt">subduction</span> megathrust across the Sagimi trough and Tokyo bay, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Beneath the metropolitan Tokyo, the Philippine Sea plate, in particular the fore arc portion of the Izu-Bonin island arc, has been <span class="hlt">subducted</span>. <span class="hlt">Subduction</span> megathrust beneath Tokyo generated M-8 class earthquakes, such as the 1923 Kanto (M7.9) and 1703 Genroku (M8.0) earthquakes. Due to the buyant <span class="hlt">subduction</span> of the Izu-Bonin arc, the megathrust lies very shallow part of the crust. The</p> <div class="credits"> <p class="dwt_author">Hiroshi Sato; Takaya Iwasaki; Susumu Abe; Hideo Saito; Taku Kawanaka; Naoshi Hirata</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">83</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUSM.S51C..07V"> <span id="translatedtitle">Upper Mantle Shear Wave Anisotropy for Stations in Mexico and its Relationship to <span class="hlt">Subduction</span> at the Middle America <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have calculated the splitting parameters that describe upper mantle shear wave anisotropy under stations in continental Mexico located over the <span class="hlt">subducting</span> Cocos Plate. SKS and SKKS arrivals recorded on both the radial and transverse horizontal components were used. The splitting parameters which quantify anisotropy are the delay time (?t) and the fast polarization direction (?). The anisotropy is calculated using the approach by Silver and Chan [1991]. A time segment containing the SKS arrival is selected from both horizontal components. The space of possible solutions is then searched in one-degree intervals with ? ranging between 0 and 180°. Specifically, the coordinate axes are rotated every 1 degree increment and the autocorrelation and crosscorrelation between the components is calculated. For each value of ?, the solution space is also searched in 0.05 s increments. Next the eigenvalues corresponding to each ?t and ? combination are calculated. In the presence of noise, the desired solution will be given by the matrix which is most nearly singular. In order to check our results, we apply a correction in the amount of the measured ?t and ? to the original records and then rotate them to make sure that the anisotropy disappears. The shapes and the difference in the arrival times of the fast and slow waves are compared to make sure that the result is robust. As a further check, the polarization of the particle motion for the radial and transverse components before and after correction is plotted. The records used were taken from Mexico's Servicio Sismológico Nacional broadband network [Singh et al., 1997]. The orientation of the fast polarization direction, ?, can be explained by the absolute motion of the North American plate for some of the stations. Most of the stations, however, require a different explanation for the orientation of ?. For example, the orientation of ? for stations Platanillo (PLIG), Yautepec (YAIG), and Popocatépetl (PPIG) is aligned with the direction of absolute motion for the North American plate [Van Benthem, 2005]. The orientation of ? under Cayaco (CAIG) is close to the orientation of the relative plate motion vector between the Cocos and North American plates. The only measurement available under Ciudad Universitaria (CUIG) indicates that the orientation of ? is consistent with the extensional regime in the Trans- Mexican Volcanic Belt, with normal faults running east-west.</p> <div class="credits"> <p class="dwt_author">van Benthem, S. A.; Valenzuela, R. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">84</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1999JGR...10428803D"> <span id="translatedtitle">Slab temperature and thickness from seismic tomography: 2. Izu-Bonin, <span class="hlt">Japan</span>, and Kuril <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Delay times from teleseismic and local P wave arrivals are used to invert for a high-resolution three-dimensional velocity model beneath the northwest Pacific. The model shows high-velocity slabs with average velocity anomalies of the order of 3-4%. Assuming the positive velocity deviations in the <span class="hlt">subducting</span> lithosphere are to first order due to a temperature anomaly, the results of a theoretical slab temperature profile based on the diffusion equation are converted to a synthetic slab velocity model. Temperature variations between the ambient mantle and the interior of the slab are converted to P wave velocity perturbations using dVp/dT ? 4.8 × 10-4 km s-1 °C-1. A nonlinear optimization scheme compares the tomograms obtained via tomography to the theoretically predicted models in order to determine the optimal values for slab thickness and mantle potential temperature. Using 1180±100°C as the potential temperature, thickness estimates of 88±8 km, 85±8 km, and 84±8 km are obtained for the Izu-Bonin, <span class="hlt">Japan</span>, and Kuril slabs, respectively. A correlation exists between slab thickness and age, which is strong if mantle temperature variations along the slab strike can be ruled out. In the process of estimating slab thickness the predicted slab velocity model is used as a filter to enhance the initial minimum-norm tomographic result. The initial tomogram is modified to closely resemble the synthetic slab tomogram by using only null-space components. The use of the null-space components guarantees that the enhanced solution will satisfy the original seismic delay times. The enhanced slab images show very continuous and narrow slabs compared to the initial tomographic results.</p> <div class="credits"> <p class="dwt_author">Deal, Michael M.; Nolet, Guust</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">85</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JGRB..118.3037C"> <span id="translatedtitle">Petro-fabrics and seismic properties of blueschist and eclogite in the North Qilian suture zone, NW China: Implications for the low-velocity upper layer in <span class="hlt">subducting</span> slab, <span class="hlt">trench</span>-parallel seismic anisotropy, and eclogite detectability in the <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">potential seismological contributions of metamorphosed and deformed oceanic crust in a <span class="hlt">subduction</span> zone environment were studied in a detailed petro-fabric analysis of blueschist and eclogite in the North Qilian suture zone, NW China. The calculated whole-rock seismic properties based on the measured lattice preferred orientations of the constituting minerals show increasing P-wave and S-wave velocities and decreasing seismic anisotropies from blueschist to eclogite, mainly due to the decreasing volume proportion and deformation extent of glaucophane. The low velocity of the upper layer in the <span class="hlt">subducting</span> oceanic crust can be explained by the existence of blueschist and foliated eclogite, which induces a 3-12% reduction in velocity compared to that induced by the surrounding mantle rocks. This low-velocity layer may gradually disappear when blueschist and foliated eclogite are replaced by massive eclogite at a depth in excess of 60-75 km for the paleo North Qilian <span class="hlt">subduction</span> zone. <span class="hlt">Trench</span>-parallel seismic anisotropy with a moderate delay time (0.1-0.3 s) can only effectively contribute to deformed blueschist and eclogite in a high-angle (>45-60°) <span class="hlt">subducting</span> slab, regardless of the direction of slab movement. The calculated reflection coefficients (Rc = 0.04-0.20) at the lithologic interfaces between eclogite and blueschist imply that it may be possible to detect eclogite bodies in shallow <span class="hlt">subduction</span> channels using high-resolution seismic reflection profiles. However, the imaging of eclogite bodies located in deep <span class="hlt">subduction</span> zones could be challenging.</p> <div class="credits"> <p class="dwt_author">Cao, Yi; Jung, Haemyeong; Song, Shuguang</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">86</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFMDI31A1948A"> <span id="translatedtitle">Non-elastic Plate Weakening at Tonga, Costa Rica and Japanese <span class="hlt">Subduction</span> Zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Traditionally studies of plate bending in <span class="hlt">subduction</span> zones have utilized elastic, viscous or elastic-plastic rheologies to model the deformation of <span class="hlt">subducting</span> plates, yet they are based on averaged plate properties and do not take into account variations in plate strength. Direct measurements of plate strength at <span class="hlt">subduction</span> zones could permit more detailed models of how plates deform during <span class="hlt">subduction</span> and may allow differentiation between the elastic and viscous or plastic rheologies. Additionally, weakening of the <span class="hlt">subducting</span> plate is important for understanding the degree of coupling of the surface plate to the negative buoyancy of descending slabs. To obtain quantitative measurements of changes in plate strength along profiles parallel to the <span class="hlt">trench</span>, we use analysis of the gravity-topography admittance in three <span class="hlt">subduction</span> zones: Tonga, Costa Rica and <span class="hlt">Japan</span>. We show that the plate flexural rigidity decreases near and inside the <span class="hlt">trench</span> of the Tonga and <span class="hlt">Japan</span> <span class="hlt">subduction</span> zones, in agreement with previous results for the Kermadec <span class="hlt">subduction</span> zone (1). Near the <span class="hlt">trench</span> the flexural rigidity values are consistently smaller than those predicted by an elastic rheology and the plate age (2). This degree of weakening, by up to 3 orders magnitude, suggests that the plate does not act elastically as it is <span class="hlt">subducted</span>, possibly due to lithospheric-scale weakening by extensional faulting and plastic yielding at depth. In contrast lithospheric-scale weakening in the Costa Rica <span class="hlt">subduction</span> zone is less clear. This may be due to the younger age of the <span class="hlt">subducting</span> plate and the small age difference between the seamounts and surrounding plate, which limits the sensitivity of the gravity field to changes in the non-isostatic support of topographic feature. These results suggest that this technique is only applicable to older plates with large seamounts that are appreciably younger than the <span class="hlt">subducting</span> plate. Comparison of the flexural rigidity results to the tectonic characteristics of all three <span class="hlt">subduction</span> zones suggest that plate age (thickness) has a strong affect on the length scale and degree of weakening of the <span class="hlt">subducting</span> plate. References: 1. Billen, M. I., Gurnis, M. 2005. Constraints on <span class="hlt">subducting</span> plate strength within the Kermadec <span class="hlt">Trench</span>. Journal of Geophysical Research, 110(B05407). 2. Caldwell, J. G., Turcotte, D. L. 1979. Dependence of the thickness of the elastic oceanic lithosphere on age. J. of Geophys. Res., 84(B13):7572-7576, December 1979.</p> <div class="credits"> <p class="dwt_author">Arredondo, K.; Billen, M. I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">87</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003PhDT........23K"> <span id="translatedtitle">Cocos plate structure along the Middle America <span class="hlt">subduction</span> zone off Oaxaca and Guerrero, Mexico: Influence of <span class="hlt">subducting</span> plate morphology on tectonics and seismicity</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Two new bathymetric and magnetic surveys are presented from which the history and recent tectonics of the Cocos plate off the Middle America <span class="hlt">subduction</span> zone are determined. The East O'Gorman fracture zone, a previously proposed outer rise feature, is not present along the Oaxaca <span class="hlt">trench</span> outer rise near the <span class="hlt">trench</span> axis. Several parallel ridges of seamounts are entering the <span class="hlt">subduction</span> zone 15--20° from orthogonal to the <span class="hlt">trench</span> axis. These ridges lie roughly parallel to the spreading direction and were created as off-axis volcanism. The southern Mexico <span class="hlt">trench</span> outer rise exhibits reactivation of the inherited abyssal-hill and <span class="hlt">trench</span>-parallel faults to accommodate extension from plate flexure. Plate boundary forces also produce a new unusual family of normal faults parallel to and flanking the seamounts. An anomalous increase in outer rise earthquakes accompany these faults indicating they are seismically active. <span class="hlt">Trench</span>-parallel extension related to the geometry of the <span class="hlt">trench</span> axis bend and increasing plate convergence angle may contribute to their genesis. Unusual outer-rise faulting off of the <span class="hlt">Japan</span> <span class="hlt">trench</span> (Kobayashi et al., 1998) which is coincident with a <span class="hlt">trench</span> axis bend is used to argue that specific conditions at <span class="hlt">subduction</span> zones may activate inherited fracture-zone-parallel weakness. This controls fault orientation at the <span class="hlt">Japan</span> and Mexico outer rises. Seafloor morphology and seismicity evidence leads to a "slivered" ocean-crust model that is broken along the seamount-parallel faults at the <span class="hlt">subduction</span> zone. This accounts for the consistent rupture geometry (40--100 km fault failure) and the uniformity in the character of the thrust waveforms. Limited magnitudes of shallow thrust earthquakes appear to be a consequence of the <span class="hlt">subducted</span> slivering crust. A review of regions whose structures and forces are similar to those present in the <span class="hlt">subducting</span> Cocos plate off Oaxaca indicates that crustal slivering is not unique. Forces other than a <span class="hlt">trench</span> axis bend must be present to furnish the entirely unique seamount-parallel outer-rise faulting. Either/both convergence direction and spreading-parallel inherited weakness orientation may determine outer-rise fault strike. Methods for resolving ambiguous data are proposed.</p> <div class="credits"> <p class="dwt_author">Kanjorski, Nancy Marie</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">88</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.deepseadrilling.org/87/volume/dsdp87_16.pdf"> <span id="translatedtitle">16. CHEMISTRY, CARBON AND OXYGEN ISOTOPE RATIOS, AND ORIGIN OF DEEP-SEA CARBONATES AT SITES 438, 439, AND 584: INNER SLOPE OF THE <span class="hlt">JAPAN</span> <span class="hlt">TRENCH</span>1</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Carbonate concretions in Pliocene to Miocene diatomaceous sediments at Sites 438, 439, and 584 on the deep-sea terrace near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> are composed of calcite, dolomite, and siderite with varying degrees of chemical substitu- tion. ?18? ranges from -0.81 to +5.15‰ for calcite and +2.00 to +7.29‰ for dolomite. ?13C values vary widely be- tween -36.96 and + 11.45‰</p> <div class="credits"> <p class="dwt_author">Ryo Matsumoto; Yukihiro Matsuhisa</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">89</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/22875769"> <span id="translatedtitle">Locomotory activity and feeding strategy of the hadal munnopsid isopod Rectisura cf. herculea (Crustacea: Asellota) in the <span class="hlt">Japan</span> <span class="hlt">Trench</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Benthic fauna in the hadal zone (6500-11,000 m) rely on maintaining sufficient locomotory activity to exploit a low, patchy and uniquely distributed food supply while exposed to high pressure, low temperatures and responding to predator-prey interactions. Very little is currently known about the locomotory capabilities of hadal fauna. In situ video footage of the isopod Rectisura cf. herculea (Birstein 1957) (Asellota, Munnopsidae) was obtained from 6945 and 7703 m deep in the <span class="hlt">Japan</span> <span class="hlt">Trench</span> (NW Pacific Ocean). Measurements of locomotion revealed routine walking speeds of 0.19 ± 0.04 BL s(-1) (mean ± s.d.), increasing to 0.33 ± 0.04 BL s(-1) if naturally perturbed by larger organisms. When immediately threatened by the presence of predators (decapod crustaceans), the isopods are capable of eliciting backward escape jumps and burst swimming escape responses of 2.6 ± 1.5 BL s(-1) and 4.63 ± 0.9 BL s(-1), respectively. These data suggest no significant reduction in locomotory capability despite the extreme depths in which they inhabit. These observations also revealed the isopod to be a bait-attending and aggregative species and suggest that it may not be obligatorily selecting infaunal food sources as previously thought. PMID:22875769</p> <div class="credits"> <p class="dwt_author">Jamieson, Alan J; Fujii, Toyonobu; Priede, Imants G</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">90</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48906298"> <span id="translatedtitle">Slab stiffness control of <span class="hlt">trench</span> motion: Insights from numerical models</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Subduction</span> zones are not static features, but <span class="hlt">trenches</span> retreat (roll back) or advance. Here, we investigate the dominant dynamic controls on <span class="hlt">trench</span> migration by means of two- and three-dimensional numerical modeling of <span class="hlt">subduction</span>. This investigation has been carried out by systematically varying the geometrical and rheological model parameters. Our viscoplastic models illustrate that advancing style <span class="hlt">subduction</span> is promoted by a</p> <div class="credits"> <p class="dwt_author">E. Di Giuseppe; J. van Hunen; F. Funiciello; C. Faccenna; D. Giardini</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">91</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5589789"> <span id="translatedtitle">On the initiation of <span class="hlt">subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote <span class="hlt">trench</span> formation. Three environments proposed as preferential sites of incipient <span class="hlt">subduction</span> are investigated: passive continental margins, transform faults/fracture zones, and extinct ridges. None of these are predicted to convert into <span class="hlt">subduction</span> zones simply by the accumulation of local gravitational stresses. <span class="hlt">Subduction</span> cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins. The attempted <span class="hlt">subduction</span> of buoyant material at a mature <span class="hlt">trench</span> can result in large compressional forces in both <span class="hlt">subducting</span> and overriding plates. This is the only tectonic force sufficient to trigger the nucleation of a new <span class="hlt">subduction</span> zone. The ubiquitous distribution of transform faults and fracture zones, combined with the common proximity of these features to mature <span class="hlt">subduction</span> complexes, suggests that they may represent the most likely sites of <span class="hlt">trench</span> formation if they are even marginally weaker than normal oceanic lithosphere.</p> <div class="credits"> <p class="dwt_author">Mueller, S.; Phillips, R.J. (Southern Methodist Univ., Dallas, TX (USA))</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-10</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">92</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUSM.T33A..03C"> <span id="translatedtitle">Adjoint Tomography of the Crust and Upper Mantle in the <span class="hlt">Japan</span> <span class="hlt">Subduction</span> Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The adjoint tomography technique is an effective tool for using 3-D models as initial models and refining them by iteratively minimizing the misfit between synthetics and data. In this study, we use this technique to obtain a more detailed 3-D image of the descending slab in the <span class="hlt">Japan</span> <span class="hlt">Subduction</span> Zone and its neighboring regions. We have very dense station coverage of our study area with a total of 845 stations, including Hi-net (more than 600 stations), F-net and Global Seismographic Network (GSN) stations. We use Zhao et al's (1994) 3-D slab model embedded in Lebedev and Nolet's (2003) regional model as the initial model in the tomographic inversion and calculate synthetics for each event. According to finite-frequency theory, the sensitive region along the ray path is given by a 3-D 'banana-doughnut' kernel, and the overall spatial distribution of the sum of all available event-station kernels determines the resolvable volume in the inversion. Using the automated windowing code FLEXWIN, we select a set of 206 events. We processed the data and synthetics using two types of bandpass filters: 6--30 s for all the records and 24--120 s for F-net and GSN records. For the first iteration, the frequency-dependent traveltime misfit measurements between synthetics and data are made in 44,709 windows for the period range of 24-120 s and 119,376 windows for the period range of 6-30 s. The combined adjoint sources are thus constructed based on these traveltime misfit measurements. Given the adjoint sources, we use the adjoint spectral-element method to calculate banana-doughnut kernels for P, S and surface waves for the selected records. The weighted sums of the banana-doughnut kernels for all event-station pairs, with weights determined by the traveltime measurements, are used to construct misfit kernels. These gradients are then used in a non-linear conjugate gradient algorithm to further improve the existing 3-D models. We are currently at the first iteration of the 3-D models. The preliminary results indicate that seismic velocities of the Pacific slab need to be faster to reduce the misfit; the observed small-scale features requiring slower seismic velocities might be related to mantle wedge melts, but this needs further investigation in subsequent iterations.</p> <div class="credits"> <p class="dwt_author">Chen, M.; Tromp, J.; van der Hilst, R.; Liu, Q.; Kanamori, H.; Maeda, T.; Obara, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">93</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.T13B1935C"> <span id="translatedtitle">Adjoint Tomography of the Crust and Upper Mantle in the <span class="hlt">Japan</span> <span class="hlt">Subduction</span> Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The adjoint tomography technique is an effective tool for using 3-D models as initial models and refining them by iteratively minimizing the misfit between synthetics and data. In this study, we use this technique to obtain a more detailed 3-D image of the descending slab in the <span class="hlt">Japan</span> <span class="hlt">Subduction</span> Zone and its neighboring regions. We have very dense station coverage of our study area with a total of 845 stations, including Hi-net (more than 600 stations), F-net and Global Seismographic Network (GSN) stations. We use Zhao et al.'s (1994) 3-D slab model embedded in Lebedev and Nolet's (2003) regional model as the initial model in the tomographic inversion and calculate synthetics for each event. According to finite-frequency theory, the sensitive region along the ray path is given by a 3-D 'banana-doughnut' kernel, and the overall spatial distribution of the sum of all available event-station kernels determines the resolvable volume in the inversion. Using the automated windowing code FLEXWIN, we select a set of 206 events. We processed the data and synthetics using two types of bandpass filters: 6--30 s for all the records and 24--120 s for F-net and GSN records. For the first iteration, the frequency-dependent traveltime misfit measurements between synthetics and data are made in 44,709 windows for the period range of 24--120~s and 119,376 windows for the period range of 6--30~s. The combined adjoint sources are thus constructed based on these traveltime misfit measurements. Given the adjoint sources, we use the adjoint spectral-element method to calculate banana-doughnut kernels for P, S and surface waves for the selected records. The weighted sums of the banana-doughnut kernels for all event-station pairs, with weights determined by the traveltime measurements, are used to construct misfit kernels. These gradients are then used in a non-linear conjugate gradient algorithm to further improve the existing 3-D models. We are currently at the first iteration of the 3-D models. The preliminary results indicate that seismic velocities of the Pacific slab need to be faster to reduce the misfit; the observed small-scale features requiring slower seismic velocities might be related to mantle wedge melts, but this needs further investigation in susequent iterations.</p> <div class="credits"> <p class="dwt_author">Chen, M.; Liu, Q.; Maggi, A.; Tromp, J.; Kanamori, H.; Maeda, T.; Obara, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">94</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002AGUFM.G71A0944T"> <span id="translatedtitle">Three-dimensional Crustal Velocity Field of the Nankai Forearc, Southwest <span class="hlt">Japan</span>: Oblique <span class="hlt">Subduction</span> and Forearc Slip</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Oblique <span class="hlt">subduction</span> of the Philippine Sea plate (PH) is the dominant factor controlling crustal deformation field of southwest <span class="hlt">Japan</span>. Interseismic crustal shortening in the direction of plate convergence has been clearly illustrated by the nationwide continuous GPS array measurements. On the other hand, oblique <span class="hlt">subduction</span> should generate small but permanent lateral slip of the Nankai forearc along the arc-parallel strike-slip fault system (the Median Tectonic Line: MTL) that separates the forearc from the main part of southwest <span class="hlt">Japan</span>. Since station spacing of the continuous array is still too sparse to investigate this possibility, we use velocities obtained from GPS campaign measurements along a 200km-long margin-normal traverse across the MTL. By combining 23 campaign velocities with the velocities at 60 continuous stations, we obtain a dense three-dimensional velocity map. Crustal shortening observed is well reproduced by the elastic deformation due to the PH <span class="hlt">subduction</span>, using multi-rectangular plate interface segments, depth-dependent plate coupling, and newly determined PH velocity relative to southwest <span class="hlt">Japan</span>. Vertical velocity field observed also shows good accordance with the PH <span class="hlt">subduction</span>. The subsidence-uplift pattern is consistent with the leveling results but space coverage and time resolution have been greatly improved. After subtracting the elastic deformation from the observed velocity field, the residual velocity field shows right-lateral strike-slip block motion of about 5mm/yr across the MTL, consistent with long-term slip rate estimated from geological observation. New finding is that the block boundary (narrow zone of a high velocity gradient) does not coincide with the surface trace of the MTL, being displaced 20-30km to the north. The residual velocity field is reproduced by a model with a 35-45deg northward-dipping fault plane, full locking of the upper portion to a depth of 15km, and steady slip of 5mm/yr below. These results are supported by imaging of an inclined fault plane revealed by recent seismic profiling and currently low activity of shallow earthquakes.</p> <div class="credits"> <p class="dwt_author">Tabei, T.; Ohta, Y.; Hashimoto, M.; Miyazaki, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">95</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005DSRII..52.1505K"> <span id="translatedtitle">Diagnoses of simulated water-mass <span class="hlt">subduction</span>/formation/transformation in the <span class="hlt">Japan</span>/East Sea (JES)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The impacts of surface atmospheric forcing of different time-space scales on the simulation of water-mass formation and spreading of formed water are investigated by quantifying water-mass <span class="hlt">subduction</span>/formation/transformation for the <span class="hlt">Japan</span>/East Sea (JES). The Princeton Ocean Model (POM) was implemented for the JES (JES-POM) to simulate interannual, seasonal, and mesoscale variations in velocity and mass fields. Three sets of atmospheric flux data were used; (1) 6-h fluxes calculated from 6-h atmospheric variables (syn), (2) monthly means of 6-h fluxes (empm), and (3) fluxes calculated from monthly averaged atmospheric variables (mont). The mass exchange between the mixed layer and interior in the JES was diagnosed in terms of annual <span class="hlt">subduction</span> rate ( Sann). Three areas of local maximum Sann (>500 m/yr) occurred: area V (41-43°N west of 137°E), K (36-39°N west of 132°E), and KB (near Korea Bay). Area V corresponds to the "flux center" (i.e., maximum heat and momentum fluxes) described by Kawamura and Wu [1998. Formation mechanism of <span class="hlt">Japan</span> Sea Proper Water in the flux center off Vladivostok. J. Geophys. Res. 103 (C10), 21611-21622] the <span class="hlt">subduction</span> region suggested by Senjyu and Sudo [1994. The upper portion of the <span class="hlt">Japan</span> Sea proper water: its source and circulation as deduced from isopycnal analysis. J. Oceanogr. 50, 663-690; 1996. Interannual variation of the upper portion of the <span class="hlt">Japan</span> proper water and its probable cause. J. Oceanogr. 52, 72-42] and Yoshikawa et al. [1999. Formation and circulation processes of intermediate water in the <span class="hlt">Japan</span> Sea. J. Phys. Oceanogr. 29 (8), 1701-1722], and the wintertime convection location identified by Seung and Yoon [1995. Some features of winter convection in the <span class="hlt">Japan</span> Sea. J. Oceanogr. 51, 61-73]. With monthly forcing (mont), there is no localized maximum value off Vladivostok, while with forcing influenced by synoptic events (monthly; empm and 6-h; syn), either one or two localized areas with a high <span class="hlt">subduction</span> rate occur with year-to-year variations. The presence of simulated dense surface water ( >??=26.8) in the northern JES is due to the effects of synoptic events during winter months when large heat loss and strong wind stress associated with cold-air outbreaks and extratropical cyclones occur. The convection magnitudes as a result of air-sea interaction are 3.0, 4.0, and 6.0 Sv for mont, empm, and syn, respectively. A net flux of mass from the interior to the mixed layer (entrainment) occurs in the density range between ??=24.0 and ??=26.2 for both empm (3.5 Sv) and syn (3.0 Sv), while it occurs in the density range between ??=24.0 and ??=25.8 for mont (2.8 Sv). The diffusive fluxes across the winter mixed layer base are about 0.8, 1.0, and 1.4 Sv for mont, empm, and syn, respectively. An undiagnosed eddy-induced turbulent mixing (the residual of the balance after removing discretization error) for syn is almost twice that for the other two cases (mont and empm). These results indicate that without synoptic atmospheric forcing, the diagnostics using the numerical circulation model may significantly underestimate buoyancy loss at the surface, and, hence, water-mass formation, as well as mixing and spreading of the formed water mass.</p> <div class="credits"> <p class="dwt_author">Kang, HeeSook; Mooers, Christopher N. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">96</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6988920"> <span id="translatedtitle">Circum-Pacific modes of <span class="hlt">subduction</span>, collision, and metallogenesis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Tectonic processes in <span class="hlt">trench</span>-arc-back-arc regions, as depicted on the Plate-Tectonic Map of the Circum-Pacific Region, are controlled by different modes of <span class="hlt">subduction</span>. In one end member, the Chilean or high-stress <span class="hlt">subduction</span> zone, the stress regime in the overriding lithosphere is compressive; whereas in the other end member, the Mariana or low-stress <span class="hlt">subduction</span> zone, extensional tectonics prevails. The two modes are characterized by porphyry copper and massive sulfide metallogenesis, respectively. In both modes, sediment that fills grabens on the <span class="hlt">subducting</span> plate may be <span class="hlt">subducted</span>. When a large buoyant feature such as drifting continental crust arrives at the <span class="hlt">trench</span>, collision-accretion tectonics with a strong compressive stress ensues. In such a collision zone, however, buoyant <span class="hlt">subduction</span> of the light crust continues to a considerable extent, such as in the doubling of crust under Tibet and the <span class="hlt">subduction</span> of the Izu block under central <span class="hlt">Japan</span>. When continental crust and oceanic sediments <span class="hlt">subduct</span>, they can begin melting at low temperature and shallow depth, generating more felsic granitoids than those that originate at greater depth under andesitic volcanic arcs. In the northwest Pacific, felsic granitic arcs are extensive, mostly S type, and ilmenite bearing, and they are accompanied by the world's largest tin and tungsten belt. They contrast with, but are parallel to many andesitic volcanic arcs characterized by rich copper-zinc-gold metallogenesis. The authors speculate that the extensive tin-tungsten granitic arcs have their genesis in the buoyant <span class="hlt">subduction</span>, remelting, and large-scale anataxis of sediment-dominated crust as a result of collision-accretion tectonism.</p> <div class="credits"> <p class="dwt_author">Nishiwaki, C.; Uyeda, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">97</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.3737F"> <span id="translatedtitle">Advancing <span class="hlt">trenches</span>: tectonic significance and dynamic implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent global kinematic studies reveal that most of the <span class="hlt">trenches</span> roll back but a significant number of them advance toward the upper plate. Those advancing <span class="hlt">trenches</span> are mostly located in the Western Pacific and correspond to the <span class="hlt">subduction</span> of very old, Mesozoic oceanic lithosphere. While retreating <span class="hlt">trenches</span> are commonly explained by the slab pull action of the descending lithosphere, the origin of advancing <span class="hlt">trenches</span> is still debated. Since this relationships is dependent upon the adopted reference frame, we select region where geological studies show the variability of <span class="hlt">trench</span> migration style with time. The Izu-Bonin-Mariana (IBM) region represents a key example. The detailed reconstruction of the <span class="hlt">trench</span> migration of the IBM <span class="hlt">subducting</span> system reveals that after a long episode of asymmetric rollback, the IBM <span class="hlt">trench</span> recently started advancing. We propose that this change from retreating to advancing <span class="hlt">trench</span> mode results from the <span class="hlt">subduction</span> of progressively older and stiffer lithospheric material. We test this hypothesis by means of two-dimensional (2-D) numerical models, reproducing the effects of the lithospheric aging during <span class="hlt">subduction</span>. The result of our numerical tests show that the entrance of old and stiff lithosphere forces the <span class="hlt">trench</span> to advance because the increasing stiffness of the slab prevents the slab to unbend once it has <span class="hlt">subducted</span>.</p> <div class="credits"> <p class="dwt_author">Faccenna, Claudio; di Giuseppe, Erika; Funiciello, Francesca; van Hunen, Jeroen; Lallemand, Serge</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">98</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40494661"> <span id="translatedtitle"><span class="hlt">Subduction</span> influence of Philippine Sea plate on the mantle beneath northern Kyushu, SW <span class="hlt">Japan</span>: An examination of boron contents in basaltic rocks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Northern Kyushu, characterized by the <span class="hlt">subduction</span> of two oceanic slabs (a hot Shikoku basin and a cold Philippine Sea plate) beneath the Eurasian plate, forms a complex portion of Southwestern <span class="hlt">Japan</span> arc.In order to evaluate the effect of slab-derived fluids from these two contrasting oceanic plates, we determined the boron (B) contents in basaltic rocks from ten volcanoes and three</p> <div class="credits"> <p class="dwt_author">Masaya Miyoshi; Takaaki Fukuoka; Takashi Sano; Toshiaki Hasenaka</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">99</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFMDI33C..05K"> <span id="translatedtitle">Serpentine preferred orientation and variation in <span class="hlt">subduction</span> zone anisotropy</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Serpentine has a strong crystallographic anisotropy, which is several times greater than olivine, and the occurrence of serpentine is expected where water infiltrates into the mantle. Accordingly, one possible explanation of the spatial variation of seismic anisotropy in <span class="hlt">subduction</span> zones is the crystal-preferred orientation of serpentine. In the <span class="hlt">Japan</span> <span class="hlt">subduction</span> systems, delay time of shear wave splitting is ~1-2 sec beneath the Ryukyu arc, whereas northeast <span class="hlt">Japan</span> shows much shorter delay time ~0.1-0.2 sec. Although seismic anisotropy in the upper mantle is generally attributed to the crystal-preferred orientation of olivine, the strong anisotropy (dt ~1-2 sec) observed in the Ryukyu arc cannot be explained in terms of olivine anisotropy, even if the entire mantle wedge were to act as an anisotropic source. Here we report that the crystal-preferred orientation of serpentine can produce the strong <span class="hlt">trench</span>-parallel anisotropy and results variations of seismic anisotropy observed in the <span class="hlt">subduction</span> systems. High-pressure deformation experiments reveal that the serpentine c-axis tends to rotate to an orientation normal to the shear plane; consequently, seismic velocity propagating normal to the shear plane (plate interface) is much slower than that in other directions. The seismic anisotropy estimated for deformed serpentine aggregates (AVs of ~32%) is much greater than that for olivine; consequently, the alignment of serpentine in the hydrated mantle wedge results in a strong <span class="hlt">trench</span>-parallel seismic anisotropy in the case of a steeply <span class="hlt">subducting</span> slab. This hypothesis is consistent with the presence of a hydrous phase in the mantle wedge beneath the Ryukyu arc, as inferred from anomalously low seismic velocities. In contrast, if the <span class="hlt">subduction</span> angle is a relatively flat, the serpentine slowest c-axis is oriented normal to the <span class="hlt">subducting</span> plate, resulting a much smaller detectable seismic anisotropy. This may explain the weak seismic anisotropy in the Cascadia <span class="hlt">subduction</span> zone where the presence of serpentine is also inferred.</p> <div class="credits"> <p class="dwt_author">Katayama, I.; Hirauchi, K.; Michibayashi, K.; Ando, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">100</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48910763"> <span id="translatedtitle">Asperity map along the <span class="hlt">subduction</span> zone in northeastern <span class="hlt">Japan</span> inferred from regional seismic data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In an attempt to examine the characteristic behavior of asperities, we studied the source processes of large interplate earthquakes offshore of the Tohoku district, northeastern <span class="hlt">Japan</span>, over the past 70 years. In this area, earthquakes of M7 class have a recurrence interval of about 30 years. Seismic observation using a strong-motion seismometer has been carried out by the <span class="hlt">Japan</span> Meteorological</p> <div class="credits"> <p class="dwt_author">Yoshiko Yamanaka; Masayuki Kikuchi</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_4");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a 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showDiv("page_7");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">101</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.7492L"> <span id="translatedtitle">A global view of shear wave splitting and mantle flow in <span class="hlt">subduction</span> systems</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The character of the mantle flow field in <span class="hlt">subduction</span> zone regions remains poorly understood, despite its importance for our understanding of <span class="hlt">subduction</span> dynamics. Observations of seismic anisotropy, which manifests itself in shear wave splitting, can shed light on the geometry of mantle flow in <span class="hlt">subduction</span> zones, but placing constraints on anisotropy in various parts of the <span class="hlt">subduction</span> system (including the overriding plate, the mantle wedge, the <span class="hlt">subducting</span> slab, and the sub-slab mantle) remains challenging from an observational point of view. In order to identify dynamic processes that make first-order contributions to the pattern of mantle flow in <span class="hlt">subduction</span> zones, we analyze a global compilation of shear wave splitting measurements for a variety of ray paths, including SK(K)S and teleseismic S phases as well as local S and source-side splitting from slab earthquakes. Key challenges associated with assembling such a compilation include correctly assessing and accounting for any dependence of local S splitting parameters on frequency and correctly characterizing any contribution to SKS splitting measurements from anisotropy within the <span class="hlt">subducting</span> slab that is unrelated to active mantle flow. We present local case studies from the <span class="hlt">Japan</span> and Izu-Bonin-Marianas <span class="hlt">subduction</span> zones that explore frequency-dependent splitting due to heterogeneous anisotropy in the mantle wedge and that use a variety of raypath combinations to isolate the contribution from anisotropy within the slab. Keeping these results in mind, we have compiled shear wave splitting measurements from <span class="hlt">subduction</span> zones globally from the literature and from our own work to produce estimates of average shear wave splitting parameters - and their spatial variation - for the mantle wedge and the sub-wedge region for individual <span class="hlt">subduction</span> segments. These estimates are then compared to other parameters that describe <span class="hlt">subduction</span>. The sub-wedge splitting signal is relatively simple and is dominated by <span class="hlt">trench</span>-parallel fast directions in most <span class="hlt">subduction</span> zones worldwide (with a few notable exceptions). Average sub-wedge delay times correlate with the absolute value of <span class="hlt">trench</span> migration velocities in a Pacific hotspot reference frame, which supports a model in which sub-slab flow is usually <span class="hlt">trench</span>-parallel and is induced by <span class="hlt">trench</span> migration. Shear wave splitting patterns in the mantle wedge are substantially more complicated, with large variations in local S delay times and complicated spatial patterns that often feature sharp transitions between <span class="hlt">trench</span>-parallel and <span class="hlt">trench</span>-perpendicular fast directions. Using our global compilation of local S splitting measurements and other <span class="hlt">subduction</span>-related parameters (such as convergence and <span class="hlt">trench</span> migration velocities, the age, dip, and morphology of the <span class="hlt">subducting</span> slab, thickness and stress state of the overriding plate, volcanic production, and depth to volcanism), we carry out hypothesis testing of the wide variety of models that have been proposed to explain mantle wedge anisotropy. These include models that invoke corner flow, transpression due to oblique <span class="hlt">subduction</span>, <span class="hlt">trench</span>-parallel flow, crustal foundering, B-type olivine fabric, the LPO of serpentinite, melt-controlled anisotropy, or a combination of these mechanisms. We are currently working to integrate our seismological results with the results from geodynamical modeling (both numerical and analog) to test the geodynamic plausibility of our proposed model for mantle flow in <span class="hlt">subduction</span> systems and to explore the implications of the model for <span class="hlt">subduction</span> zone processes and, more generally, for mantle dynamics.</p> <div class="credits"> <p class="dwt_author">Long, Maureen; Silver, Paul; Hanna, Jenny; Wirth, Erin; Kincaid, Chris; Montesi, Laurent</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">102</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EP%26S...64.1239S"> <span id="translatedtitle">Coulomb stress change for the normal-fault aftershocks triggered near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> by the 2011 Mw 9.0 Tohoku-Oki earthquake</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Coulomb stress triggering is examined using well-determined aftershock focal mechanisms and source models of the 2011 Mw 9.0 off the Pacific coast of Tohoku Earthquake. We tested several slip distributions obtained by inverting onshore GPS-derived coseismic displacements under different a priori constraints on the initial fault parameters. The aftershock focal mechanisms are most consistent with the Coulomb stress change calculated for a slip distribution having a center of slip close to the <span class="hlt">trench</span>. This demonstrates the capability of the Coulomb stress change to help constrain the slip distribution that is otherwise difficult to determine. Coulomb stress changes for normal-fault aftershocks near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> are found to be strongly dependent on the slip on the shallow portion of the fault. This fact suggests the possibility that the slip on the shallow portion of the fault can be better constrained by combining information of the Coulomb stress change with other available data. The case of normal-fault aftershocks near some <span class="hlt">trench</span> segment which are calculated to be negatively stressed shows such an example, suggesting that the actual slip on the shallow portion of the fault is larger than that inverted from GPS-derived coseismic displacements.</p> <div class="credits"> <p class="dwt_author">Sato, T.; Hiratsuka, S.; Mori, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">103</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/15020278"> <span id="translatedtitle">Earthquake hazards on the cascadia <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Large <span class="hlt">subduction</span> earthquakes on the Cascadia <span class="hlt">subduction</span> zone pose a potential seismic hazard. Very young oceanic lithosphere (10 million years old) is being <span class="hlt">subducted</span> beneath North America at a rate of approximately 4 centimeters per year. The Cascadia <span class="hlt">subduction</span> zone shares many characteristics with <span class="hlt">subduction</span> zones in southern Chile, southwestern <span class="hlt">Japan</span>, and Colombia, where comparably young oceanic lithosphere is also</p> <div class="credits"> <p class="dwt_author">T. H. Heaton; S. H. Hartzell</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">104</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53174768"> <span id="translatedtitle">Electrical conductivity at around 400 km depth in the western Pacific <span class="hlt">subduction</span> region (Invited)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The western Pacific area is a field of significant mantle downwelling. The old Pacific plate (125-150 Ma) <span class="hlt">subducts</span> at the Kurile-<span class="hlt">Japan</span>, Izu-Bonin, and Mariana <span class="hlt">trenches</span>. The slabs penetrating into the mantle beneath the back arc regions were imaged as high-velocity anomalies by seismic tomography (e.g., Fukao et al., 2001; Obayashi et al., 2009). The high-velocity anomalies tend to be distributed</p> <div class="credits"> <p class="dwt_author">K. Baba; H. Utada; H. Shimizu</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">105</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.T42A..03H"> <span id="translatedtitle">Mega-thrust and Intra-slab Earthquakes beneath Tokyo Metropolitan Area around <span class="hlt">subduction</span> and collision zones in <span class="hlt">JAPAN</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In central <span class="hlt">Japan</span> the Philippine Sea plate (PSP) <span class="hlt">subducts</span> beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9). The vertical proximity of this down going lithospheric plate is of concern because the greater Tokyo urban region has a population of 42 million and is the center of approximately 40 % of the nation's economic activities. A M7+ earthquake in this region at present has high potential to produce devastating loss of life and property with even greater global economic repercussions.The M7+ earthquake is evaluated to occur with a probability of 70 % in 30 years by the Earthquake Research Committee of <span class="hlt">Japan</span>.We started the Special Project for Earthquake Disaster Mitigation in Tokyo metropolitan areas, a project to improve information needed for seismic hazards analyses of the largest urban centers. Under the project we will deploy a 400-sation dense seismic array in metropolitan Tokyo and Kanto, referred to as the Metropolitan Seismic Observation network (MeSO-net) in next 4 years. The target area of the present project is unique in tectonic setting because two oceanic plates, Philippine Sea plate (PSP) and Pacific plate (PAC), are <span class="hlt">subducting</span> beneath the Kanto and also a volcanic arc, Izu-Bonin arc, is colliding with Honshu arc. The situation makes the tectonics complicated: there are both zones of smooth <span class="hlt">subduction</span> and collision of the oceanic plate with the landward plate, either the Eurasian plate or the North American plate. Furthermore, the PSP encounters the PAC at shallow depth in the eastern Kanto region. The newly developing MeSO-net will contribute to understand the generation mechanism associated with the plate <span class="hlt">subduction</span> and collision. Assessment in Kanto of the seismic hazard requires identification of all significant faults and possible earthquake scenarios and rupture behavior, regional characterizations of the PSP geometry and the overlying Honshu arc physical properties. Our study addresses (1) improved regional characterization of the PSP geometry based on new deep seismic reflection profiles (Sato etal.,2005), reprocessed off-shore profiles (Kimura et al.,2005), and a dense seismic array in the Boso peninsula (Hagiwara et al., 2006) and (2) identification of collision of internal heterogeneity (Wu et al., 2007). We compile these results and present a new model which will be verified by data from the planned MeSO-net. We present a relatively high resolution tomographic image from so far obtained data to show a low velocity zone which suggests a possible internal failure of the slab; a source region of the M7+ intra-slab earthquake. Our study contributes a new assessment of the seismic hazard in the Tokyo metropolitan area. tokyo.ac.jp/shuto/EN/index.html</p> <div class="credits"> <p class="dwt_author">Hirata, N.; Kasahara, K.; Hagiwara, H.; Satow, H.; Shimazaki, K.; Koketsu, K.; Wu, F.; Okaya, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">106</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFM.T42A..03H"> <span id="translatedtitle">Mega-thrust and Intra-slab Earthquakes beneath Tokyo Metropolitan Area around <span class="hlt">subduction</span> and collision zones in <span class="hlt">JAPAN</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In central <span class="hlt">Japan</span> the Philippine Sea plate (PSP) <span class="hlt">subducts</span> beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9). The vertical proximity of this down going lithospheric plate is of concern because the greater Tokyo urban region has a population of 42 million and is the center of approximately 40 % of the nation's economic activities. A M7+ earthquake in this region at present has high potential to produce devastating loss of life and property with even greater global economic repercussions.The M7+ earthquake is evaluated to occur with a probability of 70 % in 30 years by the Earthquake Research Committee of <span class="hlt">Japan</span>.We started the Special Project for Earthquake Disaster Mitigation in Tokyo metropolitan areas, a project to improve information needed for seismic hazards analyses of the largest urban centers. Under the project we will deploy a 400-sation dense seismic array in metropolitan Tokyo and Kanto, referred to as the Metropolitan Seismic Observation network (MeSO-net) in next 4 years. The target area of the present project is unique in tectonic setting because two oceanic plates, Philippine Sea plate (PSP) and Pacific plate (PAC), are <span class="hlt">subducting</span> beneath the Kanto and also a volcanic arc, Izu-Bonin arc, is colliding with Honshu arc. The situation makes the tectonics complicated: there are both zones of smooth <span class="hlt">subduction</span> and collision of the oceanic plate with the landward plate, either the Eurasian plate or the North American plate. Furthermore, the PSP encounters the PAC at shallow depth in the eastern Kanto region. The newly developing MeSO-net will contribute to understand the generation mechanism associated with the plate <span class="hlt">subduction</span> and collision. Assessment in Kanto of the seismic hazard requires identification of all significant faults and possible earthquake scenarios and rupture behavior, regional characterizations of the PSP geometry and the overlying Honshu arc physical properties. Our study addresses (1) improved regional characterization of the PSP geometry based on new deep seismic reflection profiles (Sato etal.,2005), reprocessed off-shore profiles (Kimura et al.,2005), and a dense seismic array in the Boso peninsula (Hagiwara et al., 2006) and (2) identification of collision of internal heterogeneity (Wu et al., 2007). We compile these results and present a new model which will be verified by data from the planned MeSO-net. We present a relatively high resolution tomographic image from so far obtained data to show a low velocity zone which suggests a possible internal failure of the slab; a source region of the M7+ intra-slab earthquake. Our study contributes a new assessment of the seismic hazard in the Tokyo metropolitan area. tokyo.ac.jp/shuto/EN/index.html</p> <div class="credits"> <p class="dwt_author">Hirata, N.; Kasahara, K.; Hagiwara, H.; Satow, H.; Shimazaki, K.; Koketsu, K.; Wu, F.; Okaya, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">107</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.T32C..01K"> <span id="translatedtitle">Structure of a paleo <span class="hlt">subduction</span> décollement, Suzume Fault, Okitsu Mélange, Shimanto Accretionary Complex, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Suzume fault is an internal thrust of an exhumed duplex of underplated rock in the Shimanto accretionary complex. On the basis of structure, age, and paleo-temperature of rock in the duplex, the thrust is a <span class="hlt">subduction</span> décollement exhumed from the shallow region of the seismogenic zone. Mesoscale structure of the thrust was characterized to investigate slip processes and structural evolution of the décollement. The thrust exhibits an asymmetric structure characterized by a decimeter-thick ultracataclasite bounded by a several-meter-thick zone of fractured basalt in the hanging wall and a 20-meter-thick zone of ductily sheared sedimentary rock in the footwall. The structure of the thrust is similar to that of active décollements drilled at the frontal portions of prisms, but differs in the greater intensity of ductile deformation and the occurrence of ultracataclasite. Hence, the footwall of the Suzume fault records aseismic, distributed shear in poorly consolidated sediment during shallow underthrusting followed by coseismic, localized-slip in lithified sedimentary rock during underplating at depth. The hanging wall, in contrast, records only the later stage of coseismic, localized-slip associated with underplating. The ultracataclasite layers in the Suzume fault exhibit shear localization onto a through-going fracture surface and fabrics indicative of distributed flow, which are likely associated with the seismic cycle, i.e., alternating co- and inter-seismic slip. Off-fault fracture fabric in the hanging wall, related to thrusting at depth, records predominantly up-dip propagation of fault slip events. /// A synthesis of observations of ~20 <span class="hlt">subduction</span> megathrusts representing the 0-15 km depth range, combined with the findings from the Suzume fault and modern Nankai megathrusts, documents a systematic decrease in the thickness of the slip zone, changes in deformation mechanisms and fluid-rock reactions, and an increase in shear heating, with depth. These changes may correlate with a decrease in friction rate-dependence and the progression in the mode of slip with depth that occurs in the up-dip regions of <span class="hlt">subduction</span> megathrusts.</p> <div class="credits"> <p class="dwt_author">Kanaya, T.; Chester, F. M.; Sakaguchi, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">108</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AGUFMMR43C1095O"> <span id="translatedtitle">Mineral Growth Controlled By Aperture Of Fluid-filled Cracks In <span class="hlt">Subduction</span> Zones: An Example From The Sanbagawa Belt, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Sealed cracks in high-pressure metamorphic rocks have been regarded as a direct evidence of the fracture- controlled fluid flow in <span class="hlt">subduction</span> zones. Although various growth microstructures of vein minerals have been reported, the relationship between microstructures and fluid flow remains unclear. The pelitic schists from Nagatoro area of the Sanbagawa metamorphic belt, <span class="hlt">Japan</span> contain two types of veins composed of quartz + albite + K-feldspar + chlorite (type I) and quartz + albite + calcite (type II). Both veins cut the foliation and the stretching lineation of the host rocks, indicating the formation at the exhumation stage (about 300 degC). Within type I veins, elongate quartz and albite grains grew from the fractured quartz and albite grains of the vein wall, respectively, and K-feldspar and chlorite form corresponding to muscovite + chlorite-rich layers of host rocks. In contrast, type II veins have euhedral quartz grains with concentric zoning, and the mineral distribution is independent of those of host rocks. The veins systematically change from type I to type II with increasing vein width, and the critical width is about 1 mm. Both veins show the evidences of multiple crack- seal events, but the aperture width of each crack are 0.01 - 0.05 mm for type I, whereas 0.5 - 3.0 mm for type II. Considering the cubic dependence of the permeability on crack aperture, the permeability of type II veins was 103 - 106 times larger than type I veins. The materials for forming vein minerals come from deeper parts of the <span class="hlt">subduction</span> zones, or from the surrounding host rocks. The mineral distribution of type I veins suggests that material diffused into fluid-filled cracks from the host rocks, and that the effect of fluid advection was very small. In contrast, for type II veins with wide aperture, the upward fluid flow would have brought the high concentration of Si into the crack, that leaded to the homogeneous nucleation of quartz. Although the frequency of type II veins is about 10 % of total veins in the Nagatoro area, this type veins would have played an important roll on fluid and material transport within the <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Okamoto, A.; Kikuchi, T.; Tsuchiya, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">109</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMDI44B..01Z"> <span id="translatedtitle">Multiscale seismic imaging of the Western-Pacific <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We used multiscale seismic tomography to determine the detailed 3-D structure of the crust and mantle under the Western-Pacific <span class="hlt">subduction</span> zone. The <span class="hlt">subducting</span> Pacific and Philippine Sea (PHS) slabs are imaged clearly from their entering the mantle at the oceanic <span class="hlt">trenches</span> to their reaching the mantle transition zone and finally to the core-mantle boundary (CMB). High-resolution local tomography of Northeast <span class="hlt">Japan</span> has imaged the shallow portion of the slab from the <span class="hlt">Japan</span> <span class="hlt">Trench</span> down to about 200 km depth under <span class="hlt">Japan</span> Sea. The 3-D Vp and Vs structures of the forearc region under the Pacific Ocean are constrained by locating suboceanic events precisely with sP depth phases. Strong structural heterogeneity is revealed in the megathrust zone under the forearc region, and there is a good correlation between the heterogeneity and the distribution of large thrust earthquakes including the great 2011 Tohoku-oki earthquake (Mw 9.0). A joint inversion of local and teleseismic data imaged the <span class="hlt">subducting</span> Pacific slab down to 670 km depth under the <span class="hlt">Japan</span> Islands and the <span class="hlt">Japan</span> Sea. The PHS slab is detected down to 500 km depth under SW <span class="hlt">Japan</span>. A mantle upwelling is found under SW <span class="hlt">Japan</span> that rises from about 400 km depth right above the Pacific slab up to the PHS slab. Regional and global tomography revealed the Pacific slab that is stagnant in the mantle transition zone under Eastern China. A big mantle wedge (BMW) has formed in the upper mantle above the stagnant slab. Convective circulations in the BMW and deep dehydration of the stagnant slab may have caused the intraplate volcanoes in NE Asia, such as the Changbai and Wudalianchi volcanoes. The active Tengchong volcanism in SW China is caused by a similar process in the BMW above the <span class="hlt">subducting</span> Burma (or Indian) slab. Global tomography shows pieces of fast anomalies in the middle and lower mantle as well as in the D" layer above the CMB, suggesting that the stagnant slab finally collapses down to the lower mantle and CMB as a result of very large gravitational instability from phase transitions. Prominent slow anomalies are also revealed in the mantle under the <span class="hlt">subducting</span> slabs, which may represent either mantle plumes or upwelling flows associated with the deep <span class="hlt">subduction</span> of the slabs.</p> <div class="credits"> <p class="dwt_author">Zhao, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">110</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/v6776852640n1875.pdf"> <span id="translatedtitle">Prediction of long-period ground motions from huge <span class="hlt">subduction</span> earthquakes in Osaka, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">There is a high possibility of reoccurrence of the Tonankai and Nankai earthquakes along the Nankai Trough in <span class="hlt">Japan</span>. It is\\u000a very important to predict the long-period ground motions from the next Tonankai and Nankai earthquakes with moment magnitudes\\u000a of 8.1 and 8.4, respectively, to mitigate their disastrous effects. In this study, long-period (>2.5 s) ground motions were\\u000a predicted using an</p> <div class="credits"> <p class="dwt_author">H. Kawabe; K. Kamae</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">111</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ea.c.u-tokyo.ac.jp/earth/Members/Isozaki/07Ota-JAES.pdf"> <span id="translatedtitle">Geology of the Gorny Altai <span class="hlt">subduction</span>–accretion complex, southern Siberia: Tectonic evolution of an Ediacaran–Cambrian intra-oceanic arc-<span class="hlt">trench</span> system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Gorny Altai region in southern Siberia is one of the key areas in reconstructing the tectonic evolution of the western segment of the Central Asian Orogenic Belt (CAOB). This region features various orogenic elements of Late Neoproterozoic–Early Paleozoic age, such as an accretionary complex (AC), high-P\\/T metamorphic (HP) rocks, and ophiolite (OP), all formed by ancient <span class="hlt">subduction</span>–accretion processes. This</p> <div class="credits"> <p class="dwt_author">Tsutomu Ota; Atsushi Utsunomiya; Yuko Uchio; Yukio Isozaki; Mikhail M. Buslov; Akira Ishikawa; Shigenori Maruyama; Koki Kitajima; Yoshiyuki Kaneko; Hiroshi Yamamoto; Ikuo Katayama</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">112</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AGUFM.T41A1532O"> <span id="translatedtitle">Phenomenology of non-volcanic deep tremor, slow slip and the third slow earthquake in southwest <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Coupling phenomena of the non-volcanic low-frequency tremor and short-term slow slip event reflect the <span class="hlt">subduction</span> process at the transition zone of deeper plate interface. In southwest <span class="hlt">Japan</span>, non-volcanic tremors are distributed in some clusters along the 30km depth contour line of the upper boundary of the <span class="hlt">subducting</span> Philippine Sea plate [Obara, 2002]. Peak of tremor activity recurs with regular intervals accompanying to short- term slow slip event lasting for a several days [Obara, et al., 2004]. In western Shikoku, the episodic tremor and slow slip have been clearly detected every six months. On the other hand, in central and eastern Shikoku, the tremor occurs with a few months interval. This suggests that the periodic stick-slip behavior has a spatial variation along the same slab. The regularity of recurrence interval is sometimes distorted by other seismic phenomena. In western Shikoku, the episodic tremor and slip occurred in winter and summer during two years of 2001 and 2002. However, during and after the period of the long-term slow slip event on the latter half of 2003 in this area, the recurrence interval was shortened to three months. Then, the half-year interval returned again since 2005. Northern Kii and Tokai areas, located on both sides of the Ise Bay, central part of <span class="hlt">Japan</span>, are active tremor and slip source areas with the recurrence interval of six months. In December 2004 and July 2005, the episodic tremor and slip occurred in both areas independently with time gap of a few weeks. On the other hand, in January 2006, the tremor and slow slip began from the central part of Kii peninsula and gradually migrated to northeast. The activity at last went across the Ise Bay and advanced through the Tokai area. This continuous activity extending for 200km is the first accident since the tremor monitoring has started from 2001. Beneath the Ise Bay area, the configuration of the <span class="hlt">subducting</span> Philippine Sea plate has a small ridge structure estimated from the receiver function study [Shiomi et al., 2006]. The slab geometry usually acts a barrier for the tremor and slip event, however, the episode 2006 may have a potential to override the barrier and extend the rupture area. Very recently we succeeded to detect the very low frequency seismic signal with a predominant period of 20 seconds accompanying to active tremor stage [Ito et al., 2006]. This very low frequency (VLF) earthquake is determined at the same location to the tremor source and the focal mechanism is the reverse fault type coincident with the slow slip event estimated by the centroid moment tensor analysis. During the episode 2006 in Kii and Tokai areas, many VLF earthquakes migrating with the tremor and slow slip event were identified. There exists a spectrum gap between the VLF earthquake and tremor with predominant frequency ranging from 1.5 to 5 Hz. Therefore these seismic phenomena are basically generated by different source processes with a strong relationship reflecting the inhomogeneous structure on the plate interface at the transition zone. One possible idea is that the source of the VLF earthquake is a relatively strong patch surrounded by the short- term slow slip source fault. When the accumulated stress in the patch exceeds the failure strength according to the progress of slow slip, the VLF earthquake may occur at the patch interface saturated by fluid.