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1

Marine magnetic anomaly and magnetization of subducting Pacific Plate around the Japan Trench  

NASA Astrophysics Data System (ADS)

We studied marine magnetic anomaly in the northwestern margin of the Pacific Plate off Japan to examine whether the magnetic anomaly varies due to tectonic phenomenon caused by the plate subduction. For the sake of this study, we newly collected magnetic data aboard JAMSTEC cruises in the seaward area where was sparsely surveyed, and made a magnetic anomaly map by compilation of our data, data published by Geological Survey of Japan, and data from NGDC. The seafloor of the seaward slope of the Japan Trench is characterized by a series of parallel magnetic anomalies (Japanese Lineation Set) during M11-M7 (135-127 Ma). The anomalies are well lineated and have high-amplitudes of ~500-1000 nT peak-to-trough. The amplitudes of the anomalies gradually decay to the landward from the trench axis associated with the plate subduction. Equivalent magnetization was calculated from the magnetic anomaly to correct for effects of seafloor topography and increasing depth of subducting plate. Densely distributed seismic survey profiles in the study area enabled us to constrain the depth of the plate. On the seaward trench slope from the trench axis to a distance of ca. 100 km, horst-graben structure is developed and large steps grow associated with plate bending and normal faulting, which would cause some kind of destruction and mechanical disorganization of the magnetic layer by faulting. However, the magnetization is not influenced apparently there. The magnetization gradually decreases as the plate subduction proceeded. The apparent decay could reflect destruction and mechanical disorganization and/or chemical demagnetization of the topmost part of the oceanic crust along the plate boundary. The magnetization in reverse polarity decays larger than that in normal polarity. The result is indicative of reduction of remanence in the oceanic crust and induced magnetization possibly due to serpentinized uppermost mantle.

Fujiwara, T.

2013-12-01

2

Seismic velocity structure of subducting Pacific Ocean slab near Japan trench deduced by airgun-OBS surveys  

Microsoft Academic Search

Recent seismic studies around the Japan trench subduction zone have revealed that both the interplate and intraplate earthquakes occur under strong influence of fluid, in particular the water. Although it is believed that the subducted slab is the most significant carrier of the water into the earth interior, it is not fully understood how the water is transported into the

R. Azuma; R. Hino; Y. Ito; T. Takanami; R. Miura; K. Ichijo; K. Mochizuki; T. Igarashi; K. Uehira; T. Sato; M. Shinohara; T. Kanazawa

2008-01-01

3

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

4

Flow Pattern of the Island-Arc Rock-Mass under the Japan Trench Inner-slope overriding the Subducting Oceanic Plate  

Microsoft Academic Search

This paper reports that a flow pattern of the island-arc rock-mass was revealed on the seismic reflection profile under the Japan Trench Inner-slope, off Sanriku, overriding the subducting oceanic plate. An example of the seismic reflection profile is presented. The flow pattern is featured by the combination of the partial flat slip-planes and the large-scale dipping fault plane. This flow

S. Nagumo; T. Tsuru

2001-01-01

5

The alkaline magma squeezed upward by the plate flexure prior to subduction off the Chile and Japan Trenches  

NASA Astrophysics Data System (ADS)

The petit-spot monogenetic volcanoes on the NW Pacific Plate represent a new type of volcanism on their tectonic settings (Hirano et al., 2006). The most important feature of petit-spot volcanoes is that they do not derive their heat supply from the deep mantle (in contrast to hotspot volcanoes), despite their occurrence as intra-plate volcanoes. Instead, the magma probably originates within the asthenosphere and erupts along fractures in the lithosphere where it is flexed prior to subduction. Although it is clear that the surface morphology and distribution of petit-spot volcanoes are influenced by cracks in the lithospheric that reach the surface, it remains uncertain whether petit-spot volcanoes form wherever the plate flexes and fractures. The project “Expedition of petit-spot VI” was carried out off the Chile Trench on March 2009 using R/V Mirai in order to find such young volcanoes. The area, off Valparaiso, Chile, is characterized by trench-parallel normal faults (horsts and graben) resulting from extensional bending of the subducting Nazca Plate. An important difference between the area with trench-parallel normal faults and other parts of the subducting plate is the presence of tiny knolls. Dredged rocks at the knoll are highly vesicular, and fresh specimens with quench features are associated with lava lobes and breccias within the pelagic sediments. The rock and bathymetry are similar to the petit-spot volcanoes on the NW Pacific Plate. Therefore, the widespread occurrence of petit-spot is indicated by the discovery of petit-spots at the Nazca Plate. The most important process to occur the petit-spot volcanoes could be the plate flexures and their tectonic forces.

Hirano, N.; Machida, S.; Abe, N.

2010-12-01

6

Constraints on interseismic deformation at Japan trench from VLBI data  

NASA Technical Reports Server (NTRS)

Space geodetic data from very long baseline interferometry (VLBI) was used to estimate velocity relative to the plate interiors of two sites on the deforming leading edge at the Japan trench. Elastic models of interseismic deformation and results obtained were used to put constraints on the slip rate along the main thrust of the Japan subduction zone. Observed velocities reflect the sum of permanent west-northwest shortening in Honshu, elastic deformation due to locking of the main thrust fault at the Japan trench, and deformation associated with the subducting Phillipine plate. These velocities limit the locked segment of the main thrust at the Japan trench to 27 km vertically and 100 km along the dip. This indicates that the main Pacific plate thrust fault is not strongly coupled and probably does not generate strong earthquakes.

Argus, Donald F.; Lyzenga, Gregory A.

1993-01-01

7

Trench-parallel crustal anisotropy along the trench in the fore-arc region of Japan  

NASA Astrophysics Data System (ADS)

northeastern Japan, the Pacific plate is descending beneath the North American plate. It is generally understood that trench-normal principal stress is dominant in the crust along the Japanese island arc, because the stress field is controlled by the force of the subducting slab. Observations of shear wave splitting using crustal earthquakes reveal a marked lateral variation in fast-polarization direction with distance from the trench. Trench-normal and trench-parallel fast-polarization directions are observed on the back-arc and fore-arc sides, respectively. In this study, two-dimensional finite element modeling with subducting slab was conducted to investigate the interseismic stress field during earthquake cycles, taking into account linear viscoelasticity. In the model, trench-normal compression is found to dominate in the island arc region. However, an extensional field appears in the shallow upper crust of the fore-arc region during earthquake cycles. The trench-parallel crustal anisotropy can be explained by this extensional field.

Iidaka, Takashi; Muto, Jun; Obara, Kazushige; Igarashi, Toshihiro; Shibazaki, Bunichiro

2014-03-01

8

Plume head - trench interaction: impact on subduction dynamics  

NASA Astrophysics Data System (ADS)

The geologic record provides numerous examples where plumes and their associated buoyancy swell have disrupted convergent plate margins. These interactions have produced a variety of responses in the overriding plate including transient episodes of arc amagmatism, transient episodes of crustal shortening followed by plume-related magmatism in the overriding plate. The latter observation implies the plume must have transitioned from the subducting plate to the overriding plate. We present several 3D Underworld numerical models of plume heads of variable dimension and buoyancy interacting with a subduction trench. The models indicate that plume heads impact enormously on trench geometry. Arcuate trenches are created as the trench retreats around the edges of the plume head, whereas trench advance occurs in front of the plume resulting in transient crustal shortening in the overriding plate. Stalling of subduction when the plume head impacts the trench causes slab windowing. The size of the slab window is dependent on the size and buoyancy of the plume. The creation of the slab window provides a potential conduit for plume migration to the overriding plate. Alternatively, the plume head may be transferred to the overriding plate as subduction is re-established behind the plume. Models with "strong" slabs, characterized by high yield strengths, display different behavior. Plume-heads are entrained in the slab and are subducted without the development of a slab window.

Betts, P. G.; Moresi, L. N.; Mason, W. G.; Willis, D.

2013-12-01

9

The Japan Trench and its juncture with the Kuril Trench: cruise results of the Kaiko project, Leg 3  

USGS Publications Warehouse

This paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V "Jean Charcot". The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km2 and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65?? oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is offset left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary? ?? 1987.

Cadet, J. -P.; Kobayashi, K.; Aubouin, J.; Boulegue, J.; Deplus, C.; Dubois, J.; von, Huene, R.; Jolivet, L.; Kanazawa, T.; Kasahara, J.; Koizumi, K.; Lallemand, S.; Nakamura, Y.; Pautot, G.; Suyehiro, K.; Tani, S.; Tokuyama, H.; Yamazaki, T.

1987-01-01

10

Trench-parallel fluid flow in subduction zones resulting from temperature differences  

Microsoft Academic Search

Differences in the thermal state of subducting crust along the trench of a subduction zone cause differences in subduction zone temperature that persist to tens of kilometers down-dip of the trench. The resulting differences in fluid viscosity, permeability, and hydraulic conductivity can lead to trench-parallel variations in fluid pressure on the plate boundary fault. Temperature differences in locations with low

Glenn A. Spinelli; Demian M. Saffer

2007-01-01

11

Dehydration of incoming sediments at the Japan Trench  

NASA Astrophysics Data System (ADS)

In the 2011 Tohoku-oki earthquake, the seismic fault slip propagated close to the axis of the Japan Trench and caused an extremely large tsunami (Ide et al., 2011). It is generally considered that ductile deformation of unconsolidated sediments is commonly prominent in the aseismic shallow parts of the subduction zone. Therefore, it is unknown how the seismic rupture reached the nearby trench axis. The plate-boundary megathrust of the Japan Trench is characterized by a prominent seismic reflector, suggesting that the megathrust may host highly pressurized fluids (Kimura et al., 2012). Based on the result of Deep Sea Drilling Project (DSDP) Leg 56 at site 436 (reference, 1977), it is expected that the subducting sediments at the Japan Trench mainly consist of vitric diatomaceous and radiolarian ooze with pelagic clay intervals. Opal-A in the pelagic sediments transforms into quartz, and smectite transforms into illite. Kinetic modeling demonstrated that these reactions will progress with active dehydration at 50-60 km horizontally away from the deformation front and with a temperature of 100-120°C. This region coincides with the plate-boundary marked by a prominent seismic reflector, and suggests that the main source of highly pressured fluids is the dehydration of pelagic sediments (Kimura et al., 2012). However, detailed dehydration processes are still unclear mainly due to lack of quantitative sediment composition data. Therefore, in this study, we examined whole rock composition including amorphous silica of the core samples recovered at site 436 as well as those from the Japan Trench by the IODP 343 Japan Trench Fast Drilling Project (JFAST). Analysis of amorphous silica at site 436 documents that dehydration of the sediments is able to contribute to excess pressure at the shallow part of the megathrust if they underthrust as the same composition. At the drilling site of JFAST, a plate-boundary shear zone was identified around 820 mbsf, which was supposed to cause the 2011 Tohoku-oki earthquake (Chester., et al., 2012). Our analysis showed that the shear zone is characterized by extremely high concentration of smectite (~70 wt.%). These results suggest that the abundant smectite may have possibly fostered localized rupture and slip during the earthquake, because smectite has low frictional coefficient.

Shimizu, M.; Kameda, J.; Hamada, Y.; Kimura, G.

2013-12-01

12

Rapid weakening of subducting plates from trench-parallel estimates of flexural rigidity  

NASA Astrophysics Data System (ADS)

The negative buoyancy force of sinking lithosphere (slabs) is the principle driving force for subducting plates, but transmission of this force to the subducting plate depends on the strength of the slab (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, brittle-ductile layered). Because the applicability of these rheologic models cannot be distinguished based on trench-perpendicular plate bending models (Forsyth, 1980), 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. The observed plate weakening provides further evidence for a plate rheology that leads to significant 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 estimates of energy dissipation related to plate bending, compared to recent calculations assuming high plate strength and constant plate curvature.

Arredondo, Katrina M.; Billen, Magali I.

2012-04-01

13

Flexural bending of the oceanic plates near the Mariana, Japan, and Philippines trenches  

NASA Astrophysics Data System (ADS)

We conducted a detailed analysis of flexural bending of oceanic plates near the Mariana, Japan, and Philippines trenches to better understand the similarities and differences among these major subduction systems in the western Pacific Ocean. For each of the systems, we first obtained a 3-D deformation surface of the subducting plate by removing from the seafloor bathymetry the estimated topographic effects of sediment thickness, seamounts, and age-related thermal subsidence. We then calculated theoretical models of plate deformation along a series of trench-perpendicular profiles and inverted for the vertical force (Vo) and bending moment (Mo) at the trench axis, as well as variations in the elastic plate thickness (Te) that can best explain the observed plate deformation. From analysis of profiles across all trenches, we found that Te is reduced significantly from a value seaward of the outer rise (TeMax) to a value near the trench (TeMin), with the transition at distance Xr from the trench axis. Results of analysis reveal that the Mariana trench has the greatest amplitude of flexural bending (i.e., the greatest trench depth) in the range of 1.39 - 5.67 km and an average of 2.91 km, comparing to the Japan trench (range of 1.0 - 4.08 km, average of 2.59 km) and the Philippines trench (range of 0.48 - 4.04 km, average of 2.41 km). In contrast, the Philippines trench has the relatively narrow trench width (Xr range of 36 - 107 km, average of 68 km), in comparison to the Japan trench (Xr range of 47 - 122 km, average of 83 km) and the Mariana trench (Xr range of 60 - 125 km, average of 92 km). The best-fitting models reveal that for the Mariana trench, the effective elastic thickness is reduced significantly from a value seaward of the outer rise (TeMax = 45 - 55 km) to a value trench-ward of the outer rise region (TeMin = 19 - 40 km), with a corresponding reduction in Te in the range of 20 - 60%. In comparison, for the Japan trench, TeMax = 35 - 55 km, TeMin = 14 - 43 km, with Te reduction ranging 20 - 60%; for the Philippines trench, TeMax = 36 - 52 km, TeMin = 14 - 35 km, with Te reduction ranging 23 - 60%. Together these results illustrate that the elastic strength of the oceanic plates is significantly reduced near trenches, most likely due to pervasive trench-parallel normal faulting caused by flexural bending.

Tang, M.; Lin, J.; Zhang, F.

2013-12-01

14

Paleoseismology off northern Japan: Sediments in the Japan Trench record earthquake activity  

NASA Astrophysics Data System (ADS)

The Japan Trench subduction zone has repeatedly been affected by large earthquakes as most recently in 2011 by the giant magnitude 9 Tohoku-Oki earthquake. Several studies indicate that the 2011 earthquake has induced large seafloor displacements and triggered submarine landslides and gravity flows. The depression of the Japan Trench floor acts as sediment trap, where earthquake triggered mass flows originating from the landward slope are deposited. Thus, the deep Trench floor (>7500 m water depth) is a suitable area to trace the paleoseismicity in the region. During the R/V SONNE cruise (SO219A) in 2012, sediment cores have been collected east of the 2011 earthquake epicenter in a 60 km north-south transect along the Japan Trench floor axis, as well as from a small basin on the upper mid slope. The sediment cores contain several turbidite sequences (few cm to m thick), mainly revealing a coarse sand layer on an erosive base and a gradually fining upward to hemipelagic diatomaceous mud. Tephrochronological analyses on intercalated ash layers within the records provide an age control and show that the cores cover the past ~15 ka. Detailed analyses of these records, by using their sedimentological and lithological characteristics, their physical properties (Multi Sensor Core Logging, MSCL) as well as their elemental composition (X-ray Fluorescence, XRF) allow to characterize and to identify specific turbidite units. We observe particular turbidite units with the same characteristics in different cores along the trench axis and on the mid slope. Besides the top-unit turbidite, being related to the 2011 Tohoku earthquake, we detect a widespread unique calcareous nanno fossil bearing turbidite mud as well as some sand turbidite units of similar elemental composition within the records. Their large spatial extent suggests earthquake related trigger mechanisms. Thus, these event deposits sampled from the deep Japan Trench provide important information on the paleoseismic activity of the off Tohoku.

Fink, H. G.; Ikehara, K.; Kanamatsu, T.; Nagahashi, Y.; Koelling, M.; Strasser, M.; Wefer, G.

2013-12-01

15

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

16

Subduction of the Ogasawara Plateau in the Southern Izu-Ogasawara (Bonin) Trench  

NASA Astrophysics Data System (ADS)

The Ogasawara Plateau is a topographic high located on the Pacific plate at the junction of the Izu-Ogasawara Trench and the Mariana Trench. The plateau has 2000 to 3000 m of relief above the ocean floor, and several guyots rest on it. This plateau is the largest subducting seamount in the Western Pacific area. In November 2000, multi-channel seismic reflection data of 3 EW and 4 NS survey lines were collected by M/V Geco Emerald, chartered by Metal Mining Agency of Japan and Japan National Oil Company, in the southern Izu-Ogasawara (Bonin) Trench area,. Seismic reflection data were acquired using a 240-channel streamer of 6000 m length and 134.4 l air gun seismic source. The seismic source was fired every 50 m, except for the line D00-1, which was fired every 100 m due to depth constraints. We processed 3 EW lines (D00-1, "typical" subduction of oceanic plate; D00-2, central part of subducting Ogasawara Plateau; D00-3, southern part of subducting Ogasawara Plateau). Processing included f-k filtering to suppress multiple, followed by common mid-point (CMP) stacking. Post-stack time migration was applied after CMP stacking. These three seismic profiles clarify the geologic structure of the subducting Ogasawara Plateau and the adjacent area. There is no evidence for compressional features such as thrusts or folds in the plateau and the adjacent ocean floor. Normal faults, probably formed during bending of the subducting oceanic plate, are commonly observed in the seaward (Pacific) plate. In contrast, several thrusts are observed in the frontal part of the landward (Philippine Sea) plate, and a very small and accretionary prism is also observed. The top of the subducting plateau is located beneath a fore-arc serpentinite seamount on the Philippine Sea Plate. This observation indicates that the Ogasawara Plateau has been subducting beneath the landward plate, and is not accreting to the overriding plate. The structural features of the plateau and the deformed landward plate, imaged using seismic profiling, suggest high-relief oceanic plateaus or seamounts do not necessarily accrete to the overriding plate as ophiolites.

Miura, R.; Nakamura, Y.; Tokuyama, H.; Tamaki, K.; Koda, K.

2002-12-01

17

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

18

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

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

2006-01-01

19

High heat flow anomalies on an old oceanic plate observed seaward of the Japan Trench  

Microsoft Academic Search

Thirty-three new measurements on the seaward slope and outer rise of the Japan Trench along a parallel of 38°45?N revealed\\u000a the existence of high heat flow anomalies on the subducting Pacific plate, where the seafloor age is about 135 m.y.. The most\\u000a prominent anomaly with the highest value of 114 mW\\/m2 is associated with a small mound on the outer rise, which

Makoto Yamano; Masataka Kinoshita; Shusaku Goto

2008-01-01

20

Oblique subduction modelling indicates along-trench tectonic transport of sediments.  

PubMed

Convergent plate margins are currently distinguished as 'accretional' or 'erosional', depending on the tendency to accumulate sediments, or not, at the trench. Accretion and erosion can coexist along the same margin and we have noticed that this mostly occurs where subduction is oblique. Here we show that at oblique subduction zones, sediments that enter the trench are first buried, and later migrate laterally parallel to the trench and at various depths. Lateral migration of sediments continues until they reach a physical barrier where they begin to accumulate. The accretionary wedge size decreases along the trench moving away from the barrier. We therefore suggest that the gradual variation of the accretionary wedge size and sediment amount at the trench along one single subduction zone, as observed in many active plate margins worldwide, can be explained by the lateral tectonic migration of sediments driven by obliquity of subduction as well. PMID:24030161

Malatesta, Cristina; Gerya, Taras; Crispini, Laura; Federico, Laura; Capponi, Giovanni

2013-01-01

21

The Relationships of Upper Plate Ridge-Trench-Trench and Ridge-Trench-Transform Triple Junction Evolution to Arc Lengthening, Subduction Zone initiation and Ophiolitic Forearc Obduction  

NASA Astrophysics Data System (ADS)

The principal enigma of large obducted ophiolite slabs is that they clearly must have been generated by some form of organized sea-floor spreading/plate-accretion, such as may be envisioned for the oceanic ridges, yet the volcanics commonly have arc affinity (Miyashiro) with boninites (high-temperature/low-pressure, high Mg and Si andesites), which are suggestive of a forearc origin. PT conditions under which boninites and metamorphic soles form and observations of modern forearc systems lead us to the conclusion that ophiolite formation is associated with overriding plate spreading centers that intersect the trench to form ridge-trench-trench of ridge-trench-tranform triple junctions. The spreading centers extend and lengthen the forearc parallel to the trench and by definition are in supra-subduction zone (SSZ) settings. Many ophiolites likewise have complexly-deformed associated mafic-ultramafic assemblages that suggest fracture zone/transform along their frontal edges, which in turn has led to models involving the nucleation of subduction zones on fracture zones or transpressional transforms. Hitherto, arc-related sea-floor-spreading has been considered to be either pre-arc (fore-arc boninites) or post-arc (classic Karig-style back arc basins that trench-parallel split arcs). Syn-arc boninites and forearc oceanic spreading centers that involve a stable ridge/trench/trench triple or a ridge-trench-transform triple junction, the ridge being between the two upper plates, are consistent with large slab ophiolite formation in an obduction-ready settting. The direction of subduction must be oblique with a different sense in the two subduction zones and the oblique subduction cannot be partitioned into trench orthogonal and parallel strike-slip components. As the ridge spreads, new oceanic lithosphere is created within the forearc, the arc and fore-arc lengthen significantly, and a syn-arc ophiolite forearc complex is generated by this mechanism. The ophiolite ages along arc-strike; a distinctive diachronous MORB-like to boninitic to arc volcanic stratigraphy develops vertically in the forearc and eruption centers progressively migrate from the forearc back to the main arc massif with time. Dikes in the ophiolite are commonly highly oblique to the trench (as are back-arc magnetic anomalies in modern environments). Boninites and high-mg andesites are generated in the fore-arc under the aqueous, low pressure/high temperature, regime at the ridge above the instantaneously developed subducting and dehydrating slab. We review both modern subduction environments and ancient obducted ophiolite analogues that illustrate this tectonic model for subduction initiation and the creation and rapid divergent-convergent plate tectonic transitions to ophiolitic forearcs.

Casey, J.; Dewey, J. F.

2013-12-01

22

Relation between subduction megathrust earthquakes, trench sediment thickness and upper plate strain  

NASA Astrophysics Data System (ADS)

Giant earthquake (moment magnitude Mw ? 8.5) forecasts for subduction zones have been empirically related to both tectonic stresses and geometrical irregularities along the subduction interface. Both of these controls have been suggested as able to tune the ability of rupture to propagate laterally and, in turn, exert an important control on giant earthquake generation. Here we test these hypotheses, and their combined influence, by compiling a dataset of trench fill thickness (a proxy for smoothing of subducting plate relief by sediment input into the subduction channel) and upper plate strain (a proxy for the tectonic stresses applied to the subduction interface) for 44 segments of the global subduction network. We statistically compare relationships between upper plate strain, trench sediment thickness and maximal earthquake magnitude. We find that the combination of both large trench fill (?1 km) and neutral upper plate strain explains spatial patterns of giant earthquake occurrence to a statistically significant degree. In fact, the concert of these two factors is more highly correlated with giant earthquake occurrence than either factor on its own. Less frequent giant earthquakes of lower magnitude are also possible at subduction zones with thinner trench fill and compressive upper plate strain. Extensional upper plate strain and trench fill < 0.5 km appear to be unfavorable conditions, as giant earthquakes have not been observed in these geodynamical environments during the last 111 years.

Heuret, A.; Conrad, C. P.; Funiciello, F.; Lallemand, S.; Sandri, L.

2012-03-01

23

Geophysical evidence of trench-breaching slip along megathrust plate interface in the Japan Trench  

NASA Astrophysics Data System (ADS)

Repeated bathymetry and seismic surveys along a profile in the central part of the rupture of the 2011 Tohoku-oki earthquake show that a co-seismic fault reaches the trench axis, forming a deformed sediment mass seaward of the frontal prism above a graben, probably due to large trench-ward movement of the hanging wall block. If the seismic structures we observed in the trench axis represent a structural proxy showing trench-breaching slip, it can be possible by using seismic data, to map an area where co-seismic slip reaches the trench axis. In order to test this hypothesis, we have started a high-resolution seismic imaging project along the entire Japan Trench axis, and the survey has been completed from 38 N to 40 N by the summer of 2013. Based on preliminary results from the survey, we found along the trench axis continuation of key structures which consist of a small-scale fold-and-thrust zone at the trench axis and seismically transparent zone at the landward, except 39.5 N to 40 N where extremely thin incoming sediments are observed due to rough geometry of the top of the igneous crust. Those structures are interpreted to be formed by overprinting "basal friction-driven thrust fault" and "gravity-driven normal fault" that alternatively occurred during an earthquake cycle with slip to the trench. Although we believe that the high-resolution seismic data have a potential to define the spatial distribution of slips to the trench, those data do not yield any information about temporal variations of the slip. In order to examine the temporal variation of slip to the trench, we will therefore integrate the seismic images with geological studies, such as piston-coring. Furthermore, in order to know even longer records of earthquake slips and evidences of seismic fault motions (i.e., high velocity slip) along megathrust interface at the trench axis, we proposed a new ocean drilling project, called JTRACK, which consists of along-and-across trench axis drilling transect in the Japan Trench.

Kodaira, Shuichi; Nakamura, Yasuyuki; Miura, Seiichi; Fujiwara, Toshiya; Kanamatsu, Toshiya; Ikehara, Ken

2014-05-01

24

Low Intensity Characteristic of Plate-Boundary S-S Reflections Within a Region of Strong Plate-Boundary P-P Reflections and low Seismicity Along the Japan Trench Subduction Zone  

NASA Astrophysics Data System (ADS)

It has been pointed out that the epicenters of the microearthquakes along the forearc slope of the Japan Trench are not uniformly distributed but clustered in seismically active zones that are oriented perpendicular to the trench axis. One of the clear seismic-aseismic boundaries of such seismic clusters can be identified in latitude 39° N. A seismic survey was conducted in 1996 with one profile running across the boundary and parallel to the trench axis, and a P-wave velocity structure model was obtained by travel-time inversion (Fujie, 1999). A strong anti-correlation between the seismicity and the intensity of the plate-boundary P-P reflected waves was found: strong plate-boundary P-P reflected waves were observed in a region where seismicity is quite low, and vice versa (Fujie et al., 2002). They discussed that a thin layer of low P-wave velocities (3~4 km/s) with its thickness up to a few hundred meters along the plate boundary could explain the intensity of the reflections. Results of finite-difference waveform calculations support this estimation (Moghaddam, 2002). Another seismic survey was carried out in 2001 with 7 trench-parallel profiles in the same region as the 1996 survey in order to map and verify the strong anti-correlation. The strong anti-correlation was observed over the seismic-aseismic boundary region, and it was inferred that a thin layer with low P-wave velocities along the plate boundary exists beneath the aseismic zone in the region. Understanding the characteristics of plate-boundary S-S reflections in addition to those of P-P reflections would greatly help put better constraints on the physical properties along the plate boundary. Substantial P-to-S conversion at the base of the sedimentary layers was observed. S-wave velocities, especially those of the sedimentary layers, should be precisely determined in order to have good estimates of the arrival times of the plate-boundary S-S reflected waves. The S-wave velocities of the sedimentary layers were obtained by the tau-p analysis of the OBS horizontal-component waveforms. The Vp/Vs ratios within the sediment layers were estimated to be 5.2 and 2.3 from top to bottom. The Vp/Vs ratios within the deeper structure were assumed to be 1.8 to 1.74 as the Vp varies from 4.5 km/s to 8.0 km/s. The calculated travel times explain well the observed travel times of P-S-converted refraction arrivals. Expected arrival times of the plate-boundary S-S reflected waves were calculated with respect to the obtained Vs structure. Such intense amplitude as observed for the plate-boundary P-P reflections was not identified for the S-S reflections. Irregularity of the interfaces within the structure or differences in the reflectivity coefficients between P-P and S-S reflections at the plate boundary does not explain the opposite appearances of those reflections. Although the strong plate-boundary P-P reflections could be explained by putting a thin low-velocity layer, some additional features for S-S reflections along the plate boundary may be required, such as very low Q values (high attenuation) for the S-wave propagation.

Mochizuki, K.; Kasahara, J.; Hino, R.; Nishino, M.; Yamada, T.; Shinohara, M.; Kanazawa, T.

2003-12-01

25

Relation between subduction megathrust earthquakes, sediment thickness at trench, and plate coupling  

NASA Astrophysics Data System (ADS)

Extreme seismic events (Mw 8.5 and higher) are uniformly characterized by trench-parallel rupture lengths longer than about 250 km, whereas downdip rupture width ranges from less than 70 km (e.g., Central Aleutians) to more than 200 km (e.g., Andaman-Sumatra). The ability of rupture to propagate in the trench-parallel direction thus appears to play a fundamental role in determining the potential magnitude that an earthquake can achieve for a given subduction zone. The rupture length may be influenced by the nature of the plate interface and the normal stresses applied to the plate interface (plate coupling). The nature of the plate interface is potentially modified by sediment subduction. Subduction of a thick section of trench sediment constructs a laterally homogenous layer between upper and lower plates that smoothes subducted sea-floor relief and strength-coupling asperities (Ruff, 1989). Such a homogeneous interface running parallel to the subduction zone tends to favor long trench-parallel propagation of rupture, and thus large earthquake magnitudes. Compressive normal stresses applied along the plate interface may also tune the earthquake magnitude potential (Ruff & Kanamori, 1980). This plate coupling across the subducting interface can be indirectly estimated by Upper Plate Strain analysis, by using the back-arc as a strain sensor from which we can infer the back-arc stress state. Compressive back-arcs indicate that large stresses are transmitted across the plate interface whereas extensional settings indicate weak plate coupling. Here we present the results of a study funded by the European Science Foundation - EURYI project titled "Convergent margin and seismogenesis". Maximal earthquake magnitude, sediment thickness at the trench and Upper Plate Strain are characterized for worldwide subduction zones in order to test how plate coupling and sediment thickness combine to explain the occurrence of mega-events at the subduction interface. Subduction zones are described through an initial set of 505 transects, systematically extracted each 1° of trench, and merged into 62 subduction segments of homogeneous seismogenetic conditions. Maximal earthquake magnitude has been estimated by combining instrumental and historical seismicity. Trench sediment thickness has been constrained for 48 subduction segments; based on a compilation of 165 different seismic-reflection lines (33% of the initial set of transects).

Heuret, A.; Conrad, C. P.; Funiciello, F.; Lallemand, S.

2011-12-01

26

Structure and Kinematic History of the Japan Trench toe off Tohoku  

NASA Astrophysics Data System (ADS)

Recent slip models show that the 2011 Tohoku-Oki earthquake (Mw 9.0) ruptured to the trench. Differential bathymetric analysis from before and after the event confirms ~ 50 m of seaward displacement near the toe, which is predominantly responsible for the destructive tsunami. Interpretation of high-resolution depth migrated seismic reflection data across the Japan Trench near the 2011 earthquake epicentral region provide the structural context for subduction-related deformation. To constrain possible structural interpretations, we conducted fault restorations using Landmark's LithoTect software. The subducting Pacific plate is covered by ~400 m of pelagic and hemipelagic sediment. The outer trench slope margin is characterized largely by basement-displacing flexural related normal faults that generate horsts and graben. The morphologic trench in this area is a graben, conjugate to a subducted landward horst and an incoming seaward horst block. Seismic correlation across the seaward margin horst reveals displacement of ~140 m and shows that a small amount, less than ~50 m, of trench fill, likely deposited by slumping. The incoming sediment section in the trench is cut by landward-dipping thrusts that sole into a basal décollement, which ascends over the landward horst block, appearing to connect with the surface identified as the décollement at the J-FAST drill site. This décollement step down of ~200 m into the graben sediments is clearly imaged as a strong reflector with up to a ~20 degree seaward dip. Restoration along this fault plane step down creates an original steep inclination for the local seafloor, a potential driving force for slumping. Furthermore, this rupture pathway of down stepping into a graben may be a mechanism for the farther landward slumps and wedge morphology. Uplift at the toe is recorded by deformed offset horizons that coincide with local topographic highs of the seafloor. These compressional structures are interpreted to consist of three main thrusts branching from the décollement at less than 400 m below the seafloor. Although our method cannot distinguish co-seismic slip, it indicates that the rupture path for the Tohoku earthquake likely followed the basal décollement and propagated to the toe thrust faults in the trench , then breaching the surface. Kinematic restoration of this low angle prism toe shows thrust faults dipping ~10-40 degrees landward with over 1,000 m of displacement along the basal décollement in the graben. These results provide geologic constraints on slumping and uplift geometries and reveal deformational histories near the trench.

Boston, B.; Moore, G. F.; Nakamura, Y.; Kodaira, S.

2012-12-01

27

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

28

Isotopic Composition of Lead in the Sediments Near Japan Trench.  

National Technical Information Service (NTIS)

The isotopic composition of lead in the sediments near the Japan Trench was determined. The values are: (206) PB/204PB=18.45; (207)PB/(204) PB=15.63; and (208)PB/(204)PB=38.68. The mu and kappa values of the source material are also calculated to be 8.8 a...

T. J. Chow M. Tatsumoto

1964-01-01

29

Deep scientific dives in the Japan and Kuril Trenches  

Microsoft Academic Search

In the summer of 1985, during the French-Japanese Kaiko program, ten dives to depths of 6000 m in the Japan and Kuril Trenches were made in the newly launched submersible ``Nautile''. The sites of the dives were selected on the basis of surface geophysical surveys made during the preceding summer involving Seabeam mapping, geomagnetic and gravimetric measurements, and single-channel seismic

Jean Paul Cadet; Kazuo Kobayashi; Serge Lallemand; Laurent Jolivet; Jean Aubouin; Jacques Boulègue; Jacques Dubois; Hiroshi Hotta; Teruaki Ishii; Kenji Konishi; Nobuaki Niitsuma; Hideki Shimamura

1987-01-01

30

Fracture zone subduction and reactivation across the Puysegur ridge\\/trench system, southern New Zealand  

Microsoft Academic Search

A two-dimensional kinematic model for lithospheric thrusting that considers the flexural interaction between the underriding and overriding plates was used to assess the mechanical implications of subducting trench-parallel fracture zones on the topography and free-air gravity anomalies of the Puysegur ridge\\/trench system. Fracture zones in the underriding plate are simulated by vertical discontinuities across which bending and shearing stresses cannot

Jean-Frédéric Lebrun; Garry D. Karner; Jean-Yves Collot

1998-01-01

31

The relationship between plate velocity and trench viscosity in Newtonian and power-law subduction calculations  

NASA Technical Reports Server (NTRS)

The relationship between oceanic trench viscosity and oceanic plate velocity is studied using a Newtonian rheology by varying the viscosity at the trench. The plate velocity is a function of the trench viscosity for fixed Rayleigh number and plate/slab viscosity. Slab velocities for non-Newtonian rheology calculations are significantly different from slab velocities from Newtonian rheology calculations at the same effective Rayleigh number. Both models give reasonable strain rates for the slab when compared with estimates of seismic strain rate. Non-Newtonian rheology eliminates the need for imposed weak zones and provides a self-consistent fluid dynamical mechanism for subduction in numerical convection models.

King, Scott D.; Hager, Bradford H.

1990-01-01

32

Subduction of the Kula Ridge at the Aleutian Trench  

Microsoft Academic Search

A simple model of the probable topographic and thermal consequences of subducting an oceanic spreading center at an island arc predicts three geologic effects: shoaling and subaerial emergence of the crest of the arc; decrease or cessation of subduction-related magmatism; and regional low-grade thermal metamorphism (..delta..T approximately equal to 100 to 300°C) of the arc rocks. All three of these

STEPHEN E. DELONG; PAUL J. FOX; FRED W. MCDOWELL

1978-01-01

33

Marine incursions of the past 1500 years and evidence of tsunamis at Suijin-numa, a coastal lake facing the Japan Trench  

Microsoft Academic Search

Sandy deposits of marine origin underlie the floor of Suijin-numa, a coastal lake midway along the subduction zone marked by the Japan Trench. The deposits form three units that are interbedded with lacustrine peat and mud above a foundation of marine, probably littoral sand. Unlike the lacustrine deposits, all three sandy units contain marine and brackish diatoms. The middle unit

Yuki Sawai; Yushiro Fujii; Osamu Fujiwara; Takanobu Kamataki; Junko Komatsubara; Yukinobu Okamura; Kenji Satake; Masanobu Shishikura

2008-01-01

34

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

35

Development of Observatories for the Japan Trench Fast Drilling Project  

NASA Astrophysics Data System (ADS)

The Mw 9.0 Tohoku earthquake and accompanying tsunami produced the largest slip ever recorded in an earthquake and devastated much of northern Japan on March 11, 2011. The IODP proposal for JFAST (Japan Trench Fast Drilling project) planned to drill into the Tohoku subduction zone using the research ship Chikyu, measure the fault zone physical properties, recover fault zone material, and install an observatory to directly record the temperature anomaly caused by frictional slip during the earthquake. Considering the significant technical and operational challenges related to the great water depth of ~7,000 meters, and timing constraints, the observatory needed to be both robust and simple. After frequent discussions among scientists, engineers and operators, we decided to prepare two different types of observatories. 1. Autonomous MTL (Miniature Temperature Logger) observatory. The important temperature monitoring is accomplished by 55 MTLs attached to a string (Vectran rope) which is suspended inside a 4.5" casing in the borehole. The string latches at the top of the casing to allow retrieval using the remotely operated vehicle (ROV) Kaiko operated by JAMSTEC. This observatory avoids risks associated with a thermistor cable and wellhead data logger, and increases reliability by applying proven technologies. Perhaps most importantly, this configuration allows flexibility in defining the final depth distribution of the temperature sensors. This is advantageous since information of the exact depth of the fault zone will be known only after drilling and logging. Also, the judicious placement of weak links along the string helps to minimize possible loss of the entire sensor string if it is clamped by post-seismic movements that deform the casing. 2. Telemetered PT (Pressure and Temperature) observatory. Based on the previous deployment experience of the NanTroSEIZE C0010 observatory, we prepared another system that enables long term monitoring and repeated ROV data recovery. Two 0.25" stainless steel hydraulic lines are banded with protectors to the outside of 3.5" casing. The bottom ends of pressure lines terminate at permeable screens (mini-screens) that are exposed formation-fluid pressure. The mini-screens are positioned close to and above the fault. The top end of each pressure line is connected to a pressure logging package (including valves, pressure transducers, and data logger) at the wellhead. In addition, a temperature measurement string consisting of 21 channels of thermistors is installed inside the 3.5" casing. The thermistor string passes through a side entry port at the top of the casing where it is connected to a temperature logging package. The spacing intervals of the thermistors are fixed in the manufacturing process, but the total length is adjustable on board. Data recorded by both loggers can be recovered thorough wet mate connectors on the ROV, or the data loggers can be retrieved. Additionally, an acoustic modem installed onto the temperature logger can transfer some data to the receiver without a physical connection. During IODP Expeditions 343 and 343T, we successfully deployed the autonomous MTL observatory into an 854.81 meter deep borehole in 6,897.5 meter water depth. Unfortunately because of limited time and technical difficulties with drilling the second hole, we could not deploy the telemetered PT observatory.

Kyo, N.; Namba, Y.; Saruhashi, T.; Sawada, I.; Eguchi, N.; Toczko, S.; Kano, Y.; Yamano, M.; Muraki, H.; Fulton, P. M.; Brodsky, E. E.; Davis, E. E.; Sun, T.; Mori, J. J.; Chester, F. M.

2012-12-01

36

Hydrothermal heat mining in an incoming oceanic plate due to aquifer thickening: Explaining the high heat flow anomaly observed around the Japan Trench  

NASA Astrophysics Data System (ADS)

explain the origin of a high heat flow anomaly observed within 150 km seaward of the Japan Trench, we construct a thermal model for an oceanic plate prior to subduction that includes the effect of hydrothermal circulation within a high-permeability aquifer in its uppermost part. The model includes the effects of aquifer thickening, which is expected to occur near subduction zones where plate bending prior to subduction causes fracturing and faulting within the oceanic plate. Using typical parameter values for the Japan Trench, we find that hydrothermal circulation in the thickening aquifer mines heat from the underlying basement and can account for the observed high heat flow anomaly. The ratio of heat supply below the aquifer as a result of aquifer thickening to the inverse of the thermal resistance of the sediment layer is a control parameter for the system. As long as the aquifer permeability is higher than ˜10-13 m2, a typical value for the uppermost part of the oceanic plate, variations in other details of the hydrothermal circulation such as the exact value of the aquifer permeability and the size of the convection cells do not significantly change model results. Despite its strong influence on seafloor heat flow seaward of the trench, this hydrothermal heat mining does not affect significantly the thermal structure of the subducted oceanic plate. This finding indicates that surface heat flow anomaly around the trench may not correspond to temperature anomaly within the subducted oceanic plate and the megathrust seismogenic zone.

Kawada, Yoshifumi; Yamano, Makoto; Seama, Nobukazu

2014-04-01

37

Perspectives on the Dynamics of Subduction and Trench Rollback: From the Birth of Subduction to Global Plate Motions (Invited)  

NASA Astrophysics Data System (ADS)

We will provide a brief overview of two classes of dynamic models of subduction zones and address issues associated with the forces driving plate tectonics and initiating new subduction zones. A common thread between the models is the origin of the intense back arc spreading and rapid roll back associated with some ocean-ocean subduction zones. We will look at the dynamics driving global plate motions and then look at the time-dependence of trench rollback regionally. Plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries, but observationally constrained high-resolution models of global mantle flow have remained a computational challenge. We capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions, with individual plate margins resolved down to a scale of 1 kilometer. We find that cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high-viscosity slabs, altering the velocity of oceanic plates. Back-arc extension and slab rollback are emergent consequences of slab descent in the upper mantle. We will show that most back arc extension follows subduction initiation and show how this arises in dynamic models.

Gurnis, M.; Leng, W.; Alisic, L.; Stadler, G.

2013-12-01

38

Secular Subsidence and Deep Basal Subduction Erosion at the Northeastern Japan Forearc  

Microsoft Academic Search

Subduction erosion has two basic mechanisms, (1) material collapsed from the landward slope is trapped in horst-graben structure of the subducting plate (frontal erosion), and\\/or (2) materials at the base of the upper plate are scraped off by the subducting slab (basal erosion). These processes let the upper plate material subduct with the slab, and make the trench retreat landward

K. Heki

2003-01-01

39

Seismic constraints on mantle hydration during subduction: Mariana versus Middle America Trench  

NASA Astrophysics Data System (ADS)

We will present new results from active-source seismic experiments that constrain the amount of seawater entering the upper mantle along bending-induced faults at the outer rise of the Mariana and Middle America Trenches. This seawater may fill cracks in the upper mantle with free water; react strongly with olivine in upper mantle peridotite, filling cracks and fault zones with the hydrous mineral serpentinite; and/or diffuse between fault zones, pervasively serpentinizing the upper mantle. The upper mantle accounts for a large portion of the subducting lithosphere, and a hydrated upper mantle may supply the majority of water fluxing into arcs. Serpentinite is not stable at high temperatures and pressures, and, once subducted, would undergo a reverse reaction, releasing water into the mantle at depth and driving many arc- and global-scale geochemical and geodynamic processes. Hydration of the subducting upper mantle by fluid flow along bending-induced faults should depend on the density and depth of this faulting, as well as on the plate convergence rate and upper mantle temperature, which together control the rate of serpentinization reactions. Thus, a test of the outer-rise hydration hypothesis is to compare observations of the distribution of serpentinization in the upper mantle from subduction zones with different plate ages (temperatures); convergence rates; and angles between the relic abyssal-hill fabric, plate motion direction, and the trench (i.e. subduction obliquity), which control patterns of faulting. We will compare new seismic observations of faulting and serpentinization at the outer rise of the Middle America Trench offshore Nicaragua to observations from the central Mariana Trench. At the Middle America Trench, a moderately aged slab (24 Ma), and thus hot upper mantle, is subducting rapidly (85 mm/yr), both conditions that can limit serpentinization. Offshore Nicaragua, bending reactivates relic abyssal-hill fabric, which is oriented parallel to the trench. Here, measurements of seismic anisotropy and slow absolute wavespeeds suggest that these faults penetrate into the upper-most mantle and supply seawater that serpentinizes the mantle by up to ~13% (~1 wt% water). At the Mariana Trench, the slab is much older (140 Ma), and thus colder, and the convergence rate is slower (41 mm/yr), conditions expected to promote serpentinization. Here, preliminary analysis of new data suggests that upper mantle velocities are also significantly reduced under the outer rise. This velocity reduction is most extreme where bending-induced faulting is most pronounced, consistent with serpentinization via fluid flow along faults, although Cretaceous-age off-axis magmatism and the faults themselves may also affect seismic wavespeed. The goal of in-progress work on these Mariana data is to separate these wavespeed effects, enabling an estimate of serpentinization that can be compared to results from a similar analysis of the Middle America data, advancing our understanding of processes controlling the water input to subduction zones in general.

Miller, N. C.; Lizarralde, D.; Wiens, D. A.; Collins, J. A.; Holbrook, W.; Van Avendonk, H. J.

2013-12-01

40

A regime diagram for subduction dynamics from thermo-mechanical models with a mobile trench and an overriding plate  

NASA Astrophysics Data System (ADS)

The penetration or stagnation of subducted slabs in mantle transition zone and lower mantle influences Earth's thermal, chemical and tectonic evolution. Yet, the mechanisms responsible for the wide range of observed slab morphologies within the transition zone remain debated. Here, we investigate how downgoing and overriding plate ages controls the interaction between subducted slabs and mantle transition zone. We use 2-D thermo-mechanical models of a two-plate subduction system, modeled with the finite-element, adaptative-mesh code Fluidity. We implement a temperature- and stress-dependent rheology, and viscosity increases 30-fold from upper to lower mantle. Trench position evolves freely in response to plate dynamics. Such an approach self-consistently captures feedbacks between temperature, density, flow, strength and deformation. Our results indicate that key controls on subduction dynamics and slab morphology are: (i) the slab's ability to induce trench motion; and (ii) the evolution of slab strength during sinking. We build a regime diagram that distinguishes four subduction styles: (1) a "vertical folding" mode with stationary trench (young subducting plates, comparatively old overriding plates); (2) slabs that are "horizontally deflected" along the 660-km deep viscosity jump (initially young subducting and overriding plates); (3) an inclined slab morphology, resulting from strong trench retreat (old subducting plates, young overriding plates); and (4) a two-stage mode, displaying bent (rolled-over) slabs at the end of upper-mantle descent, that subsequently unbend and achieve inclined morphologies, with late trench retreat (old subducting and overriding plates). We show that all seismically observed slab morphologies can arise from changes in the initial plates ages at the onset of subduction.

Garel, Fanny; Davies, Rhodri; Goes, Saskia; Davies, Huw; Kramer, Stephan; Wilson, Cian

2014-05-01

41

Development of precision acoustic transponders for GPS/Acoustic observation on the deep seafloor near the Japan Trench axis  

NASA Astrophysics Data System (ADS)

The 2011 Tohoku-oki earthquake has let most of researchers recognize the importance of seafloor geodetic observation, especially near the trench axis. Iinuma et al. (2012a) estimated the coseismic slip distribution combining onshore GPS data with the seafloor geodetic data. Their results reveal that a huge (> 50 m) slip occurred in a small area (about 40 km in width and 120 km in length) near the Japan Trench and generated the huge tsunami. After the Tohoku-oki earthquake, seismic coupling near the trench axis has become a key to understand giant earthquakes in subduction zones, and it is GPS/Acoustic (GPS/A) repeated seafloor positioning that can give an observational constraint to it. Observation of postseimic deformation is another and urgent task required in the Japan Trench. Seafloor geodetic observation indicates posteseimic deformation near the Japan Trench axis in the north and south of the huge slip area (Iinuma et al., 2012b). The result is clearly different from that of onshore GPS observation. Postseismic deformation is estimated to be a key observation that can discriminate proper models from several ones that can explain the occurrence of the mega thrust. Tohoku University plans to deploy extensive GPS/A observation array along the Japan Trench in 2012 with a fund from MEXT, Japan, to cope with these requests (Kido et al., in this meeting). Precision acoustic transponders have newly been developed for the array to enable the following three requests: (1) observation on the deep seafloor, (2) compatibility among three institutions in Japan, and (3) observation for ten years. The first is the observation on the deep seafloor near the trench. While the Japan Trench axis is deeper than 7000 m, the existing GPS/A sites along the Japan Trench have remained on the seafloor shallower than 2500 m except the one nearest to the trench, where we observed coseismic slip of 31 m (Kido et al., 2011). We deployed 4 units of the new transponders supplied by Kaiyo Denshi, Ltd., in July this year on the seafloor of water depth around 5570 m. We have confirmed reliable acoustic ranging up to a slant range of 13 km, which is necessary for GPS/A observation on the seafloor of 6000 m water depth. The depth of 6000 m is a limit of cost effective glass-sphere pressure housing. The new transponder can also be adaptable to the GPS/A observation systems of Japan Coast Guard and Nagoya University to increase the chance of observations and to realize mutual comparison of the observed results. The acoustic system of Tohoku University was not so different from that of Nagoya University, but was quite different from that of Japan Coast Guard. Stronger Doppler effect on a longer acoustic signal adopted by the Japan Coast Guard was the most critical problem. We deployed one unit of the new transponder on the seafloor of about 2000 m water depth, and Japan Coast Guard has confirmed precise acoustic ranging with it up to a slant range of about 6000 m by using the acoustic system installed on their survey vessel.