</p> <div class="credits"> <p class="dwt_author">Obara, K.; Ito, Y.; Sekine, S.; Hirose, H.; Shiomi, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">113</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002AGUFM.G61A0967M"> <span id="translatedtitle">Transient <span class="hlt">subduction</span> slip episodes in <span class="hlt">Japan</span> observed by the nationwide GPS array</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We observe slow thrust slip events along the Suruga-Nankai Trough where the Philippine Sea plate is <span class="hlt">subducting</span> beneath the Japanese Islands. The first event initiated around 1997.0 at the Bungo Channel, following two successive M 6.7 earthquakes off Hyuganada. The second event occurred just west (down dip) of the Tokai seismic gap. We utilize the Network Inversion Filter, recently modified by McGuire and Segall [2002] to invert the GPS observations. The improved method enables us to implement non-negativity constraints and automatic estimation of hyperparameters, including spatial and temporal smoothing. The results of the Bungo event show that the slip initiated just south of southwesternmost Shikoku Island and propagated west to the Bungo Channel. The result clearly demonstrates that the slow event has no connection with the Hyuganada earthquakes, though it may have been triggered by those preceding events. The total aseismic moment release corresponds to Mw 7.2. The Tokai event initiated following major volcanic activity in the Izu Islands (since the end of June, 2000). The slip initially accelerated during the first 8 months. The slow slip event is not yet over; the present slip-rate is the same as in 2001. Currently the cumulative moment release corresponds to Mw 6.8. We note that both events occurred at sites where the plate interface shows significant lateral bending. Such a geometry, as well as heterogeneity of fault constitutive parameters, may be important in generating slow events.</p> <div class="credits"> <p class="dwt_author">Miyazaki, S.; Segall, P.; McGuire, J. J.; Kato, T.; Hatanaka, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">114</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.U33A0031I"> <span id="translatedtitle">Wavefield and source spectra of non-volcanic low-frequency tremors in a southwest <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We investigate wave-field properties and source spectra of non-volcanic low-frequency tremors in a southwest <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone, which have not been fully understood due to a low signal-to-noise ratio of tremor signals. Geological Survey of <span class="hlt">Japan</span>, AIST, has recently started an integrated borehole observation of water levels, strains, tilts, water temperatures and seismic waves in southwest <span class="hlt">Japan</span> for monitoring of the anticipated Tonankai and Nankai earthquakes. At each observation site, we have drilled three boreholes with different depths (about 30 m, 200 m and 600 m) and installed high-sensitivity seismometers at a bottom of every borehole. In this study, we use borehole seismic data recorded by this vertical seismic array network as well as NIED Hi-net. In order to investigate wave-field properties of non-volcanic low-frequency tremors, the vertical array data are used. During tremor activities, high semblance values continuously appear at a specific apparent velocity. Because the S-wave velocity estimated by borehole logging is consistent with the apparent velocity, we conclude that the non-volcanic low-frequency tremors are composed of near vertically incident S-waves. This is supported by polarization analysis, where the particle motion is linearly polarized and the incident angle is steep. The polarization analysis also reveals that the polarization angles are almost same during each tremor activity. Because the polarization angle will have various values if the tremor signals contain large amount of scattered waves, it is likely that they are composed mostly of seismic waves coming directly from the source. A comparison of source spectrum between regular earthquakes and non-volcanic low-frequency tremors is a key to understand the difference in their physical processes. We first estimate model source spectrum for co- located regular earthquakes by Multi-Window Spectral Ratio method [Imanishi and Ellsworth, 2006]. By averaging the ratios between observed and model spectrum over all events in a cluster, we obtain the average attenuation function, which is assumed to represent the path and site effects between the source and station. The source spectrum of each tremor is then calculated by the ratio between the observed spectrum and the attenuation function. The estimated velocity spectra of tremors are flat for higher frequency, which clearly differ from those for regular earthquakes that follow f-1 decay at high frequency. It is noted that this feature of the velocity spectra can be explained by the Brownian walk model for slow earthquakes that was recently proposed by Ide [2008].</p> <div class="credits"> <p class="dwt_author">Imanishi, K.; Takeda, N.; Kuwahara, Y.; Hoshino, M.; Koizumi, N.; Ide, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">115</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012E%26PSL.355...94Y"> <span id="translatedtitle">Smooth and rapid slip near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> during the 2011 Tohoku-oki earthquake revealed by a hybrid back-projection method</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We developed a new back-projection method that uses teleseismic P-waveforms to integrate the direct P-phase with reflected phases from structural discontinuities near the source and used it to estimate the spatiotemporal distribution of the seismic energy release of the 2011 Tohoku-oki earthquake. We projected a normalized cross-correlation of observed waveforms with corresponding Green's functions onto the seismic source region to obtain a high-resolution image of the seismic energy release. Applying this method to teleseismic P-waveform data of the 2011 Tohoku-oki earthquake, we obtained spatiotemporal distributions of seismic energy release for two frequency bands, a low-frequency dataset and a high-frequency dataset. We showed that the energy radiated in the dip direction was strongly frequency dependent. The area of major high-frequency seismic radiation extended only downdip from the hypocenter, whereas the area of major low-frequency seismic radiation propagated both downdip and updip from the hypocenter. We detected a large release of seismic energy near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> in the area of maximum slip, which was also the source area of the gigantic tsunami, when we used only the low-frequency dataset. The timing of this large seismic energy release corresponded to an episode of smooth and rapid slip near the <span class="hlt">Japan</span> <span class="hlt">Trench</span>, and reflects the strong dependence of the seismic energy distribution obtained on the frequency band of the input waveform dataset. The episode of smooth and rapid slip may have been the trigger for a release of roughly all of the accumulated elastic strain in the seismic source region of the 2011 Tohoku-oki earthquake.</p> <div class="credits"> <p class="dwt_author">Yagi, Yuji; Nakao, Atsushi; Kasahara, Amato</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">116</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008NatGe...1..406."> <span id="translatedtitle">Tracking <span class="hlt">subduction</span> fluids</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Hitomi Nakamura, sometimes on her own, braved remote ravines and thick jungles in order to sample volcanic rocks that help reveal the complex geometry of two overlapping plates <span class="hlt">subducting</span> into the mantle beneath central <span class="hlt">Japan</span>.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2008-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">117</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.S51C2241P"> <span id="translatedtitle">Lateral structural change of the <span class="hlt">subducting</span> Pacific plate beneath <span class="hlt">Japan</span> inferred from high-frequency body wave analysis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We studied the detailed lateral structure of the <span class="hlt">subducting</span> Pacific plate near Honshu by analyzing waveforms from deep earthquakes recorded at fore-arc Hi-net dense high-gain network and F-net broadband stations in <span class="hlt">Japan</span>. Such waveforms explain the low-frequency precursors followed by high-frequency energies due to the multiple scattering and diffractions of seismic waves in the stochastic waveguide of the Pacific slab (Furumura and Kennett, 2005). However, recent analysis shows that for some particular source-receiver paths, the waveforms exhibit loss of high frequency energy in P-coda, loss of low-frequency precursor and presence of P-to-P or P-to-S converted phases in P-coda for deep earthquakes occurring in the subeducting Pacific plate. Such complexities in the observed waveforms indicate sudden lateral change in the wave guiding properties of the <span class="hlt">subducting</span> slab, such as expected to be caused by the thinning or tearing the slab in deeper part. To explain the observations, we employ two-dimensional finite-difference method (FDM) simulations of complete high-frequency P-SV wave propagation taking thinning of the Pacific slab into account. We expect that the observed guided wave energy must decouple from waveguide where the slab is deformed or thin. Low frequency energy leaks out of the slab and travels to the receivers along paths in the low velocity and low-Q mantle surrounding the slab, while high frequency signal of shorter wavelength can travel through thin plate. The results of this study, along with the evidence for weak velocity anomaly as inferred from seismic tomography (Obayashi et al., 2009) and observations of slab tear in the Pacific plate (Kennett and Furumura, 2010), we expect a local velocity anomaly or thinning in the oceanic lithosphere along the junction between Izu-Bonin and Honshu arc. It is necessary to examine these effects further with a 3D FDM simulation for different slab geometries and source depths.</p> <div class="credits"> <p class="dwt_author">Padhy, S.; Furumura, T.; Maeda, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">118</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013Tecto..32..377C"> <span id="translatedtitle">Zircon and apatite thermochronology of the Nankai Trough accretionary prism and <span class="hlt">trench</span>, <span class="hlt">Japan</span>: Sediment transport in an active and collisional margin setting</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Nankai accretionary complex is the most recent addition to the accretionary complexes of southwest <span class="hlt">Japan</span> and has preserved a record of sediment flux to the <span class="hlt">trench</span> during its construction. In this study, we use U-Pb zircon and fission track analysis of both zircons and apatites from sediments taken from the forearc and <span class="hlt">trench</span> of the Nankai Trough, as well as rivers from southwest <span class="hlt">Japan</span> to examine the exhumation history of the margin since the Middle Miocene. Modern rivers show a flux dominated by erosion of the Mesozoic-Eocene Shimanto and Sanbagawa accretionary complexes. Only the Fuji River, draining the collision zone between the Izu and Honshu arcs, is unique in showing much faster exhumation. Sediment from the Izu-Honshu collision is not found 350-500 km along the margin offshore Kyushu indicating limited along-strike sediment transport. Sediment deposited since 2 Ma on the midtrench slope offshore the Muroto Peninsula of Shikoku (ODP Site 1176) and on the lower slope trenchward of the Kumano Basin (IODP Sites C0006E and C00007E) shares the dominant source in the Shimanto and Sanbagawa complexes seen in the modern rivers. Prior to 5 Ma, additional sediment was being sourced from further north in more slowly exhumed terrains, ~350 km from the <span class="hlt">trench</span> axis. Around 9.4 Ma, U-Pb zircon ages of ~1800 Ma indicate enhanced erosion from the North China Craton, exposed in northern Honshu. In the middle Miocene, at ~15.4 Ma, the sediment was being derived from a much wider area including the Yangtze Craton (U-Pb ages ~800 Ma). We suggest that this enhanced catchment may have reflected the influence of the Yangtze River in supplying into the Shikoku Basin prior to rifting of the Okinawa Trough at 10 Ma and migration of the Palau-Kyushu Ridge to form a barrier to transport. The restriction of Nankai Trough provenance to Mesozoic source partly reflects continued uplift of the Shimanto and Sanbagawa complexes since the Middle Miocene.</p> <div class="credits"> <p class="dwt_author">Clift, Peter D.; Carter, Andrew; Nicholson, Uisdean; Masago, Hideki</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">119</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/39832583"> <span id="translatedtitle">Structure of the Sunda <span class="hlt">Trench</span> lower slope off sumatra from multichannel seismic reflection data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Multichannel seismic reflection profiles across the Sunda <span class="hlt">Trench</span> slope off central Sumatra reveal details of <span class="hlt">subduction</span> zone structure. Normal faults formed on the outer ridge of the <span class="hlt">trench</span> offset deep strate and the oceanic crust, but die out upsection under the <span class="hlt">trench</span> sediments. At the base of the inner <span class="hlt">trench</span> slope, shallow reflectors are tilted seaward, while deeper reflectors dip</p> <div class="credits"> <p class="dwt_author">Gregory F. Moore; Joseph R. Curray</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">120</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.nlm.nih.gov/medlineplus/ency/article/001044.htm"> <span id="translatedtitle"><span class="hlt">Trench</span> mouth</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://medlineplus.gov/">MedlinePLUS</a></p> <p class="result-summary">... that involves swelling (inflammation) and ulcers in the gums (gingivae). ... <span class="hlt">Trench</span> mouth is a painful form of gum swelling ( gingivitis ). The term "<span class="hlt">trench</span> mouth" comes from World War I, when the disorder was common among soldiers. The mouth normally contains a ...</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_5");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return 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src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">121</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3398547"> <span id="translatedtitle">Substrate-specific pressure-dependence of microbial sulfate reduction in deep-sea cold seep sediments of the <span class="hlt">Japan</span> <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">The influence of hydrostatic pressure on microbial sulfate reduction (SR) was studied using sediments obtained at cold seep sites from 5500 to 6200 m water depth of the <span class="hlt">Japan</span> <span class="hlt">Trench</span>. Sediment samples were stored under anoxic conditions for 17 months in slurries at 4°C and at in situ pressure (50 MPa), at atmospheric pressure (0.1 MPa), or under methanic conditions with a methane partial pressure of 0.2 MPa. Samples without methane amendment stored at in situ pressure retained higher levels of sulfate reducing activity than samples stored at 0.1 MPa. Piezophilic SR showed distinct substrate specificity after hydrogen and acetate addition. SR activity in samples stored under methanic conditions was one order of magnitude higher than in non-amended samples. Methanic samples stored under low hydrostatic pressure exhibited no increased SR activity at high pressure even with the amendment of methane. These new insights into the effects of pressure on substrate specific sulfate reducing activity in anaerobic environmental samples indicate that hydrostatic pressure must be considered to be a relevant parameter in ecological studies of anaerobic deep-sea microbial processes and long-term storage of environmental samples.</p> <div class="credits"> <p class="dwt_author">Vossmeyer, Antje; Deusner, Christian; Kato, Chiaki; Inagaki, Fumio; Ferdelman, Timothy G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">122</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/nv35328r47480727.pdf"> <span id="translatedtitle">Oblique <span class="hlt">subduction</span> of a Newtonian fluid slab</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A Newtonian fluid model is proposed to describe the oblique <span class="hlt">subduction</span> of a planar 2-D slab. The slab is assumed to <span class="hlt">subduct</span> in response to the ridge push force exerted along the <span class="hlt">trench</span>, the slab pull force at the downdip of the slab, the gravitational body force within the slab, and the frictional resistance force at the upper surface of</p> <div class="credits"> <p class="dwt_author">Zheng-Kang Shen</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">123</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40843803"> <span id="translatedtitle">Metamorphic rocks of the Yap arc-<span class="hlt">trench</span> system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Yap <span class="hlt">trench</span>-arc is a link between the Mariana and Philippine arcs; the latter are both loci of acive volcanism and seismicity but the Yap arc is formed of metamorphic rocks and has had few historic earthquakes. It does not appear to be an active <span class="hlt">subduction</span> zone. The 8-9 km deep Yap <span class="hlt">trench</span> has a steep west well, it has</p> <div class="credits"> <p class="dwt_author">J. Hawkins; R. Batiza</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">124</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.U53D0083M"> <span id="translatedtitle">The reasons why the M9 earthquake in the northeastern <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone could not be anticipated and why it really occurred</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The M9 Tohoku earthquake on 11 March 2011 had a great impact on the seismologists all over the world. This is because the northeastern <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone was one of the most investigated <span class="hlt">subduction</span> zones and the interplate coupling there was thought to be too weak to generate M9 earthquakes. The bases of the judgment of weak coupling are as follows: (1) The portion of the Pacific plate <span class="hlt">subducting</span> beneath the <span class="hlt">subduction</span> zone is older than 100 my, which is older than most of the other ocean floors in the world. Note that although some researchers have casted doubt on the relationship between the M9 potential and plate convergence rate and back-arc spreading proposed by Ruff and Kanamori (1980) after the 2004 M9 Sumatra-Andaman earthquake (e.g., McCaffrey, 2007, 2008; Stein and Okal, 2007), the dependency on the age of the oceanic plate had not been rejected. (2) Around 100 year geodetic survey shows dilatational areal strain is dominant in Tohoku (northeastern Honshu, <span class="hlt">Japan</span>) (Hashimoto, 1990; Ishikawa and Hashimoto, 1999), indicating all the 'locked' areas on the plate boundary might be loosened by M7 earthquakes occurring with repeating intervals of several tens of years. (3) Although the analyses of GPS (e.g., Suwa et al., 2006) and small repeating earthquake data (Uchida and Matsuzawa, 2011) indicate a large 'locked' area off southern Tohoku, the data in the late 2000s show large portions of the locked area seemed to be released by large earthquakes of M6-7 and their afterslip. (4) The activity of moderate-sized earthquakes there is the highest in <span class="hlt">Japan</span>. (5) Large interplate earthquakes with M6 or larger are usually followed by large afterslip whose scalar moment is sometimes as large as that of the seismic slip of the main shock. Moreover, Hasegawa et al. (2011) shows that the stress on the plate boundary was not large according to the stress rotation after the M9 earthquake. All of these observations indicate that the plate boundary was not strongly locked over 100 years. Then why did the M9 earthquake really occur there? The reason is still under the debate. One of the probable explanations is that the plate boundary had been weakly coupled but the slip of the M9 earthquake was exceptionally large releasing total stress on the boundary. The Pacific plate descending beneath Tohoku is old and cold but the inclination of the plate is less than around 30 degrees and interplate earthquakes can occur as deep as 60 km because the plate is very cold. The shallow <span class="hlt">subduction</span> angle and deep sesimogenic limit causesd the seismogenic plate boundary as wide as more than 200 km, which was large enough to accumulate slip deficit of more than 20m without large stress increase (Iio et al., 2011). Most of the aftershocks occurring in the hanging plate are of normal fault type (Asano et al., 2011) indicating the seismic slip of the M9 earthquake was overshot (Ide et al., 2011), which might be caused by thermal pressurization of pore fluid (Mitsui and Iio, 2011).</p> <div class="credits"> <p class="dwt_author">Matsuzawa, T.; Iio, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">125</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55025154"> <span id="translatedtitle">Shortening deformation of the back-arc rift basin in the central northern Honshu, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Pacific plate is being <span class="hlt">subducted</span> beneath northern Honshu, <span class="hlt">Japan</span>, forms a classical example of <span class="hlt">trench</span>-arc-back arc system. The compressional stress, perpendicular to the northern Honshu arc, has produced the shortening deformation in the Miocene back arc rift basins since the Pliocene. Two narrow up-rift zones run parallel to the arc: Dewa hills on the west and Ou Backbone range</p> <div class="credits"> <p class="dwt_author">N. Kato; H. Sato</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">126</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55478221"> <span id="translatedtitle">Pull-down basin in the central part of <span class="hlt">Japan</span> due to <span class="hlt">subduction</span>-induced mantle flow</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Driving force for the basin subsiding against isostatic balance in and around Lake Biwa in the Kinki district, <span class="hlt">Japan</span> is discussed. Lake Biwa is the largest lake in <span class="hlt">Japan</span>. The Paleo Lake Biwa can be traced back to almost 4 million years ago. The lake region is characterized by strong negative Bouguer anomalies, especially by a steep horizontal gradient zone</p> <div class="credits"> <p class="dwt_author">T. Kudo; K. Yamaoka</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">127</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41269558"> <span id="translatedtitle">From normal to oblique <span class="hlt">subduction</span>: Tectonic relationships between Java and Sumatra</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The convergent motion of the Indian-Australian and the Eurasian Plates results in <span class="hlt">subduction</span> at the Sunda Arc. Obliquity of <span class="hlt">subduction</span> beneath Sumatra induces large strike-slip faults in Sumatra and its margin, whereas the <span class="hlt">subduction</span> is almost perpendicular to the <span class="hlt">trench</span> southwest of Java. The nature of the transition between these two <span class="hlt">subduction</span> regimes is of major interest. New data collected</p> <div class="credits"> <p class="dwt_author">J. A. Malod; Komar Karta; M. O. Beslier; M. T. Zen</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">128</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003AGUFM.T52B0256M"> <span id="translatedtitle">Low-velocity Oceanic Crusts at the top of <span class="hlt">Subducting</span> Plates Beneath <span class="hlt">Japan</span> Islands Imaged by Tomographic Method Using the NIED Hi-net Data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In the original grid-type tomographic method (Zhao et al., 1992), the resolution of the images is equal to the grid spacing. It is more realistic to use as many grid nodes as possible for representing heterogeneous velocity distribution. However, the increasing of grid nodes introduces the instability in tomographic image having an artificially rough structure. We introduce correlation among velocities at surrounding grid nodes (Matsubara et al., 2001) to stable the solution. Thus the obtained structure might be more close to the real. We apply this modified method to 1,125,272 P- and 854,717 S-wave arrival times from 21,656 earthquakes recorded by 664 stations of the high-sensitivity seismograph network of <span class="hlt">Japan</span>, NIED Hi-net, during 2000 to 2002. In the inversion process, the configuration of the Moho discontinuity is fixed according to Yoshii et al. (2002) without considering the upper boundary of the Pacific plate. A high-velocity (high-V) zone is imaged as the Pacific plate in the northeastern (NE) <span class="hlt">Japan</span> arc. A low-velocity (low-V) layer above the high-V zone with about -(4-10)% velocity anomalies, considered as oceanic crust, coincides with the upper part of the double-seismic zone in the upper part of the slab. A high-V zone at depths of 20-60 km beneath the southwestern (SW) <span class="hlt">Japan</span> is imaged as the Philippine Sea plate. Low-V zones, as oceanic crust, are found beneath the central and SW <span class="hlt">Japan</span> except around the collision zone of Izu Peninsula at the northern edge of the Izu-Bonin arc. In the Kanto region, the central part of <span class="hlt">Japan</span>, the Pacific and Philippine Sea plates <span class="hlt">subduct</span> beneath the North-American plate and the velocity structure is complicate. We also find that the low-V zone of the Pacific plate is harmonious with the existence of the S-wave reflector found by Obara and Sato (1988). The low-V oceanic crust of the Philippine Sea plate is consistent with the results obtained from the block-type tomographic method (Ohmi and Hurukawa, 1996). The VP/V_S ratio above the Philippine Sea plate is about 1.90 corresponding to the serpentined wedge mantle by Kamiya and Kobayashi (2000). Beneath the Tohoku region, NE <span class="hlt">Japan</span>, low-V zones of the Pacific plate coincide with the oceanic crust with velocity 6% lower than that in the mantle wedge by the analysis of P-to-S converted waves (Matsuzawa et al, 1986). Low-V oceanic crusts of the Philippine Sea plate beneath Chubu, southern Kinki, and western Shikoku region, the central and SW <span class="hlt">Japan</span>, are consistent with the result of the analysis by channel waves (Hori, 1990). The low-V zone beneath the Shukoku region is harmonious with the model derived from receiver function analysis (Shiomi, 2002). Low-V zones are also continuously <span class="hlt">subducted</span> beneath the volcanic front at a depth of 40 km in the shallower part of the mantle wedge with -(3-7)% anomalies in the NE <span class="hlt">Japan</span>.</p> <div class="credits"> <p class="dwt_author">Matsubara, M.; Sekine, S.; Obara, K.; Kasahara, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">129</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMDI31A2160L"> <span id="translatedtitle">Effects of <span class="hlt">Subduction</span> Parameters on the Style of Dynamic Buckling of <span class="hlt">Subducting</span> Slabs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Buckling of <span class="hlt">subducting</span> slabs has been suggested to explain the apparent thickening of the <span class="hlt">subducting</span> slab in the shallow lower mantle, constrained by seismic tomography images. Previous analog/numerical model experiments show that the buckling of <span class="hlt">subducting</span> slabs develops due to viscosity increases across the upper-lower mantle boundary and/or phase transformations. Our 2-d numerical model studies conducted before show that buckling of <span class="hlt">subducting</span> slab is fairly consistent with the scaling laws derived for buckling of falling fluids. However, effects of diverse <span class="hlt">subduction</span> parameters on the style of dynamic buckling of <span class="hlt">subducting</span> slabs are still not well known. Therefore, we conduct a series of 2-d numerical model experiments allowing dynamic <span class="hlt">subduction</span> to evaluate the effects of <span class="hlt">subduction</span> parameters including: 1) viscosity increases across the upper-lower mantle boundary, 2) strength of <span class="hlt">subducting</span> slab, 3) phase transformations from olivine to wadsleyite (~410 km depth) and from ringwoodite to perovskite plus magnesiowüstite (~660 km depth) in the mantle, 4) <span class="hlt">trench</span> migrations/mantle wind, and 5) mantle compressibility. Results of the experiments can be summarized below; 1) Higher viscosity increases across the upper-lower mantle boundary create more cycles of slab buckling, slow <span class="hlt">subduction</span> rate and longer <span class="hlt">subduction</span> life. 2) Stronger <span class="hlt">subducting</span> slab creates longer periods of slab buckling, slow <span class="hlt">subduction</span> rate and longer <span class="hlt">subduction</span> life. 3) The phase transformation from olivine to wadsleyite is crucial in development of slab buckling. However, the phase transformation from ringwoodite to perovskite plus magnesiowüstite only contributes a minor role in development of slab buckling. 4) Even low migration rate/mantle wind (~1cm/year) significantly reduces buckling of <span class="hlt">subducting</span> slab. Stagnant slab is well established if higher migration rate/mantle wind is applied with phase transformations and/or higher viscosity increases across the upper-lower mantle boundary. 5) Mantle compressibility develops irregular buckling of <span class="hlt">subducting</span> slab compared with the experiments without compressibility. However, the effect of mantle compressibility is minor. Most of the experiments which allow buckling of <span class="hlt">subducting</span> slab are fairly consistent with the scaling laws. However, slab buckling is significantly reduced by <span class="hlt">trench</span> migration/mantle wind. Since most of the <span class="hlt">subduction</span> zones have been experiencing <span class="hlt">trench</span> migration, slab buckling observed in the mantle implies that buckling of <span class="hlt">subducting</span> slab results from relatively stable <span class="hlt">trench</span> such as the Mariana <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Lee, C.; King, S. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">130</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFMDI33A1127L"> <span id="translatedtitle">Deep Slab <span class="hlt">Subduction</span> and Dehydration and Their Geodynamic Consequences: New Insights From Seismology and Mineral Physics</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Fluids play important roles in the dynamics and evolution of the Earth, such as lowering the melting temperature of the mantle, transporting elements, enhancing diffusion and creep, and possibly changing the location of phase boundaries such as the 410 and 670 km discontinuities. Fluids are also intimately linked to a variety of earthquake faulting processes. In this work we present new pieces of evidence from seismology and mineral physics for the existence of significant low-velocity anomalies in the deep part of the upper-mantle wedge and the transition zone that are caused by fluids from the deep <span class="hlt">subduction</span> and deep dehydration of the Pacific and Philippine Sea (PHS) slabs under western Pacific and East Asia. The PHS slab is found to <span class="hlt">subduct</span> down to the mantle transition zone depth though the seismicity within the slab occurs only down to 200-300 km depths. The PHS slab dehydration has contributed to the formation of the Okinawa Trough and the Quaternary and active volcanism in SW <span class="hlt">Japan</span>. Combining with the convective circulation processes in the mantle wedge, deep dehydration of the <span class="hlt">subducting</span> Pacific slab has affected the morphology of the <span class="hlt">subducting</span> PHS slab and its seismicity under SW <span class="hlt">Japan</span>. The Pacific slab is found to stagnate in the mantle transition zone under East Asia, which has contributed to the formation of the continental rift system and intraplate volcanism in Northeast Asia (such as the active Changbai and Wudalianchi volcanoes). Slow anomalies are also found in the mantle under the <span class="hlt">subducting</span> Pacific slab, which may represent (a) small mantle plumes, (b) mantle upwellings associated with the deep slab <span class="hlt">subduction</span>, or (c) slab dehydration associated with deep earthquakes caused by the reactivation of large faults in the slab which are generated by the large normal-faulting earthquakes in the oceanic plate near the <span class="hlt">trench</span> and are preserved during the slab <span class="hlt">subduction</span>.</p> <div class="credits"> <p class="dwt_author">Liu, L.; Zhao, D.; Ohtani, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">131</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55249316"> <span id="translatedtitle">Cocos plate structure along the Middle America <span class="hlt">subduction</span> zone off Oaxaca and Guerrero, Mexico: Influence of <span class="hlt">subducting</span> plate morphology on tectonics and seismicity</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Two new bathymetric and magnetic surveys are presented from which the history and recent tectonics of the Cocos plate off the Middle America <span class="hlt">subduction</span> zone are determined. The East O'Gorman fracture zone, a previously proposed outer rise feature, is not present along the Oaxaca <span class="hlt">trench</span> outer rise near the <span class="hlt">trench</span> axis. Several parallel ridges of seamounts are entering the <span class="hlt">subduction</span></p> <div class="credits"> <p class="dwt_author">Nancy Marie Kanjorski</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">132</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.U21D..06K"> <span id="translatedtitle">Tectonic Settings of Great Outer-Rise/Outer-<span class="hlt">Trench</span>-Slope (OR/OTS) Earthquakes in the Instrumental Record</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Great off-<span class="hlt">trench</span> earthquakes in <span class="hlt">subduction</span> zones are rare in the instrumental seismic record. Only five, or possibly six such events are presently known or suspected (2 May 1917 in vicinity of Kermadec <span class="hlt">Trench</span>; 26 June 1917 in vicinity of Tonga <span class="hlt">Trench</span>; 2 March 1933 in Sanriku, <span class="hlt">Japan</span> under outer-<span class="hlt">trench</span> slope; 19 August 1977 near the Sunda <span class="hlt">Trench</span> off Sumbawa Island, Indonesia, 13 January 2007 seaward of Kuriles in Russia, and the recent 29 September 2009 in northern Tonga that spawned destructive tsunami waves that swept the Samoan Islands). This number compares with 59 great mega-thrust earthquakes that have occurred since 1900. Based on recent research on the great 1933 Sanriku earthquake (Kirby et al., Fall 2008 AGU) we have identified some features common to great off-<span class="hlt">trench</span> shocks: (i) All have occurred in <span class="hlt">subduction</span> systems in which convergence rates are greater than about 65 mm/a and the incoming bending oceanic plate is old (Mesozoic), thermally mature, and, by inference, mechanically thick. Seafloor bending strains and strain rates estimated from these observations are high. (ii) Large outer-rise gravity anomalies attest to high bending stresses in these source regions. (iii) Focal mechanisms indicate that the ruptures cross ocean spreading fabric at angles greater than 30 degrees and, in the two cases for which there are high-resolution swath maps available, they have fault scarps with significant relief. (iv) For those events for which seismological constraints on depth and/or focal mechanisms are available, they show that the earthquakes were very shallow normal-faulting ruptures (< 30 km). These common features of great off-<span class="hlt">trench</span> earthquakes are consistent with a model of shallow seismic deformation by large-scale bending at high stresses and strain rates. That such events occur in deep water and involve steeply-dipping (?45°) dip-slip ruptures gives insight into the large tsunami runups and damage, and loss of life that are expected on a regional scale near such earthquake sources compared to those due to mega-thrust earthquakes of comparable magnitudes. These common features of source regions for great off-<span class="hlt">trench</span> earthquakes are used to identify potential sites for future great off-<span class="hlt">trench</span> earthquakes that share the above attributes. Methods are also suggested for estimating the rates of slip accumulation and average recurrence times of such earthquakes.</p> <div class="credits"> <p class="dwt_author">Kirby, S. H.; Hino, R.; Geist, E. L.; Wright, D. J.; Okal, E.; Wartman, J. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">133</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40449487"> <span id="translatedtitle">Pull-down basin in the central part of <span class="hlt">Japan</span> due to <span class="hlt">subduction</span>-induced mantle flow</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The driving force for the basin subsiding against isostatic balance in and around Lake Biwa in the Kinki district, <span class="hlt">Japan</span> is discussed. The lake region is characterized by strong negative Bouguer anomalies, especially by a steep horizontal gradient zone of gravity anomaly running along the western margin of the lake. The large negative anomaly (>50 mgal) cannot be explained by</p> <div class="credits"> <p class="dwt_author">Takeshi Kudo; Koshun Yamaoka</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">134</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFMDI41B..02S"> <span id="translatedtitle">Slab width control on current global plate and <span class="hlt">trench</span> velocities, and on Cenozoic western North America tectonics</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Subduction</span> of tectonic plates into the Earth's mantle is accommodated by <span class="hlt">subducting</span> plate motion and <span class="hlt">trench</span> migration. How these two modes contribute to the <span class="hlt">subduction</span> velocity and what controls their partitioning remain unsolved. Here we present a global compilation for 17 active <span class="hlt">subduction</span> zones and three-dimensional numerical models of progressive free <span class="hlt">subduction</span> showing that slab width (W) provides a first-order control on <span class="hlt">subduction</span> partitioning, <span class="hlt">subducting</span> plate velocity and <span class="hlt">trench</span> velocity. In nature, <span class="hlt">subducting</span> plate velocity increases progressively from -1 to 3 cm/yr for W = 300-600 km to 5-7 cm/yr for W = 7000 km, while the models show an increase from 2.5-3 cm/yr to 6 cm/yr. Furthermore, <span class="hlt">trench</span> velocity decreases from 1-7 cm/yr for W = 300-600 km to -1 to 1 cm/yr for W = 7000 km in nature, whilst the models show an decrease from 6-7 cm/yr to ~1.5 cm/yr. The <span class="hlt">subduction</span> zone data, numerical models and a scaling formulation for sinking of slabs in the upper mantle show that <span class="hlt">subducting</span> plate velocity scales with ~Wexp(2/3), while <span class="hlt">trench</span> velocity scales with ~1/W. Correlation coefficients for the numerical models with respect to the scaling formulation are in the range 0.95-0.99 for <span class="hlt">subducting</span> plate velocity, <span class="hlt">trench</span> velocity and <span class="hlt">subduction</span> partitioning, while those for the natural data are in the range 0.70-0.72. It is thus found that slab width provides a first-order control plate velocity, <span class="hlt">trench</span> velocity and <span class="hlt">subduction</span> partitioning. Comparison of slab age and <span class="hlt">subduction</span> kinematics for natural <span class="hlt">subduction</span> zones gives significantly lower correlation coefficients (0.29-0.38), indicating that slab age provides a second-order control on <span class="hlt">trench</span> velocity and <span class="hlt">subducting</span> plate velocity. Our findings provide an explanation for the Cenozoic progressive decrease in <span class="hlt">subducting</span> plate velocity and <span class="hlt">subduction</span> partitioning of the Farallon plate, which we interpret as resulting from the progressive decrease in <span class="hlt">trench</span>-parallel width of the Farallon slab during the Cenozoic from ~14000 km to only 1400 km at present. This decrease in slab width also explains the change from Sevier-Laramide orogenesis to Basin and Range extension in North America in the Eocene to Miocene. Shortening took place during wide-slab <span class="hlt">subduction</span> and overriding-plate-driven <span class="hlt">trench</span> retreat (push-back), whilst extension took place during intermediate to narrow-slab <span class="hlt">subduction</span> and slab-driven <span class="hlt">trench</span> retreat (pull-back).</p> <div class="credits"> <p class="dwt_author">Stegman, D. R.; Schellart, W. P.; Farrington, R. J.; Freeman, J. C.; Moresi, L. N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">135</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3169062"> <span id="translatedtitle"><span class="hlt">Trench</span> Connection</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">‘<span class="hlt">Trench</span> Connection’ was the first international symposium focusing primarily on the hadal zone (depths greater than 6000 m). It was held at the University of Tokyo's Atmosphere and Ocean Research Institute in November 2010. The symposium was successful in having attracted an international collective of scientists and engineers to discuss the latest developments in the exploration and understanding of the deepest environments on Earth. The symposium sessions were categorized into three themes: (i) new deep-submergence technology; (ii) <span class="hlt">trench</span> ecology and evolution; and (iii) the physical environment. Recent technological developments have overcome the challenges of accessing the extreme depths, which have in turn prompted an international renewed interest in researching physical and biological aspects of the hadal ecosystems. This bringing together of international participants from different disciplines led to healthy discussions throughout the symposium, providing potential opportunities and realizations of where the future of unravelling hadal ecology lies. Hadal science is still at relatively rudimentary levels compared with those of shallower marine environments; however, it became apparent at the symposium that it is now an ever-expanding scientific field.</p> <div class="credits"> <p class="dwt_author">Jamieson, Alan J.; Fujii, Toyonobu</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">136</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFM.T53D..01M"> <span id="translatedtitle">Evolution of <span class="hlt">subducted</span> slab morphology in the Western Pacific based on seismic tomography and paleogeographic reconstructions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Plate motions and <span class="hlt">subducting</span> slab morphology are intricately connected. Through the integration of seismicity, tomographic images, and relative plate motions the evolution of mantle structure can be interpreted. Tomographic images of P-wave, shear wave-speed, and bulk sound speed perturbations of the Northwest Pacific region have been interpreted to define the extent and geometry of the <span class="hlt">subducting</span> Pacific plate in the upper mantle. The morphology of the <span class="hlt">subducted</span> Pacific plate along the Kurile-<span class="hlt">Japan</span>-Izu-Bonin-Mariana arc system was found to vary both in geometry and dip along the entire length of the margin. To understand these differences and evolution to the current slab morphology a tectonic reconstruction for the Western Pacific was created, which describes the geologic history of the past 20 million years. The paleogeographic reconstruction illustrates the collision of the <span class="hlt">Japan</span> and Kurile arcs, the opening of the Kurile Basin and Sea of <span class="hlt">Japan</span>, change in motion of the Izu-Bonin arc, developing curvature of the Mariana arc, disparity in Pacific plate velocities along the convergent margin, and variation in rates of <span class="hlt">trench</span> retreat along different segments of the arc system. The new plate motion model and interpretations of the physical properties of the mantle imaged with the P-wave and joint tomography are tools to assess the spatial and temporal evolution of the Pacific plate morphology from the mid-Miocene to the present and provide limitations in plausible plate motions for the region.</p> <div class="credits"> <p class="dwt_author">Miller, M. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">137</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70020988"> <span id="translatedtitle">Aeromagnetic legacy of early Paleozoic <span class="hlt">subduction</span> along the Pacific margin of Gondwana</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Comparison of the aeromagnetic signatures and geology of southeastern Australia and northern Victoria Land, Antarctica, with similar data from ancient <span class="hlt">subduction</span> zones in California and <span class="hlt">Japan</span>, provides a framework for reinterpretation of the plate tectonic setting of the Pacific margin of early Paleozoic Gondwana. In our model, the plutons in the Glenelg (south-eastern Australia) and Wilson (northern Victoria Land) zones formed the roots of continental-margin magmatic arcs. Eastward shifting of arc magmatism resulted in the Stavely (south-eastern Australia) and Bowers (northern Victoria Land) volcanic eruptions onto oceanic forearc crust. The turbidites in the Stawell (southeastern Australia) and Robertson Bay (northern Victoria Land zones) shed from the Glenelg and Wilson zones, respectively, were deposited along the <span class="hlt">trench</span> and onto the <span class="hlt">subducting</span> oceanic plate. The margin was subsequently truncated by thrust faults and uplifted during the Delamerian and Ross orogenies, leading to the present-day aeromagnetic signatures.</p> <div class="credits"> <p class="dwt_author">Finn, C.; Moore, D.; Damaske, D.; Mackey, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">138</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/42049997"> <span id="translatedtitle">Present-day principal horizontal stress orientations in the Kumano forearc basin of the southwest <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone determined from IODP NanTroSEIZE drilling Site C0009</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A 1.6 km riser borehole was drilled at site C0009 of the NanTroSEIZE, in the center of the Kumano forearc basin, as a landward extension of previous drilling in the southwest <span class="hlt">Japan</span> Nankai <span class="hlt">subduction</span> zone. We determined principal horizontal stress orientations from analyses of borehole breakouts and drilling-induced tensile fractures by using wireline logging formation microresistivity images and caliper data.</p> <div class="credits"> <p class="dwt_author">Weiren Lin; Mai-Linh Doan; J. Casey Moore; Lisa McNeill; Timothy B. Byrne; Takatoshi Ito; Demian Saffer; Marianne Conin; Masataka Kinoshita; Yoshinori Sanada; Kyaw Thu Moe; Eiichiro Araki; Harold Tobin; David Boutt; Yasuyuki Kano; Nicholas W. Hayman; Peter Flemings; Gary J. Huftile; Deniz Cukur; Christophe Buret; Anja M. Schleicher; Natalia Efimenko; Kuniyo Kawabata; David M. Buchs; Shijun Jiang; Koji Kameo; Keika Horiguchi; Thomas Wiersberg; Achim Kopf; Kazuya Kitada; Nobuhisa Eguchi; Sean Toczko; Kyoma Takahashi; Yukari Kido</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">139</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EGUGA..14.5291G"> <span id="translatedtitle"><span class="hlt">Subduction</span> dynamics: effects of downgoing-plate density and strength</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Subduction</span> dynamics are a crucial component of plate tectonics. Although the negative age-dependent buoyancy of the downgoing plate is the primary driving force, <span class="hlt">subduction</span> behaviour cannot be described simply as a function of age. Interaction with global mantle flow, the upper plate and the resistance of the downgoing plate to deformation may all influence plate and <span class="hlt">trench</span> motions and <span class="hlt">subducting</span> slab morphology and stress. 2- and 3-D models of free <span class="hlt">subduction</span>, driven solely by the buoyancy of the downgoing plate, and resisted by a passive viscous mantle and downgoing plate strength provide a useful end-member scenario to start unraveling the relative importance of the different <span class="hlt">subduction</span> forces. The comparison of motions and morphology predicted by such models with Cenozoic <span class="hlt">subduction</span> motions at major <span class="hlt">trenches</span> show that 80% of the slabs move as expected if controlled by upper-mantle slab pull. Only in a few cases, do young plates move at velocities that require a higher driving force (possibly supplied by lower-mantle-slab induced flow). In free <span class="hlt">subduction</span>, <span class="hlt">trenches</span> retreat, except for viscoelastic plates of high strength, and about 80% of the Cenozoic <span class="hlt">trenches</span> retreat. However, retreat accounts for only about 10% of the Cenozoic convergence, much less than for most modeled free-<span class="hlt">subduction</span> cases. Furthermore, <span class="hlt">trench</span> motions are often very oblique to the direction of downgoing plate motion, indicating that the upper-plate and/or mantle exert an important control on movement of the <span class="hlt">trench</span>. High present-day slab dips are compatible with largely upper-mantle slab-pull driven <span class="hlt">subduction</span> of relatively weak plates, where motion partitioning and slab geometry adjust to external constraints/forces on <span class="hlt">trench</span> motion.</p> <div class="credits"> <p class="dwt_author">Goes, S.; Capitanio, F. A.; Morra, G.; Fourel, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">140</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.deepseadrilling.org/67/volume/dsdp67_36.pdf"> <span id="translatedtitle">36. STRATIGRAPHY AND STRUCTURES OF THE MIDDLE AMERICA <span class="hlt">TRENCH</span>: DEEP SEA DRILLING PROJECT LEG 67 TRANSECT OFF GUATEMALA1</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The eight holes drilled at Sites 499 and 500 in the axis of the Middle America <span class="hlt">Trench</span> are the first to recover the com- plete sedimentary section of an active <span class="hlt">trench</span>. These holes demonstrate extension of the <span class="hlt">subducting</span> Cocos Plate and its sedimentary overburden, even at the edge of the Guatemalan margin. A depression within the turbidites filling the <span class="hlt">Trench</span></p> <div class="credits"> <p class="dwt_author">William T. Coulbourn</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_6");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">141</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/v089/iB11/JB089iB11p09171/JB089iB11p09171.pdf"> <span id="translatedtitle">A Geophysical Study of the Manila <span class="hlt">Trench</span>, Luzon, Philippines 1. Crustal Structure, Gravity, and Regional Tectonic Evolution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Manila <span class="hlt">Trench</span> <span class="hlt">subduction</span> zone is an active convergent plate margin between the South China Sea and the northern Philippines. The <span class="hlt">trench</span> trends northerly and is associated with a volcanic arc, an east dipping Benioff zone beneath Luzon, and a well-developed fore arc basin system. The Luzon Trough fore arc basins lie landward of the Manila <span class="hlt">Trench</span> and contain up</p> <div class="credits"> <p class="dwt_author">Dennis E. Hayes; Stephen D. Lewis</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">142</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.T51D2085N"> <span id="translatedtitle">Interplate coupling along the central Ryukyu <span class="hlt">Trench</span> inferred from GPS/acoustic seafloor geodetic observation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Ryukyu <span class="hlt">trench</span> is a major convergent plate boundary where the Philippine Sea plate is <span class="hlt">subducting</span> at a rate of about 8 cm/yr. Large earthquakes have not been reported along the Ryukyu <span class="hlt">subduction</span> for the last 300 years. Because the rate of release of seismic moment in the Ryukyu <span class="hlt">Trench</span> over the last 80 years is 5% in consideration of the plate convergence rate, interseismic coupling in the <span class="hlt">trench</span> is assumed to be weak.The GPS measurements by <span class="hlt">Japan</span> Geographical Survey Institute also show the southward motion (2.5 cm/yr) of Ryukyu arc relative to the Amurian plate, which is due to extensional rifting of Okinawa Trough. Backslip by the interplate coupling between the <span class="hlt">subducting</span> Philippine Sea plate and the overriding Eurasian plate cannot have been detected in the GPS network along the Ryukyu Islands. We have started the GPS/acoustic seafloor observation to detect the inter-plate coupling in the central Ryukyu <span class="hlt">trench</span>. For this measurement, we used a system capable of performing two main tasks: precise acoustic ranging between a ship station (observation vessel) and seafloor transponders, and kinematic GPS positioning of observation vessels. The seafloor reference point was set at about 33 km landward from the axis of the Ryukyu <span class="hlt">trench</span> (southeast of Okinawa Island). A set of three acoustic transponders has been installed on the seafloor, at a depth of about 2900m. The transponders are placed to form a triangular. Five campaign observations were carried out for the period from January 2008 to November 2009. Each epoch consists of three observation days. The coordinates of the seafloor benchmark were calculated using the least-squares technique (Ikuta et al., 2008); this technique minimizes the square sum of acoustic travel-time residuals. The RMS of travel time residuals for each campaign analysis is about 70 micro-seconds. The result shows that the benchmark moved to northwest direction for two years at a rate of 4 cm/yr relative to the Amurian plate. Then we estimated the length and width of interplate coupling area using observed movement of the benchmark. The movements of the GPS stations on the Ryukyu Islands and the benchmark are described as the combination of the block rotation of the Ryukyu arc (Nakamura, 2004) and the displacement by the backslip in the coupled area. The results show that the estimated width of the interplate coupling area is 40-50 km from the Ryukyu <span class="hlt">trench</span>. The results also show that the length of the coupled area is over 40 km. Since the calculated displacements are not sensitive to the change in the length of the coupled area, the accurate length is uncertain. These suggest that the interplate coupling occurs up-dip of the seismogenic zone in the Ryukyu <span class="hlt">subduction</span> zone. The tsunami earthquake (M8.1) occurred near the south Ryukyu <span class="hlt">Trench</span> in 1771. This suggests the interplate coupling near the <span class="hlt">Trench</span> would be the cause of the tsunami earthquakes.</p> <div class="credits"> <p class="dwt_author">Nakamura, M.; Tadokoro, K.; Okuda, T.; Ando, M.; Watanabe, T.; Sugimoto, S.; Miyata, K.; Matsumoto, T.; Furukawa, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">143</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.S44A..07H"> <span id="translatedtitle">Seismic imaging of the 1923 Kanto Earthquake Source Area on the <span class="hlt">subducting</span> Philippine Sea plate, in <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Large devastating earthquakes sometimes occur on a mega-thrust source fault which underlies the Tokyo metropolitan region. The source faults are located on the upper boundary of the <span class="hlt">subducting</span> the Philippine Sea plate (PSP), which was so far estimated mainly from seismicity distribution. To get better prediction of the strong ground motion, we need to precisely characterize the source fault of those large earthquakes. A depth and geometry of the PSP is a key for characterization. We deployed four controlled source seismic lines in the Kanto area from 2002 to 2003: The 150-km long Boso line in 2002, the 80-km Sagami line in 2003, the 80-km Tokyo Bay line in 2003, and the 165-km Eastern part of the Kanto Mountain line in 2003. We, for the first time, directly identify the source fault using deep seismic reflection profiling images to be the upper surface of the PSP, which is found to be much shallower than previous indirect estimation based on seismicity distribution by 10 to 20 km. This geometry serves as a new constraint for studies of Kanto seismotectonics and seismic imaging using earthquakes such as high resolution 3D tomography and receiver function analysis. In the seismic profiles, we also found that highly reflective zones correspond to regions of silent slip plus areas outside the asperity zones of the 1923 Kanto earthquake. We propose that an asperity on a plate boundary can be detected by an evaluation of its reflectivity and represents possible regions of rupture for future earthquakes. Together with the obtained velocity structure, our result provides the essential control for the research on crustal deformation, modeling of source fault and strong ground motion estimation.</p> <div class="credits"> <p class="dwt_author">Hirata, N.; Sato, H.; Koketsu, K.; Okaya, D.; Iwasaki, T.; Ito, T.; Kasahara, K.; Ikawa, T.; Abe, S.; Kawanaka, T.; Matsubara, M.; Harder, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">144</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.T23D..02P"> <span id="translatedtitle">Geochemical Tracing of Mantle Flow above <span class="hlt">Subduction</span> Zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Geochemical tracing may be used to track mantle flow above and behind <span class="hlt">subduction</span> zones and so provide an independent test of the applicability of seismic anisotropy measurements. The theory is that, if mantle flow is accompanied by decompression, then extraction of small degree melts from multi-component mantle leads to compositional gradients in the mantle in both isotope and trace element space. These gradients may be obtained by inverting geochemical data from the products of mantle melting. If mantle flow is accompanied by addition of a <span class="hlt">subduction</span> fluid, then simultaneous melting and <span class="hlt">subduction</span> component addition may also produce compositional gradients. Numerical experiments enable compositional gradients to be quantified in terms of the extent of melt extraction, mantle temperature and other variables. In addition, isotope and trace element systematics provide evidence for the provenance of the mantle entering the <span class="hlt">subduction</span> system, with Hf isotopes and immobile trace elements providing a means of establishing provenance even from magmas generated directly above the dehydrating <span class="hlt">subducted</span> plate. This work focuses on a series of geochemical maps which enable mantle flow to be traced for range of oceanic arc basin systems (Izu-Bonin-Mariana, Tonga-Vanuatu, Scotia, Manus) and, provisionally, some continental systems (<span class="hlt">Japan</span>, Cascades). Using maps based on geochemical proxies for melt extraction (such as Ta/Yb), <span class="hlt">subduction</span>-addition (such as Th/Ta) and mantle provenance (such as epsilon-Hf v epsilon Nd), it is possible to demonstrate the existence of a wide range of mantle flow regimes. Thus, the Izu and <span class="hlt">Japan</span> systems appear to be characterised by simple <span class="hlt">trench</span>-orthogonal flow, the Mariana system by dispersion away from several separate centers of mantle upwelling, the Tonga-Vanuatu system by unidirectional flow from beneath the Pacific plate in the north, and the Scotia system by bi-directional flow from both north and south. In a number of these cases, isotopic fingerprinting using immobile isotope ratios is critical for establishing the ultimate source of the mantle: for example, the mantle entering the Scotia system may be seen to originate from the Atlantic Bouvet domain rather than the Atlantic Tristan or the Pacific domains. These results are broadly in keeping with seismic anisotropy measurements to date while providing greater coverage but, of course, geochemical tracing is restricted to areas of magmatic activity. Integration of geophysical and geochemical methods may therefore be necessary to provide the maximum information on mantle flow.</p> <div class="credits"> <p class="dwt_author">Pearce, J. A.; Barry, T. L.; Millar, I. L.; Leat, P. T.; Stern, R. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">145</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/44255528"> <span id="translatedtitle">Link between ridge <span class="hlt">subduction</span> and gold mineralization in southern Alaska</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">40Ar\\/39Ar geochronology reveals that turbidite-hosted gold deposits in the southern Alaska accretionary prism are the same age as nearby near-<span class="hlt">trench</span> plutons. These early Tertiary plutons and gold lodes formed above a slab window during <span class="hlt">subduction</span> of an oceanic spreading center. Ridge <span class="hlt">subduction</span> is a previously unrecognized tectonic process for the generation of lode gold.</p> <div class="credits"> <p class="dwt_author">Peter J. Haeussler; Dwight Bradley; Richard Goldfarb; Lawrence Snee; Cliff Taylor</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">146</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48921955"> <span id="translatedtitle">Physical characteristics of <span class="hlt">subduction</span> interface type seismogenic zones revisited</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Based on global earthquake catalogs, the hypocenters, nodal planes, and seismic moments of worldwide <span class="hlt">subduction</span> plate interface earthquakes were extracted for the period between 1900 and 2007. Assuming that the seismogenic zone coincides with the distribution of 5.5 ? M < 7 earthquakes, the <span class="hlt">subduction</span> interface seismogenic zones were mapped for 80% of the <span class="hlt">trench</span> systems and characterized with geometrical</p> <div class="credits"> <p class="dwt_author">Arnauld Heuret; Serge Lallemand; Francesca Funiciello; Claudia Piromallo; Claudio Faccenna</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">147</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.S41C1928S"> <span id="translatedtitle">Waveform through the <span class="hlt">subducted</span> plate under the Tokyo region in <span class="hlt">Japan</span> observed by a ultra-dense seismic network (MeSO-net) and seismic activity around mega-thrust earthquakes area</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In central <span class="hlt">Japan</span>, the Philippine Sea plate (PSP) <span class="hlt">subducts</span> beneath the Tokyo Metropolitan area, the Kanto region, where it causes mega-thrust earthquakes, such as the 1703 Genroku earthquake (M8.0) and the 1923 Kanto earthquake (M7.9) which had 105,000 fatalities. A M7 or greater earthquake in this region at present has high potential to produce devastating loss of life and property with even greater global economic repercussions. The Central Disaster Management Council of <span class="hlt">Japan</span> estimates the next great earthquake will cause 11,000 fatalities and 112 trillion yen (1 trillion US$) economic loss. This great earthquake is evaluated to occur with a probability of 70 % in 30 years by the Earthquake Research Committee of <span class="hlt">Japan</span>. We had started the Special Project for Earthquake Disaster Mitigation in Tokyo Metropolitan area (2007-2012). Under this project, the construction of the Metropolitan Seismic Observation network (MeSO-net) that consists of about 400 observation sites was started [Kasahara et al., 2008; Nakagawa et al., 2008]. Now, we had 178 observation sites. The correlation of the wave is high because the observation point is deployed at about 2 km intervals, and the identification of the later phase is recognized easily thought artificial noise is very large. We also discuss the relation between a deformation of PSP and intra-plate M7+ earthquakes: the PSP is <span class="hlt">subducting</span> beneath the Honshu arc and also colliding with the Pacific plate. The <span class="hlt">subduction</span> and collision both contribute active seismicity in the Kanto region. We are going to present a high resolution tomographic image to show low velocity zone which suggests a possible internal failure of the plate; a source region of the M7+ intra-plate earthquake. Our study will contribute a new assessment of the seismic hazard at the Metropolitan area in <span class="hlt">Japan</span>. Acknowledgement: This study was supported by the Earthquake Research Institute cooperative research program.</p> <div class="credits"> <p class="dwt_author">Sakai, S.; Kasahara, K.; Nanjo, K.; Nakagawa, S.; Tsuruoka, H.; Morita, Y.; Kato, A.; Iidaka, T.; Hirata, N.; Tanada, T.; Obara, K.; Sekine, S.; Kurashimo, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">148</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/12177912"> <span id="translatedtitle"><span class="hlt">Japan</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><span class="hlt">Japan</span> is composed of 4 main islands and more than 3900 smaller islands and has 317.7 persons/square kilometer. This makes it one of the most densely populated nations in the world. Religion is an important force in the life of the Japanese and most consider themselves Buddhists. Schooling is free through junior high but 90% of Japanese students complete high school. In fact, <span class="hlt">Japan</span> enjoys one of the highest literacy rates in the world. There are over 178 newspapers and 3500 magazines published in <span class="hlt">Japan</span> and the number of new book titles issued each year is greater than that in the US. Since WW1, <span class="hlt">Japan</span> expanded its influence in Asia and its holdings in the Pacific. However, as a direct result of WW2, <span class="hlt">Japan</span> lost all of its overseas possessions and was able to retain only its own islands. Since 1952, <span class="hlt">Japan</span> has been ruled by conservative governments which cooperate closely with the West. Great economic growth has come since the post-treaty period. <span class="hlt">Japan</span> as a constitutional monarchy operates within the framework of a constitution which became effective in May 1947. Executive power is vested in a cabinet which includes the prime minister and the ministers of state. <span class="hlt">Japan</span> is one of the most politically stable of the postwar democracies and the Liberal Democratic Party is representative of Japanese moderate conservatism. The economy of <span class="hlt">Japan</span> is strong and growing. With few resources, there is only 19% of Japanese land suitable for cultivation. Its exports earn only about 19% of the country's gross national product. More than 59 million workers comprise <span class="hlt">Japan</span>'s labor force, 40% of whom are women. <span class="hlt">Japan</span> and the US are strongly linked trading partners and after Canada, <span class="hlt">Japan</span> is the largest trading partner of the US. Foreign policy since 1952 has fostered close cooperation with the West and <span class="hlt">Japan</span> is vitally interested in good relations with its neighbors. Relations with the Soviet Union are not close although <span class="hlt">Japan</span> is attempting to improve the situation. US policy is based on the following 3 principles: 1) the US views <span class="hlt">Japan</span> as an equal trade partner, 2) that the relationship is global in scope, and 3) that <span class="hlt">Japan</span> has become increasingly assertive in world matters and plays a greater international role. The combined efforts of the US and <span class="hlt">Japan</span> will be utilized to promote world peace. PMID:12177912</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1987-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">149</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T52C..06A"> <span id="translatedtitle">Collision and <span class="hlt">subduction</span> structure of the Izu-Bonin arc, central <span class="hlt">Japan</span>: Recent studies from refraction/wide-angle reflection analysis and seismic tomography</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Since the middle Miocene, the Izu-Bonin arc has been colliding from south with the Honshu arc in central <span class="hlt">Japan</span> associated with <span class="hlt">subduction</span> of the Philippine Sea plate. This process is responsible for forming a complex crustal structure called the Izu collision zone. Geological studies indicate the several geological blocks derived from the Izu-Bonin arc, such as the Misaka Mountains (MM), the Tanzawa Mountains (TM) and the Izu Peninsula (IP), were accreted onto the Honshu crust in the course of the collision, forming several tectonic boundaries in and around this collision zone (e.g. Amano, 1991). Recent seismic experiments succeeded in revealing the deep crustal structure in the eastern part of the Izu collision zone by reflection analysis (Sato et al., 2005) and refraction/wide-angle reflection analysis (Arai et al., 2009). Although these studies delineate the collision boundary between the Honshu crust and TM, and the upper surface of the <span class="hlt">subducting</span> Philippine Sea plate, the southern part of the profile including the Kozu-Matsuda Fault (KMF, the tectonic boundary between TM and IP) is not well constrained due to the poor ray coverage. Moreover, clear images of tectonic boundaries are not obtained for the central or western part of the collision zone. In order to construct the structure model dominated by collision and <span class="hlt">subduction</span> for the whole part of the collision zone, we carried out the following two analyses: (1) refraction tomography of active source data including another profile line in the western part of the collision zone (Sato et al., 2006), and (2) seismic tomography combining active and passive source data. In the analysis (1), we applied first arrival seismic tomography (Zelt and Barton, 1998) to the refraction data .We inverted over 39,000 travel times to construct a P wave velocity model for the 75-km-long transect, and a fine-scale structure with strong lateral heterogeneity was recovered. We conducted checkerboard resolution test to evaluate a spatial resolution, and confirmed that the final model has an enough resolution down to the depth of 5 km. We also performed a Monte Carlo uncertainty analysis (Korenaga et al, 2000) to estimate the posteriori model variance, showing that most velocities are well constrained with standard deviation of less than 0.20 km/s. Our result strongly indicates the existences of low velocity zones (< 6.0 km/s) along the tectonic boundaries and high velocity bodies (> 6.0 km/s) just beneath MM and TM, which correspond to the middle crust of the Izu-Bonin arc (Kodaira et al., 2007). In the analysis (2), hypocenters and velocity structure were simultaneously determined based on the double-difference method (Zhang and Thurber, 2003). The hypocenter distribution and final velocity structure obtained indicate several interesting features, including low velocity sedimentary layer (< 6.0 km/s) along the KMF and prominent seismic activity in the middle-lower crust (6.0-6.8 km/s) in the Izu-Bonin arc (10-25 km depth beneath TM). These results give us very important constraints for the collision process ongoing in our research area.</p> <div class="credits"> <p class="dwt_author">Arai, R.; Iwasaki, T.; Sato, H.; Abe, S.; Hirata, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">150</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54787977"> <span id="translatedtitle"><span class="hlt">Subduction</span> Zone Processes and Implications for Changing Composition of the Upper and Lower Mantle</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">With ca. forty thousand kilometers of <span class="hlt">subduction</span> zones and convergence rates from 30 km Ma-1 to 180 km Ma-1, <span class="hlt">subduction</span> carries massive amounts of material into seafloor <span class="hlt">trenches</span>, and beyond. Most of the <span class="hlt">subducting</span> plate is made of mantle material returning to the depths from which it originated. The hydrated and altered upper oceanic section and the overlying sediments, however,</p> <div class="credits"> <p class="dwt_author">J. D. Morris; J. G. Ryan</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">151</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://host.uniroma3.it/dipartimenti/geologia/db/35.pdf"> <span id="translatedtitle">From <span class="hlt">subduction</span> to collision: Control of deep processes on the evolution of convergent plate boundary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Using laboratory experiments, we investigate the dynamics of the collisional process that follows the closure of an oceanic basin. The evolution of these experiments systematically shows four successive episodes of deformation, which correspond to (1) the initiation of oceanic <span class="hlt">subduction</span>, (2) a mature period of oceanic <span class="hlt">subduction</span>, (3) an episode of continental <span class="hlt">subduction</span>, during which the <span class="hlt">trench</span> absorbs all the</p> <div class="credits"> <p class="dwt_author">Vincent Regard; Claudio Faccenna; Joseph Martinod; Olivier Bellier; Jean-Charles Thomas</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">152</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/60435708"> <span id="translatedtitle">Circum-Pacific modes of <span class="hlt">subduction</span>, collision, and metallogenesis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Tectonic processes in <span class="hlt">trench</span>-arc-back-arc regions, as depicted on the Plate-Tectonic Map of the Circum-Pacific Region, are controlled by different modes of <span class="hlt">subduction</span>. In one end member, the Chilean or high-stress <span class="hlt">subduction</span> zone, the stress regime in the overriding lithosphere is compressive; whereas in the other end member, the Mariana or low-stress <span class="hlt">subduction</span> zone, extensional tectonics prevails. The two modes are</p> <div class="credits"> <p class="dwt_author">C. Nishiwaki; S. Uyeda</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">153</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004E%26PSL.226..275."> <span id="translatedtitle"><span class="hlt">Subduction</span> initiation: spontaneous and induced</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The sinking of lithosphere at <span class="hlt">subduction</span> zones couples Earth's exterior with its interior, spawns continental crust and powers a tectonic regime that is unique to our planet. In spite of its importance, it is unclear how <span class="hlt">subduction</span> is initiated. Two general mechanisms are recognized: induced and spontaneous nucleation of <span class="hlt">subduction</span> zones. Induced nucleation (INSZ) responds to continuing plate convergence following jamming of a <span class="hlt">subduction</span> zone by buoyant crust. This results in regional compression, uplift and underthrusting that may yield a new <span class="hlt">subduction</span> zone. Two subclasses of INSZ, transference and polarity reversal, are distinguished. Transference INSZ moves the new <span class="hlt">subduction</span> zone outboard of the failed one. The Mussau <span class="hlt">Trench</span> and the continuing development of a plate boundary SW of India in response to Indo Asian collision are the best Cenozoic examples of transference INSZ processes. Polarity reversal INSZ also follows collision, but continued convergence in this case results in a new <span class="hlt">subduction</span> zone forming behind the magmatic arc; the response of the Solomon convergent margin following collision with the Ontong Java Plateau is the best example of this mode. Spontaneous nucleation (SNSZ) results from gravitational instability of oceanic lithosphere and is required to begin the modern regime of plate tectonics. Lithospheric collapse initiates SNSZ, either at a passive margin or at a transform/fracture zone, in a fashion similar to lithospheric delamination. The theory of hypothesis predicts that seafloor spreading will occur in the location that becomes the forearc, as asthenosphere wells up to replace sunken lithosphere, and that seafloor spreading predates plate convergence. This is the origin of most boninites and ophiolites. Passive margin collapse is a corollary of the Wilson cycle but no Cenozoic examples are known; furthermore, the expected strength of the lithosphere makes this mode unlikely. Transform collapse SNSZ appears to have engendered new <span class="hlt">subduction</span> zones along the western edge of the Pacific plate during the Eocene. Development of self-sustaining <span class="hlt">subduction</span> in the case of SNSZ is signaled by the beginning of down-dip slab motion, causing chilling of the forearc mantle and retreat of the magmatic arc to a position that is 100 200 km from the <span class="hlt">trench</span>. INSZ may affect only part of a plate margin, but SNSZ affects the entire margin in the new direction of convergence. INSZ and SNSZ can be distinguished by the record left on the upper plates: INSZ begins with strong compression and uplift, whereas SNSZ begins with rifting and seafloor spreading. Understanding conditions leading to SNSZ and how hinged subsidence of lithosphere changes to true <span class="hlt">subduction</span> promise to be exciting and fruitful areas of future research.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2004-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">154</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004E%26PSL.226..275S"> <span id="translatedtitle"><span class="hlt">Subduction</span> initiation: spontaneous and induced</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The sinking of lithosphere at <span class="hlt">subduction</span> zones couples Earth's exterior with its interior, spawns continental crust and powers a tectonic regime that is unique to our planet. In spite of its importance, it is unclear how <span class="hlt">subduction</span> is initiated. Two general mechanisms are recognized: induced and spontaneous nucleation of <span class="hlt">subduction</span> zones. Induced nucleation (INSZ) responds to continuing plate convergence following jamming of a <span class="hlt">subduction</span> zone by buoyant crust. This results in regional compression, uplift and underthrusting that may yield a new <span class="hlt">subduction</span> zone. Two subclasses of INSZ, transference and polarity reversal, are distinguished. Transference INSZ moves the new <span class="hlt">subduction</span> zone outboard of the failed one. The Mussau <span class="hlt">Trench</span> and the continuing development of a plate boundary SW of India in response to Indo-Asian collision are the best Cenozoic examples of transference INSZ processes. Polarity reversal INSZ also follows collision, but continued convergence in this case results in a new <span class="hlt">subduction</span> zone forming behind the magmatic arc; the response of the Solomon convergent margin following collision with the Ontong Java Plateau is the best example of this mode. Spontaneous nucleation (SNSZ) results from gravitational instability of oceanic lithosphere and is required to begin the modern regime of plate tectonics. Lithospheric collapse initiates SNSZ, either at a passive margin or at a transform/fracture zone, in a fashion similar to lithospheric delamination. The theory of hypothesis predicts that seafloor spreading will occur in the location that becomes the forearc, as asthenosphere wells up to replace sunken lithosphere, and that seafloor spreading predates plate convergence. This is the origin of most boninites and ophiolites. Passive margin collapse is a corollary of the Wilson cycle but no Cenozoic examples are known; furthermore, the expected strength of the lithosphere makes this mode unlikely. Transform collapse SNSZ appears to have engendered new <span class="hlt">subduction</span> zones along the western edge of the Pacific plate during the Eocene. Development of self-sustaining <span class="hlt">subduction</span> in the case of SNSZ is signaled by the beginning of down-dip slab motion, causing chilling of the forearc mantle and retreat of the magmatic arc to a position that is 100-200 km from the <span class="hlt">trench</span>. INSZ may affect only part of a plate margin, but SNSZ affects the entire margin in the new direction of convergence. INSZ and SNSZ can be distinguished by the record left on the upper plates: INSZ begins with strong compression and uplift, whereas SNSZ begins with rifting and seafloor spreading. Understanding conditions leading to SNSZ and how hinged subsidence of lithosphere changes to true <span class="hlt">subduction</span> promise to be exciting and fruitful areas of future research.</p> <div class="credits"> <p class="dwt_author">Stern, Robert J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">155</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5823997"> <span id="translatedtitle"><span class="hlt">Subduction</span> zone tectonic studies to develop concepts for the occurrence of sediment <span class="hlt">subduction</span> (Phase I). Final technical report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The objective was to determine the fate of sediments at convergent lithospheric plate boundaries. The study focuses on the structures of the Circum-Pacific <span class="hlt">trenches</span> and shallow portions of the associated <span class="hlt">subduction</span> zones. Sediment distribution and the nature of sediment deformation was defined through the various stages of plate convergence to determine if the sediments are <span class="hlt">subducted</span> or accreted. The controlling factors for sediment <span class="hlt">subduction</span> and/or accretion were determined. 50 figs. (ACR)</p> <div class="credits"> <p class="dwt_author">Hilde, T.W.C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">156</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://eric.ed.gov/?q=rituals+AND+lessons&pg=3&id=ED249123"> <span id="translatedtitle"><span class="hlt">Japan</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p class="result-summary">|Materials for a secondary level, interdisciplinary social studies course on <span class="hlt">Japan</span> are divided into introductory information, 14 classroom units, and study and evaluation materials. Introductory material includes lists of objectives and skills, an outline of Japanese history, and an explanation of <span class="hlt">Japan</span>'s name and flag. The units cover the…</p> <div class="credits"> <p class="dwt_author">Jones, Savannah C.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">157</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=ADA177158"> <span id="translatedtitle">Seamarc II Studies of <span class="hlt">Subducting</span> Seamounts.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">Effects of <span class="hlt">subduction</span> related tectonic processes on the oceanic plate are expressed in the morphology of some of these seamounts located in or very near the axes of the Mariana and Izu/Bonin submarine <span class="hlt">trenches</span>. Fractures, presumably caused by bending of t...</p> <div class="credits"> <p class="dwt_author">P. Fryer D. M. Hussong</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">158</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1992LPICo.789...97S"> <span id="translatedtitle">Evidence for retrograde lithospheric <span class="hlt">subduction</span> on Venus</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Though there is no plate tectonics per se on Venus, recent Magellan radar images and topographic profiles of the planet suggest the occurrence of the plate tectonic processes of lithospheric <span class="hlt">subduction</span> and back-arc spreading. The perimeters of several large coronae (e.g., Latona, Artemis, and Eithinoha) resemble Earth <span class="hlt">subduction</span> zones in both their planform and topographic profile. The planform of arcuate structures in Eastern Aphrodite were compared with <span class="hlt">subduction</span> zones of the East Indies. The venusian structures have radii of curvature that are similar to those of terrestrial <span class="hlt">subduction</span> zones. Moreover, the topography of the venusian ridge/<span class="hlt">trench</span> structures is highly asymmetric with a ridge on the concave side and a trough on the convex side; Earth <span class="hlt">subduction</span> zones generally display the same asymmetry.</p> <div class="credits"> <p class="dwt_author">Sandwell, David T.; Schubert, Gerald</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">159</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..1513492F"> <span id="translatedtitle">Development of seismic anisotropy during <span class="hlt">subduction</span>-induced mantle flow</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Subduction</span> zones are convergent margins where the rigid lithosphere sinks into the Earth's mantle inducing complex 3D flow patterns. Seismic anisotropy generated by strain-induced lattice/crystal preferred orientation (LPO/CPO) of intrinsically anisotropic minerals is commonly used to study flow in the mantle and its relations with plate motions. We present a new methodology to compute the seismic anisotropy directly from the flow in the upper mantle of 3-D numerical models of Earth-like <span class="hlt">subduction</span>. This computational strategy accounts for the non-steady-state evolution of <span class="hlt">subduction</span> zones yielding mantle fabrics that are more consistent with the deformation history than previously considered. In the <span class="hlt">subduction</span> models a strong mantle fabric develops throughout the upper mantle with a magnitude of the anisotropy that is proportional to the amount of <span class="hlt">subduction</span>, and is independent of the <span class="hlt">subduction</span> rate. The subslab upper mantle is characterized by two domains with different fabrics: at shallow depth the mantle entrained with the <span class="hlt">subducting</span> slab develops <span class="hlt">trench</span>-perpendicular directed anisotropy due to simple shear deformation, while in the deeper mantle slab rollback induces pure shear deformation causing <span class="hlt">trench</span>-parallel extension and fast seismic directions. <span class="hlt">Subducting</span> plate advance favours the development of the fabric in the entrained mantle domain, while slab retreat increases the <span class="hlt">trench</span>-parallel anisotropy in the deeper upper mantle. In the deeper domain the strength of the fabric is proportional to the horizontal divergence of the flow and weakens from the slab edges toward the centre. As such, strong <span class="hlt">trench</span>-parallel anisotropy forms below retreating and relatively narrow slabs or at the margins of wider plates. The synthetic SKS splitting patterns calculated in the fore-arc are controlled by the magnitude of the anisotropy in the upper domain, with <span class="hlt">trench</span>-perpendicular fast azimuths in the centre of large plates and <span class="hlt">trench</span>-parallel toward the plate edges. Instead, above relatively narrow, retreating slabs (? 600 km and low <span class="hlt">subduction</span> partitioning ratio (SPR)), azimuths are <span class="hlt">trench</span>-parallel due to the strong anisotropy in the lower subslab domain. In all models the anisotropy in the back-arc and on the sides of the <span class="hlt">subducting</span> plate is, respectively, <span class="hlt">trench</span>-perpendicular and sub-parallel to the return flow at depth. Results from our regional scale models may help to infer the flow and composition of the upper mantle by comparison with the wide range of <span class="hlt">subduction</span> zones seismic data observed globally</p> <div class="credits"> <p class="dwt_author">Faccenda, Manuele; Capitanio, Fabio Antonio</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">160</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51730701"> <span id="translatedtitle">Fluid flow in ocean crust cools the Cascadia <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Temperatures along <span class="hlt">subduction</span> zone plate boundary faults have been used to estimate the area and extent of the seismogenic zone. Recent studies of the well-constrained Nankai margin of <span class="hlt">Japan</span> show that hydrothermal circulation in the <span class="hlt">subducting</span> crust cools the <span class="hlt">subduction</span> zone and widens the area of the plate boundary fault that is between the key temperatures of 150 and 350</p> <div class="credits"> <p class="dwt_author">B. D. Cozzens; G. A. Spinelli</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_7");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">161</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48833474"> <span id="translatedtitle"><span class="hlt">JAPAN</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">\\u000a Japanese populations are genetically different from other populations. Mass screening of newborns in <span class="hlt">Japan</span> revealed that the\\u000a frequency of hyperphenylalanemia (PKU) was one-tenth and that of galactosemia one-twelfth of the frequency in other countries.1,2 Genetic diseases specific to the Japanese are acatalasia, Fukuyama muscular dystrophy and a few others. The incidence in\\u000a <span class="hlt">Japan</span> of other common single gene disorders, including</p> <div class="credits"> <p class="dwt_author">Ichiro Matsuda</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">162</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1983Tecto...2...51L"> <span id="translatedtitle">Development of Forearcs of Intraoceanic <span class="hlt">Subduction</span> Zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The uplifted Costa Rican forearc landward of the Middle America <span class="hlt">Trench</span> and the Mariana forearc drilled on IPOD leg 60 both lack the thick clastic sequences, complex deformation, and abundant evidence of accretion which characterize more widely known forearcs that border continents. Both regions contain significant in situ accumulations of pelagic and hemipelagic sediments in place of thick <span class="hlt">trench</span> and <span class="hlt">trench</span> slope basin sequences composed of terrigenous turbidites. The Nicoya Peninsula of Costa Rica contains no significant melange terranes. Deformation of the mafic igneous basement and its thin cover of pelagic, hemipelagic, and first-cycle volcanogenic material is mild overall, with discrete zones of intense deformation disrupting otherwise well-preserved stratigraphic sections. Intraoceanic <span class="hlt">subduction</span> zones lacking longitudinal <span class="hlt">trench</span> feed are sites of little or no accretion of sediments, and recently suggested experimental and theoretical models of <span class="hlt">subduction</span> zone processes involving flow melanges are inappropriate for intraoceanic forearcs. Intraoceanic forearcs generally lack high-grade exotic components such as blueschist and eclogite tectonically incorporated as blocks in lower-grade matrix, although uplift and erosion of the forearc basement may provide detritus of amphibolite and ultramafic rock to the <span class="hlt">trench</span> and <span class="hlt">trench</span> slope.</p> <div class="credits"> <p class="dwt_author">Lundberg, Neil</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">163</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55458228"> <span id="translatedtitle">The force balance at convergent margins: implication for <span class="hlt">trench</span> motions and mantle flow</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The balance of the forces acting on convergent margins is the key to understand the dynamics of <span class="hlt">subduction</span> and its control on plate motions, <span class="hlt">trench</span> migration and the deformation in the overriding plate. In the <span class="hlt">subduction</span> system, driving forces of slab pull and ridge push are resisted by viscous drag of the mantle around sinking slabs and at the base</p> <div class="credits"> <p class="dwt_author">F. A. Capitanio; L. N. Moresi</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">164</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.U51D..02E"> <span id="translatedtitle"><span class="hlt">Subduction</span> zone plate bending earthquakes and implications for the hydration of the downgoing plate</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The greatest uncertainty in the amount of water input into the Earth at <span class="hlt">subduction</span> zones results from poor constraints on the degree and depth extent of mantle serpentinization in the downgoing slab. The maximum depth of serpentinization is thought to be partly controlled by the maximum depth of tensional earthquakes in the outer rise and <span class="hlt">trench</span> and is expected to vary from <span class="hlt">subduction</span> zone to <span class="hlt">subduction</span> zone or even along-strike for a single <span class="hlt">subduction</span> zone. We explore the maximum depth of extensional faulting on the incoming plate for various <span class="hlt">subduction</span> zones in order to gain insight into the possible extent of slab serpentinization. We relocate <span class="hlt">trench</span> events at island arc <span class="hlt">subduction</span> zones using hypocentroidal decomposition to determine which earthquakes occurred within the incoming plate. For earthquakes with Mw ~5.5+, we determine accurate depths and refine the CMT focal mechanism by inverting teleseismic P and SH waveforms. Results from the Mariana outer rise indicate that extensional earthquakes occur in the Pacific plate at depths ranging from 10-20 km beneath the top of the crust, with the character of <span class="hlt">trench</span> seismicity changing significantly between the northern and southern portions of the <span class="hlt">subduction</span> zone. In comparision, results from the Aleutian <span class="hlt">subduction</span> zone show extensional <span class="hlt">trench</span> earthquakes occurring from 5-30 km below the surface of the <span class="hlt">subducting</span> slab. Compressional incoming plate earthquakes occur only near the Alaskan Peninsula, possibly due to stronger coupling between the slab and overriding plate in this region. Further results from oceanic arc <span class="hlt">subduction</span> zones will be presented and differences between <span class="hlt">subduction</span> zones as well as along-strike differences in the character of <span class="hlt">trench</span> seismicity will be highlighted. If the presence of extensional faulting indicates <span class="hlt">subducting</span> lithosphere hydration, then we expect that as much as the top 30 km of the slab may be hydrated and that the degree of slab serpentinization may vary significantly between <span class="hlt">subduction</span> zones, potentially affecting arc geochemistry, intermediate depth seismicity, and the <span class="hlt">subduction</span> zone water budget.</p> <div class="credits"> <p class="dwt_author">Emry, E. L.; Wiens, D. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">165</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2001PEPI..127...25C"> <span id="translatedtitle">Geodynamic models of deep <span class="hlt">subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Numerical and laboratory models that highlight the mechanisms leading to a complex morphology of <span class="hlt">subducted</span> lithospheric slabs in the mantle transition zone are reviewed. An increase of intrinsic density with depth, an increase of viscosity, or phase transitions with negative Clapeyron slope have an inhibiting influence on deep <span class="hlt">subduction</span>. The impingement of slabs on a viscosity and density interface has been studied in laboratory tanks using corn syrup. Slab interaction with equilibrium and non-equilibrium phase transitions has been modelled numerically in two dimensions. Both the laboratory and the numerical experiments can reproduce the variety of slab behaviour that is found in tomographic images of <span class="hlt">subduction</span> zones, including cases of straight penetration into the lower mantle, flattening at the 660-km discontinuity, folding and thickening of slabs, and sinking of slabs into the lower mantle at the endpoint of a flat-lying segment. Aside from the material and phase transition properties, the tectonic conditions play an important role. In particular, the retrograde motion of the point of <span class="hlt">subduction</span> (<span class="hlt">trench</span>-rollback) has an influence on slab penetration into the lower mantle. A question that still needs to be clarified is the mutual interaction between plate kinematics and the <span class="hlt">subduction</span> process through the transition zone.</p> <div class="credits"> <p class="dwt_author">Christensen, Ulrich</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">166</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/v086/iB06/JB086iB06p04949/JB086iB06p04949.pdf"> <span id="translatedtitle">Nonuniform seismic slip rates along the Middle America <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Revised estimates of seismic slip rates along the Middle America <span class="hlt">Trench</span> are lower on the average than plate convergence rates but match them locally (for example, Oaxaca). Along the Cocos-North American plate boundary this can be explained by nonuniformities in slip at points of aseismic ridge or fracture zone <span class="hlt">subduction</span>. For at least 81 yr (and possibly several hundred years),</p> <div class="credits"> <p class="dwt_author">Karen C. McNally; J. Bernard Minster</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">167</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17789780"> <span id="translatedtitle">Earthquake hazards on the cascadia <span class="hlt">subduction</span> zone.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Large <span class="hlt">subduction</span> earthquakes on the Cascadia <span class="hlt">subduction</span> zone pose a potential seismic hazard. Very young oceanic lithosphere (10 million years old) is being <span class="hlt">subducted</span> beneath North America at a rate of approximately 4 centimeters per year. The Cascadia <span class="hlt">subduction</span> zone shares many characteristics with <span class="hlt">subduction</span> zones in southern Chile, southwestern <span class="hlt">Japan</span>, and Colombia, where comparably young oceanic lithosphere is also <span class="hlt">subducting</span>. Very large <span class="hlt">subduction</span> earthquakes, ranging in energy magnitude (M(w)) between 8 and 9.5, have occurred along these other <span class="hlt">subduction</span> zones. If the Cascadia <span class="hlt">subduction</span> zone is also storing elastic energy, a sequence of several great earthquakes (M(w) 8) or a giant earthquake (M(w) 9) would be necessary to fill this 1200-kilometer gap. The nature of strong ground motions recorded during <span class="hlt">subduction</span> earthquakes of M(w) less than 8.2 is discussed. Strong ground motions from even larger earthquakes (M(w) up to 9.5) are estimated by simple simulations. If large <span class="hlt">subduction</span> earthquakes occur in the Pacific Northwest, relatively strong shaking can be expected over a large region. Such earthquakes may also be accompanied by large local tsunamis. PMID:17789780</p> <div class="credits"> <p class="dwt_author">Heaton, T H; Hartzell, S H</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-04-10</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">168</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54159186"> <span id="translatedtitle">High Attenuation Zone Beneath the <span class="hlt">Subducting</span> Pacific Plate?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Interesting systematic change in waveform observed in seismic networks on <span class="hlt">Japan</span> islands from events in Java - Tonga <span class="hlt">subduction</span> zones (the epicentral distances are from 40-80 degrees). Some waveforms sampling eastern region (oceanward) of <span class="hlt">Japan</span> <span class="hlt">subduction</span> zones from Tohoku to Izu have been broadened and the amplitude has been decayed. These characteristics can be due to anelasticity in the propagating</p> <div class="credits"> <p class="dwt_author">A. Shito; H. Kawakatsu; K. Obara</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">169</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53879720"> <span id="translatedtitle">Submarine slope failures along the convergent continental margin of the Middle America <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We present the first comprehensive study of mass wasting processes in the continental slope of a convergent margin of a <span class="hlt">subduction</span> zone where tectonic processes are dominated by <span class="hlt">subduction</span> erosion. We have used multibeam bathymetry along ˜1300 km of the Middle America <span class="hlt">Trench</span> of the Central America <span class="hlt">Subduction</span> Zone and deep-towed side-scan sonar data. We found abundant evidence of large-scale</p> <div class="credits"> <p class="dwt_author">Rieka Harders; César R. Ranero; Wilhelm Weinrebe; Jan H. Behrmann</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">170</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.T41C1220G"> <span id="translatedtitle">Bathymetry of Mariana <span class="hlt">Trench</span>-Arc System and Formation of the Challenger Deep as a Consequence of Weak Plate Coupling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Challenger Deep in the southernmost Mariana <span class="hlt">Trench</span> (western Pacific Ocean) is the deepest point on the earth's surface (10,920 m below sea level). Its location within a <span class="hlt">subduction</span> <span class="hlt">trench</span>, where one plate bends and descends below another, is not surprising. However, why is it located in the southernmost Mariana <span class="hlt">Trench</span> and not at its central part, where the rate of <span class="hlt">subduction</span> is higher, where the lithosphere is the oldest (and densest) on Earth, and where the <span class="hlt">subducted</span> lithosphere pulling down is the longest in Earth (~1000 km or more according to seismic tomography)? We suggest that although <span class="hlt">subduction</span> rate and slab age generally control <span class="hlt">trench</span> depth, here, the width of the Plate Coupling Zone is more important and counteracts <span class="hlt">trench</span> deepening. Beneath the central Marianas the <span class="hlt">subducted</span> slab is attached to the upper plate along a 150-km-wide surface that holds the shallow portion of the <span class="hlt">subducted</span> plate nearly horizontal, in spite of its great load and, thus, counters <span class="hlt">trench</span> deepening. In contrast, along the south Mariana <span class="hlt">Trench</span> the <span class="hlt">subducted</span> length of the lithosphere is much shorter, but its attachment to the upper plate is only along a relatively narrow, 50-km-wide, surface. In addition, a tear in the slab beneath this region helps it to sink rapidly through the mantle and this combination of circumstances allows the slab to roll back, steepen, and form the deepest <span class="hlt">trench</span> on Earth. In a wider perspective, the interrelations shown here between <span class="hlt">trench</span> deepening, ridge shallowing, slab steepening, and forearc narrowing may shed light on other <span class="hlt">subduction</span> zones located near edges of rapidly retreating slabs.</p> <div class="credits"> <p class="dwt_author">Gvirtzman, Z.; Stern, R. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">171</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.4279C"> <span id="translatedtitle">Rheological effects on slab stagnation and <span class="hlt">trench</span> rollback</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Trench</span> rollback has been a widely discussed phenomenon in recent years, and multiple studies have concentrated on various parameters that may influence <span class="hlt">trench</span> migration and related aspects of slab deformation in the (upper) mantle. Here we concentrate on the effects of rheology in controlling the rollback and associated stagnation of slabs in the transition zone. We perform numerical simulations of slab evolution in a 2D Cartesian model with strongly nonlinear rheology combining diffusion creep, dislocation creep and a power-law stress limiter. Decoupling of the <span class="hlt">subducting</span> and overriding plates is facilitated by a low-viscosity crustal layer prescribed on top of the <span class="hlt">subducting</span> plate. We investigate models with the age of the <span class="hlt">subducting</span> plate varying between 70 Myr and 150 Myr at the <span class="hlt">trench</span>. We study the effects of the yield stress of the stress-limiting rheology (0.2-1 GPa) and of the crustal strength. We demonstrate that retrograde <span class="hlt">trench</span> migration develops in most models considered, regardless of the <span class="hlt">subducting</span> plate age or prescribed strength. Rollback then mostly produces slabs that are horizontally deflected at the 660-km phase boundary and remain subhorizontal at the bottom of the transition zone. Slab morphologies are in agreement with stagnant, horizontally deflected structures reported in the transition zone by seismic tomography. Furthermore, if the strength of the slab is limited to less than 0.5 GPa, the slab experiences a significant amount of horizontal buckling. Both <span class="hlt">subducting</span> plate velocity and <span class="hlt">trench</span> rollback velocity then exhibit periodic time variations with dominant periods of around 20 Myr with rollback velocity maxima occurring at plate velocity minima and vice versa. These oscillations are reflected also in dip-angle variations that may further influence, for example, the exhumation of high-pressure metamorphic rocks. The amplitude of the rollback velocity is sensitive to several model parameters. As one might expect, it increases with the age of the <span class="hlt">subducting</span> plate, thus reflecting its increasingly negative buoyancy. On the other hand, rollback velocity decreases if we increase the viscosity of the crust and strengthen the coupling between the <span class="hlt">subducting</span> and overriding plates. High friction on the contact between the <span class="hlt">subducting</span> and overriding plates may even result in slabs penetrating into the lower mantle after a period of temporary stagnation. Also, the reduction in extra negative buoyancy associated with the 410-km exothermic phase transition suppresses <span class="hlt">trench</span> rollback. The interpretation of the effects that control slab rollback and stagnation may be rather complex in strongly nonlinear rheological models, where, for example, the buoyancy effects may be counteracted by associated yield-stress weakening.</p> <div class="credits"> <p class="dwt_author">Cizkova, Hana; Bina, Craig</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">172</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.T22B..06I"> <span id="translatedtitle">Shallow very-low-frequency earthquakes around <span class="hlt">Japan</span>: Recent studies and observation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Very-low-frequency (VLF) earthquakes have been observed in three regions around <span class="hlt">Japan</span>. (1) Deep VLF earthquakes have occurred in the down-dip part of the Nankai <span class="hlt">subduction</span> zone [Ito et al., 2007]. (2) Shallow VLF earthquakes have occurred within the accretionary prism in the up-dip portion of the Nankai <span class="hlt">subduction</span> zone [Obara and Ito, 2005; Ito and Obara, 2006]. The stress drops of these shallow VLF events were very low, in the range 0.1--10kPa; this corresponds to 0.1--1% of the range for ordinary earthquakes [Ito and Obara, 2006]. Ito and Obara [2006] suggested that the largest shallow VLF earthquake (MW 4.0) occurred on a circular fault of radius ~5--10 km. They proposed that the shallow VLF events were related to numerous reverse fault systems located in areas of high fluid pressure within the accretionary prism. (3) Shallow VLF earthquakes have occurred in the region off Tokachi, northern <span class="hlt">Japan</span>, along the <span class="hlt">Japan</span> <span class="hlt">Trench</span> [Asano et al., 2008], where the Pacific Plate <span class="hlt">subducts</span> beneath the Japanese land area. The occurrence of these shallow VLF earthquakes suggests that VLF events can occur on the plate boundary at depths shallower than that of the main seismogenic zone [Asano et al., EPS, 2008]. The megasplay faults in the Nankai <span class="hlt">subduction</span> zone are observed to generate a reverse-polarity reflection on seismic reflection profiles [Park et al.,2002]; this may indicate the existence of an elevated fluid process in the fault zones [Shipley et al., 1994]. Hydrodynamics phenomena responsible for the seismic signals detected by ocean bottom seismometers were first reported by Brown et al. (2005) using osmotically-driven fluid flow meters (CAT meters); these meters were used to detect temporal changes in the rate of cold seepage of a shallow <span class="hlt">subduction</span> system in the regions of the Costa Rica <span class="hlt">subduction</span> zone. The Pacific plate is <span class="hlt">subducting</span> beneath Tohoku, northeastern <span class="hlt">Japan</span>, at the <span class="hlt">Japan</span> <span class="hlt">Trench</span>. An aseismic slip has been observed to occur as a post- seismic slip following the occurrence of large earthquakes. Tsunami earthquakes, a type of slow earthquakes, have also occurred in the vicinity of the <span class="hlt">Japan</span> <span class="hlt">Trench</span>; thus far, there have been no observations of non-volcanic tremors, VLF earthquakes, and short-term slow slips in NE <span class="hlt">Japan</span>, and the lack of observations can be attributed to the difficulty in detecting slow earthquakes near the <span class="hlt">trench</span>. Recently, we have deployed ocean bottom seismographs and have set up geodetic and hydraulic stations in northeastern <span class="hlt">Japan</span> to detect and observe shallow slow earthquakes and the corresponding transient hydrotectonic processes. The CAT meters were installed on cold seeps that were discovered by diving surveys of the manned submersible SHINKAI 6500. We found Calyptogena, which suggested the existence of a cold seep, during the diving survey. The seeps are distributed near a splay fault that was detected from a seismic reflection image [Tsuji et al., 2008], suggesting that the fluid in the cold seeps migrates from the splay fault to the seafloor. The Calyptogena colonies are distributed along the strike of the landward slope. We have also developed a simplified ocean-bottom benchmark (SOBB) that comprises three types of sensors; short-period seismometers, broadband seismometers, and pressure gauges.</p> <div class="credits"> <p class="dwt_author">Ito, Y.; Obara, K.; Asano, Y.; Fujimoto, H.; Hino, R.; Ashi, J.; Tsuji, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">173</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/59199622"> <span id="translatedtitle">Chapter 2.11: <span class="hlt">Subduction</span> zone processes and implications for changing composition of the upper and lower mantle</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">With ca. forty thousand kilometers of <span class="hlt">subduction</span> zones and convergence rates from 30 km Ma-1 to 180 km Ma-1, <span class="hlt">subduction</span> carries massive amounts of material into seafloor <span class="hlt">trenches</span>, and beyond. Most of the <span class="hlt">subducting</span> plate is made of mantle material returning to the depths from which it originated. The hydrated and altered upper oceanic section and the overlying sediments, however,</p> <div class="credits"> <p class="dwt_author">J D Morris; Jeffrey G Ryan</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">174</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.jcie.org/researchpdfs/Guidance/guide_yamamoto.pdf"> <span id="translatedtitle"><span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">There is in <span class="hlt">Japan</span> today a growing sense of crisis that something is fundamentally wrong with society. Some causes for the current intense public soul-searching are a decade-long recession, the inability of the government to deal with critical issues in the face of a rapidly graying society, and successive instances of corruption among government bureaucrats. Many Japanese feel that the</p> <div class="credits"> <p class="dwt_author">Yamamoto Tadashi</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">175</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUFM.T13F..01P"> <span id="translatedtitle">Constraints and Simple Models for Arc and <span class="hlt">Subduction</span> Geotherms</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">There are many constraints on geotherms beneath arcs [1]. Metamorphic PT estimates for arc lower crustal rocks yield Moho temperatures > 800 C at 1 GPa, consistent with estimated mantle equilibration for some primary arc magmas at 1300 C and 1.5 GPa, and with regionally high heat flow in the Oregon and NE <span class="hlt">Japan</span> arcs. However, none of these data indicate whether high T is steady state, or the result of transient heating due to ascending magma. Slow P- and S-wave velocities immediately beneath arc Moho suggest partial melt is common in the shallow mantle. Topography and gravity constraints for arcs indicate that the uppermost 100 km of the mantle wedge beneath arcs is >10x weaker than the surrounding mantle at the same depth. The geophysical observations suggest that high T(P) is regionally extensive, and so probably continues for long periods. Many recent thermal models for <span class="hlt">subduction</span> zones emphasize the important effect of temperature dependent viscosity, the possible consequences of stress dependent viscosity and 3D flow, and the importance of accurately tracking the <span class="hlt">subduction</span> interface [2]. However, most models incorporate a rigid upper layer. Omitting this rigid layer and modeling the entire upper plate with a temperature dependent viscosit, yields a variable thickness thermal boundary layer [1,3]. Where the thermal boundary layer is thinnest, the PT constraints in the previous paragraph are satisfied at steady state. The predicted distance of the highest heatflow from the <span class="hlt">trench</span> is uncertain, however, because the models do not fully treat the shallow geometry of the <span class="hlt">subducting</span> plate. There are fewer constraints on <span class="hlt">subduction</span> geotherms. Low heat flow in forearcs precludes substantial shear heating of the top of the <span class="hlt">subducting</span> plate while it is colder than about 500 C [4]. However, recent work on viscous heating in narrow, pre-existing shear zones suggests that instabilities arising at temperatures > 500 C can heat a region by a few hundred C over hundreds of meters around the shear zone [5]. This could be important along the <span class="hlt">subduction</span> zone, and within pre-existing shear zones in both footwall and hanging wall, beneath arcs where heat flow data do not constrain the amount of shear heating. High P, blueschist facies rocks, thought to record <span class="hlt">subduction</span> conditions, generally record T(P) higher than in most thermal models. Many ultra-high pressure (UHP) terranes, <span class="hlt">subducted</span> to > 2 GPa, record peak T at or above aqueous fluid saturated solidii for metabasalt and metasediment, hotter than in most thermal models. Some terranes record T(P) higher than fluid undersaturated solidii as well. Because exhumed high P and UHP rocks crossed the <span class="hlt">subduction</span> interface to transfer from footwall to hanging wall, they may have undergone nearly isobaric, conductive heating at peak P. Transfer from footwall to hanging wall limits the utility of high P and UHP samples for tracking Benioff zone conditions, but illustrates possibilities for partial melting and/or diapirism of <span class="hlt">subducted</span> metasediment and metabasalt [6]. 1. Kelemen et al AGU03 2. Van Keken et al G302, Conder et al GRL02, Conder PEPI 04, Kincaid and Griffiths G304 3. Rowland and Davies GRL99 4. Peacock AGU03 5. Kelemen and Hirth EOS04 6. Kelemen et al TOG03, Gerya and Yuen EPSL03, Gerya et al Geol04</p> <div class="credits"> <p class="dwt_author">Parmentier, E.; Kelemen, P.; Hacker, B.; Hirth, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">176</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.V31D2000D"> <span id="translatedtitle">Three-dimensional laboratory modeling of the Tonga <span class="hlt">trench</span> and Samoan plume interaction</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Plume processes occurring near ridge centers (e.g. Iceland) or mid-plate (e.g. Hawaii) have been well studied; however, the behavior of a plume near a <span class="hlt">subducting</span> plate is still poorly understood and may in fact differ from the typical expected plume surfacing patterns. We investigate how three-dimensional <span class="hlt">subduction</span>-driven flow relates to the deformation and dispersal of nearby upwelling plume material and the associated geochemical spatial patterns, with site-specific comparisons to the Tonga <span class="hlt">trench</span> and Samoan plume system. Eighteen plume-<span class="hlt">trench</span> laboratory experiments were conducted with varied combinations of <span class="hlt">subduction</span> motions (down-dip, <span class="hlt">trench</span> rollback, slab steepening and back-arc extension) and plume parameters (position and temperature.) A phenolic plate and glucose syrup, with a temperature dependent viscosity, are used to model the slab and upper mantle, respectively. Hydraulic pistons control longitudinal, translational and steepening motions of the slab as a simplified kinematic approach to mimic dynamic experiments. Results show that the <span class="hlt">subduction</span>-induced flow dominates the upwelling strength of the plume, causing a significant portion of the plume head to <span class="hlt">subduct</span> before reaching the melt zone. The remaining material is entrained around the slab edge into the mantle wedge by the <span class="hlt">trench</span> rollback-induced flow. The proportion of <span class="hlt">subducted</span> verses entrained material is predominantly dependent on plume location (relative to the <span class="hlt">trench</span>) and thermal strength, with additional effects from back-arc extension and plate steepening.</p> <div class="credits"> <p class="dwt_author">Druken, K. A.; Kincaid, C. R.; Pockalny, R. A.; Griffiths, R. W.; Hart, S. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">177</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009GGG....1012016P"> <span id="translatedtitle">Deep mantle <span class="hlt">subduction</span> flux</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We assess the flux of incompatible trace elements into the deep mantle in the Aleutian, Central America, Izu-Bonin, Kurile, Lesser Antilles, Mariana, Sunda, and Tonga <span class="hlt">subduction</span> zones. We use a simple mass balance approach in which we assume that all of the material lost from the <span class="hlt">subducting</span> crust and sediment (the "slab") is incorporated into the magmas erupted above the <span class="hlt">subduction</span> zone, and we use these assumptions to calculate a residual slab composition. The calculated residual slabs are enriched in incompatible elements compared to mid-ocean ridge basalts and highly enriched compared to primitive or depleted mantle. Almost all of the <span class="hlt">subducted</span> Nb, Ta, and intermediate and heavy rare earths survive into the deep mantle, as do most of the light rare earths. On average, 73% of Th and Pb, 74% of K, 79% of U, 80% of Rb, 80% of Sr, and 82% of Ba survive into the deep mantle. Pb/Ce ratios are systematically lower, and Nb/U ratios are systematically higher, in the deep mantle flux than they are in the flux of material into the <span class="hlt">trench</span>. Nevertheless, most residual slabs have Pb/Ce and Nb/U ratios outside the typical mantle range. Changes to U/Pb and Th/U ratios tend to be small and are not systematic. Rb/Sr ratios significantly decrease in some <span class="hlt">subduction</span> zones but increase in others. In contrast, Sm/Nd ratios increase by small but significant amounts in most arcs. Based on these results, we attempt to predict the Sr, Nd, and Pb composition of anciently recycled material now in the mantle. We find that such material would most resemble enriched mantle II-type oceanic island basalts (OIB). None of our calculated residual slabs would evolve to Sr-Nd-Pb isotopic compositions similar to either high 238U/204Pb or enriched mantle I. The range of Sr and Pb isotope ratios in anciently recycled material is similar to that seen in modern OIB, but Nd isotopic compositions do not range to ?Nd values as low as those in some modern OIB. Neither radiogenic nor unradiogenic Pb isotope compositions can be exclusively associated with recycled material.</p> <div class="credits"> <p class="dwt_author">Porter, Katherine A.; White, William M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">178</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002GeoRL..29.1372F"> <span id="translatedtitle">Morphology and origin of the Challenger Deep in the Southern Mariana <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A high resolution bathymetry survey reveals the detailed morphology of the Southern Mariana <span class="hlt">Trench</span>. Distinct right stepping, N80°E trending en echelon deeps were found on the <span class="hlt">trench</span> bottom within the Challenger Deep. Horst and graben structures were revealed on the outer swell of the Southern Mariana <span class="hlt">Trench</span>. These structures, as well as slope-failure on the inner and outer slopes of the <span class="hlt">trench</span> are similar to features observed in other deep sea <span class="hlt">trenches</span>. We propose here that the Southern Mariana <span class="hlt">Trench</span> is a transform fault based on swath mapping, morphological analysis and tectonic interpretation. The en echelon deeps formed in a right-lateral strike-slip stress regime related to oblique Pacific/Caroline Plate <span class="hlt">subduction</span> under the Southern Mariana <span class="hlt">Trench</span> combined with the Mariana Trough backarc spreading. We confirm that the world's deepest point lies in the western portion of the Challenger Deep, among the en echelon deeps.</p> <div class="credits"> <p class="dwt_author">Fujioka, Kantaro; Okino, Kyoko; Kanamatsu, Toshiya; Ohara, Yasuhiko</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">179</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51433647"> <span id="translatedtitle">Nonvolcanic tremors in the Mexican <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Nonvolcanic low frequency tremors (NVT) have been discovered and studied recently in <span class="hlt">Japan</span> and Cascadia <span class="hlt">subduction</span> zones and deep beneath the San Andreas Fault. The tremors activity is increasing during so-called silent earthquakes (SQ) in <span class="hlt">Japan</span> and Cascadia. NVT clusters also migrate following the propagation of the SQ. The origin of the NVT is still unclear. The studies of NVT</p> <div class="credits"> <p class="dwt_author">J. S. Payero; V. Kostoglodov; T. Mikumo; X. Perez-Campos; A. Iglesias; R. Clayton</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">180</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004Tecto..23.2011G"> <span id="translatedtitle">Bathymetry of Mariana <span class="hlt">trench</span>-arc system and formation of the Challenger Deep as a consequence of weak plate coupling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Challenger Deep in the southernmost Mariana <span class="hlt">Trench</span> (western Pacific Ocean) is the deepest point on the Earth's surface (10,920 m below sea level). Its location within a <span class="hlt">subduction</span> <span class="hlt">trench</span>, where one plate bends and descends below another, is not surprising. However, why is it located in the southernmost Mariana <span class="hlt">Trench</span> and not at its central part, where the rate of <span class="hlt">subduction</span> is higher, where the lithosphere is the oldest (and densest) on the Earth, and where the <span class="hlt">subducted</span> lithosphere pulling down is the longest in the Earth (˜1000 km or more according to seismic tomography)? We suggest that although <span class="hlt">subduction</span> rate and slab age generally control <span class="hlt">trench</span> depth, the width of the plate-coupling zone is more important. Beneath the central Marianas the <span class="hlt">subducted</span> slab is attached to the upper plate along a 150-km-wide surface that holds the shallow portion of the <span class="hlt">subducted</span> plate nearly horizontal, in spite of its great load and, thus, counters <span class="hlt">trench</span> deepening. In contrast, along the south Mariana <span class="hlt">Trench</span> the <span class="hlt">subducted</span> length of the lithosphere is much shorter, but its attachment to the upper plate is only along a relatively narrow, 50-km-wide, surface. In addition, a tear in the slab beneath this region helps it to sink rapidly through the mantle, and this combination of circumstances allows the slab to steepen and form the deepest <span class="hlt">trench</span> on the Earth. In a wider perspective, the interrelations shown here between <span class="hlt">trench</span> deepening, ridge shallowing, slab steepening, and forearc narrowing may shed light on other <span class="hlt">subduction</span> zones located near edges of rapidly steepening slabs.</p> <div class="credits"> <p class="dwt_author">Gvirtzman, Zohar; Stern, Robert J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-04-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_8");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" 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showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_11");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">181</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.3365S"> <span id="translatedtitle">The Banda Arc <span class="hlt">subduction</span> enigma</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The spectacularly curved Banda arc comprises young oceanic crust enclosed by a volcanic inner arc, outer arc islands, and a trough parallel to the Australian continental margin. Seismicity defines a spoon-shaped lithospheric fold in the upper mantle for which there are two contrasting explanations: deformation of a single <span class="hlt">subducted</span> slab, or two different slabs <span class="hlt">subducted</span> from north and south. We show that the Banda arc resulted from <span class="hlt">subduction</span> of a single slab. Based on geology and seismic tomography, we argue that the arc formed since 15 Ma by <span class="hlt">subduction</span> of a Jurassic oceanic embayment within the Australian plate. Viewed in an Atlantic-Indian hotspot reference frame, the stationary E-W striking Java <span class="hlt">trench</span> propagated ESE into the Banda embayment by hinge rollback. Extension of the upper plate formed oceanic crust in the present Banda Sea between stretched continental crust of Australian origin. Slab morphology depends primarily on the geometry of the continental margin enclosing the embayment. Our model explains the first order tectonic development of the Banda region and links slab deformation to absolute plate motion.</p> <div class="credits"> <p class="dwt_author">Spakman, Wim; Hall, Robert</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">182</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011GeoJI.184...43B"> <span id="translatedtitle"><span class="hlt">Subduction</span> and exhumation of continental crust: insights from laboratory models</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">When slivers of continental crust and sediment overlying oceanic lithosphere enter a <span class="hlt">subduction</span> zone, they may be scraped off at shallow levels, <span class="hlt">subducted</span> to depths of up to 100-200 km and then exhumed as high pressure (HP) and ultra-high pressure (UHP) rocks, or <span class="hlt">subducted</span> and recycled in the mantle. To investigate the factors that influence the behaviour of <span class="hlt">subducting</span> slivers of continental material, we use 3-D dynamically consistent laboratory models. A laboratory analogue of a slab-upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. A sliver of continental material, also composed of silicone putty, overlies the <span class="hlt">subducting</span> lithosphere, separated by a syrup detachment. The density of the sliver, viscosity of the detachment, geometry of the <span class="hlt">subducting</span> system (attached plate versus free ridge) and dimensions of the sliver are varied in 34 experiments. By varying the density of the sliver and viscosity of the detachment, we can reproduce a range of sliver behaviour, including <span class="hlt">subduction</span>, <span class="hlt">subduction</span> and exhumation from various depths and offscraping. Sliver <span class="hlt">subduction</span> and exhumation requires sufficient sliver buoyancy and a detachment that is strong enough to hold the sliver during initial <span class="hlt">subduction</span>, but weak enough to allow adequate sliver displacement or detachment for exhumation. Changes to the system geometry alter the slab dip, <span class="hlt">subduction</span> velocity, pattern of mantle flow and amount of rollback. Shallower slab dips with more <span class="hlt">trench</span> rollback produce a mantle flow pattern that aids exhumation. Steeper slab dips allow more buoyancy force to be directed in the up-dip direction of the plane of the plate, and aide exhumation of <span class="hlt">subducted</span> slivers. Slower <span class="hlt">subduction</span> can also aide exhumation, but if slab dip is too steep or <span class="hlt">subduction</span> too slow, the sliver will <span class="hlt">subduct</span> to only shallow levels and not exhume. Smaller slivers are most easily <span class="hlt">subducted</span> and exhumed and influenced by the mantle flow.