Fujimoto, H.; Kido, M.

2012-12-01

42

Complex submarine landsliding processes caused by subduction of large seamounts along the Middle America Trench  

NASA Astrophysics Data System (ADS)

Subduction of kms-tall and tens-of-km wide seamounts cause important landsliding events at subduction zones around the word. Along the Middle America Trench, previous work based on regional swath bathymetry maps (with 100 m grids) and multichannel seismic images have shown that seamount subduction produces large-scale slumping and sliding. Some of the mass wasting event may have been catastrophic and numerical modeling has indicated that they may have produced important local tsunamis. We have re-evaluated the structure of several active submarine landlide complexes caused by large seamount subduction using side scan sonar data. The comparison of the side scan sonar data to local high-resolution bathymetry grids indicates that the backscatter data has a resolution that is somewhat similar to that produced by a 10 m bathymetry grid. Although this is an arbitrary comparison, the side scan sonar data provides comparatively much higher resolution information than the previously used regional multibeam bathymetry. We have mapped the geometry and relief of the head and side walls of the complexes, the distribution of scars and the different sediment deposits to produce a new interpretation of the modes of landsliding during subduction of large seamounts. The new higher resolution information shows that landsliding processes are considerably more complex than formerly assumed. Landslides are of notably smaller dimensions that the lower resolution data had previously appear to indicate. However, significantly large events may have occur far more often than earlier interpretations had inferred representing a more common threat that previously assumed.

Harders, Rieka; Ranero, Cesar R.; Weinrebe, Wilhelm; von Huene, Roland

2014-05-01

43

Subduction of Serpentinized and Weathered Ultramafic Rocks in the Puerto Rico Trench: Preliminary Results  

NASA Astrophysics Data System (ADS)

Exposure of mantle peridotite and its interactions with seawater to form serpentinite are integral parts of seafloor spreading, and play a key role in affecting the rheology, chemistry, and microbial habitability of the oceanic lithosphere at slow- and ultra-slow spreading ridges. Away from the spreading centers, within subduction zones, the formation and dehydration of serpentinized peridotite impacts seismicity, element cycling, and melt generation. Here we present preliminary results of a petrographic and spectroscopic study of altered rocks recovered from the from the north wall of the trench Puerto Rico Trench (PRT). In fact, the PRT represents one of two subduction zones worldwide where slow spreading oceanic lithosphere is presently subducted, and where serpentinized peridotite has been directly evidenced by seafloor sampling {Bowin, 1966}. Thin section petrography, XRF analysis, scanning electron microscopy, and confocal Raman spectroscopy reveal that the peridotite, which in all likelihood originated at the Mid-Atlantic Ridge during the early Cretaceous, was virtually completely serpentinized under static conditions (as it is evidenced by the preserved mesh texture after olivine and bastite after orthopyroxene), and underwent subsequent seafloor weathering. While it is questionable where exactly serpentinization and subsequent seafloor weathering took place, our preliminary results strongly suggest that the material presently subducted in the PRT is not simply composed of serpentine, magnetite, and brucite; it is rather a complex disequilibrium assemblage of minerals including serpentine, brucite, chlorite, talc, magnetite, hematite, goethite, sulfur-rich sulfides and various clay minerals. Furthermore, our results imply that serpentinite and its weathering products influence the loci of dehydration and mineral replacement reactions, as well as the water input and element recycling in subduction zones.

Horning, G.; Klein, F.

2012-12-01

44

Frictional behavior of the plate boundary décollement zone in the Japan Trench, sampled during the Japan Trench Fast Drilling Project (JFAST): Implications for shallow coseismic slip propagation  

NASA Astrophysics Data System (ADS)

One of the outstanding features of the 2011 Mw = 9.0 Tohoku earthquake was unusually large coseismic slip which propagated all the way to the trench. The fault zone processes that allow shallow reaches of subduction faults to rupture to the seafloor, rather than arresting slip, remains a critical and outstanding question. High-velocity friction experiments have shown that rupture propagation is aided by a variety of dynamic weakening effects, but these only become active at rates of × 1 cm/s. Coseismic slip propagation must also probably be governed by the frictional properties of the fault zone at lower slip rates, as it is driven from low to high sliding velocity. Drilling offshore in the Japan Trench was undertaken a year after the Tohoku earthquake during Integrated Ocean Drilling Program (IODP) Expedition 343, the Japan Trench Fast Drilling Project (J-FAST). During this expedition, core samples were recovered from a one-meter-thick highly sheared scaly-clay layer interpreted to be the plate-boundary fault zone, as well as from the overlying prism and underthrust sediments. We conducted laboratory experiments in a true-triaxial double-direct shear device to measure the frictional strength and velocity-dependence of these samples (wall rock as intact wafers, décollement as fault breccia) under stress conditions approximating those in situ. We observe that the décollement sample is weak (coefficient of friction ? = 0.17) compared to the hanging wall and footwall (approximately 0.5). The velocity-dependence of friction increases from velocity-weakening at sliding velocities ˜ 1 ?m/s to velocity-strengthening at higher rates. The décollement is more velocity-weakening than the wall rock at these low velocities. Flow-through measurements made perpendicular to the shear direction after deformation show that the décollement sample exhibits permeability which is nearly 2 orders of magnitude lower than the sheared wall rock samples. X-ray diffraction analysis of the < 2 ?m size fraction shows that the smectite content of the décollement sample is >20

Ikari, Matt; Kameda, Jun; Kopf, Achim; Saffer, Demian; Marone, Chris

2013-04-01

45

Constraints of subducted slab geometries on trench migration and subduction velocities: flat slabs and slab curtains in the mantle under Asia  

NASA Astrophysics Data System (ADS)

The past locations, shapes and polarity of subduction trenches provide first-order constraints for plate tectonic reconstructions. Analogue and numerical models of subduction zones suggest that relative subducting (Vs) and overriding (Vor) plate velocities may strongly influence final subducted slab geometries. Here we have mapped the 3D geometries of subducted slabs in the upper and lower mantle of Asia from global seismic tomography. We have incorporated these slabs into plate tectonic models, which allows us to infer the subducting and overriding plate velocities. We describe two distinct slab geometry styles, ';flat slabs' and ';slab curtains', and show their implications for paleo-trench positions and subduction geometries in plate tectonic reconstructions. When compared to analogue and numerical models, the mapped slab styles show similarities to modeled slabs that occupy very different locations within Vs:Vor parameter space. ';Flat slabs' include large swaths of sub-horizontal slabs in the lower mantle that underlie the well-known northward paths of India and Australia from Eastern Gondwana, viewed in a moving hotspot reference. At India the flat slabs account for a significant proportion of the predicted lost Ceno-Tethys Ocean since ~100 Ma, whereas at Australia they record the existence of a major 8000km by 2500-3000km ocean that existed at ~43 Ma between East Asia, the Pacific and Australia. Plate reconstructions incorporating the slab constraints imply these flat slab geometries were generated when continent overran oceanic lithosphere to produce rapid trench retreat, or in other words, when subducting and overriding velocities were equal (i.e. Vs ~ Vor). ';Slab curtains' include subvertical Pacific slabs near the Izu-Bonin and Marianas trenches that extend from the surface down to 1500 km in the lower mantle and are 400 to 500 km thick. Reconstructed slab lengths were assessed from tomographic volumes calculated at serial cross-sections. The ';slab curtain' geometry and restored slab lengths indicate a nearly stationary Pacific trench since ~43 Ma. In contrast to the flat slabs, here the reconstructed subduction zone had large subducting plate velocities relative to very small overriding plate velocities (i.e. Vs >> Vor). In addition to flat slabs and slab curtains, we also find other less widespread local subduction settings that lie at other locations in Vs:Vor parameter space or involved other processes. Slabs were mapped using Gocad software. Mapped slabs were restored to a spherical model Earth surface by two approaches: unfolding (i.e. piecewise flattening) to minimize shape and area distortions, and by evaluated mapped slab volumes. Gplates software was used to integrate the mapped slabs with plate tectonic reconstructions.

Wu, J. E.; Suppe, J.; Renqi, L.; Lin, C.; Kanda, R. V.

2013-12-01

46

Subduction erosion: the cause of sediment-starved trenches and the birth of new forearc above the seismogenic interface?  

NASA Astrophysics Data System (ADS)

Subduction erosion is usually thought to occur at ';sediment starved' margins with trench sediments limited to a layer <400m thick. In the region of CRISP drilling along the Osa Peninsula in Central America, trench sediment thicknesses vary from 100-200m. Here, a pulse of extreme subduction erosion occurred at ~2.5Ma. This episode was linked to the rapid formation of a deep (~1 km) sediment-filled forearc basin where sediment accumulation reached a peak rate of 1035 m/Myr. The most recent sediments in this basin do not come from high Talamanca inland from Osa, but instead from the nearshore Osa mélange within the Osa Peninsula. While rapid sediment accumulation has occurred within this forearc basin, the adjacent trench has remained unfilled, as indicated by IODP Site U1381, 5 km outboard of the trench, where a thin (96 m) veneer of recent to middle Miocene (Serravallian) sediment mantling the aseismic Cocos Ridge was recovered. Thus the highly erosive margin off the Osa Peninsula has had a large volume of sediment delivered offshore, but this sediment never reached the trench and was instead captured within a rapidly subsiding forearc basin. From this example, it is clear that sediment-starved trenches do not necessarily imply low rates of sediment supply to the margin. At this margin, the thin sediment layer in the trench is not the controlling factor for subduction erosion, but rather the consequence of rapid subduction erosion that created a rapidly subsiding forearc basin. A further consequence for Osa is that the forearc is rapidly being transformed from eroded material to the new basin fill. If this material differs rheologically from ';old forearc', this may have further implications for changing seismic characteristics at erosive subduction margins.

Vannucchi, P.; Morgan, J.; Sak, P. B.; Balestrieri, M.

2013-12-01

47

Evolution of Subduction Zone Curvature and its Dependence on the Trench Velocity and the Slab to Upper Mantle Viscosity Ratio  

Microsoft Academic Search

Three-dimensional laboratory models of upper mantle subduction are presented investigating the effect of the trench velocity (vt) and the slab to upper mantle viscosity ratio (?SP\\/?UM) on trench curvature and slab curvature. One set of experiments varies ?SP\\/?UM from 66 to 1375. Another set of experiments modifies vt through applying different velocities at the trailing plate. The results show that

W. P. Schellart

2010-01-01

48

Initiation and propagation of subduction along the Philippine Trench: evidence from the temporal and spatial distribution of volcanoes  

NASA Astrophysics Data System (ADS)

K-Ar ages of 37 samples collected from the Bicol peninsula, the Luzon island, Philippines, were determined by the unspiked sensitivity method in order to constrain the timing of initiation of subduction along the Philippine Trench. The measured K-Ar ages range from 0 to 7 Ma with two old outliers of 27 and 43 Ma. Together with K-Ar ages previously reported on volcanics in Leyte and eastern Mindanao, subduction volcanism has likely propagated from north to south: ˜6.6 Ma in Bicol and ˜3.5 Ma in Leyte and its vicinity. The temporal and spatial distribution suggests that the subduction volcanism started earlier in the north than in the south. This is consistent with the southern propagation of subduction along the Philippine Trench from ˜8 Ma.

Ozawa, Ayako; Tagami, Takahiro; Listanco, Eddie L.; Arpa, Carmencita B.; Sudo, Masafumi

2004-03-01

49

Development of GPS/A Seafloor Geodetic Network Along Japan Trench and Onset of Its Operation  

NASA Astrophysics Data System (ADS)

The Tohoku-oki earthquake in 2011 revealed that an M9-class giant earthquake could occur even in the old subduction zone and that coseismic slip can reach its frontal wedge, where we considered no significant stress had been accumulated in. One of the leading figure of such finding is in situ seafloor geodetic measurement, such as GPS/A technique for horizontal displacement and pressure gauge for vertical displacement. Japan Coast Guard and Japanese university group had developed several GPS/A sites near the source region of the Tohoku-oki earthquake and detected quite large coseismic movements over 20 m in there. Displacement vectors observed these sites showed systematic variation, i.e., mainly confined in the off-Miyagi area and getting larger near the trench. However, subsequent post-seismic deformation shows inexplicable distribution. In order to elucidate this complex feature, MEXT Japan has decided to construct dense and widely-extended GPS/A network along Japan trench, including deep area (~6000m). We, Tohoku and Nagoya universities, have firstly developed high-powered seafloor transponders with an omnidirectional acoustic unit that works at 6000 m deep ocean and enable acoustic ranging over 13 km slant length. In addition, using high-energy density battery, its lifetime is expected 10 years with normal operation. Secondly, we examined the optimal distribution of GPS/A sites forming a network, taken pre-existing sites into consideration. The new network consists of 20 sites (roughly four transponders at a single site and 86 transponders in total). The distribution is dense near the area of complex post-seismic deformation and extended over 400 km to cover the adjacent area of the source region, in where induced earthquake may be expected. The largest obstacle to draw network plan is seafloor topography. Because a GPS/A site is a seafloor benchmark, its installation must be on flat and locally stable spot. Since a single GPS/A site consists of three or more transponders in an area extending roughly the same dimension of its depth, flat spot is quite limited especially near the trench. The positions of the 20 sites were carefully determined using a high-definition bathymetry map. We already have constructed two sites, one of which is 5500 m depth, and successfully obtained acoustic data. In September, we will install rest of the sites (18 sites) and begin initial campaign survey. The second campaign is planned in November. We will introduce details of the network and report updated result in the talk.

Kido, M.; Fujimoto, H.; Osada, Y.; Ohta, Y.; Yamamoto, J.; Tadokoro, K.; Okuda, T.; Watanabe, T.; Nagai, S.; Kenji, Y.

2012-12-01

50

Alteration of the Subducting Oceanic Lithosphere at the Southern Chile Trench-Outer Rise  

NASA Astrophysics Data System (ADS)

Hydrothermal circulation and brittle faulting process within the oceanic lithosphere is usually confined to the upper crust for oceanic lithosphere created at intermediate-to-fast spreading rates. Lower crust and mantle, however, are relatively dry and undeformed. Recent studies at subduction zones suggest that hydration of the oceanic plate is most vigorous at the trench-outer rise where extensional bending-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 Southern Chile (~ 43° S) as part of the TIPTEQ (from The Incoming Plate to mega-Thrust EarthQuake processes) initiative. Seismic wide-angle and multichannel data are used to derive 2D velocity model using joint refraction and reflection travel time tomography. The ~ 250 km wide-angle seismic profile starts seaward of the trench axis on the 14.5 Ma old oceanic Nazca Plate, offshore of the rupture area of the Great 1960 Chile earthquake (Mw=9.5). The profile runs perpendicular to the Chile Ridge and parallel to the Chiloe and Guafo Fracture Zones. The velocity model derived from the tomography inversion consists of a ~ 5.5-km thick oceanic crust and shows P-wave velocities typical for mature fast-spreading structures in the seaward section of the profile, with uppermost mantle velocities as fast as ~ 8.3 km/s. Approaching the Chile trench, however, seismic velocities appear to be lower, suggesting a certain degree of hydration and alteration either in the oceanic crust and the uppermost mantle. The reduction of the velocities roughly starts at the outer rise and continues up to the trench, defining a clear low velocity zone. In addition, anomalous low heat flow values at the outer rise indicate an efficient inflow of cold seawater into the oceanic crust through a high basement outcrop.

Contreras-Reyes, E.; Grevemeyer, I.; Flueh, E.; Scherwath, M.; Heesemann, M.

2006-12-01

51

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. Four types of sedimentary basins have been recognized: 1) flysch basins with local olistostromes at the front of seaward propagating thrust sheets; 2) 5-10 km wide turbidite-rich trench-slope basins between uplifting structural ridges (i.e. anticlines) associated with shortening within 100 km of the subduction front at the seafloor; 3) 30-40 km wide trench-slope basins associated with an upslope increase in thrust and ridge spacing; and 4) mixed siliciclastic-carbonate shelves formed in association with margin uplift after filling of the wider (30-40 km) trench-slope basins. The lateral and vertical successions of basin geometries and sedimentary infill are consistent with the overall progressive uplift of the subduction wedge. Formation of some of the wide trench-slope basins may be accompanied by significant local subsidence and normal faulting synchronous with active shortening at the subduction front. Margin-wide normal faulting during the Middle-Late Miocene may have formed due to upslope collapse related to tectonic erosion. All of the basins studied contain major unconformities at their base and top, with basin strata deposited over about 2-8 Myr. The short life span of these lower trench-slope sedimentary basins is consistent with a succession of short paroxysmal tectonic episodes rather than continuous deformation for the duration of subduction. Stratigraphic discontinuities within basins (e.g., facies changes and reversal of paleo-currents) also record short-term tectonic events (c. 1-2 Myr) on the basin-bounding structures and attest to the episodic nature of upper-plate deformation in response to continuous subduction beneath the active margin.

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

2013-04-01

52

Heat flow and bending-related faulting at subduction trenches: Case studies offshore of Nicaragua and Central Chile  

Microsoft Academic Search

Detailed heat flow surveys on the oceanic trench slope offshore Nicaragua and Central Chile indicate heat flow values lower than the expected conductive lithospheric heat loss and lower than the global mean for crust of that age. Both areas are characterised by pervasive normal faults exposing basement in a setting affected by bending-related faulting due to plate subduction. The low

Ingo Grevemeyer; Norbert Kaul; Juan L. Diaz-Naveas; Heinrich W. Villinger; Cesar R. Ranero; Christian Reichert

2005-01-01

53

Subduction of Louisville Ridge seamounts: Effects on Tonga-Kermadec Trench and forearc morphology and seismic structure  

NASA Astrophysics Data System (ADS)

Geophysical profiling normal and oblique to the Tonga-Kermadec Trench between 23° and 28° S highlights forearc and trench deformation structures in the vicinity of the subducting Louisville Ridge. A fast southwards migration of the ridge-trench collision zone (~180 km/myr), and the obliquity of the seamount chain to the trench make this an ideal case study for the effects of seamount subduction on lithospheric structure. Wide-angle and multichannel seismic, swath bathymetry and potential field data on four profiles are used to image seafloor and crustal structure. The study area covers three main deformation zones from north to south: post-, current and pre-seamount subduction. Mo'unga Seamount lies in the centre of the trench at the collision zone creating a disparity between the geomorphic and tectonic trench locations and broadening the trench floor. The geomorphic trench, the deepest part of the collision zone, is seaward of the seamount at the base of a graben formed by extensional bending faults on the down-going Pacific Plate. The true plate boundary lies ~16 km west, on the arcward side of Mo'unga Seamount, where a detachment fault separates forearc from Pacific Plate-derived trench fill. The steepness of the detachment fault indicates that the impinging seamount induces arcward rotation of the lower trench slope. Arcward rotation is also observed in the dipping sedimentary layers of the mid-slope basin. As no unconformable overlying sediments are observed, the deformation is inferred to be recent and ongoing. There is a southward decrease in the slope angle of the inner-trench wall and this is reflected in the style of extensional deformation structures in the mid-slope basin. A 30 km wide basin of distributed deformation on the shallow dipping mid-trench slope is observed in the south and a 10 km wide, ~2 km deep, fault-bounded basin on the steeply dipping mid-trench slope is observed in the collision zone and to the north. A greater degree of tectonic collapse of the steep inner-trench slope in the north is indicated by a 15% decrease in arc basement velocities to 4 km below the mid-slope basin floor. These low velocities are attributed to deep fracturing extending into the upper crust and may record the tectonic collapse of the forearc after seamount subduction. P-wave velocity and gravity models of crustal structure also indicate an along-arc increase in crust and plate interface thickness from north to south. Low mantle Pn velocities of 7.8 kms-1 below the forearc are indicative of serpentinisation of the mantle wedge. Transient effects of a north to south progression of enhanced mantle hydration, basal erosion and oversteepening and collapse of the forearc are inferred. This project has enabled the study of mature, active and pre-seamount subduction effects on forearc and trench structure, and highlights the speed at which evidence of these disappear from the seabed geomorphology.

Stratford, W. R.; Peirce, C.; Funnell, M.; Paulatto, M.; Watts, A. B.; Grevemeyer, I.; Bassett, D.; Hunter, J.

2013-12-01

54

Two-dimensional modelling of subduction zone anisotropy with application to southwestern Japan  

NASA Astrophysics Data System (ADS)

We present a series of 2-D numerical models of viscous flow in the mantle wedge induced by a subducting lithospheric plate. We use a kinematically defined slab geometry approximating the subduction of the Philippine Sea plate beneath Eurasia. Through finite element modelling we explore the effects of different rheological and thermal constraints (e.g. a low-viscosity region in the wedge corner, power law versus Newtonian rheology, the inclusion of thermal buoyancy forces and a temperature-dependent viscosity law) on the velocity and finite strain field in the mantle wedge. From the numerical flow models we construct models of anisotropy in the wedge by calculating the evolution of the finite strain ellipse and combining its geometry with appropriate elastic constants for effective transversely isotropic mantle material. We then predict shear wave splitting for stations located above the model domain using expressions derived from anisotropic perturbation theory, and compare the predictions to ~500 previously published shear wave splitting measurements from seventeen stations of the broad-band F-net array located in southwestern Japan. Although the use of different model parameters can have a substantial effect on the character of the finite strain field, the effect on the average predicted splitting parameters is small. However, the variations with backazimuth and ray parameter of individual splitting intensity measurements at a given station for different models are often different, and rigorous analysis of details in the splitting patterns allows us to discriminate among different rheological models for flow in the mantle wedge. The splitting observed in southwestern Japan agrees well with the predictions of trench-perpendicular flow in the mantle wedge along with B-type olivine fabric dominating in a region from the wedge corner to about 125 km from the trench.

Long, Maureen D.; Hager, Bradford H.; de Hoop, Maarten V.; van der Hilst, Rob D.

2007-08-01

55

Faulting within the Pacific plate at the Mariana Trench: Implications for plate interface coupling and subduction of hydrous minerals  

NASA Astrophysics Data System (ADS)

investigate faulting within the incoming Pacific plate at the Mariana subduction trench to understand stresses within the bending plate, regional stresses acting upon the plate interface, and the extent of possible faulting-induced mantle serpentinization. We determine accurate depths by inverting teleseismic P and SH waveforms for earthquakes occurring during 1990-2011 with Global Centroid Moment Tensor (GCMT) solutions. For earthquakes with Mw 5.0+, we determine centroid depths and source time functions and refine the fault parameters. Results from Central Mariana indicate that all earthquakes are extensional and occur at centroid depths down to 11 km below the Moho. At the Southern Mariana Trench, extensional earthquakes continue to 5 km below the Moho. One compressional earthquake at 34 km below the seafloor suggests stronger plate interface coupling here. In addition, we model the stress distribution within the Pacific plate along two bathymetric profiles extending seaward from the Mariana subduction trench axis to better understand whether our earthquake depth solutions match modeled scenarios for plate bending under applied external forces. Results from our flexure models match the locations of extensional and compressional earthquakes and suggest that the Pacific plate at Southern Mariana is experiencing larger, compressional stresses, possibly due to greater interplate coupling. Additionally, we conclude that if extensional faulting promotes the infiltration of water into the subducting plate mantle, then the top 5-15 km of the Pacific plate mantle are partially serpentinized, and a higher percentage of serpentinization is located near the Central Mariana trench where extensional events extend deeper.

Emry, Erica L.; Wiens, Douglas A.; Garcia-Castellanos, Daniel

2014-04-01

56

Confirmation that Large-Magnitude Megathrust Earthquakes Are Linked to the Subduction of Thick, Laterally Continuous Bodies of Trench Sediment  

NASA Astrophysics Data System (ADS)

THE HYPOTHESIS: Ruff (1989) surmised that subduction of a thick section of trench-floor sediment would construct a laterally homogenous layer between upper and lower plates that would smooth the roughness of subducted sea-floor relief and strength-coupling asperities. During a megathrust earthquake (Eq), an even distribution of interplate strength (coupling) running parallel to the subduction zone (SZ) would favor long trench-parallel ruptures. Rupture zones exceeding about 250 km in length are characteristic of great (Mw 8.0 and higher) and giant (Mw 8.5 and higher) megathrust Eqs. Ruff observed that roughly half of all recorded megathrust Eqs of Mw 8.2 and larger broke adjacent to sediment-flooded trenches, thus suggesting a link between subduction of thick sediment sequences and rupture areas of high magnitude Eqs. TESTING THE HYPOTHESIS: We examined Ruff’s conjecture by compiling a database of well-documented instrumentally and historically recorded great and giant megathrust Eqs. We compared this listing with the global distribution of trench-axis sediment bodies that have along-trench dimension of 250 km or longer. Epicenters of great and giant Eqs were plotted along trench sectors classified as having a Very Thin (less than 0.5 km), Thin (0.5-1.0 km), Thick (1.0-3.0 km), or Very Thick (greater than 3.0 km) section of sediment entering the SZ. The highest Mw Eq recorded in each sediment sector (27 in all, 15 of which are thickly sedimented) was tabulated. Using only instrumentally recorded Eqs plus the geologically well-vetted Cascadia rupture of 1700 (19 events), trench sectors with axial deposits thicker than 1.0 km are associated with the occurrence of: 53 percent of Mw8.0 and larger (10 of 19), 67 percent of Mw8.3 and larger (6 of 9), 75 percent of Mw8.5 and larger (6 of 8), 80 percent of Mw9.0 and larger (4 of 5), 100 percent of Mw larger than 9.0 (3 of 3). Combining instrumental and historic EQs (27 events) changes the corresponding occurrence percentages to 55, 59, 57, 80, and 100. CONCLUSION: As noted by Ruff (1989), a number of physical parameters (e.g., subducted seamounts and ridges) contribute to the locations and rupture lengths of great and giant megathrust Eqs. But the observations listed above make it clear that subduction of a thick, laterally continuous section of sediment is a major determinant. Presumably, thickness is relative, i.e., it need only be adequate to smooth subducting relief sufficient to reduce lateral patchiness of asperities. The Ruff conjecture that sediment subduction of adequate thickness promotes large-magnitude megathrust rupturing seems to be confirmed. [Ruff, L., 1989, Do trench sediments affect great earthquakes occurrence in subduction zones, Pure and Applied Geophysics, v. 129, Nos. 1/2, p. 263-282].

Scholl, D. W.; Kirby, S. H.; Keranen, K. M.; Blakely, R. J.; Wells, R. E.

2010-12-01

57

Hadal disturbance in the Japan Trench induced by the 2011 Tohoku-Oki Earthquake  

PubMed Central

In situ video observations and sediment core samplings were performed at two hadal sites in the Japan Trench on July, 2011, four months after the Tohoku–Oki earthquake. Video recordings documented dense nepheloid layers extending ~30–50?m above the sea bed. At the trench axis, benthic macrofauna was absent and dead organisms along with turbid downslope current were observed. The top 31?cm of sediment in the trench axis revealed three recent depositions events characterized by elevated 137Cs levels and alternating sediment densities. At 4.9?km seaward from the trench axis, little deposition was observed but the surface sediment contained 134Cs from the Fukushima Dai–ichi nuclear disaster. We argue that diatom blooms observed by remote sensing facilitated rapid deposition of 134Cs to hadal environment and the aftershocks induced successive sediment disturbances and maintained dense nepheloid layers in the trench even four months after the mainshock.

Oguri, Kazumasa; Kawamura, Kiichiro; Sakaguchi, Arito; Toyofuku, Takashi; Kasaya, Takafumi; Murayama, Masafumi; Fujikura, Katsunori; Glud, Ronnie N.; Kitazato, Hiroshi

2013-01-01

58

Hadal disturbance in the Japan Trench induced by the 2011 Tohoku-Oki earthquake.  

PubMed

In situ video observations and sediment core samplings were performed at two hadal sites in the Japan Trench on July, 2011, four months after the Tohoku-Oki earthquake. Video recordings documented dense nepheloid layers extending ~30-50 m above the sea bed. At the trench axis, benthic macrofauna was absent and dead organisms along with turbid downslope current were observed. The top 31 cm of sediment in the trench axis revealed three recent depositions events characterized by elevated (137)Cs levels and alternating sediment densities. At 4.9 km seaward from the trench axis, little deposition was observed but the surface sediment contained (134)Cs from the Fukushima Dai-ichi nuclear disaster. We argue that diatom blooms observed by remote sensing facilitated rapid deposition of (134)Cs to hadal environment and the aftershocks induced successive sediment disturbances and maintained dense nepheloid layers in the trench even four months after the mainshock. PMID:23715086

Oguri, Kazumasa; Kawamura, Kiichiro; Sakaguchi, Arito; Toyofuku, Takashi; Kasaya, Takafumi; Murayama, Masafumi; Fujikura, Katsunori; Glud, Ronnie N; Kitazato, Hiroshi

2013-01-01

59

S-wave velocities and anisotropy in sediments entering the Nankai subduction zone, offshore Japan  

NASA Astrophysics Data System (ADS)

P and mode-converted S waves from airgun shots recorded along a line of ocean bottom seismometers were used to construct a 2-D velocity section across the Nankai Trough and the toe of the accretionary complex, offshore southeast Japan. The site was chosen because of plans to drill into the seismogenic zone of the main subduction thrust, which has a history of M ~ 8 earthquakes. The section is constrained by well-log data from three Ocean Drilling Program boreholes. S-wave velocities of the sediments over the entire section, down to >1.1 km below seafloor, range from 107 to 915 ms-1. Shear wave splitting indicates anisotropy in all the sediments except possibly the distal trench fill. If interpreted conventionally as being due to vertical stress-aligned cracks, the anisotropy in both the trench and the toe of the accretionary wedge is consistent with crack orientation NW-SE, parallel to the direction of maximum tectonic compression. Crack density is ~0.01-0.03, consistent with closeness to fracture criticality.

Peacock, S.; Westbrook, G. K.; Bais, G.

2010-02-01

60

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

61

Trench-parallel shortening in the forearc caused by subduction along a seaward-concave plate boundary: Insights from analogue modelling experiments  

NASA Astrophysics Data System (ADS)

Three-dimensional thermo-mechanical analogue experiments are employed to test the hypothesis that oceanic subduction along a seaward-concave plate boundary can generate trench-parallel shortening in the forearc near the axis of curvature. The model deformation is analyzed with a Particle Imaging Velocimetry (PIV) system that allows for comparison of forearc deformation along the oblique limbs of the curved plate boundary and near the axis of curvature. Moreover, PIV allows for separation of the trench-parallel and trench-perpendicular components of strain, regardless of trench orientation. The resulting deformation maps show a remarkable symmetry and indicate drag of the forearc above the interplate coupling area towards the axis of curvature. Trench-perpendicular profiles show that along the oblique limbs of the plate boundary, the forearc is submitted to trench-normal shortening and trench-parallel shearing but not trench-parallel shortening or extension. This contrasts with the situation near the axis of symmetry where the forearc is submitted to trench-parallel and trench-perpendicular normal shortening, but is not sheared. The experimental results confirm that trench-normal thrusts observed in the fore-arc of the Central-Andes can be a mechanical consequence of subduction along a seaward-concave plate boundary if the degree of interplate coupling is large.

Boutelier, D.; Oncken, O.; Cruden, A. R.

2014-01-01

62

Interaction of subducted slabs with the mantle transition-zone: A regime diagram from 2-D thermo-mechanical models with a mobile trench and an overriding plate  

NASA Astrophysics Data System (ADS)

zone slab deformation influences Earth's thermal, chemical, and tectonic evolution. However, the mechanisms responsible for the wide range of imaged slab morphologies remain debated. Here we use 2-D thermo-mechanical models with a mobile trench, an overriding plate, a temperature and stress-dependent rheology, and a 10, 30, or 100-fold increase in lower mantle viscosity, to investigate the effect of initial subducting and overriding-plate ages on slab-transition zone interaction. Four subduction styles emerge: (i) a "vertical folding" mode, with a quasi-stationary trench, near-vertical subduction, and buckling/folding at depth (VF); (ii) slabs that induce mild trench retreat, which are flattened/"horizontally deflected" and stagnate at the upper-lower mantle interface (HD); (iii) inclined slabs, which result from rapid sinking and strong trench retreat (ISR); (iv) a two-stage mode, displaying backward-bent and subsequently inclined slabs, with late trench retreat (BIR). Transitions from regime (i) to (iii) occur with increasing subducting plate age (i.e., buoyancy and strength). Regime (iv) develops for old (strong) subducting and overriding plates. We find that the interplay between trench motion and slab deformation at depth dictates the subduction style, both being controlled by slab strength, which is consistent with predictions from previous compositional subduction models. However, due to feedbacks between deformation, sinking rate, temperature, and slab strength, the subducting plate buoyancy, overriding plate strength, and upper-lower mantle viscosity jump are also important controls in thermo-mechanical subduction. For intermediate upper-lower mantle viscosity jumps (×30), our regimes reproduce the diverse range of seismically imaged slab morphologies.

Garel, F.; Goes, S.; Davies, D. R.; Davies, J. H.; Kramer, S. C.; Wilson, C. R.

2014-05-01

63

24. BENTHIC FORAMINIFERS AND PALEOBATHYMETRY OF THE JAPAN TRENCH AREA, LEG 57, DEEP SEA DRILLING PROJECT  

Microsoft Academic Search

Deep sea drilling in the Japan Trench area recovered a Late Cretaceous to Pleistocene sedimentary and biostratigraphic record unraveling the tectonic and paleobathymetric history of the conver- gent margin. Benthic foraminiferal assemblages spanning the Late Cretaceous to the late Pleistocene permit reconstruction of the paleo- bathymetric history of this area. During the Late Cretaceous a deep bathyal environment persisted, characterized

Gerta Keller

64

Attenuation anisotropy beneath the subduction zones in Japan  

NASA Astrophysics Data System (ADS)

We analyze high quality digital waveform data at stations in Japan from the POSEIDON and IRIS broad-band seismograph networks. The analysis of multiple ScS waves of the deep event beneath Sakhalin on 12 May 1990 shows that the orientation of the principal axis of horizontal ScSn particle motion is rotated clockwise from NWN-SES to N-S as the number of reflections increases. This suggests that the attenuation of the E-W component is higher than that of the N-S component of ScS waves. The spectral ratio ScS2/ScS1 differs between the two horizontal components. We estimate the quality factor QScS of the whole mantle for each horizontal component using the decay rate of spectral ratio of band-passed ScS1 and ScS2 phases in the frequency range from 0.01 to 0.03 Hz. We obtain a higher average QScS for the N-S component (141±8) than that for the E-W component (91±5). That is, the E-W component attenuates more than the N-S component. For upcoming ScS waves the N-S direction is nearly parallel to the strike of the subducting slab beneath the mantle wedge in the Japanese islands, and the E-W is perpendicular to the strike. The up-welling and downgoing flow in the mantle wedge due to drag caused by the subduction is likely to cause the difference in attenuation between the two directions, in other words, azimuthal attenuation anisotropy.

Hiramatsu, Yoshihiro; Ando, Masataka

65

Shear wave anisotropy in the crust, mantle wedge, and subducting Pacific slab under northeast Japan  

Microsoft Academic Search

To study the anisotropic structure beneath northeast (NE) Japan, we made 4366 shear wave splitting measurements using high-quality seismograms of many earthquakes occurring in the crust and the subducting Pacific slab. Our results provide important new information on the S wave anisotropy in the upper crust, lower crust, mantle wedge, and subducting Pacific slab. In the upper crust, the anisotropy

Zhouchuan Huang; Dapeng Zhao; Liangshu Wang

2011-01-01

66

Global Positioning System (GPS) and GPS-Acoustic Observations: Insight into Slip Along the Subduction Zones Around Japan  

NASA Astrophysics Data System (ADS)

The global positioning system (GPS) is one of the most powerful tools available for observation of Earth's surface deformation. In particular, coseismic, postseismic, slow transient, and interseismic deformation have all been observed globally by GPS over the past two decades, especially in subduction zones. Moreover, GPS-acoustic techniques have been developed for practical use in the past decade, allowing observation of offshore deformation immediately above slip regions. Here, we describe the application of GPS and GPS-acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around Japan, where geodetic data coverage is particularly dense. The data demonstrate temporally variable strain accumulation in the source region of the 2011 Mw 9.0 Tohoku-oki earthquake, and observation of the huge slip of the Tohoku-oki earthquake near the trench using GPS-acoustic methods has considerably advanced our knowledge of stress release and accumulation in this subduction zone.

Nishimura, Takuya; Sato, Mariko; Sagiya, Takeshi

2014-05-01

67

Marine Magnetic Anomaly and Magnetization of Oceanic Plate around the Japan Trench in the Northwestern Pacific  

Microsoft Academic Search

We have newly collected dense magnetic data around the Japan Trench in the northwestern Pacific. We present characteristics of the complied magnetic anomaly and crustal magnetization variation. The Pacific Plate in the study area has a series of parallel magnetic anomalies (Japanese Lineation Set), identified as chron M14-M7 (140-127 Ma). These anomalies are well lineated, in the direction of WSW-ENE,