</p> <div class="credits"> <p class="dwt_author">Bialas, Robert W.; Funiciello, Francesca; Faccenna, Claudio</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">183</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.exploratorium.edu/faultline/activezone/cookie.html"> <span id="translatedtitle">Cookie <span class="hlt">Subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This is a quick activity that shows how large amounts of rock and sediment are added to the edge of continents during <span class="hlt">subduction</span>. You may ask, how can such a huge phenomenon be demonstrated quickly and cheaply? The answer is simple: with a cookie!</p> <div class="credits"> <p class="dwt_author">Exploratorium</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-26</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">184</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.eas.slu.edu/Center_Env_Sci/environmental_sciences/people/TimKusky/Publications/bradley_ridge_sub_803.pdf"> <span id="translatedtitle">Geologic signature of early Tertiary ridge <span class="hlt">subduction</span> in Alaska</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A mid-Paleocene to early Eocene encounter between an oceanic spreading center and a <span class="hlt">subduction</span> zone produced a wide range of geologic features in Alaska. The most striking effects are seen in the accretionary prism (Chugach-Prince William ter- rane), where 61 to 50 Ma near-<span class="hlt">trench</span> granitic to gabbroic plutons were intruded into accreted <span class="hlt">trench</span> sediments that had been deposited only a</p> <div class="credits"> <p class="dwt_author">Dwight Bradley; Tim Kusky; Peter Haeussler; Rich Goldfarb; Marti Miller; Julie Dumoulin; Steven W. Nelson; Sue Karl</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">185</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..1211343T"> <span id="translatedtitle">Geodynamic modelling of terrane accretion, <span class="hlt">subduction</span>, and collision</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Accretion, <span class="hlt">subduction</span>, or collision of terranes can significantly affect <span class="hlt">subduction</span> zone evolution and lead to reversed <span class="hlt">subduction</span> polarity, <span class="hlt">trench</span> jumping, or breaking off the slab. Terranes such as oceanic plateaus, volcanic arcs, and continental fragments have relatively thick crusts, and their size and buoyancy can therefore can be expected to influence <span class="hlt">subduction</span> dynamics. Geological observations point out that accretion of terranes can lead to continental growth or accretionary orogenesis as evident by the collage of allochthonous terranes composing the western North American margin. Alternatively, <span class="hlt">subduction</span> of terranes, as in the Andean <span class="hlt">subduction</span> zone, has been posited to lead to flat slab <span class="hlt">subduction</span>. We examine basic models of <span class="hlt">subduction</span> zones to define the controlling parameters in accretion, <span class="hlt">subduction</span>, or collision of such terranes with the thermo-mechanical numerical code SULEC. SULEC is a 2-D, Arbitrary Lagrangian-Eulerian, finite element code that incorporates a free surface and a visco-elasto-plastic rheology. Our models test the buoyancy of three end-member terranes; oceanic plateaus, volcanic arcs, and continental fragments by varying terrane length, terrane crustal thickness, and terrane rheology. We seek to evaluate whether terrane buoyancy is enough to induce <span class="hlt">subduction</span> zone rearrangement or if another variable, such as terrane crustal detachment or a thick <span class="hlt">subduction</span> accretionary channel, are necessary.</p> <div class="credits"> <p class="dwt_author">Tetreault, Joya; Buiter, Susanne</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">186</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6988691"> <span id="translatedtitle"><span class="hlt">Subduction</span> zone tectonic studies to develop concepts for the occurrence of sediment <span class="hlt">subduction</span> (Phase 2): Volume 3</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The objectives of this study represent a continuation and refinement of the objectives addressed in Phase 1. This study focuses on trying to define the tectonics of sediment <span class="hlt">subduction</span> at the <span class="hlt">trench</span> axis through the use of accepted plate tectonic principles and the application of new <span class="hlt">subduction</span> theory. The fundamental methods include: (1) compilation of all available bathymetric data from our Global Marine Geophysical Data Collection for all major ocean <span class="hlt">trenches</span>, (2) generation of stacked bathymetric profiles and corresponding navigational maps, and structural maps, (3) selection and analysis of appropriate seismic reflection and refraction profiles and additional supporting data such as side-scan sonar, SEABEAM, magnetic, gravity and drilling data, and (4) detailed study of selected <span class="hlt">trench</span> regions in which data quality and/or quantity is exceptional. Phase 2 of this project represents a unique compilation and synthesis of existing data for the world's deep ocean <span class="hlt">trenches</span>. The analysis of data and discussion of results in the context of current literature aids our understanding of the sediment distribution and nature of sediment deformation through various stages of plate convergence, the determination of whether sediments are <span class="hlt">subducted</span> or accreted, and the evaluation of the controlling factors for sediment <span class="hlt">subduction</span> and/or accretion. A major emphasis in our analysis of the data was to try and map the seaward-of-the-<span class="hlt">trench</span> distribution of faults and associated surface roughness. Illustrations and an extensive bibliography are included in the report.</p> <div class="credits"> <p class="dwt_author">Payne, J.; Bandy, B.; Altis, S.; Lee, M.C.; Dwan, S.F.; Ku, K.; Hilde, T.W.C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">187</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6914217"> <span id="translatedtitle">Anomalous heat flow from a Miocene ridge crest-<span class="hlt">trench</span> collision, Antarctic Peninsula</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">In January 1985 a marine heat-flow survey was carried out aboard the British Antarctic Survey research ship RRS Discovery southwest of the Anvers fracture zone where a ridge crest-<span class="hlt">trench</span> collision occurred approximately 15 million years ago. Anomalously high heat flow has been discovered coming from the oceanic crust and continental margin to the west of the Antarctic Peninsula. The purpose of this study was to examine the thermal state of one section of the Antarctic Peninsula where young oceanic lithosphere has been <span class="hlt">subducted</span>. At the time of arrival of the ridge crest to the <span class="hlt">trench</span>, <span class="hlt">subduction</span> and spreading of the ridge both stopped. A heat-flow anomaly should still be present around the <span class="hlt">subduction</span> zone since newly formed crust was in the <span class="hlt">trench</span> at the time of collision. Heat-flow patterns around <span class="hlt">trench</span> arc systems <span class="hlt">subducting</span> old ocean crust in the West Pacific show a distinctive low heat-flow zone centered around the <span class="hlt">trench</span> axis. Locations of the heat-flow stations were chosen to determine best the thermal state of the surviving flank of the spreading center as well as that of the collision and <span class="hlt">subduction</span> complex. A table gives a summary of the locations and heat-flow data for each successful measurement. Corrections to the raw gradients include adjustments for sedimentation and seasonal variations in bottom-water temperature.</p> <div class="credits"> <p class="dwt_author">Dougherty, M.E.; Von Herzen, R.P.; Barker, P.F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">188</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013E%26PSL.367...82S"> <span id="translatedtitle"><span class="hlt">Subduction</span> of oceanic asthenosphere: A critical appraisal in central Alaska</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Song and Kawakatsu (2012) have shown that the sub-slab fast splitting pattern observed in most <span class="hlt">subduction</span> zones can be a direct consequence of <span class="hlt">subduction</span> of the oceanic asthenosphere that has strong radial anisotropy. This model not only explains the non-intuitive <span class="hlt">trench</span>-parallel splitting pattern in most of <span class="hlt">subduction</span> zones, but also predicts the <span class="hlt">trench</span>-normal behavior (fast polarization direction sub-parallel to the absolute plate motion of the incoming plate) observed in several shallow <span class="hlt">subduction</span> zones. The general validity of such a scenario is crucial to fundamental understandings of the development of mantle anisotropy in sub-lithosphere or/and sub-slab conditions, the nature and formation of oceanic asthenosphere as well as the flow pattern and mass transport near <span class="hlt">subduction</span> zones. To validate this scenario, we examine SKS splitting patterns observed across the fore-arc in central Alaska. Here the fast splitting direction varies from plate motion sub-parallel near the <span class="hlt">trench</span> to mostly <span class="hlt">trench</span>-parallel beyond the 100 km slab-isodepth contour, while being strongly variable in between. After taking into account the rotation of anisotropy symmetry in the oceanic asthenosphere with respect to the local plate motion obliquity and down-dip variations in the slab dip, we reproduce a general 90-degree switch in fast splitting direction as well as the back azimuth dependent splitting pattern across the entire fore-arc. The current validation further augments the idea that, apart from anisotropy in the mantle wedge and the <span class="hlt">subducting</span> slab, <span class="hlt">subduction</span> of the oceanic asthenosphere is likely to be the dominant source of seismic anisotropy in central Alaska and potentially in many <span class="hlt">subduction</span> zones. Furthermore, this result also provides alternative views to models of seismic anisotropy in the mantle wedge and on the length scale in which the 3D mantle flow may be important.</p> <div class="credits"> <p class="dwt_author">Song, Teh-Ru Alex; Kawakatsu, Hitoshi</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">189</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55499859"> <span id="translatedtitle"><span class="hlt">Subduction</span> hinge migration: The backwards component of plate tectonics</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">There are approximately 50 distinct segments of <span class="hlt">subduction</span> zones in the world, of which 40% have oceanic lithosphere <span class="hlt">subducting</span> under oceanic lithosphere. All of these ocean-ocean systems are currently experiencing hinge-rollback, with the exception of 2 (Mariana and Kermadec). In hinge-rollback, the surface trace of the suduction zone (<span class="hlt">trench</span>) is moving in the opposite direction as the plate is moving</p> <div class="credits"> <p class="dwt_author">D. Stegman; J. Freeman; W. Schellart; L. Moresi; D. May</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">190</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40449105"> <span id="translatedtitle">A new insight on the geometry of <span class="hlt">subducting</span> slabs in northern Luzon, Philippines</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We used hypocentral and focal mechanism data in order to characterize the tectonic configuration of northern Luzon and propose a model for describing the geometry of the <span class="hlt">subducted</span> slab of the Eurasian plate beneath the northern segment of the Manila <span class="hlt">Trench</span>. We took into consideration some of the observed bathymetric features (i.e. the bend in the <span class="hlt">trench</span> line of the</p> <div class="credits"> <p class="dwt_author">Bartolome C. Bautista; Maria Leonila P. Bautista; Kazuo Oike; Francis T. Wu; Raymundo S. Punongbayan</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">191</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52826607"> <span id="translatedtitle">Interplate coupling and slip distribution of the megathrust earthquakes along the southernmost part of the Kuril <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A magathrust earthquake in the <span class="hlt">subduction</span> zone is one of the destructive geohazards along the plate boundary zones. The Kuril <span class="hlt">trench</span> is known as one of the most active region of the repeated megathrust earthquakes where the Pacific plate is <span class="hlt">subducting</span> beneath Hokkaido and Kuril Islands with 8 cm\\/yr. Modern geodetic measurements started in Hokkaido along the southernmost part of</p> <div class="credits"> <p class="dwt_author">T. Nishimura</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">192</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/47655433"> <span id="translatedtitle">Crustal assimilation versus <span class="hlt">subducted</span> sediment input in west Sunda arc volcanics: An evaluation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Summary New geochemical and Sr, Nd, and Pb isotopic analyses of Quaternary to Cretaceous sediments from the northeastern Indian Ocean are used to estimate the composition of the sedimentary material <span class="hlt">subducted</span> along the Sunda <span class="hlt">Trench</span>, and to evaluate the effects of crustal contamination versus <span class="hlt">subducted</span> sediment input in the Quaternary volcanics of the west Sunda arc. Two sediment endmember components</p> <div class="credits"> <p class="dwt_author">M. Gasparon; R. Varne</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">193</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48956770"> <span id="translatedtitle">Nonvolcanic tremor along the Oaxaca segment of the Middle America <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Oaxaca <span class="hlt">subduction</span> zone is an ideal area for detailed studies of plate boundary deformation as rapid convergent rates, shallow <span class="hlt">subduction</span>, and short <span class="hlt">trench</span>-to-coast distances bring the thermally defined seismogenic and transition zones of the plate interface over 100 km inland. Previous analysis of slow slip events in southern Mexico suggests that they may represent motion in the transition zone,</p> <div class="credits"> <p class="dwt_author">Michael R. Brudzinski; Héctor R. Hinojosa-Prieto; Kristen M. Schlanser; Enrique Cabral-Cano; Alejandra Arciniega-Ceballos; Oscar Diaz-Molina; Charles DeMets</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">194</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/4010501"> <span id="translatedtitle">Tracing trace elements from sediment input to volcanic output at <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">AT ocean <span class="hlt">trenches</span>, sea-floor sediments may either be scraped off the <span class="hlt">subducting</span> plate, or accompany it into the mantle. Some of the <span class="hlt">subducted</span> sediment may then be recycled to the arc crust by magmatism1; the rest may be recycled into the mantle, and contribute to mantle heterogeneity2. Strong evidence for sediment contributions to arc volcanism has come from isotope tracers,</p> <div class="credits"> <p class="dwt_author">Terry Plank; Charles H. Langmuir</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">195</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51779579"> <span id="translatedtitle"><span class="hlt">Subduction</span> of an Aseismic Ridge: Interseismic Deformation Above the Cocos Ridge, Costa Rica</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Subduction</span> of aseismic ridges, seamounts and thickened, buoyant oceanic crust often results in deformation of the overriding plate. The Cocos Ridge and sub parallel seamount chains have been <span class="hlt">subducting</span> along the Middle America <span class="hlt">Trench</span> (MAT) for >0.5 Ma, resulting in cessation of volcanism, uplift of the Talamanca Range, deformation of the outer fore arc and shortening in the fore arc</p> <div class="credits"> <p class="dwt_author">P. C. Lafemina; T. H. Dixon; S. Scwartz; M. Protti; V. Gonzalez</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">196</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JGRB..118..775M"> <span id="translatedtitle">Three-dimensional dynamic models of <span class="hlt">subducting</span> plate-overriding plate-upper mantle interaction</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present fully dynamic generic three-dimensional laboratory models of progressive <span class="hlt">subduction</span> with an overriding plate and a weak <span class="hlt">subduction</span> zone interface. Overriding plate thickness (TOP) is varied systematically (in the range 0-2.5 cm scaling to 0-125 km) to investigate its effect on <span class="hlt">subduction</span> kinematics and overriding plate deformation. The general pattern of <span class="hlt">subduction</span> is the same for all models with slab draping on the 670 km discontinuity, comparable slab dip angles, <span class="hlt">trench</span> retreat, trenchward <span class="hlt">subducting</span> plate motion, and a concave <span class="hlt">trench</span> curvature. The narrow slab models only show overriding plate extension. <span class="hlt">Subduction</span> partitioning (vSP? / (vSP? + vT?)) increases with increasing TOP, where trenchward <span class="hlt">subducting</span> plate motion (vSP?) increases at the expense of <span class="hlt">trench</span> retreat (vT?). This results from an increase in <span class="hlt">trench</span> suction force with increasing TOP, which retards <span class="hlt">trench</span> retreat. An increase in TOP also corresponds to a decrease in overriding plate extension and curvature because a thicker overriding plate provides more resistance to deform. Overriding plate extension is maximum at a scaled distance of ~200-400 km from the <span class="hlt">trench</span>, not at the <span class="hlt">trench</span>, suggesting that basal shear tractions resulting from mantle flow below the overriding plate primarily drive extension rather than deviatoric tensional normal stresses at the <span class="hlt">subduction</span> zone interface. The force that drives overriding plate extension is 5%-11% of the slab negative buoyancy force. The models show a positive correlation between vT? and overriding plate extension rate, in agreement with observations. The results suggest that slab rollback and associated toroidal mantle flow drive overriding plate extension and backarc basin formation.</p> <div class="credits"> <p class="dwt_author">Meyer, C.; Schellart, W. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">197</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55848408"> <span id="translatedtitle">Retention of Metasedimentary Carbon during <span class="hlt">Subduction</span> through Forearcs: Evidence from HP\\/UHP Rocks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Knowledge of the degrees of retention or loss of C during <span class="hlt">trench</span>-to-subarc metamorphism of <span class="hlt">subducting</span> sediments (and altered oceanic crust) is critical in any model of deep-Earth C cycling. Existing theoretical analyses of <span class="hlt">subduction</span>-zone decarbonation indicate little decarbonation of more pure metacarbonates to great depths in relatively cool margins unless <span class="hlt">subducting</span> sediments are fluxed by H2O-rich fluids introduced from an</p> <div class="credits"> <p class="dwt_author">G. E. Bebout; L. D. Anderson; P. Agard; C. Bastoni; G. Sills; A. M. McCall</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">198</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://seismo.berkeley.edu/~rallen/teaching/S04_SanAndreas/Resources/Thorkelson1996.pdf"> <span id="translatedtitle"><span class="hlt">Subduction</span> of diverging plates and the principles of slab window formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Consumption of an ocean basin by <span class="hlt">subduction</span> commonly brings a sea-floor-spreading ridge toward a deep-sea <span class="hlt">trench</span>. If plate divergence and convergence continue after the ridge intersects the <span class="hlt">subduction</span> zone, a slab window forms between the <span class="hlt">subducted</span> parts of the diverging oceanic plates, producing anomalous thermal, physical and chemical effects in the surrounding asthenospheric mantle. In turn, these conditions alter the</p> <div class="credits"> <p class="dwt_author">Derek J. Thorkelson</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">199</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUFM.T11A0346S"> <span id="translatedtitle">Variable Rupture Mode at <span class="hlt">Subduction</span> Zones Around the Pacific</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The enormity of the 2004 Sumatra-Andaman earthquake, in comparison with 19th- and 20th-century earthquakes in its rupture area, serves as a reminder that a <span class="hlt">subduction</span> zone may produce earthquakes larger than those in recorded in the past. Historical record and paleoseismological data show that variability in rupture mode is characteristic of some <span class="hlt">subduction</span> zones. Infrequent, gigantic earthquakes predominate in geologic records, while historic data tell of more frequent, smaller earthquakes. This implies that along the Cascadia <span class="hlt">subduction</span> zone, great (M > 8) earthquake can occur more frequently than estimated from paleoseismological record. Like the 2004 Sumatra-Andaman earthquake, the giant 1960 Chilean earthquake (Mw 9.5) was unusually large. Historical predecessors of the 1960 earthquake occurred in 1837, 1737, and 1575. However, midway along the 1960 rupture, only the 1575 event produced geologic records of subsidence and tsunami as obvious as those of 1960. The 1837 and 1737 ruptures were probably small, at least at this latitude (Cisternas et al., 2005). Along the Nankai trough of southwest <span class="hlt">Japan</span>, recurrence of semi-regular earthquakes has been documented in the 1300 years' written history, with an indication of some variability. The easternmost Suruga trough was ruptured in 1854 but not in 1944, leaving a seismic gap for the anticipated Tokai earthquake. The 1707 earthquake ruptured both Nankai and Tokai sources that ruptured separately in 1854 and in 1944 and 1946. The 1605 earthquake seems to be an unusual tsunami earthquake. Near Tokyo, along the Sagami trough, historical records and marine terraces show two types of large earthquakes (1923 type and 1703 type; Shishikura, 2003); their average recurrence intervals are estimated geologically as several hundred years and a few thousand years, respectively. Earthquakes larger than Mw 8.2 can happen along the southern Kuril <span class="hlt">trench</span> even though they are unknown from the 200-year written history of Hokkaido. Plate-boundary earthquakes close to M 8, at intervals of 100 years or less, had been considered characteristic in this <span class="hlt">subduction</span> zone. The 2003 Tokachi-oki earthquake (M 8.0), for instance, was preceded by similar earthquakes, from slightly different source areas, in 1952 and 1843. However, tsunami deposits show that unusually large tsunamis repeated at intervals averaging about 500 yr, with the most recent event in the 17th century (Hirakawa et al., 2000; Nanayama et al., 2003). The inferred inundation area is much wider than those typical earthquakes, and is best explained by earthquakes that broke more than one of the historical segments. Only these multi-segment earthquakes triggered deep postseismic creep that produced decimeters of coastal uplift (Sawai et al., 2004).</p> <div class="credits"> <p class="dwt_author">Satake, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">200</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013GeoRL..40.2642W"> <span id="translatedtitle">The role of hydrous phases in the formation of <span class="hlt">trench</span> parallel anisotropy: Evidence from Rayleigh waves in Cascadia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">cause of seismic anisotropy exhibiting <span class="hlt">trench</span> parallel fast directions in <span class="hlt">subduction</span> systems has been the subject of significant recent research. We provide new constraints on the contributions of hydrous phases to seismic anisotropy from an unusually well-localized region of <span class="hlt">trench</span> parallel fast directions in Rayleigh wave phase velocities near the Cascade arc at 45 to 66 s periods. We constrain the location of the anisotropic material to within or directly above the oceanic plate, using the depth sensitivity of Rayleigh waves as a function of frequency and the accurate slab imaging available for Cascadia from scattered wave studies. We infer that the likely source of <span class="hlt">trench</span>-parallel anisotropy is either a thin layer of sheared hydrous material directly above the slab or hydrated outer rise faults in the upper part of the <span class="hlt">subducting</span> plate. Similar contributions to <span class="hlt">trench</span> parallel anisotropy from hydrous phases are likely stronger in other <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Wagner, Lara S.; Fouch, Matthew J.; James, David E.; Long, Maureen D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_9");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" 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showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_12");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">201</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/7154626"> <span id="translatedtitle"><span class="hlt">Subduction</span> zone tectonic studies to develop concepts for the occurrence of sediment <span class="hlt">subduction</span> (Phase 2): Volume 2</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The objectives of this study represent a continuation and refinement of the objectives addressed in Phase 1. This study focuses on trying to define the tectonics of sediment <span class="hlt">subduction</span> at the <span class="hlt">trench</span> axis through the use of accepted plate tectonic principles and the application of new <span class="hlt">subduction</span> theory. The fundamental methods include: (1) compilation of all available bathymetric data from our Global Marine Geophysical Data Collection for all major ocean <span class="hlt">trenches</span>, (2) generation of stacked bathymetric profiles and corresponding navigational maps, and structural maps, (3) selection and analysis of appropriate seismic reflection and refraction profiles and additional supporting data such as side-scan sonar, SEABEAM, magnetic, gravity and drilling data, and (4) detailed study study of selected <span class="hlt">trench</span> regions in which data quality and/or quantity is exceptional. Phase 2 of this project represents a unique compilation and synthesis of existing data for the world's deep ocean <span class="hlt">trenches</span>. The analysis of data and discussion of results in the context of current literature aids our understanding of the sediment distribution and nature of sediment deformation through various stages of plate convergence, the determination of whether sediments are <span class="hlt">subducted</span> or accreted, and the evaluation of the controlling factors for sediment <span class="hlt">subduction</span> and/or accretion. A discussion on petroleum and natural gas hydrate resource potential is included.</p> <div class="credits"> <p class="dwt_author">Payne, J.; Bandy, B.; Altis, S.; Lee, M.C.; Dwan, S.F.; Ku, K.; Hilde, T.W.C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">202</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6988696"> <span id="translatedtitle"><span class="hlt">Subduction</span> zone tectonic studies to develop concepts for the occurrence of sediment <span class="hlt">subduction</span> (Phase 2): Volume 1</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This is volume one of three volumes. The objectives of this study represent a continuation and refinement of the objectives addressed in Phase I. This study focuses on trying to define the tectonics of sediment <span class="hlt">subduction</span> at the <span class="hlt">trench</span> axis through the use of accepted plate tectonic principles and the application of new <span class="hlt">subduction</span> theory. The fundamental methods include: (1) compilation of all available bathymetric data from our Global Marine Geophysical Data Collection for all major ocean <span class="hlt">trenches</span>, (2) generation of stacked bathymetric profiles and corresponding navigational maps, and structural maps, (3) selection and analysis of appropriate seismic reflection and refraction profiles and additional supporting data such as side-scan sonar, SEABEAM, magnetic, gravity and drilling data, and (4) detailed study of selected <span class="hlt">trench</span> regions in which data quality and/or quantity is exceptional. Phase II of this project represents a unique compilation and synthesis of existing data for the world's deep ocean <span class="hlt">trenches</span>. The analysis of data and discussion of results in the context of current literature aids our understanding of the sediment distribution and nature of sediment deformation through various stages of plate convergence, the determination of whether sediments are <span class="hlt">subducted</span> or accreted, and the evaluation of the controlling factors for sediment <span class="hlt">subduction</span> and/or accretion. A discussion is included on forearc petroleum and natural gas hydrate resource potential. 128 figs.</p> <div class="credits"> <p class="dwt_author">Payne, J.; Bandy, B.; Altis, S.; Lee, M.C.; Dwan, S.F.; Ku, K.; Hilde, T.W.C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">203</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013Tectp.600..165Y"> <span id="translatedtitle">Interplate coupling along the Nankai Trough, southwest <span class="hlt">Japan</span>, inferred from inversion analyses of GPS data: Effects of <span class="hlt">subducting</span> plate geometry and spacing of hypothetical ocean-bottom GPS stations</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We estimated the slip-deficit rate distribution on the plate boundary between the <span class="hlt">subducting</span> Philippine Sea plate and the continental Amurian plate along the Nankai Trough, southwest <span class="hlt">Japan</span>. Horizontal and vertical displacement rates were calculated from land-based Global Positioning System (GPS) data during the 5-year period from 1 January 2005 to 31 December 2009. We employed an inversion analysis of geodetic data using Akaike's Bayesian information criterion (ABIC), including an indirect prior constraint that slip distribution is smooth to some extent and a direct prior constraint that slip is mainly oriented in the plate-convergent direction. The results show that a large slip deficit exists at depths ranging from 15 to 20 km on the plate boundary in a belt-like form. The maximum slip-deficit rate was identified off Shikoku and reached 6 cm/year. The slip-deficit rate differed by as much as 1 cm/year when using a different geometric model of the <span class="hlt">subducting</span> plate. On the basis of the spatial distribution of estimation errors and the resolution of the obtained slip-deficit rate on the plate boundary, we also found that the offshore slip-deficit rate cannot be estimated with sufficient accuracy using only land-based GPS data. Therefore, we tested the improvement in results when introducing hypothetical ocean-bottom GPS stations. The stations were arranged in four along-arc and across-arc spacings of 80 km and 40 km. The ocean-bottom data improved the estimation errors and resolutions, and successful results were obtained for a checkerboard with each square 75 km × 76 km. Our results indicate that 40-km along-arc and across-arc two-dimensional spacing of ocean-bottom GPS stations is required to obtain reliable slip-deficit distributions near the trough axis, assuming the current estimation accuracy for ocean-bottom horizontal displacement rates.</p> <div class="credits"> <p class="dwt_author">Yoshioka, Shoichi; Matsuoka, Yoshiko</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">204</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.soest.hawaii.edu/GG/FACULTY/conrad/classes/GG672/topic4/Lamb_Megathrust_JGR2006.pdf"> <span id="translatedtitle">Shear stresses on megathrusts: Implications for mountain building behind <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Shear stresses tau on a <span class="hlt">subduction</span> megathrust play an important role in determining the forces available for mountain building adjacent to a <span class="hlt">subduction</span> zone. In this study, the temperatures and shear stresses on megathrusts in 11 <span class="hlt">subduction</span> zones around the Pacific rim (Hikurangi, Tonga, Izu-Ogasawara, western Nankai, northeastern <span class="hlt">Japan</span>, Aleutians, western Alaska, Cascadia, northern Chile, southern Chile) and SE Asia</p> <div class="credits"> <p class="dwt_author">Simon Lamb</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">205</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/jb0607/2005JB003916/2005JB003916.pdf"> <span id="translatedtitle">Shear stresses on megathrusts: Implications for mountain building behind <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Shear stresses ? on a <span class="hlt">subduction</span> megathrust play an important role in determining the forces available for mountain building adjacent to a <span class="hlt">subduction</span> zone. In this study, the temperatures and shear stresses on megathrusts in 11 <span class="hlt">subduction</span> zones around the Pacific rim (Hikurangi, Tonga, Izu-Ogasawara, western Nankai, northeastern <span class="hlt">Japan</span>, Aleutians, western Alaska, Cascadia, northern Chile, southern Chile) and SE Asia</p> <div class="credits"> <p class="dwt_author">Simon Lamb</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">206</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GeoJI.190..629T"> <span id="translatedtitle">Seismic anisotropy and heterogeneity in the Alaska <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We determined P- and S-wave tomography and P-wave anisotropic structure of the Alaska <span class="hlt">subduction</span> zone using 259 283 P- and 73 817 S-wave arrival times from 7268 local shallow and intermediate-depth earthquakes recorded by more than 400 seismic stations. The results show strong velocity heterogeneities in the crust and upper mantle. Low-velocity anomalies are revealed in the mantle wedge with significant along-arc variations under the active volcanoes. In the mantle wedge, the low-velocity zone extends down to 100-150 km depth under the backarc. The results indicate that H2O and fluids brought downwards by the <span class="hlt">subducting</span> Pacific slab are released to the mantle wedge by dehydration and they are subsequently transported to the surface by the upwelling flow in the mantle wedge. Significant P-wave anisotropic anomalies are revealed under Alaska. The predominant fast velocity direction (FVD) is <span class="hlt">trench</span>-parallel in the shallow part of the mantle wedge (<90 km depth) and in the subslab mantle, whereas the FVD is <span class="hlt">trench</span>-normal within the <span class="hlt">subducting</span> Pacific slab. The <span class="hlt">trench</span>-parallel FVDs in the mantle wedge and subslab mantle may be caused by 3-D mantle flow that is induced by the complex geometry and strong curvature of the Pacific slab under Alaska. The flat and oblique <span class="hlt">subduction</span> of the Pacific slab may play a key role in forming the <span class="hlt">trench</span>-parallel FVD under the slab. The <span class="hlt">trench</span>-normal FVD in the <span class="hlt">subducting</span> Pacific slab may reflect the original fossil anisotropy when the Pacific Plate was produced at the mid-ocean ridge.</p> <div class="credits"> <p class="dwt_author">Tian, You; Zhao, Dapeng</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">207</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.5245R"> <span id="translatedtitle">Geophysical signature of hydration-dehydration processes in active <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Seismological and magneto-telluric tomographies are potential tools for imaging fluid circulation when combined with petrophysical models. Recent measurements of the physical properties of serpentine allow refining hydration of the mantle and fluid circulation in the mantle wedge from geophysical data. In the slab lithospheric mantle, serpentinization caused by bending at the <span class="hlt">trench</span> is limited to a few kilometers below the oceanic crust (<5 km). Double Wadati-Benioff zones, 20-30 km below the crust, are explained by deformation of dry peridotites, not by serpentine dehydration. It reduces the required amount of water stored in solid phases in the slab (Reynard et al., 2010). In the cold (<700°C) fore-arc mantle wedge above the <span class="hlt">subducting</span> slab, serpentinization is caused by the release of large amounts of hydrous fluids in the cold mantle above the dehydrating <span class="hlt">subducted</span> plate. Low seismic velocities in the wedge give a time-integrated estimate of hydration and serpentinization. Serpentinization reaches 50-100% in hot <span class="hlt">subduction</span>, while it is below 10% in cold <span class="hlt">subduction</span> (Bezacier et al., 2010; Reynard, 2012). Electromagnetic profiles of the mantle wedge reveal high electrical-conductivity bodies. In hot areas of the mantle wedge (> 700°C), water released by dehydration of the slab induces melting of the mantle under volcanic arcs, explaining the observed high conductivities. In the cold melt-free wedge (< 700°C), high conductivities in electromagnetic profiles provide "instantaneous" images of fluid circulation because the measured electrical conductivity of serpentine is below 0.1 mS/m (Reynard et al., 2011). A small fraction (ca. 1% in volume) of connective high-salinity fluids accounts for the highest observed conductivities. Low-salinity fluids (? 0.1 m) released by slab dehydration evolve towards high-salinity (? 1 m) fluids during progressive serpentinization in the wedge. These fluids can mix with arc magmas at depths and account for high-chlorine melt inclusions in arc lavas. High electrical conductivities up to 1 S/m in the hydrated wedge of the hot <span class="hlt">subductions</span> (Ryukyu, Kyushu, Cascadia) reflect high fluid concentration, while low to moderate (<0.01 S/m) conductivities in the cold <span class="hlt">subductions</span> (N-E <span class="hlt">Japan</span>, Bolivia) reflect low fluid flow. This is consistent with the seismic observations of extensive shallow serpentinization in hot <span class="hlt">subduction</span> zones, while serpentinization is sluggish in cold <span class="hlt">subduction</span> zones. Bezacier, L., et al. 2010. Elasticity of antigorite, seismic detection of serpentinites, and anisotropy in <span class="hlt">subduction</span> zones. Earth and Planetary Science Letters, 289, 198-208. Reynard, B., 2012. Serpentine in active <span class="hlt">subduction</span> zones. Lithos, http://dx.doi.org/10.1016/j.lithos.2012.10.012. Reynard, B., Mibe, K. & Van de Moortele, B., 2011. Electrical conductivity of the serpentinised mantle and fluid flow in <span class="hlt">subduction</span> zones. Earth and Planetary Science Letters, 307, 387-394. Reynard, B., Nakajima, J. & Kawakatsu, H., 2010. Earthquakes and plastic deformation of anhydrous slab mantle in double Wadati-Benioff zones. Geophysical Research Letters, 37, L24309.</p> <div class="credits"> <p class="dwt_author">Reynard, Bruno</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">208</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17361181"> <span id="translatedtitle">Evolution and diversity of <span class="hlt">subduction</span> zones controlled by slab width.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><span class="hlt">Subducting</span> slabs provide the main driving force for plate motion and flow in the Earth's mantle, and geodynamic, seismic and geochemical studies offer insight into slab dynamics and <span class="hlt">subduction</span>-induced flow. Most previous geodynamic studies treat <span class="hlt">subduction</span> zones as either infinite in <span class="hlt">trench</span>-parallel extent (that is, two-dimensional) or finite in width but fixed in space. <span class="hlt">Subduction</span> zones and their associated slabs are, however, limited in lateral extent (250-7,400 km) and their three-dimensional geometry evolves over time. Here we show that slab width controls two first-order features of plate tectonics-the curvature of <span class="hlt">subduction</span> zones and their tendency to retreat backwards with time. Using three-dimensional numerical simulations of free <span class="hlt">subduction</span>, we show that <span class="hlt">trench</span> migration rate is inversely related to slab width and depends on proximity to a lateral slab edge. These results are consistent with retreat velocities observed globally, with maximum velocities (6-16 cm yr(-1)) only observed close to slab edges (<1,200 km), whereas far from edges (>2,000 km) retreat velocities are always slow (<2.0 cm yr(-1)). Models with narrow slabs (< or =1,500 km) retreat fast and develop a curved geometry, concave towards the mantle wedge side. Models with slabs intermediate in width ( approximately 2,000-3,000 km) are sublinear and retreat more slowly. Models with wide slabs (> or =4,000 km) are nearly stationary in the centre and develop a convex geometry, whereas <span class="hlt">trench</span> retreat increases towards concave-shaped edges. Additionally, we identify periods (5-10 Myr) of slow <span class="hlt">trench</span> advance at the centre of wide slabs. Such wide-slab behaviour may explain mountain building in the central Andes, as being a consequence of its tectonic setting, far from slab edges. PMID:17361181</p> <div class="credits"> <p class="dwt_author">Schellart, W P; Freeman, J; Stegman, D R; Moresi, L; May, D</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-03-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">209</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/6110786"> <span id="translatedtitle">Regionality of deep low-frequency earthquakes associated with <span class="hlt">subduction</span> of the Philippine Sea plate along the Nankai Trough, southwest <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Fukuoka District Meteorological Observatory recently logged three possible deep low-frequency earthquakes (LFEs) beneath eastern Kyushu, <span class="hlt">Japan</span>, a region in which LFEs and low-frequency tremors have never before been identified. To assess these data, we analyzed band-pass filtered velocity seismograms and relocated LFEs and regular earthquakes using the double-difference method. The results strongly suggest that the three events were authentic</p> <div class="credits"> <p class="dwt_author">Shoichi Yoshioka; Mamiko Toda; Junichi Nakajima</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">210</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EGUGA..1410396M"> <span id="translatedtitle">3D Numerical simulations of oblique <span class="hlt">subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In the past 2D numerical studies (e.g. Gerya et al., 2002; Gorczyk et al., 2007; Malatesta et al., 2012) provided evidence that during intraoceanic <span class="hlt">subduction</span> a serpentinite channel forms above the downgoing plate. This channel forms as a result of hydration of the mantle wedge by uprising slab-fluids. Rocks buried at high depths are finally exhumed within this buoyant low-viscosity medium. Convergence rate in these 2D models was described by a <span class="hlt">trench</span>-normal component of velocity. Several present and past <span class="hlt">subduction</span> zones worldwide are however driven by oblique convergence between the plates, where <span class="hlt">trench</span>-normal motion of the <span class="hlt">subducting</span> slab is coupled with <span class="hlt">trench</span>-parallel displacement of the plates. Can the exhumation mechanism and the exhumation rates of high-pressure rocks be affected by the shear component of <span class="hlt">subduction</span>? And how uprise of these rocks can vary along the plate margin? We tried to address these questions performing 3D numerical models that simulate an intraoceanic oblique <span class="hlt">subduction</span>. The models are based on thermo-mechanical equations that are solved with finite differences method and marker-in-cell techniques combined with multigrid approach (Gerya, 2010). In most of the models a narrow oceanic basin (500 km-wide) surrounded by continental margins is depicted. The basin is floored by either layered or heterogeneous oceanic lithosphere with gabbro as discrete bodies in serpentinized peridotite and a basaltic layer on the top. A weak zone in the mantle is prescribed to control the location of <span class="hlt">subduction</span> initiation and therefore the plate margins geometry. Finally, addition of a third dimension in the simulations allowed us to test the role of different plate margin geometries on oblique <span class="hlt">subduction</span> dynamics. In particular in each model we modified the dip angle of the weak zone and its "lateral" geometry (e.g. continuous, segmented). We consider "continuous" weak zones either parallel or increasingly moving away from the continental margins. Moreover, we tested the effect on <span class="hlt">subduction</span>/exhumation dynamics of several values of the <span class="hlt">trench</span>-parallel component of convergence-rate vector. Gerya T., Stöckhert B., Perchuk A.L. (2002). Exhumation of high-pressure metamorphic rocks in a <span class="hlt">subduction</span> channel: a numerical simulation. Tectonics, vol. 21, n. 6, 1056. Gerya, T. V., 2010. Introduction to numerical geodynamic modelling. Cambridge University Press, Cambridge. Gorczyk W., Guillot S., Gerya T.V., Hattori K. (2007a). Asthenospheric upwelling, oceanic slab retreat, and exhumation of UHP mantle rocks: insights from Greater Antilles. Geophysical research letters, vol. 34, L21309. Malatesta C., Gerya T., Scambelluri M., Federico L., Crispini L., Capponi G. (2012). Intraoceanic <span class="hlt">subduction</span> of "heterogeneous" oceanic lithosphere in narrow basins: 2D numerical modeling. Lithos, http://dx.doi.org/10.1016/j.lithos.2012.01.003</p> <div class="credits"> <p class="dwt_author">Malatesta, C.; Gerya, T.; Scambelluri, M.; Crispini, L.; Federico, L.; Capponi, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">211</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMDI44B..02T"> <span id="translatedtitle">The Role of Slab Windows in <span class="hlt">Subduction</span> Cycles</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Active continental margins are enduring features which commonly record a history of <span class="hlt">subduction</span> spanning tens of millions of years. A <span class="hlt">subduction</span> history is commonly divisible into distinct intervals of <span class="hlt">subduction</span> activity separated by periods of non-<span class="hlt">subduction</span>. The intervals of non-<span class="hlt">subduction</span> are dominated by transform, transtensional or transpressional regimes. The recognition of <span class="hlt">subduction</span> cycles as a normal pattern of active continental margins was an essential step forward in the understanding of ancient continental margin assemblages, plate evolution and global tectonics. The causes of interruptions of <span class="hlt">subduction</span> are varied, and include collision of island arcs or oceanic plateaus, swerves in the motions of large plates, plate deformation and microplate formation, and <span class="hlt">subduction</span> of oceanic spreading ridges. These processes punctuate <span class="hlt">subduction</span> that may have occurred unbroken for millions or tens of millions of years, but do not necessarily lead to destruction of the continental margin as fundamentally convergent and active. The intersection of a mid-ocean spreading ridge with a <span class="hlt">subduction</span> zone brings two distinctive tectono-magmatic systems together at the same location. The style of ridge-<span class="hlt">subduction</span> zone interaction varies considerably, depending on factors such as the obliquity of ridge-<span class="hlt">trench</span> intersection, relative plate motions, plate integrity and thermal conditions. Where the ridge intersects the <span class="hlt">trench</span>, a triple junction exists which, in most cases, migrates along the continental margin. The two oceanic plates that flank the spreading ridge naturally have different motion vectors relative to the overriding plate, and as the triple junction migrates, a given part of the continental margin will be in contact with one plate, and at a later time, the other plate. One or both of the oceanic plates may be convergent with the continent but in all cases a gap in the extent of the <span class="hlt">subducted</span> slab, termed a slab window, will develop beneath the continent in the region near the triple junction. The slab window is a product of simple geometrical divergence between the oceanic plates in concert with more cryptic processes including thermal erosion and physical degradation of the <span class="hlt">subducting</span> slab edge(s). Slab windows and their geological products are thereby linked to one of the most common interruptions to <span class="hlt">subduction</span> beneath active continental margins, i.e, where one oceanic plate replaces another at the locus of a migrating ridge-<span class="hlt">trench-trench</span> or ridge-<span class="hlt">trench</span>-transform triple junction. Slab windows have played an important role in the evolution of many continental (and oceanic) convergent margins, most notably the west coast of the Americas during the Cenozoic. All of these windows have been, or are, involved with the replacement of a metasomatized mantle wedge by drier asthenosphere, modification or elimination of the volcanic arc, and changes to the regional structural and tectonic system. Despite the proliferation of slab windows, and the interruption of <span class="hlt">subduction</span> for long intervals, the fundamental nature of the western margin of South, Central and North America as an enduring belt of plate convergence and <span class="hlt">subduction</span> remains intact.</p> <div class="credits"> <p class="dwt_author">Thorkelson, D. J.; Breitsprecher, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">212</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.3301H"> <span id="translatedtitle">Numerical investigation of dewatering and fluid pressure in the western Nankai <span class="hlt">subduction</span> zone: Implications for fluid flow and mechanical behavior of the <span class="hlt">subduction</span> thrust</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Excess pore water pressure is one of crucial factors that controls the nature and physical property of the plate boundary and, thus, the updip limit of the seismogenic zone. Variation of sediment composition and lithostratigraphy are key players for the spatial distribution and magnitude of fluid pressures. To investigate their impact we chose the underthrust sequence of the western Nankai <span class="hlt">subduction</span> zone offshore <span class="hlt">Japan</span> for our study. Sand layers characterize the incoming sediment sequence at the western Nankai margin with a total thickness of up to >200 m within a matrix of hemipelagic mud. We use a coupled loading and diffusion model that allows continuous sediment deformation. To investigate the impact of sand layers on fluid flow and fluid pressures hydrogeological properties are updated in the models based on new laboratory reference data of clays and sands from the Nankai margin area. The simulations demonstrate that ~79-89% of the incoming pore water in the underthrust sediment may be expelled by lateral fluid flow along the sands, which are at least partially cycled back to the ocean. Different deformation behavior of sands and clays enhances the effective sand permeability to be 5-24 times higher than the matrix sediment. The average pore pressure ratio along the base of the accretionary prism is lower than along the central Nankai margin where sand layers are absent. This result emphasizes that sediment lithostratigraphy is a key player for the along-strike variation in mechanical strength of the <span class="hlt">subduction</span> thrust. The numerical study also suggests that lateral fluid flow mediates the distribution of effective stress in the underthrusting sediments, and may cause downstepping of the décollement ~20-30 km landward of the <span class="hlt">trench</span> (as observed in seismic reflection profiles) and initiates underplating in the Nankai <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Huepers, Andre; Saffer, Demian M.; Kopf, Achim J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">213</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011PEPI..184....1G"> <span id="translatedtitle">Signatures of downgoing plate-buoyancy driven <span class="hlt">subduction</span> in Cenozoic plate motions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The dynamics of plate tectonics are strongly related to those of <span class="hlt">subduction</span>. To obtain a better understanding of the driving forces of <span class="hlt">subduction</span>, we compare relations between Cenozoic <span class="hlt">subduction</span> motions at major <span class="hlt">trenches</span> with the trends expected for the simplest form of <span class="hlt">subduction</span>. i.e., free <span class="hlt">subduction</span>, driven solely by the buoyancy of the downgoing plate. In models with an Earth-like plate stiffness (corresponding to a plate-mantle viscosity contrast of 2-3 orders of magnitude), free plates <span class="hlt">subduct</span> by a combination of downgoing plate motion and <span class="hlt">trench</span> retreat, while the slab is draped and folded on top of the upper-lower mantle viscosity transition. In these models, the slabs sink according to their Stokes’ velocities. Observed downgoing-plate motion-plate-age trends are compatible with >80% of the Cenozoic slabs sinking according to their upper-mantle Stokes’ velocity, i.e., <span class="hlt">subducting</span>-plate motion is largely driven by upper-mantle slab pull. Only in a few cases, do young plates move at velocities that require a higher driving force (possibly supplied by lower-mantle-slab induced flow). About 80% of the Cenozoic <span class="hlt">trenches</span> retreat, with retreat accounting for about 10% of the total convergence. The few advancing <span class="hlt">trench</span> sections are likely affected by regional factors. The low <span class="hlt">trench</span> motions are likely encouraged by low asthenospheric drag (equivalent to that for effective asthenospheric viscosity 2-3 orders below the upper-mantle average), and low lithospheric strength (effective bending viscosity ˜2 orders of magnitude above the upper-mantle average). Total Cenozoic <span class="hlt">trench</span> motions are often very oblique to the direction of downgoing-plate motion (mean angle of 73°). This indicates that other forces than slab buoyancy exert the main control on upper-plate/<span class="hlt">trench</span> motion. However, the component of <span class="hlt">trench</span> retreat in the direction of downgoing plate motion (? slab pull) correlates with downgoing-plate motion, and this component of retreat generally does not exceed the amount expected for free buoyancy-driven <span class="hlt">subduction</span>. High present-day slab dips (on average about 70°) are compatible with largely upper-mantle slab-pull driven <span class="hlt">subduction</span> of relatively weak plates, where motion partitioning and slab geometry adjust to external constraints/forces on <span class="hlt">trench</span> motion.</p> <div class="credits"> <p class="dwt_author">Goes, S.; Capitanio, F. A.; Morra, G.; Seton, M.; Giardini, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">214</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013GeoRL..40...88F"> <span id="translatedtitle">Systematic changes in the incoming plate structure at the Kuril <span class="hlt">trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent seismic structural studies in <span class="hlt">trench</span>-outer rise regions have shown that Vp within the incoming oceanic plate systematically decreases toward the <span class="hlt">trench</span>, probably owing to bending and fracturing of the plate. To understand the mechanisms acting to reduce Vp, Vs is critical because the Vp/Vs ratio is a sensitive indicator of lithology, porosity, and the presence of fluid. In the outer rise region of the Kuril <span class="hlt">trench</span>, we conducted an extensive seismic refraction and reflection survey that revealed systematic changes in Vp, Vs, and Vp/Vs. Our results suggest that water content within the incoming oceanic plate increases toward the <span class="hlt">trench</span> accompanied by the development of bending-related fractures at the top of the oceanic crust, consistent with the seawater percolation. Our results support the idea that plate bending and fracturing during the bending in the outer rise of the <span class="hlt">trench</span> play an important role in the water cycle of <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Fujie, Gou; Kodaira, Shuichi; Yamashita, Mikiya; Sato, Takeshi; Takahashi, Tsutomu; Takahashi, Narumi</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">215</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AGUFM.S43C..02M"> <span id="translatedtitle">3D Finite-Difference Modeling of Scattered Teleseismic Wavefields in a <span class="hlt">Subduction</span> Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">For a teleseismic array targeting <span class="hlt">subducting</span> crust in a zone of active <span class="hlt">subduction</span>, scattering from the zone underlying the <span class="hlt">trench</span> result in subhorizontally-propagating waves that could be difficult to distinguish from converted P- and S- wave backscattered from the surface. Because back-scattered modes often provide the most spectacular images of <span class="hlt">subducting</span> slabs, it is important to understand their differences from the arrivals scattered from the <span class="hlt">trench</span> zone. To investigate the detailed teleseismic wavefield in a <span class="hlt">subduction</span> zone environment, we performed a full-waveform, 3-D visco-elastic finite-difference modeling of teleseismic wave propagation using a Beowulf cluster. The synthetics show strong scattering from the <span class="hlt">trench</span> zone, dominated by the mantle and crustal P-waves propagating at 6.2-8.1.km/s and slower. These scattered waves occupy the same time and moveout intervals as the backscattered modes, and also have similar amplitudes. Although their amplitude decay characters are different, with the uncertainties in the velocity and density structure of the <span class="hlt">subduction</span> zone, unambiguous distinguishing of these modes appears difficult. However, under minimal assumptions (in particular, without invoking slab dehydration), recent observations of receiver function amplitudes decreasing away from the <span class="hlt">trench</span> favor the interpretation of <span class="hlt">trench</span>-zone scattering.</p> <div class="credits"> <p class="dwt_author">Morozov, I. B.; Zheng, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">216</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005EP%26S...57..973F"> <span id="translatedtitle">Propagation of the 2001-2002 silent earthquake and interplate coupling in the Oaxaca <span class="hlt">subduction</span> zone, Mexico</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The aseismic slow slip event of 2001-2002 in Guerrero, Mexico, with an equivalent magnitude MW ~ 7.5, is the largest silent earthquake (SQ) among many recently recorded by GPS in different <span class="hlt">subduction</span> zones (i.e. <span class="hlt">Japan</span>, Alaska, Cascadia, New Zealand). The sub-horizontal and shallow plate interface in Central Mexico is responsible for specific conditions for the ~100 km long extended transient zone where the SQs develop from ~80 to ~190 km inland from the <span class="hlt">trench</span>. This wide transient zone and relatively large slow slips of 10 to 20 cm displacements on the <span class="hlt">subduction</span> fault result in noticeable surface displacements of 5-6 cm during the SQs. Continuous GPS stations allow one to trace the propagation of SQs, and to estimate their arrival time, duration and geometric attenuation. These propagation parameters must be accounted in order to locate source of slow slips events and to understand the triggering effect that they have on large <span class="hlt">subduction</span> earthquakes. We use longbaseline tiltmeter data to define new time limits (onset and duration) for the SQs and continuous records from 8 GPS stations to determine the propagation of the 2001-2002 SQ in Central Mexico. Data from the CAYA and IGUA GPS stations, separated by ~170 km and located along the profile perpendicular to the <span class="hlt">trench</span>, are used to determine that the surface deformation from the 2001-2002 SQ started almost instantaneously. It propagated parallel to the coast at ~2 km/day with an exponential attenuation of the horizontal surface displacement and a linear decrease of its duration with distance. Campaign data obtained yearly from 2001 to 2005 at the Oaxaca GPS network have been modeled according to a propagation of the 2001-2002 SQ step-like displacement anomaly. This modeling shows that the SQ ceased gradually in the central part of the Oaxaca segment of the <span class="hlt">subduction</span> zone (west of Puerto Angel, PUAN) and then it apparently triggered another SQ in SE Oaxaca (between PUAN and Salina Cruz, SACR). The estimated horizontal velocities for inter-event epochs at each GPS site are used to assess an average interplate coupling in the Central Oaxaca <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Franco, S. I.; Kostoglodov, V.; Larson, K. M.; Manea, V. C.; Manea, M.; Santiago, J. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">217</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013E%26PSL.365..132M"> <span id="translatedtitle">Mantle flow and deformation of <span class="hlt">subducting</span> slab at a plate junction</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">At junctions between plate boundaries there are several general characteristic features. These include <span class="hlt">trench</span>-normal fast polarization direction of S-wave splitting in the mantle wedge, along-arc variation of the angle of <span class="hlt">subduction</span>, and the different behavior of slab stagnation along the strike of the <span class="hlt">trench</span>. In this paper, we focus on the junction of the Tohoku-Kurile arc. We show the dynamical effects of the junction using a numerical model of mantle convection with a realistic curved shape of the <span class="hlt">trench</span>. We obtain 3D flow in the mantle wedge which is consistent with the observation of seismic anisotropy even with the oblique <span class="hlt">subduction</span>. We also find the along-arc variation of <span class="hlt">subduction</span> angle which agrees with the observations, although the match becomes worse when we include the effect of dislocation creep, that is, non-linear viscosity. Along-arc variation of the angle of <span class="hlt">subduction</span> partly contributes to the different behavior of slab stagnation in the Tohoku-Kurile arc. Our results show that the shape of the <span class="hlt">trench</span> is an important factor which considerably affects mantle flow and deformation of <span class="hlt">subducting</span> slabs. Thus, 3D modeling is necessary to constrain the dynamics of <span class="hlt">subduction</span> zones near the junction.