T. Fujiwara; A. Obi; Y. Noda; Y. Kido; M. Nakanishi; N. Hirano; N. Abe; Y. Ogawa

2005-01-01

68

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 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/2002EGSGA..27.5701N"> <span id="translatedtitle">Partitioning At Very Oblique <span class="hlt">Subduction</span> Zones: A Comparative Marine Study Between The Burma <span class="hlt">Trench</span> and The Western Termination of The Hellenic <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">On the Ionian Islands area, the cumulated motion of the slow African convergence and rapid rotation of the Anatolian Block induces oblique convergence at the western termination of the Hellenic <span class="hlt">Trench</span>. The rate of convergence, constrained by several GPS studies, is about 35 mm/yr more or less NS oriented. MEDEE Cruise data (Labo- ratoire de Géologie, ENS 1995) including multibeam bathymetry and shallow seismic profiles, indicate that this highly oblique convergence is partitioned into a frontal com- pressive wedge and N160E to N170E dextral strike-slip. Strike slip faults are local- ized within the Mediterranean Ridge and at the boundary between the backstop and the wedge. Faults within the wedge progressively curve and connect to the compressive horse tailed termination of the N20E dextral Kephalonia Fault. The accretionary front is also curved and thrusts seem to become parallel to the Kephalonia Fault. The obser- vations there are complicated by the gravity sliding of the Calabrian wedge, covering the active structures of the Mediterranean Ridge at the termination of the Kephalo- nia Fault. A comparative study in a similar tectonic setting, the Indo-Burman <span class="hlt">Trench</span>, helps to better understand the termination of the Mediterranean oblique <span class="hlt">subduction</span>. The Indo-Burman <span class="hlt">trench</span> presents the same type of obliquity and velocity. The AN- DAMAN Cruise data (Laboratoire de Géologie,ENS, 2000) were used to constrain the offshore deformation along the Burma <span class="hlt">Trench</span>. The front of the wedge is marked by N30E trending dextral strike slip faults, and the absence of accretionary struc- tures despite large infill of the Bengal fan. In contrast with the Mediterranean case, partitioning of the very oblique convergence induces the motion of an independent sliver located between the Indian plate and the Sunda Block (the "Burmese" platelet). In the Mediterranean case, we suggest that forces that drive the upper plate, plus the northwestern locking by the Apulian platform, overcome forces that would allow the motion of a large independent crustal sliver. The obliquity is thus accommodated at the boundary between the backstop and the wedge, resulting in a deforming "wedge sliver" rather than a rigid crustal sliver.</p> <div class="credits"> <p class="dwt_author">Nielsen, C.; Chamot-Rooke, N. Rangin, 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">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/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">71</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/48925925"> <span id="translatedtitle">On the biannually repeating slow-slip events at the Ryukyu <span class="hlt">Trench</span>, southwestern <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">Global positioning system data show that about 20 slow-slip events occurred during 1997–2007 in the southwestern part of the Ryukyu Arc, <span class="hlt">Japan</span>, where large interplate thrust earthquakes are not known to have occurred in spite of relatively fast plate convergence. They recur fairly regularly on one patch of the <span class="hlt">subduction</span> fault, which is as deep as 20–40 km and mechanically</p> <div class="credits"> <p class="dwt_author">Kosuke Heki; Takeshi Kataoka</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">72</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/2014EGUGA..16.4732R"> <span id="translatedtitle">Numerical modeling of <span class="hlt">subduction</span> beneath non-uniform overriding plates: Time-dependent evolution of slab geometry and <span class="hlt">trench</span>-parallel 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">Seismic anisotropy measurements show that the fast spreading direction below the slab is aligned parallel to the <span class="hlt">trench</span> in the central region and perpendicular near the edges. Above the slab it has a complex pattern, often showing abrupt transitions between <span class="hlt">trench</span>-parallel and <span class="hlt">trench</span>-perpendicular directions and sharp changes in intensity. The origin of this complex pattern is poorly understood, however, previous models have shown that variations in slab geometry can cause <span class="hlt">trench</span>-parallel flow above the slab. In turn, overriding plate thermal state influences the slab dip, which suggests a causal link between overriding plate structure, slab geometry and mantle flow in <span class="hlt">subduction</span> zones. We study the effect of along-strike variations in thermal thickness of the overriding plate on the evolution of slab geometry and induced mantle flow. To perform the study we implement generic 3D time dependent thermo mechanical numerical models of buoyancy driven <span class="hlt">subduction</span> using CitcomS. We find that increased hydrodynamic suction beneath the colder portion of the overriding plate causes shallower slab dip. The variation in slab geometry drives strong <span class="hlt">trench</span>-parallel flow beneath the slab and a complex flow pattern above the slab. The mantle flow pattern responds to the changing geometry of the slab, which makes the process strongly time-dependent. The location and strength of <span class="hlt">trench</span>-parallel flow vary throughout the simulations, which suggests that the global variability in seismic anisotropy in present-day observations is in part due to the non-steady-state behavior of <span class="hlt">subduction</span> systems. This new mechanism for driving <span class="hlt">trench</span>-parallel flow provides a good explanation for seismic anisotropy observations from the Middle and South America <span class="hlt">subduction</span> zones, where both slab dip and overriding plate thermal state are strongly variable and correlated.</p> <div class="credits"> <p class="dwt_author">Rodriguez-Gonzalez, Juan; Billen, Magali; Negredo, Ana</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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://www.osti.gov/scitech/biblio/5472520"> <span id="translatedtitle">Changes in the crust and upper mantle near the <span class="hlt">Japan</span>-Bonin <span class="hlt">trench</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">Depths and reflection times to mantle have been computed in the west Pacific from 60 sonobuoy refraction solutions, many of which could be compared with observed mantle reflection depths from multichannel data obtained at the same time. After repicking some of these sonobuoy records, all were eventually adjusted to agree within 0.005 s with the observed mantle reflection times. This added constraint produces solutions that are clearly more reliable. Crustal velocities (exclusive of water and sediment) from the study area are rather tightly distributed about a mean value of 6.53 km/s with a standard deviation of only 0.23 km/s (n=47). Results show that the crust thickens in a westerly direction from the west Pacific basin, where mantle depths are 11--11.5 km to a belt 200 km east of the <span class="hlt">Japan</span> <span class="hlt">trench</span>, coinciding with the outer gravity high, where mantle is at an average depth of 14 km. Several sonobuoys in the zone of maximum crustal thickness just east of the outer slope of the <span class="hlt">Japan</span> <span class="hlt">trench</span> record two deep reflectors about 0.6 s apart in the vicinity of the upper mantle. Two values of interval velocity obtained from a reduced T/sup 2//X/sup 2/ analysis of the layer bounded by these reflectors are 7.5 and 7.2 km/s. These sonobuoys and a few others with weaker double reflections are all located within the outer gravity high. To the south a well-observed mantle reflection and its strong 8.2-km/s refraction disappear from our records just as the crust begins its descent into the Bonin <span class="hlt">trench</span>. Within the outer <span class="hlt">trench</span> slope a 7.3-km/s refractor, which is a weak arrival elsewhere, becomes the dominant refractor.</p> <div class="credits"> <p class="dwt_author">Houtz, R.; Windisch, C.; Murauchi, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-01-10</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/2012AGUFM.T13F2692E"> <span id="translatedtitle">The <span class="hlt">Japan</span> <span class="hlt">Trench</span> Fast Drilling Project (IODP Exp. 343&343T JFAST): Making Scientific Drilling History 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The international scientific community began planning the <span class="hlt">Japan</span> <span class="hlt">Trench</span> Fast Drilling Project (JFAST) soon after the 11 March Tohoku Earthquake occurred. Predicted rapid decay of any thermal anomaly resulting from shear heating, which may allow the frictional strength of the main slip zone to be calculated, dictated that temperature measurements needed to be made within 18 months of the initial earthquake. Based on the drilling and observatory request from the science team, the Center for Deep Earth Exploration (CDEX) began scoping activities for this project, and rapidly became aware of some of the daunting technical challenges involved in drilling in approximately 7 km of water. The deepest water depth drilling in scientific ocean drilling history was in the Marianas <span class="hlt">Trench</span> in 1978 in water depth of 7,049.5 m with 15.5 m penetration. The original plan of JFAST required logging-while-drilling (LWD) and sample collection from 1,000 m below the seafloor in 7,000 m water depth in the <span class="hlt">Japan</span> <span class="hlt">Trench</span>. Beyond this, temperature observatories needed to be deployed into the borehole. A scientific drilling proposal was submitted to the Integrated Ocean Drilling Program (IODP) by 1 August 2011 and our preparation for the operation began in parallel. To reach the plate boundary target, and to install an observatory, we had to develop several new tools (e.g., a casing running tool). The strength and performance of the drill string was also a major technical and engineering issue. Taking the limitations of the operational time window into account, our original strategy was, in about 7,000 m of water depth near the axis of the <span class="hlt">Japan</span> <span class="hlt">Trench</span>, to 1) drill a 8-1/2" hole with LWD and install an observatory 900 m below the seafloor, 2) drill a 10-5/8" hole with coring assembly and collect core samples from the deeper part of the hole then install another observatory 900 m below the seafloor. IODP Expedition 343 (JFAST) started on 1 April 2012 (less than 13 months after the earthquake). Several mechanical and weather issues prohibited completion of the above planned operations but we had reached the following operational targets by the end of this expedition of 24 May 2012: 1. Penetrated 850.5 m below seafloor and obtained geophysical data by LWD which allowed the plate boundary interface to be located. 2. Collected core samples from 648 m to 844.5 m below the seafloor, including samples of the plate boundary fault zone. Both operations were completed in water depth of 6889.5 m. However, due to a lack of operational time, the installation of temperature observatories was not performed. Consequently, IODP and CDEX/JAMSTEC decided to return to the site, in a follow-up expedition (IODP Expedition 343T), to install a temperature observatory into a borehole started by the original part of the expedition. IODP Expedition 343T began on 5 July 2012 and successfully installed a temperature observatory into an 854.8 m borehole in 6,897.5 m of water, operations completed on 19 July 2012.</p> <div class="credits"> <p class="dwt_author">Eguchi, N.; Toczko, S.; Maeda, L.; Sawada, I.; Saruhashi, T.; Kyo, N.; Namba, Y.; Chester, F.; Mori, J. J.; Science Party, I.</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">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/2004E%26PSL.219...13H"> <span id="translatedtitle">Space geodetic observation of deep basal <span class="hlt">subduction</span> erosion in northeastern <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">Observation of tectonic erosion [Von Huene and Scholl, Rev. Geophys. 29 (1991) 279-316] in a <span class="hlt">subduction</span> zone has been difficult as it leaves little geological and geophysical evidence. Three-dimensional velocity profiles of crustal movement obtained by Global Positioning System across NE and SW <span class="hlt">Japan</span> agree well with those predicted by the elastic loading of the <span class="hlt">subducting</span> slabs. However, vertical velocities in the NE <span class="hlt">Japan</span> forearc show significant negative deviation (relative subsidence). This may indicate loss of material at the plate interface that can be attributed to the erosion of the upper plate by the underthrusting slab (basal <span class="hlt">subduction</span> erosion). The estimated rate (15 mm/yr down to a slab depth of 90 km) is somewhat faster than the geological average; the erosion speed may be variable being controlled by the surface roughness of <span class="hlt">subducting</span> slabs.</p> <div class="credits"> <p class="dwt_author">Heki, Kosuke</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-02-01</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/40850792"> <span id="translatedtitle">Seismic evidence for a metastable olivine wedge in the <span class="hlt">subducting</span> Pacific slab under <span class="hlt">Japan</span> Sea</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 apply a forward-modeling approach to high-quality arrival time data from 23 deep earthquakes greater than 400 km depth to investigate the detailed structure of the <span class="hlt">subducting</span> Pacific slab beneath the <span class="hlt">Japan</span> Sea. Our results show that a finger-like anomaly exists within the <span class="hlt">subducting</span> Pacific slab below 400 km depth, which has a P-wave velocity 5% lower than the surrounding slab velocity</p> <div class="credits"> <p class="dwt_author">Guoming Jiang; Dapeng Zhao; Guibin Zhang</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">77</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/70014749"> <span id="translatedtitle">Reflections from midcrustal rocks within the Mesozoic <span class="hlt">subduction</span> complex near the eastern Aleutian <span class="hlt">Trench</span>.</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">Seismic reflection data show that highly reflective rocks make up the midcrust of the convergent margin adjacent to the eastern Aleutian <span class="hlt">Trench</span>. These rocks form an arch that strikes obliquely across the strongly expressed NE-SW structural grain of exposed Mesozoic rocks. Deep reflections could be from underplated rocks that have been arched by the imbrication or underplating of strata below the reflective rocks. Speculates that one band of reflections that rises toward but does not reach the surface is from the Eagle River thrust fault, which separates Late Cretaceous melange from deformed turbidite sequences of the same age. -from Authors</p> <div class="credits"> <p class="dwt_author">Fisher, M. A.; Von Huene, R.; Smith, G. L.</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">78</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/1991Tecto..10..475M"> <span id="translatedtitle">Well-documented travel history of Mesozoic pelagic chert in <span class="hlt">Japan</span>: From remote ocean to <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 Mino-Tanba belt in southwest <span class="hlt">Japan</span>, a segment of the Cordilleran-type orogenic chain of Jurassic east Asia, is composed mainly of a Middle-Upper Jurassic <span class="hlt">subduction</span>-accretion complex in which Triassic and Lower Jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with Middle-Upper Jurassic clastic rocks. High-resolution microfossil (conodont and radiolaria) research has identified very low average sedimentation rates of about 0.5 g/cm²/1000 yr in the chert units, similar to those of modern pelagic sediments accumulated in open ocean environments. Judging from the low average sedimentation rate, high purity of biogenic silica, long duration of continuous deposition (>50 m.y.), and wide along-strike extent (>1000 km), the bedded radiolarian cherts in the Mino-Tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments; accordingly, the alleged origin in smaller marginal basins is untenable. Upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a <span class="hlt">trench</span>. The tectonic interlayering of these cherts and coarse-grained terrigenous elastics is a secondary feature that was added through duplexing-underplating in the <span class="hlt">subduction</span> zone. On the basis of the primary stratigraphy and field occurrence of Triassic bedded chert in the Mino-Tanba belt, newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a Cordilleran-type bedded chert from its birth at a mid-oceanic ridge to its demise at a <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Matsuda, Tetsuo; Isozaki, Yukio</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-04-01</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://academic.research.microsoft.com/Publication/40447732"> <span id="translatedtitle">Detection of the <span class="hlt">subducting</span> crust of oceanic plates beneath the Kanto district, <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">Low-velocity crustal layers on the top of the <span class="hlt">subducting</span> slabs beneath the Kanto district, central <span class="hlt">Japan</span>, were detected by a travel time inversion using 40,763 P-wave arrival times from 3038 local earthquakes recorded by a local network of 41 seismic stations. The inversion covered 188 × 228 × 110 km volume of the target region and the model was parameterized</p> <div class="credits"> <p class="dwt_author">Shiro Ohmi; Nobuo Hurukawa</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</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/2013AGUFM.T51I..03B"> <span id="translatedtitle">Crustal structure and seismicity associated with seamount <span class="hlt">subduction</span>: A synthesis of results from the Tonga-Kermadec <span class="hlt">Trench</span> - Louisville Ridge collision 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 Tonga-Kermadec plate boundary is the most linear, fastest converging and most seismically active <span class="hlt">subduction</span> zone on Earth. The margin is intersected at ~26° S by the Louisville Ridge seamount chain. Crustal structure of both the overthrusting Indo-Australian and <span class="hlt">subducting</span> Pacific plate are sufficiently uniform north and south of the contemporary collision zone to make this an ideal location to study the mechanics and seismological consequences of seamount <span class="hlt">subduction</span>. We present here a synthesis and interpretation of structural observations from the Louisville collision zone made during three marine geophysical surveys onboard R/V Sonne in 2004, 2007-2008 and 2011. The Louisville collision zone is characterized by a 3000 m reduction in <span class="hlt">trench</span> depth and a 15° anticlockwise rotation of the <span class="hlt">trench</span> axis. Swath bathymetry data reveal a pronounced forearc high (~ 2000 m relative to adjacent regions), which is correlated with a free-air gravity and magnetic anomaly high (50 mGal and 200 nT peaks respectively). Morphological characteristics are accompanied by a 40 % reduction in seismicity compared to regions immediately to the north and south. Forward modeling of active source seismic travel-times constrain the <span class="hlt">subducting</span> Pacific plate to ~30 km depth and suggests that it is ~6 km thick and has Vp 6.2-6.8 km/sec. The overthrusting Indo-Australian plate has Vp 4.5-6.8 km/sec and a Moho depth of 15 km. The mantle wedge has Vp ~8.0 km/sec. Beneath the forearc high, seismic wave-speeds within the upper-plate are 0.3-0.5 km/sec slower than regions to the north and south and a up to 3 km thick volume of anomalously low Vp (<4.5 km/sec at > 10 km depth) is inferred to overlie the <span class="hlt">subduction</span> interface. This latter observation is interpreted as <span class="hlt">subducting</span> and underplated volcaniclastic sediments, which reach up to 1-2 km in thickness within the flanking flexural moats of the Louisville Ridge. The projected width of the ridge and flanking moats are well correlated with the seismic gap suggesting a gap causality related to <span class="hlt">subducting</span> sediments and possibly high pore-fluid pressure. In addition to the development of fracture networks in the overthrusting plate, which likely result in lower Vp, we suggest the presence of <span class="hlt">subducting</span> sediments likely contribute to forming conditions favoring intact and aseismic seamount <span class="hlt">subduction</span>. Moreover, <span class="hlt">subducting</span> seamounts and aseismic ridges uplift the overlying wedge resulting in a translation of anomalous plate-interface to anomalous <span class="hlt">trench</span>-slope topography. We note a strong correlation between the sharp up-dip limit of anomalous <span class="hlt">trench</span>-slope topography and the intersection of the <span class="hlt">subducting</span> slab with the forearc Moho. Hence, we extend existing mechanical models of seamount <span class="hlt">subduction</span> in suggesting the influence of <span class="hlt">subducting</span> relief on the structure of the overthrusting plate is limited by the slab - forearc Moho intersection. Global observations of <span class="hlt">subducting</span> relief are presented in support of this extension.</p> <div class="credits"> <p class="dwt_author">Bassett, D.; Watts, A. B.; Paulatto, M.; Stratford, W. R.; Peirce, C.; Grevemeyer, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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 onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a style="font-weight: 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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 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> <a style="font-weight: bold;">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' 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 onClick='return showDiv("page_17");' href="#">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_6");' 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">81</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/51225732"> <span id="translatedtitle">Waveform Modeling Of The <span class="hlt">Subducting</span> Slab Beneath <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">Deep earthquakes (400-600 km) occurring in the down-going Pacific plate produce detailed waveform patterns recorded by the Japanese Hi-net array (>500 stations), at distance from about 7o to 12o, with ray paths densely and uniformly sampling the vicinity of the <span class="hlt">subducting</span> slab. Most P-wave direct arrivals are well predicted by a 1-D model. However, observations along paths sampling the slab</p> <div class="credits"> <p class="dwt_author">M. Chen; J. Tromp; D. Helmberger; H. Kanamori</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">82</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/2003EAEJA....12469L"> <span id="translatedtitle"><span class="hlt">Subduction</span> of the South China Sea ridge along the Manila <span class="hlt">trench</span> : implication for the localisation of the Philippine Fault in north Luzon, Philippines</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 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 <span class="hlt">trench</span> to the east and the left-lateral Philippine Fault. Further north, the convergence is transferred to the west to the Manila <span class="hlt">trench</span>, along which the South China Sea is <span class="hlt">subducted</span>. The Philippine Fault extends and connects the Central Cordillera of Luzon, built on the volcanic arc. The ridge of the South China Sea, inactive since 15 Myr, is a 2 km high seamounts chain, trending NE-SW, which enters the Manila <span class="hlt">subduction</span> zone in front of North Luzon. We propose to investigate the effect of this <span class="hlt">subducted</span> ridge on the present deformation in the Central Cordillera of Luzon, exactly above it, and on the localisation of the northern extension of the Philippine Fault. We combine for this study the seismicity, the morphologic and geological data together with the instantaneous kinematics. Based on the seismicity, the <span class="hlt">subduction</span> of the South China Sea is associated with a dipping slab, except along the oceanic ridge. This suggests that this hot structure with high topography is <span class="hlt">subducted</span> along a rather horizontal plane. Moreover, the geometry and the structures of the Central Cordillera of Luzon, above the <span class="hlt">subducted</span> ridge, are in agreement with the indentation of the volcanic arc by this seamounts chain. We thus propose, based on geomorphology and extensive mapping of the recent structures, that the building and the present deformation of the Central Cordillera of Luzon is controlled by the <span class="hlt">subduction</span> of the South China Sea ridge. We finally propose that this system controls the north Philippine Fault and localises the strike-slip deformation along the eastern side of the Central Cordillera. Kinematic model of north Luzon based on GPS measurements is consistent with this large effect of the South China Sea ridge on the present deformation of north Luzon and on the northern Philippine Fault.</p> <div class="credits"> <p class="dwt_author">Loevenbruck, A.; Le Pichon, X.; Pubellier, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-04-01</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/2008AGUFM.U53A0048M"> <span id="translatedtitle">Evidence of sequential deformation from peridotite to serpentinite: an implication for seismic properties in the <span class="hlt">trench</span> side of the mantle wedge along 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">Hida Gaien belt, central Honshu, <span class="hlt">Japan</span>, consists of high pressure metamorphic rocks and mafic/ultramafic rocks. Happo peridotite complex is the largest ultramafic complexes in Hida Gaien belt (e.g., Nozaka, 2006, JMG). Peridotites were classified into coarse-type peridotites and fine-type peridotites based on their microstructures, whereas serpentinites were classified into massive-type and foliated-type. The coarse-type peridotites, which occur with the massive-type serpentinites, show coarse granular textures. Crystal preferred orientations (CPOs) of the coarse-type peridotites were dominantly D-type and locally A- or E-type. The fine- type peridotites, which occur commonly with the foliated-type serpentinites, consist of remarkably elongated coarse olivine grains and fine olivine grains. Their olivine CPOs appears to be B-type that is characterized by [001](010) slip, although a- and c-axes of olivine grains were arranged on serpentine foliations. The distribution of peridotites and serpentinites in the Happo peridotite complex suggests that the original peridotite structures were overprinted by serpentinite structures. Since olivine CPOs within the fine-type peridotites were subparallel to the serpentinite foliations and lineations, it is likely that the foliated serpentinites would have subsequently occurred after the development of the fine-type peridotites. Seismic anisotropies of Happo peridotites have been estimated based on olivine CPOs, density and elastic constant of olivine (e.g., Tasaka et al., 2008, EPSL). As a result, mean velocities of P waves were 8.33-8.57 (km/s), whereas the mean velocities of P waves of serpentinites were reported 5.03-7.30 (km/s). These seismic anisotropies were compatible with seismic velocities of serpentinized area in the <span class="hlt">trench</span> side of the mantle wedge, such as the Izu-Bonin <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Michibayashi, K.; Fujii, A.</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">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/2011AGUFM.T12A..01H"> <span id="translatedtitle">Thermal Studies at the Middle America <span class="hlt">Trench</span> Offshore Costa Rica and Nankai Trough, <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">Knowledge of the temperature distribution at convergent margins is important to understanding physical and chemical processes such as fluid flow, diagenesis, and faulting mechanics in the forearc region. Seafloor probe measurements offer an economical method for obtaining transects of heat flow across the forearc and along strike. Because these measurements only prick the seafloor they are sensitive to near seafloor processes such as bottom water temperature variations, deformation, and shallow fluid circulation and, although important in their own right, can obfuscate thermal inferences at depth. Ocean drilling provides access to deeper environments where downhole tools, acoustic measurements, and logging technologies can provide important scientific insight. We review recent heat flow results from the Costa Rica and Nankai convergent margins emphasizing ocean drilling transects where measurements of heat flow are available from seafloor probe and ocean drilling. Heat flow measurements offshore the erosive Costa Rican margin show strong along strike variations that reflect different styles of fluid flow and have important impacts on forearc processes. Along both the Nicoya and CRISP drilling transects, heat flow from seafloor probes and ocean drilling are consistent and indicate hydrothermal circulation prior to and after <span class="hlt">subduction</span>. Fluid flow advects heat from deeper along the <span class="hlt">subduction</span> thrust and deposits it near the seafloor cooling and warming these regions, respectively. The accretionary Nankai trough also shows important along strike changes in heat flow related to the age of oceanic crust at the <span class="hlt">trench</span>. Heat flow and geochemical results are consistent with basement fluid flow at the Muroto transect but are more ambiguous at the NanTroSEIZE transect.</p> <div class="credits"> <p class="dwt_author">Harris, R. N.; Solomon, E. A.; Spinelli, G. A.; Scientific Team of IODP Drilling Expedition 334</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">85</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/54089257"> <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://academic.research.microsoft.com/">Microsoft Academic Search </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</p> <div class="credits"> <p class="dwt_author">J. Nakajima; A. Hasegawa; N. Umino; T. Demachi</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">86</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.aob.geophys.tohoku.ac.jp/~nakajima/research/article/PDF/Nakajima_GRL_2006_Kanto.pdf"> <span id="translatedtitle">Anomalous low-velocity zone and linear alignment of seismicity along it in the <span class="hlt">subducted</span> Pacific slab beneath Kanto, <span class="hlt">Japan</span>: Reactivation of <span class="hlt">subducted</span> fracture 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">A detailed investigation of the hypocenter distribution beneath Kanto, <span class="hlt">Japan</span>, reveals a NW-SE-trending linear alignment of seismicity within the <span class="hlt">subducted</span> Pacific slab. We estimate the 3D seismic velocity structure in the Pacific slab to understand the factors controlling the genesis of such intraslab earthquakes. A narrow low-velocity zone is imaged within the <span class="hlt">subducted</span> slab over a length of ~150 km,</p> <div class="credits"> <p class="dwt_author">Junichi Nakajima; Akira Hasegawa</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">87</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/48932006"> <span id="translatedtitle">Anomalous low-velocity zone and linear alignment of seismicity along it in the <span class="hlt">subducted</span> Pacific slab beneath Kanto, <span class="hlt">Japan</span>: Reactivation of <span class="hlt">subducted</span> fracture 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">A detailed investigation of the hypocenter distribution beneath Kanto, <span class="hlt">Japan</span>, reveals a NW-SE-trending linear alignment of seismicity within the <span class="hlt">subducted</span> Pacific slab. We estimate the 3D seismic velocity structure in the Pacific slab to understand the factors controlling the genesis of such intraslab earthquakes. A narrow low-velocity zone is imaged within the <span class="hlt">subducted</span> slab over a length of ?150 km,</p> <div class="credits"> <p class="dwt_author">Junichi Nakajima; Akira Hasegawa</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">88</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/2013AGUFM.T41F..02U"> <span id="translatedtitle">The huge shallow slip during the 2011 Tohoku-Oki earthquake as a result of very low coseismic shear strength of the <span class="hlt">Japan</span> <span class="hlt">Trench</span> décollement material</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">Megathrust earthquakes commonly occur in <span class="hlt">subduction</span> zones at depths where there is strong coupling between the plates and long-term strain accumulation. Unconsolidated sediments in the shallow plate-boundary décollement were thought to slip aseismically and have low levels of coupling. However, the 2011 Tohoku-Oki earthquake (Mw9.0) produced unprecedented slip of >50 m near the <span class="hlt">Japan</span> <span class="hlt">Trench</span>, resulting in the devastating tsunami. IODP Expedition 343, <span class="hlt">Japan</span> <span class="hlt">Trench</span> Fast Drilling Project (JFAST) successfully drilled the décollement in the maximum slip area of the 2011 earthquake. The décollement mostly consists of highly sheared pelagic clays. To investigate the mechanisms of the huge shallow seismic slip, we conducted high-velocity (1.3 m/s) friction experiments on the <span class="hlt">Japan</span> <span class="hlt">Trench</span> décollement material at normal stresses of ~2.0 MPa and displacements of ~60 m. To simulate both permeable and impermeable conditions during high-velocity shearing, the water-saturated gouge was placed between a pair of solid cylinders of porous Berea sandstone and Indian gabbro, respectively. The results show rapid slip weakening properties with very low peak and steady-state shear strength. The steady-state values for the effective coefficient of friction at normal stress of 2 MPa are 0.2 and 0.1 for the permeable and impermeable tests, respectively. The steady-state shear stress is independent of normal stress, suggesting the fluid-like behavior of the gouge during high-velocity shearing. The fluid-like behaved gouge is also supported by microstructural observations showing the evidence of fluidization effects such as injection structures and mixing flow. The axial displacement data indicate that the specimen compacted and dilated during permeable and impermeable tests, respectively. For the same amount of displacement, the temperature in the gouge is always smaller for the impermeable tests compared to the permeable tests. These results indicate that high-velocity weakening is more pronounced in the impermeable tests due to more effective thermal pressurization than in the permeable tests. Similar behaviors were also obtained from the high-velocity friction experiments on the Nankai Trough décollement material. However, when we compare the data obtained under the same experimental conditions for the two different regions, the décollement material from the <span class="hlt">Japan</span> <span class="hlt">Trench</span> has overall lower effective coefficient of friction than material from the Nankai Trough. The weaker décollement during seismic slip is likely due to higher smectite content in the <span class="hlt">Japan</span> <span class="hlt">Trench</span> (80%) than that in the Nankai Trough (30%). The presence of a smectite-rich décollement with very low effective coefficient of friction is incompatible with the idea that large strain accumulates in the region of the plate-boundary during the interseismic period. Our results indicate that large slip result from an extremely low dynamic shear strength due to the abundance of smectite and thermal pressurization effects. Large coseismic displacement could be promoted even in unstrained portions at shallow depths as the earthquake rupture propagates through the smectite-rich fault material particularly under fluid-saturated, impermeable conditions. This provides an explanation for the very large slip and resultant tsunami during the 2011 earthquake.</p> <div class="credits"> <p class="dwt_author">Ujiie, K.; Tanaka, H.; Saito, T.; Tsutsumi, A.; Mori, J. J.; Kameda, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://academic.research.microsoft.com/Publication/52984479"> <span id="translatedtitle">Seismic activity of very low-frequency earthquake on the <span class="hlt">subducting</span> Philippine Sea plate near 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 Nankai trough <span class="hlt">subduction</span> zone in southwest <span class="hlt">Japan</span> is characterized by some kinds of _gslow earthquake_h. Around the deep side of the seismogenic zone on the <span class="hlt">subducting</span> Philippine Sea plate, non-volcanic tremor is distributed in a narrow belt along the strike of the plate (Obara, 2002). On the other hand, on shallower parts of the seismogenic zone, an anomalous seismic</p> <div class="credits"> <p class="dwt_author">K. Obara; Y. Ito</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">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/51997389"> <span id="translatedtitle">Imaging the <span class="hlt">Subducting</span> Pacific Slab Beneath Southwestern <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">We have used 4th root receiver function stacks, and pre-stack receiver function depth migrations to study the transition zone discontinuity structure beneath southwestern <span class="hlt">Japan</span>. Receiver functions were calculated from the quiet short-period seismograms recorded by a recently deployed borehole network, Hi-net. We found that a relatively broad frequency band can be retrieved from a short-period seismogram by deconvolution of the</p> <div class="credits"> <p class="dwt_author">A. Levander; F. Niu; S. Ham; M. Obayashi</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">91</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/2014GGG....15..691K"> <span id="translatedtitle">Diverse magmatic effects of <span class="hlt">subducting</span> a hot slab in SW <span class="hlt">Japan</span>: Results from forward 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">response to the <span class="hlt">subduction</span> of the young Shikoku Basin of the Philippine Sea Plate, arc magmas erupted in SW <span class="hlt">Japan</span> throughout the late Cenozoic. Many magma types are present including ocean island basalt (OIB), shoshonite (SHO), arc-type alkali basalt (AB), typical subalkalic arc basalt (SAB), high-Mg andesite (HMA), and adakite (ADK). OIB erupted since the <span class="hlt">Japan</span> Sea back-arc basin opened, whereas subsequent arc magmas accompanied <span class="hlt">subduction</span> of the Shikoku Basin. However, there the origin of the magmas in relation to hot <span class="hlt">subduction</span> is debated. Using new major and trace element and Sr-Nd-Pb-Hf isotope analyses of 324 lava samples from seven Quaternary volcanoes, we investigated the genetic conditions of the magma suites using a geochemical mass balance model, Arc Basalt Simulator version 4 (ABS4), that uses these data to solve for the parameters such as pressure/temperature of slab dehydration/melting and slab flux fraction, pressure, and temperature of mantle melting. The calculations suggest that those magmas originated from slab melts that induced flux melting of mantle peridotite. The suites differ mostly in the mass fraction of slab-melt flux, increasing from SHO through AB, SAB, HMA, to ADK. The pressure and temperature of mantle melting decreases in the same order. The suites differ secondarily in the ratio of altered oceanic crust to sediment in the source of the slab melt. The atypical suites associated with hot <span class="hlt">subduction</span> result from unusually large mass fractions of slab melt and unusually cool mantle temperatures.</p> <div class="credits"> <p class="dwt_author">Kimura, Jun-Ichi; Gill, James B.; Kunikiyo, Tomoyuki; Osaka, Isaku; Shimoshioiri, Yusuke; Katakuse, Maiko; Kakubuchi, Susumu; Nagao, Takashi; Furuyama, Katsuhiko; Kamei, Atsushi; Kawabata, Hiroshi; Nakajima, Junichi; van Keken, Peter E.; Stern, Robert J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-03-01</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://academic.research.microsoft.com/Publication/42038069"> <span id="translatedtitle">Crustal deformation at the Nankai <span class="hlt">subduction</span> zone, southwest <span class="hlt">Japan</span>, derived from GPS measurements</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 interseismic strain accumulation process at the Nankai <span class="hlt">subduction</span> zone, the plate-boundary region between the Philippine Sea and the Eurasian plates off Southwest <span class="hlt">Japan</span>, has been revealed by GPS measurements spanning five years. Large strains characterized by a contraction of 2.2~3.4×10-7\\/yr have accumulated in a narrow region extending parallel to the strike of the plate boundary. The contraction axes lie</p> <div class="credits"> <p class="dwt_author">Takao Tabei; Taku Ozawa; Yuki Date; Kazuro Hirahara; Takehide Nakano</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">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/2012GeoJI.190..816Z"> <span id="translatedtitle">Imaging the <span class="hlt">subducting</span> slabs and mantle upwelling under the <span class="hlt">Japan</span> Islands</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 P-wave tomography of the crust and mantle down to 700 km depth beneath the <span class="hlt">Japan</span> Islands is determined using a large number of high-quality arrival-time data from local earthquakes and teleseismic events simultaneously. The tomography shows that the Philippine Sea slab is <span class="hlt">subducting</span> aseismically down to 430 km depth under southwest <span class="hlt">Japan</span>, though the seismicity within the slab ends at 180 km depth. A low-velocity (low-V) zone in the mantle wedge under Tohoku and Kyushu is found to extend westward from the volcanic front to the backarc under the <span class="hlt">Japan</span> Sea and East China Sea. Significant low-V anomalies are revealed in the deep portion of the mantle wedge (400-500 km depth) above the Pacific slab under southwest <span class="hlt">Japan</span>, which may reflect hot mantle upwelling associated with fluids from the deep dehydration of the Pacific slab. Low-V anomalies appear at 420-700 km depths beneath the Pacific slab under eastern <span class="hlt">Japan</span>, which may reflect hot mantle upwelling associated with the deep <span class="hlt">subduction</span> of the Pacific slab and its collapsing down to the lower mantle.</p> <div class="credits"> <p class="dwt_author">Zhao, Dapeng; Yanada, T.; Hasegawa, A.; Umino, N.; Wei, Wei</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</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/2005AGUFM.T42A..01P"> <span id="translatedtitle">3-D Prestack Depth Imaging of the Nankai <span class="hlt">Subduction</span> Zone off Shikoku Island, SW <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 Nankai Trough <span class="hlt">subduction</span> zone off southwest <span class="hlt">Japan</span> is one of the best-suited convergent plate margins for studying large interpolate <span class="hlt">subduction</span>-zone earthquakes as well as the formation of accretionary prisms. At this margin, the Philippine Sea Plate (PSP) is <span class="hlt">subducting</span> beneath the Eurasian Plate (EP) to the NNW. The plate convergence rate is estimated to be 4 - 5 cm/yr. Large thrust earthquakes have repeatedly occurred along the Nankai <span class="hlt">subduction</span> zone with a recurrence interval of 100-200 years. The most recent interplate earthquake was the Nankai earthquake (Mw=8.2), which occurred in 1946 off the Kii Peninsula. In order to figure out seismic structure and stratigraphy of the Nankai accretionary wedge off Cape Muroto of Shikoku Island, southwest <span class="hlt">Japan</span>, we have conducted three-dimensional (3-D) multichannel seismic (MCS) reflection survey using R/V Ewing in 1999. We acquired the MCS data on 81 separate lines with 100 m line spacing, each 80 km long, producing 8 X 80 km 3-D seismic volume. To obtain the 3-D prestack depth migration images, we constructed and updated a 3-D interval velocity model using the CDP bin gathers for which preconditioning processings including amplitude recovery, deconvolution, and multiple suppression were applied. Miocene to Pliocene Shikoku Basin sediments underthrusts the overlying accretionary prism along a decollement as the PSP <span class="hlt">subducts</span> beneath the EP. The oceanic crust of the <span class="hlt">subducting</span> PSP is traceable over the entire inlines. Several imbricate thrust faults are observed in the overlying accretionary wedge. The decollement steps down on the top of <span class="hlt">subducting</span> oceanic crust around ~30 km landward from the deformation front. We recognize several sigmoid, landward dipping out-of-sequence thrust (OOST) faults in the landward thick wedge package. Most of the OOSTs are apparently developed from the <span class="hlt">subducting</span> oceanic basement to the seafloor in the forearc region, cutting both underthrust sediments and the overriding accretionary prism. In this paper, we will show and discuss recent results of the 3-D prestack depth migration, visualization, and seismic structural/stratigraphic interpretation.</p> <div class="credits"> <p class="dwt_author">Park, J.; Tsuru, T.; Sato, S.; Kaneda, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</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/2012AGUFM.T13C2623S"> <span id="translatedtitle"><span class="hlt">Subduction</span> mega-thrust beneath Mt. Fuji, 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">The Philippine Sea plate (PHS) is being <span class="hlt">subducted</span> beneath Honshu, associated with the buoyant <span class="hlt">subduction</span> of the Izu-Bonin arc. Many scientists estimated the plate boundary along the northwestern part of the Izu collision zone, however, covered by volcanic products from Mt. Fuji and Hakone volcanoes, no active fault system is recognized. To reveal the location of plate boundary mega-trust and to evaluate the seismic hazards produced by these active faults, we performed deep and shallow high -resolution seismic reflection profiling across the flank of Mt. Fuji and Hakone volcanoes. Deep seismic data were acquired for 34-km-long seismic line, using four vibroseis trucks and explosives (<50 kg), 780 fixed channels. Shallow high-resolution seismic reflection data were collected across the frontal part of the fault system, using Mini-vib (IVI) and a 200 channels recording system. On the deep seismic section, westward dipping reflectors are dominant beneath the Hakone volcano on the PHS and extend to the west at the depth of 7 km beneath sub-horizontal reflectors. The top surface of the west dipping reflectors is interpreted as a plate boundary mega-thrust. The velocity profile obtained by refraction tomography suggests that the high velocity zone on the hanging wall and low velocity westward dipping layer in the footwall, which corresponds the volcanic products of Hakone volcano. The hanging-wall unit consists of the accreted arc crust from the Izu-Bonin arc, Quaternary coarse trough fill and Quaternary volcanic products. On the seismic section, the vertical offset of the top of Vp 5.4 km/sec zone is 2.5 km. Probable Quaternary coarse trough fill, deposited in the trough between the Izu-Bonin arc and Honshu arc, distributed on the mega-thrust forming wedge-shaped geometry. The high-resolution seismic section suggests that the plate boundary fault zone consists of several branching faults. The frontal thrust controlled the thickness of the deposits, probably younger than 300 ka, for 1-km-vertical offset, suggesting that the net slip rate of the major thrust is about 10 mm/y. Based on morphotectonic observation and high-resolution shallow seismic sections, it is highly probable that the thrust displaced the Gotemba debris avalanche deposits dated 2.9 ka (Miyachi et al., 2004). From the seismic hazard point of view, such large slip rate of this thrust indicates that the estimated magnitude of earthquake reaches to be M8-. As the seismogenic source fault is located beneath Mt. Fuji, strong ground motions produced by the movement of this fault, may cause the debris avalanche of the flank of Mt. Fuji and it has potential to produce devastative damage to the cities distributed on the flank of Mt. Fuji. Further research will be needed to obtain more precise estimate the seismic hazards produced by this mega-thrust.</p> <div class="credits"> <p class="dwt_author">Sato, H.; Ishiyama, T.; Iwasaki, T.; Abe, S.; Kato, N.; Imaizumi, T.; Hirata, N.</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">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.agu.org/journals/gl/gl1020/2010GL044609/2010GL044609.pdf"> <span id="translatedtitle">Spatial changes of interplate coupling inferred from sequences of small repeating earthquakes 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">We extract sequences of small repeating earthquakes to clarify inter-plate coupling of <span class="hlt">subducting</span> plates over a large area of the Japanese Islands. As a result, many sequences are detected at the Philippine Sea plate <span class="hlt">subducting</span> from the Ryukyu <span class="hlt">trench</span> and Pacific plate <span class="hlt">subducting</span> from the Kuril-<span class="hlt">Japan</span> <span class="hlt">trench</span>. The average slip-rates and standard deviations estimated from the sequences show substantial spatial</p> <div class="credits"> <p class="dwt_author">Toshihiro Igarashi</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">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/2012AGUFM.T21F..03C"> <span id="translatedtitle">The <span class="hlt">Japan</span> <span class="hlt">Trench</span> Fast Drilling Project (JFAST): Success in logging, sampling and instrumenting the megathrust in the region of large slip during the 2011 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">The very large fault slip during the 11 March 2011 Tohoku-Oki earthquake, reaching a maximum of >50 m near the <span class="hlt">Japan</span> <span class="hlt">Trench</span>, is the largest ever observed for an earthquake and responsible for the peak tsunami heights of 20 to 40 meters that devastated a large portion of the coast of northeast Honshu. Although the cause of significant seismic slip at shallow depths is not entirely understood, a number of possible contributing factors have been identified. Key questions include how displacement was accommodated near the <span class="hlt">trench</span>, and whether coseismic weakening of the shallow megathrust had a role in the mechanics of such large displacement. These and other questions are being addressed with data from the recently completed rapid-response expedition undertaken by the Integrated Ocean Drilling Program (IODP). Drilling the plate boundary interface was technically challenging because of the 6.9 km water depth and the need to penetrate > 800 m through the prism to reach the <span class="hlt">subducting</span> plate. Nonetheless, three successful holes were drilled to the target depth. Logging and spot coring data from the first two boreholes indicate that the location of the plate-boundary décollement is tens of meters above bedded chert on the basaltic crust of the <span class="hlt">subducting</span> plate. Notably, the décollement is considerably thinner than <span class="hlt">subduction</span> thrusts drilled elsewhere. Distinguishing characteristics of the décollement that are compatible with coseismic weakening include the pronounced localization of shear to a meters-thick layer of scaly clay and to mesoscale slip surfaces within the layer. A one meter section of the scaly clay was retrieved, which provides ample material for characterization of structural, physical, chemical and mechanical properties of the plate interface, and post-cruise analyses of samples are already producing new results. The third hole was completed during the second leg of the expedition, and a temperature measurement string was successfully installed across the plate boundary to quantify heat generated in this shallow region of the fault zone and allow determination of the fault shear strength during the earthquake.</p> <div class="credits"> <p class="dwt_author">Chester, F. M.; Mori, J. J.; Eguchi, N.; Toczko, S.; Fulton, P. M.; Brodsky, E. E.</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">98</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..703O"> <span id="translatedtitle">Statistical forecasts and tests for small interplate repeating earthquakes along 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Earthquake predictability is a fundamental problem of seismology. Using a sophisticated model, a Bayesian approach with lognormal distribution on the renewal process, we theoretically formulated a method to calculate the conditional probability of a forthcoming recurrent event and forecast the probabilities of small interplate repeating earthquakes along the <span class="hlt">Japan</span> <span class="hlt">Trench</span>. The numbers of forecast sequences for 12 months were 93 for July 2006 to June 2007, 127 for 2008, 145 for 2009, and 163 for 2010. Forecasts except for 2006-07 were posted on a web site for impartial testing. Consistencies of the probabilities with catalog data of two early experiments were so good that they were statistically accepted. However, the 2009 forecasts were rejected by the statistical tests, mainly due to a large slow slip event on the plate boundary triggered by two events with M 7.0 and M 6.9. All 365 forecasts of the three experiments were statistically accepted by consistency tests. Comparison tests and the relative/receiver operating characteristic confirm that our model has significantly higher performance in probabilistic forecast than the exponential distribution model on the Poisson process. Therefore, we conclude that the occurrence of microrepeaters is statistically dependent on elapsed time since the last event and is not random in time.</p> <div class="credits"> <p class="dwt_author">Okada, M.; Uchida, N.; Aoki, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</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/2014E%26PSL.396...34Y"> <span id="translatedtitle">Seismicity and structural heterogeneities around the western Nankai Trough <span class="hlt">subduction</span> zone, southwestern <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 Nankai and Hyuga-nada seismogenic segments, in the western part of the Nankai <span class="hlt">subduction</span> zone off southwestern <span class="hlt">Japan</span>, have sometimes ruptured separately and sometimes simultaneously. To investigate the relationships among heterogeneities of seismic structure, spatial variation of the incoming plate, and the seismogenic segments, we carried out seismic observations in the western Nankai <span class="hlt">subduction</span> zone and modeled the area with 3D seismic tomography using both onshore and offshore seismic data. Our seismic observations suggested that the pattern of seismicity is related to heterogeneities within the <span class="hlt">subducted</span> plate rather than the seismogenic segments. The up-dip depth limit of seismicity along the plate boundary and in the oceanic crust is typically around 15 km, corresponding to the depth of dehydration of the oceanic crust. In addition, the seaward-extended seismicity observed where the <span class="hlt">subducted</span> plate was considered to have rough internal structures. In the resulting velocity model, the up-dip limit of the area where the P-wave velocity just above the plate boundary exceeds 6 km/s corresponds to the up-dip limit of coseismic slip in the 1968 Hyuga-nada and 1946 Nankai earthquakes. Between the two coseismic rupture zones is an area of lower P-wave velocity about 40 km wide that is evidence of lateral heterogeneities in the upper plate along the trough-parallel direction. Structural heterogeneities in the upper plate may explain the variety of coseismic slip patterns in this region.</p> <div class="credits"> <p class="dwt_author">Yamamoto, Yojiro; Obana, Koichiro; Takahashi, Tsutomu; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</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://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_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> 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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/2011AGUFM.T21B2328H"> <span id="translatedtitle">Variation of excess pore pressures in underthrust sediments as a result of lithostratigraphic heterogeneity along strike the 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">At the Nankai <span class="hlt">subduction</span> zone offshore <span class="hlt">Japan</span>, the incoming sediment sequence consists of hemipelagic mud with variable sand layers proportions along strike. In the western Nankai <span class="hlt">subduction</span> zone offshore Cape Ashizuri, the total sand fraction is up to 208.6m thick, i.e. half of the overall ~400m thick underthrust sequence in the Nankai <span class="hlt">subduction</span> zone complex. In contrast, in the central portion of the Nankai trough offshore Cape Muroto sand layers are absent, while in the east offshore Kii peninsula the total sand layer thickness is approx. 80m. These permeable sand layers provide lateral pathways for fluids in the underthrust sediments, a fact which has rarely been considered in previous studies of <span class="hlt">subduction</span> zone hydrogeology. In this study, fluid flow is simulated along three transects perpendicular to the <span class="hlt">trench</span> to determine the role of sand layers in Nankai subdcution zone complex. For each transect, we use a coupled loading and diffusion model in combination with new permeability measurements of clay and sand samples recovered from the Nankai margin area. The simulations show that pore pressure ratios (absolute pore water pressure/lithostatic stress) are the highest in the central portion of the Nankai margin where sand layers are absent. The results reveal a weak decollement that facilitates the small taper angle in this area. In contrast, simulations for the sand layer influenced western and eastern Nankai areas demonstrate localized fluid flow along sand beds that enhances the overall dewatering and thus minimize excess pore pressures in the underthrusts sediments. Accordingly, the normal effective stresses along the decollement are higher and therefore, shear stresses are high as well. This is consistent with the higher taper angles in these areas. The results also demonstrate that drainage along sand layers controls the depth of minimum effective stress. Our best fitting models show a step down of the minimum effective stress that is consistent with the observed downstepping of the decollement in seismic images at ~25 km from the <span class="hlt">trench</span>. Therefore, we suggest that effective stress minimum causes the decollement to step down into the underthrust sediment. This may influence the decollement position in the sand layer starved central portion of the Nankai <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Huepers, A.; Kopf, 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">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/2013Tectp.608.1094Y"> <span id="translatedtitle">Two-dimensional thermal modeling of <span class="hlt">subduction</span> of the Philippine Sea plate beneath 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">In this study, we constructed a two-dimensional thermal convection model associated with <span class="hlt">subduction</span> of the Philippine Sea (PHS) plate beneath southwest <span class="hlt">Japan</span> to estimate the thermal state. To evaluate the validity of the calculated temperature distribution, we compared the calculated heat flows with observed heat flow data such as the High Sensitivity Seismograph Network <span class="hlt">Japan</span> (Hi-net) borehole, land borehole, marine probe, and bottom-simulating reflectors. Hi-net heat flow data, which have never been used for thermal modeling, have spatially high resolutions on land and enable detailed estimation of the thermal state beneath the Japanese islands. We considered the spatio-temporal change in the age of the PHS plate, change in its plate motion direction at 3 Ma, and the geometry of its upper surface. Calculated heat flows associated solely with <span class="hlt">subduction</span> of the PHS plate, passing through central and eastern Shikoku and the Kii Peninsula, were not consistent with observations. They tended to be lower on the seaward side of the corner of the mantle wedge and to have much longer spatial wavelengths on the continental side. To explain heat flow data in southwest <span class="hlt">Japan</span>, frictional heating at the plate interface on the seaward side of the corner of the mantle wedge and temperature changes due to surface erosion and sedimentation on land associated with crustal deformation during the Quaternary must be incorporated into the model. The most suitable pore pressure ratio to explain the heat flow data is estimated to be 0.95. Temperatures on the upper surface of the PHS plate obtained in this study are lower at shallow depths and higher at greater depths than those obtained by Hyndman et al. (1995), indicating that the seismogenic zone inferred from this study is narrower than that of their model. Microearthquakes within the <span class="hlt">subducting</span> PHS plate occur at temperatures below 700-800 °C.