</p> <div class="credits"> <p class="dwt_author">Morishige, Manabu; Honda, Satoru</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">218</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.T21B2334S"> <span id="translatedtitle">Stable Isotope Data from Nankai Sites C0011B and C0012A Constrain Fluid Processes in the Pre-<span class="hlt">Subduction</span> Inputs for the Nantroseize Project, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report data from drill sites C0011B and C0012A from Expedition 322 along the Nankai margin. This research is part of a larger effort designed to investigate the pre-<span class="hlt">subduction</span> inputs of sediment and oceanic basement for the NanTroSEIZE Project. C0011B is entirely in the Shikoku Basin section on the flank of the Kashinosaki Knoll basement high, and C0012A is in a thinner equivalent section from the top of the knoll. Previous work suggests there may have been recent lateral flow of fluids from the accretionary prism into the section penetrated by C0011B. At C0012A, however, there is less evidence for lateral flow, however, there are indications for the presence of a seawater-like fluid flowing through the upper basaltic crust. We analyzed S isotopes from dissolved sulfate in interstitial waters from C0012A, and carbon and oxygen isotopes of carbonate minerals from both sites as proxies for fluids during carbonate formation. The sulfate profile differs from other sites along the Nankai Trough in that it never drops to zero, but decreases to a minimum at 244 CSF (core depth below seafloor in meters), and then fluctuates in value. S isotopes range from +6.96 to +34.40 % relative to the VCDT standard. The data can be divided into two distinct groups. An upper group above ~250 CSF shows a concave-upward profile with increasing ?34S values consistent with a zone of sulfate reduction, leaving residual sulfate increasingly enriched in the heavy isotope 34S. Below this depth the ?34S values drop back to lower values similar, but slightly higher than, global seawater. Carbonates are relatively widespread at both sites, and may be an important diagenetic phase altering sediment physical properties before <span class="hlt">subduction</span>. Average values are 2.3 wt% and 3.3 wt% at C0011B and C0012A, respectively. Carbonates are mainly low-Mg calcite, dolomite, and siderite. A plot of ?13C vs. ?18O (VPDB) of carbonates in C0011B shows a range of ?13C = -23.36 to -2.58% and ?18O = -11.86 to +1.86%. Generally the lowest ?18O values occur deepest in the sediment section, but the pattern is complicated. C isotope values are scattered with depth. In C0012A there is a strong covariance between C and O isotopes (R2 > 0.65), ?18O values range from -12.23 to +3.98%, and ?13C values from -22.48 to -6.39%. Both C and O isotopes values generally decrease with depth. At both sites the C isotopes are consistent with inputs from a combination of methane and dissolved inorganic carbon (DIC), though we cannot discern whether methane has a bacterial or thermogenic source. The C isotopes of carbonates and DIC, however, are consistent with deep-seated zone of AMO, where methane is oxidized by sulfate supplied via seawater-like fluids flowing through basement. The O isotope data show that many of the samples are out of equilibrium with pore waters. The lowest ?18O values suggest warm fluids may have circulated upward through the sediments during carbonate formation. This is most pronounced for C0012A, where the lowest ?18O value of -12.23% occurs at a depth of only 430 CSF. Both O and S isotope data at C0012A are consistent with some upward flow of fluids from basaltic basement, with a seawater sulfate signature and elevated temperatures.</p> <div class="credits"> <p class="dwt_author">Sample, J. C.; Torres, M. E.; Joseph, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">219</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GeoJI.190.1673P"> <span id="translatedtitle">Comparison of characteristic and Gutenberg-Richter models for time-dependent M ? 7.9 earthquake probability in the Nankai-Tokai <span class="hlt">subduction</span> zone, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Earthquake forecasts are usually underinformed, and can be plagued by uncertainty in terms of the most appropriate model, and parameter values used in that model. In this paper, we explore the application of two different models to the same seismogenic area. The first is a renewal model based on the characteristic earthquake hypothesis that uses historical/palaeoseismic recurrence times, and fixed rupture geometries. The hazard rate is modified by the Coulomb static stress change caused by nearby earthquakes that occurred since the latest characteristic earthquake. The second model is a very simple earthquake simulator based on plate-motion, or fault-slip rates and adoption of a Gutenberg-Richter magnitude-frequency distribution. This information is commonly available even if historical and palaeoseismic recurrence data are lacking. The intention is to develop and assess a simulator that has a very limited parameter set that could be used to calculate earthquake rates in settings that are not as rich with observations of large-earthquake recurrence behaviour as the Nankai trough. We find that the use of convergence rate as a primary constraint allows the simulator to replicate much of the spatial distribution of observed segmented rupture rates along the Nankai, Tonankai and Tokai <span class="hlt">subduction</span> zones. Although we note rate differences between the two forecast methods in the Tokai zone, we also see enough similarities between simulations and observations to suggest that very simple earthquake rupture simulations based on empirical data and fundamental earthquake laws could be useful forecast tools in information-poor settings.</p> <div class="credits"> <p class="dwt_author">Parsons, Tom; Console, Rodolfo; Falcone, Giuseppe; Murru, Maura; Yamashina, Ken'ichiro</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">220</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.2909G"> <span id="translatedtitle">All the way up and deep down: new insights on the seismogenic portion of <span class="hlt">subduction</span> megathrusts from recent giant earthquakes and thermal modeling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Until less than 10 years ago, there was a fairly broad consensus that seismogenic rupture could only occur between the forearc basement and the downgoing oceanic plate. This conceptual model considered that the mantle wedge was serpentinized and weak and likewise that the shallowest portion of the forearc, typically the accretionary wedge, was composed of high-porosity overpressured sediments, and that neither of these domains were capable of storing and releasing elastic stress and thus contribute to seismogenic rupture. This paradigm has been challenged by the detailed observations following the series of great megathrust earthquakes starting with the M9.1 Sumatra-Andaman Dec. 2004 earthquake and ending with the most recent M9.0 Tohoku Mar. 2011 earthquake. Deep crustal seismic surveys as well as aftershock distribution and focal mechanism studies now provide compelling evidence that seismogenic rupture commonly extends beneath the entire accretionary wedge and right up to the deep-sea <span class="hlt">trench</span>, with low-angle thrust type focal mechanisms throughout this zone. Conversely, the down-dip limit of the seismogenic zone for both NW Sumatra and NE <span class="hlt">Japan</span> clearly extends to well below the tip of the mantle wedge. Numerical modeling of forearc thermal structure for these two zones, considering the 100-150°C and 350-450°C isotherms as proxies for the up-dip and down-dip limits, respectively, successfully predicts the very wide extent (200 km downdip width) of the NW Sumatra seismogenic zone. For NE <span class="hlt">Japan</span>, the thermal model successfully predicts the downdip limit, but the updip limit near the <span class="hlt">trench</span> is more problematical. Using the same low values of interplate shear stress for both Sumatra and <span class="hlt">Japan</span>, thermal modeling predicts a position of about 80km inboard from the <span class="hlt">trench</span> for the 100°C isotherm along the <span class="hlt">subduction</span> megathrust. However, both the distribution of thrust type aftershocks and published slip models indicate that the Tohoku earthquake ruptured up to the <span class="hlt">trench</span> (where preliminary thermal models predict a temperature of only about 10°C at the decollement). We propose the hypothesis that a much higher degree of effective friction and strong shear heating along the oceanic basement - forearc basement contact could provide an explanation for this apparent paradox. Indeed, the <span class="hlt">Japan</span> forearc has very little sediment at the <span class="hlt">trench</span> (typically about 0.5 km) and is considered a non-accretionary (erosive) margin and thus has very different rheological properties than the NW Sumatra forearc. The hypothesis of higher effective friction and elevated shear heating for this margin configuration will be explored in greater detail in future work.</p> <div class="credits"> <p class="dwt_author">Gutscher, Marc-Andre; Duarte, Joao C.; Schellart, Wouter P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_10");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> 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showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_13");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">221</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51257724"> <span id="translatedtitle">Upper mantle structure beneath the <span class="hlt">Japan</span> Islands imaged by receiver function With Hi-net tiltmeter data-</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">In the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone where the Pacific plate is <span class="hlt">subducting</span>, we can investigate the dynamics of the upper mantle beneath the <span class="hlt">subduction</span> zone by imaging the detailed structure beneath the <span class="hlt">Japan</span> Islands. Recently, the undulation of the seismic discontinuities in the upper mantle beneath the <span class="hlt">Japan</span> Islands has been well detected by receiver function (RF) analysis based on the</p> <div class="credits"> <p class="dwt_author">T. Tonegawa; K. Hirahara; T. Shibutani; K. Shiomi</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">222</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.T43H..02S"> <span id="translatedtitle"><span class="hlt">Subducted</span> lithosphere, slab tearing and continental delamination under Taiwan: arc-continent collision at the junction of quasi-orthogonal <span class="hlt">subduction</span> systems</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The present-day oblique arc-continent collision in Taiwan has a map-view reversal in <span class="hlt">subduction</span> polarity, with the Eurasian plate <span class="hlt">subducting</span> under the Philippine Sea plate south of Taiwan and the Philippine Sea plate <span class="hlt">subducting</span> under the Eurasian continental margin northeast of Taiwan. Tomographic imaging of <span class="hlt">subducted</span> lithosphere under Taiwan allows us to test models of collision and polarity reversal, because each model makes different predictions of the geometries of the <span class="hlt">subducted</span> slabs. Furthermore the tomography reveals previously unpredicted phenomena, including the delamination of Eurasian continental mantle lithosphere with lateral inflow of hot upper mantle. The two <span class="hlt">subduction</span> systems are quasi-orthogonal where they meet at Taiwan and therefore are not well-represented in the classic 2D cross-sectional models of arc-continent collision. The 3D models proposed for Taiwan recognize that either [1] the <span class="hlt">subduction</span> reversal is inherited from a former <span class="hlt">trench-trench</span> transform that is obliterated upon collision or [2] there is a progressive tearing of the Eurasian plate along the continental margin at the north end of the actively <span class="hlt">subducting</span> Eurasian slab, which allows the quasi-orthogonal <span class="hlt">subduction</span> reversal to translate stably with the oblique collision, with no true slab breakoff. The progressive tearing model [2] has a kinematically stable <span class="hlt">trench-trench</span> juncture, whereas the transform obliteration model [1] is unstable, requiring a discontinuity in behavior, for example a change to [2]. More complex mixed models have also been proposed, all of which make testable predictions of <span class="hlt">subducted</span> slab geometry. Modern global tomography, augmented with local and regional tomography near Taiwan, provides good imaging of the <span class="hlt">subducted</span> Eurasian and Philippine-Sea lithosphere in the upper mantle, including the torn <span class="hlt">subducted</span> edge of the Eurasian slab. Slab geometries are in close agreement with the progressive tearing of model [2] and in strong disagreement with the transform obliteration of model [1]. No <span class="hlt">subducted</span> <span class="hlt">trench-trench</span> transform is observed, instead the <span class="hlt">subducted</span> western edge of the Philippine Sea plate continues northward ~900km, nearly to the latitude of Shanghai, in agreement with model [2]. Furthermore, no slab breakoff is observed. However, it is surprising that the active tear at the north end of the <span class="hlt">subducting</span> Eurasian slab is not at the edge of the continent but ~250km to the north under the Eurasian continental shelf north of Taipei. The <span class="hlt">subducted</span> continent-ocean boundary is clearly shown in the seismic velocities within the <span class="hlt">subducted</span> Eurasian slab. Furthermore the tear does not propagate through the overlying continental shelf, therefore the continental mantle lithosphere and lower crust are <span class="hlt">subducting</span> by delamination attached to the oceanic part of the Eurasian plate. Delamination occurs instantaneously adjacent to the active tear and involves the progressive lateral intrusion of hot mantle from the Okinawa-Ryukyu mantle wedge, which lies above the <span class="hlt">subducting</span> Philippine-Sea plate east and northeast of Taiwan. Active magmatism is spatially associated with delamination in northernmost Taiwan, near Taipei.</p> <div class="credits"> <p class="dwt_author">Suppe, J.; Carena, S.; Wu, Y.; Ustaszewski, K. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">223</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013E%26PSL.377..106H"> <span id="translatedtitle">The earliest mantle fabrics formed during <span class="hlt">subduction</span> zone infancy</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Harzburgites obtained from the oldest crust–mantle section in the Philippine Sea plate (˜52 Ma) along the landward slope of the southern Izu–Ogasawara <span class="hlt">Trench</span>, preserve mantle fabrics formed during the infancy of the <span class="hlt">subduction</span> zone; that is during the initial stages of Pacific plate <span class="hlt">subduction</span> beneath the Philippine Sea plate. The harzburgites have relatively fresh primary minerals despite of their heavy serpentinizations, and show inequigranular interlobate textures, and crystal preferred orientation patterns in olivine (001)[100] and Opx (100)[001]. The harzburgites have the characteristics of residual peridotites, whereas the dunites, obtained from the same location as the harzburgites, provide evidence for the earliest stages of arc volcanism during the inception of <span class="hlt">subduction</span>. We propose that the (001)[100] olivine patterns began forming in immature fore-arc mantle with an increase in slab-derived hydrous fluids during the initial stages of <span class="hlt">subduction</span> in in situ oceanic island arc.</p> <div class="credits"> <p class="dwt_author">Harigane, Yumiko; Michibayashi, Katsuyoshi; Morishita, Tomoaki; Tani, Kenichiro; Dick, Henry J. B.; Ishizuka, Osamu</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">224</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6212534"> <span id="translatedtitle">Accretionary processes along the Middle America <span class="hlt">Trench</span> off Costa Rica</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The geometry of large-scale structures within modern accretionary prisms is known entirely from seismic reflection studies using single or grids of two-dimensional profiles. Off Costa Rica the authors collected a three-dimensional reflection data set covering a 9 km wide {times} 22 km long {times} 6 km thick volume of the accretionary prism just arcward of the Middle America <span class="hlt">Trench</span>. The three-dimensional processing and ability to examine the prism as a volume has provided the means to map structures from a few hundred meters to kilometers in size with confidence. Reflections from within the prism define the gross structural features and tectonic processes active along this particular portion of the Middle America <span class="hlt">Trench</span>. So far in the analysis, these data illustrate the relationships between the basement, the prism shape, and overlying slope sedimentary deposits. For instance, the <span class="hlt">subducted</span> basement relief (of several hundred meters amplitude) does seem to affect the larger scale through-going faults within the prism. Offscraping of the uppermost 45 m of sediments occurs within 4 km of the <span class="hlt">trench</span> creating a small pile of sediments at the base of the <span class="hlt">trench</span>. How this offscraped sediment is incorporated into the prism is still being investigated. Underplating of parts of the 400 m thick <span class="hlt">subducted</span> section begin: at a very shallow structural level, 4 to 10 km arcward of the <span class="hlt">trench</span>. Amplitude anomalies associated with some of the larger arcward dipping structures in the prism and surface mud volcanoes suggest that efficient fluid migration paths may extend from the top of the downgoing slab at the shelf edge out into the lower and middle slope region, a distance of 50 to 100 km.</p> <div class="credits"> <p class="dwt_author">Shipley, T.H.; Stoffa, P.L. (Univ. of Texas, Austin (USA)); McIntosh, K.; Silver, E.A. (Univ. of California, Santa Cruz (USA))</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">225</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.5089H"> <span id="translatedtitle"><span class="hlt">Trench</span> migration and upper plate strain over a convecting mantle</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Trench</span> motion and upper plate deformation ultimately respond to mantle flow. Herein I build upon the mantle flow model results of Conrad and Behn (2010) and compute the drag forces underneath all plates, and show that they control the dynamics of plates and plate boundaries. The small misfit angle between between the traction azimuths of mantle traction and absolute plate motion corroborates the idea that convective mantle drag is a prominent driver of plate tectonics. Less intuitive is the fact that the interplay between the drag forces from the upper and lower plates, that amounts to -5 to 8.5 TN/m (per unit <span class="hlt">trench</span> length), dictates both <span class="hlt">trench</span> migration rates and upper plate deformation. At odds with the classic view that assigns the prime role to the idiosyncrasies of <span class="hlt">subduction</span> zones (slab age, interplate friction, water content etc), I find that the intrinsic properties of <span class="hlt">subduction</span> zones in fact only modulate this behavior. More specifically, the mean value of the integrated trenchward mantle drag force from the lower and upper plates (from -2 to 6.5 TN/m) controls upper plate deformation. Conversely, it is the difference between the lower and upper plates mantle drag forces (from -3 to 10 TN/m) that controls <span class="hlt">trench</span> migration rates. In addition, I find that a minimum trenchward force of ~2.5 TN/m must be supplied by mantle drag before <span class="hlt">trenches</span> can actually advance, and before upper plates undergo compression. This force results from the default tendency of slabs to rollback when solely excited by their own buoyancy, and is thus the effective tensional force that slab pull exerts on the plate interface.</p> <div class="credits"> <p class="dwt_author">Husson, Laurent</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">226</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.T13A2179B"> <span id="translatedtitle">Collapse of the northern Jalisco continental slope:<span class="hlt">Subduction</span> erosion, forearc slivering, or <span class="hlt">subduction</span> beneath the Tres Marias escarpment?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Jalisco <span class="hlt">subduction</span> zone exhibits several interesting characteristics. Among these is that convergence between the Rivera and North American plate is highly oblique, especially north of 20N, the obliquity progressively increasing to the NW. By analogy to other better studied <span class="hlt">subduction</span> zones, this distribution of forces should produce a NW-SE extension in the overriding plate, especially north of 20N. This has led to the proposal that the <span class="hlt">trench</span> perpendicular Bahia de Banderas is an expression of this extension [Kostoglodov and Bandy, JGR, vol. 100, 1995]. To further investigate this proposal, multibeam bathymetric data and seafloor backscatter images, seismic reflection sub-bottom profiles and marine magnetic data were collected during the MORTIC08 campaign of the B.O. EL PUMA in March 2009. The bathymetric data provides for 100% coverage (20 to 200 meter spacing of the actual measured depth value depending on the water depth) of the continental slope and <span class="hlt">trench</span> areas north of 20N. These data indicate that a marked change occurs in the morphology of the continental slope at 20N. To the north the slope consists of a broad, fairly flat plain lying between a steep lower inner <span class="hlt">trench</span> slope to the west and a steep, concave seaward, escarpment to the east. In contrast, to the south the continental slope exhibits a more gradual deepening until the steep lower inner <span class="hlt">trench</span> slope. A prominent submarine canyon deeply incises the continental slope between these two morphotectonic domains. This canyon appears to represent the boundary between two NW-SE diverging forearc blocks or slivers, consistent with the presence of oblique convergence. In contrast, the broad, fairly flat plain is better explained by subsidence induced by <span class="hlt">subduction</span> erosion (i.e. erosion of the base of the overriding plate underneath the continental slope area). The shoaling of the <span class="hlt">trench</span> axis northward towards the Puerto Vallarta Graben and subsequent deepening may be related to <span class="hlt">subduction</span> of the Rivera Plate beneath the Tres Marias Escarpment.</p> <div class="credits"> <p class="dwt_author">Bandy, W. L.; Mortera-Gutierrez, C. A.; Ortiz-Zamora, G.; Ortega-Ramirez, J.; Galindo Dominguez, R. E.; Ponce-Núñez, F.; Pérez-Calderón, D.; Rufino-Contreras, I.; Valle-Hernández, S.; Pérez-González, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">227</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.P41A..03S"> <span id="translatedtitle">A Regime Diagram for <span class="hlt">Subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Regime diagrams and associated scaling relations have profoundly influenced our understanding of planetary dynamics. Previous regime diagrams characterized the regimes of stagnant-lid, small viscosity contrast, transitional, and no-convection for temperature-dependent (Moresi and Solomatov, 1995), and non-linear power law rheologies (Solomatov and Moresi, 1997) as well as stagnant-lid, sluggish-lid, and mobile-lid regimes once the finite strength of rock was considered (Moresi and Solomatov, 1998). Scalings derived from such models have been the cornerstone for parameterized models of thermal evolution of rocky planets and icy moons for the past decade. While such a theory can predict the tectonic state of a planetary body, it is still rather incomplete in regards to predicting tectonics. For example, the mobile-lid regime is unspecific as to how continuous lithospheric recycling should occur on a terrestrial planet. Towards this goal, Gerya et al., (2008) advanced a new regime diagram aiming to characterize when <span class="hlt">subduction</span> would manifest itself as a one-sided or two-sided downwelling and either symmetric or asymmetric. Here, we present a regime diagram for the case of a single-sided, asymmetric type of <span class="hlt">subduction</span> (most Earth-like type). Using a 3-D numerical model of a free <span class="hlt">subduction</span>, we describe a total of 5 different styles of <span class="hlt">subduction</span> that can possibly occur. Each style is distinguished by its upper mantle slab morphology resulting from the sinking kinematics. We provide movies to illustrate the different styles and their progressive time-evolution. In each regime, <span class="hlt">subduction</span> is accommodated by a combination of plate advance and slab rollback, with associated motions of forward plate velocity and <span class="hlt">trench</span> retreat, respectively. We demonstrate that the preferred <span class="hlt">subduction</span> mode depends upon two essential controlling factors: 1) buoyancy of the downgoing plate and 2) strength of plate in resisting bending at the hinge. We propose that a variety of <span class="hlt">subduction</span> regimes are generated primarily as a product of two mechanisms. The first mechanism is that of the competition between the weight of the slab and the strength of the plate, which can be understood in terms of the applied bending moment, and this competition results in a particular radius of curvature (for which we provide a simple scaling theory). The second mechanism is the interaction between the slab and the more viscous lower mantle, which produces each regime's distinct slab morphology. Thus, the emergence of five distinct styles of <span class="hlt">subduction</span> is a direct consequence of the presence of the modest barrier to flow into the lower mantle. Although only 2 of these styles presently operate on Earth, the possibility exists that other modes may have been the predominant mode in the past. Based on these models, we propose that the lithosphere is the primary factor in describing key elements of the plate tectonics system over time, rather than the convecting mantle. We discuss the various factors that may have influenced secular changes in Earth's tectonic behavior, some of which may have interesting consequences for the geochemical evolution of the Earth.</p> <div class="credits"> <p class="dwt_author">Stegman, D. R.; Farrington, R.; Capitanio, F. A.; Schellart, W. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">228</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.eri.u-tokyo.ac.jp/seno/Papers/2002JB001918.pdf"> <span id="translatedtitle">Double seismic zone and dehydration embrittlement of the <span class="hlt">subducting</span> slab</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Dehydration embrittlement of metamorphosed oceanic crust and mantle in the <span class="hlt">subducting</span> slab may be responsible for the occurrence of intermediate-depth earthquakes. We explore the possibility that this hypothesis can explain the morphology of the double seismic zones observed in northeast <span class="hlt">Japan</span>, southwest <span class="hlt">Japan</span>, northeast Taiwan, northern Chile, Cape Mendocino, and eastern Aleutians. We calculate transient temperature structures of slabs based</p> <div class="credits"> <p class="dwt_author">Tadashi Yamasaki; Tetsuzo Seno</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">229</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002AGUFM.T62B1303M"> <span id="translatedtitle">Temperature Models for the Mexican <span class="hlt">Subduction</span> Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">It is well known that the temperature is one of the major factors which controls the seismogenic zone. The Mexican <span class="hlt">subduction</span> zone is characterized by a very shallow flat <span class="hlt">subducting</span> interplate in its central part (Acapulco, Oaxaca), and deeper <span class="hlt">subduction</span> slabs northern (Jalisco) and southern (Chiapas). It has been proposed that the seismogenic zone is controlled, among other factors, by a temperature. Therefore, we have developed four two-dimensional steady state thermal models for Jalisco, Guerrero, Oaxaca and Chiapas. The updip limit of the seismogenic zone is taken between 100 §C and 150 §C, while the downdip limit is thought to be at 350 §C because of the transition from stick-slip to stable-sliding. The shape of the <span class="hlt">subducting</span> plate is inferred from gravity and seismicity. The convergence velocity between oceanic and continental lithospheric plates is taken as the following: 5 cm/yr for Jalisco profile, 5.5 for Guerrero profile, 5.8 for Oaxaca profile, and 7.8 for Chiapas profile. The age of the <span class="hlt">subducting</span> plates, since they are young, and provides the primary control on the forearc thermal structure, are as the following: 11 My for Jalisco profile, 14.5 My for Guerrero profile, 15 My for Oaxaca profile, and 28 My for Chiapas profile. We also introduced in the models a small quantity of frictional heating (pore pressure ratio 0.98). The value of 0.98 for pore pressure ratio was obtained for the Guerrero profile, in order to fit the intersection between the 350 §C isotherm and the <span class="hlt">subducting</span> plate at 200 Km from <span class="hlt">trench</span>. The value of 200 km coupling zone from <span class="hlt">trench</span> is inferred from GPS data for the steady interseismic period and also for the last slow aseismic slip that occurred in Guerrero in 2002. We have used this value of pore pressure ratio (0.98) for all the other profiles. For the others three profiles we obtained the following coupling extents: Jalisco - 100 km, Oaxaca - 170 km and Chiapas - 125 km (from the <span class="hlt">trench</span>). Independent constrains of the thermal models come from the surface thermal measurements (offshore - Prol-Ledesma et al (1989) and onshore - Ziagos et al. (1985)). Unfortunately these measurements are very sparse, and present an important dispersion and have large uncertainties. In our models, all profiles show a decrease in heat flow from the <span class="hlt">trench</span> towards the continent, which is characteristic for <span class="hlt">subduction</span> zones. We also have included a mantle wedge flow current in order to keep a constant depth to the lithosphere-asthenosphere boundary. This mantle wedge convection provides an increase in heat flow near the volcanic arc which is consistent with the surface observations. Our models indicate that the seismogenic zone in Mexico comprised between 100 §C and 350 §C is in good agreement with the coseismic rupture width inferred from the megathrust earthquake aftershocks and seismic models of rupture. These thermal models will be used to calculate the thermal stresses induced by the <span class="hlt">subducting</span> plate.</p> <div class="credits"> <p class="dwt_author">Manea, V. C.; Kostoglodov, V.; Currie, C.; Manea, M.; Wang, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">230</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004EOSTr..85..349T"> <span id="translatedtitle">New Seafloor Map of the Puerto Rico <span class="hlt">Trench</span> Helps Assess Earthquake and Tsunami Hazards</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Puerto Rico <span class="hlt">Trench</span>, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is <span class="hlt">subducting</span> under the Caribbean plate (Figure 1). The <span class="hlt">trench</span> region may pose significant seismic and tsunami hazards to Puerto Rico and the U.S. Virgin Islands, where 4 million U.S. citizens reside. Widespread damage in Puerto Rico and Hispaniola from an earthquake in 1787 was estimated to be the result of a magnitude 8 earthquake north of the islands. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico, although their ages are unknown. The Puerto Rico <span class="hlt">Trench</span> is atypical of oceanic <span class="hlt">trenches</span>. <span class="hlt">Subduction</span> is highly oblique (10°-20°) to the <span class="hlt">trench</span> axis with a large component of left-lateral strike-slip motion. Similar convergence geometry is observed at the Challenger Deep in the Mariana <span class="hlt">Trench</span>, the deepest point on Earth. In addition to its extremely deep seafloor, the Puerto Rico <span class="hlt">Trench</span> is also characterized by the most negative free-air gravity anomaly on Earth, -380 mGal, located 50 km south of the <span class="hlt">trench</span>, where water depth is 7950 m (Figure 2). A tilted carbonate platform provides evidence for extreme vertical tectonism in the region. This platform was horizontally deposited over Cretaceous to Paleocene arc rocks starting in the Late Oligocene. Then, at 3.5 Ma, the carbonate platform was tilted by 4° toward the <span class="hlt">trench</span> over a time period of less than 40 kyr, such that its northern edge is at a depth of 4000 m and its reconstructed elevation on land in Puerto Rico is at +1300 m (Figures 1 and 2).</p> <div class="credits"> <p class="dwt_author">ten Brink, Uri; Danforth, William; Polloni, Christopher; Andrews, Brian; Llanes, Pilar; Smith, Shepard; Parker, Eugene; Uozumi, Toshihiko</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">231</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51655225"> <span id="translatedtitle">Spatial and Temporal Variability in the Circulation and Thermal Evolution of the Mantle in <span class="hlt">Subduction</span> Zones: Insights From 3-D Laboratory Experiments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The <span class="hlt">subduction</span> of oceanic lithosphere plays a key role in plate tectonics, the thermal evolution of the mantle and recycling processes between Earth's interior and surface. The majority of <span class="hlt">subduction</span> models are two-dimensional (2-D), assuming limited variability in the direction parallel to the <span class="hlt">trench</span>. Observationally based models increasingly appeal to three-dimensional (3-D) flow associated with <span class="hlt">trench</span> migration and the sinking</p> <div class="credits"> <p class="dwt_author">C. Kincaid; R. W. Griffiths</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">232</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013GeoJI.195...47D"> <span id="translatedtitle">Three-dimensional dynamic laboratory models of <span class="hlt">subduction</span> with an overriding plate and variable interplate rheology</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Subduction</span> zones are complex 3-D features in which one tectonic plate sinks underneath another into the deep mantle. During <span class="hlt">subduction</span> the overriding plate (OP) remains in physical contact with the <span class="hlt">subducting</span> plate and stresses generated at the <span class="hlt">subduction</span> zone interface and by mantle flow force the OP to deform. We present results of 3-D dynamic laboratory models of <span class="hlt">subduction</span> that include an OP. We introduce new interplate materials comprising homogeneous mixtures of petrolatum and paraffin oil to achieve progressive <span class="hlt">subduction</span>. The rheology of these mixtures is characterized by measurements using a strain rate controlled rheometer. The results show that the strength of the mixture increases with petrolatum content, which can be used as a proxy for the degree of mechanical coupling along the <span class="hlt">subduction</span> interface. Results of <span class="hlt">subduction</span> experiments are presented with different degrees of mechanical coupling and the influence this has on the dynamics and kinematics of <span class="hlt">subduction</span>. The modelling results show that variations in the degree of mechanical coupling between the plates have a major impact on <span class="hlt">subduction</span> velocities, slab geometry and the rate of OP deformation. In all experiments the OP is displaced following <span class="hlt">trench</span> migration and experiences overall extension localized in the plate interior. This suggests that OP deformation is driven primarily by the toroidal component of <span class="hlt">subduction</span>-related mantle return flow. The <span class="hlt">subduction</span> rate is always very slow in experiments with medium mechanical coupling, and <span class="hlt">subduction</span> stops prematurely in experiments with very high coupling. This implies that the shear forces along the plate interface in natural <span class="hlt">subduction</span> zone systems must be relatively low and do not vary significantly. Otherwise a higher variability in natural <span class="hlt">subduction</span> velocities should be observed for mature, non-perturbed <span class="hlt">subduction</span> zones. The required low shear force is likely controlled by the rheology of highly hydrated sedimentary and basaltic rocks.</p> <div class="credits"> <p class="dwt_author">Duarte, João C.; Schellart, Wouter P.; Cruden, Alexander R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">233</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFMDI51A..07G"> <span id="translatedtitle">Signatures of Downgoing Plate-Buoyancy Driven <span class="hlt">Subduction</span> in Cenozoic Plate Motions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The dynamics of plate tectonics are strongly related to those of <span class="hlt">subduction</span>. We gain new insights in the thus far elusive dominant forces in <span class="hlt">subduction</span>, by comparing relations between <span class="hlt">subduction</span> motions and dips as predicted by a fully dynamic model for free <span class="hlt">subduction</span> (i.e., driven solely by downgoing plate buoyancy while resisted passively by the mantle and upper plate), with data for the major <span class="hlt">subduction</span> zones from the Cenozoic compilation by Sdrolias & Müller (2006). We find that: (a) Around 90% of Cenozoic plate convergence is achieved by advance of the downgoing plate towards the <span class="hlt">trench</span>, requiring a low-drag asthenosphere (as for a viscosity 10-2 to 10-3 times the upper-mantle average), as well as plate widths > 2000 km. (b) Present-day sinking velocities, and downgoing-plate motions throughout the Cenozoic are as expected for slabs driven by their own upper-mantle buoyancy. In a few cases, young plates move at velocities that require a higher driving force, most likely supplied by lower-mantle-slab induced flow (c) Steep present-day slab dips imply that plate resistance to bending is low, as for effective viscosities 102 times that of the upper mantle. Dips either in- or decrease with plate age, evidence of a nonlinear response of the plate to high bending stresses. (d) Throughout the Cenozoic, 80% of the <span class="hlt">trench</span> sections retreat. <span class="hlt">Trench</span>-plate motion correlations range from strongly positive to strongly negative. This variability can be explained by regional factors that encourage/hamper plate motion or hamper/encourage <span class="hlt">trench</span> motions. On average, <span class="hlt">trench</span> motion is small, and often very oblique (mean angle of 73°) to the direction of downgoing-plate motion, most likely due to constraints imposed by the upper plate. Thus emerges a picture of (upper-mantle) slab pull driven, relatively free, <span class="hlt">subduction</span>, where motion partitioning and slab geometry adjust to external constraints on <span class="hlt">trench</span> motions.</p> <div class="credits"> <p class="dwt_author">Goes, S.; Capitanio, F. A.; Morra, G.; Seton, M.; Giardini, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">234</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1985JGR....90.4495L"> <span id="translatedtitle">Stress distribution and <span class="hlt">subduction</span> of aseismic ridges in the Middle America <span class="hlt">Subduction</span> Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The regional distribution of stresses associated with the <span class="hlt">subduction</span> of the Cocos plate is inferred from a synthesis of 190 earthquake focal mechanisms, body and surface wave analyses of large earthquakes, and seismicity distributions. Broad patterns of consistent behavior are found across the region, from the Rivera Plate boundary in the northwest to the Guatemala/El Salvador border in the southeast, and are used as a framework to evaluate evidence for variations in local stresses due to the <span class="hlt">subduction</span> of two aseismic ridges, the Tehuantepec Ridge and the Orozco Fracture Zone. Information which bears on the seismic potential at locations of aseismic ridge <span class="hlt">subduction</span> is particularly important in that no large (Ms ? 7.5) earthquakes have occurred historically. We identify three major zones with consistent patterns in focal mechanisms and hypocentral distributions of seismicity. The first, closest to the <span class="hlt">trench</span> and reflecting the mechanical interaction of the converging plates, is a zone of shallow thrust earthquakes extending 100-150 km inland from the <span class="hlt">trench</span>. The second is a zone of normal faulting, beginning at about 200 km inland from the <span class="hlt">trench</span>, h ? 60 km, which extends continuously along the entire length of the descending plate throughout the region. The third distinct zone exhibits a relatively low level of activity and separates the zones of thrust and normal faulting at about 150-200 km inland from the <span class="hlt">trench</span>. This zone extends from the Rivera plate boundary in the northwest to the Guatamala region in the southeast. At this point, the quiet region pinches out, and the thrust and normal faulting zones abut and overlap. Superimposed on this overall pattern, we find locally only minor changes in areas of aseismic ridge <span class="hlt">subduction</span>, aside from the prominent seismic slip gaps. Furthermore, on October 25, 1981, the Playa Azul earthquake (Ms = 7.3) occurred in the midregion of the Orozco Fracture Zone. Body and surface wave analyses of this event show a simple source rupture and shallow thrust fault mechanism, as are found elsewhere in the region. The seismic moment is MO = 1.3 × 1020 N m; the calculated stress drop is 4.5 MPa, not extraordinarily high, as might be expected in these pervasive seismic gaps. An event in the Tehuantepec Ridge region, on January 24, 1983, Ms = 6.7, was a large normal faulting event, but further interpretation is ambiguous due to the proximity of other normal faulting. We conclude that while aseismic slip may be occurring in the areas of ridge <span class="hlt">subduction</span>, the possibility of large thrust earthquakes cannot be ruled out, due to the overall similarities with adjacent regions.</p> <div class="credits"> <p class="dwt_author">Lefevre, L. Victoria; McNally, Karen C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">235</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/11110653"> <span id="translatedtitle"><span class="hlt">Subduction</span> and slab detachment in the Mediterranean-Carpathian region.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Seismic tomography models of the three-dimensional upper mantle velocity structure of the Mediterranean-Carpathian region provide a better understanding of the lithospheric processes governing its geodynamical evolution. Slab detachment, in particular lateral migration of this process along the plate boundary, is a key element in the lithospheric dynamics of the region during the last 20 to 30 million years. It strongly affects arc and <span class="hlt">trench</span> migration, and causes along-strike variations in vertical motions, stress fields, and magmatism. In a terminal-stage <span class="hlt">subduction</span> zone, involving collision and suturing, slab detachment is the natural last stage in the gravitational settling of <span class="hlt">subducted</span> lithosphere. PMID:11110653</p> <div class="credits"> <p class="dwt_author">Wortel, M J; Spakman, W</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">236</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011E%26PSL.303...59C"> <span id="translatedtitle">Are diamond-bearing Cretaceous kimberlites related to low-angle <span class="hlt">subduction</span> beneath western North America?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Diamond-bearing Cretaceous kimberlites of western North America were emplaced 1000-1500 km inboard of the Farallon plate <span class="hlt">subduction</span> margin and overlap with the development of the Western Interior Seaway, shut-down of the Sierra Nevada arc, and the Laramide orogeny. These events are consistent with a decrease in <span class="hlt">subduction</span> angle along much of the margin, which placed the <span class="hlt">subducted</span> Farallon plate in close proximity to the continental interior at the time of kimberlite magmatism. Our numerical models demonstrate that low-angle <span class="hlt">subduction</span> can result from high plate convergence velocities and enhanced westward motion of North America. Further, rapid <span class="hlt">subduction</span> allows hydrous minerals to remain stable within the cool interior of the <span class="hlt">subducting</span> plate to more than 1200 km from the <span class="hlt">trench</span>. Destabilization of these minerals provides a fluid source that can infiltrate the overlying material, potentially triggering partial melting and kimberlite/lamproite magmatism.</p> <div class="credits"> <p class="dwt_author">Currie, Claire A.; Beaumont, Christopher</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">237</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.1209O"> <span id="translatedtitle">Present-day chaotic formations around the Japanese <span class="hlt">trenches</span>: Comparison to the on land examples from the Shimanto and Miura-Boso, and from the Franciscan, Mineoka and Ankara</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Four different types of chaotic formations were recognized by the submersible observation around the Japanese <span class="hlt">trenches</span>, including the Nankai and Sagami troughs, Boso triple junction, <span class="hlt">Japan</span> <span class="hlt">trench</span>, and Izu-Bonin arc, and each type is summarized and discussed in view of comparison to the on land examples, such as from the Franciscan, Shimanto and Miura-Boso belts in the circum Pacifc margins, and the Ankara. The submarine geologies are present actual examples to give us a critical key to understanding the formation processes and emplacement mechanisms for the so-called mélange bodies, either sedimentary, tectonic or diapiric. Some are made of alternated beds of sandstone and mudstone that show broken or block-in-matrix fashion, in most cases in muddy matrix. These are commonly developed on the <span class="hlt">trench</span> landward slope toe of the Nankai and Sagami troughs and Boso triple junction area as well as the <span class="hlt">Japan</span> <span class="hlt">trench</span> slope. One type is from the landward slope, but another type is from the oceanward slopes. The former type is in places calcareous cemented, probably caused by hydraulic fracturing by high pore pressure along the thrust fault and oxidized methane-made carbonate precipitation. They are seen on the feet of the thrust-dominated slope and to be compared to the so-called sedimentary mélanges due to the gravitational sliding, which occur because of tectonically induced steep slopes. Most of such thrusts are related to large <span class="hlt">subduction</span> type earthquakes, and await for further critical consideration on to the relation to the asperity problem. Some of large scale gravitational collapses may be related to the seamount or ridge <span class="hlt">subduction</span> to the <span class="hlt">trench</span>, both in case of accretionary and non-accretionary type margins, the former is for the examples from the Nankai and Sagami troughs and the Boso triple junction, latter for the <span class="hlt">Japan</span> <span class="hlt">trench</span>. In all cases on land and under the sea in the <span class="hlt">trench</span> landward slope, some calcareous breccias are associated with methane-fluid supported animals within injection or diapiric intrusion. On the other hand, in the Nankai prism and the on land Miura-Boso Peninsulas, many examples of sandy matrix supported mudstone breccia are a result of liquefaction and injection of such coarse-grained clastic fragments during the earthquake shake and subsequent landsliding. Those deposits are faulted, folded and injected in various stages, some before accretionary prism incorporation, some after. Some are of sedimentary origin by gravitational process, others tectonic or diapiric, but in most cases thrust duplexes and complex folds are common. The third and fourth are mélanges including igneous, metamorphic and/or ophiolitic rock blocks. They look similar to the on land examples in the Franciscan, Mineoka (Boso, central <span class="hlt">Japan</span>) and the Ankara, and used to be attributable to the diapiric origin, as those that have been already known as serpenitine mud volcanoes with metamorphic block at the foot of the Izu-Bonin-Mariana forearc. However, such analogue need careful consideration how the rock association would form to the final emplacement. As the fourth new type, we found an example of deep (1.5 to 2 GPa) metamorphic rock blocks of eclogitic conditions from the fault line in the schistose serpentinite (antigorite-dominated) in the middle part of the Izu arc near the Ohmachi seamount. This implies for the incorporation and exhumation of igneous and metamorphic rocks in the island arc setting, and may give an adequate analogue to the specific mélange formation of the Franciscan, Mineoka and Ankara.</p> <div class="credits"> <p class="dwt_author">Ogawa, Yujiro; Kawamura, Kiichiro; Tsunogae, Toshiaki; Mori, Ryota; Chiba, Tae; Sasaki, Tomoyuki</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">238</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFM.T53D..03L"> <span id="translatedtitle">The <span class="hlt">subduction</span> zone flow field from seismic anisotropy: A global view</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Understanding the flow field that accompanies <span class="hlt">subduction</span> remains one of the important unsolved problems in the Earth sciences, since it has implications for mantle dynamics, the tectonics of the back-arc region, and the physical and chemical characteristics of arc volcanism. An important constraint on this flow field is provided by observations of seismic anisotropy, as manifested by shear-wave splitting. We have compiled a global splitting data set (including previously published studies and new measurements) for 12 <span class="hlt">subduction</span> zones worldwide and have searched for trends by comparing splitting observations with tectonic parameters. We find systematic variations in both mantle-wedge and sub-slab anisotropy with <span class="hlt">trench</span>-migration velocity, Vt, referenced to a hotspot reference frame. These variations are most simply explained by the creation of a three-dimensional <span class="hlt">trench</span>-parallel flow field induced by this <span class="hlt">trench</span> motion. In particular, we find that in the subslab region, <span class="hlt">trench</span>- parallel flow dominates the flow field and its magnitude scales with Vt. In the mantle wedge, the <span class="hlt">trench</span>- parallel flow field interacts with classical 2-D corner flow produced by the convergence of the two plates. The relative influence of these two flows is governed by the relative magnitude of Vt and the convergence velocity, Vc. Thus, <span class="hlt">trench</span> migration constitutes a first-order property in controlling the flow field accompanying the <span class="hlt">subduction</span> process.</p> <div class="credits"> <p class="dwt_author">Long, M. D.; Silver, P. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">239</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EGUGA..14.1433G"> <span id="translatedtitle">New approach to analysis of strongest earthquakes with upper-value magnitude in <span class="hlt">subduction</span> zones and induced by them catastrophic tsunamis on examples of catastrophic events in 21 century</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The study of generation of strongest earthquakes with upper-value magnitude (near above 9) and induced by them catastrophic tsunamis, is performed by authors on the basis of new approach to the generation process, occurring in <span class="hlt">subduction</span> zones under earthquake. The necessity of performing of such studies is connected with recent 11 March 2011 catastrophic underwater earthquake close to north-east <span class="hlt">Japan</span> coastline and following it catastrophic tsunami which had led to vast victims and colossal damage for <span class="hlt">Japan</span>. The essential importance in this study is determined by unexpected for all specialists the strength of earthquake occurred (determined by magnitude M = 9), inducing strongest tsunami with wave height runup on the beach up to 10 meters. The elaborated by us model of interaction of ocean lithosphere with island-arc blocks in <span class="hlt">subduction</span> zones, with taking into account of incomplete stress discharge at realization of seismic process and further accumulation of elastic energy, permits to explain arising of strongest mega-earthquakes, such as catastrophic earthquake with source in <span class="hlt">Japan</span> deep-sea <span class="hlt">trench</span> in March, 2011. In our model, the wide possibility for numerical simulation of dynamical behaviour of underwater seismic source is provided by kinematical model of seismic source as well as by elaborated by authors numerical program for calculation of tsunami wave generation by dynamical and kinematical seismic sources. The method obtained permits take into account the contribution of residual tectonic stress in lithosphere plates, leading to increase of earthquake energy, which is usually not taken into account up to date.</p> <div class="credits"> <p class="dwt_author">Garagash, I. A.; Lobkovsky, L. I.; Mazova, R. Kh.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">240</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFMDI31A1932B"> <span id="translatedtitle">2D numerical modelling of intra-oceanic arc extension and <span class="hlt">trench</span> migration</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Modern intra-oceanic <span class="hlt">subduction</span> zones often develop series of magmatic chains and basins (Stern et al., 2002), (Takahashi, 2008/09), (Larter 2003) and it is not yet fully understood how and why these structures develop. We performed systematic numerical experiments with a 2D coupled petrological-thermo-mechanical numerical model of an intra-oceanic <span class="hlt">subduction</span> process. Our model includes different slab push velocities, different weakening effects (dehydration of the <span class="hlt">subducted</span> crust, aqueous fluid transport, partial melting of both crustal and mantle rocks and melt extraction processes), different ages of the <span class="hlt">subduction</span> slab and the overriding plate as well as spontaneous slab bending. With a long-term model of <span class="hlt">subduction</span> dynamics, we tested the effects of geometry, rheology, composition, dehydration and melting processes and their influences to the development of extension or compression in intra-oceanic arcs. Based on numerical results we established three different types of extension regimes: i) extension in the fore-arc, ii) extension within the magmatic arc, and iii) no extension, but compression. In general, in all our experiments, the first spreading episode mostly occurs in the fore-arc. Such fore-arc spreading can be observed in the very eastern part of the Aleutian arc system, where decompression melt pierces the thin crust and/or pushes the magmatic arc away from the <span class="hlt">trench</span> and it becomes a paleoarc, similar to the Kyushu-Palau Ridge (Stern et al., 2003). At the same time a new magmatic arc grows between the <span class="hlt">trench</span> and the spreading centre. Some experiments show an intra-arc-spreading, such as the active Mariana arc and the inactive West Mariana Ridge (split an initially homogeneous arc into two distinct parts), (Stern et al., 2003). We also found four different <span class="hlt">trench</span> migration patterns depending on the degree of coupling between the plates: i) <span class="hlt">trench</span> retreating, ii) episodic retreating and advancing with a total retreat of the <span class="hlt">trench</span>, iii) <span class="hlt">trench</span> advancing, iv) stable <span class="hlt">trench</span> position over time. Our numerical results on episodic <span class="hlt">trench</span> movements match well with natural observations (Clark et al., 2008) concerning the periodicity in the back-arc tectonic regimes.</p> <div class="credits"> <p class="dwt_author">Baitsch Ghirardello, B.; Gerya, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_11");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" 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showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_14");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">241</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.geology.wisc.edu/~chuck/PDF/FCM_Oax_GJI08.pdf"> <span id="translatedtitle">Interplate coupling and transient slip along the <span class="hlt">subduction</span> interface beneath Oaxaca, Mexico</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We describe and model GPS measurements of surface deformation from the Oaxaca segment of the Mexican <span class="hlt">subduction</span> zone to characterize interseismic strain accumulation and episodic transient slip in this region and test seismologically-based models of strain accumulation and release along <span class="hlt">subduction</span> interfaces. Deformation measured from 2001 to 2007 within our dense 31-station GPS array has consisted of (1) <span class="hlt">trench</span>-normal horizontal</p> <div class="credits"> <p class="dwt_author">F. Correa-Mora; C. Demets; E. Cabral-Cano; B. Marquez-Azua; O. Diaz-Molina</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">242</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52225377"> <span id="translatedtitle">Episodic tremor and slip along the Rivera and Cocos <span class="hlt">subduction</span> zones of southern Mexico</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The southern coast of Mexico is marked by active <span class="hlt">subduction</span> of the Rivera and Cocos plates, producing frequent megathrust earthquakes with a 50-100 year recurrence. The variable convergence rate, <span class="hlt">subduction</span> angle, and <span class="hlt">trench</span>-to-coast distance affects the distribution of the seismogenic and transition zone, making an ideal study area for characterizing the relationship between earthquakes, nonvolcanic tremor (NVT) and slow slip</p> <div class="credits"> <p class="dwt_author">K. M. Schlanser; M. R. Brudzinski; N. J. Kelly; S. P. Grand; E. Cabral-Cano; C. Demets</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">243</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GeoRL..3923301K"> <span id="translatedtitle">Elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the Nankai Trough <span class="hlt">subduction</span> megathrust</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent seismic reflection and ocean bottom seismometer (OBS) studies reveal broad regions of low seismic velocity along the Nankai <span class="hlt">subduction</span> plate boundary megathrust offshore SW <span class="hlt">Japan</span>. These low velocity zones (LVZ's) extend ˜55 km landward from the <span class="hlt">trench</span>, corresponding to depths of >˜10 km below sea floor. Here, we estimate the in-situ pore pressure and stress state within these LVZ's by combining P-wave velocities obtained from the geophysical surveys with new well-constrained empirical relations between P-wave velocity, porosity, and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment. We document excess pore pressures of 17-87 MPa that extend ˜55 km into the <span class="hlt">subduction</span> zone, indicating that trapped pore fluids support ˜45-91% of the overburden stress along the base of the upper plate and surrounding major fault zones. The resulting effective stresses in the LVZ are limited to ˜1/3 of the values expected for non-overpressured conditions. These low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary. The region of lowest effective stress coincides with precisely located very low frequency earthquakes, providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure.</p> <div class="credits"> <p class="dwt_author">Kitajima, Hiroko; Saffer, Demian M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">244</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.T22B..03C"> <span id="translatedtitle">Fluid flow in ocean crust cools the Cascadia <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Temperatures along <span class="hlt">subduction</span> zone plate boundary faults have been used to estimate the area and extent of the seismogenic zone. Recent studies of the well-constrained Nankai margin of <span class="hlt">Japan</span> show that hydrothermal circulation in the <span class="hlt">subducting</span> crust cools the <span class="hlt">subduction</span> zone and widens the area of the plate boundary fault that is between the key temperatures of 150 and 350 °C. Here, we present new thermal models for the Cascadia <span class="hlt">subduction</span> zone that include the effects of fluid flow in the <span class="hlt">subducting</span> crust. This fluid circulation cools the <span class="hlt">subduction</span> zone and widens the thermally-defined seismogenic zone by shifting the intersection of 350 °C with the plate boundary fault ˜35-50 km landward. Temperatures in the region of episodic tremor and slip are ~350-450 °C, ˜100 °C cooler than based on estimates that do not include fluid circulation. In contrast to the Nankai margin, the observed surface heat flux pattern for the thickly sedimented Cascadia margin provides only a weak constraint on <span class="hlt">subduction</span> zone temperature. We use the tomographically-defined basalt-to-eclogite transition in the <span class="hlt">subducting</span> slab as an additional constraint on the Cascadia <span class="hlt">subduction</span> zone thermal models. The model most consistent with both the slab alteration observations and surface heat flux measurements includes moderate to vigorous fluid flow in an ocean crust aquifer with permeability ~10-10 to 10-9 m2, consistent with previous observations and inferences.</p> <div class="credits"> <p class="dwt_author">Cozzens, B. D.; Spinelli, G. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">245</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JGeo...66..134C"> <span id="translatedtitle">Sediment loading at the southern Chilean <span class="hlt">trench</span> and its tectonic implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Non erosive margins are characterized by heavily sedimented <span class="hlt">trenches</span> which obscure the morphological expression of the outer rise; a forebulge formed by the bending of the <span class="hlt">subducting</span> oceanic lithosphere seaward of the <span class="hlt">trench</span>. Depending on the flexural rigidity (D) of the oceanic lithosphere and the thickness of the <span class="hlt">trench</span> sedimentary fill, sediment loading can affect the lithospheric downward deflection in the vicinity of the <span class="hlt">trench</span> and hence the amount of sediment <span class="hlt">subducted</span>. We used seismic and bathymetric data acquired off south central Chile, from which representative flexural rigidities are estimated and the downward deflection of the oceanic Nazca plate is studied. By flexural modeling we found that efficient sediment <span class="hlt">subduction</span> preferentially occurs in weak oceanic lithosphere (low D), whereas wide accretionary prisms are usually formed in rigid oceanic lithosphere (high D). In addition, well developed forebulges in strong oceanic plates behaves as barrier to seaward transportation of turbidites, whereas the absence of a forebulge in weak oceanic plates facilitates seaward turbidite transportation for distances >200 km.</p> <div class="credits"> <p class="dwt_author">Contreras-Reyes, Eduardo; Jara, Jorge; Maksymowicz, Andrei; Weinrebe, Wilhelm</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">246</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53550555"> <span id="translatedtitle">The Elephant <span class="hlt">Trench</span> at Dewlish</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">IN the hope of finding an explanation as to the origin of the so-called elephant <span class="hlt">trench</span> at Dewlish, Mr. Clement Reid (NATURE, vol. xcii., p. 96), asks if; under desert conditions, there is any tendency for winds to cut <span class="hlt">trenches</span> with rounded blind ends in soft limestone deposits. Having travelled in the Egyptian and other deserts, and having camped for</p> <div class="credits"> <p class="dwt_author">H. T. Ferrar</p> <p class="dwt_publisher"></p> <p class="publishDate">1913-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">247</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009GeoJI.176..951H"> <span id="translatedtitle">Developing framework to constrain the geometry of the seismic rupture plane on <span class="hlt">subduction</span> interfaces a priori - a probabilistic approach</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A key step in many earthquake source inversions requires knowledge of the geometry of the fault surface on which the earthquake occurred. Our knowledge of this surface is often uncertain, however, and as a result fault geometry misinterpretation can map into significant error in the final temporal and spatial slip patterns of these inversions. Relying solely on an initial hypocentre and CMT mechanism can be problematic when establishing rupture characteristics needed for rapid tsunami and ground shaking estimates. Here, we attempt to improve the quality of fast finite-fault inversion results by combining several independent and complementary data sets to more accurately constrain the geometry of the seismic rupture plane of <span class="hlt">subducting</span> slabs. Unlike previous analyses aimed at defining the general form of the plate interface, we require mechanisms and locations of the seismicity considered in our inversions to be consistent with their occurrence on the plate interface, by limiting events to those with well-constrained depths and with CMT solutions indicative of shallow-dip thrust faulting. We construct probability density functions about each location based on formal assumptions of their depth uncertainty and use these constraints to solve for the `most-likely' fault plane. Examples are shown for the <span class="hlt">trench</span> in the source region of the Mw 8.6 Southern Sumatra earthquake of March 2005, and for the Northern Chile <span class="hlt">Trench</span> in the source region of the November 2007 Antofagasta earthquake. We also show examples using only the historic catalogues in regions without recent great earthquakes, such as the <span class="hlt">Japan</span> and Kamchatka <span class="hlt">Trenches</span>. In most cases, this method produces a fault plane that is more consistent with all of the data available than is the plane implied by the initial hypocentre and CMT mechanism. Using the aggregated data sets, we have developed an algorithm to rapidly determine more accurate initial fault plane geometries for source inversions of future earthquakes.