</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">2013-11-01</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://adsabs.harvard.edu/abs/2011AGUFM.T21E..06K"> <span id="translatedtitle"><span class="hlt">Japan</span> <span class="hlt">trench</span> studies on earthquake, mass-wasting deposits and related tsunami based on most recent submarine survey</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">On 11 March 2011, Tohoku, northeast <span class="hlt">Japan</span>, experienced a great earthquake (Mw 9.0, Mt 9.1). Seismic and tsunami inversion analyses have shown that tsunami waves with a maximum run-up height of 38 m were generated after the mainshock by topographic changes on the seafloor in the toe region of the <span class="hlt">Japan</span> <span class="hlt">Trench</span> slope off Sendai. These inversion analyses (Maeda et al., 2011) and bathymetric surveys (Fujiwara, JAMSTEC press release, 2011) indicate that the toe region slipped about 50 m along the thrust. If the thrust fault rapidly deformed the seafloor, as suggested by Ide et al. (2011), the basic theory of tsunamigenesis would predict the generation of tsunamis all along the axis of the <span class="hlt">Japan</span> <span class="hlt">trench</span>. The <span class="hlt">Japan</span> <span class="hlt">Trench</span> slope can be divided into an upper slope, a midslope terrace, and a lower slope. The average slope angle of the upper and lower slopes is 5°, but the angle of the midslope terrace is only a few degrees (von Huene and Lallemand, 1990). Some residual convex parts of the upper and lower slopes have slope angles of ~10°, particularly in the region from 39°10'N to 40°30'N. These include many large, convex upward, arcuate topographic features that indicate submarine sliding of sediment masses with widths and lengths of several kilometers (Sasaki, 2004). These submarine slides have been attributed to tectonic erosion (von Huene and Lallemand, 1990). Most of the slides on the upper slope are characterized by many normal faults (Tsuru et al., 2002; von Huene and Lallemand, 1990). In our study area, an active normal fault may have ruptured during the 2011 Tohoku earthquake as shown by Tsuji et al. (2011). Our deep-sea camera observations suggest that the sliding is still occurring, and also that sliding might have been triggered by the 2011 Tohoku earthquake. We demonstrate a new scenario to excite the tsunami that the toe of the slope moves by the double effect of seismic slip and submarine sliding. This scenario has been proposed to have occurred in the Nankai accretionary prism, southwestern <span class="hlt">Japan</span> (Kawamura et al., 2011). If this scenario is correct, the mechanisms of both the tsunami generation and the overshoot at the toe of the <span class="hlt">trench</span> slope can be explained by this double movement. Authors: Kiichiro Kawamura, Takafumi Kasaya, Tomoyuki Sasaki, Toshiya Kanamatsu, Arito Sakaguchi, Takeshi Tsuji, Yujiro Ogawa, YK11-E04 Leg1 and YK11-R06 Leg1 Shipboard Scientists</p> <div class="credits"> <p class="dwt_author">Kawamura, K.; Kasaya, T.; Sasaki, T.; Kanamatsu, T.; Sakaguchi, A.; Tsuji, 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">104</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/2013PEPI..225...41S"> <span id="translatedtitle">Global correlations between maximum magnitudes of <span class="hlt">subduction</span> zone interface thrust earthquakes and physical parameters of <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 maximum earthquake magnitude recorded for <span class="hlt">subduction</span> zone plate boundaries varies considerably on Earth, with some <span class="hlt">subduction</span> zone segments producing giant <span class="hlt">subduction</span> zone thrust earthquakes (e.g. Chile, Alaska, Sumatra-Andaman, <span class="hlt">Japan</span>) and others producing relatively small earthquakes (e.g. Mariana, Scotia). Here we show how such variability might depend on various <span class="hlt">subduction</span> zone parameters. We present 24 physical parameters that characterize these <span class="hlt">subduction</span> zones in terms of their geometry, kinematics, geology and dynamics. We have investigated correlations between these parameters and the maximum recorded moment magnitude (MW) for <span class="hlt">subduction</span> zone segments in the period 1900-June 2012. The investigations were done for one dataset using a geological <span class="hlt">subduction</span> zone segmentation (44 segments) and for two datasets (rupture zone dataset and epicenter dataset) using a 200 km segmentation (241 segments). All linear correlations for the rupture zone dataset and the epicenter dataset (|R| = 0.00-0.30) and for the geological dataset (|R| = 0.02-0.51) are negligible-low, indicating that even for the highest correlation the best-fit regression line can only explain 26% of the variance. A comparative investigation of the observed ranges of the physical parameters for <span class="hlt">subduction</span> segments with MW > 8.5 and the observed ranges for all <span class="hlt">subduction</span> segments gives more useful insight into the spatial distribution of giant <span class="hlt">subduction</span> thrust earthquakes. For segments with MW > 8.5 distinct (narrow) ranges are observed for several parameters, most notably the <span class="hlt">trench</span>-normal overriding plate deformation rate (vOPD?, i.e. the relative velocity between forearc and stable far-field backarc), <span class="hlt">trench</span>-normal absolute <span class="hlt">trench</span> rollback velocity (vT?), <span class="hlt">subduction</span> partitioning ratio (vSP?/vS?, the fraction of the <span class="hlt">subduction</span> velocity that is accommodated by <span class="hlt">subducting</span> plate motion), <span class="hlt">subduction</span> thrust dip angle (?ST), <span class="hlt">subduction</span> thrust curvature (CST), and <span class="hlt">trench</span> curvature angle (?T). The results indicate that MW > 8.5 <span class="hlt">subduction</span> earthquakes occur for rapidly shortening to slowly extending overriding plates (-3.0 ? vOPD? ? 2.3 cm/yr), slow <span class="hlt">trench</span> velocities (-2.9 ? vT? ? 2.8 cm/yr), moderate to high <span class="hlt">subduction</span> partitioning ratios (vSP?/vS? ? 0.3-1.4), low <span class="hlt">subduction</span> thrust dip angles (?ST ? 30°), low <span class="hlt">subduction</span> thrust curvature (CST ? 2.0 × 10-13 m-2) and low <span class="hlt">trench</span> curvature angles (-6.3° ? ?T ? 9.8°). Epicenters of giant earthquakes with MW > 8.5 only occur at <span class="hlt">trench</span> segments bordering overriding plates that experience shortening or are neutral (vOPD? ? 0), suggesting that such earthquakes initiate at mechanically highly coupled segments of the <span class="hlt">subduction</span> zone interface that have a relatively high normal stress (deviatoric compression) on the interface (i.e. a normal stress asperity). Notably, for the three largest recorded earthquakes (Chile 1960, Alaska 1964, Sumatra-Andaman 2004) the earthquake rupture propagated from a zone of compressive deviatoric normal stress on the <span class="hlt">subduction</span> zone interface to a region of lower normal stress (neutral or deviatoric tension). Stress asperities should be seen separately from frictional asperities that result from a variation in friction coefficient along the <span class="hlt">subduction</span> zone interface. We have developed a global map in which individual <span class="hlt">subduction</span> zone segments have been ranked in terms of their predicted capability of generating a giant <span class="hlt">subduction</span> zone earthquake (MW > 8.5) using the six most indicative <span class="hlt">subduction</span> zone parameters (vOPD?, vT?, vSP?/vS?, ?ST, CST and ?T). We identify a number of <span class="hlt">subduction</span> zones and segments that rank highly, which implies a capability to generate MW > 8.5 earthquakes. These include Sunda, North Sulawesi, Hikurangi, Nankai-northern Ryukyu, Kamchatka-Kuril-<span class="hlt">Japan</span>, Aleutians-Alaska, Cascadia, Mexico-Central America, South America, Lesser Antilles, western Hellenic and Makran. Several <span class="hlt">subduction</span> segments have a low score, most notably Scotia, New Hebrides and Mariana.</p> <div class="credits"> <p class="dwt_author">Schellart, W. P.; Rawlinson, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2014E%26PSL.397..101M"> <span id="translatedtitle">Scattering of teleseismic P-waves by the <span class="hlt">Japan</span> <span class="hlt">Trench</span>: A significant effect of reverberation in the seawater column</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 detected a scattered wave train in data from the high-sensitivity seismograph network in <span class="hlt">Japan</span> (Hi-net) following the arrival of the near-vertically incident P-wave generated by the 2009 earthquake (Mw 7.8) off the South Island of New Zealand. The scattered wave train represented predominantly vertical ground motion at a period of 20 to 50 s and with an apparent velocity of 3.5 km/s; it propagated cylindrically westward through the Kanto area of central <span class="hlt">Japan</span>. Array analysis showed that the scattered wave train developed beneath the Pacific Ocean near the Boso triple junction, southeast of the Kanto area. A 3D finite-difference simulation of seismic wave propagation using a high-resolution model incorporating subsurface structure, topography, and bathymetry revealed that the strong scattered waves that were generated along the <span class="hlt">Japan</span> <span class="hlt">Trench</span> and propagated normal to the <span class="hlt">trench</span> axis represented multiple reverberations of seismic waves between the seafloor and the Pacific plate boundary. In addition, strong reverberation of acoustic waves in the seawater column above the Boso triple junction causes elongated scattered waves, which reasonably explains our observations.</p> <div class="credits"> <p class="dwt_author">Maeda, Takuto; Furumura, Takashi; Obara, Kazushige</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-07-01</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/2013AGUFM.T31G2592H"> <span id="translatedtitle">Anomalously high porosity in <span class="hlt">subduction</span> inputs to the Nankai Trough (SW <span class="hlt">Japan</span>) potentially caused by volcanic ash and pumice</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 convergent margins, the sedimentary section seaward of the <span class="hlt">trench</span> on the <span class="hlt">subducting</span> oceanic lithosphere provides the source material for accretionary prisms and eventually becomes the host rock of the plate boundary megathrust. The mechanical properties of the sediments seaward of the <span class="hlt">subduction</span> zone have therefore a first order control on <span class="hlt">subduction</span> zone forearc mechanics and hydrogeology. At the Nankai Trough (SW <span class="hlt">Japan</span>) the majority of sediment approaching the <span class="hlt">subduction</span> zone is clay-rich. Scientific drilling expeditions in the framework of the Ocean Drilling Program (ODP) and the Integrated Ocean Drilling Program (IODP) have revealed an anomalous zone of high porosity in a major lithologic unit known as the Upper Shikoku Basin facies (USB), which is associated with elevated volcanic ash content and high amounts of silica in the interstitial water. The existence of the high porosity zone has previously been associated with advanced silica cementation, driven by the dual diagenetic transition of opal-A to opal-CT, and opal-CT to quartz. However, temperature estimates from recent drilling expeditions offshore the Kii peninsula reveal different in situ temperatures at the proposed diagenetic boundary in the Shikoku Basin. Furthermore, laboratory measurements using core samples from the USB show that cohesive strength is not elevated in the high porosity zone, suggesting that a process other than cementation may be responsible. The USB sediment is characterized by abundant volcanic ash and pumice, therefore the high porosity zone in the USB may be closely linked to the mechanical behavior of this phase. We conducted consolidation tests in the range 0.1 to 8 MPa effective vertical stress on artificial ash-smectite and pumice-smectite mixtures, as well as intact and remolded natural samples from the IODP Sites C0011 and C0012 to investigate the role of the volcanic constituent on porosity loss with progressive burial. Our results show that both remolded and intact natural samples have high porosities of up to ~71 to 75% at a vertical effective stress of 0.1 MPa, which decreases to 39 to 49% at 8 MPa vertical effective stress. The behavior of the remolded samples is in good accordance with compiled in-situ porosity vs. depth profiles from the high porosity zone. This suggests that cementation is not the cause for the anomalously high porosity. The consolidation tests on the artificial samples document that pure ash and pumice samples are highly resistant to consolidation. Between 0.1 to 8 MPa vertical effective stress, the porosity decreases from 51 to 47% for the ash sample and 60% to 46% for the pumice sample. The higher initial porosity in the pumice may be explained by a porous internal grain structure that allows storage of additional water. Mixtures with smectite are characterized by higher compressibility and higher porosity. For a mixture of 80% smectite and 20% pumice the porosity decreases from 65% to 39%, similar to that of the natural samples. Our results suggest that the high porosity zone is caused by the bulk mechanical behavior of pumice in the USB.</p> <div class="credits"> <p class="dwt_author">Huepers, A.; Ikari, M.; Underwood, M.; Kopf, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://academic.research.microsoft.com/Publication/40492950"> <span id="translatedtitle">A kinematic <span class="hlt">subduction</span> model for the genesis of back-arc low-K volcanoes at a two-overlapping <span class="hlt">subduction</span> zone, central <span class="hlt">Japan</span>: another volcanic front originated from the Philippine Sea plate <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">Systematic geochemical and volumetric variations have been documented across many island arcs. Volcanism in the Shinetsu highland, the northeastern part of central <span class="hlt">Japan</span>, shows various anomalies in such variations, though located in a <span class="hlt">subduction</span> zone. In this highland, the distribution density of volcanoes and total volume of erupted materials decrease from the volcanic front toward the back-arc side. However, they</p> <div class="credits"> <p class="dwt_author">Takayuki Kaneko</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">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/2012AGUFM.T13F2689M"> <span id="translatedtitle">Re-examination of large 20th century earthquakes along the southern <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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We re-examine hypocenters, focal mechanisms and fault models for large earthquakes off Fukushima and off Boso regions along the southern <span class="hlt">Japan</span> <span class="hlt">trench</span>. The 1938 off Fukushima earthquakes, which consist of five earthquakes of Mjma ranging from 6.9 to 7.5, occurred in the southern part of the 2011 Tohoku earthquake source, where many M~6 aftershocks occurred since March 2011. To the south, off Boso region, the 1927 (Mjma 6.9) and 1953 (Mjma 7.4) earthquakes occurred, but the details are not well known. The 1938 off Fukushima (Shioya-oki) earthquakes were the only M>7 earthquakes recorded in the southern part of the 2011 Tohoku earthquake source. The earthquake sequence consists of 5 events as shown in Table. Abe (1977, Tectonophysics) studied these events and estimated the focal mechanisms and seismic moments. However, the slip distributions are not known. We first examined the teleseismic waveforms recorded at Pasadena, De Bilt and Christchurch. Comparison of waveforms from the five earthquakes shows that P wave and following phases from event 4 are the largest. Event 4 at CHR and event 5 at DBN show clear downward initial motions. While the above three stations are located near nodal planes on focal sphere, the comparison indicates the focal mechanism of event 4 and 5 are different each other. After the 2011 Tohoku earthquake, many aftershocks with M~6 occurred in this region with various focal mechanisms, including reverse fault, normal fault and strike-slip fault. We compared the teleseismic waveforms of these aftershocks and the 1938 earthquakes. Few of the teleseismic waveforms from the 2011 aftershocks are comparable with the 1938 events, because the aftershocks were smaller in M and waveforms from many aftershocks overlap. Off the Boso region, the southern neighbor of the 2011 Tohoku earthquake source, several large earthquakes and tsunami earthquakes (e.g., 1677 Empo earthquake) have occurred, but their recurrence is not known. Two earthquakes, one on August 18, 1927 with Mjma 6.9 and Mt 7.4, and the other on November 25 1953 with Mjma 7.4 and Mt 7.8, have different epicenters and the tsunami source areas. While the 1927 epicenter was located to southeast of the 1953 epicenter, the 1927 tsunami source was estimated to the northwest of the 1953 tsunami source (Hatori, 1975). The S-P times at 9 Japanese stations and at University of Tokyo station indicate are larger for the 1927 earthquake than that of the 1953 event, indicating that the epicenter was at far southeast of the tsunami source area.The 1938 off Fukushima earthquakes;</p> <div class="credits"> <p class="dwt_author">Murotani, S.; Satake, K.</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">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/2013AGUFM.G11B0914Y"> <span id="translatedtitle">Interplate locking derived from seafloor geodetic measurement at the shallow <span class="hlt">subduction</span> zone of the northernmost Suruga Trough, <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">Observation of seafloor crustal deformation is crucial for megathrust earthquake because most of the focal areas are located below seafloor. Seafloor crustal deformation can be observed GPS/Acoustic technique, and this technique has been carried out at <span class="hlt">subduction</span> margins in <span class="hlt">Japan</span>, e.g., <span class="hlt">Japan</span> <span class="hlt">Trench</span>, Suruga Trough, and Nankai Trough. At the present, the accuracy of seafloor positioning is one to several centimeters for each epoch. Velocity vectors at seafloor site are estimated through repeated observations. Co- and post- seismic slip distribution and interseismic deformation are estimated from results of seafloor geodetic measurement (e.g., Iinuma et al., 2012; Tadokoro et al., 2012). We repeatedly observed seafloor crustal deformations at two sites across the Suruga Trough from 2005 to investigate interplate locking condition at the focal area of the anticipated megathrust, Tokai, earthquake. We observed 12 and 16 times at an east site of the Suruga Trough (SNE) and at an west site of the Suruga Trough (SNW), respectively. We reinstalled seafloor benchmarks at both sites because of run out of batteries in 2012. We calculated and removed the bias between the old and new seafloor benchmarks. Furthermore, we evaluated two type of analysis. One is Fixed triangular configuration Analysis (FTA). When we determine the seafloor benchmark position, we fix the triangular configuration of seafloor units averaging all the measurements to improve trade-off relation between seafloor benchmark position and sound speed structure. Sound speed structure is assumed to be horizontal layered structure. The other one is Fixed Triangle and Gradient structure of sound speed structure (FTGA). We fixed triangular configuration same as FTA. Sound speed structure is assumed to have gradient structure. Comparing FTA with FTGA, the RMS of horizontal position analyzed through FTA is smaller than that through FTGA at SNE site. On the other hand, the RMS of horizontal position analyzed through FTA is larger than that through FTGA at SNW site. We estimated the displacement velocities with relative to the Amurian plate from the result of repeated observation. The estimated displacement velocity vectors at SNE and SNW are 42×8 mm/y to N94W direction and 46×13 mm/y to N77W direction, respectively. The directions are the same as those measured at the on-land GPS stations. The magnitudes of velocity vector indicate significant shortening by approximately 11 mm/y between SNW and on-land GPS stations at the western part of the Suruga Trough. We also calculated the theoretical surface deformation pattern to depict the interplate locking condition. These results show that the plate interface at the shallow zone of the northernmost Suruga trough is strongly locked.</p> <div class="credits"> <p class="dwt_author">Yasuda, K.; Tadokoro, K.; Ikuta, R.; Watanabe, T.; Nagai, S.; Sayanagi, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://pubs.er.usgs.gov/publication/70018813"> <span id="translatedtitle">Evolution of a <span class="hlt">trench</span>-slope basin within the Cascadia <span class="hlt">subduction</span> margin: the Neogene Humboldt Basin, California</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">The Neogene Humboldt (Eel River) Basin is located along the north-eastern margin of the Pacific Ocean within the Cascadia <span class="hlt">subduction</span> zone. This sedimentary basin originated near the base of the accretionary prism in post-Eocene time. <span class="hlt">Subduction</span> processes since that time have elevated strata in the south-eastern portion of the basin above sea level. High-resolution chronostratigraphic data from the onshore portion of the Humboldt Basin enable correlation of time-equivalent lithofacies across the palaeomargin, reconstruction of slope-basin evolution, and preliminary delineation of climatic and tectonic influence on lithological variation. -from Author</p> <div class="credits"> <p class="dwt_author">McCrory, P. A.</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">111</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.S11A1692M"> <span id="translatedtitle"><span class="hlt">Trench</span>-parallel Anisotropy in <span class="hlt">Subduction</span> Zones: Evaluating the Contributions of Olivine Fabric Transitions and Flow Around Slab Edge in Numerical Flow 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">Mantle circulation in the mantle wedge is often described based on corner flow theory, modified to include the temperature dependence of mantle viscosity. However, corner flow is only a 2D abstraction, whereas <span class="hlt">subduction</span> zones are fundamentally 3D objects, featuring slab edges and <span class="hlt">trench</span> curvature. Seismic anisotropy, often detected using the shear wave splitting methods developed by Paul Silver and coworkers, is now commonly used to map the mantle flow field, and has demonstrated clearly that simple consideration of corner flow is not enough. <span class="hlt">Trench</span> parallel anisotropy contradicts direct corner flow models if the mantle adopts the type of olivine fabric most commonly observed in natural samples, the A-type fabric. Therefore, several alternative views of anisotropy development have proposed, including two that we address in this work: 1) The high stresses and water content of the mantle wedge produce an alternative fabric, B-type, for which the fast axis of olivine is perpendicular to flow lines. The difficulties with this proposition are that stresses in the wedge may not be high enough and the strain necessary to replace the A-fabric of mantle entering the wedge may be too great to occur in the wedge. 2) Flow around slab edges from the subslab to the wedge domains induces <span class="hlt">trench</span> parallel flow in addition to corner flow, aligning the fast axis of olivine with the slab. Difficulties with this model include the low intensity of this flow observed in the absence of lateral obstacles to flow, like the tank walls of analogue experiments, and the long distance along the <span class="hlt">trench</span> where this flow must penetrate. However, this model can explain the dependence of the intensity of anisotropy with the ratio of <span class="hlt">trench</span> migration velocity to convergence velocity, and the presence of sub-slab anisotropy. Subslab anisotropy is more consistently <span class="hlt">trench</span>-parallel than wedge anisotropy and is more intense when the rate of slab advance or retreat is high (Long and Silver, 2008). To date, flow around slab edges associated with slab advance or retreat is the only explanation proposed to explain the characteristics of sub-slab anisotropy. A new and efficient empirical method of modeling the development of anisotropy for different fabrics in numerical mantle flow model (see poster by Miller and Montési in DI07), provides us with the tools necessary to compare the anisotropy patterns expected by each model. We can follow flow trajectories in the mantle wedge and around slab edge and track fabric evolution as the A- or D-type fabric of dry incoming mantle is progressively replaced by a C- or B- type fabric in the mantle wedge, following hydration by slab-released fluids. Thus, it is possible to determine for each <span class="hlt">trench</span> advance or retreat rate where slab parallel anisotropy is most likely due to slab-parallel flow or B-type fabrics, and under which circumstances a region of <span class="hlt">trench</span>-perpendicular anisotropy may be expected away from slab edges.</p> <div class="credits"> <p class="dwt_author">Montesi, L. G.; Behn, M. D.; Long, M. D.; Miller, K. J.</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">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/2014JGRB..119.1094L"> <span id="translatedtitle">Seismic attenuation tomography of the Northeast <span class="hlt">Japan</span> arc: Insight into the 2011 Tohoku earthquake (Mw 9.0) and <span class="hlt">subduction</span> dynamics</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">three-dimensional (3-D) P and S wave attenuation (Qp and Qs) models of the crust and upper mantle under the entire Northeast <span class="hlt">Japan</span> (Tohoku) arc from the <span class="hlt">Japan</span> <span class="hlt">Trench</span> to the <span class="hlt">Japan</span> Sea coast are determined, for the first time, using a large number of high-quality t* data measured precisely from P and S wave spectra of local earthquakes. The suboceanic earthquakes used in this work are relocated precisely using sP depth phases. Our results reveal a prominent landward dipping high-Q zone representing the <span class="hlt">subducting</span> Pacific slab, a landward dipping intermediate- to high-Q zone in the mantle wedge between the Pacific coast and the volcanic front, and significant low-Q anomalies in the crust and mantle wedge between the volcanic front and the <span class="hlt">Japan</span> Sea coast. Prominent high-Q patches surrounded by low-Q anomalies are revealed in the interplate megathrust zone under the Tohoku fore arc where the great 2011 Tohoku-oki earthquake (Mw 9.0) occurred. The high-Q patches in the megathrust zone generally exhibit large coseismic slips of megathrust earthquakes and large slip deficit on the plate interface. We think that these high-Q patches represent asperities in the megathrust zone, whereas the low-Q anomalies reflect weakly coupled areas. We also find that the hypocenters of the 2011 Tohoku-oki interplate earthquakes (Mw > 7.0) are located in areas where Qp, Qs, and Qp/Qs change abruptly. These results suggest that structural heterogeneities in the megathrust zone control the interplate seismic coupling and the nucleation of megathrust earthquakes.</p> <div class="credits"> <p class="dwt_author">Liu, Xin; Zhao, Dapeng; Li, Sanzhong</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-02-01</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://www.ntis.gov/search/product.aspx?ABBR=ADA418416"> <span id="translatedtitle"><span class="hlt">Subduction</span> Dynamics at the Middle America <span class="hlt">Trench</span>: New Constraints from Swath Bathymetry, Multichannel Seismic Data, and (10)Be.</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">The cosmogenic radionuclide (10)Be is a unique tracer of shallow sediment <span class="hlt">subduction</span> in volcanic arcs. The range in (10)Be enrichment in the Central American Volcanic Arc between Guatemala and Costa Rica is not controlled by variations in (10)Be concentra...</p> <div class="credits"> <p class="dwt_author">R. K. Kelly</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">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/2001AGUFM.V11B..01S"> <span id="translatedtitle">Mass Flux of Continental Material at Cenozoic <span class="hlt">Subduction</span> Zones--New Global and <span class="hlt">Trench</span>-sector Calculations Using New 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">INTRODUCTION: A decade ago, then available geophysical and geological data implied that more than 65 percent of ocean floor sediment entering most <span class="hlt">subduction</span> zones (SZ) accompanied the oceanic crust to the mantle (= sediment <span class="hlt">subduction</span> or SS). The underthrusting slab also eroded the margin's crustal framework and conveyed this material to the mantle (= <span class="hlt">subduction</span> erosion or SE). Globally, the mass of continental material recycled to the mantle was estimated at 1.3-1.8 km3 / yr (SS. = 0.7 km3 + SE = 0.6-1.1 km3). SEDIMENT <span class="hlt">SUBDUCTION</span>: New and enhanced seismic reflection data, new drilling observations, and reevaluation of older information stress that the efficacy of SS is higher than earlier assessed. In detail, it appears that 100 percent SS occurs at non-accreting margins (19,000 km), at least 80 percent at accreting margins (16,000 km) where small to moderate size accretionary prisms (width=5-40 km) are forming, and 40-45 percent where larger prisms are accumulating (8,000 km). At Cenozoic SZs (~43,000 km), it is now estimated that the long-term (i.e., >10 Myr) rate of SS is at least 1.0 km3 / yr (solid volume). <span class="hlt">SUBDUCTION</span> EROSION: New and reassessed seismic, drilling, submersible, coastal mapping and arc-retreat observations suggest a higher long-term rate of SE than formerly estimated at 30 km3 / Myr / km of <span class="hlt">trench</span>. We now estimate that, except perhaps where large accretionary bodies are forming, the long-term rate of forearc erosion averages at least 40 km3 / Myr (range = 28-62), which corresponds to a global recycling rate of 1.4 km3 / yr. The matching average rate of landward truncation of the submerged forearc is 2.5 km / Myr (range = 1.8-4.2). SUMMARY: The late Cenozoic rate at which continental crust is recycled at SZs is currently estimated at 2.4 km3 / yr (ss=1+ se=1.4) +/- 25 percent, which is basically that now approximated for arc magmatic additions. It can thus be inferred that at Cenozoic SZs rates of crustal addition and recycling have been in general balance. This quasi-stasis may be applicable to the Phanerozoic.</p> <div class="credits"> <p class="dwt_author">Scholl, D. W.; von Huene, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-12-01</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/2004AGUFM.S43D..04S"> <span id="translatedtitle">High-Resolution <span class="hlt">Subduction</span> Zone Seismicity and Velocity Structure in Ibaraki, <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 use double-difference tomography (tomoDD) [Zhang and Thurber, 2003] and waveform-derived cross-correlation differential arrival times to invert for the earthquake locations and P- and S-wave velocity distributions in the <span class="hlt">subduction</span> zone under Ibaraki Prefecture of north-central Honshu, <span class="hlt">Japan</span>. The Ibaraki region is attractive for its high rate of slab seismicity and for the presence of an intermediate-depth double seismic zone. We relocate ~8000 events occurring in this region between June 2002 and June 2004. We use a combination of ~200,000 absolute travel times, ~5 million catalog-derived differential times, and ~5 million cross-correlation differential times derived from more than 150,000 waveforms, with roughly equal numbers of P- and S-wave data. Many of the waveforms are from HiNet borehole stations that provide particularly high-quality data. We also use data from JMA, the University of Tokyo, and Tohoku University. Since it is natural to expect sharp velocity contrasts in a <span class="hlt">subduction</span> zone, we regularize the inversion using the total variation (TV) approach implemented through iteratively reweighted least squares. Because TV is an L1-norm regularization, sharp changes in velocity are penalized no more than gradual ones, but undulations in the velocity model remain damped. We will compare the TV results with those determined by standard least-squares, L2-norm regularization. Our results show increasingly organized seismicity including narrowing by up to 50% of the upper and lower limbs of the double seismic zone as viewed in cross-section. We find a zone of interplate events extending as deep as 60 km, forming a very distinct lineation in cross-section. Focal mechanisms support the interpretation that these are low angle, <span class="hlt">subduction</span> interface events. These earthquakes are accompanied by a zone of very high Vp/Vs ratio within the downgoing plate, just beneath the seismicity, suggesting that high pore-pressures may enable seismic slip on the <span class="hlt">subduction</span> interface at depths where aseismic slip would otherwise predominate. These events represent significantly deeper seismic coupling than the 37-43 km maximum depth observed in this area previously by Tichelaar and Ruff [1993], but are consistent with the maximum depth of 50-70 km for low-angle thrust events found by Igarashi et al. [2001] farther to the north.</p> <div class="credits"> <p class="dwt_author">Shelly, D. R.; Beroza, G. C.; Zhang, H.; Thurber, C. H.; Ide, 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">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/2012AGUFMNH43B1650K"> <span id="translatedtitle">Rockmagnetic characterization of event deposits induced by March 2011 Tohoku-oki Earthquake 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A study on differences in bathymetric data between before and after the 11 March 2011Tohoku-Oki earthquake revealed a large coseismic displacement (up to 50 m horizontally) of the overriding plate. The study also identified that a topographic high had appeared in the <span class="hlt">trench</span> axis after the earthquake. This bulge is interpreted as a possible mass of remobilized deposit derived by the landsliding (Fujiwara et al., 2011). Accompanied by this mass transportation, event deposits (e.g. slump, debris, or turbidite) could be formed in the seafloor as evidences of the mega-earthquake. In order to characterize the sediment deposition or disturbance by the earthquake, six sediment coring using a piston corer were conducted and collected the surface sediment around the topographic high in the deep <span class="hlt">trench</span> axis. Intervals in the upper several ten-cm of recovered cores consist of graded units, which are considered to have been formed just after the earthquake. Other graded units are also recognized in the deeper intervals than those of 2011 event. However, there is no interval indicating a mass transportation in cores, even in the core taken from the top of topographic high. Rock magnetic studies on samples were carried out to analyze their depositional process. Magnetic susceptibility profiles show several upward decreasing patterns, and they can be interpreted as upward fining cycles. Anisotropy of magnetic susceptibility were measured to estimate paleo-current directions which controlled the top sequence depositions. The results show that Kmin axes are normal to the horizontal plane. It indicates that all cycling sequences were not formed by chaotic deposition (e.g. debris flow), and that the topographic high appeared after the earthquake was not formed by landsliding. On the other side, Kmax directions are parallel to the horizontal plane and those alignments generally show clusters in two major directions. It is interpreted that such variation was formed by different paleo-currents occurred during the event. A combination of <span class="hlt">trench</span> parallel and down slope currents, which are almost perpendicular each other, might make this pattern. A variation in lineation parameter of anisotropy of magnetic susceptibility suggests different current speed during deposition of the top sequences. These data indicates that the depositional process of 2011 event sediment in the <span class="hlt">trench</span> system was not simple. Figuring out this process is important not only for understanding the deposition of 2011 event but for understanding the older event deposits took place previously in the <span class="hlt">Japan</span> <span class="hlt">trench</span>.</p> <div class="credits"> <p class="dwt_author">Kanamatsu, T.; Ikehara, K.; Arai, K.; Sato, T.</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">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/2013AGUFM.T41F..04T"> <span id="translatedtitle">Permeability in sediments and their role in large slip near the surface of the plate boundary fault 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Fluid transport properties such as permeability, porosity, and specific storage are significant parameters that affect earthquake dynamic process. Thermal pressurization model (Mitsui et al., 2012, Earth and Planetary Science Letters) and shallow strong patch model (Kato and Yoshida, 2011, Geophysical Research Letters) were proposed to explain the giant earthquake in the Tohoku area, and transport property around the plate boundary fault is an important factor that impact on both models. Therefore we measured the transport properties of shallow sediments sampled around the plate boundary near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> in the IODP expedition 343 at confining pressures up to 40 MPa. The permeabilities of samples from the shallow plate boundary fault at 820 mbsf were very low at 10 -20 m2, equivalent to a hydraulic diffusivity of 10-10 m2/s. Permeability in the core of the fault zone at the plate boundary were lower than those in the immediately overlying and underling sediments and the surrounding intact sediment, suggesting that the plate boundary fault can act as a barrier for fluid flow. Low permeability and high specific storage in the shallow plate boundary fault create a strong potential for dynamic fault weakening due to fluid pressurization with frictional heating, even when the initial shear stress is low. Our investigation supports the hypothesis that thermal pressurization on the fault plane induced the extremely large slip in the shallow part of the <span class="hlt">subduction</span> zone during the Tohoku earthquake. As the fault zone has a lower permeability than the surrounding sediments and a higher clay content, pore pressure generation at depth by dehydration of clay minerals can explain formation of the shallow strong patch on the fault more reasonably than continuous fluid influx from the <span class="hlt">subducting</span> oceanic crust proposed by Yoshida and Kato (2011, Geophysical Research Letters). Although there are many possible mechanisms of fault weakening, thermal pressurization can act relatively efficiently as slip begins, even at shallow depths. Therefore thermal pressurization is the most likely trigger mechanism for the large shallow displacement of the Tohoku earthquake.</p> <div class="credits"> <p class="dwt_author">Tanikawa, W.; Hirose, T.; Mukoyoshi, H.; Tadai, O.; Lin, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2014PrOce.123...54K"> <span id="translatedtitle">Bathymetric patterns of ? and ? diversity of harpacticoid copepods at the genus level around the Ryukyu <span class="hlt">Trench</span>, and turnover diversity between <span class="hlt">trenches</span> around <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 diversity of harpacticoid copepods was investigated around the Ryukyu <span class="hlt">Trench</span> (430–7150 m), which lies below an oligotrophic subtropical ocean. The ? diversity, which is based on the number of genera and Shannon diversity decreased with increasing water depth. The community structure of harpacticoids gradually changed as the water depth increased from the bathyal zone to the hadal zone. Turnover (?) diversity values were equally high between the <span class="hlt">trench</span> slope, <span class="hlt">trench</span> floor and abyssal plain. We compared the harpacticoid assemblage obtained from the Ryukyu region with the assemblage from a region around the Kuril <span class="hlt">Trench</span> (Kitahashi et al., 2013). Turnover diversity values between the two regions (? diversity) were relatively low at shallow depths, but they increased with increasing water depth and reached their maximum between the <span class="hlt">trench</span> floors and abyssal plains. These findings indicate that the bathymetric patterns of harpacticoid assemblages differ among regions and that these discrepancies reflect differences in environmental conditions, such as primary productivity level.</p> <div class="credits"> <p class="dwt_author">Kitahashi, Tomo; Kawamura, Kiichiro; Kojima, Shigeaki; Shimanaga, Motohiro</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</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://adsabs.harvard.edu/abs/2004AGUFM.G21A0111T"> <span id="translatedtitle">Dense GPS Array Observations Across 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Interseismic deformation in an oblique <span class="hlt">subduction</span> zone is a mixture of short-term crustal shortening in the direction of plate convergence and permanent margin-parallel movement of a forearc block. We have deployed two dense GPS traverse arrays across the southwest <span class="hlt">Japan</span> arc to better illustrate strain partitioning in the Nankai <span class="hlt">subduction</span> zone. In 1998 we constructed the first array that composed of 22 stations along a 200km-long arc-normal line. The second array with 15 stations was constructed in 2002 nearly parallel to and 120km west of the first one. Both arrays cross the Median Tectonic Line (MTL), the arc-parallel strike-slip fault system dividing the forearc block from the rest of the overriding plate. More than 100 crustal velocities from these arrays and the nationwide continuous GPS arrays are used for inversion analysis to estimate back slip vectors on plate interface, a rate of margin-parallel forearc movement, and slip deficits on the upper fault zone of the MTL. Plate interface and MTL fault plane are reproduced by multi-rectangular segments and inversions are conducted for various dip-angles of the MTL. The optimum model shows that strong plate coupling causes a margin-parallel forearc movement at a rate of 3mm/yr together with a crustal shortening of 0.3-0.4 micro strain/yr in the direction of plate convergence. Slip deficits on the MTL are nearly equivalent to the rate of margin-parallel forearc movement in the opposite direction, showing a full locking of the upper fault zone of the MTL. Moreover inversion result favors northward dipping fault segments of the MTL throughout from east to west than the vertical. The rate of margin-parallel forearc movement is consistent with the geological slip rate of the MTL in the late Quaternary.</p> <div class="credits"> <p class="dwt_author">Tabei, T.; Miyazaki, S.; Hashimoto, M.; Matsushima, T.; Kato, T.; Kato, 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">120</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/2013AGUFM.T23C2603K"> <span id="translatedtitle">Characterization of event deposits induced by Tohoku-oki Earthquakes in the <span class="hlt">Japan</span> <span class="hlt">Trench</span> using paleo and rockmagnetic techniques</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 study on differences in bathymetric data between before and after 2011 Tohoku-Oki earthquake revealed a large coseismic displacement of the overriding plate, and a topographic high formation in the <span class="hlt">trench</span> axis (e.g. Strasser et al., 2013). In order to define the sediment deposition or disturbance occurred by these events, sediment piston cores were collected from the surface sediment around the topographic high in the <span class="hlt">trench</span> axis. Intervals in the upper several ten-cm of recovered cores consist of turbidite units, which are considered to have been formed just after the earthquake. Other turbidite units are also recognized in the older than 2011 event, and they are regarded as evidences of past-other Tohoku earthquakes. Rockmagnetic studies on samples were carried out to analyze their depositional process. Several upward decreasing patterns of magnetic susceptibility in the core tops are interpreted as repeating turbidite cycles of 2011 event. Anisotropy of magnetic susceptibility data show that most Kmin axes are normal to the horizontal plane, and suggest that all intervals were not formed by chaotic deposition (e.g. debris flow). Besides Kmax directions are parallel to the horizontal plane and those alignments generally show clusters in two major directions, which are perpendicular each other. It is interpreted that such variation was induced by changing turbidity current state. Paleomagnetic directions in the turbidite intervals display large swinging patterns, probably due to DRM. However, the records in background intervals reveal a consistent inclination variation within obtained cores. Preliminary interpretation for this record is that the trend represents a record of secular geomagnetic variation in a time span. Parameters of magnetic grain size (e.g. kARM/k) indicate that the grain distribution of background sediment and those of older turbidite are clearly distinct, but the distribution of 2011 event is very similar to those of background sediments. Because the <span class="hlt">trench</span> sediment is generally very fine and it is hard to recognize the sedimentary characteristics visually, paleomagnetic and rock magnetic characterizations are useful to analyze their depositional history. Figuring out this process is important not only for understanding the deposition of 2011 event but for understanding the older event deposits took place before in the <span class="hlt">Japan</span> <span class="hlt">trench</span>.</p> <div class="credits"> <p class="dwt_author">Kanamatsu, T.; Ikehara, K.; Usami, K.; Fink, H.; Strasser, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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_5");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" 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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_8");' 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">121</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/40760216"> <span id="translatedtitle">Evidence for 17th-century tsunamis generated on the Kuril–Kamchatka <span class="hlt">subduction</span> zone, Lake Tokotan, Hokkaido, <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 the seventeenth century, two tsunamis that were generated by earthquakes on the Kuril–Kamchatka <span class="hlt">subduction</span> zone inundated the eastern coast of Hokkaido, northern <span class="hlt">Japan</span>. Stratigraphic evidence for these two tsunamis and related land-level change in coastal Hokkaido consists of two landward-thinning sand layers in the sediments of Lake Tokotan, a coastal lagoon on the Hokkaido coast. The marine origin of</p> <div class="credits"> <p class="dwt_author">Yuki Sawai</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</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://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">123</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://mgg.coas.oregonstate.edu/classes/zhang.pdf"> <span id="translatedtitle">High-resolution <span class="hlt">subducting</span>-slab structure beneath northern Honshu, <span class="hlt">Japan</span>, revealed by double-difference tomography</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 high-resolution seismic velocity structure of the <span class="hlt">subducting</span> slab beneath northern Honshu, <span class="hlt">Japan</span>, has been obtained by double-difference tomography, capitalizing on the existence of two planes of seismicity. The upper plane lies in the region with average to high Vp\\/Vs ratios (1.72 1.85), which may correspond to the transformations of metabasalt and metagabbro to blueschist. The lower plane is associated</p> <div class="credits"> <p class="dwt_author">Haijiang Zhang; Clifford H. Thurber; David Shelly; Satoshi Ide; Gregory C. Beroza; Akira Hasegawa</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">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/2012AGUFM.T54A..03K"> <span id="translatedtitle">Origin of co-existing basalts, high-Mg andesites, and adakites in the SW <span class="hlt">Japan</span> hot <span class="hlt">subduction</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">In response to <span class="hlt">subduction</span> of the young, hot Shikoku Basin of the Philippine Sea Plate (PSP) slab, arc magmas have been active throughout the late Cenozoic (<13 Ma) in the SW <span class="hlt">Japan</span> arc. Extremely variable magma types occurred including oceanic island-type basalt (OIB), shoshonitc to mildly alkalic to sub-alkalic basalts with arc signatures, high-Mg andesites (HMAs), and adakitic andesites and dacites. The OIB-type basalts preceded the arc-type magmas. Therefore, the transition from OIB- to arc-types was related to opening of the <span class="hlt">Japan</span> of Sea back-arc basin and subsequent re-initiation of PSP <span class="hlt">subduction</span>. However, both the origin and tectonic implications of this magmatism are debated. Consequently, we analyzed the bulk rock geochemistry of 340 lava samples from seven Quaternary volcanoes and investigated their sources and melting conditions using a geochemical mass balance model, Arc Basalt Simulator version 4 (ABS4). Comparison to basement granitoids precludes adakite genesis in the lower crust. Instead, the ABS4 model suggests that the adakites are mostly slab melts plus minor interaction with mantle wedge peridotite (PERID). Increasing involvement of PERID during slab melt-fluxed mantle melting explains fairly well the geochemical variations of the shoshonites, mildly alkalic to sub-alkalic basalts, and HMAs. We propose that the generation of various magma types in the late Cenozoic SW <span class="hlt">Japan</span> arc originated simply by "slab melt-fluxed mantle melting" with large variations in melting conditions including depth, temperature, degree of melting, and flux fractions. Such volcanism has been continuous from 13 Ma (Setouchi HMA) to the present, so that the hot <span class="hlt">subduction</span> system, involving <span class="hlt">subduction</span> of the Shikoku Basin spreading ridge, should be continuous since 13 Ma beneath the SW <span class="hlt">Japan</span> arc. Our results further suggest that this atypically hot system generated diverse primary arc magmas from various degrees of flux melting even though the slab source components and sub-arc mantle are fairly homogeneous.</p> <div class="credits"> <p class="dwt_author">Kimura, J.; Kunikiyo, T.; Osaka, I.; Shimoshioiri, Y.; Katakuse, M.; Kakubuchi, S.; Nagao, T.; Furuyama, K.; Kamei, A.; Nakajima, J.; Stern, R. J.; Gill, J. B.</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">125</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.T13D2421P"> <span id="translatedtitle">Sandstone matrix olistostrome deposited on intra-<span class="hlt">subduction</span> complex serpentinite, <span class="hlt">trench</span> slope basin deposits, and nappe and fold architecture and chronology, Franciscan Complex, Marin County, California</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 mapping and U/Pb detrital zircon geochronology in the Franciscan <span class="hlt">subduction</span> complex in Marin County, California offers insight into intra-<span class="hlt">subduction</span> complex ultramafic rock accretion, mélange development, and fold geometry. From structurally low to high, the study area units comprise coherent sandstone, Nicasio Reservoir terrane (NRT) prehnite-pumpellyite grade pillow basalt and gabbro, serpentinized harzburgite, and two sandstone-matrix olistostromes. The two olistostromes were distinguished in the study area based on field relationships, detrital zircon ages, and differences in sandstone composition. The western olistostrome, with a maximum depositional age of 122 Ma, comprises lithic-rich sandstone matrix enclosing volcanic blocks; the eastern olistostrome has a maximum depositional age of 100 Ma and includes both volcanic and chert blocks. Both olistostromes exhibit minimal strain, indicating pre-tectonic sedimentary origins as submarine slide masses. Sedimentary breccia adjacent to the eastern olistostrome contact with serpentinite includes serpentinite clasts; combined with observed inverted sandstone facing directions within eastern olistostrome near the contact, these data indicate an overturned, depositional contact of olistostrome on intra-Franciscan serpentinized harzburgite. The serpentinite body appears internally coherent, with widespread preservation of relict peridotite textures. Coherent sandstone, deposited at ?122 Ma, dips beneath the NRT and exhibits moderate foliation development. Contact relationships with the serpentinite, sandstone bedding, and serpentinite foliation indicate folding of serpentinite and adjacent units into multi-kilometer scale isoclinal overturned folds verging SW and trending NW-SE. The coherent, intra-<span class="hlt">subduction</span> complex nature of the serpentinite suggests derivation as a coherent fault sheet from the downgoing plate, rather than a klippe of the tectonically overlying Coast Range ophiolite, as previously suggested, or as sedimentary serpentinite as recently proposed for several intra-Franciscan serpentinite bodies. The outcrop pattern of the NRT and sandstone bedding orientations illustrate a second generation of multi-kilometer scale sub-horizontal open to gentle folds trending NE-SW, consistent with outcrop patterns observed elsewhere in the NRT, Yolla Bolly, and Novato Quarry terranes. The study area units structurally overlie the San Bruno Mountain terrane (SBMT), which has a maximum depositional age of 52 Ma and which in turn structurally (or stratigraphically) overlies rocks with a maximum depositional age of 92 Ma. These rock ages and structural relationships suggest that rather than being offscraped and underplated to the Franciscan accretionary stack, the SBMT originated as a <span class="hlt">trench</span>-slope basin deposit. Applied elsewhere within the Franciscan Complex and other accretionary margins, these data imply significantly less structural thickness of the accretionary complex than structural thicknesses implied by the regional dips of strata and nappe contacts.</p> <div class="credits"> <p class="dwt_author">Prohoroff, R. E.; Wakabayashi, J.; Dumitru, T. 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">126</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/2013AGUFM.S11A2294S"> <span id="translatedtitle">Seismic anisotropy within the <span class="hlt">subducting</span> Philippine Sea slab beneath the 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"><span class="hlt">Subduction</span> of the Philippine Sea slab (PHS) causes recurrent megathrust earthquakes every 100 to 150 years. Knowledge of slab geometry has been increased by using the recently established dense seismograph networks in <span class="hlt">Japan</span>, but anisotropic feature, which is related to the tectonic stress field and/or rock properties, within the slab is still unclear. In order to reveal depth-dependent anisotropic feature within the PHS by using teleseismic receiver functions (RFs), we select 33 stations located in the Kii Peninsula, central <span class="hlt">Japan</span>. We choose teleseismic events (M>6.0) from October 2000 to April 2013 for RF analysis, and use seismograms with good signal-to-noise ratio. Low-pass filters with fc = 1.0 and 1.5 Hz are applied to estimate RFs. To estimate the orientation of anisotropy symmetry axis, we apply the harmonic expansion method to the RFs at each station. In the depth range just below the slab Moho (slab mantle), the symmetry axes correspond to the dip direction of the PHS well, and 2-lobe component is dominant. Within the oceanic crust, this trend is the almost same in the eastern Kii Peninsula, though the 4-lobe component is larger than those in deeper part. On the other hand, the axes show EW direction in the southeastern part of the peninsula, and NS direction in the southwestern part. These directions are not consistent with the slab geometry or the regional stress field. This disturbance of seismic anisotropy may reflect complex local stress field as the PHS slab is bending like a valley at this region.</p> <div class="credits"> <p class="dwt_author">Shiomi, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://adsabs.harvard.edu/abs/2007AGUFM.T53A1113A"> <span id="translatedtitle">Crustal features along the southern Kuril <span class="hlt">Trench</span>, <span class="hlt">Japan</span>, obtained by a refraction/reflection seismic survey</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 seismogenic zone in the southern Kuril <span class="hlt">Trench</span> can be divided into two segments by the Kushiro Canyon, the Nemuro segment to the east and the Tokachi segment to the west. Except for the giant compound earthquake in 17th century, [e.g. Sawai et al., 2002], M8 class earthquakes have occurred repeatedly within each of these segments. The 1952 and 2003 Tokachi earthquakes are considered to be repeated rupture of the asperity of the Tokachi-oki segment. In order to reveal the seismic velocity structure related to the rupture propagation or suspension along the plate boundary, we made a seismic survey across the segment boundary between the Nemuro and Tokachi segments. In the experiment, we deployed 16 OBSs along a seismic line with about 180 km length and shot 75 liter airgun to correct wide-angle seismic data, and MCS survey was also made simultaneously. The profile ran through the focal areas of the 2003 Tokachi and the 1973 Nemuro earthquakes along the strike of the Kuril <span class="hlt">Trench</span>. The first arrival times observed by the OBSs are inverted for 2-D P-wave velocity distribution and locations of major reflectors are imaged by using traveltime mapping method (TMM) [Fujie et al., 2005]. In the obtained crustal velocity model, sedimentary layers with Vp < 4.8 km/s shows significant variation along the profile. In the rupture area of the 2003 Tokachi earthquake, their total thickness is about 8 km, it decrease to about 4 km in the segment boundary zone around the Kushiro Canyon. In the Vp model obtained by Nakanishi et al [2004], the layer with Vp of about 5~6 km/s was interpreted as the upper crustal layer of the Kuril arc. But the present result of the TMM shows that there is a distinct reflective boundary within the layer, which separating the layer into upper and lower units. Judging from its large vertical velocity gradient, the upper unit may be old sedimentary unit. Wells et al [2003] pointed out the correlation between the low gravity anomaly (LGA) zones and areas of large coseismic slip. Based on this relation, they discussed that sedimentary basins are developed above locked portions of the plate boundaries due to basal erosion, including the Tokachi segment. Our structure model demonstrates that a thick sedimentary pond is actually developed in the LGA corresponding to the asperity of the Tokachi segment.</p> <div class="credits"> <p class="dwt_author">Azuma, R.; Hino, R.; Machida, Y.; Murai, Y.; Takanami, T.; Mochizuki, K.; Yamada, T.; Shinohara, M.; Kanazawa, T.; Sato, T.</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">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/2012EGUGA..1410487M"> <span id="translatedtitle">Hydrodynamics of tsunamis in <span class="hlt">subduction</span> zones. The differences between the Chile 2010 and <span class="hlt">Japan</span> 2011 tsunamis</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">Tsunamis due to large earthquakes in <span class="hlt">subduction</span> zones have different hydrodynamic behaviors, depending on the location, the bathymetry and the geometry of the rupture associated to the large earthquake. When the width of the rupture (related to the length of the tsunami) is larger than its distance to the shore, the hydrodynamics in the near zone is completely different than the alternate case. In the first case, the earthquake triggers a tsunami composed by one or a group of a few waves with a few minutes in between propagating from the rupture, which reach the coast a few minutes after the earthquake. In the second case, the earthquake triggers a deformation in the water surface which cannot create a complete tsunami wave; there is not enough distance to complete it. Then, a succession of secondary effects are triggered, which are composed by several floods, up to seven or eight, separated several minutes (up to forty or more) and propagate parallel to the coast, which can be even perpendicular to the coast. This case is still poorly understood, even it has been observed and described in the literature over the past three centuries. The difference in hydrodynamic behavior was evidenced in the tsunamis of February of 2010 in Chile and March of 2011 in <span class="hlt">Japan</span>. In this work we show a theory, which has been validated by field observations and numerical simulations based only on the hydrodynamics of the area, that explains the phenomena and it has been extended to other historical tsunamis in Chile. The effects of the Chile 2010 tsunami in the near field zone were complex. The small township of Cobquecura, located at 20 km from the epicenter, did not suffer major damage from the tsunami. The major port zone of Talcahuano at 100 km from the epicenter, received four destructive waves every forty minutes approximately, and lasted three hours after the occurrence of the earthquake, while the bay of San Vicente, adjacent to the above, only suffered a minor, but abrupt, rise in the sea level about 20 minutes after the end of the earthquake. Flux in general was reported to be parallel to the coast, from the north. In the case of <span class="hlt">Japan</span> 2012 tsunami, the first wave arrived to shore from 1 to 50 min after the earthquake, depending on the distance to the rupture. This first wave was in the order of a few centimeters. The maximum wave arrived from 30 minutes to two hours after the earthquake, with high waves larger than 3 m, with flux perpendicular/diagonal to the coast.</p> <div class="credits"> <p class="dwt_author">Monardez, P.; Salinas, R.; Comte, D.</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">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/2012AGUFMNH41C..02I"> <span id="translatedtitle">Past "earthquake/tsunami" event deposits found in the <span class="hlt">Japan</span> <span class="hlt">Trench</span>: Results from the Sonne SO219A and Mirai MR12-E01 cruises</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">Epicenter of the 2011 off the Pacific Coast of Tohoku earthquake located under the sea floor. The large sea-floor displacement is inferred from the repeated bathymetric surveys. Because the <span class="hlt">Japan</span> <span class="hlt">Trench</span> is a remarkable depression near the epicenter, the gravity flows generated by the earthquake and its related phenomena might be focused in the depression (more than 7500 m in water depth) and might form the gravity flow deposits. Therefore, the <span class="hlt">Japan</span> <span class="hlt">Trench</span> is a target area to detect the past earthquake event deposits. To obtain the past earthquake records, we conducted two cruises; Sonne SO219A and Mirai MR12-E01 cruises. All of the cores obtained from the <span class="hlt">Japan</span> <span class="hlt">Trench</span> floor by two cruises showed the same lithostratigraphy. The 2011 event deposits, which were composed of thin sand at base and diatomaceous mud/ooze with multistoried upward fining grading structure, occurred at the uppermost part of the cores. Below the 2011 event deposit, at least three thick (several tens cm to a few meter thick) turbidite units were recognized. Third turbidite unit was very unique and was characterized by the calcareous nanno fossil bearing turbidite muds suggesting the transportation from upper-mid slope. A volcanic ash from the Towada volcano intercalated in hemipelagic mud between second and third turbidite units. Preliminary results on our tephra correlation using geochemical and petrographic properties suggest that the ash might be correlative to Towada-a ash, which occurred just above the Jogan tsunami deposits on the Sendai Plain. Exact correlation of the ash layer is very important to connect the deep-sea event deposits in the <span class="hlt">Japan</span> <span class="hlt">Trench</span> and on-shore tsunami deposits on the Sendai Plain.</p> <div class="credits"> <p class="dwt_author">Ikehara, K.; Kanamatsu, T.; Strasser, M.; Fink, H.; Nagahashi, Y.; Usami, K.; Wefer, G.</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">130</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/51655233"> <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://academic.research.microsoft.com/">Microsoft Academic Search </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</p> <div class="credits"> <p class="dwt_author">Y. Tsuji; J. Nakajima; T. Okada; T. Matsuzawa; A. Hasegawa</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">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/56369146"> <span id="translatedtitle">Seismic Imaging of Metastable Olivine Wedge in the <span class="hlt">Subducting</span> Slab Beneath <span class="hlt">Japan</span> via Vectorial Receiver Function</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 image the <span class="hlt">subducting</span> Pacific plate better, we have extended the treatment of Kawakatsu and Watada (2007, Science) in which they had corrected for the effect of a dipping interface on seismic receiver functions (RF) to image a low-velocity layer atop of the <span class="hlt">subducting</span> slab. The dip angle of the Pacific plate estimated from seismicity is employed to correct the</p> <div class="credits"> <p class="dwt_author">H. Kawakatsu</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">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/2004AGUFM.S53A0174O"> <span id="translatedtitle">Seismic activity of very low-frequency earthquake on the <span class="hlt">subducting</span> Philippine Sea plate near 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Nankai trough <span class="hlt">subduction</span> zone in southwest <span class="hlt">Japan</span> is characterized by some kinds of _gslow earthquake_h. Around the deep side of the seismogenic zone on the <span class="hlt">subducting</span> Philippine Sea plate, non-volcanic tremor is distributed in a narrow belt along the strike of the plate (Obara, 2002). On the other hand, on shallower parts of the seismogenic zone, an anomalous seismic activity has been detected. The waveform of the earthquake is characterized by a band-limited low-frequency content of between 10 and 20 seconds. We call the earthquake _gvery low-frequency (VLF) earthquake_h. The filtered seismogram with a passband of 10 to 100 seconds periods operated on the output from high-sensitivity accelerometer (tiltmeter) installed in every NIED Hi-net station is used for detection and location analysis. The waveform of the VLF earthquake looks like to that of teleseismic event, however the spatial pattern of the amplitude and the apparent velocity of the VLF earthquake are quite different from those of teleseismic events. Because waveforms of the VLF earthquake are quite similar in neighbor stations, epicenters are estimated by using a cross correlation analysis. The Hi-net stations in southwest <span class="hlt">Japan</span> are divided into some groups with a diameter of about 100km. The cross correlation is calculated for every pair of stations in each group in order to measure the time lag which gives the highest cross correlation coefficient. Then, the set of time lags obtained in each group are used to estimate the propagation direction and the apparent velocity. Finally, the epicenter of the VLF earthquake is estimated by focusing the back projection of the ray propagation calculated with good resolution in each group. In the year of 2003, there are two active clusters of the VLF event near the Nankai trough; off Cape Muroto and the Hyuga-nada region. The VLF seismic activity usually lasts for a month in each cluster. Both activities are located on the seaward updip portion of the seismogenic zone on the <span class="hlt">subducting</span> Philippine Sea plate. Just after the occurrence of 2003 Tokachi Earthquake in northeast <span class="hlt">Japan</span> on September 26, 2003, the VLF seismic activity in the eastern part of Hyuga-nada region became very active and continued for a month. Considering the reverse fault type mechanism and shallow depth estimated by the centroid moment tensor (CMT) analysis, the VLF earthquakes might occur in the accretionary prism or on the decollement. Moreover, both active clusters correspond to the extension of the chain-like sea mounts on the ocean floor of the Philippine Sea. Therefore, the occurrence of the VLF earthquake might be related to the existence of the <span class="hlt">subducting</span> sea mount. At present, there is no clear relationship between the episodic tremor and the VLF earthquake activity in their time histories. However, both seismic phenomena are located on transition zones between the locked zone and decoupled aseismic zones at the deeper part and shallower part on the <span class="hlt">subducting</span> plate boundary. Therefore, these low-frequency families must be representing the <span class="hlt">subduction</span> process of the young oceanic plate.</p> <div class="credits"> <p class="dwt_author">Obara, K.; Ito, Y.</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">133</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">134</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19910037624&hterms=subduction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dsubduction"> <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://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</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, Steve; Phillips, Roger J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</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://academic.research.microsoft.com/Publication/55241485"> <span id="translatedtitle">The alkaline magma squeezed upward by the plate flexure prior to <span class="hlt">subduction</span> off the Chile and <span class="hlt">Japan</span> <span class="hlt">Trenches</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 petit-spot monogenetic volcanoes on the NW Pacific Plate represent a new type of volcanism on their tectonic settings (Hirano et al., 2006). The most important feature of petit-spot volcanoes is that they do not derive their heat supply from the deep mantle (in contrast to hotspot volcanoes), despite their occurrence as intra-plate volcanoes. Instead, the magma probably originates within</p> <div class="credits"> <p class="dwt_author">N. Hirano; S. Machida; N. Abe</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">136</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/2913478"> <span id="translatedtitle">Crustal velocity field of southwest <span class="hlt">Japan</span>: <span class="hlt">Subduction</span> and arc-arc collision</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 investigate crustal deformation in southwest <span class="hlt">Japan</span> over a 3-year period revealed by a permanent dense Global Positioning System (GPS) array. Southwest <span class="hlt">Japan</span> is a part of the Amurian Plate, a microplate moving about 10 mm\\/yr toward the east with respect to the Eurasian Plate. It overrides the Philippine Sea Plate at the Nankai Trough and collides with the northeast</p> <div class="credits"> <p class="dwt_author">Shin'ichi Miyazaki; Kosuke Heki</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">137</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.V23B2065S"> <span id="translatedtitle">An old HIMU seamount chain near the <span class="hlt">Japan</span> <span class="hlt">Trench</span>: implications for Long-lasting HIMU magmatism in the South 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 northwest Pacific Ocean is known to contain abundant mid-Cretaceous seamounts and several large igneous provinces (LIPs) [Winterer, 1993; Coffin and Eldholm, 1994; Koppers et al., 1998]. These seamounts and LIPs are considered to have been formed by “superplume” activity that is inferred to be caused by large-scale mantle upwelling originating from the core-mantle boundary [Larson, 1991]. Therefore, documenting superplume activity over both space and time may provide clues into understanding material recycling throughout the silicate Earth. In spite of their potential importance, mid-Cretaceous seamounts have been studied in less detail than their present-day ocean island counterparts, probably due to their less accessibility and the effect of submarine alteration. As the magmatism in the mid-Cretaceous was considerably more vigorous than it is today, the seamounts that formed during the mid-Cretaceous could provide essential information regarding the causes of superplume activity. Seamount trails in the northwest Pacific are thus important, as they are expected to have been formed in response to mid-Cretaceous superplume activity, which continues in the South Pacific region today. One such seamount trail is the Joban Seamount Chain, which is currently <span class="hlt">subducting</span> beneath the NE <span class="hlt">Japan</span> arc. Compared to other seamount chains in the West Pacific Seamount Province [e.g. Koppers et al., 2003], the geochemistry of the Joban Seamount Chain has been less extensively studied, and the Pb, Nd or Sr isotopic composition of the Joban Seamounts has not been investigated to date. This study was therefore conducted to elucidate the as-yet ambiguous geochemical characteristics of the Joban Seamount Chain using Pb, Nd, Sr isotopic composition analysis and 40Ar-39Ar dating as a key to clarifying previous superplume activity. The isotopic compositions and 40Ar-39Ar age of the Joban Seamount Chain show that these seamounts were produced by HIMU-type magmatism around 120 Ma. In addition, seamount chains in the western Pacific, which is coeval with the Joban Seamount chain, also exhibit a HIMU isotopic signature. These isotopic features suggest that HIMU-type magmatism must have been active in the superplume since the initial, most intense, phase of magmatism. In addition, total Pb-Nd-Sr isotopic ranges of the superplume over time are relatively constant and are comparable to those of the present-day seamounts and ocean islands in the South Pacific. It is thus possible that the isotopically anomalous magmatism in the south Pacific region may have lasted for approximately 120 million years, suggesting that the magmatism in the south Pacific was induced by plume activity rather than extensional magmatism.</p> <div class="credits"> <p class="dwt_author">Shimoda, G.; Yamashita, K.; Yoshitake, M.; Masatsugu, O.; Yuasa, 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">138</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/2013JVGR..268...46S"> <span id="translatedtitle">Volatile flux from <span class="hlt">subduction</span> zone volcanoes: Insights from a detailed evaluation of the fluxes from volcanoes 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">Global volatile fluxes from subaerial volcanoes at <span class="hlt">subduction</span> zones were estimated based on a compilation of fluxes from various sources, including persistent degassing, hot and cold springs, soil degassing, and eruptions. Because worldwide comprehensive datasets are not available, especially for diffuse volatile discharges, volatile fluxes from <span class="hlt">Japan</span> arcs were estimated based on detailed datasets, and the regional fluxes were extrapolated to the global flux with consideration of the regional characteristics of volcanic volatile compositions, which were estimated based on volcanic gas compositions of persistent degassing. The estimated global fluxes indicate that persistent degassing is the major source of volatiles, especially for S with a contribution of 80%. Diffuse discharges and persistent degassing are similarly important sources of H2O, CO2, and Cl, but the contribution of explosive eruptions is less than 15% for all the volatiles. The estimates of diffuse degassing fluxes include large errors due to limited data. However, the potential impact of these sources on the global flux indicates the importance of further studies to quantify these fluxes. The volatile budget of <span class="hlt">subduction</span> zone volcanism was evaluated by comparing the estimated volatile fluxes, the volatile contents in the crust, and the primitive magma volatile contents. The contribution of volatiles remaining in the crust are not significant; however, consideration of lower crust foundering significantly alters the volatile budget estimate because the primitive magma supply rate should be significantly increased to account for the lower crust foundering.</p> <div class="credits"> <p class="dwt_author">Shinohara, Hiroshi</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://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 " 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://adsabs.harvard.edu/abs/2008AGUFM.S14C..03K"> <span id="translatedtitle">Seismic Imaging of Meta-stable Olivine Wedge in the <span class="hlt">Subducting</span> Slab Beneath <span class="hlt">Japan</span> via Vectorial Receiver Function</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 image the <span class="hlt">subducting</span> Pacific plate better, we have extended the treatment of Kawakatsu and Watada (2007, Science) in which they had corrected for the effect of a dipping interface on seismic receiver functions (RF) to image a low-velocity layer atop of the <span class="hlt">subducting</span> slab. The dip angle of the Pacific plate estimated from seismicity is employed to correct the effect of the dipping interface. For each potential conversion point, only a P-S conversion which satisfies the Snell's law on the dipping interface is used for RF. Two horizontal component RFs are then rotated to the direction of expected polarization of P-S converted waves from the interface, and stacked at the conversion point in such a way that the amplitude corresponds to the possible S-wave velocity jump at the interface. This method is applied to Hi-net recording of teleseismic events from 2001 to the end of 2006. The total number of events analyzed is 681, and the number of RFs is more than 300,000. The results show a clear image of a bottom boundary of the <span class="hlt">subducting</span> Pacific plate; the thickness of the plate is estimated to be ~80km (Tonegawa et al., 2006, EPSL). Below 350km right beneath central/southwestern <span class="hlt">Japan</span>, there also exist signatures inside of the slab which we attribute to those originated from the postulated meta-stable olivine wedge (MOW; Iidaka and Suetsugu, 1992, Nature). We observe both velocity decrease (from shallow to deep) and increase corresponding respectively to the upper and lower edge of the MOW which is expected to have several percent slower seismic velocity relative to the surrounding normal slab (Kaneshima et al., 2007, EPSL). The catalogue seismicity by JMA indicates that deep earthquakes are located along the lower edge of the MOW. The detailed investigation of the relative locations of these features should give a tight constraint on the origin of deep earthquakes. The existence of the MOW indicates insignificant amount of water present in the <span class="hlt">subducting</span> slab in the region (Hosoya et al., 2005, GRL); together with the observed deep depression (~40km) of the 660-km discontinuity in the same area, the effective Clapeylon slope of dry slab for the 660km discontinuity should be significantly steeper than those predicted by recent high-pressure experiments (e.g., Katsura et al., 2003, PEPI).</p> <div class="credits"> <p class="dwt_author">Kawakatsu, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-12-01</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" 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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_9");' 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">141</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/41336056"> <span id="translatedtitle">A Global Survey of Possible <span class="hlt">Subduction</span> Sites on Venus</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">About 10,000 km of <span class="hlt">trenches</span> in chasmata and coronae have been identified as possible sites of retrograde <span class="hlt">subduction</span> on Venus. All the sites have narrow deep <span class="hlt">trenches</span> elongate along strike with arcuate planforms, ridge-<span class="hlt">trench</span>-outer rise topographic profiles typical of terrestrial <span class="hlt">subduction</span> zones, large outer rise curvatures >10-7 m-1, fractures parallel to the strike of the <span class="hlt">trench</span> on the outer <span class="hlt">trench</span></p> <div class="credits"> <p class="dwt_author">G. Schubert; D. T. Sandwell</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">142</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/54122116"> <span id="translatedtitle">P to S scattered-wave imaging of the <span class="hlt">subducting</span> slabs beneath <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 developments in seismic observations make it possible to apply scattered wave imaging techniques developed for petroleum exploration, such as the pre-stack depth migration, to investigate the crustal and upper mantle structures with unprecedented detail. In this study, we used P to S scattered waves to image the top 1000 km beneath <span class="hlt">Japan</span> islands. We are particularly interested in imaging</p> <div class="credits"> <p class="dwt_author">F. Niu; A. Levander; M. Obayashi</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">143</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=https://www.ees.nmt.edu/Geop/Classes/Geop558/obara_slow_slip_tremors_GRL2004.pdf"> <span id="translatedtitle">Episodic slow slip events accompanied by non-volcanic tremors 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://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Episodic slow slip events have been recognized by means of tilt changes in the western Shikoku area, southwest <span class="hlt">Japan</span>. The crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non-volcanic deep tremor activities in this area. Observed tilt changes can be explained by slow slip events occurring around the</p> <div class="credits"> <p class="dwt_author">Kazushige Obara; Hitoshi Hirose; Fumio Yamamizu; Keiji Kasahara</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">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/2013AGUFM.S43B2515T"> <span id="translatedtitle">Seismic interferometry imaging of <span class="hlt">subducting</span> Philippine Sea plate and crustal structure in Tokai region, central <span class="hlt">Japan</span> using natural earthquakes</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">Seismic interferometry is an imaging method of subsurface structures using passive seismic records without artificial energy sources. Using natural earthquake records, seismic reflection imaging of deep crustal structures and plate boundaries is expected. We applied seismic interferometry to natural earthquake records, acquired by a wide-aperture linear seismometer array called Tokai Array, to image the P- and S-wave seismic structures in the Tokai region, central <span class="hlt">Japan</span>. The Tokai Array observation was conducted from April to August 2008 with 81 three-component seismometers spanning about 100km in length. Records of 8 Hi-net stations near the array were also used. At first, we applied auto-correlation analysis to the record of deep earthquakes. Since the auto-correlation analysis assumes one-dimensional wave propagation, we searched deep earthquakes that could be considered as normal incidence using Fresnel zone concept. We selected 13 events of deep earthquakes for the P-wave and 10 events for the S-wave analysis, which occurred along <span class="hlt">subducting</span> Pacific Sea plate at 200 - 300km in depth. After correcting seismometer response, we applied the band-pass filter from 1.0 to 2.5 Hz and 0.5 to 1.0 Hz for P- and S-wave, respectively, corresponding to the dominant frequency of the seismic records. Then we removed the records showing low S/N ratio. Afterwards, we calculated the auto-correlation to obtain virtual shot record, which is equivalent to zero-offset shot record. We applied a filter that transforms source functions into the simple Ricker wavelet, to remove the effects associated with source functions. After whitening deconvolution to remove multiples, we stacked auto-correlation of every earthquake record, and applied Kirchoff depth migration using the velocity model estimated by seismic tomography method (Kato et al., 2010). The result of auto-correlation analysis shows good agreement with previous researches in the area, such as seismic tomography, receiver function (Kato et al., 2010; Takaoka, et al., 2012). P- and S-wave virtual reflection profiles show reflectors corresponding to continental Moho and <span class="hlt">subducting</span> Philippine Sea plate interface. Discontinuity of reflectors is found at the interface of geological structure in shallow part. These results indicate auto-correlation analysis has the potential to image plate boundary and crustal structures. In the Tokai Array observation, the seismometers were not evenly located. Creating a virtual shot gather using cross-correlation analysis improves the spatial density of the records. Therefore, the reliability of lateral variation of reflector amplitude may be improved. Application of the cross-correlation analysis is underway. We will discuss the lateral change in the reflection strength along <span class="hlt">subducting</span> Philippine Sea plate boundary in the presentation. Reference: Kato, A. et al. (2010). Variations of fluid pressure within the <span class="hlt">subducting</span> oceanic crust and slow earthquakes. Geophys.Res.Lett., 37, L14310, doi: 10.1029/2010GL043723. Takaoka H. et al. (2012). Three-dimensional Attenuation Structure beneath the Tokai Region, Central <span class="hlt">Japan</span> Derived Using Local Earthquakes Spectra. Zisin 2, 65, 175-187, doi: 10.4294/zisin.65.175 (in Japanese)</p> <div class="credits"> <p class="dwt_author">Totani, M.; Watanabe, T.; Yamaoka, K.; Kato, A.; Iidaka, T.; Ikuta, R.; Tsumura, N.; Okubo, M.; Suzuki, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://adsabs.harvard.edu/abs/2013AGUFMDI23B..04W"> <span id="translatedtitle">Modeling the effects of 3-D slab geometry and oblique <span class="hlt">subduction</span> on <span class="hlt">subduction</span> zone thermal structure</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 this study, we revisit the effects of along-strike variation in slab geometry and oblique <span class="hlt">subduction</span> on <span class="hlt">subduction</span> zone thermal structures. Along-strike variations in slab dip cause changes in the descending rate of the slab and generate <span class="hlt">trench</span>-parallel pressure gradients that drive <span class="hlt">trench</span>-parallel mantle flow (e.g., Kneller and van Keken, 2007). Oblique <span class="hlt">subduction</span> also drives <span class="hlt">trench</span>-parallel mantle flow. In this study, we use a finite element code PGCtherm3D and examine a range of generic <span class="hlt">subduction</span> geometries and parameters to investigate the effects of the above two factors. This exercise is part of foundational work towards developing detailed 3-D thermal models for NE <span class="hlt">Japan</span>, Nankai, and Cascadia to better constrain their 3-D thermal structures and to understand the role of temperature in controlling metamorphic, seismogenic, and volcanic processes. The 3-D geometry of the <span class="hlt">subducting</span> slabs in the forearc and arc regions are well delineated at these three <span class="hlt">subduction</span> zones. Further, relatively large compilations of surface heat flow data at these <span class="hlt">subduction</span> zones make them excellent candidates for this study. At NE <span class="hlt">Japan</span>, a megathrust earthquake occurred on March 11, 2011; at Nankai and Cascadia, there has been a great effort to constrain the scale of the next <span class="hlt">subduction</span> thrust earthquake for the purpose of disaster prevention. Temperature influences the slip behavior of <span class="hlt">subduction</span> faults by (1) affecting the rheology of the interface material and (2) controlling dehydration reactions, which can lead to elevated pore fluid pressure. Beyond the depths of <span class="hlt">subduction</span> thrust earthquakes, the thermal structure is affected strongly by the pattern of mantle wedge flow. This flow is driven by viscous coupling between the <span class="hlt">subducting</span> slab and the overriding mantle, and it brings in hot flowing mantle into the wedge. The <span class="hlt">trench</span>-ward (up-dip) extent of the slab-mantle coupling is thus a key factor that controls the thermal structure. Slab-mantle decoupling at shallow depths causes mantle stagnation and a cool condition, which allows serpentinization to occur, whereas coupling at greater depths drives hot flowing mantle, providing the thermal condition required for melt generation in the mantle wedge. The flowing mantle also causes rapid heating of the <span class="hlt">subducting</span> slab and affects the occurrence of intraslab earthquakes. In the generic model calculations in the study, we also investigate the effect of local fluctuations in the depth of decoupling-coupling transition on the 3-D mantle wedge flow pattern and thermal structure. Kneller, E.A., and P.E. van Keken (2008), Effect of three-dimensional slab geometry on deformation in the mantle wedge: Implications for shear wave anisotropy, Geochem. Geophys. Geosyst., 9, Q01003, doi:10.1029/2007GC001677.</p> <div class="credits"> <p class="dwt_author">Wada, I.; Wang, K.; He, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://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">147</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/10100425"> <span id="translatedtitle">Mapping the <span class="hlt">subducting</span> Pacific slab beneath southwest <span class="hlt">Japan</span> with Hi-net receiver functions</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 used 4th root receiver function stacks, and pre-stack receiver function depth migrations to study the transition zone discontinuity structure beneath southwestern <span class="hlt">Japan</span>. Receiver functions were calculated from the quiet short-period seismograms recorded by a recently deployed borehole network, Hi-net. We found that a relatively broad frequency band can be retrieved from a short-period seismogram by a deconvolution of</p> <div class="credits"> <p class="dwt_author">Fenglin Niu; Alan Levander; Sangwon Ham; Masayuki Obayashi</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">148</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/2012AGUFM.S31A2484B"> <span id="translatedtitle">Gravity anomalies, forearc morphology and seismicity 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">We apply spectral averaging techniques to isolate and remove the long-wavelength large-amplitude <span class="hlt">trench</span>-normal topographic and free-air gravity anomaly "high" and "low" associated with <span class="hlt">subduction</span> zones. The residual grids generated illuminate the short-wavelength structure of the forearc. Systematic analysis of all <span class="hlt">subduction</span> boundaries on Earth has enabled a classification of these grids with particular emphasis placed on topography and gravity anomalies observed in the region above the shallow seismogenic portion of the plate interface. The isostatic compensation of these anomalies is investigated using 3D calculations of the gravitational admittance and coherence. In the shallow region of the megathrust, typically within 100 km from the <span class="hlt">trench</span>, isolated residual anomalies with amplitudes of up to 2.5 km and 125 mGal are generally interpreted as accreted/<span class="hlt">subducting</span> relief in the form of seamounts and other bathymetric features. While most of these anomalies, which have radii < 50km, are correlated with areas of reduced seismicity, several in regions such as <span class="hlt">Japan</span> and Java appear to have influenced the nucleation and/or propagation of large magnitude earthquakes. Long-wavelength (500 - >1000 km) <span class="hlt">trench</span>-parallel forearc ridges with residual anomalies of up to 1.5 km and 150 mGal are identified in approximately one-third of the <span class="hlt">subduction</span> zones analyzed. Despite great length along strike, these ridges are less than 100 km wide and several appear uncompensated. A high proportion of arc-normal structure and the truncation/morphological transition of <span class="hlt">trench</span>-parallel forearc ridges is explained through the identification and tracking of pre-existing structure on the over-riding and <span class="hlt">subducting</span> plates into the seismogenic portion of the plate boundary. Spatial correlations between regions with well-defined <span class="hlt">trench</span>-parallel forearc ridges and the occurrence of large magnitude interplate earthquakes, in addition to the uncompensated state of these ridges, suggest links between the morphology of the forearc and the peak earthquake stress drop on the <span class="hlt">subduction</span> megathrust. We present our classification of residual bathymetric and gravitational anomalies using examples from Sumatra, Kuril-Kamchatka, Mariana, Peru-Chile and the Tonga-Kermadec margin. We reassess proposed links between <span class="hlt">trench</span>-parallel residual topography and gravity anomalies and <span class="hlt">subduction</span> zone seismicity using global earthquake catalogs and a new compilation of published aftershock locations and distributed slip models from over 200 of the largest <span class="hlt">subduction</span> zone earthquakes. Our results highlight the role of pre-existing structure in both the over-riding and <span class="hlt">subducting</span> plates in modulating the along- and across-strike segmentation of <span class="hlt">subduction</span> zones. Understanding the genesis of long-wavelength <span class="hlt">trench</span>-parallel forearc ridges may provide further insights into links between forearc morphology, the rheology of the overriding and <span class="hlt">subducting</span> plates and seismicity in <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Bassett, D.; Watts, A. B.; Das, S.</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">149</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/48898836"> <span id="translatedtitle">Newly imaged shape of the deep seismic zone within the <span class="hlt">subducting</span> Pacific plate beneath the Hokkaido corner, <span class="hlt">Japan</span>-Kurile arc-arc junction</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 geometry of the deep seismic zone associated with the <span class="hlt">subducting</span> Pacific plate beneath the North American plate in the Hokkaido corner, <span class="hlt">Japan</span>-Kurile arc-arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three-dimensional P and S wave velocity structures. The model suggests that the lateral changes in the dip of the</p> <div class="credits"> <p class="dwt_author">Kei Katsumata; Naoto Wada; Minoru Kasahara</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">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/41300657"> <span id="translatedtitle">Tomographic imaging of hydrated crust and mantle in the <span class="hlt">subducting</span> Pacific slab beneath Hokkaido, <span class="hlt">Japan</span>: Evidence for dehydration embrittlement as a cause of intraslab earthquakes</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 estimate detailed three-dimensional seismic velocity structures in the <span class="hlt">subducting</span> Pacific slab beneath Hokkaido, <span class="hlt">Japan</span>, using a large number of arrival-time data from 6902 local earthquakes. A remarkable low-velocity layer with a thickness of ~10 km is imaged at the uppermost part of the slab and is interpreted as hydrated oceanic crust. The layer gradually disappears at depths of 70–80 km, suggesting</p> <div class="credits"> <p class="dwt_author">Junichi Nakajima; Yusuke Tsuji; Akira Hasegawa; Saeko Kita; Tomomi Okada; Toru Matsuzawa</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">151</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/52398418"> <span id="translatedtitle">A Detailed 3D Seismic Velocity Structure of the <span class="hlt">Subducting</span> Pacific Slab Beneath Hokkaido, Tohoku and Kanto, <span class="hlt">Japan</span>, by Double-Difference Tomography</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 heterogeneous structure beneath northeastern (NE) <span class="hlt">Japan</span> has been investigated by previous studies and an inclined seismic low-velocity zone is imaged in the mantle wedge sub-parallel to the down-dip direction of the <span class="hlt">subducting</span> slab (Zhao et al., 1992, Nakajima et al., 2001). However, the heterogeneous structure within the slab has not been well studied even though it is very important</p> <div class="credits"> <p class="dwt_author">Y. Tsuji; J. Nakajima; S. Kita; T. Okada; T. Matsuzawa; A. Hasegawa</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">152</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.T23C0502K"> <span id="translatedtitle">Seismic Evidence for the Dehydration of the <span class="hlt">Subducted</span> Oceanic Crust Beneath <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 have extended our receiver function (RF) analysis to map the seismic discontinuity structure beneath the Japanese islands using Hi-net data (Kawakatsu and Watada, 2005). From earthquakes occurred between January of 2001 and May of 2005, we select those in a distant range of 30-90 degrees with Mw > 5.5, which results in a total of 473 events. Receiver functions (RFs) are constructed for instrument response corrected seismograms employing the water level correction (C=0.001) in a frequency range of 0.1-0.5Hz. Out of 281,000 RFs, we select RFs with decent S/N ratio to make 84,315 RFs. As the structure of the mantle transition zone discontinuities had been previously discussed, here we mainly present the shallow (<250km) structure. The RF images beneath the Tohoku arc show clear images of the top of the <span class="hlt">subducting</span> Pacific plate. Positive RFs, corresponding to velocity increase with depth due to the presence of a cold slab, are mapped continuously parallel to the upper plane of the double seismic zone; we believe that this feature represents the oceanic Moho, as negative RFs, indicating velocity decrease due to the presence of the hydrous oceanic crust, are observed on top of it. What is remarkable is that the strength of this combination of the negative and positive RFs is reduced drastically around a depth of 70-80km, even though they can be traced downwards parallel to the seismicity. We attribute this reduction of the RF amplitudes to the dehydration process of the <span class="hlt">subducted</span> oceanic crust taking place at the depth range: the seismic velocity of the hydrous oceanic crust (e.g., blueschist) is known to be significantly slower than the surrounding mantle, while that of the anhydrous eclogitic crust may be slightly faster. Thus the degree of dehydration would strongly control the reflectivity property at the top part of the slab. The overall feature of our image appears quite consistent with the result of the numerical simulation by Iwamori and Zhao (2000), including a possible signature of the serpentine layer in the mantle just above the slab.</p> <div class="credits"> <p class="dwt_author">Kawakatsu, H.; Watada, S.</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">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/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">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/2013AGUFMDI11A2184K"> <span id="translatedtitle">S-wave anisotropy estimated by seismic interferometry using ambient noise record in the Nankai Trough <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">In the Nankai Trough <span class="hlt">subduction</span> zone, located beneath the Pacific Ocean off the southeast coast of <span class="hlt">Japan</span>, interplate earthquakes can be generated repeatedly in association with stress accumulation and release cycle. In this study, we aim to obtain the information of S-wave anisotropy beneath the seafloor, which could be interpreted as a proxy of stress and strain field above the <span class="hlt">subduction</span> zone. For this purpose, we apply the seismic interferometry technique to ambient noise records acquired by seafloor and subseafloor seismometers deployed above the Nankai Trough <span class="hlt">subduction</span> zone. In this area, we have twenty seafloor seismometers as a part of DONET (Dense Oceanfloor Network System for Earthquake and Tsunamis) and a borehole seismometer installed in the IODP (Integrated Ocean Drilling Program) C0002G observatory at the bottom of the borehole, 900 m below seafloor. Both observatories were designed and installed to monitor the seismic activity and the process of earthquake generation including the stress accumulation. In this study, we apply the seismic interferometry to ambient noise records observed by these DONET and C0002G seismometers. Seismic interferometry is a method to retrieve the impulse response by the cross-correlation of seismic records simultaneously acquired by the two seismometers. Because the horizontal components are dominated by S-wave energy, we expected that auto- and cross-correlation functions (ACF and CCF), calculated from the horizontal components of each seismometer, would provide us the knowledge of S-wave velocity and anisotropy beneath seafloor, as a proxy of strain and stress field, and fluid migration above the plate boundary. We obtained zero offset 4-C ACF and CCFs comprising V11, V12, V21, and V22, calculated form continuous ambient noise records observed by horizontal components of each seismometer. Vij are ACF and CCFs calculated from ambient noise record observed by i- and j-direction receiver components, and represents impulse response which has i-direction source and j-direction receiver of each seismometer. We used each 1 hour dataset for more than 6 months and obtained Vij as 30 s zero offset impulse responses for each seismometer. In the obtained ACF and CCFs, several coherent events are visible. However, the events in each component are not consistent with that of others. It might result from S-wave splitting affected by anisotropy. S-wave split into two orthogonal directions along anisotropy direction in propagating anisotropy media. We then applied the Alford rotation and the layer stripping method to the obtained 4-C ACF and CCFs to estimate S-wave anisotropy direction and amplitude beneath each seismometer in each layer, shallow sediment and accretionary prism above the plate boundary. Obtained results, including the azimuth and magnitude of anisotropy as functions of depth, show good agreement with S-wave anisotropy directions and principle shear stress directions estimated from two of the other methods, i.e., borehole breakout analysis in the IODP C0009 borehole, and P-S converted wave analysis using airgun OBS data. We expect that our method could make it possible to monitor temporal changes in the azimuth and the magnitude in anisotropy, as a proxy of stress field, using real-time ambient noise records in the <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Kimura, T.; Mikada, H.; Araki, E.; Kitada, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://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 " 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://adsabs.harvard.edu/abs/2006GeoJI.165..565R"> <span id="translatedtitle">Imaging <span class="hlt">subduction</span> from the <span class="hlt">trench</span> to 300 km depth beneath the central North Island, New Zealand, with Vp and Vp/Vs</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 dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central North Island of New Zealand. Here we use a subset of the best-recorded earthquakes in an inversion for the 3-D Vp and Vp/Vs structure. The data set includes 39123 P observations and 18331 S observations from 1239 earthquakes and nine explosions. The <span class="hlt">subducted</span> plate is imaged as a high Vp, low Vp/Vs feature. Vp within the mantle of the <span class="hlt">subducted</span> slab is almost always >8.5 km s-1, which requires the ca. 120 Myr slab to be unusually cold. The low Vp/Vs within the <span class="hlt">subducted</span> plate closely parallels the lower plane of the dipping seismic zone. It most likely indicates fluid resulting from dehydration of serpentine in the slab mantle, and the earthquakes themselves are likely to be promoted by dehydration embrittlement. We identify a region with Vp < 8.0 km s-1 which coincides with the upper plane of the dipping seismic zone and extends to ca. 65 km depth with the <span class="hlt">subducted</span> Hikurangi Plateau, which is about 17 km thick prior to <span class="hlt">subduction</span>. The mantle wedge is generally imaged as a low Vp, high Vp/Vs feature. However, there are significant changes evident in the wedge along the strike of the <span class="hlt">subduction</span> zone. The region where Vp is lowest (7.4 km s-1) and Vp/Vs is highest (1.87) occurs at 65 km depth, immediately west of the Taupo caldera. This region is best interpreted as a significant volume of partial melt, produced by the reaction of fluid released by dehydration of the <span class="hlt">subducted</span> plate with the convecting mantle wedge. The region with lowest Vp, while paralleling the underlying dipping seismic zone, is located about 30 km from the upper surface of the zone. Material with Vp > 8.0 km s-1 directly above the dipping seismic zone can be interpreted as sinking, entrained with the motion of the <span class="hlt">subducted</span> slab and forming a viscous blanket that insulates the slab from the high-temperature mantle wedge. Material in the overlying low Vp region can be interpreted as rising within a return flow within the wedge. The volcanic front appears to be controlled by where this dipping low Vp region meets the base of the crust. The thickness of the backarc crust also shows significant variation along strike. In the central Taupo Volcanic Zone (TVZ) the crust is ca. 35 km thick, while southwest of Mt Ruapehu the crust thickens by ca. 10 km. There is no significant low Vp zone in the mantle wedge in this southwestern region, suggesting that this thicker crust has choked off mantle return flow. The seismic tomography results, when combined with constraints on mantle flow from previous shear-wave splitting results, provide a plausible model for both the distribution of volcanism in the central North Island, and the exceptional magmatic productivity of the central TVZ.</p> <div class="credits"> <p class="dwt_author">Reyners, Martin; Eberhart-Phillips, Donna; Stuart, Graham; Nishimura, Yuichi</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-05-01</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://adsabs.harvard.edu/abs/2012JGRB..11710204U"> <span id="translatedtitle">Relationship between 3He/4He ratios and <span class="hlt">subduction</span> of the Philippine Sea plate beneath 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">Regional and local variations in mantle helium provide insight into the coupling of mantle-crust tectonics, and heat and/or mass transfer from the Earth's interior. In order to further elucidate the geographic distribution of3He/4He ratios in southwest <span class="hlt">Japan</span>, the data from a total of 924 sites were compiled and synthesized. These include data from 48 additional hot spring and drinking water well sites on the northern Kyushu Island and in the northern Chugoku region. There appears to be good correlation between variations in helium isotope ratios and the geophysical evidence used to determine the configuration of the <span class="hlt">subducting</span> Philippine Sea plate (PHS). Seismological studies reveal that the leading edge of the aseismic slab does not extend to the northern Chugoku region nor to the Osaka Bay area, where gas samples with significantly elevated 3He/4He ratios occur. This is consistent with a mantle-derived helium in these areas, from melts and/or mantle fluids ascribed to upwelling asthenosphere without being hindered by the descending PHS slab. In contrast, gas samples in the regions where the overriding crust comes into direct contact with the <span class="hlt">subducting</span> PHS are dominated by radiogenic helium derived from the crust because of the absence of a mantle wedge, the most plausible source of mantle helium. Owing to the abrupt changes in the seismicity and focal mechanisms of intraplate earthquakes, the PHS is considered to have slab tears beneath the Kii Channel and/or the eastern Kii Peninsula oriented in a NW-SE direction. However, the lenear alignment of anomalously high3He/4He ratios does not appear to be NW-SE trending along the assumed slab tears but rather forms an broad, ENE-WSW trending zone between the tears where low-frequency events occur. The emanation of gas with elevated3He/4He ratios in the central peninsula can be explained by the upward mobilization of mantle volatiles derived from the mantle wedge above the PHS and/or transferred from the hydrated slab mantle through the N-S trending fractured medium within the PHS. Accordingly, the helium isotopes observed on the Earth's surface may be efficient geochemical indicators of the configuration of a relatively younger, warm aseismic slab, and be especially useful in seismically inactive areas.</p> <div class="credits"> <p class="dwt_author">Umeda, Koji; Kusano, Tomohiro; Asamori, Koichi; McCrank, Glen F.</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">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/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 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/2013AGUFM.T31G2603M"> <span id="translatedtitle">Paleomagnetic records of core samples of the plate-boundary thrust drilled during the IODP <span class="hlt">Japan</span> <span class="hlt">Trench</span> Fast Drilling Project (JFAST)</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">IODP Expedition 343, <span class="hlt">Japan</span> <span class="hlt">Trench</span> Fast Drilling Project (JFAST), drilled across the plate-boundary décollement zone near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> where large slip occurred during the March 2011 Tohoku-oki earthquake. We conducted paleomagnetic measurements of the core sample retrieved from the highly-deformed sediments comprising the plate-boundary décollement zone. Whole-round samples for structural analyses from five depth intervals of the core (0-12 cm, 12-30 cm, 43-48 cm, 48-58 cm, and 87.5-105 cm), were trimmed into oriented slabs with typical dimensions of 3x3x5 cm that are now being used to make petrographic sections for microstructural and chemical study. The remainder of the core sample was split into working and archive halves. We measured remanent magnetization of 16 trimmed slabs and the archive half of the core sample. The slabs were subjected to natural remanent magnetization (NRM) measurements in 0.5-1 cm intervals and progressive alternating field demagnetization (AFD) up to 80 mT with a 2G755 pass-through superconducting rock magnetometer at Kochi University. The archive half of the core sample was subjected to NRM measurement and AFD up to 20 mT with a 2G760 superconducting rock magnetometer installed on R/V Chikyu. Typically, two or three paleomagnetic components were isolated during the AFD of slab samples up to 80 mT. One ';soft' component was demagnetized below 20-30 mT, and another ';hard' component was not demagnetized even with AFD in 80 mT. A third component may be separated during AFD at the intermediate demagnetizing field, and may overlap the soft and hard components. The multiple slab samples cut from an identical whole-round sample have generally consistent paleomagnetic direction of the hard component. Contrastingly, the direction of the soft component is less consistent between adjacent slabs, and even varies within a single slab. The direction variation of the soft component possibly reflects the cm-scale strain and rotation of the highly-deformed sediments within the plate-boundary décollement zone. Studies of the relationship of the direction variation to the microstructure are ongoing, and will be reported at the meeting. The consistency of the hard component direction within highly deformed sediment implies it was recently acquired. Further studies of the acquisition mechanism of the hard component are also intended.</p> <div class="credits"> <p class="dwt_author">Mishima, T.; Yang, T.; Ujiie, K.; Kirkpatrick, J. D.; Chester, F. M.; Moore, J. C.; Rowe, C. D.; Regalla, C.; Remitti, F.; Kameda, J.; Wolfson-Schwehr, M.; Bose, S.; Ishikawa, T.; Toy, V. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://adsabs.harvard.edu/abs/2013AGUFM.S43A2465S"> <span id="translatedtitle">Stress Drops of Earthquakes on the <span class="hlt">Subducting</span> Pacific Plate in the South-East off Hokkaido, <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 earthquakes have been occurring repeatedly in the South-East of Hokkaido, <span class="hlt">Japan</span>, where the Pacific Plate <span class="hlt">subducts</span> beneath the Okhotsk Plate in the north-west direction. For example, the 2003 Tokachi-oki earthquake (Mw8.3 determined by USGS) took place in the region on September 26, 2003. Yamanaka and Kikuchi (2003) analyzed the slip distribution of the earthquake and concluded that the 2003 earthquake had ruptured the deeper half of the fault plane of the 1952 Tokachi-oki earthquake. Miyazaki et al. (2004) reported that a notable afterslip was observed at adjacent areas to the coseismic rupture zone of the 2003 earthquake, which suggests that there would be significant heterogeneities of strength, stress and frictional properties on the surface of the Pacific Plate in the region. In addition, some previous studies suggest that the region with a large slip in large earthquakes permanently have large difference of strength and the dynamic frictional stress level and that it would be able to predict the spatial pattern of slip in the next large earthquake by analyzing the stress drop of small earthquakes (e.g. Allmann and Shearer, 2007 and Yamada et al., 2010). We estimated stress drops of 150 earthquakes (4.2 ? M ? 5.0), using S-coda waves, or the waveforms from 4.00 to 9.11 seconds after the S wave arrivals, of Hi-net data. The 150 earthquakes were the ones that occurred from June, 2002 to December, 2010 in south-east of Hokkaido, <span class="hlt">Japan</span>, from 40.5N to 43.5N and from 141.0E to 146.5E. First we selected waveforms of the closest earthquakes with magnitudes between 3.0 and 3.2 to individual 150 earthquakes as empirical Green's functions. We then calculated source spectral ratios of the 150 pairs of interested earthquakes and EGFs by deconvolving the individual S-coda waves. We finally estimated corner frequencies of earthquakes from the spectral ratios by assuming the omega-squared model of Boatwright (1978) and calculated stress drops of the earthquakes by using the model of Madariaga (1976). The estimated values of stress drop range from 1 to 10 MPa with a little number of outliers(Fig.(a)). Fig.(b) shows the spatial distribution of stress drops in south-east off Hokkaido, <span class="hlt">Japan</span>. We found that earthquakes occurred around 42N 145E had larger stress drops. We are going to analyze smaller earthquakes and investigate the spatial pattern of the stress drop in the future. Fig. (a) Estimated values of stress drop with respect to seismic moments of earthquakes. (b) Spatial distribution of stress drops.</p> <div class="credits"> <p class="dwt_author">Saito, Y.; Yamada, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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_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");' 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href="#">10</a> <a onClick='return showDiv("page_11");' 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 onClick='return showDiv("page_17");' href="#">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_10");' 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">161</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">162</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=PB85227320"> <span id="translatedtitle">Comparative Laboratory Study of Sewage Treatment by a Capillary Siphon <span class="hlt">Trench</span> System Versus a Conventional Leaching <span class="hlt">Trench</span> System.</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">Laboratory tests were conducted to investigate the performance of the 'Niimi Process' or capillary siphon <span class="hlt">trench</span>, a soil based wastewater disposal system common in <span class="hlt">Japan</span>. The system is similar to conventional septic tank leaching field <span class="hlt">trenches</span> except tha...</p> <div class="credits"> <p class="dwt_author">T. A. Dillaha W. J. Zolan</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</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://adsabs.harvard.edu/abs/2013AGUFM.G31A0931H"> <span id="translatedtitle">Application of InSAR to the Detection of Interseismic Deformation of <span class="hlt">Subduction</span> Zones: A Case Study of 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">Geodetic data, especially GNSS, is useful for the purpose of the long-term seismic hazard evaluation in <span class="hlt">subduction</span> zones. However dense GNSS networks are under operation only in limited areas in the world. Furthermore, some GNSS stations are affected by local disturbances. Therefore it is necessary to establish complementary techniques to cover the defects of GNSS observations. Synthetic Aperture Radar may play this role. In order to examine the ability to detect interseismic deformation with a high spatial resolution, we have been conducting SAR interferometry and stacking analysis of PALSAR images in Southwest <span class="hlt">Japan</span>, where GNSS velocity field is at hand for the ground truth. We are going to report the results for Shikoku and Kyushu as well as technical issues we have found during these processes. We used images of the ascending paths 417 - 420, which were acquired during mid 2006 to 2010, to detect deformation of Shikoku. In total there were more than 20 acquisitions for each path. We stacked images having small artificial changes possibly due to ionospheric disturbances. The variation in stacked interferogram of the path 419 that covers the central part of Shikoku is as large as that simulated from GNSS velocities, but we recognize a different trend in GNSS velocities than the stacking interferogram for the path 417 (eastern Shikoku). Furthermore, fringes in the Chugoku districts are inconsistent with GNSS. We find significant NW-SE trends in the azimuth offsets for the pairs of images acquired on the day of large GNSS-TEC variation. It is worth noting that the wavelength of variation in azimuth offset is much shorter than that seen in GNSS-TEC. Therefore it may be difficult to correct interferograms with GNSS-TEC. On the other hand, it may be suitable for the analysis of interseismic deformation to use descending images of Shikoku, though the number of observation is less than that of ascending. We find less ionospheric disturbances than ascending images. We could obtain consistent result with the GNSS velocity field in eastern Kyushu and Shikoku. On the basis of the above results, we can conclude that it is essential to ensure enough number of observations and careful selection of interferograms to be stacked. A proper correction of ionospheric disturbances is desired for the use of more images. Azimuth offsets may be useful for the evaluation of ionospheric disturbances.