</p> <div class="credits"> <p class="dwt_author">Hayes, Gavin P.; Wald, David J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">248</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..1512192C"> <span id="translatedtitle"><span class="hlt">Subduction</span> of fracture zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Since Wilson proposed in 1965 the existence of a new class of faults on the ocean floor, namely transform faults, the geodynamic effects and importance of fracture zone <span class="hlt">subduction</span> is still little studied. It is known that oceanic plates are characterized by numerous fracture zones, and some of them have the potential to transport into <span class="hlt">subduction</span> zones large volumes of water-rich serpentinite, providing a fertile water source for magma generated in <span class="hlt">subduction</span>-related arc volcanoes. In most previous geodynamic studies, <span class="hlt">subducting</span> plates are considered to be homogeneous, and there is no clear indication how the <span class="hlt">subduction</span> of a fracture zone influences the melting pattern in the mantle wedge and the slab-derived fluids distribution in the subarc mantle. Here we show that <span class="hlt">subduction</span> of serpentinized fracture zones plays a significant role in distribution of melt and fluids in the mantle wedge above the slab. Using high-resolution tree-dimensional coupled petrological-termomechanical simulations of <span class="hlt">subduction</span>, we show that fluids, including melts and water, vary dramatically in the region where a serpentinized fracture zone enters into <span class="hlt">subduction</span>. Our models show that substantial hydration and partial melting tend to concentrate where fracture zones are being <span class="hlt">subducted</span>, creating favorable conditions for partially molten hydrous plumes to develop. These results are consistent with the along-arc variability in magma source compositions and processes in several regions, as the Aleutian Arc, the Cascades, the Southern Mexican Volcanic Arc, and the Andean Southern Volcanic Zone.</p> <div class="credits"> <p class="dwt_author">Constantin Manea, Vlad; Gerya, Taras; Manea, Marina; Zhu, Guizhi; Leeman, William</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">249</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48931482"> <span id="translatedtitle">Kinematics and flow patterns in deep mantle and upper mantle <span class="hlt">subduction</span> models: Influence of the mantle depth and slab to mantle viscosity ratio</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Three-dimensional fluid dynamic laboratory simulations are presented that investigate the <span class="hlt">subduction</span> process in two mantle models, an upper mantle model and a deep mantle model, and for various <span class="hlt">subducting</span> plate\\/mantle viscosity ratios (?SP\\/?M = 59–1375). The models investigate the mantle flow field, geometrical evolution of the slab, sinking kinematics, and relative contributions of <span class="hlt">subducting</span> plate motion and <span class="hlt">trench</span> migration to</p> <div class="credits"> <p class="dwt_author">W. P. Schellart</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">250</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012E%26PSL.353...29C"> <span id="translatedtitle">Complex mantle flow around heterogeneous <span class="hlt">subducting</span> oceanic plates</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The foundering of oceanic lithospheres controls the circulation patterns of the mantle around <span class="hlt">subducting</span> slabs. Here, we investigate the sensitivity of the mantle flow to slab buoyancy variations along convergent margins using three-dimensional numerical models of <span class="hlt">subduction</span> in a viscous mantle. The models illustrate that in a buoyancy-driven system varying <span class="hlt">subduction</span> velocity arising from negative buoyancy variations effectively drives pressure gradients and confers a general flow component sub-parallel to the margin's strike, allowing for material transport over large distances around the slabs. The along-slab velocity component introduces widespread horizontal simple shear in the mantle flow which is maximized beneath the slab between ˜100 and ˜350 km. Mantle flow complexities develop rapidly, although not instantaneously, upon <span class="hlt">subduction</span> of heterogeneous plates. The resulting slab pull gradients are mostly accommodated by internal slab deformation, decoupling the mantle flow from motions at surface. Moderate slab pull variations have a minor impact on plate velocity, and might not result in <span class="hlt">trench</span> motions, although effectively rearrange the flow. Slab buoyancy heterogeneities are firstly associated with age-dependent thickness variations, but also with slab break offs and windows, varying depth of <span class="hlt">subduction</span> and entrainment of buoyant blocks. Because these are observed at all <span class="hlt">subduction</span> zones, the process shown here should have a global relevance for the flow around slabs.</p> <div class="credits"> <p class="dwt_author">Capitanio, Fabio A.; Faccenda, Manuele</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">251</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFM.V43D1636H"> <span id="translatedtitle">Regional variation in shear-wave splitting in <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Nakajima and Hasegawa [2004] and Nakajima et al. [2006] investigated shear-wave splitting in northeastern <span class="hlt">Japan</span> and found a striking rotation of fast direction across the arc, suggesting the different nature of anisotropy between the fore-arc and back-arc sides. <span class="hlt">Trench</span>-parallel fast directions are observed in the fore-arc side, while fast directions observed in the back-arc side show approximately E-W or ESE-WNW in the NE <span class="hlt">Japan</span> arc and N-S in the southwestern Kurile arc, which are characterized by the local dip direction of the <span class="hlt">subducted</span> Pacific plate. In this study, we investigate shear-wave splitting beneath SW <span class="hlt">Japan</span> using local S phases to constrain a spatial pattern of mantle flow generated by the <span class="hlt">subduction</span> of the Pacific and Philippine Sea plates. The <span class="hlt">subduction</span> of the two oceanic plates probably has resulted in a complicated upper mantle structure. Therefore this region is an excellent natural laboratory for studying the effect of local slab geometry and the <span class="hlt">subduction</span> of two slabs on mantle corner flow. We applied the cross-correlation method [Ando et al., 1983] to S-wave arrivals of local events to constrain fast polarization directions and delay time between fast- and slow-shear waves for each event and station pair. In the cross-correlation method, seismograms are rotated at angles ranging from 0 to 175 degrees in steps of 5 degrees. One of the horizontal components is shifted by a time lag ranging from 0 to 1 sec with an interval of 0.01 sec. The length of the time window used to calculate the correlation coefficient was set to nearly equal to one cycle of the wave. When the value of cross-correlation coefficient reaches its maximum, the direction of rotation is regarded as the fast direction, and the amount of time lag as the delay time. If the maximum cross-correlation coefficient is less than 0.8, the data is rejected. All of the observed seismograms were filtered with band-passed ranges of 2-8 Hz. Waveforms of 557 intermediate-depth earthquakes recorded at 457 seismic stations were used, and 2062 splitting parameters, the leading shear-wave polarization direction (fast direction) and delay time between two split waves, were observed. The obtained results show that most fast directions observed in SW <span class="hlt">Japan</span> are nearly E-W, which is roughly consistent with the direction of the maximum dip direction of the Pacific plate. We also found that fast directions polarized in N-S are locally observed around the Hida Mountains, central <span class="hlt">Japan</span>, which has been pointed out by the previous studies [e.g., Ando et al., 1983; Hiramatsu et al., 1998]. This direction is sub-parallel to the maximum-dip direction of the <span class="hlt">subducted</span> Philippine Sea plate and hence this anisotropy is inferred to be related to a mantle return flow generated by the <span class="hlt">subduction</span> of the Philippine Sea plate.</p> <div class="credits"> <p class="dwt_author">Hori, S.; Nakajima, J.; Hasegawa, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">252</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AGUFM.T11D..08F"> <span id="translatedtitle">Lithospheric Scale Deformation in Mega-thrust <span class="hlt">Subduction</span> Zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Although the general plate tectonic model of <span class="hlt">subduction</span> zone deformation and its relationship to the earthquake cycle for mega-thrust earthquakes is well known, there is neither consistency in such descriptions nor compatibility among seismological, geodetic, and geologic frameworks for such events. In particular in most seismologic studies of mega-thrust earthquakes there is an implicit assumption that the co-seismic slip is essentially symmetric across the fault surface - that is both the upper and lower plates moved equal amounts (but in opposite directions) during the rupture. Implicit in many geologic studies along convergent margins is the assumption that most permanent deformation is within the upper plate and the <span class="hlt">subducting</span> slab basically transits the seismogenic zone with little permanent deformation. This perspective serves as the framework for many animations of <span class="hlt">subduction</span> zone tectonics. Two <span class="hlt">subduction</span> zone locales, the Kuriles and Solomon Islands, that have hosted recent Mw 8+ earthquakes demonstrate two end-member styles of <span class="hlt">subduction</span> zone processes neither consistent with the conventional view. The November 2006 (thrust) and January 2007 (normal) earthquake pair in the Kuriles provide an opportunity to quantify the deformation within the <span class="hlt">subducting</span> Pacific slab during the interseismic period. Based on the correspondence in slip during these events, we are able to both estimate the deformation (dominantly in the <span class="hlt">subducting</span> slab and not in the overriding plate) and place a constraint on the static frictional strength of the megathrust interface of approximately 2-5 MPa. The 2007 Solomon Island Mw 8+ earthquake shows a distinctly different pattern of interseismic deformation. During this event, the propagating rupture traversed an active transform plate boundary between the separately <span class="hlt">subducting</span> Australia and Solomon Sea plates. We interpret this to represent a situation in which interseismic deformation is primarily in the upper (Pacific) plate allowing the rupture to jump the fundamental barrier of a plate boundary. This is also compatible with limited GPS data available for the Australia plate near the <span class="hlt">trench</span> indicating unimpeded <span class="hlt">subduction</span> of Australia and thus little internal deformation of the <span class="hlt">subducting</span> slab. These two <span class="hlt">subduction</span> regimes indicate that there is likely a full continuum in how deformation is accommodated during <span class="hlt">subduction</span>, and implies that attempts to determine the megathrust (and associated tsunami) potential of <span class="hlt">subduction</span> zones using observations of upper-plate deformation is problematic.</p> <div class="credits"> <p class="dwt_author">Furlong, K. P.; Ammon, C.; Lay, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">253</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMDI43B..04K"> <span id="translatedtitle"><span class="hlt">Subduction</span>: The Gatekeeper for Mantle Melting.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Geodynamic models are used to show the importance of <span class="hlt">subduction</span> in controlling vertical thermal and chemical fluxes from Earth's interior to surface. In our models <span class="hlt">subduction</span>-induced circulation produces conditions favorable to both steady-state and episodic melt production and also plays the role of gatekeeper in thwarting large scale melt production from rising plumes. We use laboratory experiments to characterize three-dimensional (3D) flow fields in convergent margins in response to a range of <span class="hlt">subduction</span> and back-arc deformation styles, and how these flows interact with upwellings. Models utilize a glucose working fluid with a temperature dependent viscosity to represent the upper 2000 km of the mantle. <span class="hlt">Subducting</span> lithosphere is modeled with a descending Phenolic plate and back-arc extension is produced by moving Mylar sheets. Thermal plumes are generated from a pressurized, temperature controlled source. Our results show that naturally occurring transitions from downdip- to rollback-dominated <span class="hlt">subduction</span> produce conditions that favor both widespread decompression melting in the mantle wedge and short-lived pulses of extensive slab melting. For cases of plume-<span class="hlt">subduction</span> interaction, 3D slab-induced flow quickly converts the active upwelling to a passive thermal anomaly that bears little to no resemblance to traditional models for plume surface expressions. Instead of rising to make LIPs with age-progressive chains, the bulk of the original plume material is trapped below depths of melt production before being re-<span class="hlt">subducted</span> by the slab. A limited volume of this passive, former plume material is capable of surfacing. Interestingly, this is seen to occur through a range of morphologies that are consistently offset from the original rise location (e.g., conduit). Surface expressions include anything from small circular patches to long, linear features with complex age trends (e.g., progressive or regressive) resulting from the competition between plate motions and deeper mantle flow. Spatial-temporal patterns in melt production, beyond those from background 3D flow, are extremely sensitive to the position of the deep plume relative to the <span class="hlt">trench</span>. For example, the timing, volume and distribution of melt for upwellings originating beneath the back-arc plate (e.g. Yellowstone) are fundamentally different from those rising under the ocean side of the slab (e.g. Samoa).</p> <div class="credits"> <p class="dwt_author">Kincaid, C. R.; Druken, K. A.; Griffiths, R. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">254</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41154763"> <span id="translatedtitle">Aligned buoyant highs, across-<span class="hlt">trench</span> deformation, clustered volcanoes, and deep earthquakes are not aligned with plate-tectonic theory</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Bathymetry shows the regional interaction of aseismic, buoyant highs in northern Pacific <span class="hlt">subduction</span> zones. Seamounts, ridges, and fractures on the seaward side of the <span class="hlt">trench</span> are associated with events that do not support the accepted plate-tectonics paradigm, including an altered slab dip angle (Benioff zone) and the clustered volcanoes and earthquakes within the convergent margin. Most of the examples in</p> <div class="credits"> <p class="dwt_author">N. Christian Smoot</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">255</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40845934"> <span id="translatedtitle"><span class="hlt">Subduction</span> of the South China Sea axial ridge below Luzon (Philippines)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Scarborough Seamount chain, present at the axis of the extinct South China Sea spreading center, is being <span class="hlt">subducted</span> obliquely along the Manila <span class="hlt">Trench</span>. A detailed Seabeam survey of this convergent zone reveals that the fabric of the ridge is characterized by N60°E trending normal faults and N130°E transform faults. This ridge can be traced into the forearc area. This</p> <div class="credits"> <p class="dwt_author">G. Pautot; C. Rangin</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">256</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/41988356"> <span id="translatedtitle">On the mechanism of seismic decoupling and back arc spreading at <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">To address the problem of the great variability of the mechanical state of <span class="hlt">subduction</span> zones, we investigate the mechanics of back arc spreading and seismic decoupling. Back arc spreading is assumed to be due to rifting of the upper plate and hence occurs when <span class="hlt">trench</span>-normal tension reaches a critical value. Seismic decoupling is assumed to occur when the normal stress</p> <div class="credits"> <p class="dwt_author">C. H. Scholz; J. Campos</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">257</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/49306965"> <span id="translatedtitle">The timescales of <span class="hlt">subduction</span> initiation and subsequent evolution of an oceanic island arc</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The Bonin Ridge and <span class="hlt">trench</span> slope preserves the geological record of <span class="hlt">subduction</span> initiation and subsequent evolution of the Izu–Bonin–Mariana (IBM) arc. Diving and dredging in this region has revealed a bottom to top stratigraphy of: 1) mantle peridotite, 2) gabbroic rocks, 3) a sheeted dyke complex, 4) basaltic pillow lavas, 5) boninites and magnesian andesites, 6) tholeiites and calcalkaline arc</p> <div class="credits"> <p class="dwt_author">Osamu Ishizuka; Kenichiro Tani; Mark K. Reagan; Kyoko Kanayama; Susumu Umino; Yumiko Harigane; Izumi Sakamoto; Yuki Miyajima; Makoto Yuasa; Daniel J. Dunkley</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">258</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012E%26PSL.355..262K"> <span id="translatedtitle">Shear-wave splitting at the edge of the Ryukyu <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Intraslab events recorded by ocean-bottom seismometers in the Okinawa trough provide an extended depiction of shear wave splitting in the southwest section of the Ryukyu <span class="hlt">subduction</span> zone. At 100-200 km from the western edge of the <span class="hlt">subduction</span> system, we observed <span class="hlt">trench</span>-normal fast polarization direction in the back arc compatible with 2D slab- or rifting-driven corner flow. Towards the edge, the fast directions are sub-parallel to the <span class="hlt">trench</span> in the arc—back arc region, and rotate to <span class="hlt">trench</span>-normal within 50 km of the edge. Splitting constrained by land stations with paths mostly in the mantle wedge exhibits similar <span class="hlt">trench</span>-normal fast directions in the <span class="hlt">subduction</span> edge zone. Further inland, the dominant component of fast directions becomes roughly parallel to the Taiwan orogenic fabric. Splitting of P-to-S phases converted at the Moho of the Okinawa trough and of S phases from shallow events suggest that crustal anisotropy may affect the measured splitting, but the observed pattern reflects predominantly mantle anisotropy. The variation in splitting along the Okinawa trough cannot be explained by a B-type-A-type olivine fabric transition in the mantle wedge. It may indicate the presence of an along-arc flow in the mantle wedge towards the edge where it is blocked and deflected by the Eurasian lithosphere. This scenario bolsters previous studies suggesting a significant impact of Eurasian lithosphere on the dynamics of the Ryukyu <span class="hlt">subduction</span> system.</p> <div class="credits"> <p class="dwt_author">Kuo, Ban-Yuan; Wang, Chau-Chang; Lin, Shu-Chuan; Lin, Ching-Ren; Chen, Po-Chi; Jang, Jia-Pu; Chang, Hsu-Kuang</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">259</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53240190"> <span id="translatedtitle">Slip histories of six large <span class="hlt">subduction</span> earthquakes from 1990 to 2004</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Recent studies reveal a statistically significant correlation between the high slip regions of large <span class="hlt">subduction</span> earthquakes and local geological and geophysical anomalies in the forearc, such as <span class="hlt">trench</span> parallel gravity anomalies (TPGA, Song and Simons, 2003) and deep-sea terrace lows (DSTL, Wells, et al., 2003). To verify and further quantify such a relationship and to explore the relationship between rupture</p> <div class="credits"> <p class="dwt_author">G. Shao; C. Ji; M. Simons</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">260</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54738807"> <span id="translatedtitle">Comparison of slip distribution of large slow slip events in Guerrero <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Aseismic slow slip events (SSEs) have been reported in most of the well geodetically instrumented <span class="hlt">subduction</span> zones worldwide (<span class="hlt">Japan</span>, Cascadia, Mexico, New Zealand, Costa Rica, Alaska). For most of the observed SSEs, the slip distribution on the <span class="hlt">subduction</span> interface was inferred from the surface GPS displacements to be located at the downdip extension of the seismogenic zone, in the conditionally</p> <div class="credits"> <p class="dwt_author">F. Cotton; M. Vergnolle; O. Thollon; M. Campillo; I. Manighetti; N. Cotte; A. Walpersdorf; V. Kostoglodov</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_12");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">261</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007AGUFM.T53A1107M"> <span id="translatedtitle">Crustal structure around the asperity regions of large earthquakes along the southernmost Kuril <span class="hlt">trench</span> revealed by two Airgun-OBS seismic profilings</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In the southeast off Hokkaido, <span class="hlt">Japan</span>, large earthquakes have occurred repeatedly with temporal and spatial regularities along the Kuril <span class="hlt">trench</span> due to the <span class="hlt">subduction</span> of Pacific plate at a rate of 80 mm/year (DeMets et al., 1990) [e.g. the 1952 Tokachi-oki earthquake (Mw=8.2), the 1973 Nemuro-oki earthquake (Mw=7.8) and the 2003 Tokachi-oki earthquake (Mw=8.2)]. It is considered that the next large earthquake will occur at the source region of the 1973 Nemuro-oki earthquake in the near future because a low seismic activity has been found in the off shore region of the Nemuro peninsula. In order to clarify the relation between asperity and the recurrence of large earthquake, it is necessary to determine a detailed crustal structure running across the two asperities of the 2003 Tokachi-oki earthquake and 1973 Nemuro-oki earthquake. Therefore we conducted a wide-angle survey across the coseismic rupture areas of the 2003 Tokachi-oki and 1973 Nemuro-oki earthquakes and the afterslip area of the 2003 Tokachi-oki earthquake parallel (profile-A) and perpendicular (profile-B) to the Kuril <span class="hlt">trench</span> using Ocean Bottom Seismometers (OBSs). In profile-A, 19 OBSs were deployed at a spacing of about 10km and three 25 liter air-guns were fired every 90 seconds which corresponds to a shot interval of about 230m. In profile-B, 11 OBSs were deployed at a spacing of about 11km and two 25 liter airguns were fired every 60 seconds which corresponds to a shot interval of about 150m. In this presentation, we report on the crustal structure using the data obtained in the profile A and B and compare our results with past researches around this region. This study is founded by the Ministry of Education, Culture, Sports, Science and Technology, <span class="hlt">Japan</span>.</p> <div class="credits"> <p class="dwt_author">Machida, Y.; Takanami, T.; Murai, Y.; Amamiya, S.; Nishimura, Y.; Shinohara, M.; McHizuki, K.; Yamada, T.; Nakahigashi, K.; Kuwano, A.; Kanazawa, T.; Hino, R.; Azuma, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">262</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013SolE....4..179G"> <span id="translatedtitle">The dynamics of laterally variable <span class="hlt">subductions</span>: laboratory models applied to the Hellenides</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We designed three-dimensional dynamically self-consistent laboratory models of <span class="hlt">subduction</span> to analyse the relationships between overriding plate deformation and <span class="hlt">subduction</span> dynamics in the upper mantle. We investigated the effects of the <span class="hlt">subduction</span> of a lithosphere of laterally variable buoyancy on the temporal evolution of <span class="hlt">trench</span> kinematics and shape, horizontal flow at the top of the asthenosphere, dynamic topography and deformation of the overriding plate. Two <span class="hlt">subducting</span> units, which correspond to a negatively buoyant oceanic plate and positively buoyant continental one, are juxtaposed via a <span class="hlt">trench</span>-perpendicular interface (analogue to a tear fault) that is either fully-coupled or shear-stress free. Differential rates of <span class="hlt">trench</span> retreat, in excess of 6 cm yr-1 between the two units, trigger a more vigorous mantle flow above the oceanic slab unit than above the continental slab unit. The resulting asymmetrical sublithospheric flow shears the overriding plate in front of the tear fault, and deformation gradually switches from extension to transtension through time. The consistency between our models results and geological observations suggests that the Late Cenozoic deformation of the Aegean domain, including the formation of the North Aegean Trough and Central Hellenic Shear zone, results from the spatial variations in the buoyancy of the <span class="hlt">subducting</span> lithosphere. In particular, the lateral changes of the <span class="hlt">subduction</span> regime caused by the Early Pliocene <span class="hlt">subduction</span> of the old oceanic Ionian plate redesigned mantle flow and excited an increasingly vigorous dextral shear underneath the overriding plate. The models suggest that it is the inception of the Kefalonia Fault that caused the transition between an extension dominated tectonic regime to transtension, in the North Aegean, Mainland Greece and Peloponnese. The <span class="hlt">subduction</span> of the tear fault may also have helped the propagation of the North Anatolian Fault into the Aegean domain.</p> <div class="credits"> <p class="dwt_author">Guillaume, B.; Husson, L.; Funiciello, F.; Faccenna, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">263</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2001GeoJI.145..809F"> <span id="translatedtitle">History of <span class="hlt">subduction</span> and back-arc extension in the Central Mediterranean</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Geological and geophysical constraints to reconstruct the evolution of the Central Mediterranean <span class="hlt">subduction</span> zone are presented. Geological observations such as upper plate stratigraphy, HP-LT metamorphic assemblages, foredeep/<span class="hlt">trench</span> stratigraphy, arc volcanism and the back-arc extension process are used to define the infant stage of the <span class="hlt">subduction</span> zone and its latest, back-arc phase. Based on this data set, the time dependence of the amount of <span class="hlt">subducted</span> material in comparison with the tomographic images of the upper mantle along two cross-sections from the northern Apennines and from Calabria to the Gulf of Lyon can be derived. Further, the reconstruction is used to unravel the main evolutionary trends of the <span class="hlt">subduction</span> process. Results of this analysis indicate that (1) <span class="hlt">subduction</span> in the Central Mediterranean is as old as 80Myr, (2) the slab descended slowly into the mantle during the first 20-30Myr (<span class="hlt">subduction</span> speeds were probably less than 1cmyear-1), (3) <span class="hlt">subduction</span> accelerated afterwards, producing arc volcanism and back-arc extension and (4) the slab reached the 660km transition zone after 60-70Myr. This time-dependent scenario, where a slow initiation is followed by a roughly exponential increase in the <span class="hlt">subduction</span> speed, can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull. Finally, the third stage is controlled by the interaction between the slab and the 660km transition zone. In the southern region, this results in an important re-shaping of the slab and intermittent pulses of back-arc extension. In the northern region, the decrease in the <span class="hlt">trench</span> retreat can be explained by the entrance of light continental material at the <span class="hlt">trench</span>.</p> <div class="credits"> <p class="dwt_author">Faccenna, Claudio; Becker, Thorsten W.; Lucente, Francesco Pio; Jolivet, Laurent; Rossetti, Federico</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">264</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.7794A"> <span id="translatedtitle">Magmatism and crustal deformation during <span class="hlt">subduction</span> and tearing of a ridge-transform system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Chile ridge <span class="hlt">subducts</span> underneath South American plate at latitude 46S, forming a ridge-<span class="hlt">trench-trench</span> type triple junction that migrated to the north along the Pacific coast. At ~6 Ma, a short segment of the Chile ridge system collided and <span class="hlt">subducted</span> in the south of the present triple junction. This ridge <span class="hlt">subduction</span> event resulted in emplacement of the Taitao ophiolite (5. 7 to 5. 2 Ma) and contemporaneous granite intrusions (5.7 to 4.9 Ma) and rapid crustal uplift (partly emerged after 4.9 Ma) in the <span class="hlt">trench</span>-side, and adakitic volcanisms (dating in progress), subsidence and > 1 km thick basin-fill sedimentation behind the ophiolite. Recent acoustic survey by JAMSTEC R/V Mirai revealed that a graben is still developing in this area. Gabbro and ultramafic sections were folded due to high-T deformation. Gabbro structures restored using paleomagnetic data indicate that it was eastern part of the ridge center that was obducted. Presence of ~ 5 Ma mafic and dacitic volcanism along the eastern margin of the ophiolite (Chile Margin Unit) with higher Sr isotopic ratios suggests perhaps that a transform fault <span class="hlt">subducted</span> prior to the ridge segments started opening as the <span class="hlt">subducted</span> ridge torn away by slab-pull.</p> <div class="credits"> <p class="dwt_author">Anma, Ryo; Orihashi, Yuji; Veloso, Eugenio; Shin, Kicheol</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">265</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004GeoJI.157..737Z"> <span id="translatedtitle">Crustal deformation and stress localization in Kanto-Tokai, central <span class="hlt">Japan</span> revealed by GPS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Horizontal deformation associated with plate interaction in the Kanto-Tokai district, central <span class="hlt">Japan</span> has been determined using the Japanese permanent Global Positioning System (GPS) array with an accuracy of better than +/- 2.5 mm yr-1. Previous analysis of the GPS observations mainly focused on the pattern of deformation or strain and did not attempt to assess stress change associated with plate <span class="hlt">subduction</span>. In this study, using the GPS observations and the geometry of <span class="hlt">subducting</span> slabs as constraints, we constructed a 3-D kinematic model to simulate the <span class="hlt">subduction</span> of the Philippine Sea Plate at the Suruga and Sagami troughs and the Pacific Plate at the <span class="hlt">Japan</span> <span class="hlt">trench</span>. The model incorporating the effects of major plate driving forces (ridge push, slab pull and drag force) associated with plate <span class="hlt">subduction</span> provides an overall fit to the horizontal deformation observed by GPS during 1996-2001 in the Kanto-Tokai region. The horizontal motion of the Philippine Sea Plate is estimated to be 41 +/- 5 mm yr-1 (60 +/- 5°NW), consistent with that (ca 43-50 mm yr-1) inferred from earthquake slip vectors and geological data. The horizontal motion of the Pacific Plate is estimated to be 78 +/- 6 mm yr-1 (84 +/- 5°NW), close to that (ca 73-79 mm yr-1) deduced from earthquake slip vectors. After extracting the regional deformation associated with <span class="hlt">subduction</span> of the Philippine Sea and Pacific Plates from the GPS observations, two types of motion trends are revealed for the northern part of the Kanto-Tokai region. The southeastward motion of the GPS stations revealed by the residual displacements in northern Tokai indicates a possible resistance force from the north. In northern Kanto, the west-southwestward residual motion of the GPS stations indicates the motion of the North American Plate relative to the Eurasian Plate. The distinct boundary between these two different types of motion trends provides strong support for the presence of the North American Plate in the region, which demonstrates that the model has delineated the main characteristics of plate interaction. Further, a stress analysis indicates that stress is accumulating on the Suruga trough at a rate of approximately 0.7 bar yr-1, at a depth of 15 km. Our results indicate that the pattern of stress localization is mainly controlled by the kinematic characteristics of the <span class="hlt">subducted</span> slabs (geometry and slip distribution) and the persistent stress concentration is responsible for repeated large interplate earthquakes in the region.</p> <div class="credits"> <p class="dwt_author">Zhao, S.; Wu, X.; Hori, T.; Kaneda, Y.; Takemoto, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">266</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.T14B..01S"> <span id="translatedtitle">Exploring a Link Between Great and Giant Megathrust Earthquakes and Relative Thickness of Sediment and Eroded Debris in the <span class="hlt">Subduction</span> Channel to Roughness of <span class="hlt">Subducted</span> Relief</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">SEDIMENT <span class="hlt">SUBDUCTION</span> AND SEISMICITY: At sediment-nourished (>1-2 km) <span class="hlt">subduction</span> zones (SZs), instrumentally recorded great and giant earthquakes (Eqs) plus the geologically well-vetted Cascadia's Mw9.0 of 1700, corresponds to the occurrence of: 52 percent of Mw8.0 and larger (12 of 23), 57 percent of Mw8.3 and larger (8 of 14), 67 percent of Mw8.5 and larger (8 of 12), 71 percent of Mw8.8 and larger (5 of 7), 67 percent of Mw9.0 and larger (4 of 6), and 100 percent of Eqs larger than Mw9.0 (3 of 3). The implications of this observation were first explored by Ruff (1989, Pure and Applied Geophysics, v. 129, p. 263-282). SIGNIFICANT EXCEPTIONS: A significant percentage of powerful megathrust Eqs have nucleated at poorly sedimented <span class="hlt">trenches</span> (<1.0-0.5 km). For example, the 1952 Kamchatka Mw9.0 event, and the horrendous March 11, 2011 Tohoku-Oki Mw9.0 megathrust. Other great megathrust ruptures have also torn the Peru-Chile SZ opposite the sediment-starved <span class="hlt">trench</span> sectors of southern Peru (2001 Mw8.4) and northern Chile (1922 Mw8.3), and probably at higher magnitudes in the pre-instrumental 19th century. RELATIVE THICKNESS AND THE SMOOTHNESS CONJECTURE: Ruff (1989) surmised that excess sediment (i.e., at least 1-2 km thick) entering a <span class="hlt">subduction</span> zone constructs a laterally homogenous layer within the plate-separating <span class="hlt">subduction</span> channel where seismogenic rupturing occurs. The layer of <span class="hlt">subducted</span> sediment works to even the <span class="hlt">trench</span>-parallel distribution of coupling strength (asperities) by smothering the roughness or rugosity of <span class="hlt">subducted</span> sea-floor relief. In doing so sediment <span class="hlt">subduction</span> contributes to the lengthy (>300-500 km) rupturing of great and giant megathrust Eqs. Larger Mw Eqs do not correlate with increasing thickness of <span class="hlt">subducted</span> sediment. We add here the observation that great and giant Eqs occurring along sediment-poor SZs are typically underthrust by wide sectors of seafloor of low average bathymetric relief, in particular that caused by seamounts and fracture zones. These SZs also exhibit evidence of active basal <span class="hlt">subduction</span> erosion and the progressive tilting of the margin downward toward the <span class="hlt">trench</span> and the consequent shedding of avalanche and slide debris to the <span class="hlt">trench</span> floor. Pilling of material along the landward side of <span class="hlt">trench</span> buries underthrusting relief, including that of horst and graben bathymetry. Frontal <span class="hlt">subduction</span> erosion and sediment <span class="hlt">subduction</span> convey this material into the <span class="hlt">subduction</span> channel. As documented by von Huene et al (1994, JGR v. 99, n. B11, p. 22, 349), these inferred megathrust-conditioning processes and an exceptionally smooth underthrusting oceanic plate are applicable to the Tohoku-Oki rupture area. We conjecture that at sediment-poor SZs tectonic erosion and mass wasting can thicken the <span class="hlt">subduction</span> channel adequately to overwhelm and smother low underthrusting bathymetric roughness and thus contribute favorably to lengthy megathrusting rupturing.</p> <div class="credits"> <p class="dwt_author">Scholl, D. W.; Kirby, S. H.; von Huene, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">267</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003PJAB...79...51T"> <span id="translatedtitle">Origin of negative gravity anomaly landward of <span class="hlt">trench</span> junction</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Off Urakawa, Hokkaido district landward of a junction of Chishima <span class="hlt">trench</span> and <span class="hlt">Japan</span> <span class="hlt">trench</span>, there is a large negative gravity anomaly of about 200 mgals. Off Miyazaki, Kyushu district landward of a junction of Ryukyu <span class="hlt">trench</span> and Nankai trough, there is also large negative gravity anomaly. If the oceanic plate uniformly moves, an excess mass is produced at the <span class="hlt">trench</span> junction and the excess mass should be observed as a positive gravity anomaly. However, on the contrary, large negative anomaly is actually observed. The idea presented in this paper is that, the excess mass falls in the mantle, and this causes a depression of earth surface (free surface), and lack of mass at the surface produces negative free air gravity anomaly. The problems of surface deformation due to falling ball which is rigid and denser than the surround viscous material, were discussed by Morgan in 1965, 1), 2) and excellent papers were published. The deformations of the surface due to a rigid falling ball are divided into two parts. The one is due to direct attraction of the ball and gravity does not change though the surface sink in. The other is due to a current within the viscous fluid and the surface sink in and gravity changes. The amount of the change in gravity is roughly twice as large as gravity due to descending ball, with opposite sign. The water contained in sediment on the ocean floor is transported to a deeper part of the mantle by a descending plate. The water is released into a mantle of continent at the depth of about 150 km and, lowers melting temperature there and negative buoyancy of the plate changes to buoyancy. Therefore the depth is a limit of negative buoyancy of the plate. According to the idea, the excess mass at <span class="hlt">trench</span> junction off Urakawa and off Miyazaki were estimated and tried to explain origin of negative gravity anomaly landward of <span class="hlt">trench</span> junction</p> <div class="credits"> <p class="dwt_author">Tomoda, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">268</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012Tectp.526...16I"> <span id="translatedtitle">Varying mechanical coupling along the Andean margin: Implications for <span class="hlt">trench</span> curvature, shortening and topography</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Convergent margins often exhibit spatial and temporal correlations between <span class="hlt">trench</span> curvature, overriding plate shortening and topography uplift that provide insights into the dynamics of <span class="hlt">subduction</span>. The Andean system, where the Nazca plate plunges beneath continental South America, is commonly regarded as the archetype of this class of tectonics systems. There is distinctive evidence that the degree of mechanical coupling between converging plates, i.e. the amount of resistive force mutually transmitted in the direction opposite to their motions, may be at the present-day significantly higher along the central Andean margin compared to the northern and southern limbs. However quantitative estimates of such resistance are still missing and would be desirable. Here we present laboratory models of <span class="hlt">subduction</span> performed to investigate quantitatively how strong lateral coupling variations need to be to result in <span class="hlt">trench</span> curvature, tectonic shortening and distribution of topography comparable to estimates from the Andean margin. The analogue of a two-layers Newtonian lithosphere/upper mantle system is established in a silicone putty/glucose syrup tank-model where lateral coupling variations along the interface between <span class="hlt">subducting</span> and overriding plates are pre-imposed. Despite the simplicity of our setup, we estimate that coupling in the central margin as large as 20% of the driving force is sufficient to significantly inhibit the ability of the experimental overriding plate to slide above the <span class="hlt">subducting</span> one. As a consequence, the central margin deforms and shortens more than elsewhere while the <span class="hlt">trench</span> remains stationary, as opposed to the advancing lateral limbs. This causes the margin to evolve into a peculiar shape similar to the present-day <span class="hlt">trench</span> of the Andean system.</p> <div class="credits"> <p class="dwt_author">Iaffaldano, G.; Di Giuseppe, E.; Corbi, F.; Funiciello, F.; Faccenna, C.; Bunge, H.-P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">269</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012Tectp.568..230W"> <span id="translatedtitle"><span class="hlt">Subducted</span> sedimentary serpentinite mélanges: Record of multiple burial-exhumation cycles and <span class="hlt">subduction</span> erosion</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Serpentinite matrix mélanges give insight into large-scale convergent plate margin processes, particularly because of the derivation of the serpentinite from oceanic mantle. Similar to shale-matrix mélanges, a field geologist may easily recognize the sedimentary origins of little-deformed serpentinite matrix mélanges, but mélanges within accretionary prisms have undergone significant deformation and recrystallization of matrix. Serpentinite mélanges of the Franciscan <span class="hlt">subduction</span> complex of California have a seemingly intact and foliated matrix. Such exposures contrast sharply with the granular undeformed sedimentary serpentinite mélanges of the coeval Great Valley Group (GVG) forearc basin deposits that depositionally overlie Coast Range Ophiolite (that structurally overlies the Franciscan). Nonetheless, Franciscan serpentinite mélanges display evidence of sedimentary origins, including sedimentary breccia composed of exotic block material (Tolay Ridge), sedimentary serpentinite breccia (Panoche Pass Road), basal serpentinite conglomerate with exotic clasts (Sunol Regional Wilderness), and serpentinite sandstones and conglomerates, including a basal conglomerate overlying coherent metagraywacke (Tiburon Peninsula). These examples record two burial-exhumation cycles to blueschist facies depths. In addition, a mélange/breccia in the Panoche Pass area may have components that record three burial-exhumation cycles to blueschist (or greater) depth. Exhumation rates for various cycles ranged from about 1.2 to 10 mm/year. The Tiburon Peninsula serpentinite mélange occupies the structurally highest horizon in the Franciscan of the San Francisco Bay area, and regional field relationships indicate deposition at ca. 100 Ma. Apparently, about 65 Ma of <span class="hlt">subduction</span> erosion/non accretion followed initiation of Franciscan <span class="hlt">subduction</span> in this region. The oldest Franciscan serpentinite mélanges are at least 35 Ma younger than sedimentary serpentinites of the GVG. <span class="hlt">Subduction</span> erosion may have facilitated reworking of forearc sedimentary serpentinite deposits into the <span class="hlt">trench</span>. Evidence of multiple-burial exhumation cycles indicates reworking of <span class="hlt">subduction</span> complex material, consistent with existence of clastic units that have fossils indicative of significantly older ages than detrital zircon ages.</p> <div class="credits"> <p class="dwt_author">Wakabayashi, John</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">270</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005JGRB..110.6404T"> <span id="translatedtitle">Vertical motions of the Puerto Rico <span class="hlt">Trench</span> and Puerto Rico and their cause</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Puerto Rico <span class="hlt">trench</span> exhibits great water depth, an extremely low gravity anomaly, and a tilted carbonate platform between (reconstructed) elevations of +1300 m and -4000 m. I argue that these features are manifestations of large vertical movements of a segment of the Puerto Rico <span class="hlt">trench</span>, its forearc, and the island of Puerto Rico that took place 3.3 m.y. ago over a time period as short as 14-40 kyr. I explain these vertical movements by a sudden increase in the slab's descent angle that caused the <span class="hlt">trench</span> to subside and the island to rise. The increased dip could have been caused by shearing or even by a complete tear of the descending North American slab, although the exact nature of this deformation is unknown. The rapid (14-40 kyr) and uniform tilt along a 250 km long section of the <span class="hlt">trench</span> is compatible with scales of mantle flow and plate bending. The proposed shear zone or tear is inferred from seismic, morphological, and gravity observations to start at the <span class="hlt">trench</span> at 64.5°W and trend southwestwardly toward eastern Puerto Rico. The tensile stresses necessary to deform or tear the slab could have been generated by increased curvature of the <span class="hlt">trench</span> following a counterclockwise rotation of the upper plate and by the <span class="hlt">subduction</span> of a large seamount.</p> <div class="credits"> <p class="dwt_author">ten Brink, Uri</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">271</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.3739C"> <span id="translatedtitle">Nazca plate <span class="hlt">subduction</span>, mantle flow and Cordilleras formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Nazca-South America convergence represents a unique natural laboratory to probe our understanding of <span class="hlt">subduction</span>, mantle flow and stress coupling at Andean-type margins. Here, it is shown that the most fundamental balance of forces associated with the downgoing slab, the upper plates and the mantle can account for the Nazca plate motions, although it does not adequately explain the variations of the Cordilleran tectonics found along the ~6000 km wide margin. Using three-dimensional numerical models it is shown that <span class="hlt">trench</span>-parallel gradients in both the driving and resisting forces are an essential component of the force balance, and necessary to reproduce the macroscopic features observed. When along-<span class="hlt">trench</span> buoyancy variations similar to the Nazca plate's are included, the slab dips and upper plate deformations observed in the Nazca slab, in the Cordilleras and South American continent interiors can be reproduced. The models show that gradients in the resisting shear force along the <span class="hlt">trench</span> can be as relevant, as they modulate the <span class="hlt">trench</span> retreat to form the concave Bolivian Orocline. Pressure gradients in the mantle follow the Nazca buoyancy gradients, and effectively rearrange the flow introducing a <span class="hlt">trench</span>-parallel component, similar to what suggested by seismic anisotropy in this area. Although they introduce only secondary variations to the primary <span class="hlt">subduction</span> and mantle flow dynamics, the regional features of the Nazca and South American plates exert a primary control at the margin-local scale. This suggests that far-field forces, e.g. from spreading Atlantic or large-scale convection, should play a minor role in the formation of the Cordilleras.</p> <div class="credits"> <p class="dwt_author">Capitanio, Fabio A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">272</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://geoscience-meeting.scnatweb.ch/sgm2006/SGM06_abstracts/11_From_core_to_crust/Cantieni_Curdin_Poster.pdf"> <span id="translatedtitle"><span class="hlt">Subduction</span> of an aseismic ridge under an active margin: 1) topographic evolution and effects of slab density</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">At about 15 o south the Nazca Ridge enters the <span class="hlt">subduction</span> zone. In this region we can observe prominent geological and geophysical features such as a shallower deep sea <span class="hlt">trench</span>, a volcanic gap and more active seismicity. Assuming that ridge <span class="hlt">subduction</span> is responsible for the development of these features we used a coupled petrological-thermomechanical computer code I2VIS based on finite-differences</p> <div class="credits"> <p class="dwt_author">Cantieni Curdin; Fossati David; Gerya Taras; Seward Diane</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">273</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1981JGR....86.4949M"> <span id="translatedtitle">Nonuniform seismic slip rates along the Middle America <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Revised estimates of seismic slip rates along the Middle America <span class="hlt">Trench</span> are lower on the average than plate convergence rates but match them locally (for example, Oaxaca). Along the Cocos-North American plate boundary this can be explained by nonuniformities in slip at points of aseismic ridge or fracture zone <span class="hlt">subduction</span>. For at least 81 yr (and possibly several hundred years), no major (Ms ? 7.5) shallow earthquake is known to have occurred near the Orozco Fracture Zone and Tehuantepec Ridge areas. Compared with the average recurrence periods for large earthquakes (33 ± 8 yr since 1898 and 35 ± 24 yr between 1542 and 1979), this suggests that either a large (M ? 8.4) event may be anticipated at such locations, or that these are points of aseismic <span class="hlt">subduction</span>. Large coastal terraces and evidence suggesting tectonic uplift are found onshore near the Orozco Fracture zone. The larger discrepancy between plate convergence and seismic slip rates along the Cocos-Carribbean plate boundary is more likely due to decoupling and downbending of the <span class="hlt">subducted</span> plate. We used the limited statistical evidence available to characterize both spatial and temporal deficiencies in recent seismic slip. The observations appear consistent with a possible forthcoming episode of more intense seismic activity. Based on a series of comparisons with carefully delineated aftershock zones, we conclude that the zones of anomalous seismic activity can be identified by a systematic, automated analysis of the worldwide earthquake catalog (mb ? 4).</p> <div class="credits"> <p class="dwt_author">McNally, Karen C.; Minster, J. Bernard</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">274</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.9847H"> <span id="translatedtitle">Flexural modelling of gravity anomalies seaward of Pacific <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The strength of the lithosphere is determined by its flexural rigidity, which is commonly expressed through the effective elastic thickness, Te. In oceanic regions, it is widely accepted that Te increases as a function of age at the time of loading, due to cooling and thickening of the lithosphere. Evidence for this comes from studies of free-air gravity anomalies and bathymetry at seamounts, fracture zones and <span class="hlt">subduction</span> zone outer-rises. 75% of Te estimates from seamounts lie between the 300 ° C and 600 ° C isotherms as predicted by a cooling plate model, whilst the majority of <span class="hlt">subduction</span> zone and fracture zone estimates lie between the 500 ° C and 800 ° C isotherms. Recent outer-rise investigations, however, have questioned whether such a simple relationship exists and suggested that either the strength of the lithosphere is independent of plate age, or that Te cannot be measured with sufficient accuracy to reveal such a relationship. In order to reassess the relationship between lithospheric strength and age, we use <span class="hlt">trench</span>-normal, ensemble-averaged profiles of satellite-derived free-air gravity anomalies to model the outer-rise of all the major Pacific <span class="hlt">subduction</span> zones. Profiles are corrected for sediment loading, as well as for thermal cooling effects. A broken elastic plate model is used, with a finite difference solution that allows Teto vary as a function of distance from the <span class="hlt">trench</span>. We use an inverse approach, iterating Te values and inverting for end-conditioning forces (a vertical shear force and a bending moment). Results show that oceanic lithosphere younger than 90 Ma clearly strengthens with age, with Te roughly following the 550 ° C isotherm. For example, the Middle America <span class="hlt">trench</span> (4 - 25 Ma) has a mean Te of 14.1 ± 2.8 km, whilst the Alaska-Aleutian <span class="hlt">trench</span> (43 - 60 Ma) has a mean Te of 34.3 ± 8.0 km. For older lithosphere, the pattern is not as clear. We suggest that this is due to thermal rejuvenation, which has two effects: it weakens the lithosphere, lowering Te estimates; the associated magmatism masks the flexural signal, producing scatter. For many of the <span class="hlt">subduction</span> zones, gravity profiles require that the lithosphere has been weakened in the region of the seaward wall of the <span class="hlt">trench</span>. We attribute this to inelastic yielding - a combination of brittle fracture of the upper lithosphere and ductile flow of the lower lithosphere - due to high bending moments. Evidence for this can be seen in swath bathymetry data, which reveals zones of pervasive extensional faulting. Hydrothermal alteration of the lithosphere might also contribute to weakening, if bend faulting allows hydration and serpentinization of the upper mantle.</p> <div class="credits"> <p class="dwt_author">Hunter, Johnny; Watts, Anthony; Bassett, Daniel</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">275</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011MarGR..32..455N"> <span id="translatedtitle">A precise bathymetric map of the world's deepest seafloor, Challenger Deep in the Mariana <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Data from three bathymetric surveys by R/V Kairei using a 12-kHz multibeam echosounder and differential GPS were used to create an improved topographic model of the Challenger Deep in the southwestern part of the Mariana <span class="hlt">Trench</span>, which is known as the deepest seafloor in the world. The strike of most of the elongated structures related to plate bending accompanied by <span class="hlt">subduction</span> of the Pacific plate is N70°E and is not parallel to the <span class="hlt">trench</span> axis. The bending-related structures were formed by reactivation of seafloor spreading fabric. Challenger Deep consists of three en echelon depressions along the <span class="hlt">trench</span> axis, each of which is 6-10 km long, about 2 km wide, and deeper than 10,850 m. The eastern depression is the deepest, with a depth of 10,920 ± 5 m.</p> <div class="credits"> <p class="dwt_author">Nakanishi, Masao; Hashimoto, Jun</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">276</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AGUFM.G42A..07O"> <span id="translatedtitle">Deformation of <span class="hlt">Japan</span> as measured by improved analysis of GEONET data</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone represents a complex set of plate interfaces with significant <span class="hlt">trench</span>-parallel variability in great earthquakes and transient deep slip events. Within the <span class="hlt">Japan</span> arc the Nankai segment of the Eurasian-Philippine plate boundary is one of the classic <span class="hlt">subduction</span> zone segments that last produced a set of temporally linked great earthquakes in the 1940's. Recently, down-dip of the Nankai seismogenic portion of the plate interface, transient slip events and seismic tremor events were observed. Through analysis of the GEONET GPS data, the spatial and higher frequency temporal characteristics of transient slip events can be captured. We describe our analysis methods, the spatial filtering technique that has been developed for use on large networks, a periodic signal filtering method that improves on commonly-used sinusoidal function models, and the resultant velocities and time series. Our newly developed analysis method, the GPS Network Processor, gives us the ability to process large volumes of data extremely fast. The basis of the GPS Network Processor is the JPL-developed GIPSY-OASIS GPS analysis software and the JPL-developed precise point positioning technique. The Network Processor was designed and developed to efficiently implement precise point positioning and bias fixing on a 1000-node (2000 cpu) Beowulf cluster. The entire 10 year ~1000-station GEONET data set can be reanalyzed using the Network Processor in a matter of days. This permits us to test different processing strategies, each with potentially large influence on our ability to detect strain transients from the <span class="hlt">subduction</span> zones. For example, we can test different ocean loading models, which can effect the diurnal positions of coastal GPS sites by up to 2 cm. We can also test other potentially important factors such as using reprocessed satellite orbits and clocks, the parameterization of the tropospheric delay, or the implementation of refined solid body tide estimates. We will present the results of tests that we have run to date at the meeting.</p> <div class="credits"> <p class="dwt_author">Owen, S. E.; Dong, D.; Webb, F. H.; Newport, B. J.; Simons, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">277</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..12.2471F"> <span id="translatedtitle">Strain Partitioning Between the Slab and the Upper Plate: Implications for the Deformational Efficiency of <span class="hlt">Subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The conventional view of plate boundary strain during the seismic cycle in <span class="hlt">subduction</span> zones portrays the accretionary margin and upper-plate wedge as the primary site of intra-seismic strain accumulation and co-seismic strain release. This textbook model provides a mechanism for tsunamigenesis, and the accumulation of residual deformation over numerous cycles produces the observed upper plate deformation. In general however we know little about the nature of this strain partitioning and the associated efficiency with which the <span class="hlt">subduction</span> cycle permanently deforms the upper plate. In fact there is accumulating evidence that along some <span class="hlt">subduction</span> segments, the <span class="hlt">subducting</span> slab may be the dominant player in hosting the elastic strain accumulation and release during the seismic cycle. A series of recent great <span class="hlt">subduction</span> earthquakes is allowing us to investigate this intra-seismic strain partitioning, and begin to identify the spectrum of strain conditions seen in <span class="hlt">subduction</span> zones. In particular, the 2006/2007 pair of great earthquakes along the Kurile <span class="hlt">trench</span>, the 2007 Solomon Islands great earthquake, and the 2009 Samoa/Tonga great earthquake point to there being a significant variability in intra-seismic strain accumulation and co-seismic strain release among various <span class="hlt">subduction</span> systems (and likely even along different rupture segments of the same <span class="hlt">trench</span>). One implication of this variability is that the permanent deformation within the accretionary wedge and upper plate, driven by residual (inelastic) strain accumulating during the seismic cycle, likely varies significantly in both space and time. Inferences of the nature of slab/wedge coupling derived from observations of upper plate deformation are thus suspect. Young <span class="hlt">subduction</span> systems with minimal amounts of total <span class="hlt">subduction</span> may provide the best environment to observe and constrain the linkage between plate boundary kinematics and upper plate deformation.</p> <div class="credits"> <p class="dwt_author">Furlong, Kevin P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">278</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.T44B..08F"> <span id="translatedtitle">Strain Partitioning Between the Slab and the Upper Plate: Implications for the Deformational Efficiency of <span class="hlt">Subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The conventional view of plate boundary strain during the seismic cycle in <span class="hlt">subduction</span> zones portrays the accretionary margin and upper-plate wedge as the primary site of intra-seismic strain accumulation and co-seismic strain release. This textbook model provides a mechanism for tsunamigenesis and the accumulation of residual deformation over numerous cycles produces the observed upper plate deformation. In general however we know little about the nature of this strain partitioning and the associated efficiency with which the <span class="hlt">subduction</span> cycle permanently deforms the upper plate. In fact there is accumulating evidence that along some <span class="hlt">subduction</span> segments, the <span class="hlt">subducting</span> slab may be the dominant player in hosting the elastic strain accumulation and release during the seismic cycle. A series of recent great <span class="hlt">subduction</span> earthquakes is allowing us to investigate this intra-seismic strain partitioning, and begin to identify the spectrum of strain conditions seen in <span class="hlt">subduction</span> zones. In particular, the 2006/2007 pair of great earthquakes along the Kurile <span class="hlt">trench</span>, the 2007 Solomon Islands great earthquake, and the 2009 Samoa/Tonga great earthquake point to there being a significant variability in intra-seismic strain accumulation and co-seismic strain release among various <span class="hlt">subduction</span> systems (and likely even along different rupture segments of the same <span class="hlt">trench</span>). One implication of this variability is that the permanent deformation within the accretionary wedge and upper plate, driven by residual (inelastic) strain accumulating during the seismic cycle, likely varies significantly in both space and time. Inferences of the nature of slab/wedge coupling derived from observations of upper plate deformation are thus suspect. Young <span class="hlt">subduction</span> systems with minimal amounts of total <span class="hlt">subduction</span> may provide the best environment to observe and constrain the linkage between plate boundary kinematics and upper plate deformation.</p> <div class="credits"> <p class="dwt_author">Furlong, K. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">279</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011E%26PSL.312..360L"> <span id="translatedtitle">Dynamic buckling of <span class="hlt">subducting</span> slabs reconciles geological and geophysical observations</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Ever since the early days of the development of plate tectonic theory, <span class="hlt">subduction</span> zones have been engrained in geological thinking as the place where steady, linear slabs descend into the mantle at a constant, uniform dip angle beneath volcanic arcs. However, growing evidence from geological and geophysical observations as well as analog and numerical modeling indicates that <span class="hlt">subducting</span> slabs buckle in a time-dependent manner, in contrast to the steady-state, linear cartoons that dominate the literature. To evaluate the implication of time-dependent slab buckling of geological events, we conduct a series of 2-D numerical dynamic/kinematic <span class="hlt">subduction</span> experiments by varying the viscosity increase across the 660 km discontinuity and the strength of the <span class="hlt">subducting</span> slab. Our results show that slab buckling is a universal figure in all the experiments when rate of the <span class="hlt">trench</span> migration ( Vtrench) is relatively slow ( Vtrench| < 2 cm/a) and viscosity increases across the 660 km discontinuity are greater than a factor of 30. Slab buckling is expressed as alternate shallowing and steepening dip of the <span class="hlt">subducting</span> slab (from ~ 40 to ~ 100°) which is correlated with increasing and decreasing convergent rate of the incoming oceanic plate toward the <span class="hlt">trench</span>. Further, the slab buckling in our experiments is consistent with the previously developed scaling laws for slab buckling; using reasonable parameters from <span class="hlt">subducted</span> slabs the buckling amplitude and period are ~ 400 km and ~ 25 Myr, respectively. The slab buckling behavior in our experiments explains a variety of puzzling geological and geophysical observations. First, the period of slab buckling is consistent with short periodic variations (~ 25 Myr) in the motions of the oceanic plates that are anchored by <span class="hlt">subduction</span> zones. Second, the scattered distributions of slab dips (from ~ 20 to ~ 90°) in the upper mantle are snapshots of time-dependent slab dip. Third, the current compressional and extensional stress environments in back-arcs are well correlated with shallowing and steeping slab dip resulting from slab buckling. Fourth, the temporal evolution of stress environments in the Andes is well correlated with alternate slab dip. These correlations indicate that time-dependent slab buckling is a major factor controlling <span class="hlt">subduction</span> zone dynamics.