</p> <div class="credits"> <p class="dwt_author">Hashimoto, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://pubs.er.usgs.gov/publication/70016680"> <span id="translatedtitle">Observations at convergent margins concerning sediment <span class="hlt">subduction</span>, <span class="hlt">subduction</span> erosion, and the growth of continental crust</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">At ocean margins where two plates converge, the oceanic plate sinks or is <span class="hlt">subducted</span> beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The <span class="hlt">subduction</span> process either builds juvenile masses of terrestrial crust through arc volcanism or new areas of crust through the piling up of accretionary masses (prisms) of sedimentary deposits and fragments of thicker crustal bodies scraped off the <span class="hlt">subducting</span> lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment <span class="hlt">subduction</span>, and terrestrial matter can be removed from the upper plate by processes of <span class="hlt">subduction</span> erosion. Sediment <span class="hlt">subduction</span> occurs where sediment remains attached to the <span class="hlt">subducting</span> oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment <span class="hlt">subduction</span> occurs at two types of convergent margins: type 1 margins where accretionary prisms form and type 2 margins where little net accretion takes place. At type 2 margins (???19,000 km in global length), effectively all incoming sediment is <span class="hlt">subducted</span> beneath the massif of basement or framework rocks forming the landward <span class="hlt">trench</span> slope. At accreting or type 1 margins, sediment <span class="hlt">subduction</span> begins at the seaward position of an active buttress of consolidated accretionary material that accumulated in front of a starting or core buttress of framework rocks. Where small-to-mediumsized prisms have formed (???16,300 km), approximately 20% of the incoming sediment is skimmed off a detachment surface or decollement and frontally accreted to the active buttress. The remaining 80% <span class="hlt">subducts</span> beneath the buttress and may either underplate older parts of the frontal body or bypass the prism entirely and underthrust the leading edge of the margin's rock framework. At margins bordered by large prisms (???8,200 km), roughly 70% of the incoming <span class="hlt">trench</span> floor section is <span class="hlt">subducted</span> beneath the frontal accretionary body and its active buttress. In rounded figures the contemporary rate of solid-volume sediment <span class="hlt">subduction</span> at convergent ocean margins (???43,500 km) is calculated to be 1.5 km3/yr. Correcting type 1 margins for high rates of terrigenous seafloor sedimentation during the past 30 m.y. or so sets the long-term rate of sediment <span class="hlt">subduction</span> at 1.0 km3/yr. The bulk of the <span class="hlt">subducted</span> material is derived directly or indirectly from continental denudation. Interstitial water currently expulsed from accreted and deeply <span class="hlt">subducted</span> sediment and recycled to the ocean basins is estimated at 0.9 km3/yr. The thinning and truncation caused by <span class="hlt">subduction</span> erosion of the margin's framework rock and overlying sedimentary deposits have been demonstrated at many convergent margins but only off northern <span class="hlt">Japan</span>, central Peru, and northern Chile has sufficient information been collected to determine average or long-term rates, which range from 25 to 50 km3/m.y. per kilometer of margin. A conservative long-term rate applicable to many sectors of convergent margins is 30 km3/km/m.y. If applied to the length of type 2 margins, <span class="hlt">subduction</span> erosion removes and transports approximately 0.6 km3/yr of upper plate material to greater depths. At various places, <span class="hlt">subduction</span> erosion also affects sectors of type 1 margins bordered by small- to medium-sized accretionary prisms (for example, <span class="hlt">Japan</span> and Peru), thus increasing the global rate by possibly 0.5 km3/yr to a total of 1.1 km3/yr. Little information is available to assess <span class="hlt">subduction</span> erosion at margins bordered by large accretionary prisms. Mass balance calculations allow assessments to be made of the amount of <span class="hlt">subducted</span> sediment that bypasses the prism and underthrusts the margin's rock framework. This subcrustally <span class="hlt">subducted</span> sediment is estimated at 0.7 km3/yr. Combined with the range of terrestrial matter removed from the margin's rock framework by <span class="hlt">subduction</span> erosion, the global volume of subcrustally <span class="hlt">subducted</span> materia</p> <div class="credits"> <p class="dwt_author">Von Huene, R.; Scholl, D. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</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://academic.research.microsoft.com/Publication/51945561"> <span id="translatedtitle"><span class="hlt">Subduction</span> Erosion Processes Along the Northwestern Margin of South America</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> erosion is one of the dominant processes that shape convergent margins. Mechanisms favoring <span class="hlt">subduction</span> erosion occur at both highly- and weakly-coupled margins. Multibeam bathymetry and MCS data collected along the Ecuador-SW Colombia <span class="hlt">trench</span> show an erosional margin fronted by a narrow wedge of imbricated slope sediment. Ubiquitous arcuate slump scarps on the relatively steep inner <span class="hlt">trench</span> slope denote frequent</p> <div class="credits"> <p class="dwt_author">J. Collot; F. Sage; A. Calahorrano; W. Agudelo; A. Ribodetti</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">166</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/55927258"> <span id="translatedtitle"><span class="hlt">Subduction</span> Erosion Processes Along the Northwestern Margin of South America</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> erosion is one of the dominant processes that shape convergent margins. Mechanisms favoring <span class="hlt">subduction</span> erosion occur at both highly- and weakly-coupled margins. Multibeam bathymetry and MCS data collected along the Ecuador-SW Colombia <span class="hlt">trench</span> show an erosional margin fronted by a narrow wedge of imbricated slope sediment. Ubiquitous arcuate slump scarps on the relatively steep inner <span class="hlt">trench</span> slope denote frequent</p> <div class="credits"> <p class="dwt_author">J. Collot; F. Sage; A. Calahorrano; W. Agudelo; A. Ribodetti</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">167</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/55427833"> <span id="translatedtitle">Are earthquakes in the <span class="hlt">subducting</span> slab reactivating faults formed during bending of the incoming ocean 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">Intermediate depth earthquakes in <span class="hlt">subducting</span> slab (~50-350 km depth) have been interpreted to occur by reactivation of faults formed at the outer rise- <span class="hlt">trench</span> prior to <span class="hlt">subduction</span>. Nevertheless, a comparison of the structure of ocean <span class="hlt">trenches</span> to focal mechanisms of the corresponding <span class="hlt">subducting</span> slab has not been possible due to the lack of high resolution information on the structure of</p> <div class="credits"> <p class="dwt_author">J. Phipps Morgan; C. R. Ranero; A. Villasenor</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">168</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/2013AGUFM.T54B..02K"> <span id="translatedtitle">Marine electromagnetics: A new tool for mapping fluids at <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 recent adoption of marine electromagnetic (EM) methods by the hydrocarbon exploration industry has driven technological innovations in acquisition hardware and modeling software that have created new opportunities for studying plate boundary structure at <span class="hlt">subduction</span> zones. Because the bulk electrical resistivity measured by EM surveys is strongly dependent on crustal porosity and hence fluid content, EM data can provide valuable constraints on crustal hydration in the incoming oceanic plate, fluids released through sediment compaction and dehydration reactions occurring after the plate is <span class="hlt">subducted</span>, and fluids escaping through the overlying forearc crust. Since water also plays an important role in regulating <span class="hlt">subduction</span> earthquake processes and frictional behavior along the plate boundary, EM data have the potential to reveal new insights on the causes of large <span class="hlt">subduction</span> zone earthquakes and their potential for generating tsunamis. As a demonstration of this novel technique, we present new results from the first controlled-source EM survey of a <span class="hlt">subduction</span> zone, carried out at the Middle America <span class="hlt">Trench</span> offshore Nicaragua in 2010. During this survey 50 seafloor EM receivers were deployed along a 280 km profile extending from the abyssal plain, across the <span class="hlt">trench</span> and onto the forearc. Controlled-source EM signals were broadcast to the receivers by deep-towing a low-frequency electric dipole transmitter close to the seafloor along the entire survey profile, generating diffusive EM waves that traveled through the crust and uppermost mantle. Non-linear two-dimensional inversion of the data reveals a significant decrease in crustal resistivity with the onset of bending faults at the <span class="hlt">trench</span> outer rise and images a continuous zone of low resistivity porous sediments being carried down with the <span class="hlt">subducting</span> plate to at least 10 km down dip from the <span class="hlt">trench</span>. Further landward at about 25 km from the <span class="hlt">trench</span>, a sub-vertical low-resistivity zone extending from the plate boundary into the overlying forearc crust is consistent with the fluid release expected from the smectite-illite transformation and occurs directly beneath the location of known seafloor fluid seeps. Potential future surveys at other margins such as Cascadia, Alaska, New Zealand and <span class="hlt">Japan</span> and integrated interpretation with other geophysical, geochemical and geological studies offers the chance for greatly enhancing our understanding of <span class="hlt">subduction</span> processes.</p> <div class="credits"> <p class="dwt_author">Key, K.; Naif, S.; Constable, S.; Evans, R. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://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 " 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://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 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/2012AGUFM.V21C..08N"> <span id="translatedtitle">Generation of adakites in a cold <span class="hlt">subduction</span> zone due to double <span class="hlt">subducting</span> 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">Adakites have been found in various tectonic settings, since the first report for the distinct lavas as a product of slab melting in Adak Island by Kay (1978). In this study, we present geochemical data for an 'adakite' and 'adakitic rock' suite in central <span class="hlt">Japan</span> with a cold <span class="hlt">subduction</span> environment due to the two overlapping subudcting plates, the Pacific Plate and the Philippine Sea Plate. Based on the major, trace and isotopic compositions of the rocks, elemental transport from initial slab inventory at the <span class="hlt">trench</span> to the volcanic rocks as a final product is quantitatively analyzed, considering the thermal structure, slab dehydration, elemental mobility, slab-fluid migration and melting of fluid-added mantle. The analysis demonstrates a large compositional impact of slab-fluid in the arc magma generation in central <span class="hlt">Japan</span>. The melting conditions have been also estimated inversely by optimizing the predicted magma composition to the observed composition of volcanic rock, with the two parameters: the degree of melting and the proportion of spinel- and garnet-lherzolites involved in melting. Consequently, a low degree of melting of dominantly garnet-lherzolite with a high fluid flux from the two overlapping slabs beneath the region has been argued to be responsible for the compositional characteristics, including the adakitic signatures, of the studied rocks. These results imply that the geochemical approach may provide useful constraints on the P-T condition of melting in the mantle wedge and the thermal structure in <span class="hlt">subduction</span> zones, being complementary to the geophysical approach. We have also applied this geochemical approach to the adjacent NE <span class="hlt">Japan</span> where the Pacific plate <span class="hlt">subducts</span>, which revealed the thermal regime in the mantle beneath the arc-arc transition.</p> <div class="credits"> <p class="dwt_author">Nakamura, H.; Iwamori, H.</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">172</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=PIA11229&hterms=pET&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DpET"> <span id="translatedtitle">Phoenix <span class="hlt">Trenches</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><p/> [figure removed for brevity, see original site] Annotated Version<p/> [figure removed for brevity, see original site] Left-eye view of a stereo pair [figure removed for brevity, see original site] Right-eye view of a stereo pair <p/> This image is a stereo, panoramic view of various <span class="hlt">trenches</span> dug by NASA's Phoenix Mars Lander. The images that make up this panorama were taken by Phoenix's Surface Stereo Imager at about 4 p.m., local solar time at the landing site, on the 131st, Martian day, or sol, of the mission (Oct. 7, 2008). <p/> In figure 1, the <span class="hlt">trenches</span> are labeled in orange and other features are labeled in blue. Figures 2 and 3 are the left- and right-eye members of a stereo pair. <p/> For scale, the 'Pet Donkey' <span class="hlt">trench</span> just to the right of center is approximately 38 centimeters (15 inches) long and 31 to 34 centimeters (12 to 13 inches) wide. In addition, the rock in front of it, 'Headless,' is about 11.5 by 8.5 centimeters (4.5 by 3.3 inches), and about 5 centimeters (2 inches) tall. <p/> The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.</p> <div class="credits"> <p class="dwt_author"></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">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/48533906"> <span id="translatedtitle">Intra-oceanic <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">\\u000a Modern intra-oceanic <span class="hlt">subduction</span> zones comprise around 17,000 km (~40%) of the convergent margins of the Earth and are subjects\\u000a of intense cross-disciplinary studies that are reviewed in this chapter. Most of these <span class="hlt">subduction</span> zones exhibit <span class="hlt">trench</span> retreat,\\u000a do not accrete sediments and are affected by back-arc extension processes. Initiation of intra-oceanic <span class="hlt">subduction</span> zones is\\u000a partly enigmatic although two major types of</p> <div class="credits"> <p class="dwt_author">T. V. Gerya</p> <p class="dwt_publisher"></p> <p class="publishDate"></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://adsabs.harvard.edu/abs/2014NatGe...7..470T"> <span id="translatedtitle">Changbaishan volcanism in northeast China linked to <span class="hlt">subduction</span>-induced mantle upwelling</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">Volcanism that occurs far from plate margins is difficult to explain with the current paradigm of plate tectonics. The Changbaishan volcanic complex, located on the border between China and North Korea, lies approximately 1,300 km away from the <span class="hlt">Japan</span> <span class="hlt">Trench</span> <span class="hlt">subduction</span> zone and is unlikely to result from a mantle plume rising from a thermal boundary layer at the base of the mantle. Here we use seismic images and three-dimensional waveform modelling results obtained from the NECESSArray experiment to identify a slow, continuous seismic anomaly in the mantle beneath Changbaishan. The anomaly extends from just below 660 km depth to the surface beneath Changbaishan and occurs within a gap in the stagnant <span class="hlt">subducted</span> Pacific Plate. We propose that the anomaly represents hot and buoyant sub-lithospheric mantle that has been entrained beneath the sinking lithosphere of the Pacific Plate and is now escaping through a gap in the <span class="hlt">subducting</span> slab. We suggest that this <span class="hlt">subduction</span>-induced upwelling process produces decompression melting that feeds the Changbaishan volcanoes. <span class="hlt">Subduction</span>-induced upwelling may also explain back-arc volcanism observed at other <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Tang, Youcai; Obayashi, Masayuki; Niu, Fenglin; Grand, Stephen P.; Chen, Yongshun John; Kawakatsu, Hitoshi; Tanaka, Satoru; Ning, Jieyuan; Ni, James F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</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://academic.research.microsoft.com/Publication/14801504"> <span id="translatedtitle">Hot spot and <span class="hlt">trench</span> volcano separations</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 suggest that the distribution of separations between <span class="hlt">trench</span> volcanoes located along <span class="hlt">subduction</span> zones reflects the depth of partial melting, and that the separation distribution for hot spot volcanoes near spreading centres provides a measure of the depth of mantle convection cells.</p> <div class="credits"> <p class="dwt_author">R. E. Lingenfelter; G. Schubert</p> <p class="dwt_publisher"></p> <p class="publishDate">1974-01-01</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://ntrs.nasa.gov/search.jsp?R=19920070460&hterms=SANDWELL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DSANDWELL"> <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://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Annular moats and outer rises around large Venus coronas such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the <span class="hlt">trenches</span> and outer rises of terrestrial <span class="hlt">subduction</span> zones. On earth, <span class="hlt">trenches</span> and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the <span class="hlt">subducted</span> slab; this lithospheric flexure model also accounts for the <span class="hlt">trenches</span> and outer rises outboard of the major coronas on Venus. Accordingly, it is proposed that retrograde lithospheric <span class="hlt">subduction</span> may be occurring on the margins of the large Venus coronas while compensating back-arc extension is occurring in the expanding coronas interiors. Similar processes may be taking place at other deep arcuate <span class="hlt">trenches</span> or chasmata on Venus such as those in the Dali-Diana chasmata area of aestern Aphrodite Terra.</p> <div class="credits"> <p class="dwt_author">Sandwell, David T.; Schubert, Gerald</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</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/1993LPI....24..235B"> <span id="translatedtitle">Buoyant <span class="hlt">subduction</span> on Venus: Implications for <span class="hlt">subduction</span> around coronae</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">Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven <span class="hlt">subduction</span> and a global system of plate tectonics/crustal recycling on that planet. No evidence for a global plate tectonic system was found so far, however, specific features strongly resembling terrestrial <span class="hlt">subduction</span> zones in planform and topographic cross-section were described, including <span class="hlt">trenches</span> around large coronae and chasmata in eastern Aphrodite Terra. The cause for the absence, or an altered expression, of plate tectonics on Venus remains to be found. Slab buoyancy may play a role in this difference, with higher lithospheric temperatures and a tendency toward positive buoyancy acting to oppose the descent of slabs and favoring under thrusting instead. The effect of slab buoyancy on <span class="hlt">subduction</span> was explored and the conditions which would lead to under thrusting versus those allowing the formation of <span class="hlt">trenches</span> and self-perpetuating <span class="hlt">subduction</span> were defined. Applying a finite element code to assess the effects of buoyant forces on slabs <span class="hlt">subducting</span> into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences <span class="hlt">subduction</span> angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease <span class="hlt">subduction</span> angle to near an under thrusting position when the <span class="hlt">subducting</span> lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, <span class="hlt">subduction</span> angles are expected to increase. An initial stage involved estimating the changes in slab buoyancy due to slab healing and pressurization over the course of <span class="hlt">subduction</span>. Modeling a slab, descending at a fixed angle and heated by conduction, radioactivity, and the heat released in phase changes, slab material density changes due to changing temperature, phase, and pressure were derived.</p> <div class="credits"> <p class="dwt_author">Burt, J. D.; Head, J. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-03-01</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://ntrs.nasa.gov/search.jsp?R=19940007658&hterms=Plate+Tectonics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3D%2522Plate%2BTectonics%2522"> <span id="translatedtitle">Buoyant <span class="hlt">subduction</span> on Venus: Implications for <span class="hlt">subduction</span> around coronae</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven <span class="hlt">subduction</span> and a global system of plate tectonics/crustal recycling on that planet. No evidence for a global plate tectonic system was found so far, however, specific features strongly resembling terrestrial <span class="hlt">subduction</span> zones in planform and topographic cross-section were described, including <span class="hlt">trenches</span> around large coronae and chasmata in eastern Aphrodite Terra. The cause for the absence, or an altered expression, of plate tectonics on Venus remains to be found. Slab buoyancy may play a role in this difference, with higher lithospheric temperatures and a tendency toward positive buoyancy acting to oppose the descent of slabs and favoring under thrusting instead. The effect of slab buoyancy on <span class="hlt">subduction</span> was explored and the conditions which would lead to under thrusting versus those allowing the formation of <span class="hlt">trenches</span> and self-perpetuating <span class="hlt">subduction</span> were defined. Applying a finite element code to assess the effects of buoyant forces on slabs <span class="hlt">subducting</span> into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences <span class="hlt">subduction</span> angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease <span class="hlt">subduction</span> angle to near an under thrusting position when the <span class="hlt">subducting</span> lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, <span class="hlt">subduction</span> angles are expected to increase. An initial stage involved estimating the changes in slab buoyancy due to slab healing and pressurization over the course of <span class="hlt">subduction</span>. Modeling a slab, descending at a fixed angle and heated by conduction, radioactivity, and the heat released in phase changes, slab material density changes due to changing temperature, phase, and pressure were derived.</p> <div class="credits"> <p class="dwt_author">Burt, J. D.; Head, J. W.</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">179</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/2013AGUFMDI33A2224F"> <span id="translatedtitle">Global overview of <span class="hlt">subduction</span> 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">In the framework of the EURYI Project ';Convergent margins and seismogenesis: defining the risk of great earthquakes by using statistical data and modelling', we propose the first global overview of <span class="hlt">subduction</span> seismicity. Previous studies have been focused on interplate seismicity, intraslab seismicity, upper plate deformation, or relation between interplate and intraslab seismicity, but the three components of <span class="hlt">subduction</span> seismicity have been never approached in an systematic and exhaustive study. To allow such a study, nodal planes and seismic moments of worldwide <span class="hlt">subduction</span>-related earthquakes heve been extracted by EHB hypocenter and CMT Harvard catalogues for the period 1976 - 2007. Data were collected for centroid depths between sea level and 700 km and for magnitude Mw 5.5. For each <span class="hlt">subduction</span> zone, a set of <span class="hlt">trench</span>-normal transects were constructed choosing a 120km width of the cross-section on each side of a vertical plane and a spacing of 1 degree along the <span class="hlt">trench</span>. For each of the 505 resulting transects, the whole <span class="hlt">subduction</span> seismogenic zone was mapped as focal mechanisms projected on to a vertical plane after their faulting type classification according to the Aki-Richards convention. Transect by transect, fist the seismicity that can be considered not related to the <span class="hlt">subduction</span> process under investigation was removed, then was selected the upper plate seismicity (i.e. earthquakes generated within the upper plate as a result of the <span class="hlt">subduction</span> process). After deletion from the so obtained event subset of the interplate seismicity as identified in the framework of this project by Heuret et al. (2011), we can be reasonably confident that the remaining seismicity can be related to the <span class="hlt">subducting</span> plate. Among these earthquakes we then selected the shallow (0-70 km), intermediate (70-300 km) and deep (300-660 km) depth seismicity. Following Heuret et al. (2011), the 505 transects were merged into 62 larger segments that were ideally homogeneous in terms of their seismogenic zone characteristics. For each <span class="hlt">subduction</span> around the world, interplate, intraslab and upper plate seismicity have been estimated and compared to each other through several parameters (seismic rate, moment released rate, maximal expressed magnitude) order to obtain a snapshot on the general behaviour of global <span class="hlt">subduction</span>-related seismicity. In a second step, the seismological parameters have been compared to long-term geodynamical parameters (e.g., <span class="hlt">subduction</span> velocity, plate and <span class="hlt">trench</span> absolute motions, slab age, thermal parameter and geometry, sediment thickness at <span class="hlt">trench</span>) with the aim to find possible cause-effect relationships.</p> <div class="credits"> <p class="dwt_author">Funiciello, F.; Presti, D.; Heuret, A.; Piromallo, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2014EGUGA..16.9819S"> <span id="translatedtitle">Approximate General Coulomb Model for Accretionary Prisms: An Integrated Study of the Kumano Transect, 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In accretionary wedges, the mechanical and hydrologic properties along splay faults and the plate boundary fault at the base of the wedge are intimately related to properties within the wedge itself, as well as to sedimentation and/or mass wasting at the wedge surface, and accretionary flux at the wedge toe; Coulomb wedge theories tie these processes together and have been successful in their application to convergent margins. Most such theories assume for the sake of simplicity that mechanical parameters (e.g. bulk density, compressibility, frictional strength) and pore pressure are constant throughout the overlying wedge. However, the values of these parameters must necessarily change with depth and distance from the <span class="hlt">trench</span>. Here, we derive a model for a fully general Coulomb wedge, parameterized using data specific to the Kumano transect at Nankai, to better understand the location of the basal plate interface and the properties of material composing an actively accretionary prism. We use shear strength data collected for incoming sediments at Integrated Ocean Drilling Program Site C0011 of the NanTroSEIZE project to parameterize the wedge's coefficient of friction. Preliminary results of models where the friction coefficient of the wedge decreases with depth, with other parameters constant and zero cohesion, indicate that including depth dependent frictional strength in the wedge decreases the taper angle of the wedge, with the effect becoming more pronounced with distance from the <span class="hlt">trench</span>. This model will be further refined by including seismically and numerically determined spatial variations in fluid pressure within the wedge, as well as detailed locations of the upper and basal wedge surfaces along the Kumano transect determined from 3-D seismic data.</p> <div class="credits"> <p class="dwt_author">Skarbek, Rob; Ikari, Matt; Hüpers, Andre; Rempel, Alan; Wilson, Dean; Kitajima, Hiroko</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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 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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_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://www.aob.geophys.tohoku.ac.jp/~nakajima/research/article/PDF/Tsuji_GRL_2008.pdf"> <span id="translatedtitle">Tomographic evidence for hydrated oceanic crust of the Pacific slab beneath northeastern <span class="hlt">Japan</span>: Implications for water transportation in <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">We estimate detailed seismic-velocity structure around the Pacific slab beneath northeastern <span class="hlt">Japan</span> by double-difference tomography. A remarkable low-velocity zone with a thickness of ~10 km, which corresponds to much hydrated oceanic crust, is imaged coherently along the arc at the uppermost part of the slab. The zone gradually disappears at depths of 70-90 km, suggesting the occurrence of intensive dehydration</p> <div class="credits"> <p class="dwt_author">Yusuke Tsuji; Junichi Nakajima; Akira Hasegawa</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">182</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/gl/gl0814/2008GL034461/2008GL034461.pdf"> <span id="translatedtitle">Tomographic evidence for hydrated oceanic crust of the Pacific slab beneath northeastern <span class="hlt">Japan</span>: Implications for water transportation in <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">We estimate detailed seismic-velocity structure around the Pacific slab beneath northeastern <span class="hlt">Japan</span> by double-difference tomography. A remarkable low-velocity zone with a thickness of ?10 km, which corresponds to much hydrated oceanic crust, is imaged coherently along the arc at the uppermost part of the slab. The zone gradually disappears at depths of 70–90 km, suggesting the occurrence of intensive dehydration</p> <div class="credits"> <p class="dwt_author">Yusuke Tsuji; Junichi Nakajima; Akira Hasegawa</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">183</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/2013CoMP..165.1107N"> <span id="translatedtitle">Generation of adakites in a cold <span class="hlt">subduction</span> zone due to double <span class="hlt">subducting</span> 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">Adakites have been found in various tectonic settings, since the first report for the distinct lavas as a product of slab melting in Adak Island by Kay (J Volcanol Geotherm Res 4:117-132, 1978). In this study, we present geochemical data for an `adakite' and `adakitic rock' suite in central <span class="hlt">Japan</span> with a cold <span class="hlt">subduction</span> environment due to the two overlapping <span class="hlt">subducting</span> plates: the Pacific plate and the Philippine sea plate. Based on the major, trace and isotopic compositions of the rocks, elemental transport from initial slab inventory at the <span class="hlt">trench</span> to the volcanic rocks as a final product is quantitatively analyzed, considering the thermal structure, slab dehydration, elemental mobility, slab-fluid migration and melting of fluid-added mantle. The analysis demonstrates a large compositional impact of slab-fluid in the arc magma generation in central <span class="hlt">Japan</span>. The melting conditions have been also estimated inversely by optimizing the predicted magma composition to the observed composition of volcanic rock, with the two parameters: the degree of melting and the proportion of spinel and garnet lherzolites involved in melting. Consequently, a moderately low degree of near-solidus melting of dominantly garnet lherzolite with a high fluid flux from the two overlapping slabs beneath the region has been argued to be responsible for the compositional characteristics, including the adakitic signatures, of the studied rocks. These results imply that the geochemical approach may provide useful constraints on the P- T condition of melting in the mantle wedge and the thermal structure in <span class="hlt">subduction</span> zones, being complementary to the geophysical approach.</p> <div class="credits"> <p class="dwt_author">Nakamura, Hitomi; Iwamori, Hikaru</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">184</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/2013AGUFM.G23B0780M"> <span id="translatedtitle">Characterizing decadal transient deformation and aseismic fault slip in the northeastern <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone prior to the 2011 M 9 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">Postseismic deformation and slow-slip events are well documented by modern geodesy, yet transient deformation not related to postseismic effects spanning decades has not yet been observed. From analysis of GPS data from <span class="hlt">Japan</span>'s GEONET, we previously reported spatially coherent patterns of transient deformation in various regions of <span class="hlt">Japan</span>, spanning the 15 years prior to the 2011 M 9 Tohoku earthquake. While several of these transients are clearly postseismic effects, an apparent decrease in the rate of deformation in southeastern Tohoku is surprising, since it implies a decadal decrease in the degree of coupling on the plate interface prior to the 2011 M 9 Tohoku earthquake. Given that this inference, if correct, has profound implications for our understanding of the earthquake cycle, it is important to investigate how assumptions in removing postseismic deformation due to the many M 6 and 7 earthquakes during this time period may bias the estimation of residual transient deformation. The ultimate question is whether there is robust evidence for accelerating aseismic slip on the plate interface and, if so, how its spatial distribution compares with known locked ';asperities', including the rupture area of the M 9 Tohoku earthquake. To correct for postseismic slip of M > 6.3 earthquakes, we construct a model of the <span class="hlt">Japan</span> <span class="hlt">trench</span> plate interface, which consists of circular asperities that represent rupture areas of interplate earthquakes that occurred after 2003. Coseismic slip distributions are computed assuming uniform stress drops. Afterslip is assumed to be space-time separable, with its temporal evolution represented by the solution for a steady-state, rate-strengthening spring-slider including steady load-point velocity. The spatial distribution of cumulative afterslip is computed such that it fully relaxes coseismic stress increase anywhere on the fault except for the asperities, which remain locked. Surface displacements are then computed using elastic half-space Green's functions. Preliminary results reveal that the patterns of coseismic and time-dependent postseismic surface displacements predicted from this model are in good agreement with GPS observations. Notably, the data require afterslip from two earthquakes before 2011 overlapping the coseismic slip area of the M 9 Tohoku earthquake. Removing postseismic effects as accurately as possible, including the effects of intraplate earthquakes, will provide a robust estimate of any residual transient deformation, and hence inference of as yet unexplained transient slip on the plate interface, in the years leading up to the Tohoku earthquake.</p> <div class="credits"> <p class="dwt_author">Mavrommatis, A. P.; Johnson, K. M.; Segall, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2012AGUFM.T14A..02B"> <span id="translatedtitle">Seismic behavior and geodetic locking in areas of rough seafloor <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"><span class="hlt">Subduction</span> of rough seafloor occurs throughout the global <span class="hlt">subduction</span> zones. This rough seafloor introduces heterogeneity in the fault zone that will affect the geodetic coupling and earthquake behavior in these regions. It is often hypothesized that large earthquakes are linked to the presence of <span class="hlt">subducted</span> seamounts, even as recently as for the 2011 M=9 Tohoku earthquake. However, detailed study of the northern <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone suggests fairly smooth incoming seafloor in the main Tohoku slip zone, with very rough seafloor <span class="hlt">subducting</span> near the southern terminus of the 2011 rupture. This rough zone, which includes a large seamount, had been geodetically defined as a partially locked, or creeping, portion of the megathrust. These rough zones also produce smaller magnitude earthquakes rather than the M 8 or 9 earthquakes observed in zones with smoother incoming plate. We propose here that megathrust fault creep is fairly common in areas of rough incoming plate, and that it is increasingly being illuminated by denser seismic and geodetic observations. Segments of the Costa Rica margin show heterogeneity in earthquake magnitude and geodetic coupling that mimic the heterogeneity in the incoming Cocos Plate. The Nazca Ridge <span class="hlt">subducting</span> offshore Peru has repeatedly served as a rupture barrier for adjacent great earthquakes, and recent geodetic modeling suggests the megathrust is primarily creeping where the ridge <span class="hlt">subducts</span>. Along the northern Hikurangi margin, several large seamounts <span class="hlt">subduct</span> in the region of frequent small-medium sized earthquakes. The <span class="hlt">subduction</span> fault is geodetically shown to undergo significant creeping that is episodically manifested as near-<span class="hlt">trench</span> slow slip events. The classic end-member Marianas <span class="hlt">subduction</span> zone is another example of a <span class="hlt">subduction</span> zone with very heterogeneous incoming plate that is likely creeping, producing only small magnitude earthquakes. These rough areas are in contrast to <span class="hlt">subduction</span> zones with fairly smooth incoming plate, such as Chile, Alaska, Cascadia, Sumatra, and Nankai, which have a history of great earthquakes and little to no creep during the interseismic period. To explain the seismic and geodetic observations of these areas, we suggest a model where the rough seafloor <span class="hlt">subducts</span> predominantly aseismically. Deformation and small magnitude earthquakes occur in the structurally complex fault zone and within fracture networks in the upper and lower plates. The complex structure and heterogeneous stresses of this environment provide a favorable condition for aseismic creep and small earthquakes but an unfavorable condition for the generation and propagation of large ruptures.</p> <div class="credits"> <p class="dwt_author">Bilek, S. L.; Wang, K.</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">186</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=ainu&id=EJ340786"> <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">Analyzes the intergroup relations in Japanese society and <span class="hlt">Japan</span>'s educational system. Challenges the view that <span class="hlt">Japan</span> is a homogeneous society by presenting the various forms of discrimination against Koreans, Ainu, and the burakumin. Suggests that despite ostracism and isolation, groups can affect public policy and achieve social advancement. (SA)</p> <div class="credits"> <p class="dwt_author">Hawkins, John N.</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">187</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/2012AGUFM.T13C2625I"> <span id="translatedtitle">Crustal structure and configuration of the <span class="hlt">subducting</span> Philippine Sea plate beneath the Pacific coast industrial zone in <span class="hlt">Japan</span> inferred from receiver function 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 apply receiver function (RF) analyses to estimate the crustal structure and configuration of the <span class="hlt">subducting</span> Philippine Sea (PHS) plate beneath the Pacific coast industrial zone stretching from Tokyo to Fukuoka in <span class="hlt">Japan</span>. Destructive earthquakes often occurred at the plate interface of the PHS plate, and seismic activities increase after the 2011 Tohoku earthquake (Mw9.0) around the Tokyo metropolitan area. Investigation on the crustal structure is the key to understanding the stress concentration and strain accumulation process, and information on configuration of the <span class="hlt">subducting</span> plate is important to mitigate future earthquake disasters. In this study, we searched for the best-correlated velocity structure model between an observed receiver function at each station and synthetic ones by using a grid search method. Synthetic RFs were calculated from many assumed one-dimensional velocity structures that consist of four layers with positive velocity steps. Observed receiver functions were stacked without considering back azimuth or epicentral distance. We further constructed the vertical cross-sections of depth-converted RF images transformed the lapse time of time series to depth by using the estimated structure models. Telemetric seismographic network data covered on the Japanese Islands including the Metropolitan Seismic Observation network, which constructed under the Special Project for Earthquake Disaster Mitigation in the Tokyo Metropolitan area and maintained by Special Project for Reducing Vulnerability for Urban Mega Earthquake Disasters, are used. We selected events with magnitudes greater or equal to 5.0 and epicentral distance between 30 and 90 degrees based on USGS catalogues. As a result, we clarify spatial distributions of the crustal S-wave velocities. Estimated average one-dimensional S-wave velocity structure is approximately equal to the JMA2011 structural model although the velocity from the ground surface to 5 km in depth is slow. In particular, the Kanto plain and Boso peninsula are covered in thick sediment layers. The velocity perturbations in the crust are consistent with existing tomography models. There are low-velocity zones in the upper crust to the crust-mantle boundary corresponding to volcanoes. In contrast, non-volcanic mountain foothills are relatively high-velocity zones. We also elucidated the configuration of PHS plate to a depth of about 60 km. The PHS plate <span class="hlt">subducts</span> to the northwest and the direction coincides with plate motion. The northeastern margin of PHS plate is estimated from the plate thickness, which gradually decreases to the northeast after contact with the underlying Pacific plate beneath the Tokyo metropolitan area. Asperities of some large earthquakes seem to be corresponded to the high-velocity area in the PHS slab. On the other hand, non-volcanic low-frequency earthquakes located in the plate interface are characterized by relatively low-velocity areas. They may indicate the serpentinized mantle wedge which reflects dehydration of the <span class="hlt">subducting</span> oceanic crust.</p> <div class="credits"> <p class="dwt_author">Igarashi, T.; Iidaka, T.; Sakai, S.; Hirata, N.</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">188</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 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://ntrs.nasa.gov/search.jsp?R=19740052372&hterms=hot+Volcanos&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dhot%2BVolcanos"> <span id="translatedtitle">Hot spot and <span class="hlt">trench</span> volcano separations</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">It is suggested that the distribution of separations between <span class="hlt">trench</span> volcanos located along <span class="hlt">subduction</span> zones reflects the depth of partial melting, and that the separation distribution for hot spot volcanoes near spreading centers provides a measure of the depth of mantle convection cells. It is further proposed that the lateral dimensions of mantle convection cells are also represented by the hot-spot separations (rather than by ridge-<span class="hlt">trench</span> distances) and that a break in the distribution of hot spot separations at 3000 km is evidence for both whole mantle convection and a deep thermal plume origin of hot spots.</p> <div class="credits"> <p class="dwt_author">Lingenfelter, R. E.; Schubert, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1974-01-01</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://adsabs.harvard.edu/abs/1984STIN...8427005Z"> <span id="translatedtitle">A critical assessment of viscous models of <span class="hlt">trench</span> topography and corner 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">Stresses for Newtonian viscous flow in a simple geometry (e.g., corner flow, bending flow) are obtained in order to study the effect of imposed velocity boundary conditions. Stress for a delta function velocity boundary condition decays as 1/R(2); for a step function velocity, stress goes as 1/R; for a discontinuity in curvature, the stress singularity is logarithmic. For corner flow, which has a discontinuity of velocity at a certain point, the corresponding stress has a 1/R singularity. However, for a more realistic circular-slab model, the stress singularity becomes logarithmic. Thus the stress distribution is very sensitive to the boundary conditions, and in evaluating the applicability of viscous models of <span class="hlt">trench</span> topography it is essential to use realistic geometries. Topography and seismicity data from northern Hoshu, <span class="hlt">Japan</span>, were used to construct a finite element model, with flow assumed tangent to the top of the grid, for both Newtonian and non-Newtonian flow (power law 3 rheology). Normal stresses at the top of the grid are compared to the observed <span class="hlt">trench</span> topography and gravity anomalies. There is poor agreement. Purely viscous models of <span class="hlt">subducting</span> slables with specified velocity boundary conditions do not predict normal stress patterns compatible with observed topography and gravity. Elasticity and plasticity appear to be important for the <span class="hlt">subduction</span> process.</p> <div class="credits"> <p class="dwt_author">Zhang, J.; Hager, B. H.; Raefsky, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-06-01</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/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">192</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/2014EGUGA..16.3976J"> <span id="translatedtitle">Structure and properties of the lithosphere <span class="hlt">subducting</span> beneath Indonesia, consequences on <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">We make inferences on the structure, age and physical properties of the <span class="hlt">subducting</span> northern Wharton Basin lithosphere by (1) modeling the structure and age of the lithosphere <span class="hlt">subducted</span> under the Sumatra <span class="hlt">trench</span> through two- and three-plate reconstructions involving Australia, Antarctica, and India, and (2) superimposing the resulting fracture zones and magnetic isochrons to the geometry of the <span class="hlt">subducting</span> plate as imaged by seismic tomography. This model provides an effective means to study the effect of varying physical properties of the <span class="hlt">subducting</span> lithosphere on the <span class="hlt">subduction</span> along the Sumatra <span class="hlt">trench</span>. The age of the oceanic lithosphere determines its thickness and buoyancy, then its ability to comply with or resist <span class="hlt">subduction</span>. The "<span class="hlt">subductability</span>" of the lithosphere is the extra weight applied on the asthenosphere by the part of the bulk lithospheric density exceeding the asthenospheric density. A negative <span class="hlt">subductability</span> means that the bulk lithospheric density is lower than the asthenospheric density, i.e. the plate will resist <span class="hlt">subduction</span>, which is the case for lithosphere younger than ~23 Ma. The area off Sumatra corresponds to oceanic lithosphere formed between 80 and 38 Ma, with a lower <span class="hlt">subductability</span> than other areas along the Sunda <span class="hlt">Trench</span>. The spreading rate at which the oceanic lithosphere was formed has implications of the structure and composition of the oceanic crust, and therefore on its rheology. In a <span class="hlt">subduction</span> zone, the contact between the <span class="hlt">subducting</span> and overriding plates is considered to be the top of the oceanic crust and the overlying sediments. The roughness of this interface and the rheology of its constitutive material are essential parameters constraining the slip of the downgoing plate in the seismogenic zone, and therefore the characteristics of the resulting earthquakes. Whereas the rough topography of a slow crust may offer more asperities than the smooth topography of a fast crust, the weak rheology of serpentines in a slow crust would favor a regular slip, unlike the brittle magmatic rocks of the fast crust and the underlying dry olivine mantle. The presence of peculiar features such as fracture zones, seamounts, or oceanic plateaus also affects the seismic segmentation of the <span class="hlt">subduction</span> zone at different scales. Many seamounts have been mapped in the Wharton Basin between 10°S and 15°S, and similar seamounts belonging to the same province may have existed further north and <span class="hlt">subducted</span> in the Sunda <span class="hlt">Trench</span> from southern Sumatra to Java and eastward. Conversely, the Roo Rise, a larger plateau located south of Eastern Java, may resist the <span class="hlt">subduction</span>, as suggested by the geometry of the Sunda <span class="hlt">Trench</span> in this area, diverting from the regular arc by a maximum of 60 km.</p> <div class="credits"> <p class="dwt_author">Jacob, Jensen; Dyment, Jerome</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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://www.ncbi.nlm.nih.gov/pubmed/12904789"> <span id="translatedtitle">Unusually large earthquakes inferred from tsunami deposits 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://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The Pacific plate converges with northeastern Eurasia at a rate of 8-9 m per century along the Kamchatka, Kuril and <span class="hlt">Japan</span> <span class="hlt">trenches</span>. Along the southern Kuril <span class="hlt">trench</span>, which faces the Japanese island of Hokkaido, this fast <span class="hlt">subduction</span> has recurrently generated earthquakes with magnitudes of up to approximately 8 over the past two centuries. These historical events, on rupture segments 100-200 km long, have been considered characteristic of Hokkaido's plate-boundary earthquakes. But here we use deposits of prehistoric tsunamis to infer the infrequent occurrence of larger earthquakes generated from longer ruptures. Many of these tsunami deposits form sheets of sand that extend kilometres inland from the deposits of historical tsunamis. Stratigraphic series of extensive sand sheets, intercalated with dated volcanic-ash layers, show that such unusually large tsunamis occurred about every 500 years on average over the past 2,000-7,000 years, most recently approximately 350 years ago. Numerical simulations of these tsunamis are best explained by earthquakes that individually rupture multiple segments along the southern Kuril <span class="hlt">trench</span>. We infer that such multi-segment earthquakes persistently recur among a larger number of single-segment events. PMID:12904789</p> <div class="credits"> <p class="dwt_author">Nanayama, Futoshi; Satake, Kenji; Furukawa, Ryuta; Shimokawa, Koichi; Atwater, Brian F; Shigeno, Kiyoyuki; Yamaki, Shigeru</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-08-01</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://dx.doi.org/10.1038/nature01864"> <span id="translatedtitle">Unusually large earthquakes inferred from tsunami deposits 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://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">The Pacific plate converges with northeastern Eurasia at a rate of 8-9 m per century along the Kamchatka, Kuril and <span class="hlt">Japan</span> <span class="hlt">trenches</span>. Along the southern Kuril <span class="hlt">trench</span>, which faces the Japanese island of Hokkaido, this fast <span class="hlt">subduction</span> has recurrently generated earthquakes with magnitudes of up to ???8 over the past two centuries. These historical events, on rupture segments 100-200 km long, have been considered characteristic of Hokkaido's plate-boundary earthquakes. But here we use deposits of prehistoric tsunamis to infer the infrequent occurrence of larger earthquakes generated from longer ruptures. Many of these tsunami deposits form sheets of sand that extend kilometres inland from the deposits of historical tsunamis. Stratigraphic series of extensive sand sheets, intercalated with dated volcanic-ash layers, show that such unusually large tsunamis occurred about every 500 years on average over the past 2,000-7,000 years, most recently ???350 years ago. Numerical simulations of these tsunamis are best explained by earthquakes that individually rupture multiple segments along the southern Kuril <span class="hlt">trench</span>. We infer that such multi-segment earthquakes persistently recur among a larger number of single-segment events.</p> <div class="credits"> <p class="dwt_author">Nanayama, F.; Satake, K.; Furukawa, R.; Shimokawa, K.; Atwater, B. F.; Shigeno, K.; Yamaki, S.</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">195</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/2012AGUFM.V31B2779F"> <span id="translatedtitle">Amplitude Comparison of Teleseismic P-Wave Phases from the <span class="hlt">Japan</span> <span class="hlt">Subduction</span> Zone and the South Sandwich Islands recorded at Uturuncu Volcano, Bolivia</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">Uturuncu volcano (22° 15' S, 67° 12'W) has been shown to be inflating at a rate of 1-1.5 cm per year by a satellite geodetic survey from May 1996-present. This inflation is centered just southwest of the volcano's summit and at a depth of 15-17 km. This may be caused by the injection of magma into the system. Seismic studies performed as part of the multi-university PLUTONS project can help constrain the location and nature of this inflation. By looking at how teleseismic peak-to-peak waveform amplitudes (velocities in nm/s) vary across the network, we can begin to pinpoint the size and location of attenuating zones beneath the edifice. Analysis of 5 P-wave phases from 4 earthquakes with origins in the <span class="hlt">Japan</span> <span class="hlt">subduction</span> zone (NW of the network, ~155° distant) shows a consistent 'shadow zone' of decreased amplitudes in a 13.6 by 33.3 km zone to the SE of the summit. Observations from two teleseismic events originating in the South Sandwich Islands (~45° distant) show similar effects although the geometry differs with respect to individual stations. We expect this trend to hold true for events originating to the NE and SW of the volcano, which would indicate a zone of decreased amplitude in the same region SE of the summit. The attenuation of P-waves that would otherwise be of uniform amplitude could be the result of some ray paths traveling through a shallow, low-velocity and highly attenuating zone of either magma/mush, highly fractured rock, or some other cause. This attenuating zone may be located at or near the center of the inflation zone, and physical processes associated with it could well be closely related to the observed inflation.</p> <div class="credits"> <p class="dwt_author">Farrell, A. K.; McNutt, S. R.; West, M. E.</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">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/2013AGUFM.G44A..04M"> <span id="translatedtitle">Finite element modeling on stress field of <span class="hlt">subduction</span> zones and island arcs during megathrust earthquake 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">A <span class="hlt">subduction</span> zone earthquake cycle includes a great earthquake and subsequent strain accumulation in to the next earthquake. Such cycles in viscoelastic earth perturbs crustal stresses. The observations of shear-wave splitting during crustal earthquakes in the forearc of the NE <span class="hlt">Japan</span> have revealed the presence of almost NS polarization azimuths, while the volcanic front to backarc show the EW polarization azimuths. This indicates that the stress field in the forearc crust is not horizontal EW compression during the interseismic period. In order to clarify how crustal stress fields are perturbed during earthquake cycles, we have conducted a finite element model on <span class="hlt">subduction</span> zones earthquake cycles in the NE <span class="hlt">Japan</span>. We developed a two-dimensional finite element model oriented perpendicular to the <span class="hlt">Japan</span> <span class="hlt">Trench</span> extending 1000 km to the west and 600 km to the east of the <span class="hlt">Trench</span> and 800 km depth. The model also transects an area of large coseismic slip of the 2011 Tohoku Oki earthquake with the slip magnitude exceeding 60 m. The subsurface crustal and mantle wedge structures, and <span class="hlt">subducting</span> slab geometry were developed based on an offshore seismic reflection survey and high-precision seismic tomography of the crust, mantle wedge structures, and <span class="hlt">subducting</span> slab in this region. Deformation along plate boundary is the kinematically assigned using the split node method. For a <span class="hlt">subduction</span> plate boundary, a shallow portion is assumed to be locked and from a certain depth downdip, the boundary is assumed to slip at the full plate convergence rate of 80 mm/yr during interseismic period. At the coseismic step, the amount of slip corresponding to slip deficit during the interseismic period is achieved along the shallow portion. From preliminary results for cycles up to 10 earthquakes, the horizontal stress was oscillated through the cycles: horizontal EW compression during interseismic periods and sudden extension by coseismic deformations. The horizontal stress in the shallower portion of the forearc side just prior to an earthquake gradually becomes extension regime with cycles. The portion of this extension regime roughly corresponds to the region with NS polarization azimuths of the shear wave splitting of crustal earthquakes in the NE <span class="hlt">Japan</span>. This indicates that the formation of extensional stress regime in the forearc during intersesimic period might be originated from the buckling of the island arc lithosphere and relaxation of compressive stress during the intersesimic period.</p> <div class="credits"> <p class="dwt_author">Muto, J.; Shibazaki, B.; Iidaka, T.; Ohzono, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://ntrs.nasa.gov/search.jsp?R=20060035731&hterms=subduction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dsubduction"> <span id="translatedtitle">GPS Monitoring of <span class="hlt">Subduction</span> Zone Deformation in Costa Rica</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The <span class="hlt">subduction</span> of the Cocos plate beneath Costa Rica is among the highest convergence rates in the world. The high <span class="hlt">subduction</span> rate and nearness of the Nicoya Peninsula, Costa Rica to the Middle America <span class="hlt">Trench</span> (MAT) provide a unique opportunity to map variations in interseismic strain of the crust above the seismogenic zone in response to variations in seismic coupling.</p> <div class="credits"> <p class="dwt_author">Lundgren, Paul</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</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://adsabs.harvard.edu/abs/2014GeoJI.197.1627B"> <span id="translatedtitle">Scattering beneath Western Pacific <span class="hlt">subduction</span> zones: evidence for oceanic crust in the mid-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">Small-scale heterogeneities in the mantle can give important insight into the dynamics and composition of the Earth's interior. Here, we analyse seismic energy found as precursors to PP, which is scattered off small-scale heterogeneities related to <span class="hlt">subduction</span> zones in the upper and mid-mantle. We use data from shallow earthquakes (less than 100 km depth) in the epicentral distance range of 90°-110° and use array methods to study a 100 s window prior to the PP arrival. Our analysis focuses on energy arriving off the great circle path between source and receiver. We select coherent arrivals automatically, based on a semblance weighted beampower spectrum, maximizing the selection of weak amplitude arrivals. Assuming single P-to-P scattering and using the directivity information from array processing, we locate the scattering origin by ray tracing through a 1-D velocity model. Using data from the small-aperture Eielson Array (ILAR) in Alaska, we are able to image structure related to heterogeneities in western Pacific <span class="hlt">subduction</span> zones. We find evidence for ˜300 small-scale heterogeneities in the region around the present-day <span class="hlt">Japan</span>, Izu-Bonin, Mariana and West Philippine <span class="hlt">subduction</span> zones. Most of the detected heterogeneities are located in the crust and upper mantle, but 6 per cent of scatterers are located deeper than 600 km. Scatterers in the transition zone correlate well with edges of fast features in tomographic images and <span class="hlt">subducted</span> slab contours derived from slab seismicity. We locate deeper scatterers beneath the Izu-Bonin/Mariana <span class="hlt">subduction</span> zones, which outline a steeply dipping pseudo-planar feature to 1480 km depth, and beneath the ancient (84-144 Ma) Indonesian <span class="hlt">subduction</span> <span class="hlt">trench</span> down to 1880 km depth. We image the remnants of <span class="hlt">subducted</span> crustal material, likely the underside reflection of the <span class="hlt">subducted</span> Moho. The presence of deep scatterers related to past and present <span class="hlt">subduction</span> provides evidence that the <span class="hlt">subducted</span> crust does descend into the lower mantle at least for these steeply dipping <span class="hlt">subduction</span> zones. Applying the same technique to other source-receiver paths will increase our knowledge of the small-scale structure of the mantle and will provide further constraints on geodynamic models.</p> <div class="credits"> <p class="dwt_author">Bentham, H. L. M.; Rost, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</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/2011AGUFM.T51G2447C"> <span id="translatedtitle">A Crustal Structure Study of the Southern Ryukyu <span class="hlt">Subduction</span> Zone by Using the Aftershock 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 region along the Ryukyu <span class="hlt">subduction</span> zone is known as a tsunami disaster zone. The biggest tsunami (85 m) of <span class="hlt">Japan</span> history was recorded in the Ishigaki Island, Ryukyu, in 1771. The paleo-tsunami events show that it has a frequency of about 150 years. This thread makes the Ryukyu <span class="hlt">subduction</span> zone as a concerned field for the earthquake studies. However, due to the long distance from the east coast of Taiwan, this is an area out of the effective earthquake detection zone from the Central Weather Bureau network. A main shock of M = 6.9 occurred near the Ishigaki Island in 2009 August 17. After this event, we quickly deployed the OBS and found many aftershocks with the magnitude greater than 5.0. The main shock was 240 km, NE direction from the Hualien city, Taiwan. If a tsunami occurred, it took only less than 15 minutes to arrive the coast. From the recorded data, we picked the P- and S-wave using the 1-D module (iasp91). There were 1500 recorded events during those time range, and most of the earthquakes were located around the Nanao Basin. Based on this, we study the southern Ryukyu <span class="hlt">subduction</span> zone structure by using the results from focal mechanism solution. From the earthquake relocation it shows that two main groups of aftershocks. They tend in northwest - southeast with a left-lateral strike-slip fault. The left-lateral strike-slip fault is the main structures that link with the splay faults at the southern Ryukyu <span class="hlt">Trench</span>. The stability and extension of the splay faults are one of the major concerns for the occurrence of mega earthquake. More than 500-km long of the splay fault, such as that in the Indonesia, Chile and <span class="hlt">Japan</span> <span class="hlt">subduction</span> zones, has attacked by mega earthquakes in the recent years. The second group of those aftershocks was located in the Gagua Ridge near the Ryukyu <span class="hlt">Trench</span>. This group may represent the ridge structure relate to the Taitung canyon fault. The front of Ryukyu <span class="hlt">Trench</span> was being as a locked <span class="hlt">subduction</span> zone where it is easily to accumulate the earthquake stress. Because of these two earthquake groups are out of range of Taiwan Central Weather Bureau network and lack of information, it is worthwhile to focus our attentions on it.</p> <div class="credits"> <p class="dwt_author">Cho, Y.; Lin, J.; Lee, C.</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">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/2011EOSTr..92...91S"> <span id="translatedtitle">Strong Quake Strikes <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">As Eos was about to go to press, a powerful earthquake with a preliminary estimated magnitude of 8.9 shook the northeast coast of <span class="hlt">Japan</span> on 11 March at 05:46:23 UTC. It is the largest known earthquake along the <span class="hlt">Japan</span> <span class="hlt">Trench</span> <span class="hlt">subduction</span> zone since 869 A.D. or earlier, Brian Atwater, geologist with the U.S. Geological Survey (USGS), told Eos. The quake's magnitude would place it fifth in terms of any earthquake magnitude worldwide since at least 1900, according to information from the USGS Earthquake Hazards Program. The amount of energy released in the quake—which occurred 130 kilometers east of Sendai, Honshu, at a depth of 24.4 kilometers—was equivalent to the energy from 30 earthquakes the size of the 1906 quake in San Francisco, Calif., according to David Applegate, USGS senior science advisor for earthquake and geologic hazards. He said the economic losses from the shaking are estimated to be in the tens of billions of dollars.</p> <div class="credits"> <p class="dwt_author">Showstack, Randy</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-03-01</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" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' 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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://adsabs.harvard.edu/abs/2013EaSci.tmp...16H"> <span id="translatedtitle">Focal depth, magnitude, and frequency distribution of earthquakes along oceanic <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">The occurrence of earthquakes in oceanic <span class="hlt">trenches</span> can pose a tsunami threat to lives and properties in active seismic zones. Therefore, the knowledge of focal depth, magnitude, and time distribution of earthquakes along the <span class="hlt">trenches</span> is needed to investigate the future occurrence of earthquakes in the zones. The oceanic <span class="hlt">trenches</span> studied, were located from the seismicity map on: latitude +51° to +53° and longitude -160° to 176° (Aleutian <span class="hlt">Trench</span>), latitude +40° to +53° and longitude +148° to +165° (<span class="hlt">Japan</span> <span class="hlt">Trench</span>), and latitude -75° to -64° and longitude -15° to +30° (Peru-Chile <span class="hlt">Trench</span>). The following features of seismic events were considered: magnitude distribution, focal depth distribution, and time distribution of earthquake. The results obtained in each <span class="hlt">trench</span> revealed that the earthquakes increased with time in all the regions. This implies that the lithospheric layer is becoming more unstable. Thus, tectonic stress accumulation is increasing with time. The rate of increase in earthquakes at the Peru-Chile <span class="hlt">Trench</span> is higher than that of the <span class="hlt">Japan</span> <span class="hlt">Trench</span> and the Aleutian <span class="hlt">Trench</span>. This implies that the convergence of lithospheric plates is higher in the Peru-Chile <span class="hlt">Trench</span>. Deep earthquakes were observed across all the <span class="hlt">trenches</span>. The shallow earthquakes were more prominent than intermediate and deep earthquakes in all the <span class="hlt">trenches</span>. The seismic events in the <span class="hlt">trenches</span> are mostly of magnitude range 3.0-4.9. This magnitude range may indicate the genesis of mild to moderate tsunamis in the <span class="hlt">trench</span> zone in near future once sufficient slip would occur with displacement of water column.</p> <div class="credits"> <p class="dwt_author">Hammed, O. S.; Popoola, O. I.; Adetoyinbo, A. A.; Awoyemi, M. O.; Badmus, G. O.; Ohwo, O. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-01</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://adsabs.harvard.edu/abs/2013AGUFMEP43B0848C"> <span id="translatedtitle">Island-Arc Collision Dominates <span class="hlt">Japan</span>'s Sediment Flux to the Pacific Ocean</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">Quantifying volumes and rates of delivery of terrestrial sediment to <span class="hlt">subduction</span> zones is indispensable for refining estimates of the thickness of <span class="hlt">trench</span> fills that may eventually control the location and timing of submarine landslides and tsunami-generating mega-earthquakes. Despite these motivating insights, knowledge about the rates of erosion and sediment export from the Japanese islands to their Pacific <span class="hlt">subduction</span> zones has somewhat stagnated despite the increasing availability of highly resolved data on surface deformation, climate, geology, and topography. Traditionally, natural erosion rates across the island arc have been estimated from catchment topographic predictors of reservoir sedimentation rates that were recorded over several years to decades. We correct for a systematic bias in these predictions, and present new estimates of decadal to millennial-scale erosion rates of the Japanese terrestrial inner forearc, drawing on several unprecedented inventories of mass wasting, reservoir sedimentation, and concentrations of cosmogenic 10Be in river sands. Our data reveal that catchments draining <span class="hlt">Japan</span>'s eastern seaboard have distinctly different tectonic, lithological, topographic, and climatic characteristics, underscored by a marked asymmetric pattern of erosion rates along and across the island arc. Erosion rates are highest in the Japanese Alps that mark the collision of two <span class="hlt">subduction</span> zones, where high topographic relief, hillslope and bedrock-channel steepness foster rapid denudation by mass wasting. Comparable, if slightly lower, rates characterize southwest <span class="hlt">Japan</span>, most likely due to higher typhoon-driven rainfall totals and variability rather than the similarly high relief and contemporary uplift rates that are linked to <span class="hlt">subduction</span> earthquake cycles, and outpace long-term Quaternary uplift. In contrast, our estimated erosion and flux rates are lowest in the inner forearc catchments that feed sediment into the <span class="hlt">Japan</span> <span class="hlt">Trench</span>. We conclude that collisional mountain-building of the Japanese Alps causes the highest erosion rates anywhere on the island arc despite similar uplift and precipitation controls in southwest <span class="hlt">Japan</span>. We infer that, prior to extensive river damming and reservoir construction, the gross of <span class="hlt">Japan</span>'s total sediment export to the Pacific Ocean entered the accretionary margin of the Nankai Trough as opposed to the comparatively sediment-starved <span class="hlt">Japan</span> <span class="hlt">Trench</span>. Although this pattern mimics the long-term mass balance of incoming sediment to these <span class="hlt">subduction</span> zones, future work will be needed to constrain the relative contribution of terrestrial sediment input on 103-yr timescales.</p> <div class="credits"> <p class="dwt_author">Codilean, A. T.; Korup, O.; Hayakawa, Y. S.; Matsushi, Y.; Saito, H.; Matsuzaki, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://academic.research.microsoft.com/Publication/55136439"> <span id="translatedtitle">Temporal and Spatial Correlations Between Interplate and Intraplate <span class="hlt">Subduction</span> Zone 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"><span class="hlt">Subduction</span> zone earthquakes on the interface between <span class="hlt">subducting</span> and overriding plate represent some of the world's most destructive natural disasters. Updip from this interface, the outer rise comprises an upwarping of the oceanic lithosphere just before it descends into the <span class="hlt">trench</span>. Previous work established the characteristics of the stress regime within the <span class="hlt">subducting</span> lithosphere and has suggested that a temporal</p> <div class="credits"> <p class="dwt_author">J. Polet</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">204</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">205</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..11.3885Z"> <span id="translatedtitle">3D dynamics of hydrous thermal-chemical plumes 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">Mantle wedges are identified as sites of intense thermal convection and thermal-chemical Rayleigh-Taylor instabilities ("cold plumes") controlling distribution and intensity of magmatic activity in <span class="hlt">subduction</span> zones. To investigate 3D hydrous partially molten cold plumes forming in the mantle wedge in response to slab dehydration, we perform 3D petrological-thermomechanical numerical simulations of the intraoceanic one-sided <span class="hlt">subduction</span> with spontaneously bending retreating slab characterized by weak hydrated upper interface. I3ELVIS code is used which is developed based on multigrid approach combined with marker-in-cell method with conservative finite-difference schemes. We investigated regional 800 km wide and 200 km deep 3D <span class="hlt">subduction</span> models with variable 200 to 800 km lateral dimension along the <span class="hlt">trench</span> using uniform numerical staggered grid with 405x101x101 nodal points and up to 50 million markers. Our results show three patterns (roll(sheet)-, zig-zag- and finger-like) of Rayleigh-Taylor instabilities can develop above the <span class="hlt">subducting</span> slab, which are controlled by effective viscosity of partially molten rocks. Spatial and temporal periodicity of plumes correlate well with that of volcanic activity in natural intraoceanic arcs such as <span class="hlt">Japan</span>. High laterally variable surface heat flow predicted in the arc region in response to thermal-chemical plumes activity is also consistent with natural observations.</p> <div class="credits"> <p class="dwt_author">Zhu, G.; Gerya, T.; Yuen, D.; Connolly, J. A. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-04-01</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/2013AGUFM.T43G..01H"> <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 along the landward slope of the southern Izu-Ogasawara <span class="hlt">Trench</span> in Izu-Bonin-Mariana arc, that explored by Dive 7K417 of the ROV Kaiko 7000II during R/V Kairei cruise KR08-07, and Dredge 31 of R/V Hakuho-Maru cruise KH07-02, operated by the <span class="hlt">Japan</span> Agency for Marine-Earth Science and Technology. Harzburgites 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 main constituent minerals of harzburgites are olivine (15.6%), orthopyroxene (Opx; 13.1%) and spinel (0.5%), along with serpentine (70.8%) as a secondary mineral. Microstructure shows inequigranular interlobate (or protogranular) textures. There is no secondary deformation such as porphyroclastic or fine-grained textures. The secondary serpentine shows undeformed mesh texture in the harzburgites. Harzburgites have crystal preferred orientation patterns in olivine (001)[100] and Opx (100)[001]. The mineral chemistry in harzburgites have high olivine forsterite (90.6-92.1 mol.%) and NiO (~0.4 wt%) contents, low Opx Al2O3 (<~1.5 wt%) and Na2O (<0.03 wt%), and high spinel Cr# (65-67). This has 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>. Therefore, 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, Y.; Michibayashi, K.; Morishita, T.; Tani, K.; Dick, H. J.; Ishizuka, O.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2004AGUFM.T22A..01U"> <span id="translatedtitle">Microstructures, Chemical Composition, and Viscosities of Fault-generated Friction Melts in the Shimanto Accretionary Complex, Southwest <span class="hlt">Japan</span>: Implication for Dynamics of Earthquake Faulting 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">The pseudotachylytes (PT) were recently found in the Cretaceous Shimanto accretionary complex of eastern and western Shikoku, southwest <span class="hlt">Japan</span>, but their microstructures under a backscattered electron image, chemical composition, and effects of frictional melting on co-seismic slip in the accretionary prism remains poorly understood. The PT bearing fault is the 1-2 m thick roof thrust of a duplex structure, which bounds the off-scraped coherent turbidites above from the imbricated melange below without a thermal inversion across the fault. The fault zone consists of foliated cataclasite of sandstone-shale melange in origin and dark veins. The PT commonly occurs as brecciated fragments in dark veins. The PT matrix is transparent under plane-polarized light and is optically homogeneous under cross-polarized light, similar to glass matrix. Under a backscattered electron image, the PT clearly shows the evidences for frictional melting and subsequent rapid cooling: rounded and irregularly shaped grains and vesicles in matrix and fracturing associated with grain margins. These textural features of the PT are very similar to those of experimentally generated PT. The EPMA analysis indicates that chemical composition of the PT matrix corresponds to illite with 5.7-9.9 wt% H2O and that partially melted grains are dominated by orthoclase and quartz. This indicates that the temperatures of the PT melt could reach the breakdown temperatures of orthoclase (1150 C) and quartz (1730 C), greater than the maximum temperature recorded in host rocks (170-200 C). We calculated the viscosity of friction melt, based on the chemical composition of the PT matrix and the volume fraction and aspect ratio of grains in the PT. We considered both Arrhenian and non-Arrhenian models for viscosity calculation. Our result demonstrates that the melt viscosity is much lower than PT in continental plutonic and metamorphic rocks: 10^3 Pa s (Arrhenian model) and 10^2 Pa s (non-Arrhenian model) even at 700 C and 10 Pa s (both models) at 1200 C. The extremely low melt viscosity is caused primarily by the formation of liquids (release of OH-) from hydrous illite, and secondarily by small volume fraction (< 20%) of grains in the PT. Because illite is commonly present in accretionary prisms, generation of a low viscosity melt from illite would lead to fault lubrication and hence control the efficiency of stored strain energy release and earthquake magnitude in <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Ujiie, K.; Yamaguchi, H.</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">208</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930005179&hterms=Plate+Tectonics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3D%2522Plate%2BTectonics%2522"> <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://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</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">1992-01-01</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://adsabs.harvard.edu/abs/2006JGRB..111.7401L"> <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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</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 (northern Sumatra) have been determined. The main constraint is that vertical normal stresses beneath the highlands behind the <span class="hlt">subduction</span> zone are nearly equal to horizontal normal stresses, in the plane of a <span class="hlt">trench</span>- or arc-normal section. For a typical brittle and ductile megathrust rheology, frictional shear stress ? = ??gz, for depth z, and ductile shear stress ? = A exp (B/RT) at temperature T, where ?, A, B are rheological parameters treated as constants. Rheological constants common to all the megathrusts (?crust, ?mantle, B) are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure, using a simplex minimization algorithm, taking account of the induced mantle corner flow at depth (65 ± 15 km (2?)) and constant radiogenic heating (0.65 ± 0.3 ?W m-3 (2?)) throughout the crust. The A constants are solved individually for each <span class="hlt">subduction</span> zone, assuming that the maximum depth of interplate slip earthquakes marks the brittle-ductile transition. The best fit solution shows two groupings of megathrusts, with most <span class="hlt">subduction</span> zones having a low mean shear stress in the range 7-15 MPa (?crust = 0.032 ± 0.006, ?mantle = 0.019 ± 0.004) and unable to support elevations >2.5 km. For a typical frictional sliding coefficient ˜0.5, the low effective coefficients of friction suggest high pore fluid pressures at ˜95% lithostatic pressure. Tonga and northern Chile require higher shear stresses with ?crust = 0.095 ± 0.024, ?mantle = 0.026 ± 0.007, suggesting slightly lower pore fluid pressures, at ˜81% lithostatic. Ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency, with B = 36 ± 18 kJ mol-1. Amantle values are sensitive to the precise value of B but are in the range 1-20 kPa. The power law exponent n for mantle flow is poorly constrained but is likely to be large (n > 4). The brittle-ductile transition in the crust occurs at temperatures in the range 370°C-512°C, usually close to the base of the crust and in the mantle at much lower temperatures (180°C-300°C), possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties. In <span class="hlt">subduction</span> zones where the <span class="hlt">subducted</span> slab is older than 50 Ma, a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are ?300°C. In much younger <span class="hlt">subduction</span> zones, the stress transmission is confined mainly to the crust. The shear stresses, particularly in the crust, may be kept low by some sort of lubricant such as abundant water-rich <span class="hlt">trench</span> fill, which lowers the frictional sliding coefficient or effective viscosity and/or raises pore fluid pressure. The unusual high stress <span class="hlt">subduction</span> zone in northern Chile lacks significant <span class="hlt">trench</span> fill and may be poorly lubricated, with a mean shear stress ˜37 MPa required to support elevations >4 km in the high Andes. However, where the crust is thin in sediment-starved and poorly lubricated <span class="hlt">subduction</span> zones, such as Tonga, the mean shear stress will still be low. Sediment may lubricate megathrusts accommodating underthrusting of continental crust, such as in the Himalayas or eastern central Andes, which have a low mean shear stress ˜15 MPa.</p> <div class="credits"> <p class="dwt_author">Lamb, Simon</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-07-01</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/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">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/2013AGUFM.S43A2494U"> <span id="translatedtitle">The Great 1933 Sanriku-oki Earthquake: Possible Compound Rupture of Outer <span class="hlt">Trench</span> Slope and Triggered Interplate 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">The 1933 Sanriku-oki earthquake offshore northern Honshu, <span class="hlt">Japan</span> (Mw8.4) is the largest earthquake that occurred outer-rise/outer-<span class="hlt">trench</span>-slope region. The spatial extent of the aftershocks and possibility of a triggered seismicity was estimated by using modern relocation method and velocity structure. Land-station based hypocenter determination by using 3D velocity structure was firstly applied to the off-Sanriku, near-<span class="hlt">trench</span> region where systematic hypocenter shifts are recognized in the previous studies. The improvement of hypocenter locations near the <span class="hlt">trench</span> were confirmed by examinations of recent earthquakes that are accurately located based on OBS data. The earthquakes after the 1933 Sanriku-oki earthquake are located about 200 km long region under the outer <span class="hlt">trench</span> slope that is separated from the aftershock seismicity under the inner <span class="hlt">trench</span> slope. The outer-<span class="hlt">trench</span>-slope earthquakes are shallow (depth <=50km) and has V-shape distribution in the <span class="hlt">trench</span>-normal cross-section. The aftershock distribution suggests shallow rupture area and possibly a compound rupture for the 1933 main shock. We found the V-shaped compound rupture model explains better the polarity of Tsunami waves at the Sanriku coast than a single west dipping fault. This indicates that the whole lithosphere is probably not under deviatoric tension at the time of the 1933 earthquake. The occurrence of aftershocks both in outer- and inner <span class="hlt">trench</span> slope regions was confirmed by the investigation of dominant wave frequency which is seen in the recent precisely located earthquakes in the two regions (Gamage et al., 2009). The earthquakes under the inner <span class="hlt">trench</span> slope were shallow (depth <=30km) and located where recent activity of interplate thrust earthquakes is high. This suggests the deformation of the 1933 outer-rise earthquake triggered the interplate earthquakes. Recent (2001-2012) seismicity around the source area by the same method show the seismicity at the outer <span class="hlt">trench</span>-slope region of northern Honshu can be divided into several groups of earthquakes along the <span class="hlt">trench</span>; one group roughly corresponds to the aftershock region of the 1933 earthquake. Comparison of the 1933 rupture dimension based on our relocations with the morphologies of fault scarps in the outer <span class="hlt">trench</span> slope suggest that the rupture was limited by the region where fault scarps are <span class="hlt">trench</span> parallel and cross cutting seafloor spreading fabric. These suggest bending and structural segmentation largely controls the horizontal and vertical extent of the fault. The re-examined aftershock distribution in this study provides a constraint on the stress state of the <span class="hlt">subducting</span> plate and water supply to deep earth. They also suggest triggered of interplate seismicity that imply the outer rise /outer <span class="hlt">trench</span> slope earthquake is closely involved in the earthquake cycle of interplate earthquake.</p> <div class="credits"> <p class="dwt_author">Uchida, N.; Kirby, S. H.; Umino, N.; Hino, R.; Okal, E. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2013PEPI..222....8K"> <span id="translatedtitle">Deformation fabrics of natural blueschists and implications for seismic anisotropy in <span class="hlt">subducting</span> oceanic crust</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">Investigations of microstructures are crucial if we are to understand the seismic anisotropy of <span class="hlt">subducting</span> oceanic crust, and here we report on our systematic fabric analyses of glaucophane, lawsonite, and epidote in naturally deformed blueschists from the Diablo Range and Franciscan Complex in California, and the Hida Mountains in <span class="hlt">Japan</span>. Glaucophanes in the analyzed samples consist of very fine grains that are well aligned along the foliation and have high aspect ratios and strong crystal preferred orientations (CPOs) characterized by a (1 0 0)[0 0 1] pattern. These characteristics, together with a bimodal distribution of grain sizes from some samples, possibly indicate the occurrence of dynamic recrystallization for glaucophane. Although lawsonite and epidote display high aspect ratios and a strong CPO of (0 0 1)[0 1 0], the occurrence of straight grain boundaries and euhedral crystals indicates that rigid body rotation was the dominant deformation mechanism. The P-wave (AVP) and S-wave (AVS) seismic anisotropies of glaucophane (AVP = 20.4%, AVS = 11.5%) and epidote (AVP = 9.0%, AVS = 8.0%) are typical of the crust; consequently, the fastest propagation of P-waves is parallel to the [0 0 1] maxima, and the polarization of S-waves parallel to the foliation can form a <span class="hlt">trench</span>-parallel seismic anisotropy owing to the slowest VS polarization being normal to the <span class="hlt">subducting</span> slab. The seismic anisotropy of lawsonite (AVP = 9.6%, AVS = 19.9%) is characterized by the fast propagation of P-waves subnormal to the lawsonite [0 0 1] maxima and polarization of S-waves perpendicular to the foliation and lineation, which can generate a <span class="hlt">trench</span>-normal anisotropy. The AVS of lawsonite blueschist (5.6-9.2%) is weak compared with that of epidote blueschist (8.4-11.1%). Calculations of the thickness of the anisotropic layer indicate that glaucophane and lawsonite contribute to the <span class="hlt">trench</span>-parallel and <span class="hlt">trench</span>-normal seismic anisotropy beneath NE <span class="hlt">Japan</span>, but not to that beneath the Ryukyu arc. Our results demonstrate, therefore, that lawsonite has a strong influence on seismic velocities in the oceanic crust, and that lawsonite might be the cause of complex anisotropic patterns in <span class="hlt">subduction</span> zones.</p> <div class="credits"> <p class="dwt_author">Kim, Daeyeong; Katayama, Ikuo; Michibayashi, Katsuyoshi; Tsujimori, Tatsuki</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</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/2014EGUGA..1616763O"> <span id="translatedtitle">Pronounced zonation of seismic anisotropy in the Western Hellenic <span class="hlt">subduction</span> zone and its geodynamic significance</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">Many <span class="hlt">subduction</span> zones exhibit significant retrograde motion of their arc and <span class="hlt">trench</span>. The observation of fast shear-wave velocities parallel to the <span class="hlt">trench</span> in such settings has been inferred to represent <span class="hlt">trench</span>-parallel mantle flow beneath a retreating slab. Here, we investigate this process by measuring seismic anisotropy in the shallow Aegean mantle. We carry out shear-wave splitting analysis on a dense array of seismometers across the Western Hellenic <span class="hlt">Subduction</span> Zone, and find a pronounced zonation of anisotropy at the scale of the <span class="hlt">subduction</span> zone. Fast SKS splitting directions subparallel to the <span class="hlt">trench</span>-retreat direction dominate the region nearest to the <span class="hlt">trench</span>. Fast splitting directions abruptly transition to <span class="hlt">trench</span>-parallel above the corner of the mantle wedge, and rotate back to <span class="hlt">trench</span>-normal over the back-arc. We argue that the <span class="hlt">trench</span>-normal anisotropy near the <span class="hlt">trench</span> is explained by entrainment of an asthenospheric layer beneath the shallow-dipping portion of the slab. Toward the volcanic arc this signature is overprinted by <span class="hlt">trench</span>-parallel anisotropy in the mantle wedge, likely caused by a layer of strained serpentine immediately above the slab. Arcward steepening of the slab and horizontal divergence of mantle flow due to rollback may generate an additional component of sub-slab <span class="hlt">trench</span>-parallel anisotropy in this region. Poloidal flow above the retreating slab is likely the dominant source of back-arc <span class="hlt">trench</span>-normal anisotropy. We hypothesize that <span class="hlt">trench</span>-normal anisotropy associated with significant entrainment of the asthenospheric mantle near the <span class="hlt">trench</span> may be widespread, but only observable at shallow-dipping <span class="hlt">subduction</span> zones where stations nearest the <span class="hlt">trench</span> do not overlie the mantle wedge.</p> <div class="credits"> <p class="dwt_author">Olive, Jean-Arthur; Pearce, Frederick; Rondenay, Stéphane; Behn, Mark</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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://ntrs.nasa.gov/search.jsp?R=19930030862&hterms=SANDWELL&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DSANDWELL"> <span id="translatedtitle">Flexural ridges, <span class="hlt">trenches</span>, and outer rises around coronae on Venus</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Flexural signatures outboard of Venusian coronal rims are examined with the purpose of inferring the thickness of the planet's elastic lithosphere. Topographic profiles of several prominent coronae which display clear <span class="hlt">trench</span> and outer rise signatures are presented. Via a thin elastic plate flexure model to characterize the shape of the <span class="hlt">trench</span> and outer rise, Venusian flexures are found to be similar in both amplitude and wavelength to lithospheric flexures seaward of <span class="hlt">subduction</span> zones on earth. It is shown that circumferential fractures are concentrated in areas where the topography is curved downward, in good agreement with the high tensile stress predicted by the flexure models. Two scenarios for the development of the ridge-<span class="hlt">trench</span>-outer rise flexural topography and circumferential fractures of coronae are presented. The first scenario involves reheating and thermal subsidence of the lithosphere interior to the corona, while the second involves expansion of the corona interior and roll back of the <span class="hlt">subducting</span> lithosphere exterior to the corona.</p> <div class="credits"> <p class="dwt_author">Sandwell, David T.; Schubert, Gerald</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</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://www.osti.gov/scitech/biblio/6784785"> <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.osti.gov/scitech">SciTech Connect</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/sub 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/sub w/ 8) or a giant earthquake (M/sub 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/sub w/ less than 8.2 is discussed. Strong ground motions from even larger earthquakes (M/sub 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. 35 references, 6 figures.</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">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/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">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/2012EGUGA..1411837L"> <span id="translatedtitle">Mantle flow beneath <span class="hlt">subducting</span> slabs from seismological observations and geodynamical 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">The classical model for mantle flow beneath <span class="hlt">subducting</span> slabs is simple, with viscous coupling between the downgoing slab and the mantle beneath it resulting in entrained two-dimensional flow. However, recent observations of seismic anisotropy beneath slabs have revealed inconsistencies with the predictions of the simplest models in many <span class="hlt">subduction</span> systems worldwide. We present recent observations and models of sub-slab anisotropy and mantle flow that argue for the possibility of <span class="hlt">trench</span>-parallel sub-slab mantle flow in many <span class="hlt">subduction</span> systems. We have used the source-side shear wave splitting technique to construct detailed data sets that sample sub-slab anisotropy beneath the Tonga, Scotia, and Caribbean <span class="hlt">subduction</span> zones. We find that <span class="hlt">trench</span>-parallel fast directions predominate in most of the regions we have examined, and argue that the most likely explanation is predominantly <span class="hlt">trench</span>-parallel flow. We present a series of three-dimensional numerical modeling experiments to explore the conditions under which <span class="hlt">trench</span>-parallel flow may dominate beneath <span class="hlt">subducting</span> slabs. These kinematic-dynamic <span class="hlt">subduction</span> models, implemented with the COMSOL finite element modeling software, investigate the interaction between ambient mantle flow and <span class="hlt">subducting</span> slabs, which are often retreating or advancing in a mantle reference frame. Our numerical experiments demonstrate that <span class="hlt">trench</span>-parallel sub-slab flow is predicted under a fairly wide range of conditions and is enhanced by rapid <span class="hlt">trench</span> rollback and/or weak mechanical coupling between the slab and the sub-slab mantle.</p> <div class="credits"> <p class="dwt_author">Long, M. D.; Paczkowski, K.; Montesi, L.; Lynner, C.; Foley, B.</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">218</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 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://www.agu.org/journals/jb/v102/iB10/97JB01827/97JB01827.pdf"> <span id="translatedtitle">Influences of recurrence times and fault zone temperatures on the age-rate dependence of <span class="hlt">subduction</span> zone 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">Correlations among <span class="hlt">subduction</span> zone seismicity, convergence rate and <span class="hlt">subducting</span> plate age are reassessed considering the possible roles of both recurrence times and fault zone temperatures. Distributions of earthquakes with respect to <span class="hlt">subducting</span> lithosphere age and convergence rate are grossly explained by a recurrence relation when ages and rates at the world's <span class="hlt">trenches</span> are taken into account. Correlations between maximum earthquake</p> <div class="credits"> <p class="dwt_author">Robert McCaffrey</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</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://ntrs.nasa.gov/search.jsp?R=19820036816&hterms=subduction&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dsubduction"> <span id="translatedtitle">The earthquake cycle in <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">A simplified model of a <span class="hlt">subduction</span> zone is presented, which incorporates the mechanical asymmetry induced by the <span class="hlt">subducted</span> slab to anchor the <span class="hlt">subducting</span> plate during post-seismic rebound and thus throw most of the coseismic stream release into the overthrust plate. The model predicts that the <span class="hlt">trench</span> moves with respect to the deep mantle toward the <span class="hlt">subducting</span> plate at a velocity equal to one-half of the convergence rate. A strong extensional pulse is propagated into the overthrust plate shortly after the earthquake, and although this extension changes into compression before the next earthquake in the cycle, the period of strong extension following the earthquake may be responsible for extensional tectonic features in the back-arc region.</p> <div class="credits"> <p class="dwt_author">Melosh, H. J.; Fleitout, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</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_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> <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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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://adsabs.harvard.edu/abs/2014EGUGA..1614345K"> <span id="translatedtitle">The mechanical properties of the deep portion of the <span class="hlt">subduction</span> interface and of the mantle wedge revealed by postseismic motions after Tohoku and Maule earthquakes</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 interseismic and postseismic deformations preceding and following the two large <span class="hlt">subduction</span> earthquakes of Maule (Chile, Mw8.8, 2010) and Tohoku (<span class="hlt">Japan</span>, Mw9.1, 2011) have been closely monitored with modern geodetic techniques. We dispose of large datasets, (GEONET cGPS network in <span class="hlt">Japan</span> and international collaboration networks in Chile, including survey mode GPS). In both cases, post-seismic deformations show similar behavior, with a vertical uplift on the oceanward side of the volcanic arcs, so called mid-field (between 300 and 500 km from the <span class="hlt">trench</span>), and a large scale subsidence associated with non negligible horizontal deformations in the far-field (from 500 to 2000km from the <span class="hlt">trench</span>). In addition, near-field data with complex patterns are available in Chile (thanks to the proximity between the <span class="hlt">trench</span> and the coastline) and in <span class="hlt">Japan</span> (thanks to sea bottom geodesy). We use a 3D finite element code (Zebulon Zset) to relate these deformations to the mechanical properties of the mantle in the <span class="hlt">subduction</span> zone area. The meshes feature a spherical shell-portion from the core-mantle boundary to the earth's surface, extending over more than 60 degrees in latitude and longitude. The overridding and <span class="hlt">subducting</span> plates are elastic, and the asthenosphere is viscoelastic. We test the presence and shape of two low viscosity areas in the mantle : a) a low viscosity wedge (LVW) above the <span class="hlt">subducting</span> plate, extending potentially beneath the volcanic arc, b) a low viscosity channel (LVC) extending along the lower part of the <span class="hlt">subducting</span> interface and just above it, potentially deeper. Burger rheologies have been adopted for all the viscoelastic regions. We invert for the mechanical properties and geometrical characteristics of the asthenosphere of the LVW and of the LVC. Our best fitting models feature, (i) an asthenosphere with a 'long-term' viscosity of the order of 2.1018 Pas, extending down to 300km; (ii) a LVC along the plate interface but not extending deeper in the mantle with viscosities of a few 1017 Pas, and (iii) a LVW restricted to the base of the lithosphere below the volcanic arc, with viscosities of a few 1017 Pas. Mid-field uplift is due to relaxation in both the LVW and the LVC. The viscoelastic mechanical properties deduced from the postseismic motions can also be used to model deformations through the whole seismic cycle. Predicted interseismic deformations seem to differ strongly from those predicted by purely elastic backslip models.</p> <div class="credits"> <p class="dwt_author">Klein, Emilie; Trubienko, Olga; Fleitout, Luce; Vigny, Christophe; Garaud, Jean-Didier</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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/1987PEPI...45...59F"> <span id="translatedtitle">Spherical shell tectonics: buckling of <span class="hlt">subducting</span> lithosphere</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 lithospheric plate is a spherical shell rather than a plane plate. A spherical shell must buckle when it is bent inward. We examined the possibility of lithospheric buckling upon <span class="hlt">subduction</span>. The lithosphere with its <span class="hlt">subducted</span> portion is simulated by a hemispherical elastic shell bent inward at its circumferential edge by a uniform radial load. The buoyancy force acting on the lithosphere seaward of the <span class="hlt">trench</span> is simulated by clamping the shell along a parallel. The deformable portion between the loaded and clamped edges corresponds to the <span class="hlt">subducting</span> slab of lithosphere. Buckling analyses were made using the techniques of a linear stability analysis and a finite element method. The wavelength of buckling depends on the thickness of the shell and the length of its deformable portion: a longer wavelength is associated with a thicker shell and a longer deformable portion. By scaling the shell thickness and the length of the deformable portion to the elastic thickness of lithosphere and the length of <span class="hlt">subducting</span> slab, respectively, the wavelength of buckling can be compared favourably to the length of one unit of arcuate <span class="hlt">trench</span> in a chain-like continuation of island arcs. The load to be applied for initiation of buckling is called the critical load: a lower critical load is associated with a thinner shell with a longer deformable portion. The excess weight of <span class="hlt">subducting</span> slab provides a load large enough to initiate lithospheric buckling at a relatively early stage of <span class="hlt">subduction</span>. Radial displacement of the circumferential edge at the critical state is an order of magnitude smaller than the depth of the leading edge of the Wadati-Benioff zone, indicating that most of the present <span class="hlt">subducting</span> lithospheres are under a postbuckling state. Undulation of the shell in the postbuckling state is not purely sinusoidal but a successive continuation of arcs with cusps in between, invoking the continuation of arcuate deep-sea <span class="hlt">trenches</span> with cusps at their junctions. The cuspate feature of island arc chains is thus a natural consequence of lithospheric buckling and does not require any such irregularities as seamounts colliding with a <span class="hlt">trench</span>. Collision of seamounts, however, can aid buckling greatly if they are aligned along a <span class="hlt">trench</span> at an interval not very different from the inherent buckling wavelength.</p> <div class="credits"> <p class="dwt_author">Fukao, Yoshio; Yamaoka, Koshun; Sakurai, Takamasa</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</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/2013AGUFMNH51A1605H"> <span id="translatedtitle">Tsunami Numerical Simulation for Hypothetical Giant or Great Earthquakes along the Izu-Bonin <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 performed tsunami numerical simulations from various giant/great fault models along the Izu-Bonin <span class="hlt">trench</span> in order to see the behavior of tsunamis originated in this region and to examine the recurrence pattern of great interplate earthquakes along the Nankai trough off southwest <span class="hlt">Japan</span>. As a result, large tsunami heights are expected in the Ryukyu Islands and on the Pacific coasts of Kyushu, Shikoku and western Honshu. The computed large tsunami heights support the hypothesis that the 1605 Keicho Nankai earthquake was not a tsunami earthquake along the Nankai trough but a giant or great earthquake along the Izu-Bonin <span class="hlt">trench</span> (Ishibashi and Harada, 2013, SSJ Fall Meeting abstract). The Izu-Bonin <span class="hlt">subduction</span> zone has been regarded as so-called 'Mariana-type <span class="hlt">subduction</span> zone' where M>7 interplate earthquakes do not occur inherently. However, since several M>7 outer-rise earthquakes have occurred in this region and the largest slip of the 2011 Tohoku earthquake (M9.0) took place on the shallow plate interface where the strain accumulation had considered to be a little, a possibility of M>8.5 earthquakes in this region may not be negligible. The latest M 7.4 outer-rise earthquake off the Bonin Islands on Dec. 22, 2010 produced small tsunamis on the Pacific coast of <span class="hlt">Japan</span> except for the Tohoku and Hokkaido districts and a zone of abnormal seismic intensity in the Kanto and Tohoku districts. Ishibashi and Harada (2013) proposed a working hypothesis that the 1605 Keicho earthquake which is considered a great tsunami earthquake along the Nankai trough was a giant/great earthquake along the Izu-Bonin <span class="hlt">trench</span> based on the similarity of the distributions of ground shaking and tsunami of this event and the 2010 Bonin earthquake. In this study, in order to examine the behavior of tsunamis from giant/great earthquakes along the Izu-Bonin <span class="hlt">trench</span> and check the Ishibashi and Harada's hypothesis, we performed tsunami numerical simulations from fault models along the Izu-Bonin <span class="hlt">trench</span>. Tsunami propagation was computed by the finite-difference method of the non-liner long-wave equations with Corioli's force (Satake, 1995, PAGEOPH) in the area of 130 - 145°E and 25 - 37°N. The 15-seconds gridded bathymetry data are used. The tsunami propagations for eight hours since the faulting of the various fault models were computed. As a result, large tsunamis from assumed giant/great both interplate and outer-rise earthquakes reach the Ryukyu Islands' coasts and the Pacific coasts of Kyushu, Shikoku and western Honshu west of Kanto. Therefore, the tsunami simulations support the Ishibashi and Harada's hypothesis. At the time of writing, the best yet preliminary model to reproduce the 1605 tsunami heights is an outer-rise steep fault model which extends 26.5 - 29.0°N (300 km of length) and with 16.7 m of average slip (Mw 8.6). We will examine tsunami behavior in the Pacific Ocean from this fault model. To examine our results, field investigations of tsunami deposits in the Bonin Islands and discussions on plate dynamics and seismogenic characteristics along the Izu-Bonin <span class="hlt">trench</span> are necessary.</p> <div class="credits"> <p class="dwt_author">Harada, T.; Ishibashi, K.; Satake, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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.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 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/2014JGeo...78....8H"> <span id="translatedtitle">Upper Pleistocene uplifted shorelines as tracers of (local rather than global) <span class="hlt">subduction</span> dynamics</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">Past studies have shown that high coastal uplift rates are restricted to active areas, especially in a <span class="hlt">subduction</span> context. The origin of coastal uplift in <span class="hlt">subduction</span> zones, however, has not yet been globally investigated. Quaternary shorelines correlated to the last interglacial maximum (MIS 5e) were defined as a global tectonic benchmark (Pedoja et al., 2011). In order to investigate the relationships between the vertical motion and the <span class="hlt">subduction</span> dynamic parameters, we cross-linked this coastal uplift database with the “geodynamical” databases from Heuret (2005), Conrad and Husson (2009) and Müller et al. (2008). Our statistical study shows that: (1) the most intuitive parameters one can think responsible for coastal uplift (e.g., <span class="hlt">subduction</span> obliquity, <span class="hlt">trench</span> motion, oceanic crust age, interplate friction and force, convergence variation, dynamic topography, overriding and <span class="hlt">subducted</span> plate velocity) are not related with the uplift (and its magnitude); (2) the only intuitive parameter is the distance to the <span class="hlt">trench</span> which shows in specific areas a decrease from the <span class="hlt">trench</span> up to a distance of ?300 km; (3) the slab dip (especially the deep slab dip), the position along the <span class="hlt">trench</span> and the overriding plate tectonic regime are correlated with the coastal uplift, probably reflecting transient changes in <span class="hlt">subduction</span> parameters. Finally we conclude that the first order parameter explaining coastal uplift is small-scale heterogeneities of the <span class="hlt">subducting</span> plate, as for instance <span class="hlt">subducting</span> aseismic ridges. The influence of large-scale geodynamic setting of <span class="hlt">subduction</span> zones is secondary.</p> <div class="credits"> <p class="dwt_author">Henry, Hadrien; Regard, Vincent; Pedoja, Kevin; Husson, Laurent; Martinod, Joseph; Witt, Cesar; Heuret, Arnauld</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-08-01</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://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 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/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 " 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://adsabs.harvard.edu/abs/2014EGUGA..1612900R"> <span id="translatedtitle">Frictional properties of fault rocks along the shallow part of the <span class="hlt">Japan</span> <span class="hlt">Trench</span> décollement: insights from samples recovered during the Integrated Ocean Drilling Project Expedition 343 (the JFAST project)</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">Trench</span> Fast Drilling Project (JFAST), Integrated Ocean Drilling Program (IODP) Expedition 343, successfully located and sampled the shallow slip zone of the Mw =9.0 Tohoku-Oki earthquake where the largest coseismic slip occurred (c. 50 m). Logging-while-drilling, core-sample observations and the analysis of temperature data recovered from a third borehole show that a thin (<5 m), smectite rich plate-boundary fault accommodated the large slip of the Tohoku-Oki Earthquake rupture, as well as most of the interplate motion at the drill site. Effective normal stress along the shallow plate-boundary fault is estimated to be c. 7 MPa. Single-velocity and velocity-stepping rotary-shear friction experiments on fault material were performed with the Slow to HIgh Velocity Apparatus (SHIVA) installed at INGV in Rome. Quantitative phase analysis using the combined Rietveld and R.I.R. method indicates that the starting material is mainly composed of smectite (56 wt%) and illite/mica (21 wt%) and minor quartz, kaolinite, plagioclase and K-feldspar. The amount of amorphous fraction has also been calculated and it is close to the detection limit. Each experiment used 3.5 g of loosely disaggregated gouge, following sieving to a particle size fraction <1 mm. Experiments were performed either 1) "room-dry" (40-60% humidity) at 8.5 MPa normal stress (one test at 12.5 MPa), or 2) "water-dampened" (0.5 ml distilled water added to the gouge layers) at 3.5 MPa normal stress. Slip velocities ranged over nearly seven orders of magnitude (10-5 - 3 m s-1). Total displacement is always less than 1 m. The peak and steady-state frictional strengths of the gouges are significantly lower under water-dampened conditions, with mean steady-state friction coefficients (?, shear stress/normal stress) at all investigated velocities of 0.04<?<0.1. This is consistent with the small measured frictional heat anomaly along the plate boundary fault ~1.5 years after the Tohoku-Oki earthquake. Under room-dry conditions the gouge material is velocity-strengthening at intermediate velocities (0.001 - 0.1 m s-1), but strongly velocity-weakening at > 0.1 m s-1. Instead, under water-dampened conditions, the gouge is velocity-neutral to velocity-weakening at all investigated velocities. In other words, the intermediate-velocity strengthening, which would probably act as a "barrier" to rupture propagation in the dry gouges, disappears in water-dampened gouges. This result is compatible with propagation of the Tohoku rupture to the <span class="hlt">trench</span>, and also with large coseismic slip at shallow depths. Quantitative phase analysis using the combined Rietveld and R.I.R. method has been performed also on six post-experiment gouges for the determination of both the crystalline and amorphous fractions. Preliminary results show that the mineralogical assemblage is basically the same after the experiments, with both smectite and illite phases preserved, this suggests that the weakening mechanism operating in this material is active at low temperature.</p> <div class="credits"> <p class="dwt_author">Remitti, Francesca; Smith, Steven; Gualtieri, Alessandro; Di Toro, Giulio; Nielsen, Stefan</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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://www.cpwr.com/sites/default/files/publications/TrenchingPDFforweb.pdf"> <span id="translatedtitle">Hazard Alert: <span class="hlt">Trenches</span></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">... Construction Chart Book, p. 39. CPWR. 2008. HAZARD ALERT Find out more about safe work in <span class="hlt">trenches</span>: • ... about construction hazards. Get more of these Hazard Alert cards – and cards on other topics. Call 301- ...</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">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/2004AGUFM.S51B0165K"> <span id="translatedtitle">Plate convergence along the northern Manila <span class="hlt">Trench</span>, Taiwan-Luzon region</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 Philippine Sea Plate overrides the Eurasian Plate along the east-dipping Manila <span class="hlt">Trench</span>. From Luzon to Taiwan, the plate convergence evolves gradually from normal <span class="hlt">subduction</span> to collision. Further north, the Taiwan orogen has been created. As evidenced by the earthquakes, the <span class="hlt">subduction</span>-related earthquakes become diffusive close to Taiwan. The accretionary prism has also become wider toward Taiwan. To understand the transition of the plate convergence, we have collected 6 reflection seismic profiles across the Manila <span class="hlt">Trench</span> between Luzon and Taiwan. The results show that the basement generally displays larger dipping angle in the south than in the north. The <span class="hlt">trench</span>-fill sediments near the <span class="hlt">trench</span> have larger quantity in the south than in the north. In the north, the <span class="hlt">trench</span>-fill sediments have even been uplifted. Structural analysis shows that the crustal structures close to the <span class="hlt">trench</span> area can be divided into two distinctive sub-areas: the normal fault zone and the proto-thrust zone. The normal fault zone is characterized by the distribution of numerous normal faults in the upper layer of the bent <span class="hlt">subducting</span> plate. When the normal faults approache the <span class="hlt">trench</span>, they are generally covered by <span class="hlt">trench</span>-fill sediments. It implies that the normal faults occur at a maximum bending moment of the plate. Some normal faults resumes probably due to the strong plate convergence near the accretionary prism. The proto-thrust zone is located between the normal fault zone and the frontal thrust of the accretionary prism. Proto-thrust zone contains numerous blind-thrust beneath the <span class="hlt">trench</span> area. The observation of the proto-thrust zone suggests two tectonic insights. Firstly, the compression of plate convergence comes from the base of the decollement and propagates upwards. Alternatively, the blind-thrusts come from the inheritance of the <span class="hlt">subducting</span> normal faults.</p> <div class="credits"> <p class="dwt_author">Ku, C.; Hsu, S.</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">231</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 " 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://www.agu.org/journals/jb/v084/iB03/JB084iB03p01049/JB084iB03p01049.pdf"> <span id="translatedtitle">Back-arc opening and the mode of <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"><span class="hlt">Trench</span>-arc systems (<span class="hlt">subduction</span> zones) can be classified into two types depending on whether or not actively opening back-arc basins are associated with them. This suggests that <span class="hlt">subduction</span> of an oceanic plate is not a sufficient condition for back-arc opening, though it may be necessary one. Mechanism that cause the distinction between the two types have been investigaged. Earthquake studies suggest</p> <div class="credits"> <p class="dwt_author">Seiya Uyeda; Hiroo Kanamori</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</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/2014JGRB..119....1E"> <span id="translatedtitle">Crustal-scale seismic profiles across the Manila <span class="hlt">subduction</span> zone: The transition from intraoceanic <span class="hlt">subduction</span> to incipient 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">use offshore multichannel seismic (MCS) reflection and wide-angle seismic data sets to model the velocity structure of the incipient arc-continent collision along two <span class="hlt">trench</span> perpendicular transects in the Bashi Strait between Taiwan and Luzon. This area represents a transition from a tectonic regime dominated by <span class="hlt">subduction</span> of oceanic crust of the South China Sea, west of the Philippines, to one dominated by <span class="hlt">subduction</span> and eventual collision of rifted Chinese continental crust with the Luzon volcanic arc culminating in the Taiwan orogeny. The new seismic velocity models show evidence for extended to hyperextended continental crust, ~10-15 km thick, <span class="hlt">subducting</span> along the Manila <span class="hlt">trench</span> at 20.5°N along transect T1, as well as evidence indicating that this thinned continental crust is being structurally underplated to the accretionary prism at 21.5°N along transect T2, but not along T1 to the south. Coincident MCS reflection imaging shows highly stretched and faulted crust west of the <span class="hlt">trench</span> along both transects and what appears to be a midcrustal detachment along transect T2, a potential zone of weakness that may be exploited by accretionary processes during <span class="hlt">subduction</span>. An additional seismic reflection transect south of T1 shows <span class="hlt">subduction</span> of normal ocean crust at the Manila <span class="hlt">trench</span>.