</p> <div class="credits"> <p class="dwt_author">Lee, Changyeol; King, Scott D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">280</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013SolED...5..315G"> <span id="translatedtitle">The dynamics of laterally variable <span class="hlt">subductions</span>: laboratory models applied to the Hellenides</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We design three-dimensional dynamically self-consistent laboratory models of <span class="hlt">subduction</span> to analyze the relationships between overriding plate deformation and <span class="hlt">subduction</span> dynamics in the upper mantle. We investigate the effects of the <span class="hlt">subduction</span> of a lithosphere of laterally variable buoyancy on the temporal evolution of <span class="hlt">trench</span> kinematics and shape, horizontal flow at the top of the asthenosphere, dynamic topography and deformation of the overriding plate. The interface between the two units, analogue to a <span class="hlt">trench</span>-perpendicular tear fault between a negatively buoyant oceanic plate and positively buoyant continental one, is either fully-coupled or shear-stress free. Differential rates of <span class="hlt">trench</span> retreat, in excess of 6 cm yr-1 between the two units, trigger a more vigorous mantle flow above the oceanic slab unit than above the continental slab unit. The resulting asymmetrical sublithospheric flow shears the overriding plate in front of the tear fault, and deformation gradually switches from extension to transtension through time. The consistency between our models results and geological observations suggests that the Late Cenozoic deformation of the Aegean domain, including the formation of the North Aegean Trough and Central Hellenic Shear zone, results from the spatial variations in the buoyancy of the <span class="hlt">subducting</span> lithosphere. In particular, the lateral changes of the <span class="hlt">subduction</span> regime caused by the Early Pliocene <span class="hlt">subduction</span> of the old oceanic Ionian plate redesigned mantle flow and excited an increasingly vigorous dextral shear underneath the overriding plate. The models suggest that it is the inception of the Kefalonia Fault that caused the transition between an extension dominated tectonic regime to transtension, in the North Aegean, Mainland Greece and Peloponnese. The <span class="hlt">subduction</span> of the tear fault may also have helped the propagation of the North Anatolian Fault into the Aegean domain.</p> <div class="credits"> <p class="dwt_author">Guillaume, B.; Husson, L.; Funiciello, F.; Faccenna, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span 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</span> </span> <a id="NextPageLink" onclick='return showDiv("page_16");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">281</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006E%26PSL.242..130K"> <span id="translatedtitle">The Java margin revisited: Evidence for <span class="hlt">subduction</span> erosion off Java</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The eastern Sunda margin off Indonesia (from central Java to Sumba Island) remains a little investigated <span class="hlt">subduction</span> zone, contrary to its well-studied northwestern segment. Whereas large portions of the Sunda margin are considered a classical accretionary zone, <span class="hlt">subduction</span> characteristics along the central Java sector indicate erosive processes as the dominant mode of mass transfer. The tectonic framework of the central Java margin, with a convergence rate of 6.7 cm/yr, insignificant sediment input and a pronounced seafloor roughness where the oceanic Roo Rise is <span class="hlt">subducting</span> underneath Java, facilitates <span class="hlt">subduction</span> erosion. Evidence for erosion comes from newly acquired geophysical data off central Java: local erosive processes in the wake of seamount <span class="hlt">subduction</span> are documented by a high-resolution bathymetric survey and result in an irregular trend of the deformation front sculpted by seamount collision scars. <span class="hlt">Subduction</span> of oceanic basement relief leads to large-scale uplift of the forearc, as recorded on a reflection seismic profile, and to a dismemberment of the previous outer forearc high, giving way to isolated topographic elevations. The broad retreat of the Java <span class="hlt">Trench</span> and deformation front above the leading edge of the Roo Rise has exposed an area of approximately 25,000 km2 of deeper seafloor formerly covered by the previous frontal prism. Frontal erosion coincides with a steepening of the lower slope angle in the central Java sector compared to the neighbouring segments. In global compilations, the key geological parameters of the central Java margin lie in the erosive regime, reflecting the interplay of basement relief <span class="hlt">subduction</span>, negligible sediment supply and a high convergence rate on the evolution of the margin.</p> <div class="credits"> <p class="dwt_author">Kopp, H.; Flueh, E. R.; Petersen, C. J.; Weinrebe, W.; Wittwer, A.; Scientists, Meramex</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">282</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JAESc..76..399H"> <span id="translatedtitle">Contraction and extension in northern Borneo driven by <span class="hlt">subduction</span> rollback</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">During the Paleogene the Proto-South China Sea was <span class="hlt">subducted</span> beneath northern Borneo. <span class="hlt">Subduction</span> ended with Early Miocene collision of the Dangerous Grounds/Reed Bank/North Palawan block and the Sabah-Cagayan Arc. Much of northern Borneo then became emergent forming the Top Crocker Unconformity. Later in the Early Miocene subsidence resumed. It is proposed that northward <span class="hlt">subduction</span> of the Celebes Sea initiated formation of the Sulu Sea backarc basin, followed by <span class="hlt">subduction</span> rollback to the SE. This formed a volcanic arc, which emerged briefly above sea level and collapsed in the Middle Miocene. As rollback continued the Sulu Arc was active during Middle and Late Miocene between Sabah and the Philippines. Rollback drove extension in northern Borneo and Palawan, accompanied by elevation of mountains, crustal melting, and deformation offshore. There were two important extensional episodes. The first at about 16 Ma is marked by the Deep Regional Unconformity, and the second at about 10 Ma produced the Shallow Regional Unconformity. Both episodes caused exhumation of deep crust, probably on low angle detachments, and were followed by granite magmatism. The NW Borneo-Palawan Trough and offshore Sabah fold and thrust belt are often interpreted as features resulting from collision, regional compression or <span class="hlt">subduction</span>. However, there is no seismicity, dipping slab or volcanicity indicating <span class="hlt">subduction</span>, nor obvious causes of compression. The trough developed after the Middle Miocene and is not the position of the Paleogene <span class="hlt">trench</span> nor the site of Neogene <span class="hlt">subduction</span>. Inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough. The trough is interpreted as a flexural response to gravity-driven deformation of the sediment wedge, caused by uplift on land that resulted from extension, with a contribution of deep crustal flow.</p> <div class="credits"> <p class="dwt_author">Hall, Robert</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">283</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5023538"> <span id="translatedtitle">Strength and survival of <span class="hlt">subducted</span> lithosphere during the Laramide orogeny</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The strength of <span class="hlt">subducted</span> ocean lithosphere is influenced primarily by two competing processes. During <span class="hlt">subduction</span> brittle rock strength increases because of increasing compressive stress across fracture surfaces which increases frictional resistance to sliding. The strength of rocks hot enough to be in the plastic deformation regime decreases primarily because of heat conducted from the overriding plate and the asthenosphere. A one-dimensional finite-element heat-flow program was used to simulate <span class="hlt">subduction</span> in two dimensions where conductive heat flow parallel to the slab and to the upper plate could be neglected. Temperatures determined with this method, and pressures based on depth, were then used to calculate the form of the brittle-plastic failure envelope for <span class="hlt">subducted</span> lithosphere. An olivine flow law and strain rate of 10[sup [minus]15] s[sup [minus]1] were used for the plastic part of the failure envelope. The failure envelope was then used to calculate slab-parallel compressive strength and maximum sustainable bending moment. Modeling of Maramide <span class="hlt">subduction</span> beneath southwestern North America, using slab ages and <span class="hlt">subduction</span> rates for the Farallon plate from Engebretson et al., suggests that the <span class="hlt">subducted</span> slab will not retain much strength beyond 1,000 to 1,200 km inland unless the thickness of the North American lithosphere, and depth to the top of the slab, are significantly less than 200 km. Slab survival for distances of 1000 km seems assured. Survival for much greater distances is possible. The slab is predicted to have been up to several times stronger beneath southwestern North America than at the <span class="hlt">trench</span> because much rock remains in the brittle regime and is under high confining pressure.</p> <div class="credits"> <p class="dwt_author">Spencer, J.E. (Arizona Geological Survey, Tucson, AZ (United States))</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">284</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012E%26PSL.351...45K"> <span id="translatedtitle">Electromagnetic detection of plate hydration due to bending faults at the Middle America <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Water plays an important role in the processes occurring at <span class="hlt">subduction</span> zones since the release of water from the downgoing slab impacts seismicity and enhances arc volcanism. Geochemical indicators suggest that the Nicaraguan slab is anomalously wet, yet the mechanism of slab hydration remains poorly constrained. Extensional bending faults on the incoming oceanic plate of the Middle America <span class="hlt">Trench</span> offshore Nicaragua have been observed to penetrate to mantle depths, suggesting a permeable pathway for hydration of the crust and serpentinization of the upper mantle. Low seismic velocities observed in the uppermost mantle of the incoming plate have been explained as serpentinization due to deep fluid penetration but could also be explained by intrinsic anisotropy and fractures in the absence of fluid circulation. Here we use controlled-source electromagnetic imaging to map the electrical resistivity of the crust and uppermost mantle along a 220 km profile crossing the <span class="hlt">trench</span> offshore Nicaragua. Along the incoming plate our data reveal that crustal resistivity decreases by up to a factor of five directly with the onset of the bending faults. Furthermore, a strong azimuthal anisotropy compatible with conductive vertical fault planes is observed only on the faulted <span class="hlt">trench</span> seafloor. The observed resistivity decrease and anisotropy can be explained by a porosity increase along vertical fault planes, which we interpret as evidence that the lithospheric bending faults provide the necessary permeable fluid pathways required for serpentinization of the uppermost mantle. This implies that most serpentinisation happens at the <span class="hlt">trench</span>, with the width of the faulting region and the density of fractures controlling the extent of upper mantle alteration. This observation explains why the heavily faulted <span class="hlt">trench</span> offshore Nicaragua is associated with an anomalously wet slab, whereas other sections of the Middle America <span class="hlt">Trench</span> containing fewer bending faults have less fluid flux from the <span class="hlt">subducting</span> slab.</p> <div class="credits"> <p class="dwt_author">Key, Kerry; Constable, Steven; Matsuno, Tetsuo; Evans, Rob L.; Myer, David</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">285</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5866888"> <span id="translatedtitle">Puerto Rico <span class="hlt">trench</span>: site of a shallow-water Tertiary basin and regional tectonic implications</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Until late Eocene time, the Bahamas platform extended to the present Virgin Islands, as demonstrated by magnetic, gravity, and refraction data. This interpretation is confirmed by the presence of widespread outcrops of middle Cretaceous through early Pliocene shallow-water bank carbonates below 5200 m depth in the <span class="hlt">trench</span>. Crustal thickness beneath this bank is 18-25 km. Igneous and metamorphic rocks from the base of the <span class="hlt">trench</span>'s southern slope are chemically very different from <span class="hlt">subduction</span>-zone rocks. Waters of the carbonate bank (300 x 100 km in size) transgressed southward after early Eocene time. During late Eocene time, the bank's southern margin was near today's shoreline where down-to-the-north growth faults formed. Along the bank's northern margin, block faulting produced a graben above the site of the modern Puerto Rico <span class="hlt">Trench</span>. During middle Eocene to early Pliocene time, shallow-water deposition extended from a position presently 5200 m deep in the <span class="hlt">trench</span> to central Puerto Rico, an exceptionally stable block at least 100 km wide. During middle Eocene time, the Beata Ridge dextral shear cut the <span class="hlt">trench</span> off north of Hispaniola. In early Pliocene time, the Mona Canyon dextral fault zone cut across the <span class="hlt">trench</span>, and strong northward tilting commenced. The <span class="hlt">trench</span>'s present southern slope is mainly a dip slope, inclined about 5/sup 0/. The Puerto Rico Outer Ridge formed by lateral and upward movements of mantle materials that withdrew from beneath the sinking <span class="hlt">trench</span>. Petroleum prospects presently are limited to the Tertiary (4000 m thick) and to a coastal zone 20-25 km wide (to 2000 m water depth). Traps are mainly fault seals and stratigraphic pinch-outs.</p> <div class="credits"> <p class="dwt_author">Krieg, E.A.; Meyerhoff, A.A.; Taner, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">286</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003AGUFM.T52A0241S"> <span id="translatedtitle">Interseismic Strain Along the Sumatra <span class="hlt">Subduction</span> Zone: A Case for a Locked Fault Portion Extending Well Below the Forearc Moho</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A current and most accepted view about the seismogenic zone along <span class="hlt">subduction</span> zones is that the downdip extent of the locked fault portion would correspond either to the 350° C isotherm if this temperature is reached above the Moho, or to the intersection with the forearc Moho for colder <span class="hlt">subduction</span> zones [Oleskevich et al., 1999]. This limit would reflect the transition from slip-weakening friction to aseismic stable-sliding, or else ductile flow. In the first case, when the downdip end of the locked zone is temperature-controlled, stable-sliding of quartzo-feldspathic rocks would be the controlling factor, while the systematic presence of serpentinite or other hydrated minerals is advocated to explain aseismic interplate slip in the mantle at temperatures much less that the 750° C needed for ductile flow of mantle rocks [Peacock and Hyndman, 1999]. Here, we consider the case of the Sumatra <span class="hlt">subduction</span> zone where the ~53 Myr Indian oceanic crust <span class="hlt">subducts</span> below an island-arc characterized by a relatively thin crust, with a Moho depth estimated to ~23 km. We model interseismic deformation from a creeping dislocation embedded in an elastic half-space, using the back-slip approach. In addition to recently published GPS velocities, we take advantage of recent data on the pattern and rate of interseismic uplift that have been obtained from the study of coral growth [Natawidjaja, 2003; Sieh et al., 1999]. These data are found to put tight constraints on the horizontal position of the downdip limit of the locked fault zone, at 127 +/- 4/2 km from the <span class="hlt">trench</span>. This position corresponds to a depth between 40 and 58 km and to a temperature of 269° C +/- 155° C, when compared with thermal modeling. So, in this particular setting, the locked fault portion extends well into the mantle. However, temperature is not high enough to advocate stable sliding or ductile flow of unaltered or altered mantle rocks. This case appeals to some reappraisal of the physical control on the depth of the locked fault zone along <span class="hlt">subduction</span> zones. References. Natawidjaja, D.H., Neotectonics of the Sumatran fault and paleogeodesy of the Sumatran <span class="hlt">subduction</span> zone., PhD thesis, California Institute of Technology, Pasadena, 2003. Oleskevich, D.A., R.D. Hyndman, and K. Wang, The updip and downdip limit to great <span class="hlt">subduction</span> earthquakes : thermal and structural models of Cascadia, South Alaska, SW <span class="hlt">Japan</span> and Chile., Journal of Geophysical Research, 104 (B7), 14965-14991, 1999. Peacock, S.M., and R.D. Hyndman, Hydrous minerals in the mantle wedge and the maximum depth of subdcution thrust earthquakes., Geophysical Research Letters, 26 (16), 2517-2520, 1999. Sieh, K., S.N. Ward, D. Natawidjaja, and B.W. Suwargadi, Crustal deformation at the Sumatra <span class="hlt">subduction</span> zone revealed by coral data., Geophysical Research Letters, 26 (20), 3141-3144, 1999.</p> <div class="credits"> <p class="dwt_author">Simoes, M.; Avouac, J.; Cattin, R.; Henry, P.; Natawidjaja, D. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">287</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1984JGR....89.7719B"> <span id="translatedtitle">Seismicity and tectonics of the <span class="hlt">subducted</span> Cocos Plate</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have examined teleseismic earthquake locations reported by the International Seismological Centre (ISC) for the Middle America region and selected 220 as the most reliable. These hypocenters and other data are used to delineate the deep structure of the <span class="hlt">subducted</span> Cocos Plate. The results indicate that the <span class="hlt">subducted</span> plate consists of three major segments: Segment I extends from the Panama Fracture Zone to the Nicoya Peninsula. The structure of this segment is poorly defined. Segment II is the largest and best-defined segment. This segment consists of two parts, IIA and IIB. Part IIA extends from the Nicoya Peninsula to western Guatemala and is very well defined and continuous in structure. Its strike follows the curvature of the <span class="hlt">trench</span> and dips at about 60°. Part IIB extends from western Guatemala to Orizaba, Mexico. The dip of this part of the segment decreases slightly toward the northwest, and its strike is more northward than that of the <span class="hlt">trench</span>. Segment III extends from Orizaba to the Rivera Fracture Zone, and is not well defined due to a lack of earthquake activity beneath about 100 km. Its orientation differs markedly from segment II and strikes somewhat more westward than the <span class="hlt">trench</span>. Between parts IIA and IIB of segment II the <span class="hlt">subducted</span> plate seems to be continuous, bending smoothly to accommodate the change in geometry. Local network data from Costa Rica suggest there may be a tear between segments I and II. Between segments II and III there is a gap in the hypocenters which makes it difficult to define the boundary. The change in geometry between these two segments indicates that there may be a tear, and two strike-slip focal mechanisms in the region support this conclusion. We find no convincing evidence supporting the existence of segments smaller than the three described above. If there is smaller-scale segmentation in the shallow part of the <span class="hlt">subducting</span> plate the plate must still maintain enough continuity to appear continuous at greater depths. There is no evidence for any major tear in the <span class="hlt">subducted</span> plate associated directly with either the Tehuantepec Ridge or the Orozco Fracture zone. The shallow <span class="hlt">subduction</span> at the northwestern end of segment II may be related to the bouyancy of the Tehuantepec Ridge. The Cocos Ridge is probably directly responsible for the change in geometry between segments I and II and may even be slowing or stopping <span class="hlt">subduction</span> in segment I. The structure of the <span class="hlt">subducted</span> plate in segment II and the changes in the character of volcanism along the arc can be related to the relative motion of the North American and Caribbean Plates. The present geometry of part IIB of segment II is more consistent with the probable configuration of the <span class="hlt">trench</span> about 7 Ma ago than with the present configuration, indicating that the North American plate is overriding the <span class="hlt">subduction</span> zone. Appendices 2, 3, and 4 are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009. Document B84-009; $2.50.</p> <div class="credits"> <p class="dwt_author">Burbach, George Vanness; Frohlich, Cliff; Pennington, Wayne D.; Matumoto, Tosimatu</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">288</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.T21B2322W"> <span id="translatedtitle">Seismicity, topography, and free-air gravity of the Aleutian-Alaska <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Aleutian-Alaska <span class="hlt">subduction</span> zone, extending 3400 km from the Queen Charlotte Fault to Kamchatka, has been the source of six great megathrust earthquakes in the 20th Century. Four earthquakes have ruptured the 2000-km-long Aleutian segment, where the Cenozoic Aleutian arc overlies the <span class="hlt">subducting</span> Pacific plate. These include the 1946 M 8.6 earthquake off Unimak Is., the 1957 M 8.6 and 1986 M 8.0 earthquakes off the Andreanoff Is., and the 1965 M 8.7 Rat Is. earthquake. The source regions of these earthquakes inferred from waveform inversions underlie the well-defined Aleutian deep-sea terrace. The deep-sea terrace is about 4 km deep and is underlain by Eocene arc framework rocks, which extend nearly to the <span class="hlt">trench</span>. It is bounded on its seaward and landward margins by strong topographic and fee-air gravity gradients. The main asperities (areas of largest slip) for the great earthquakes and nearly all of the Aleutian thrust CMT solutions lie beneath the Aleutian terrace, between the maximum gradients. Similar deep-sea terraces are characteristic of non-accretionary convergent margins globally (75% of <span class="hlt">subduction</span> zones), and, where sampled by drilling (e.g., <span class="hlt">Japan</span>, Peru, Tonga, Central America), are undergoing sustained subsidence. Sustained subsidence requires removal of arc crust beneath the terrace by basal <span class="hlt">subduction</span> erosion (BSE). BSE is in part linked to the seismic cycle, as it occurs in the same location as the megathrust earthquakes. Along the eastern 1400 km of the Alaskan <span class="hlt">subduction</span> zone, the Pacific plate <span class="hlt">subducts</span> beneath the North American continent. The boundary between the Aleutian segment and the continent is well defined in free-air gravity, and the distinctive deep-sea terrace observed along the Aleutian segment is absent. Instead, the Alaskan margin consists of exhumed, underplated accretionary complexes forming outer arc gravity highs. Superimposed on them are broad topographic highs and lows forming forearc basins (Shumagin, Stevenson) and islands (Kodiak, Shumagin). Two great earthquakes ruptured much of this segment: the 1938 M 8.3 earthquake SW of Kodiak and the 1964 M 9.2 earthquake, which ruptured 800 km of the margin between Prince William Sound and Kodiak Island. Large slip during the 1938 event occurred under the Shumagin and Tugidak basins, but slip in 1964 is thought to have occurred on asperities under Prince William Sound and the outer arc highs off Kodiak. Seismic profiling and industry drilling indicates sustained subsidence has also occurred along the Alaska margin. BSE is probably occurring there, but the terrace structure is buried by the high sedimentation rate. At present, the inherited accretionary structures, the ongoing collision of the Yakutat terrane, and uncertainties in finite fault modeling obscure correlation of slip with topographic and gravity signatures in the 1964 source region.</p> <div class="credits"> <p class="dwt_author">Wells, R. E.; Blakely, R. J.; Scholl, D. W.; Ryan, H. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">289</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010EGUGA..1212942H"> <span id="translatedtitle">Revisiting the physical characterisitics of the <span class="hlt">subduction</span> interplate seismogenic zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Based on the Centennial earthquake catalog, the revised 1964-2007 EHB hypocenters catalog and the 1976-2007 CMT Harvard catalog, we have extracted the hypocenters, nodal planes and seismic moments of worldwide <span class="hlt">subduction</span> earthquakes for the 1900-2007 period. For the 1976-2007 period, we combine the focal solutions provided by Harvard and the revised hypocenters from Engdahl et al. (1998). Older events are extracted from the Centennial catalogue (Engdahl and Villasenor, 2002) and they are used to estimate the cumulated seismic moment only. The selection criteria for the <span class="hlt">subduction</span> earthquakes are similar to those used by Mc Caffrey (1994), i.e., we test if the focal mechanisms are consistent with 1/ shallow thrust events (depth > 70 km, positive slips, and at least one nodal plane gets dip < 45°), and, 2/ the plate interface local geometry and orientation (one nodal plane is oriented toward the volcanic arc, the azimuth of this nodal plane ranges between ± 45° with respect to the <span class="hlt">trench</span> one, its dip ranges between ± 20° with respect to the slab one and the epicentre is located seaward of the volcanic arc). Our study concerns segments of <span class="hlt">subduction</span> zones that fit with estimated paleoruptures associated with major events (M > 8). We assume that the seismogenic zone coincides with the distribution of 5.5 < M < 7 <span class="hlt">subduction</span> earthquakes. We provide a map of the interplate seismogenic zones for 80% of the <span class="hlt">trench</span> systems including dip, length, downdip and updip limits, we revisit the statistical study done by Pacheco et al. (1993) and test some empirical laws obtained for example by Ruff and Kanamori (1980) in light of a more complete, detailed, accurate and uniform description of the <span class="hlt">subduction</span> interplate seismogenic zone. Since <span class="hlt">subduction</span> earthquakes result from stress accumulation along the interplate and stress depends on plates kinematics, <span class="hlt">subduction</span> zone geometry, thermal state and seismic coupling, we aim to isolate some correlations between parameters. The statistical analysis reveals that: 1- vs, the <span class="hlt">subduction</span> velocity is the first order controlling parameter of seismogenic zone variability, both in term of geometry and seismic behaviour; 2- steep dip, large vertical extent and narrow horizontal extent of the seismogenic zone are associated to fast <span class="hlt">subductions</span>, and cold slabs, the opposite holding for slow <span class="hlt">subductions</span> and warm slabs; the seismogenic zone usually ends in the fore-arc mantle rather than at the upper plate Moho depth; 3- seismic rate (?) variability is coherent with the geometry of the seismogenic zone: ? increases with the dip and with the vertical extent of the seismogenic zone, and it fits with vs and with the <span class="hlt">subducting</span> plate thermal state; 4- mega-events occurrence determines the level of seismic energy released along the <span class="hlt">subduction</span> interface, whatever ? is; 5- to some extent, the potential size of earthquakes fits with vs and with the seismogenic zone geometry, but second order controlling parameters are more difficult to detect; 6- the plate coupling, measured through Upper Plate Strain, is one possible second order parameter: mega-events are preferentially associated to neutral <span class="hlt">subductions</span>, i.e. moderate compressive stresses along the plate interface; high plate coupling (compressive UPS) is thought to inhibit mega-events genesis by enhancing the locking of the plate interface and preventing the rupture to extend laterally. This research was supported as part of the Eurohorcs/ESF — European Young Investigators Awards Scheme (resp. F.F.), by funds from the National Research Council of Italy and other National Funding Agencies participating in the 3rd Memorandum of Understanding, as well as from the EC Sixth Framework Programme.</p> <div class="credits"> <p class="dwt_author">Heuret, Arnauld; Lallemand, Serge; Funiciello, Francesca; Piromallo, Claudia</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">290</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.2532S"> <span id="translatedtitle">Vertical slab sinking and westward <span class="hlt">subduction</span> offshore of Mesozoic North America</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Subducted</span> slabs in the mantle, as imaged by seismic tomography, preserve a record of ancient <span class="hlt">subduction</span> zones. Ongoing debate concerns how direct this link is. How long ago did each parcel of slab <span class="hlt">subduct</span>, and where was the <span class="hlt">trench</span> located relative to the imaged slab position? Resolving these questions will benefit paleogeographic reconstructions, and restrict the range of plausible rheologies for mantle convection simulations. We investigate one of the largest and best-constrained Mesozoic slab complexes, the "Farallon" in the transition zone and lower mantle beneath North America. We quantitatively integrate observations from whole-mantle P-wave tomography, global plate reconstructions, and land geological evidence from the North American Cordillera. These three data sets permit us to test the simplest conceivable hypothesis for linking slabs to paleo-<span class="hlt">trenches</span>: that each parcel of slab sank only vertically shortly after entering the <span class="hlt">trench</span> That is, we test whether within the limits of tomographic resolution, all slab material lies directly below the location where it <span class="hlt">subducted</span> beneath its corresponding arc. Crucially and in contrast to previous studies, we do not accept or impose an Andean-style west coast <span class="hlt">trench</span> (Farallon-beneath-continent <span class="hlt">subduction</span>) since Jurassic times, as this scenario is inconsistent with many geological observations. Slab geometry alone suggests that <span class="hlt">trenches</span> started out as intra-oceanic because tomography images massive, linear slab "walls" in the lower mantle, extending almost vertically from about 800 km to 2000+ km depth. Such steep geometries would be expected from slabs sinking vertically beneath <span class="hlt">trenches</span> that were quasi-stationary over many tens of millions of years. Intra-oceanic <span class="hlt">trenches</span> west of Mesozoic North America could have been stationary, whereas a coastal Farallon <span class="hlt">trench</span> could not, because the continent moved westward continuously as the Atlantic opened. Overlap of North American west-coast positions, as reconstructed in a hotspot reference frame, with elongate slab walls predicts where and when the intra-oceanic <span class="hlt">trenches</span> would have been overridden by the westward-moving continent. Land geology plays the role of a validating data set: <span class="hlt">trench</span> override is predicted to coincide with accretion of buoyant arc terranes, deformation of the continental margin and slab window volcanism. We find excellent agreement between predicted and observed accretion episodes, validating both vertical sinking (within observational uncertainties of a few hundred kilometers laterally), and westward <span class="hlt">subduction</span> beneath an archipelago of island arcs west of Jura-Cretaceous North America. Amalgamation of the arcs with North America occurred as the intervening ocean crust was consumed. Implied slab sinking rates are of 10±2 mm/a, uniformly for three different slab walls. We conclude that the hypothesis of essentially vertical slab sinking produces a self-consistent model that explains first-order observations of 200 Ma - 50 Ma Cordilleran geology. By contrast, the standard scenario of a continental Farallon <span class="hlt">trench</span> requires massive amounts of slab to be laterally displaced by 1000+ km after <span class="hlt">subduction</span>, and offers no explanation for a long series of Cretaceous terrane accretions.</p> <div class="credits"> <p class="dwt_author">Sigloch, Karin; Mihalynuk, Mitchell G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">291</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T23B1911H"> <span id="translatedtitle">Physical characteristics of <span class="hlt">subduction</span>-type seismogenic zones revisited</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Based on both the Centennial earthquake catalog, the revised 1964-2007 EHB hypocenters and the 1976-2007 CMT Harvard catalog, we have extracted the hypocenters, nodal planes and seismic moments of worldwide <span class="hlt">subduction</span> earthquakes for the period 1900-2007. For the period 1976-2007, we use the focal solutions provided by Harvard and the revised hypocenters from Engdahl et al. (1998). Older events are extracted from the Centennial catalogue (Engdahl and Villasenor, 2002) and they are used for the estimate of the cumulated seismic moment only. The criteria used to select the <span class="hlt">subduction</span> earthquakes are similar to those used by Mc Caffrey (1994), i.e., we test if the focal mechanisms are consistent with 1/ shallow thrust events (positive slips, at least one nodal plane get dip < 45° and depth > 70 km), and, 2/ the plate interface local geometry and orientation (one nodal plane is oriented toward the volcanic arc, the azimut of this nodal plane is ± 45° with respect to the <span class="hlt">trench</span> one, its dip is ± 20° with respect to the slab one and the epicenter is located seaward of the volcanic arc). Our study concerns segments of <span class="hlt">subduction</span> zones that fit with estimated paleoruptures associated with major events (M > 8). We assume that the seismogenic zone coincides with the distribution of 5.5 < M < 7 <span class="hlt">subduction</span> earthquakes. We then provide a map of the seismogenic zone for 36% of the oceanic <span class="hlt">subduction</span> plates boundaries including dip, length, downdip and updip limits. The remnant 64% correspond to either weakly coupled oceanic <span class="hlt">subduction</span> zones, slow <span class="hlt">subduction</span> rates, or long recurrence period between earthquakes. We then revisit the statistical study done by Pacheco et al. (1993) and tested some empirical laws obtained for example by Kanamori (1986) in light of a more complete, more detailed, more accurate and more uniform description of the <span class="hlt">subduction</span> interplate seismogenic zone. Since the <span class="hlt">subduction</span> earthquakes result from stress accumulation along the interplate and that stress depends on plates kinematics, <span class="hlt">subduction</span> zone geometry, thermal state and seismic coupling, we aim to isolate some correlations between parameters.</p> <div class="credits"> <p class="dwt_author">Heuret, A.; Lallemand, S.; Piromallo, C.; Funiciello, F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">292</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.V33A2355N"> <span id="translatedtitle">A close link between serpentinization and seismogenesis in the Philippine Sea slab beneath Kanto, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Kanto district in central <span class="hlt">Japan</span>, which surrounds the Tokyo metropolitan area, is known as a unique region in the world in terms of plate tectonics. This region is located behind a <span class="hlt">trench-trench-trench</span> (TTT) triple junction with two obliquely <span class="hlt">subducting</span> oceanic plates, the Philippine Sea (PHS) and Pacific (PAC) plates. Recent studies have shown that the bottom of the PHS slab is in contact with the upper surface of the Pacific slab beneath Kanto (Uchida et al., 2009, EPSL; Nakajima et al., 2009, JGR). As a result of the <span class="hlt">subduction</span> of the two slabs, many disastrous M~8 and numerous M~7 earthquakes have struck the Tokyo metropolitan area. For example, the 1923 Kanto earthquake (M7.9), one of the most destructive earthquakes in the 20th century, caused severe damage to the Tokyo metropolitan area, along with 105,000 fatalities. We perform travel-time tomography beneath Kanto, <span class="hlt">Japan</span>, to obtain detailed structures of the <span class="hlt">subducting</span> PHS slab and to discuss the seismogenesis of interplate and intraplate earthquakes in terms of the contact of the two slabs. We detected a wedge-shaped prominent low-velocity zone with high Vp/Vs at the easternmost portion of the PHS slab. The western boundary of the low-velocity zone is sub-vertical, and seismic velocities vary by 15-20% across it over a short distance of ~10 km. This low-velocity zone is interpreted as serpentinized mantle of the PHS slab because serpentinization of the mantle of the PHS plate is observed along the Izu-Bonin <span class="hlt">trench</span> before its <span class="hlt">subduction</span> (Kamimura et al., 2002, PEPI). We found two clear relation between serpentinization and seismicity around the PHS slab. First, thrust earthquakes between the bottom of the PHS slab and the upper surface of the PAC slab occur inhomogenously in space and are almost absent along the PHS-PAC interface overlain by the serpentinized PHS-slab mantle. This observation strongly suggests that low viscosity of the serpentine prevents the plate interface from slipping seismically, and hence the serpentine can be a barrier of seismic rapture along the plate interface. Second, two intraslab earthquakes in 1921 (M7.0) and 1987 (east off Chiba earthquake, M6.7) appear to have occurred along the western boundary of the serpentinized mantle (serpentinized boundary) accompanied by right-lateral movement, based on analyses of focal mechanisms and aftershock distribution. A sub-vertical earthquake cluster penetrating the entire Philippine Sea slab is also observed along the serpentine boundary, and four earthquakes in the cluster have strike-slip focal mechanisms, similar to that of the 1987 earthquake. Focal mechanisms obtained for past large earthquakes and present-day microearthquakes suggest the concentration of right-lateral deformation along the mechanically weak serpentinized boundary.</p> <div class="credits"> <p class="dwt_author">Nakajima, J.; Hasegawa, A.; Umino, N.; Demachi, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">293</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012GeoRL..3919303I"> <span id="translatedtitle">Seismic scatterers within <span class="hlt">subducting</span> slab revealed from ambient noise autocorrelation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We reconstructed new migrated images from autocorrelation functions of ambient noise at seismic stations in northeastern <span class="hlt">Japan</span>. During the analysis period, the autocorrelation functions, having a frequency range of 0.5-2 Hz, showed some coherent signals at large lapse times of 10-50 s as well as at small lapse times of less than 10 s. These signals were also coherent in space along cross sections across the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone. The migrated images show seismic scatterers within the <span class="hlt">subducting</span> Pacific Slab at the depth range of 50-150 km. The distribution of the scatterers within the <span class="hlt">subducting</span> slab is comparable to the double seismic zone in the <span class="hlt">subduction</span> zone; in particular, the thickness of the distribution of the seismic scatterers is consistent with that of two planes of the double seismic zone. This indicates inhomogeneities in the seismic velocity structure around the upper and lower planes of the seismicity. The new migrated images suggest that seismic scatterers, such as fluid from dehydration reactions of the hydrated metamorphosed mantle, exist in the lower as well as upper plane of the seismicity in the double seismic zone; this fluid may act as a scatterer within the <span class="hlt">subducting</span> slab.</p> <div class="credits"> <p class="dwt_author">Ito, Yoshihiro; Shiomi, Katsuhiko</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">294</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011GeoJI.184..991B"> <span id="translatedtitle"><span class="hlt">Subduction</span> initiation along the inherited weakness zone at the edge of a slab: Insights from numerical models</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A preexisting weakness zone in the lithosphere is required to initiate <span class="hlt">subduction</span>. Here, we focus on a new type of weakness zone, a <span class="hlt">Subduction</span>-Transform Edge Propagator (STEP) fault, which is inherited from a tear along the edge of a slab. Using coupled thermal-mechanical models, we show that STEP fault-perpendicular convergence results in a dipping shear zone in any tectonic setting. At a continental margin, this shear zone dips towards the continent, which is an excellent starting condition for ocean-continent <span class="hlt">subduction</span>. If (far field) convergence persists, STEP faults become new <span class="hlt">subduction</span> boundaries. The <span class="hlt">trench</span> moves landward during the earliest stages of convergence. When slab pull becomes a dominant driving force, after ˜80 km convergence, <span class="hlt">trench</span> roll-back commences. The initial geometry and mechanical properties of the sub-crustal STEP fault zone affect the results; <span class="hlt">subduction</span> initiation is facilitated by a wide (˜100 km) and low-viscosity weakness zone. Incipient <span class="hlt">subduction</span> is easier for young oceanic lithosphere due to its lower flexural rigidity and is insensitive to the far field convergence rate. As STEP faults are commonly associated with young oceanic lithosphere, <span class="hlt">subduction</span> initiation is thus relatively easy along them. Of particular interest are continent-ocean margins where STEP faulting has occurred.</p> <div class="credits"> <p class="dwt_author">Baes, Marzieh; Govers, Rob; Wortel, Rinus</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">295</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFM.T21E..04H"> <span id="translatedtitle">Submarine mass wasting processes along slopes influenced by long-term tectonic erosion: The Middle America <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have studied submarine land-sliding using a seafloor topography and side-scan sonar data along the continental slope of the Middle America <span class="hlt">Trench</span>. This <span class="hlt">subduction</span> zone is dominated by tectonic erosion. Studies during the last few decades have shown mass wasting structures at submarine slopes around the world's continental margins, hot-spot volcanic islands, and volcanic island arcs. At Atlantic margins slides initiate at low slope angles and appear triggered by high sediment accumulation rates. At volcanic islands large-scale land-sliding is caused by volcano sector collapse. At <span class="hlt">subduction</span> zones with accretionary prisms, land-sliding seems associated to contractional tectonics and fluid seepage. Submarine mass movements at <span class="hlt">subduction</span> zones dominated by tectonic erosion are comparatively limited. However, tectonic erosion is active in about 50% of the world <span class="hlt">subduction</span> zones. Distinct failures have been studied at slopes in Peru, Costa Rica, Nicaragua and New Zealand but extensive surveys have not been obtained. We present a comprehensive data sets on seafloor mapping on a <span class="hlt">subduction</span> zone dominated by tectonic erosion. The data covers much of the Middle America <span class="hlt">Trench</span> (MAT) from the Mexico-Guatemala border to Costa Rica - Panama border. The goal of this contribution is to evaluate how long-term tectonics caused by <span class="hlt">subduction</span> erosion preconditions the continental slope structure to modulate the generation of land-sliding. We show that changes in <span class="hlt">subduction</span> erosion processes, interacting with the local topography of the <span class="hlt">subducting</span> plate correlate to variations in the type and distribution of failures along the slope of the region.</p> <div class="credits"> <p class="dwt_author">Harders, R.; Ranero, C. R.; Weinrebe, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">296</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T21B1793F"> <span id="translatedtitle">Role of the Overriding Plate in the <span class="hlt">Subduction</span> Process: Insights from Numerical Models</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Active convergent margins are primarily shaped by the interplay among the <span class="hlt">subducting</span> plate, overriding plate, and mantle. The effect of important forces, like far-field mantle flow, overriding plate motion, and inter-plate coupling, however, remains partially ambiguous. In a preliminary attempt to clarify their role, a self-consistent, visco-elastic, plane-strain, mechanical finite element model, in which <span class="hlt">subducting</span> plate, overriding plate and mantle interact dynamically, is developed. In this quasi-static framework with a freely moving slab, <span class="hlt">trench</span>, and inter-plate fault, the role of a compressive overriding plate on <span class="hlt">subduction</span> zone kinematics, morphology and stress-state is characterized. A slab interacting solely with a semi-analytical three-dimensional mantle flow formulation shows that local non-induced mantle flow influences slab geometry and kinematics, adding an important dynamic term to the system. The impact of an overriding plate on this system is determined completely by overriding plate <span class="hlt">trench</span>-ward motions and is only pertinent if the overriding plate actively advances the <span class="hlt">trench</span>. A <span class="hlt">trench</span>-ward moving overriding plate indents the slab and thereby enforces <span class="hlt">trench</span> retreat and decreases slab dip. It also stimulates over-thrusting of the overriding plate onto the slab, and thereby permits mountain building within the overriding plate. Frictional resistance is observed to have a dominant local effect within the overriding plate as it is increasingly dragged down, thereby inhibiting the growth of overriding plate topography. A distinguishable effect on large-scale <span class="hlt">trench</span> motions and deep slab dip is, however, absent for renormalized friction coefficients ranging up to about 0.2. Minor additional effects include a decrease in plate motions of about 15% and slab bending stresses of about 10%.</p> <div class="credits"> <p class="dwt_author">Funiciello, F.; Dinther, Y. V.; Morra, G.; Faccenna, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">297</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002AGUFM.V11A1368L"> <span id="translatedtitle">Northern Migration of Arc Volcanism in Western Panama: Evidence for <span class="hlt">Subduction</span> Erosion?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">40Ar/39Ar laser age dating of <span class="hlt">subduction</span>-related volcanic and plutonic rocks from western Panama range from 1.22 +/- 0.09 to 60.89 +/- 0.47 Ma and show that the volcanic arc migrated away from the <span class="hlt">trench</span> with decreasing age. Vulcan Baru, which belongs to the Cordillera Central volcanic arc running through central western Panama, is still active. Our ages from the Cordillera Central extend its age to 8.6 +/- 0.4 Ma. An age of 34.4 +/- 0.5 Ma was obtained from a basaltic andesite sample south of the Cordillera Central just north of the Sona Peninsula. Further south in southern Azuero and Sona Peninsulas and on Coiba Island, calcalkaline rocks range from 48.8 +/- 0.4 to 60.89 +/- 0.47 Ma. Arc volcanism migrated ~120 km northwards (away from the <span class="hlt">trench</span>) over the last 40-50 Ma, yielding a rate of ~2.7 mm/yr. This migration could either reflect: (1) <span class="hlt">Subduction</span> erosion resulting from the <span class="hlt">subduction</span> of the Galapagos hotspot track, as has been recently proposed off the coast of Costa Rica [1], or (2) a shallowing of the angle of the <span class="hlt">subducting</span> slab, possibly resulting from the <span class="hlt">subduction</span> of progressively younger and more buoyant oceanic lithosphere through time. Preliminary geochemical data suggest that the fluid flux of the Eocene-Paleocene arc and the Miocene-Holocene arc was relatively constant pointing to a uniform <span class="hlt">subduction</span> angle. Our data favor a migrating arc due to <span class="hlt">subduction</span> erosion over the last 40-50 Ma. Additional geochemical studies are underway to further distinguish between the aforementioned models. Literatur [1] Ranero, C.R. and von Huene, R., 2000, <span class="hlt">Subduction</span> erosion along the Middle America convergent margin. - Nature 404: 748-252.</p> <div class="credits"> <p class="dwt_author">Lissinna, B.; Hoernle, K.; van den Bogaard, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">298</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JAESc..63..206F"> <span id="translatedtitle">Genesis of jadeite-quartz rocks in the Yorii area of the Kanto Mountains, <span class="hlt">Japan</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This paper reports the results of U-Pb dating and REE (rare earth element) analysis of zircons separated from jadeite-quartz rocks within serpentinite mélanges in the Yorii area of the Kanto Mountains, <span class="hlt">Japan</span>. These rocks contain jadeite, albite, and quartz, with minor aegirine-augite, zircon, monazite, thorite, allanite, and titanite. Mineral textures provide evidence of a jadeite + quartz = albite reaction during formation of these jadeite-quartz rocks. Zircon crystals separated from the jadeite-quartz rocks can be split into two distinct types, here named Types I and II, based on their morphology and REE concentrations. Type I zircons are prismatic and have fluid, jadeite, quartz, and albite inclusions. Those show positive Ce and negative Eu anomalies and HREE (heavy rare earth element) enriched chondrite normalized REE patterns and have higher REE concentrations than those generally found in magmatic zircons. Type I zircons would have precipitated from a fluid. Mineralogical observation provides that Type I zircon crystallized at the same timing of the formation of the jadeite-quartz rocks. Type II zircons are porous and have REE patterns indicative of a hydrothermal zircon. Both types of zircons are fluid-related. Type I zircons yield U-Pb ages of 162.2 ± 0.6 Ma, with an MSWD (mean square weighted deviation) of 1.4. At this time, <span class="hlt">Japan</span> was still a part of the eastern margin of the Asian continent, with the <span class="hlt">subduction</span> of the oceanic paleo-Pacific Plate leading to the formation of the Jurassic Mino-Tanba-Chichibu accretionary complex in <span class="hlt">Japan</span>. The age data indicate that the jadeite-quartz rocks formed in a deep <span class="hlt">subduction</span> zone environment at the same time as the formation of the Jurassic accretionary complex in a shallower near-<span class="hlt">trench</span> <span class="hlt">subduction</span> zone environment. The jadeite-quartz rocks contain high concentrations of Zr and Nb, with low LILE (large ion lithophile elements) concentrations, suggesting that the HFSE (high field strength elements) can be concentrated into jadeite-quartz rocks prior to a fluid moving up into the mantle wedge. Typical arc volcanic rocks are depleted in the HFSE, suggesting that the high HFSE concentrations within jadeite-quartz rocks are consistent with fluids being stripped of their HFSE prior to interaction with mantle material during the formation of arc magmas. Although these jadeite-bearing rocks are rare occurrences on the surface exposure, they could be abundant in or above <span class="hlt">subducted</span> slabs.</p> <div class="credits"> <p class="dwt_author">Fukuyama, Mayuko; Ogasawara, Masatsugu; Horie, Kenji; Lee, Der-Chuen</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">299</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.indiana.edu/~g103/plate/plate2.html"> <span id="translatedtitle"><span class="hlt">Subduction</span> at Convergent Boundary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">The representation depicts <span class="hlt">subduction</span>. The narrated animated movie (simulation) shows <span class="hlt">subduction</span> of the Indian Plate as the Indian Plate and the Eurasian Plate converge at the plate boundary. The segment begins showing a world view of the Earth's plates and zooms in on the highlighted Indian and Eurasian plate activity. The animation transitions to a cross-sectional view, giving an inside-the-Earth look at what happens as these plates converge. The movie can be viewed in two ways- in continuous play or step by step.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">300</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005E%26PSL.239...18R"> <span id="translatedtitle"><span class="hlt">Subduction</span> of the Nazca Ridge and the Inca Plateau: Insights into the formation of ore deposits in Peru [rapid communication</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A large number of ore deposits that formed in the Peruvian Andes during the Miocene (15-5 Ma) are related to the <span class="hlt">subduction</span> of the Nazca plate beneath the South American plate. Here we show that the spatial and temporal distribution of these deposits correspond with the arrival of relatively buoyant topographic anomalies, namely the Nazca Ridge in central Peru and the now-consumed Inca Plateau in northern Peru, at the <span class="hlt">subduction</span> zone. Plate reconstruction shows a rapid metallogenic response to the arrival of the topographic anomalies at the <span class="hlt">subduction</span> <span class="hlt">trench</span>. This is indicated by clusters of ore deposits situated within the proximity of the laterally migrating zones of ridge <span class="hlt">subduction</span>. It is accordingly suggested that tectonic changes associated with impingement of the aseismic ridge into the <span class="hlt">subduction</span> zone may trigger the formation of ore deposits in metallogenically fertile suprasubduction environments.</p> <div class="credits"> <p class="dwt_author">Rosenbaum, Gideon; Giles, David; Saxon, Mark; Betts, Peter G.; Weinberg, Roberto F.; Duboz, Cecile</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-10-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img 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href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_17");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">301</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012PEPI..194...38D"> <span id="translatedtitle">Deformation and mantle flow beneath the Sangihe <span class="hlt">subduction</span> zone from seismic anisotropy</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Subduction</span> of oceanic lithosphere is the most direct feedback between the Earth's surface and deep interior. However, the detail of its interaction with the broader convecting mantle is still unclear. Mantle flow around <span class="hlt">subduction</span> zones can be constrained using seismic anisotropy, but despite many such studies, a simple global picture is lacking. The Sangihe <span class="hlt">subduction</span> zone (where the Molucca Sea microplate is <span class="hlt">subducting</span> westward beneath the Eurasian plate) is part of the tectonically complex Sulawesi-Philippine region, and an ideal natural laboratory to study complex <span class="hlt">subduction</span> processes. We investigate the anisotropic structure of the Sangihe <span class="hlt">subduction</span> zone with shear wave splitting measurements of local S and SKS phases at two stations (MNI in Sulawesi, DAV in the Philippines), as well as downgoing S phases at five stations at teleseismic distances. Combining different phases allows a better vertical resolution of anisotropic fabrics than is possible with a single phase. The broad depth distribution of local events (˜60-630 km) allows us to observe a change in splitting behaviour at ˜380 km depth: above, fast directions (?) are <span class="hlt">trench</span>-parallel and delay times (?t) are ˜0.34-0.53 s with no increase with depth. We suggest this anisotropy is caused by aligned cracks, possibly melt-filled beneath the volcanic arc, and fossil anisotropy in the overriding plate. Below ˜380 km, ? is predominantly <span class="hlt">trench</span>-normal and ?t are slightly higher (˜0.53-0.65 s). As no correlation is observed with inferred distance travelled inside the slab, we attribute this anisotropy to shear layers atop the slab, which are coherent from ˜200 to 400 km depth and perhaps extend into the transition zone. SKS and source-side measurements show larger ?t (˜1.53 and 1.33 s, respectively) and <span class="hlt">trench</span>-parallel ?. Since these phases predominantly sample sub-slab mantle, we consider along-strike lateral flow associated with the double-sided <span class="hlt">subduction</span> of the Molucca Sea microplate to be the most likely explanation. We thus infer three dominant regions of anisotropy at the Sangihe <span class="hlt">subduction</span> zone: one within the overriding lithosphere, one along the slab-wedge interface, and one below the <span class="hlt">subducting</span> Molucca Sea slab. The mantle wedge above 200 km depth and the slab itself do not seem to contribute notably to the measured anisotropy. This study demonstrates the insight seismic anisotropy can provide into mantle dynamics even in tectonically complex <span class="hlt">subduction</span> systems.</p> <div class="credits"> <p class="dwt_author">Di Leo, J. F.; Wookey, J.; Hammond, J. O. S.; Kendall, J.-M.; Kaneshima, S.; Inoue, H.; Yamashina, T.; Harjadi, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">302</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/2390023"> <span id="translatedtitle">Aseismic slip transients emerge spontaneously in three-dimensional rate and state modeling of <span class="hlt">subduction</span> earthquake sequences</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">[1] To investigate the possible physical mechanisms of recently observed aseismic slip events in the Cascadia, <span class="hlt">Japan</span> and Mexico <span class="hlt">subduction</span> zones, we apply a Dieterich-Ruina rate and state friction law to a three dimensional model of a shallow <span class="hlt">subduction</span> fault. That is loaded by imposed steady plate slip rate far downdip along the thrust interface. Friction properties are temperature and</p> <div class="credits"> <p class="dwt_author">Yajing Liu; James R. Rice</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">303</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48927818"> <span id="translatedtitle">Aseismic slip transients emerge spontaneously in three-dimensional rate and state modeling of <span class="hlt">subduction</span> earthquake sequences</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">To investigate the possible physical mechanisms of recently observed aseismic slip events in the Cascadia, <span class="hlt">Japan</span> and Mexico <span class="hlt">subduction</span> zones, we apply a Dieterich-Ruina rate and state friction law to a three dimensional model of a shallow <span class="hlt">subduction</span> fault. That is loaded by imposed steady plate slip rate far downdip along the thrust interface. Friction properties are temperature and hence</p> <div class="credits"> <p class="dwt_author">Yajing Liu; James R. Rice</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">304</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..1513916G"> <span id="translatedtitle">Plate Tectonics: From Initiation of <span class="hlt">Subduction</span> to Global Plate Motions (Augustus Love Medal Lecture)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Plates are driven by buoyancy forces distributed in the mantle, within cooling oceanic plates (ridge push) and within <span class="hlt">subducted</span> slabs. Although the case is often made that <span class="hlt">subducted</span> slabs provide the principle driving force on plate motion, consensus has not been achieved. This is at least partially due to the great difficulty in realistically capturing the role of slabs in observationally-constrained models as slabs act to drive and resist plate motions through their high effective viscosity. Slab buoyancy acts directly on the edge of the plate (slab pull), while inducing mantle flow that tends to drag both <span class="hlt">subducting</span> and overriding plates toward the <span class="hlt">trench</span>. While plates bend during <span class="hlt">subduction</span> they undergo a form of 'plastic failure' (as evident through faulting, seismicity and reduction of flexural parameters at the outer <span class="hlt">trench</span> wall). The birth of a new <span class="hlt">subduction</span> zone, <span class="hlt">subduction</span> initiation, provides important insight into plate motions and <span class="hlt">subduction</span> dynamics. About half of all <span class="hlt">subduction</span> zones initiated over the Cenozoic and the geophysical and geological observations of them provide first order constraints on the mechanics of how these margins evolved from their preexisting tectonic state to self-sustaining <span class="hlt">subduction</span>. We have examples of <span class="hlt">subduction</span> initiation at different phases of the initiation process (e.g. early versus late) as well as how margins have responded to different tectonic forcings. The consequences of <span class="hlt">subduction</span> initiation are variable: intense <span class="hlt">trench</span> roll back and extensive boninitic volcanism followed initiation of the Izu-Bonin-Mariana arc while both were absent during Aleutian arc initiation. Such differences may be related to the character of the preexisting plates, the size of and forces on the plates, and how the lithosphere was initially bending during initiation. I will address issues associated with the forces driving plate tectonics and initiating new <span class="hlt">subduction</span> zones from two perspectives. A common thread is the origin and evolution of intense back arc spreading and rapid roll back associated with some ocean-ocean <span class="hlt">subduction</span> zones. I will look at the dynamics driving global plate motions and the time-dependence of <span class="hlt">trench</span> rollback regionally. Capitalizing on advances in adaptive mesh refinement algorithms on parallel computers with individual plate margins resolved down to a scale of 1 kilometer, observationally constrained, high-resolution models of global mantle flow now capture the role of slabs and show how plate tectonics is regulated by the rheology of slabs. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. I will then describe regional, time-dependent models, address the causes and consequences of <span class="hlt">subduction</span> initiation, and show that most back arc extension follows <span class="hlt">subduction</span> initiation. Returning to the global models, inverse models using the full adjoint of the variable viscosity, Stokes equation are now possible and allow an even greater link between present-day geophysical observations and the dynamics from local to global scales.</p> <div class="credits"> <p class="dwt_author">Gurnis, Michael</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">305</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.6330R"> <span id="translatedtitle"><span class="hlt">Subduction</span> and break-off controls on Indentation tectonics and Western Syntaxis formation during India-Asia convergence</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The indentation of the Indian plate into the Asian lithosphere is one of the most spectacular features of plate tectonics. Large deformations of the Himalayan front and Asian continental interiors are the result of the interaction between the <span class="hlt">subducting</span> Greater India and the Asian upper plates during convergence. However, how deep <span class="hlt">subduction</span> and indentation tectonics are coupled remains unknown. Revising the links between Asian tectonics and <span class="hlt">subduction</span> of Tethys, Greater India and the breakoff episodes imaged in tomography allows formulating hypotheses on the interaction mechanisms operating. These are tested using self-consistent three-dimensional numerical models of coupled <span class="hlt">subducting</span> - upper plates in an ambient mantle. We find that the <span class="hlt">subduction</span> of the buoyant continent progressively decreases the driving force available and is followed by a convergence velocity drop, similar to the observed, however deformation is mostly accommodated along the upper plate margin. When slab detaches during <span class="hlt">subduction</span>, similar convergence rates are sustained, yet transient stresses propagate far into the upper plate interiors, localising along a belt at a high angle with the <span class="hlt">trench</span>. Breakoff at the ocean-continent boundary confers long-lived complex slab morphology, with shallow upper-plate underthrusting laterally stepping to steeper dip along the <span class="hlt">trench</span>. Following breakoff, the <span class="hlt">trench</span> curvature progressively increases as convergence proceeds. The model features are compatible with those of the India-Asia convergence zone, with the large underthrusting of the Indian lithosphere and <span class="hlt">subduction</span> far north of the Himalayan front and beneath the Hindu-Kush, to the west, and the lateral variation to the east, where long-term Indian <span class="hlt">subduction</span> occurred along a margin located closer to the actual front. Our models allow explaining the development of the Western Syntaxis as the consequences of the breakoff. By inference, the breakoff episodes likely provided the conditions for large stress surge in the Asian lithosphere that resulted in the formation of the long-lived major intra-continental faulting systems of the Red River-Altyn Tagh and Tien Shan.</p> <div class="credits"> <p class="dwt_author">Replumaz, Anne; Capitanio, Fabio A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">306</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUSM.G23A..02K"> <span id="translatedtitle">Silent Earthquakes, Structure, and Seismotectonics of the Mexican <span class="hlt">Subduction</span> Zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Based on tide gauge, levelling and GPS data, we find evidence for a sequence of silent earthquakes in 1972, 1979, 1996, 1998, 2002, and 2003 in the central part of the Mexican <span class="hlt">subduction</span> zone (Guerrero and Oaxaca states). Characteristic duration of these events was 4-6 months and the maximum equivalent magnitude exceeded Mw7.5. In all cases, with the exception of the event of 1996, the slow aseismic slips initiated in the Guerrero seismic gap and propagated laterally along the strike of the <span class="hlt">subduction</span> zone. However, the propagation velocity of ~2 km/day could be estimated reliably only for the most recent 2002 event. The observations indicate that the total area affected by the 1972 and 2002 slow events may have been greater than ~300x700 km2. The shallow, subhorizontal configuration of the plate interface in Guerrero and partly in Oaxaca appears to be a controlling factor for the physical conditions favorable for such extensive slow slip. The entire partially coupled interplate zone in Guerrero is of ~160 km width (starting ~55 km inland from the <span class="hlt">trench</span>) while the seismogenic, shallowest part of it is only ~40 km wide. The elastic half space dislocation models (EHSDM) applied to invert the observed slow aseismic slip displacements (2002 event) can not distinguish between the two main scenarios: (a) slow slip of ~10 cm occurring on the entire coupled interface, and (b) slip of 15-20 cm taking place only on the transition part of the plate interface from ~90 to 180 km. In the first case the anticipated large thrust earthquake in the Guerrero seismic gap should be somewhat delayed, while on the second case the seismic rupture may be advanced. Thermo-mechanical modeling of the Mexican <span class="hlt">subduction</span> zone shows that the coupling cutoff of ~450oC on the plate interface at ~180-205 km from the <span class="hlt">trench</span> is achievable only for the subhorizontal configuration of the <span class="hlt">subduction</span> zone. In this case the predominant metamorphic facies on the surface of <span class="hlt">subducted</span> crust should be blueschists. There are, however, several observations which can not be explained in the frame of the EHSDM, e.g., a considerable tilt observed in the coastal area and a relatively large displacement on the Popocatepetl volcano (~400 km from the <span class="hlt">trench</span>) during the 2002 silent earthquake.</p> <div class="credits"> <p class="dwt_author">Kostoglodov, V.; Larson, K. M.; Singh, S.; Lowry, A. R.; Santiago, J.; Franco, S.; Bilham, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">307</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AGUFMDI31A2166K"> <span id="translatedtitle">Distribution of Hydrous Minerals in the <span class="hlt">Subduction</span> System beneath Mexico</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Teleseismic converted phases are used to estimate the mineralogy of <span class="hlt">subducting</span> material as a function of depth along the Cocos slab in central and southern Mexico. Modeling of the receiver function (RF) conversion amplitudes of the horizontal slab, south of the Trans-Mexican Volcanic Belt (TMVB) in central Mexico, reveals a thin low-velocity zone between the Cocos plate and the continental crust that appears to absorb nearly all of the strain between the upper plate and the Cocos slab. Using Vp/Vs versus Vs in a range of likely pressures and temperatures for candidate mineral phases, this thin (~4 km thick) layer in the flat slab region of central Mexico is determined to be enriched with hydrous minerals such as talc over normal oceanic crustal compositions such as MORB-like gabbro. On the other hand, the mineralogy of the oceanic crust downdip in the steep part of the slab beneath the TMVB is enriched with lawsonite and zoisite, which then transitions into gabbroic and eclogitic assemblages at 100 km. This supports arc volcanism in the TMVB directly above the slab as well as the slab rollback. In contrast, the dominant mineral phase in the upper oceanic crust of southern Mexico beneath the Isthmus of Tehauntepec is amphibole on top of unaltered gabbroic oceanic crust. Based on the P-T curves for equilibria involving talc derived from available thermodynamic data, the generation of talc from the basaltic lithology of the oceanic crust <span class="hlt">subducting</span> from the <span class="hlt">trench</span> side is nearly impossible. We therefore propose that the talc-rich layer on top of the <span class="hlt">subducting</span> plate is generated from the mantle wedge side during the slab flattening process coupled with <span class="hlt">trench</span> rollback. The talc-rich rocks at the slab interface can be formed in the mantle by the addition of silica transported by rising fluids via the dehydration reaction from the <span class="hlt">subducting</span> oceanic crust and by mechanical mixing of mantle and siliceous rocks. Thus, it appears that the thin low-strength layer, which decouples the horizontal slab from the continental crust, originated from the mantle wedge side rather than the <span class="hlt">trench</span> side. The evolution of this low-strength zone has important implications for the dynamics of the <span class="hlt">subduction</span> system including the flattening process of the slab as well as the geochemistry of the mantle wedge and arc in central Mexico.</p> <div class="credits"> <p class="dwt_author">Kim, Y.; Clayton, R. W.; Jackson, J. M.; Asimow, P. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">308</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AGUFM.T14A..08F"> <span id="translatedtitle">Oblique Convergence, Slab Trajectories, and the Thermal-deformational Path of <span class="hlt">Subducting</span> Lithosphere: Implications for Rupture Segmentation (Invited)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Most <span class="hlt">subduction</span> zones are oriented such that convergence obliquity is relatively minimal, however several major (e.g. Sumatra-Andaman-Burma; Aleutian) and more minor (e.g. Puysegur-Fiordland; Caribbean) <span class="hlt">subduction</span> zones undergo transitions from relatively orthogonal to nearly translational interactions along the length of the <span class="hlt">subduction</span> system. Although in some cases the upper plate accommodates this obliquity through slip partitioning onto translational faults, such cases of slip partitioning do not appear to affect the overall trajectory or geometry of the slab as it transits the <span class="hlt">subduction</span> regime. Using the Sumatra-Andaman-Burma and Puysegur-Fiordland (New Zealand) <span class="hlt">subduction</span> zones as representative of major and minor <span class="hlt">subduction</span> boundaries (respectively), I analyze the implications for thermal and strain histories as the <span class="hlt">subducting</span> lithosphere transits the <span class="hlt">subduction</span> zone. Several key points are seen in an initial analysis: (1) in spite of appearing to be highly bent as the obliquity increases, the geometry/trajectory of the slab (in its plate motion reference frame) is essentially similar along the entire margin; (2) as the length of the nearly-translational plate boundary segment increases, substantial <span class="hlt">trench</span>-perpendicular stretching and/or tearing must occur; and (3) much of the seismicity along the translational segments represents this stretching/tearing deformation (i.e. intraslab) rather than more typical plate interface seismicity. Overall, these effects associated with changes in <span class="hlt">trench</span> orientation play a role in creating spatial variability in slab deformation and <span class="hlt">subduction</span> zone seismicity. Along the Sumatra-Andaman-Burma and Puysegur-Fiordland <span class="hlt">subduction</span> zones this transition occurs over short distances implying a threshold for change from interplate to intraplate dominated slab deformation.</p> <div class="credits"> <p class="dwt_author">Furlong, K. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">309</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002AGUFM.G61A0965A"> <span id="translatedtitle">Chilean Analog for 17th-Century Uplift Along the Southern Kuril <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">What caused a meter or so of widespread uplift in eastern Hokkaido in the last decades of the 17th century A.D.? Coasts along the Kamchatka, Kuril, and <span class="hlt">Japan</span> <span class="hlt">Trenches</span> lack documented modern analogs for uplift this large and geologically fast. But a meter of uplift, in 1960-1990, raised shorelines inland from the seismic rupture plane of the 1960 Chile earthquake. By this Chilean analogy, Hokkaido's 17th-century uplift may have occurred aseismically-during minutes of precursory slip and also during decades of postseismic creep, all downdip from the seismic rupture surface. Hokkaido's area of 17th-century uplift extends at least 50 km along the southern Kuril <span class="hlt">Trench</span>. It includes the estuaries Akkeshi-ko and Hichirippu, on the Pacific coast, and Furen-ko and Onneto, on the Okhotsk Sea. At each estuary, intertidal and subtidal flats rose with respect to tide level; wetland plants colonized the emerging land; and peaty wetland deposits thereby covered mud and sand of the former flats. Such evidence for uplift was first reported by Sawai and coworkers, who identified at least three uplift events from the past 2500 years at Akkeshi-ko [Quat. Res. 56, 231-241, 2001]. The youngest of the uplift events probably began in the 1660s or 1670s, as dated by tephra layers. The uplift probably exceeded 1/2 m (inferred from paleoecology) without far exceeding 1 m (estimated by comparing early descriptions of Akkeshi-ko). Though this evidence permits the Hokkaido uplift to have been coseismic or aseismic or both, depths to the <span class="hlt">subducting</span> Pacific plate probably preclude seismic rupture of the plate boundary directly beneath the uplifted area. These depths exceed 50 km and also exceed depths of seismic coupling inferred from continuous GPS [Mazzotti et al., JGR 105, 13159-13177, 2000; Ito et al., EPSL 176, 117-130, 2000]. When Hokkaido's plate boundary ruptured in earthquakes of Mw 8.1 (in 1952) and 7.8 (1973), the ruptures occurred offshore at depths less than 50 km, and the adjoining coast either subsided several centimeters or failed to change level. Perhaps more appropriate to eastern Hokkaido is analogy with the preseismic and postseismic uplift that occurred above forearc mantle, inland from the seismic rupture surface of the 1960 Chile earthquake of Mw 9.5. This uplift began in 1960 as an inner upwarp many tens of kilometers wide and up to 1 m in amplitude [GSA Bull. 81, 1001-1030, 1970]. It caused shoreline changes that residents associated with the mainshock but may have resulted instead from a slow precursory earthquake downdip from the mainshock [Linde and Silver, GRL 16, 1305-1308, 1989]. For decades since 1960, uplift has been accumulating at 2-4 cm/yr in Chile's inner upwarp and at its boundary with the coseismic downwarp [Barrientos et al., GRL 19, 701-704, 1992]. This Chilean analogy may clarify the earthquake hazard implied by 20th-century subsidence in eastern Hokkaido. The subsidence, which averaged 5-10 mm/yr, probably represents strain accumulation; the <span class="hlt">subducting</span> Pacific plate is dragging eastern Hokkaido downward. In that case, why did the offshore ruptures in 1952 and 1973 fail to reverse the subsidence [Kasahara and Kato, Pageoph 119, 392-403, 1981]? Perhaps their rupture areas and displacements were too small to allow large aseismic slip downdip from the seismic rupture surface. In that case, the 17th-century uplift entailed a Hokkaido earthquake larger than those in 1952 and 1973.</p> <div class="credits"> <p class="dwt_author">Atwater, B. F.; Ikeda, Y.; Satake, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">310</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://patft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=1&p=1&f=G&l=50&d=PTXT&S1=%22Cascadia+subduction+zone%22&OS=%22The+Cascadia+subduction+zone%22&RS=%22The+Cascadia+subduction+zone%22"> <span id="translatedtitle"><span class="hlt">Subductive</span> waste disposal method</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://patft.uspto.gov/netahtml/PTO/search-adv.htm">US Patent & Trademark Office Database</a></p> <p class="result-summary">A method for the disposal of nuclear and toxic waste materials comprising the placing of waste materials into waste repositories radiating from an access tunnel constructed into a subtending tectonic plate adjacent or as near as possible a <span class="hlt">subduction</span> zone. The waste materials descend within the tectonic plate into the mantle of the earth.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">1991-06-11</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">311</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.2133I"> <span id="translatedtitle">Nature of the Moho in <span class="hlt">Japan</span> and Kamchatka</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Kamchatka peninsula and the islands of <span class="hlt">Japan</span> are located along the eastern margin of the Asian continent. The natures of the Moho in these areas have been studied for decades, with a variety of geophysical methods, including active and passive seismic methods, gravity and other techniques. The Moho and the upper mantle structures in the NE <span class="hlt">Japan</span> and SE <span class="hlt">Japan</span> Arcs have been investigated well both from active and passive seismic source studies. The Moho depth in the NE <span class="hlt">Japan</span> is ranging from 30 to 40 km. Almost parallel to the present volcanic front, there exists a belt of deep Moho (34-36 km) with a lower Pn velocity (7.5-7.7 km/s). Amplitude analysis of the PmP phase indicates that the Moho beneath the NE <span class="hlt">Japan</span> Arc is not a simple velocity contrast, but rather a gradual transition. Toward the backarc side, remarkable crustal thinning is recognized. Actually, the Moho depth decreases from 35 km beneath the central part of NE <span class="hlt">Japan</span> to 18 km beneath the Sea of <span class="hlt">Japan</span>. This thinning is evident in the upper crust, while the lower crust remains constant in thickness. This may be explained by the continuous magmatic underplating beneath the rifted crust or deformation under a simple shear mode, allowing the lower crustal thickness to remain unchanged. The Moho in the SW <span class="hlt">Japan</span> Arc is also at a depth of 30-40 km. The Pn velocity is 7.7-7.8 km/s, slightly higher than that in the NE <span class="hlt">Japan</span>, although this value was mostly sampled in the eastern half of the SW <span class="hlt">Japan</span> Arc where the recent volcanic activity has been less effective. Fluids expelled from the <span class="hlt">subducted</span> oceanic lithosphere (the PHS plate) play an important role in controlling the structure of the mantle wedge. As these fluids leak into the mantle wedge they induce serpentinization there, transforming original mantle materials to those of lower velocity and higher Vp/Vs. The crustal thinning of the SW <span class="hlt">Japan</span> Arc is characterized by notable decrease in upper crustal thickness, which is similar to the case of the NE <span class="hlt">Japan</span> Arc. The Moho and uppermost mantle structures beneath the southern part of the Kamchatka have a lot of similarities to those beneath the NE <span class="hlt">Japan</span> Arc. Earlier DSS investigations and converted wave analyses show that Moho is situated at a depth of 38-40 km along the east coast of Kamchatka, that is beneath the volcanic front, but decreases to about 32 km near the west coast. Moho depth values based on modern receiver function methodology are also ranging from 31 to over 38 km. Moho is a fairly simple boundary under the western coast of Kamchatka, while in the Central Kamchatka Depression and especially along the eastern coast it is likely gradational. Uppermost mantle material beneath the Moho is complex, with additional impedance contrasts that are likely anisotropic in their properties being present under the entire Kamchatka peninsula. The dominant anisotorpy-inducing fabric varies from site to site along the west coast, but is almost universally <span class="hlt">trench</span>-normal along the east coast. The seismic velocities beneath Kamchatka are very low (7.4-7.8 km/s for P-wave and 4.1-4.2 km/s for S wave). Also, gradual structural change is recognized around the Moho beneath the active volcanoes. These features are quite similar to those in NE <span class="hlt">Japan</span> Arc.</p> <div class="credits"> <p class="dwt_author">Iwasaki, Takaya; Levin, Vadim; Nikulin, Alex; Iidaka, Takashi</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">312</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/42040444"> <span id="translatedtitle">How does plate coupling affect crustal stresses in Northeast and Southwest <span class="hlt">Japan</span>?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Plate <span class="hlt">subduction</span> causes compression of the continental crust in Northeast (NE) <span class="hlt">Japan</span> but not in Southwest (SW) <span class="hlt">Japan</span>. We propose that the different effects are both consistent with weak <span class="hlt">subduction</span> faults, of which the static shear stress is described using an effective coefficient of friction mu'. Stresses in the overriding plate are controlled by two competing factors, the plate coupling</p> <div class="credits"> <p class="dwt_author">Kelin Wang; Kiyoshi Suyehiro</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">313</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013GGG....14.3268R"> <span id="translatedtitle">Global analysis of the effect of fluid flow on <span class="hlt">subduction</span> zone temperatures</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Knowledge of the controls on temperature distributions at <span class="hlt">subduction</span> zones is critical for understanding a wide range of seismic, metamorphic, and magmatic processes. Here, we present the results of ˜220 thermal model simulations covering the majority of known <span class="hlt">subduction</span> zone convergence rates, incoming plate ages, and slab dips. We quantify the thermal effects of fluid circulation in the <span class="hlt">subducting</span> crust by comparing results with and without advective heat transfer in the oceanic crustal aquifer. We find that hydrothermal cooling of a <span class="hlt">subduction</span> zone is maximized when the <span class="hlt">subducting</span> slab is young, slowly converging, steeply dipping, and the crustal aquifer is ventilated near the <span class="hlt">trench</span>. Incoming plate age is one of the primary controls on the effectiveness of advective heat transfer in the aquifer, and the greatest temperature effects occur with an incoming plate <50 Ma. The thermal effects of fluid circulation decrease dramatically with increasing age of the incoming plate. Temperatures in the Cascadia, Nankai, southern Chile, Colombia/Ecuador, Mexico, and Solomon Islands <span class="hlt">subduction</span> zones are likely strongly affected by fluid circulation; for these systems, only thermal models of Cascadia and Nankai have included fluid flow in <span class="hlt">subducting</span> crust.</p> <div class="credits"> <p class="dwt_author">Rotman, Holly M. M.; Spinelli, Glenn A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">314</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009EGUGA..11.3550H"> <span id="translatedtitle">Potential Significant Tsunami Hazard in the Puysegur <span class="hlt">Subduction</span> Zone, South of New Zealand</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary"><span class="hlt">Subduction</span> zone seismogenesis and related tsunami potential have recently become a significant focus; yet none of the recent global studies have considered the Puysegur <span class="hlt">subduction</span> zone, south of New Zealand, and its hazards. While several local studies have identified the southern and southwestern (Fiordland) margins as potential tsunami hazards, those models fail to take into account the oblique nature of <span class="hlt">subduction</span> and the impact of that obliquity on earthquake slip and tsunami wave generation. We have undertaken a comprehensive study of the Puysegur <span class="hlt">subduction</span> zone and its earthquake and tsunami hazards by analyzing the historical seismicity over the entire plate boundary region south of New Zealand and using that data to constrain the earthquake potential for the Puysegur <span class="hlt">trench</span>. We have identified both seismicity clearly associated with the interplate megathrust, and using these events, determined the seismic moment deficit of the <span class="hlt">subduction</span> plate boundary over the past ~100 years. These calculations imply unreleased moment equivalent to a magnitude Mw 8.4 earthquake, and thus suggest that this <span class="hlt">subduction</span> zone has the potential to break in a great, tsunamigenic event. We model the tsunami hazard using this moment deficit and the location of the 1979 plate interface event, and find that a tsunami caused by a great earthquake on the Puysegur <span class="hlt">subduction</span> zone poses a significant threat to the southern and western coasts of the South Island of New Zealand, the coasts of Tasmania, and also to the southeastern coast of Australia, nearly 2000 km distant.</p> <div class="credits"> <p class="dwt_author">Hayes, G. P.; Furlong, K. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">315</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.7800G"> <span id="translatedtitle"><span class="hlt">Subduction</span> modelling with ASPECT</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">ASPECT (Advanced Solver for Problems in Earth's ConvecTion) is a promising new code designed for modelling thermal convection in the mantle (Kronbichler et al. 2012). The code uses state-of-the-art numerical methods, such as high performance solvers and adaptive mesh refinement. It builds on tried-and-well-tested libraries and works with plug-ins allowing easy extension to fine-tune it to the user's specific needs. We make use of the promising features of ASPECT, especially Adaptive Mesh Refinement (AMR), for modelling lithosphere <span class="hlt">subduction</span> in 2D and 3D geometries. The AMR allows for mesh refinement where needed and mesh coarsening in regions less important to the parameters under investigation. In the context of <span class="hlt">subduction</span>, this amounts to having very small grid cells at material interfaces and larger cells in more uniform mantle regions. As lithosphere <span class="hlt">subduction</span> modelling is not standard to ASPECT, we explore the necessary adaptive grid refinement and test ASPECT with widely accepted benchmarks. We showcase examples of mechanical and thermo-mechanical oceanic <span class="hlt">subduction</span> in which we vary the number of materials making up the overriding and <span class="hlt">subducting</span> plates as well as the rheology (from linear viscous to more complicated rheologies). Both 2D and 3D geometries are used, as ASPECT easily extends to three dimensions (Kronbichler et al. 2012). Based on these models, we discuss the advection of compositional fields coupled to material properties and the ability of AMR to trace the slab's path through the mantle. Kronbichler, M., T. Heister and W. Bangerth (2012), High Accuracy Mantle Convection Simulation through Modern Numerical Methods, Geophysical Journal International, 191, 12-29.</p> <div class="credits"> <p class="dwt_author">Glerum, Anne; Thieulot, Cédric; Spakman, Wim; Quinquis, Matthieu; Buiter, Susanne</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">316</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011JGeo...52..344G"> <span id="translatedtitle">Future directions in <span class="hlt">subduction</span> modeling</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">During the last four decades, <span class="hlt">subduction</span> remained one of the most challenging and captivating geodynamic processes investigated with numerical techniques. While significant progress has been made toward deciphering the diverse array of <span class="hlt">subduction</span> zone observations within the context of modeled physical processes, numerous questions remain regarding multiple aspects of <span class="hlt">subduction</span> zone dynamics. A review of recent numerical studies highlights a number of open topics that <span class="hlt">subduction</span> modeling can provide significant insight into in the future: Resolving the controversy of <span class="hlt">subduction</span> initiation. Constraining robust high-resolution models of terrestrial plate tectonics. Understanding deep slab processes in the mantle. Constraining crustal growth and differentiation in magmatic arcs. Modeling of fluid and melt transport in <span class="hlt">subduction</span> zones. Deciphering evolution of high- and ultrahigh-pressure rock complexes. Developing geochemical-thermo-mechanical models of <span class="hlt">subduction</span>. Coupling of <span class="hlt">subduction</span> models with volcanic and seismic risk assessment. Understanding the onset of plate tectonics on Earth. Progress in <span class="hlt">subduction</span> modeling will require strong input from other disciplines (rheology, phase petrology, seismic tomography, geochemistry, numerical analysis, etc.). Indeed, due to the intrinsic complexity of terrestrial <span class="hlt">subduction</span> processes, the role of geodynamic modeling will inevitably grow and provide an integrative basis for conducting quantitative cross-disciplinary <span class="hlt">subduction</span> studies combining natural observations, laboratory experiments and modeling.</p> <div class="credits"> <p class="dwt_author">Gerya, Taras</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">317</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AGUFM.S53A0185K"> <span id="translatedtitle">Global Outer-Rise/Near <span class="hlt">Trench</span> Seismicity and Focal Mechanisms: Trends and Diversity</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Based on well-constrainted hypocenter information and focal mechanism solutions, Seno and Yamanaka (1996) identify two classes of outer-rise/near-<span class="hlt">trench</span> (OR/NT) earthquakes: 1) Shallow tensional events and 2) Deeper compressional events. They indicate that <span class="hlt">subduction</span> zones with compressional deep events (DCE) also tend to have double seismic zones (DSZ), and proposed a hypothesis that earthquakes in the lower plane of the DSZ represent reactivation of faults by dehydration embrittlement previously active as DCE_fs. They suggest that plates can be hydrated even at depths as great as 40 km by passing over the superplume volcanic centers. In this study we examine the characteristics of many more earthquakes at the outer-rise/near-<span class="hlt">trench</span> region using the EHB hypocenter catalogue (Engdahl et al., 2002) and Harvard CMT focal-mechanism. We studied M>5.5 OR/NT events in the Circum-Pacific/Indonesian earthquake belts from 1977 to 2002 that occurred at depths shallower than 60 km depth and within 150 km from the <span class="hlt">trench</span> axis. In order to select <span class="hlt">trench</span>-outer-rise events, we checked carefully all event locations and CMT solutions in map- and cross-sectional-views superposed on the background seismicity. We also compared event locations with global maps of seafloor bathymetry, gravity and Kawakatsu_fs 1986 investigation of the DSZ in the Tonga <span class="hlt">subduction</span> zone. Our results are as follows: 1) Eighteen compressional and 93 tensional events were found. 2) Solitary compressional events were found in two areas (Vanuatu and Guam) where a DSZ has not been observed. 3) Thirteen compressional events are concentrated in the Tonga-Kermadec reagion. 4) Tensional events occur at depths of less than about 33 km and the compressional group occurs at greater depths in the Tonga-Kermadec region, corresponding to Kawakatsu_fs upper an lower zones but with opposite focal mechanisms. 5) Many <span class="hlt">trench</span>-outer-rise events occur where seamount/guyot volcanic chains are <span class="hlt">subducting</span>. 6) Compressional OR/NT events tend to have mb_es that are larger that those for tensional and interplate events. This implies that DCE events at <span class="hlt">trench</span>-outer-rise have higher amplitudes at high frequencies.</p> <div class="credits"> <p class="dwt_author">Kita, S.; Nakajima, J.; Hasegawa, A.; Kirby, S. H.; Engdahl, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">318</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17831621"> <span id="translatedtitle"><span class="hlt">Trench</span>-parallel flow beneath the nazca plate from seismic anisotropy.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Shear-wave splitting of S and SKS phases reveals the anisotropy and strain field of the mantle beneath the <span class="hlt">subducting</span> Nazca plate, Cocos plate, and the Caribbean region. These observations can be used to test models of mantle flow. Two-dimensional entrained mantle flow beneath the <span class="hlt">subducting</span> Nazca slab is not consistent with the data. Rather, there is evidence for horizontal <span class="hlt">trench</span>-parallel flow in the mantle beneath the Nazca plate along much of the Andean <span class="hlt">subduction</span> zone. <span class="hlt">Trench</span>-parallel flow is attributale utable to retrograde motion of the slab, the decoupling of the slab and underlying mantle, and a partial barrier to flow at depth, resulting in lateral mantle flow beneath the slab. Such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the Pacific basin to the growing mantle reservoir beneath the Atlantic basin. Trenchparallel flow may explain the eastward motions of the Caribbean and Scotia sea plates, the anomalously shallow bathymetry of the eastern Nazca plate, the long-wavelength geoid high over western South America, and it may contribute to the high elevation and intense deformation of the central Andes. PMID:17831621</p> <div class="credits"> <p class="dwt_author">Russo, R M; Silver, P G</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-02-25</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012MEEP....1....1Z"> <span id="translatedtitle">Tomography and Dynamics of Western-Pacific <span class="hlt">Subduction</span> Zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We review the significant recent results of multiscale seismic tomography of the Western-Pacific <span class="hlt">subduction</span> zones and discuss their implications for seismotectonics, magmatism, and <span class="hlt">subduction</span> dynamics, with an emphasis on the <span class="hlt">Japan</span> Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V/low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the <span class="hlt">subducting</span> slab. Seismic anisotropy seems to exist in all portions of the Northeast <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone, including the upper and lower crust, the mantle wedge and the <span class="hlt">subducting</span> Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep <span class="hlt">subduction</span> of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest <span class="hlt">Japan</span>. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, <span class="hlt">subducting</span> slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under the <span class="hlt">Japan</span> Sea and the East Asia margin may be related to a metastable olivine wedge in the <span class="hlt">subducting</span> Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep <span class="hlt">subduction</span> and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the <span class="hlt">subducted</span> continental plates. Under Kamchatka, the <span class="hlt">subducting</span> Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off by the asthenospheric flow. The stagnant slab finally collapses down to the bottom of the mantle, which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle. Suggestions are also made for future directions of the seismological research of <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Zhao, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">320</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56463745"> <span id="translatedtitle">Magmatic Volatile Variations Along a <span class="hlt">Trench</span>-Perpendicular Transect in the Central Trans-Mexican Volcanic Belt</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">To investigate volatiles (H2O, CO2, S, Cl) in <span class="hlt">subduction</span>-related basaltic magmas, we have analyzed olivine-hosted melt inclusions from five basaltic centers located at varying distances from the <span class="hlt">trench</span> in the Michoacan-Guanajuato Volcanic Field (MGVF), a part of the Trans-Mexican Volcanic Belt. Two of the cinder cones, Volcan Jorullo and Cerro El Astillero, are located near the volcanic front, about 100</p> <div class="credits"> <p class="dwt_author">E. R. Johnson; P. J. Wallace; H. Delgado Granados</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return 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href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a style="font-weight: bold;">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">321</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/42036637"> <span id="translatedtitle">The role of <span class="hlt">subduction</span> on the horizontal motions in the Tyrrhenian Basin: A numerical model</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The horizontal motions in the Tyrrhenian basin and surrounding chains, induced by <span class="hlt">subduction</span> along the Calabrian Arc and Northern Apennines, are analyzed by means of numerical models based on finite element techniques. The driving mechanism, in 2-dimensional vertical cross-sections perpendicular to the <span class="hlt">trench</span>, is the slab-pull due to the negative buoyancy of a stratified viscoelastic plate that models the Ionic</p> <div class="credits"> <p class="dwt_author">Carlo Giunchi; Paolo Gasperini; Roberto Sabadini; Gabriella D'Agostino</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">322</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1999E%26PSL.173..439C"> <span id="translatedtitle">GPS determined eastward Sundaland motion with respect to Eurasia confirmed by earthquakes slip vectors at Sunda and Philippine <span class="hlt">trenches</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">GPS measurements acquired over Southeast Asia in 1994 and 1996 in the framework of the GEODYSSEA program revealed that a large piece of continental lithosphere comprising the Indochina Peninsula, Sunda shelf and part of Indonesia behaves as a rigid `Sundaland' platelet. A direct adjustment of velocity vectors obtained in a Eurasian frame of reference shows that Sundaland block is rotating clockwise with respect to Eurasia around a pole of rotation located south of Australia. We present here an additional check of Sundaland motion that uses earthquakes slip vectors at Sunda and Philippine <span class="hlt">trenches</span>. Seven sites of the GEODYSSEA network are close to the <span class="hlt">trenches</span> and not separated from them by large active faults (two at Sumatra <span class="hlt">Trench</span>, three at Java <span class="hlt">Trench</span> and two at the Philippine <span class="hlt">Trench</span>). The difference between the vector at the station and the adjacent <span class="hlt">subducting</span> plate vector defines the relative <span class="hlt">subduction</span> motion and should thus be aligned with the <span class="hlt">subduction</span> earthquake slip vectors. We first derive a frame-free solution that minimizes the upper plate (or Sundaland) motion. When corrected for Australia-Eurasia and Philippines-Eurasia NUVEL1-A motion, the misfit between GPS and slip vectors azimuths is significant at 95% confidence, indicating that the upper plate does not belong to Eurasia. We then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of Sundaland is a uniform 7-10 mm/a eastward velocity. However, introducing the additional constraint of the fit of the GEODYSSEA sites with the Australian IGS reference ones, or tie with the NTUS Singapore station, leads to a much narrower range of solutions. We conclude that Sundaland has an eastward velocity of about 10 mm/a on its southern boundary increasing to 16-18 mm/a on its northern boundary.</p> <div class="credits"> <p class="dwt_author">Chamot-Rooke, N.; Le Pichon, X.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">323</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007GMS...172....1E"> <span id="translatedtitle">Introduction: <span class="hlt">Subduction</span>'s sharpest arrow</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In the center of the 6000-km reach of Kurile-Kamchatka-Aleutian-Alaska <span class="hlt">subduction</span> is arguably Earth's most remarkable <span class="hlt">subduction</span> cusp. The Kamchatka-Aleutian junction is a sharp arrowhead mounted on the shaft of the Emperor Seamount Chain. This collection of papers provides context, definition, and suggestions for the origin of the junction, but a comprehensive understanding remains elusive, in part because of the newness of international collaborations. Necessary cross-border syntheses have been impeded by the adversarial international relations that characterized the 20th century. For much of this period, Kamchatka and the Kurile Islands were part of the Soviet Union, a mostly closed country. The entire region was swept by World War II, abundant remnants of which are wrecked ships and planes, unexploded ordnance, and Rommel stakes.</p> <div class="credits"> <p class="dwt_author">Eichelberger, John C.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">324</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/48923293"> <span id="translatedtitle">Evolving force balance during incipient <span class="hlt">subduction</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Nearly half of all active <span class="hlt">subduction</span> zones initiated during the Cenozoic. All <span class="hlt">subduction</span> zones associated with active back arc extension have initiated since the Eocene, hinting that back arc extension may be intimately associated with an interval (several tens of Myr) following <span class="hlt">subduction</span> initiation. That such a large proportion of <span class="hlt">subduction</span> zones are young indicates that <span class="hlt">subduction</span> initiation is a</p> <div class="credits"> <p class="dwt_author">Michael Gurnis; Chad Hall; Luc Lavier</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">325</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1994PApGe.142..101R"> <span id="translatedtitle">Rupture process of large earthquakes in the northern Mexico <span class="hlt">subduction</span> zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Cocos plate <span class="hlt">subducts</span> beneath North America at the Mexico <span class="hlt">trench</span>. The northernmost segment of this <span class="hlt">trench</span>, between the Orozco and Rivera fracture zones, has ruptured in a sequence of five large earthquakes from 1973 to 1985; the Jan. 30, 1973 Colima event ( M s 7.5) at the northern end of the segment near Rivera fracture zone; the Mar. 14, 1979 Petatlan event ( M s 7.6) at the southern end of the segment on the Orozco fracture zone; the Oct. 25, 1981 Playa Azul event ( M s 7.3) in the middle of the Michoacan “gap”; the Sept. 19, 1985 Michoacan mainshock ( M s 8.1); and the Sept. 21, 1985 Michoacan aftershock ( M s 7.6) that reruptured part of the Petatlan zone. Body wave inversion for the rupture process of these earthquakes finds the best: earthquake depth; focal mechanism; overall source time function; and seismic moment, for each earthquake. In addition, we have determined spatial concentrations of seismic moment release for the Colima earthquake, and the Michoacan mainshock and aftershock. These spatial concentrations of slip are interpreted as asperities; and the resultant asperity distribution for Mexico is compared to other <span class="hlt">subduction</span> zones. The body wave inversion technique also determines the Moment Tensor Rate Functions; but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes. An appendix describes the Moment Tensor Rate Functions methodology in detail. The systematic bias between global and regional determinations of epicentral locations in Mexico must be resolved to enable plotting of asperities with aftershocks and geographic features. We have spatially “shifted” all of our results to regional determinations of epicenters. The best point source depths for the five earthquakes are all above 30 km, consistent with the idea that the down-dip edge of the seismogenic plate interface in Mexico is shallow compared to other <span class="hlt">subduction</span> zones. Consideration of uncertainties in the focal mechanisms allows us to state that all five earthquakes occurred on fault planes with the same strike (N65°W to N70°W) and dip (15±3°), except for the smaller Playa Azul event at the down-dip edge which has a steeper dip angle of 20 to 25°. However, the Petatlan earthquake does “prefer” a fault plane that is rotated to a more east-west orientation—one explanation may be that this earthquake is located near the crest of the <span class="hlt">subducting</span> Orozco fracture zone. The slip vectors of all five earthquakes are similar and generally consistent with the NUVEL-predicted Cocos-North America convergence direction of N33°E for this segment. The most important deviation is the more northerly slip direction for the Petatlan earthquake. Also, the slip vectors from the Harvard CMT solutions for large and small events in this segment prefer an overall convergence direction of about N20°E to N25°E. All five earthquakes share a common feature in the rupture process: each earthquake has a small initial precursory arrival followed by a large pulse of moment release with a distinct onset. The delay time varies from 4 s for the Playa Azul event to 8 s for the Colima event. While there is some evidence of spatial concentration of moment release for each event, our overall asperity distribution for the northern Mexico segment consists of one clear asperity, in the epicentral region of the 1973 Colima earthquake, and then a scattering of diffuse and overlapping regions of high moment release for the remainder of the segment. This character is directly displayed in the overlapping of rupture zones between the 1979 Petatlan event and the 1985 Michoacan aftershock. This character of the asperity distribution is in contrast to the widely spaced distinct asperities in the northern <span class="hlt">Japan</span>-Kuriles Islands <span class="hlt">subduction</span> zone, but is somewhat similar to the asperity distributions found in the central Peru and Santa Cruz Islands <span class="hlt">subduction</span> zones. <span class="hlt">Subduction</span> of the Orozco fracture zone may strongly affect the seismogenic character as the overlapping rupture zones are located on the </p> <div class="credits"> <p class="dwt_author">Ruff, Larry J.; Miller, Angus D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">326</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5598551"> <span id="translatedtitle"><span class="hlt">Trenching</span> in the New Madrid seismic zone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary"><span class="hlt">Trenching</span> studies of the San Andreas fault have been of great value to geologists in California for determining not only the prehistoric occurrences of earthquakes on the fault but also the age of these movements. In the New Madrid seismic zone, US Geological Survey scientists have been <span class="hlt">trenching</span> across suspected faults to try to assess earthquake frequency in the Central US. The following photographs document these <span class="hlt">trenching</span> studies.</p> <div class="credits"> <p class="dwt_author">Not Available</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">327</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1985JGR....9011397A"> <span id="translatedtitle">An ocean bottom seismometer study of shallow seismicity near the Mid-America <span class="hlt">Trench</span> offshore Guatemala</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Five ocean bottom seismometers recorded seismicity near the Mid-America <span class="hlt">Trench</span> offshore Guatemala for 27 days in 1979. The array was emplaced in the lower slope region, just above the topographic <span class="hlt">trench</span>, in the area investigated during Deep Sea Drilling Project legs 67 and 84. Approximately 170 events were recorded by three or more seismometers, and almost half were located with statistical hypocentral errors of less than 10 km. Most epicenters were located immediately landward of the <span class="hlt">trench</span> axis, and many were further confined to a zone northwest of the array. In terms of depth, most events were located within the <span class="hlt">subducting</span> Cocos plate rather than in the overlying plate or at the plate-plate boundary. Their apparent concentration in the lower crust and upper mantle may suggest that the upper crust does not have the strength to support earthquake-generating stresses. The data permit construction of a magnitude-duration scale, calibrated with mb magnitudes for events located by the World-Wide Standard Seismograph Network (WWSSN) and recorded by our array and by the network recording foreshocks and aftershocks of the 1979 Petatlan earthquake. Most magnitudes ranged between 3.0 and 4.0 mb, and the threshold magnitude of locatable events was about 2.8 mb. Two distinct composite focal mechanisms were determined. One appears to indicate high-angle reverse faulting in the <span class="hlt">subducting</span> plate, in a plane parallel to <span class="hlt">trench</span> axis strike. The other, constructed for some earthquakes in the zone northwest of the array, seems to show normal faulting along possible fault planes oriented quasi-perpendicular to the <span class="hlt">trench</span> axis. The normal faulting is consistent with the segmentation of the Cocos plate that has been proposed from land evidence. Such segmentation might be evidenced offshore by normal faulting along planes subperpendicular to <span class="hlt">trench</span> strike. Alternatively, the seismicity zone and associated normal faulting mechanism may be the subsurface expression of the tectonics responsible for the San Jose Canyon, a prominent submarine canyon located farther upslope. Finally, projection of our seismicity sample and of well-located WWSSN events from 1954 to 1980 onto a plane perpendicular to the <span class="hlt">trench</span> axis shows a distinct gap between the shallow seismicity located by our array, and the deeper Wadati-Benioff zone seismicity located by the WWSSN. We tentatively ascribe this gap to inadequate sampling, but we suggest that it requires further investigation.</p> <div class="credits"> <p class="dwt_author">Ambos, E. L.; Hussong, D. M.; Holman, C. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">328</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/hn1p528m20366077.pdf"> <span id="translatedtitle">Estimation of strong ground motions from hypothetical earthquakes on the Cascadia <span class="hlt">subduction</span> zone, Pacific Northwest</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Strong ground motions are estimated for the Pacific Northwest assuming that large shallow earthquakes, similar to those experienced in southern Chile, southwestern <span class="hlt">Japan</span>, and Colombia, may also occur on the Cascadia <span class="hlt">subduction</span> zone. Fifty-six strong motion recordings for twenty-five <span class="hlt">subduction</span> earthquakes ofMs=7.0 are used to estimate the response spectra that may result from earthquakesMwMw 9.5) is the largest event that</p> <div class="credits"> <p class="dwt_author">Thomas H. Heaton; Stephen H. Hartzell</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54704020"> <span id="translatedtitle">Estimation of strong ground motions from hypothetical earthquakes on the Cascadia <span class="hlt">subduction</span> zone, Pacific Northwest</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Strong ground motions are estimated for the Pacific Northwest assuming that large shallow earthquakes, similar to those experienced in southern Chile, southwestern <span class="hlt">Japan</span>, and Colombia, may also occur on the Cascadia <span class="hlt">subduction</span> zone. Fifty-six strong motion recordings for twenty-five <span class="hlt">subduction</span> earthquakes of M s>=7.0 are used to estimate the response spectra that may result from earthquakes M w<81\\/4. Large variations</p> <div class="credits"> <p class="dwt_author">Thomas H. Heaton; Stephen H. Hartzell</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">330</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012NatGe...5..342C"> <span id="translatedtitle">Abrupt change in the dip of the <span class="hlt">subducting</span> plate beneath north Chile</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">No large tsunamigenic earthquake has occurred in north Chile since 1877 and the region has been largely recognized as a mature seismic gap. At the southern end of the seismic gap, the 2007 Mw7.7 Tocopilla earthquake ruptured the deeper seismogenic interface, whereas the coupled upper interface remained unbroken. Seismological studies onshore show a gently varying dip of 20° to 30° of the downgoing Nazca plate, which extends from the <span class="hlt">trench</span> down to depths of 40-50km. Here, we study the lithospheric structure of the <span class="hlt">subduction</span> zone of north Chile at about 22°S, using wide-angle seismic refraction and reflection data from land and sea, complemented by hypocentre data recorded during the 2007 Tocopilla aftershocks. Our data document an abrupt increase in the dip of the <span class="hlt">subducting</span> plate, from less than 10° to about 22°, at a depth of approximately 20km. The distribution of the 2007 aftershocks indicates that the change in dip acted as a barrier for the propagation of the 2007 earthquake towards the <span class="hlt">trench</span>, which, in turn, indicates that the <span class="hlt">subduction</span> megathrust is not only segmented along the <span class="hlt">trench</span>, but also in the direction of the dip. We propose that large-magnitude tsunamigenic earthquakes must cross the barrier and rupture the entire seismogenic zone.</p> <div class="credits"> <p class="dwt_author">Contreras-Reyes, E.; Jara, J.; Grevemeyer, I.; Ruiz, S.; Carrizo, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">331</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EGUGA..14.2447W"> <span id="translatedtitle">Seismic anisotropy of the Central Andean <span class="hlt">subduction</span> zone derived from shear-wave splitting</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The occurrence of seismic anisotropy is usually explained by the preferred alignment of anisotropic crystals, e.g. olivine, due to asthenospheric mantle flow or frozen-in lithospheric anisotropy in relation to previous tectonic events. In <span class="hlt">subduction</span> zones anisotropy is often found to be dominated by fast-polarisation axes oriented sub-parallel to the <span class="hlt">trench</span>. This has led to the hypothesis of <span class="hlt">trench</span>-parallel mantle flow due to pressure gradients induced by slab geometry and <span class="hlt">trench</span> migration. However, the character of the mantle-flow field in <span class="hlt">subduction</span> zones remains poorly understood. We investigate shear-wave splitting along two profiles in the Central Andes at 21° S and 25.5° S in the downdip direction of the <span class="hlt">subducting</span> Nazca plate in order to clarify variations of the fast splitting directions and the delay times from the Pacific coast to the West. Using both, teleseismic SKS and local S phases, we aim to discriminate between effects of the crust/mantle wedge above and asthenospheric flow beneath the slab. First results of fast polarisations from SKS phases show a significant variability over relatively short distances along the northern profile and delay times ranging from 0.5 to 1.5 sec. We discuss our results in view of the recently derived dependence of olivine-crystal alignment on pressure and water content.</p> <div class="credits"> <p class="dwt_author">Wölbern, I.; Rümpker, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010GGG....11.3X12R"> <span id="translatedtitle">Fore-arc basalts and <span class="hlt">subduction</span> initiation in the Izu-Bonin-Mariana system</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent diving with the JAMSTEC Shinkai 6500 manned submersible in the Mariana fore arc southeast of Guam has discovered that MORB-like tholeiitic basalts crop out over large areas. These "fore-arc basalts" (FAB) underlie boninites and overlie diabasic and gabbroic rocks. Potential origins include eruption at a spreading center before <span class="hlt">subduction</span> began or eruption during near-<span class="hlt">trench</span> spreading after <span class="hlt">subduction</span> began. FAB trace element patterns are similar to those of MORB and most Izu-Bonin-Mariana (IBM) back-arc lavas. However, Ti/V and Yb/V ratios are lower in FAB reflecting a stronger prior depletion of their mantle source compared to the source of basalts from mid-ocean ridges and back-arc basins. Some FAB also have higher concentrations of fluid-soluble elements than do spreading center lavas. Thus, the most likely origin of FAB is that they were the first lavas to erupt when the Pacific Plate began sinking beneath the Philippine Plate at about 51 Ma. The magmas were generated by mantle decompression during near-<span class="hlt">trench</span> spreading with little or no mass transfer from the <span class="hlt">subducting</span> plate. Boninites were generated later when the residual, highly depleted mantle melted at shallow levels after fluxing by a water-rich fluid derived from the sinking Pacific Plate. This magmatic stratigraphy of FAB overlain by transitional lavas and boninites is similar to that found in many ophiolites, suggesting that ophiolitic assemblages might commonly originate from near-<span class="hlt">trench</span> volcanism caused by <span class="hlt">subduction</span> initiation. Indeed, the widely dispersed Jurassic and Cretaceous Tethyan ophiolites could represent two such significant <span class="hlt">subduction</span> initiation events.</p> <div class="credits"> <p class="dwt_author">Reagan, Mark K.; Ishizuka, Osamu; Stern, Robert J.; Kelley, Katherine A.; Ohara, Yasuhiko; Blichert-Toft, Janne; Bloomer, Sherman H.; Cash, Jennifer; Fryer, Patricia; Hanan, Barry B.; Hickey-Vargas, Rosemary; Ishii, Teruaki; Kimura, Jun-Ichi; Peate, David W.; Rowe, Michael C.; Woods, Melinda</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">333</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JAESc..51...98H"> <span id="translatedtitle">Plate coupling along the Manila <span class="hlt">subduction</span> zone between Taiwan and northern Luzon</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We use GPS data, <span class="hlt">trench</span> parallel gravity anomaly (TPGA), and bathymetry to infer plate coupling patterns along the Manila <span class="hlt">subduction</span> zone. Using a block model and a fault geometry constrained by seismicity, we simultaneously solve for the location of Euler pole and angular velocity between the Sunda and Luzon blocks as well as the slip-deficit rate on plate interface. Our estimates show that the Euler pole between the Sunda and Luzon blocks is situated at southern Palawan near 8.3°N and 119.4°E with the angular velocity of 4.6 Myr-1. The estimated convergence rate along the Manila <span class="hlt">Trench</span> continuously decreases southward from 91 mm/yr at the northern tip of Luzon to 55 mm/yr north of Mindoro. The inversion of GPS data reveals partially locked fault patches extending from the West Luzon Trough to the east of Scarborough Seamount chain. The slip-deficit rate in this region is in the range of 20-30 mm/yr corresponding to a coupling ratio of 0.4. However, the fault slip behavior is not well resolved near the North Luzon Trough. Based on a good correlation between locations of large <span class="hlt">subduction</span> zone earthquakes and areas possessing gravity low, we investigate a variety of TPGA-based plate coupling models assuming different scaling between TPGA values and plate coupling ratios. The TPGA-based plate coupling models offer plausible rupture scenarios which are not constrained by current GPS data. The partially locked fault zone near 15-16.5°N may be associated with the <span class="hlt">subducted</span> Scarborough Seamount wherein oceanic floor is highly fractured. The great <span class="hlt">subduction</span> zone earthquake propagates beneath the Scarborough Seamount seems to be unlikely. The densification of GPS network in central Luzon and seafloor geodetic observations close to <span class="hlt">trench</span> axis are crucial to distinguish the detailed fault coupling patterns and the role of <span class="hlt">subducted</span> seamounts.</p> <div class="credits"> <p class="dwt_author">Hsu, Ya-Ju; Yu, Shui-Beih; Song, Teh-Ru Alex; Bacolcol, Teresito</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AGUFM.U51A0010S"> <span id="translatedtitle">The <span class="hlt">subduction</span> reference framework</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Plate tectonic reconstructions are essential for determining the spatial and temporal context for geological and geophysical data and help distinguish competing models for regional plate kinematic histories and the relationships between tectonic features and events. Plate reconstructions, a series of relative plate motions anchored to an absolute reference frame via a plate circuit, can act as surface boundary constraints for mantle convection models, allowing us to link surface processes to the deep earth. One of the limitations in global plate motion models has been to accurately determine the positions of plates through time. Traditionally, this has been based on either palaeomagnetic or hotspot reference frames, however both these methodologies have some shortcomings. Palaeomagnetic reference frames can determine latitudes but not longitudes, with additional inaccuracies due to true polar wander. Hotspot reference frames can only be confidently tied back to about 130 Ma and there is evidence that mantle plumes have moved relative to each other. New “hybrid” reference frames are emerging, which consist of fixed or moving hotspot reference frames merged with true polar wander (TPW) corrected palaeomagnetic reference frames. We have devised a methodology to link plate reconstructions to mantle convection back to Pangaea breakup time to converge on a solution that correctly aligns slab material in the mantle to the locations of <span class="hlt">subduction</span> zones in the past. We aim to construct a “<span class="hlt">Subduction</span> Reference Frame” for plate motions since 200 Ma by iteratively matching forward geodynamic models with tomographically imaged slabs in the mantle. Our forward models involve coupling global plate kinematics, the thermal structure of the oceanic lithosphere and slab assimilation to a spherical mantle convection code, CitcomS. Preliminary results have been obtained for a plate motion model using a moving hotspot reference frame to 100 Ma and a TPW corrected reference frame for times prior to 100 Ma. Focussing on the Farallon slab and the palaeo-<span class="hlt">subduction</span> east of Australia, we find that our models reasonably reproduce the present-day location of the Farallon slab. However, there is a mismatch between the slab east of Australia and the predicted location of <span class="hlt">subduction</span> based on the TPW-corrected reference frame. Further models will allow us to test new alternative reference frames to achieve a correct alignment with the location of slabs imaged in the mantle and the location of <span class="hlt">subduction</span> along continental margins in the past.</p> <div class="credits"> <p class="dwt_author">Seton, M.; Müller, D.; Gurnis, M.; Flament, N.; Whittaker, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993PhDT........11P"> <span id="translatedtitle">Mantle melting and crustal recycling in <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Major element data for basalts from approximately 100 arc volcanoes are examined in order to test a model whereby the mantle melts to varying extents beneath different arcs. Because the downgoing plate is at a fairly constant depth (approximately 120 km) beneath arc volcanoes worldwide, the total length of the mantle column that is available for adiabatic melting is largely dependent on the thickness of the arc crust. Chemical parameters that reflect the degree of mantle melting might then correlate with crustal thickness. Major element data for arc basalts are corrected for the effects of differentiation by calculating values at 6 percent MgO. Na(6.0) and Ca(6.0) correlate strongly with the thickness of the arc crust: basalts erupted onto thick crust are rich in Na and poor in Ca. These characteristics are typical of low degree mantle melts. Thus, where the crust is thick, the mantle melting column is short and the mantle melts to a small extent, producing high Na and low Ca melts. Mantle melting variations can also explain the variations in some trace elements (e.g., Sc, Ce, Zr) but others (e.g., Ba, K, Sr) may reflect <span class="hlt">subducted</span> sediment instead. In order to test the sediment <span class="hlt">subduction</span> model, sediment fluxes into <span class="hlt">trenches</span> are estimated. Over 250 new chemical analyses are reported for marine sediments from DSDP/ODP Sites 765, 595, 596, and 183. Based on evaluation of these reference sites, relationships are found between the geochemical and lithologic variations in sediments. This lithologic approach is used to calculate the bulk composition for eight <span class="hlt">trench</span> sections (Java, Tonga, Aleutians, Antilles, Guatemala, Mexico, Vanuatu, and Marianas). The sediment input fluxes correlate well with the associated arc enrichments in K, Rb, Cs, Sr, Ba, U, and Th for the eight arc/<span class="hlt">trenches</span> pairs examined. The <span class="hlt">subducted</span> input and volcanic output fluxes can be balanced if the entire oceanic crust (sediment + basalt) loses elements to the arc. The results of this flux balance are that the sediment loses roughly 10-30 percent of all the elements to the arc, while the basalt loses more variable amounts (0 percent, 2.5 percent, 7-15 percent, and 30 percent of its Th, U, alkalis, and Ba, respectively). The relatively constant proportions from the sediment suggest that the transport phase to the mantle wedge is a sediment melt, while the variable proportions from the basalt suggest an aqueous fluid. In this model, elements are recycled in <span class="hlt">subduction</span> zones via sediment melting and basalt dehydration.</p> <div class="credits"> <p class="dwt_author">Plank, Terry Ann</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">336</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5542998"> <span id="translatedtitle">Distribution and origin of igneous rocks from the landward slopes of the Mariana <span class="hlt">Trench</span>: Implications for its structure and evolution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The landward slope of the Mariana <span class="hlt">Trench</span> is composed largely of igneous rocks. Serpentinites and serpentinized ultramafic rocks occur at nearly all structural levels on the slope from depths of 8000 to 1200 m. Seamountlike features on the <span class="hlt">trench</span> slope break are the surface expression of serpentinite diapirs. Cumulate and massive gabbros are found; several varieties of volcanic rocks are common including boninites, altered and metamorphosed basalts, andesites, and dacites. The chemical characteristics of the volcanic rocks indicate that nearly all are products of island arc volcanism. Together with the gabbros, these volcanic rocks represent what is probably a late Eocene arc complex. These rocks were probably the first volcanic products to result from the <span class="hlt">subduction</span> of the Pacific plate beneath the Phillippine Sea plate; their exposure on the <span class="hlt">trench</span> slope today implies a significant amount of tectonic erosion of the landward slope since Eocene time. Most of this removal of material appears to have occurred during the early stages of <span class="hlt">subduction</span>. There are isolated occurrences on the landward slope of rock assemblages including alkalic basalts, chert, hyaloclastites, upper Cretaceous siliceous sediments, and shallow water limestones. These assemblages are very similar to rocks dredged from seamounts on the offshore flank of the <span class="hlt">trench</span>, and their presence on the landward slope suggests that since the cessation of vigorous tectonic erosion, there has been episodic accretion of seamount fragments to the landward slope.</p> <div class="credits"> <p class="dwt_author">Bloomer, S.H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-09-10</p> </div> </div> </div> </div> <div class="float