</p> <div class="credits"> <p class="dwt_author">Eakin, Daniel H.; McIntosh, Kirk D.; Van Avendonk, H. J. A.; Lavier, Luc; Lester, Ryan; Liu, Char-Shine; Lee, Chao-Shing</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</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/2011AGUFM.T43D2357M"> <span id="translatedtitle">Surface ruptures associated with the 2011 Mw 6.6 Fukushima Hamadori earthquake (northeast Honshu, <span class="hlt">Japan</span>): normal faulting in <span class="hlt">trench</span>-normal stretching forearc subsequent to the 2011 Great Tohoku megathrust 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">On 11 April 2011 a shallow large normal faulting earthquake with Mw 6.6 occurred in southern Fukushima Prefecture, located on forearc region of northeast Honshu, <span class="hlt">Japan</span>, where significant <span class="hlt">trench</span>-normal crustal stretching has occurred since the Great Tohoku megathrust earthquake (Mw 9.0) of 11 March 2011. The earthquake resulted in two distinct surface ruptures along the previously mapped active fault traces; NNW-SSE-trending Idosawa fault on the west and NW-SE-trending Yunotake fault on the east. In order to define map distribution, geometry, slip vector pattern and slip distribution along the surface breaks as well as to archive fragile offset features before land modification, we conducted field mapping along the entire traces of the ruptures and surveyed offset cultural features using a total station since 17 April, 6 days after the earthquake. Our field mapping revealed that i) the both ruptures are predominantly normal faulting with west- to southwest-side-down on the west-dipping fault planes, which is consistent with focal mechanisms of mainshock and principal aftershocks and crustal deformation pattern as inferred from GPS and InSAR data, ii) the fault displacement is concentrated on a distinct slip surface in mountainous area underlain by the basement metamorphic rocks, while is dispersed in broad deformation zone which comprises scarp with only small vertical displacement, crestal extensional graben and hanging-wall warping that consumes a large part of the net vertical displacement in the hilly lands and terrace surfaces where unconsolidated materials are accumulated, iii) although the rupture lengths along the Idosawa and the Yunotake faults are nearly same (13.5 km and 15.6 km, respectively), vertical displacement on the Idosawa fault (2.2 m at the maximum) are four times of that on the Yunotake fault (0.5 m), iii) azimuths of slip vectors vary systematically along the Idoawa fault (pure normal slip near the center and oblique slip near the lateral tips of the rupture), but are nearly invariable along the Yunotake fault (oblique normal slip). These remarkable differences in these rupture behaviors of two surface ruptures may reflect the property of seismogenic faulting, such as degree of fault maturity, fault geometry at depth and rupture directivity.</p> <div class="credits"> <p class="dwt_author">Maruyama, T.; Awata, Y.; Azuma, T.</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">235</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/2010PEPI..183...20B"> <span id="translatedtitle">Upper mantle structure of marginal seas and <span class="hlt">subduction</span> zones in northeastern Eurasia from Rayleigh wave 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">The upper mantle structure of marginal seas (the Seas of <span class="hlt">Japan</span> and Okhotsk) and <span class="hlt">subduction</span> zones in northeastern Eurasia is investigated, using the three-stage multimode surface wave tomography incorporating finite-frequency effects. Broadband waveform data from 305 events with magnitude greater than 5.5 from 1990 to 2005 recorded at 25 stations of the IRIS network in northeastern Eurasia and <span class="hlt">Japan</span> and at 8 stations of the broadband seismic network in Far-Eastern Russia from 2005 to 2008 are employed in our analysis. The dispersion curves of the fundamental mode and first two higher modes of Rayleigh waves are simultaneously inverted for the shear-wave velocity structure of the region. The off-great circle propagation due to strong heterogeneities in the region is also taken into account in the construction of intermediary phase velocity models for each mode as a function of frequency. The obtained 3D S-wave velocity model is well resolved down to 200 km depth. Checkerboard tests show the average horizontal resolution of 5° in the study region. The <span class="hlt">subducting</span> Pacific plate is clearly imaged as a high velocity anomaly up to 6%. The mantle wedge above the Pacific plate is associated with low velocity anomalies. The absolute minimum S-wave velocity in the mantle wedge is 4 km/s in the Sea of Okhotsk in the depth range from 80 to 160 km, probably indicating the presence of partial melt. The anomalous spot with conspicuous low velocity in the southern end of the Sea of Okhotsk may indicate the existence of hot upwelling flow in the mantle. A high velocity anomaly subparallel to the present <span class="hlt">subduction</span> zone is found in the northwestern Sea of Okhotsk in the depth range from 100 to 200 km. The position of this anomaly correlates well with the high velocity anomaly found in the P-wave tomography of Gorbatov et al. (2000), which may be interpreted as a relict of the Okhotsk plate <span class="hlt">subducted</span> in the past. We also attempted a mapping of azimuthal anisotropy in this region. The fast phase velocity directions near the Pacific plate are observed subparallel to the Kuril and <span class="hlt">Japan</span> <span class="hlt">Trenches</span> at all the periods, indicating a strong effect of the <span class="hlt">subducting</span> Pacific plate on the mantle flow, while the anisotropy appears to be weak in tectonically inactive marginal seas.</p> <div class="credits"> <p class="dwt_author">Bourova, E.; Yoshizawa, K.; Yomogida, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-11-01</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/2013GGG....14.5227R"> <span id="translatedtitle">Relationship between outer forearc subsidence and plate boundary kinematics along the Northeast <span class="hlt">Japan</span> convergent margin</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">Tectonic erosion along convergent plate boundaries, whereby removal of upper plate material along the <span class="hlt">subduction</span> zone interface drives kilometer-scale outer forearc subsidence, has been purported to explain the evolution of nearly half the world's <span class="hlt">subduction</span> margins, including part of the history of northeast <span class="hlt">Japan</span>. Here, we evaluate the role of plate boundary dynamics in driving forearc subsidence in northeastern <span class="hlt">Japan</span>. A synthesis of newly updated analyses of outer forearc subsidence, the timing and kinematics of upper plate deformation, and the history of plate convergence along the <span class="hlt">Japan</span> <span class="hlt">trench</span> demonstrate that the onset of rapid fore-arc tectonic subsidence is contemporaneous with upper plate extension during the opening of the Sea of <span class="hlt">Japan</span> and with an acceleration in convergence rate at the <span class="hlt">trench</span>. In Plio-Quaternary time, relative uplift of the outer forearc is contemporaneous with contraction across the arc and a decrease in plate convergence rate. The coincidence of these changes across the forearc, arc, backarc system appears to require an explanation at the scale of the entire plate boundary. Similar observations along other western Pacific margins suggest that correlations between forearc subsidence and major changes in plate kinematics are the rule, rather than the exception. We suggest that a significant component of forearc subsidence at the northeast <span class="hlt">Japan</span> margin is not the consequence of basal tectonic erosion, but instead reflects dynamic changes in plate boundary geometry driven by temporal variations in plate kinematics. If correct, this model requires a reconsideration of the mass balance and crustal recycling of continental crust at nonaccretionary margins.</p> <div class="credits"> <p class="dwt_author">Regalla, Christine; Fisher, Donald M.; Kirby, Eric; Furlong, Kevin P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://academic.research.microsoft.com/Publication/51360965"> <span id="translatedtitle">Links Between Faulting of the Incoming Ocean Plate and Earthquakes in the Slab of <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">Recent multibeam bathymetry shows that bending of ocean plates at <span class="hlt">subduction</span> zones develops a complex system of faulting. Independently, studies of slab seismicity have interpreted that most intermediate depth earthquakes occur by reactivation of faults formed during plate bending at <span class="hlt">trenches</span>. We have studied the relation between bending faults and slab seismicity at the <span class="hlt">subduction</span> zones of Middle America and</p> <div class="credits"> <p class="dwt_author">C. R. Ranero; A. Villasenor; J. Phipps Morgan</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</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://academic.research.microsoft.com/Publication/51567412"> <span id="translatedtitle">Advanced Seismic Imaging of <span class="hlt">Subduction</span> Related Structures at the North Chile Convergent Margin</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">Within the framework of the CINCA project in 1995, the <span class="hlt">subducting</span> Nazca plate offshore Chile between approximately 19°S and 26°S has been investigated. The aim of this study was to deliver improved images of the structures of the oceanic crust as well as of the <span class="hlt">subducting</span> plate and the oceanic Moho. We processed two marine profiles crossing the <span class="hlt">trench</span> using</p> <div class="credits"> <p class="dwt_author">C. Sick; S. Buske; S. Shapiro</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">239</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 " 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://academic.research.microsoft.com/Publication/55613781"> <span id="translatedtitle">Constraints on Pore Pressure in <span class="hlt">Subduction</span> Zones From Geotechnical Tests and Physical Properties 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">At <span class="hlt">subduction</span> zones, as incoming sediments are either offscraped or underthrust at the <span class="hlt">trench</span>, elevated pore pressures result from the combination of rapid loading and low permeability. Pore pressure within underthrust sediment is especially important for the mechanical strength of the plate boundary fault system, because the main décollement localizes immediately above this sediment, and at many <span class="hlt">subduction</span> zones steps</p> <div class="credits"> <p class="dwt_author">D. M. Saffer; A. W. McKiernan</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_11");' 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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showDiv("page_12");' href="#">12</a> <a style="font-weight: bold;">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 onClick='return showDiv("page_17");' href="#">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_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://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 " 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://adsabs.harvard.edu/abs/2013NatCo...4E1720T"> <span id="translatedtitle">Louisville seamount <span class="hlt">subduction</span> and its implication on mantle flow beneath the central Tonga-Kermadec arc</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 intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in <span class="hlt">subduction</span> zones. Here we present trace element and Sr, Nd and Pb isotopic compositions of lavas from the central Tonga-Kermadec arc, west of the contemporary Louisville-Tonga <span class="hlt">trench</span> intersection, to provide new insights into the effects of Louisville seamount <span class="hlt">subduction</span>. Elevated 206Pb/204Pb, 208Pb/204Pb, 86Sr/87Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of <span class="hlt">subducted</span> alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the <span class="hlt">subducted</span> Louisville seamount chain that, combined with estimates of the timing of fluid release from the <span class="hlt">subducting</span> slab, suggests primarily <span class="hlt">trench</span>-normal mantle flow beneath the central Tonga-Kermadec arc system.</p> <div class="credits"> <p class="dwt_author">Timm, Christian; Bassett, Daniel; Graham, Ian J.; Leybourne, Matthew I.; de Ronde, Cornel E. J.; Woodhead, Jon; Layton-Matthews, Daniel; Watts, Anthony B.</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">243</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/7169479"> <span id="translatedtitle">From <span class="hlt">subduction</span> to collision: results of French POP2 program on Taiwan-Philippine festoon</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">A sea-beam, seismic, magnetic, and gravimetric survey was conducted with the R/V Jean-Charcot in three key regions off the Taiwan-Philippine festoon in the western Pacific: (1) Ryukyu active margin and its junction with Taiwan; (2) northern part of the Manila <span class="hlt">Trench</span> and its junction with the Taiwan tectonic prism; and (3) southern termination of Manila <span class="hlt">Trench</span> in front of Mindoro Island. Transitions between active <span class="hlt">subduction</span> along the Manila <span class="hlt">Trench</span> and collision of Taiwan and Mindoro, and relations between active <span class="hlt">subduction</span> and extension in the Okinawa-Ryukyu and the northeastern Taiwan systems are particularly studied.</p> <div class="credits"> <p class="dwt_author">Blanchet, R.; Stephan, J.F.; Rangin, C.; Baladad, D.; Bouysse, Ph.; Chen, M.P.; Chotin, P.; Collot, J.Y.; Daniel, J.; Drouhot, J.M.; Marsset, B.; Pelletier, B.; Richard, M.; Tardy, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-07-01</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://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">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/2013Tectp.600..217R"> <span id="translatedtitle">Ancient <span class="hlt">subduction</span> zone in Sakhalin Island</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 northern part of Sakhalin Island is an area of recent intensive tectonic movements and hydrothermal processes, as well as a place of accumulation of useful minerals. The deep structure of the lithosphere beneath the region of the Neftegorsk earthquake of May 27, 1995 in North Sakhalin, which killed residents and caused significant destruction, is examined in this paper. Our geodynamic model shows that North Sakhalin consists of the North Sakhalin Basin, Deryugin Basin and an ophiolite complex located between them. The Deryugin Basin was formed in place of an ancient deep <span class="hlt">trench</span> after <span class="hlt">subducting</span> the Okhotsk Sea Plate under Sakhalin in the Late Cretaceous-Paleogene. The North Sakhalin Basin was formed on the side of the back-arc basin at that time. The ophiolite complex is fixed in the position of ancient <span class="hlt">subduction</span> zone that was active in the Late Cretaceous-Paleogene. Approximately in the Miocene, the <span class="hlt">subduction</span> of the Okhotsk lithosphere apparently ceased. The remains of the <span class="hlt">subduction</span> zone in the form of an ophiolite complex have been identified from geological and geophysical data. On the surface, the <span class="hlt">subduction</span> zone is manifested as deep faults stretched along Sakhalin. It is probable that the Neftegorsk earthquake was a result of activation of this ancient <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Rodnikov, A. G.; Sergeyeva, N. A.; Zabarinskaya, L. P.</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">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/51342584"> <span id="translatedtitle">Relationship between bend-faulting at <span class="hlt">trenches</span> and intermediate-depth 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">We have studied faulting associated with bending of the oceanic plate prior to <span class="hlt">subduction</span> along segments of Middle America and Chile <span class="hlt">trenches</span>. The fault structure of the oceanic plate at the <span class="hlt">trench</span> has been compared to patterns of intermediate-depth intra-slab earthquakes in the corresponding slabs. Multibeam bathymetry shows that bending-related faulting forms patterns made of sets of faults with orientations</p> <div class="credits"> <p class="dwt_author">C. R. Ranero; A. Villasenor; J. Phipps Morgan; W. Weinrebe</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">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/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">248</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=PIA11203&hterms=white&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dwhite"> <span id="translatedtitle">Phoenix's Snow White <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><p/> A soil sample taken from the informally named 'Snow White' <span class="hlt">trench</span> at NASA's Phoenix Mars Lander work site produced minerals that indicate evidence of past interaction between the minerals and liquid water. <p/> This image was taken by the Surface Stereo Imager on Sol 103, the 103rd day since landing (Sept. 8, 2008). <p/> The <span class="hlt">trench</span> is approximately 23 centimeters (9 inches) long. <p/> The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by JPL, Pasadena, Calif. Spacecraft development was by Lockheed Martin Space Systems, Denver.</p> <div class="credits"> <p class="dwt_author"></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">249</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://anquetil.colorado.edu/szhong/papers/Zhong_Gurnis1997EI.pdf"> <span id="translatedtitle">Dynamic interaction between tectonic plates, <span class="hlt">subducting</span> slabs, and the 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">Mantle convection models have been formulated to investi- gate the relation between plate kinematics and mantle dynamics. The cylin- drical geometry models incorporate mobile, faulted plate margins, a phase change at 670 km depth, non-Newtonian rheology, and tectonic plates. Models with a variety of parameters indicate that a relatively stationary <span class="hlt">trench</span> is more likely to be associated with a <span class="hlt">subducted</span></p> <div class="credits"> <p class="dwt_author">Shijie Zhong; Michael Gurnis</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</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://ntrs.nasa.gov/search.jsp?R=PIA05754&hterms=route+66&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522route%2B66%2522"> <span id="translatedtitle"><span class="hlt">Trenching</span> the Trough</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><p/>This animation shows the Mars Exploration Rover Opportunity digging a <span class="hlt">trench</span> near the trough dubbed 'Anatolia' with its left front wheel on sol 73. It was taken by the rover's hazard-avoidance camera. <p/>The <span class="hlt">trench</span> was dug so that Opportunity would be able to place its Moessbauer spectrometer on a soil target (the pile of material on the right side of the <span class="hlt">trench</span>) during a four-day flight software update. The rover's alpha particle X-ray spectrometer was pointed at the sky at this time taking calibration measurements. <p/>Spirit performed a similar operation during its flight software update, but its Moessbauer was placed on a rock dubbed 'Route 66.' Since there are no rocks at Opportunity's current location, rover team members chose a patch of soil. <p/>The <span class="hlt">trench</span> itself is 95 centimeters (38 inches) long by 16 centimeters (6 inches) wide by 11 centimeters (4 inches) deep. It is the deepest hole dug by either Spirit or Opportunity to date.</p> <div class="credits"> <p class="dwt_author"></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">251</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=PIA10929&hterms=grooming&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522grooming%2522"> <span id="translatedtitle">Snow White 5 <span class="hlt">Trench</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><p/> This image was acquired by NASA's Phoenix Mars Lander's Robotic Arm Camera on the 35th Martian day of the mission, or Sol 34 (June 29, 2008), after the May 25, 2008, landing. This image shows the <span class="hlt">trench</span> informally called 'Snow White 5.' The <span class="hlt">trench</span> is 4-to-5 centimeters (about 1.5-to-1.9 inches) deep, 24 centimeters (about 9 inches) wide and 33 centimeters (13 inches) long. <p/> Snow White 5 is Phoenix's current active digging area after additional <span class="hlt">trenching</span>, grooming, and scraping by Phoenix's Robotic Arm in the last few sols to <span class="hlt">trenches</span> informally called Snow White 1, 2, 3, and 4. Near the top center of the image is the Robotic Arm's Thermal and Electrical Conductivity Probe. <p/> Snow White 5 is located in a patch of Martian soil near the center of a polygonal surface feature, nicknamed 'Cheshire Cat.' The digging site has been named 'Wonderland.' <p/> This image has been enhanced to brighten shaded areas. <p/> The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.</p> <div class="credits"> <p class="dwt_author"></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">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/2008E%26PSL.271..233F"> <span id="translatedtitle"><span class="hlt">Trench</span> migration, net rotation and slab mantle 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">Laboratory models have been conducted to improve our understanding of the role that the resistance of the slab to bending and its coupling to the ambient mantle play in <span class="hlt">subduction</span> dynamics over geological time scales. Our models are set up with a viscous plate of silicone (lithosphere) <span class="hlt">subducting</span> under negative buoyancy in a viscous layer of glucose syrup (mantle). For our study, the lithosphere/upper mantle viscosity contrast has been systematically varied, from ~ 10 to ~ 10 5 in order to explore the parameter space between weak and strong slab dynamics. We found that <span class="hlt">subduction</span> is characterized by a retreating mode for viscosity ratios > 10 4, by the coexistence of a retreating mode and an advancing mode for viscosity ratios between ~ 10 4 and ~ 10 2, and quasi-stationary, Rayleigh-Taylor like behaviour for ratios < 10 2. By combining our experimental results and kinematic data from current <span class="hlt">subduction</span> zones in four reference frames which differ in the amount of net rotation, we infer that a lithosphere/upper mantle viscosity contrast of 150-500 is necessary to obtain realistic <span class="hlt">trench/subducting</span> plate velocity ratios as well as the variability of <span class="hlt">subduction</span> styles observed in nature.</p> <div class="credits"> <p class="dwt_author">Funiciello, F.; Faccenna, C.; Heuret, A.; Lallemand, S.; Di Giuseppe, E.; Becker, T. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-07-01</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://dx.doi.org/10.1029/2004JB003031"> <span id="translatedtitle">Stress interaction between <span class="hlt">subduction</span> earthquakes and forearc strike-slip faults: Modeling and application to the northern Caribbean plate boundary</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">Strike-slip faults in the forearc region of a <span class="hlt">subduction</span> zone often present significant seismic hazard because of their proximity to population centers. We explore the interaction between thrust events on the <span class="hlt">subduction</span> interface and strike-slip faults within the forearc region using three-dimensional models of static Coulomb stress change. Model results reveal that <span class="hlt">subduction</span> earthquakes with slip vectors subparallel to the <span class="hlt">trench</span> axis enhance the Coulomb stress on strike-slip faults adjacent to the <span class="hlt">trench</span> but reduce the stress on faults farther back in the forearc region. In contrast, <span class="hlt">subduction</span> events with slip vectors perpendicular to the <span class="hlt">trench</span> axis enhance the Coulomb stress on strike-slip faults farther back in the forearc, while reducing the stress adjacent to the <span class="hlt">trench</span>. A significant contribution to Coulomb stress increase on strike-slip faults in the back region of the forearc comes from "unclamping" of the fault, i.e., reduction in normal stress due to thrust motion on the <span class="hlt">subduction</span> interface. We argue that although Coulomb stress changes from individual <span class="hlt">subduction</span> earthquakes are ephemeral, their cumulative effects on the pattern of lithosphere deformation in the forearc region are significant. We use the Coulomb stress models to explain the contrasting deformation pattern between two adjacent segments of the Caribbean <span class="hlt">subduction</span> zone. <span class="hlt">Subduction</span> earthquakes with slip vectors nearly perpendicular to the Caribbean <span class="hlt">trench</span> axis is dominant in the Hispaniola segment, where the strike-slip faults are more than 60 km inland from the <span class="hlt">trench</span>. In contrast, <span class="hlt">subduction</span> slip motion is nearly parallel to the Caribbean <span class="hlt">trench</span> axis along the Puerto Rico segment, where the strike-slip fault is less than 15 km from the <span class="hlt">trench</span>. This observed jump from a strike-slip fault close to the <span class="hlt">trench</span> axis in the Puerto Rico segment to the inland faults in Hispaniola is explained by different distributions of Coulomb stress in the forearc region of the two segments, as a result of the change from the nearly <span class="hlt">trench</span> parallel slip on the Puerto Rico <span class="hlt">subduction</span> interface to the more perpendicular <span class="hlt">subduction</span> slip beneath Hispaniola. The observations and modeling suggest that <span class="hlt">subduction</span>-induced strike-slip seismic hazard to Puerto Rico may be smaller than previously assumed but the hazard to Hispaniola remains high. Copyright 2004 by the American Geophysical Union.</p> <div class="credits"> <p class="dwt_author">ten, Brink, U.; Lin, J.</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">254</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/70021038"> <span id="translatedtitle">Deformation across the Alaska-Aleutian <span class="hlt">Subduction</span> Zone near Kodiak</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">The Kodiak-Katmai geodetic array, nine monuments distributed along a profile trending north-northwestward across Kodiak Island and the Alaska Peninsula, was surveyed in 1993, 1995 and 1997 to determine the deformation at the Alaska-Aleutian <span class="hlt">subduction</span> zone. Velocities on Kodiak Island measured relative to the stable North American plate decrease with distance from the Alaska-Aleutian <span class="hlt">trench</span> (distance range 106 to 250 km), whereas no appreciable deformation was measured on the Alaska Peninsula (distances 250 to 370 km from the <span class="hlt">trench</span>). The measured deformation is reasonably well predicted by the conventional dislocation representation of <span class="hlt">subduction</span> with the model parameters determined independently (i.e., not simply by fitting the observations). The deformation of Kodiak Island is in striking contrast to the very minor deformation measured in the similarly situated Shumagin Islands, 450 km southwest of Kodiak along the Alaska-Aleutian <span class="hlt">trench</span>.</p> <div class="credits"> <p class="dwt_author">Savage, J. C.; Svarc, J. L.; Prescott, W. H.</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">255</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/2012GGG....13.6W15B"> <span id="translatedtitle">Influence of overriding plate geometry and rheology on <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"><span class="hlt">Subduction</span> dynamics is strongly dependent on the geometry and rheology of the <span class="hlt">subducting</span> slab and adjacent plates, as well as on the induced mantle flow driven by the evolution of tectonic configurations along <span class="hlt">subduction</span> zones. However, these processes, and the associated plate tectonic driving forces, are difficult to study using time-dependent 3-dimensional computer simulations due to limitations in computing resources. We investigate these phenomena with a novel numerical approach, using BEM-Earth, a Stokes flow solver based on the Boundary Element Method (BEM) with a Fast-Multipole (FM) implementation. The initial BEM-Earth model configurations self-consistently determine the evolution of the entire lithosphere-mantle system without imposing additional constraints in a whole-Earth spherical setting. We find that models without an overriding plate overestimate <span class="hlt">trench</span> retreat by 65% in a 20 m.y. model run. Also, higher viscosity overriding plates are associated with higher velocity <span class="hlt">subducting</span> slabs, analogue to faster oceanic plates <span class="hlt">subducting</span> beneath more rigid continental lithosphere. In our models poloidal flows dominate the coupling between the down-going and overriding plates, with <span class="hlt">trench</span>-orthogonal length variations in overriding plates inducing flows at least ˜2× stronger than <span class="hlt">trench</span>-parallel width variations. However, deformation in the overriding plate is related to its length and width, with narrower and longer plates extending more than wider and shorter plates.</p> <div class="credits"> <p class="dwt_author">Butterworth, N. P.; Quevedo, L.; Morra, G.; Müller, R. D.</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">256</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.T52C..08C"> <span id="translatedtitle">High frequency waves guided by the <span class="hlt">subducted</span> plates underneath Taiwan and their association with seismic intensity anomalies</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">Energy from seismic events traveling up a <span class="hlt">subduction</span> zone reveal large-amplitude, high-frequency signal with sustained long coda. In <span class="hlt">Japan</span>, such seismic waves guided by the high wave velocity and high Q plate lead to surprisingly large intensity in the forearc area, even if the events are not felt near the epicenter. Seismic events with guided wave characteristics can explain the anomalous ground shaking, and provide useful information on the plate configuration. Taiwan, situated at the plate boundary zone between the Eurasian plate (EP) and the Philippine Sea plates (PSP), exhibits a unique interaction between the EP and PSP. In northeast Taiwan, the PSP <span class="hlt">subducts</span> beneath the rifted Eurasian plate margin along the Ryukyu <span class="hlt">Trench</span>, whereas in southwest Taiwan the Eurasian plate <span class="hlt">subducts</span> underneath PSP. The anomalous seismic intensity from intermediate-depth earthquakes should happen in Taiwan, if the <span class="hlt">subducted</span> plates are acting as an efficient waveguide for high-frequency seismic waves. Here we investigate the possible relationship between anomalous PGA patterns and the trapping effect of the high frequency signal in the PSP/EP. M>5 earthquakes along the <span class="hlt">subducted</span> PSP reveal depth dependent waveguide behavior, confirming an association with a wave guide effect in the <span class="hlt">subducting</span> slab rather than localized site amplification effects. Comparison of the PGA patterns and the seismic characteristics suggests that the abnormal intensity from intermediate-depth events is likely to be a result of excitation of high-frequency signals while propagating along the PSP. The events in EP show an extension of stronger seismic intensity and faster propagation speed along the Longitudinal Valley. This poses the question whether such an elongation of the intensity contours is associated with a fold of the Eurasian plate crust underneath eastern Taiwan. If so, we expect the guided waves to be observed at stations along the east coast or on the eastern flank of Central Range. The seismic waveform characteristics, however, reveal partial guiding across the southern portion of Taiwan and along the east coast, suggesting some of the high frequency energy may couple into the crust due to either long travel distance or thick plate. By detection and quantification of the <span class="hlt">subduction</span> zone guided waves, the geometry, thickness, velocity gradient, and heterogeneities of the plates can be further inferred through 2D and 3D finite-difference modeling and comparison with other well-established <span class="hlt">subduction</span> zones. Additionally, knowledge of waveguide characteristics and modeled parameters that fit the observations are critical inputs to connecting with the seismic intensity anomalies for ground motion and earthquake hazard estimation.</p> <div class="credits"> <p class="dwt_author">Chen, K. H.; Kennett, B. L.; Furumura, T.</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">257</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 " 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/2013AGUFM.T31F2584T"> <span id="translatedtitle">LWD lithostratigraphy, physical properties and correlations across tectonic domains at the NanTroSEIZE drilling transect, Nankai Trough <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">Since 2007 the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) has drilled a total of 15 sites across the Nankai Trough <span class="hlt">subduction</span> zone, including two sites on the incoming sediments of the Philippine Sea plate (PSP). Logging-while-drilling (LWD) data was acquired at 11 of these sites encompassing the forearc Kumano Basin, upper accretionary prism, toe region and input sites. Each of these tectonic domains is investigated for changes in physical properties and LWD characteristics, and this work fully integrates a large data set acquired over multiple years and IODP expeditions, most recently Expedition 338. Using the available logging-while-drilling data, primarily consisting of gamma ray, resistivity and sonic velocity, a log-based lithostratigraphy is developed at each site and integrated with the core, across the entire NanTroSEIZE transect. In addition to simple LWD characterization, the use of Iterative Non-hierarchical Cluster Analysis (INCA) on the sites with the full suite of LWD data clearly differentiates the unaltered forearc and slope basin sediments from the deformed sediments of the accretionary prism, suggesting the LWD is susceptible to the subtle changes in the physical properties between the tectonic domains. This differentiation is used to guide the development of tectonic-domain specific physical properties relationships. One of the most important physical property relationships between is the p-wave velocity and porosity. To fully characterize the character and properties of each tectonic domain we develop new velocity-porosity relationships for each domain found across the NanTroSEIZE transect. This allows the porosity of each domain to be characterized on the seismic scale and the resulting implications for porosity and pore pressure estimates across the plate interface fault zone.</p> <div class="credits"> <p class="dwt_author">Tudge, J.; Webb, S. I.; Tobin, H. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://adsabs.harvard.edu/abs/2003AGUFM.S11G..01H"> <span id="translatedtitle"><span class="hlt">Subduction</span> Drive of Plate 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">Don Anderson emphasizes that plate tectonics is self-organizing and is driven by <span class="hlt">subduction</span>, which rights the density inversion generated as oceanic lithosphere forms by cooling of asthenosphere from the top. The following synthesis owes much to many discussions with him. Hinge rollback is the key to kinematics, and, like the rest of actual plate behavior, is incompatible with bottom-up convection drive. <span class="hlt">Subduction</span> hinges (which are under, not in front of, thin leading parts of arcs and overriding plates) roll back into <span class="hlt">subducting</span> plates. The Pacific shrinks because bounding hinges roll back into it. Colliding arcs, increasing arc curvatures, back-arc spreading, and advance of small arcs into large plates also require rollback. Forearcs of overriding plates commonly bear basins which preclude shortening of thin plate fronts throughout periods recorded by basin strata (100 Ma for Cretaceous and Paleogene California). This requires subequal rates of advance and rollback, and control of both by <span class="hlt">subduction</span>. Convergence rate is equal to rates of rollback and advance in many systems but is greater in others. Plate-related circulation probably is closed above 650 km. Despite the popularity of concepts of plumes from, and <span class="hlt">subduction</span> into, lower mantle, there is no convincing evidence for, and much evidence against, penetration of the 650 in either direction. That barrier not only has a crossing-inhibiting negative Clapeyron slope but also is a compositional boundary between fractionated (not "primitive"), sluggish lower mantle and fertile, mobile upper mantle. Slabs sink more steeply than they dip. Slabs older than about 60 Ma when their <span class="hlt">subduction</span> began sink to, and lie down on and depress, the 650-km discontinuity, and are overpassed, whereas younger slabs become neutrally buoyant in mid-upper mantle, into which they are mixed as they too are overpassed. Broadside-sinking old slabs push all upper mantle, from base of oceanic lithosphere down to the 650, back under shrinking oceans, forcing rapid Pacific spreading. Slabs suck forward overriding arcs and continental lithosphere, plus most subjacent mantle above the transition zone. Changes in sizes of oceans result primarily from transfer of oceanic lithosphere, so backarcs and expanding oceans spread only slowly. Lithosphere parked in, or displaced from, the transition zone, or mixed into mid-upper mantle, is ultimately recycled, and regional variations in age of that submerged lithosphere may account for some regional contrasts in MORB. Plate motions make no kinematic sense in either the "hotspot" reference frame (HS; the notion of fixed plumes is easily disproved) or the no-net-rotation frame (NNR) In both, for example, many hinges roll forward, impossible with gravity drive. <span class="hlt">Subduction</span>-drive predictions are fulfilled, and paleomagnetic data are satisfied (as they are not in HS and NNR), in the alternative framework of propulsionless Antarctica fixed relative to sluggish lower mantle. Passive ridges migrate away from Antarctica on all sides, and migration of these and other ridges permits tapping fresh asthenosphere. (HS and NNR tend to fix ridges). Ridge migration and spreading rates accord with <span class="hlt">subduction</span> drive. All <span class="hlt">trenches</span> roll back when allowance is made for back-arc spreading and intracontinental deformation. Africa rotates slowly toward <span class="hlt">subduction</span> systems in the NE, instead of moving rapidly E as in HS and NNR. Stable NW Eurasia is nearly stationary, instead of also moving rapidly, and S and E Eurasian deformation relates to <span class="hlt">subduction</span> and rollback. The Americas move Pacificward at almost the full spreading rates of passive ridges behind them. Lithosphere has a slow net westward drift. Reference: W.B. Hamilton, An alternative Earth, GSA Today, in press.</p> <div class="credits"> <p class="dwt_author">Hamilton, W. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-12-01</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://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 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");' 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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">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/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 " 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/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 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/2014EGUGA..1612111D"> <span id="translatedtitle">Seismic anisotropy and texture development during early stages 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">Shear wave splitting measurements are frequently used to infer upper mantle flow trajectory, based on the fact that, under strain, olivine develops lattice-preferred orientation (LPO) textures in the convecting mantle. However, such inferences ought to be made carefully, since the relationship between splitting fast polarisation and olivine LPO depends on several factors, one of them being the deformation history of the volume of mantle in question. This is especially the case in regions such as <span class="hlt">subduction</span> zones, where complex and time-dependent mantle flow occurs. Here, we present an integrated model to simulate strain-history-dependent LPO development and measure the resulting shear wave splitting in a <span class="hlt">subduction</span> setting. We do this for a <span class="hlt">subduction</span> model that approximates the geometry of the double-sided Molucca Sea <span class="hlt">subduction</span> system in eastern Indonesia. We test a single-sided and a double-sided <span class="hlt">subduction</span> case, and compare the results to shear wave splitting observations of this region. Since the <span class="hlt">subduction</span> zone is fairly young, early textures from the slab's descent from the near-surface to the bottom of the mantle transition zone - which we simulate in our models - have not yet been overprinted by subsequent continuous flow. It further allows us to test the significance of the double-sided geometry, i.e., the need for a rear barrier to achieve <span class="hlt">trench</span>-parallel sub-slab mantle flow. We simulate olivine LPO evolution in polycrystalline aggregates as they move and deform along pathlines extracted from a 3-D mantle flow model. Interactions between crystals are described using the visco-plastic self-consistent (VPSC) approach. Unlike previous studies, we consider the entire <span class="hlt">subduction</span> history from <span class="hlt">subduction</span> initiation onwards. After calculating elastic properties associated with LPO textures, we estimate the resulting splitting parameters (fast direction ?, delay time ?t) for synthetic SKS phases. Our models demonstrate that complex, backazimuth-dependent behaviour in ? appears in even apparently simple models of <span class="hlt">subduction</span> zone mantle flow. We also show that although a rear barrier amplifies <span class="hlt">trench</span>-parallel sub-slab anisotropy due to mantle flow, it is not essential for producing <span class="hlt">trench</span>-parallel fast directions. In a simple model of one-sided <span class="hlt">subduction</span> and deformation dominated by the motion of dislocations belonging to the (010)[100] slip system, <span class="hlt">trench</span>-parallel fast directions result from a combination of simple shear and deformation by axial compression in the sub-slab mantle.</p> <div class="credits"> <p class="dwt_author">Di Leo, Jeanette; Walker, Andrew; Li, Zhong-Hai; Wookey, James; Ribe, Neil; Kendall, J.-Michael; Tommasi, Andréa</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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://ntrs.nasa.gov/search.jsp?R=PIA10909&hterms=white&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dwhite"> <span id="translatedtitle">Snow White <span class="hlt">Trenches</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><p/> This image was acquired by NASA's Phoenix Mars Lander's Surface Stereo Imager on the 25th Martian day of the mission, or Sol 24 (June 19, 2008), after the May 25, 2008, landing. This image shows the <span class="hlt">trenches</span> informally called 'Snow White 1' (left) and 'Snow White 2' (right). The <span class="hlt">trench</span> is about 5 centimeters (2 inches) deep and 30 centimeters (12 inches) long. <p/> 'Snow White' is located in a patch of Martian soil near the center of a polygonal surface feature, nicknamed 'Cheshire Cat.' The 'dump pile' is located at the top of the <span class="hlt">trench</span>, the side farthest away from the lander, and has been dubbed 'Croquet Ground.' The digging site has been named 'Wonderland.' <p/> This image has been enhanced to brighten shaded areas. <p/> The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.</p> <div class="credits"> <p class="dwt_author"></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">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/2012AGUFM.T43E2711M"> <span id="translatedtitle">Effects of <span class="hlt">subducting</span> buoyant oceanic ridges on <span class="hlt">subduction</span> zones: Area of influence and rotational effects</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">subduction</span> of buoyant oceanic ridges into <span class="hlt">subduction</span> zones is typically manifested by doming of arc rocks, shallowing of the <span class="hlt">trench</span>, and diffuse or shallowly-dipping Benioff zones. Two important questions include: 1) what distance inboard of the overriding plate are effects observed; and 2) what is the degree that colliding ridges can induce large-scale rotations of forearc terranes and consequent "back-arc opening" behind rotated forearc blocks. I describe regional effects from five relatively narrow ridges actively entering <span class="hlt">subduction</span> zones: 1) Carnegie; 2) Cocos; 3) Emperor seamount chain; 4) Louisville, and 5) D'Entrecasteaux. GPS from all areas shows a characteristic outward flow pattern in map view indicative of the strong landward push on the ridge along radial thrust systems within the overriding plate. This area of influence can extend 100s of kms. The pattern of outward flow from GPS vectors is consistent with the of bathymetry, gravity and earthquakes show some of these ridges act as strong indentors that push into the arc along strike-slip systems at their edges. In other cases likely related to thinner crust, no strong disruption of the outer forearc high or forearc basin is observed and adjacent to <span class="hlt">subducting</span> ridges. Rotating forearc blocks are most expressed by examples where the direction of <span class="hlt">subduction</span> is highly oblique and the least rotational effects are expressed where the direction of <span class="hlt">subduction</span> is orthogonal. Wider ridges also appear to have fewer rotational effects.</p> <div class="credits"> <p class="dwt_author">Mann, W. P.</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">266</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">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/2009GGG....1011006Z"> <span id="translatedtitle">Three-dimensional dynamics of hydrous thermal-chemical plumes in oceanic <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">Hydration and partial melting along <span class="hlt">subducting</span> slabs can trigger Rayleigh-Taylor-like instabilities. We use 3-D petrological-thermomechanical numerical simulations to investigate small-scale convection and hydrous, partially molten, cold plumes formed in the mantle wedge in response to slab dehydration. The simulations were carried out with the I3ELVIS code, which is based on a multigrid approach combined with marker-in-cell methods and conservative finite difference schemes. Our numerical simulations show that three types of plumes occur above the slab-mantle interface: (1) finger-like plumes that form sheet-like structure parallel to the <span class="hlt">trench</span>, (2) ridge-like structures perpendicular to the <span class="hlt">trench</span>, and (3) flattened wave-like instabilities propagating upward along the upper surface of the slab and forming zigzag patterns parallel to the <span class="hlt">trench</span>. The viscosity of the plume material is the main factor controlling the geometry of the plumes. Our results show that lower viscosity of the partially molten rocks facilitates the Rayleigh-Taylor-like instabilities with small wavelengths. In particular, in low-viscosity models (1018-1019 Pa s) the typical spacing of finger-like plumes is about 30-45 km, while in high-viscosity models (1020-1021 Pa s) plumes become rather sheet-like, and the spacing between them increases to 70-100 km. Water released from the slab forms a low-viscosity wedge with complex 3-D geometries. The computed spatial and temporal pattern of melt generation intensity above the slab is compared to the distribution and ages of volcanoes in the northeast <span class="hlt">Japan</span>. Based on the similarity of the patterns we suggest that specific clustering of volcanic activity in this region could be potentially related to the activity of thermal-chemical plumes.</p> <div class="credits"> <p class="dwt_author">Zhu, Guizhi; Gerya, Taras V.; Yuen, David A.; Honda, Satoru; Yoshida, Takeyoshi; Connolly, James A. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-11-01</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://academic.research.microsoft.com/Publication/56038150"> <span id="translatedtitle">Relationship between bend-faulting at <span class="hlt">trenches</span> and intermediate-depth 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">We have studied faulting associated with bending of the incoming oceanic plate along segments of Middle America and Chile <span class="hlt">subduction</span> zones and its relationship to intermediate-depth intraslab seismicity and slab geometry. Multibeam bathymetry shows that bending-related faulting forms patterns made of sets of faults with orientations ranging from parallel to almost perpendicular to the <span class="hlt">trench</span> axis. These fault patterns may</p> <div class="credits"> <p class="dwt_author">César R. Ranero; Antonio Villaseñor; Jason Phipps Morgan; Wilhelm Weinrebe</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">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/2003TrGeo...2..451M"> <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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</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, carry a record of low-temperature interaction with the ocean, atmosphere, and continents. <span class="hlt">Subduction</span> and recycling of these components into the mantle has the potential to change mantle composition in terms of volatile contents, heat-producing elements, radiogenic isotope systematics, and trace element abundances. Enrichments in volatile and potassium, uranium, and thorium contents could change the rheological, thermal, and geodynamical behavior of portions of the mantle. Changing isotope and trace-element systematics provide a means for tracking mantle mixing and the possible <span class="hlt">subduction</span> modification of the deep mantle. A large number of studies point to possible contributions of <span class="hlt">subducted</span> sediments and altered oceanic crust (AOC) to the mantle-source region for enriched mantle II (EMII) and high mu (HiMU) enriched oceanic island basalts. Transit through the <span class="hlt">subduction</span> zone, however, changes the composition of the <span class="hlt">subducting</span> sediment and AOC from that measured outboard of <span class="hlt">trenches</span>.This chapter focuses on <span class="hlt">subduction</span> zone processes and their implications for mantle composition. It examines <span class="hlt">subduction</span> contributions to the shallow mantle that may be left behind in the wedge following arc magma genesis, as well as the changing composition of the slab as it is processed beneath the fore-arc, volcanic front and rear arc on its way to the deep mantle. Much of this chapter uses boron and the beryllium isotopes as index tracers: boron, because it appears to be completely recycled in volcanic arcs with little to none <span class="hlt">subducted</span> into the deep mantle, and cosmogenic 10Be, with a 1.5 Ma half-life, because it uniquely tracks the contribution from the <span class="hlt">subducted</span> sediments.The focus here is on <span class="hlt">subduction</span> processes from <span class="hlt">trench</span> to rear arc. This chapter starts with a brief discussion of recent thermal models for the downgoing plate and the prograde metamorphic mineralogy of the oceanic crust and sedimentary veneer; the reader is referred to Schmidt and Poli (Chapter 3.17), for an extensive discussion. In the next step it uses 10Be to estimate the absolute mass of sediments <span class="hlt">subducted</span> to the volcanic arc, in comparison to that supplied to the <span class="hlt">subduction</span> <span class="hlt">trenches</span>. Flux balances for 10Be <span class="hlt">subducted</span> in the sediments versus that erupted in the volcanic arc provide estimates of the fraction of 10Be extracted from the downgoing plate, which can be extrapolated to other elements (cf. Plank and Langmuir, 1993). It subsequently looks at chemical changes for selected elements across the <span class="hlt">subduction</span> zone, using data from fore-arc serpentinite mud volcanoes, <span class="hlt">subduction</span>-assemblage metamorphic rocks, high-pressure eclogites, and volcanic lavas from Kurile cross-arc transects, and examines boron-isotope systematics across the convergent margin. Lithium-isotope systematics and comparison of 10Be with uranium-series systematics sometimes delineate multiple stages of <span class="hlt">subduction</span> modification of the mantle and pinpoint the compositional effects of prior <span class="hlt">subduction</span> modification on the upper mantle. This contribution ends with estimates of the efficiency of arsenic, antimony, potassium, caesium, rubidium, barium, strontium, uranium, thorium, lead, cerium, samarium, neodymium, lutetium, and hafnium recycling from <span class="hlt">trench</span> to rear arc, relative to that of boron and beryllium.2.11.2. Thermal Structure and Mineralogy of The <span class="hlt">Subducting</span> PlateCentral to understanding the recycling of <span class="hlt">subducted</span> elements in the arc or their <span class="hlt">subduction</span> to the deep mantle is the temperature variation in the <span class="hlt">subducting</span> slab, and the prograde mineral assemblages in the sediment, oceanic crust, and lithospheric mantle. Together, they determine where dehydration of the sediments, crust, and deeper <span class="hlt">subducting</span> mantle occurs, a</p> <div class="credits"> <p class="dwt_author">Morris, J. D.; Ryan, J. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-12-01</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/2013AGUFM.T54A..02W"> <span id="translatedtitle">Stress and Strength of Seismogenic and Creeping <span class="hlt">Subduction</span> Faults (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">Force balance studies of <span class="hlt">subduction</span> zone forearcs constrained by earthquake focal mechanisms, active faulting, and topography suggest very weak <span class="hlt">subduction</span> megathrusts. If represented by an effective coefficient of friction ?', the ratio of shear to normal stress at failure, the average ?' value of most megathrusts is about 0.03, seldom exceeding 0.06, an order of magnitude lower than fault strengths predicted by the Byerlee's law with hydrostatic pore fluid pressure. The ?' value required to explain heat flow observations using megathrust frictional heating modeling is usually also about 0.03, regardless of whether the megathrust is seismogenic or creeping. The mechanism for the weakness is not fully understood, although it must be a combined consequence of fault zone material, fault zone fabric, and pore fluid pressure. Prior to March 11, 2011, the <span class="hlt">Japan</span> <span class="hlt">Trench</span> was a rare exception where pervasive margin-normal compression of the upper plate made it difficult to infer megathrust strength. But wholesale stress reversal in much of the forearc due to the M 9 Tohoku earthquake dramatically verified the low-strength (?' = 0.03) prediction of Wang and Suyehiro (1999, GRL 26(35), 2307-2310). This value translates to depth-dependant shear strength of roughly 10 MPa at 10 km and 30 MPa at 30 km. With regard to how fault strength and stress affect earthquake processes, several issues deserve special attention. (1) There is little doubt that no megathrust is 'strongly' locked, but creeping megathrusts can be either weaker or stronger than locked faults. In fact, <span class="hlt">subduction</span> of extremely rugged seafloor causes creeping, despite strong resistance caused by geometrical incompatibilities. Physical meanings of regarding locked and creeping faults as 'strongly coupled' and 'weakly coupled', respectively, are in serious question. (2) A ?' value of 0.03-0.05 is a spatial average. For a smooth fault, even small changes in pore fluid pressure alone can cause local deviations from this average by a factor of two or three. Locally high locking stresses and/or greater coseismic stress drops along smooth faults are by no means surprising and are not indicative of <span class="hlt">subducted</span> topographic features such as seamounts. (3) Given the extremely low background strength and stress, the application of laboratory-observed high-rate (or dynamic) weakening of frictional contacts to natural <span class="hlt">subduction</span> faults requires much careful thinking. In the lab, the contact is usually weakened from a static strength of ?' ~ 0.6 to dynamic values ~ 0.1. No natural <span class="hlt">subduction</span> faults have an average static strength of 0.6, not even 0.1. Therefore such weakening can only take place on small fault patches of locally high strength and stress. If high-strength patches have ?' values much greater than 0.1 (to allow weakening to 0.1), most parts of the locked megathrust must have ?' values less than 0.03 (to yield an average ?' of 0.03).</p> <div class="credits"> <p class="dwt_author">Wang, K.; Bilek, S. L.; Wada, I.; Gao, X.; Brown, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2012AGUFM.S44A..06F"> <span id="translatedtitle">Numerical modeling of the deformations associated with large <span class="hlt">subduction</span> earthquakes through the seismic cycle</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 3D finite element code (Zebulon-Zset) is used to model deformations through the seismic cycle in the areas surrounding the last three large <span class="hlt">subduction</span> earthquakes: Sumatra, <span class="hlt">Japan</span> and Chile. The mesh featuring a broad spherical shell portion with a viscoelastic asthenosphere is refined close to the <span class="hlt">subduction</span> zones. The model is constrained by 6 years of postseismic data in Sumatra area and over a year of data for <span class="hlt">Japan</span> and Chile plus preseismic data in the three areas. The coseismic displacements on the <span class="hlt">subduction</span> plane are inverted from the coseismic displacements using the finite element program and provide the initial stresses. The predicted horizontal postseismic displacements depend upon the thicknesses of the elastic plate and of the low viscosity asthenosphere. Non-dimensionalized by the coseismic displacements, they present an almost uniform value between 500km and 1500km from the <span class="hlt">trench</span> for elastic plates 80km thick. The time evolution of the velocities is function of the creep law (Maxwell, Burger or power-law creep). Moreover, the forward models predict a sizable far-field subsidence, also with a spatial distribution which varies with the geometry of the asthenosphere and lithosphere. Slip on the <span class="hlt">subduction</span> interface does not induce such a subsidence. The observed horizontal velocities, divided by the coseismic displacement, present a similar pattern as function of time and distance from <span class="hlt">trench</span> for the three areas, indicative of similar lithospheric and asthenospheric thicknesses and asthenospheric viscosity. This pattern cannot be fitted with power-law creep in the asthenosphere but indicates a lithosphere 60 to 90km thick and an asthenosphere of thickness of the order of 100km with a burger rheology represented by a Kelvin-Voigt element with a viscosity of 3.1018Pas and ?Kelvin=?elastic/3. A second Kelvin-Voigt element with very limited amplitude may explain some characteristics of the short time-scale signal. The postseismic subsidence is conspicuous over Thailand and Malaysia (Satirapod et al., ASR, 2012). A low viscosity wedge, with a viscosity of the order of 3. 1018 Pas is necessary to explain data in the middle-field (volcanic arc area). Post-seismic slip on the fault plane (15% of the cosismic slip) in the months after the earthquakes explains near-field deformations. The creep law and geometry deduced from postseismic data can be used to predict deformations through the seismic cycle. Far away (500 to 1500km) sizable (5mm/yr to 1cm/yr) interseismic horizontal velocities are expected. Although one should not deny the presence of long-term intraplate geologic deformations, the seismic cycle contributes significantly to the intraplate compressive preseismic deformations in the Sunda and Amurian plates. The interseismic peak in vertical velocity, predicted by elastic backslip models over the end of the locked portion of the interface can be, in viscoelastic models, pushed over the continentward border of the LVW. This may explain the pattern of vertical velocities in Northern Honshu previous to Tohoku earthquake. The deviatoric stresses associated with the seismic cycle add up to the long-term tectonic stresses and are predicted to induce a peak in extensional stress in the <span class="hlt">subducting</span> and overriding plates with a time delay which increases with the distance to the <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Fleitout, L.; Trubienko, O.; Garaud, J.; Vigny, C.; Cailletaud, G.; Simons, W. J.; Satirapod, C.; Shestakov, N.</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">272</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.T52B0274Z"> <span id="translatedtitle">Diagenetic Phase Boundary at the Nankai Trough, SW <span class="hlt">Japan</span>: Relationship to the Decollement/ Proto-Decollement</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 <span class="hlt">subduction</span> environment, phase changes within sediments may affect their subsequent deformation during the accretion process. At the Nankai trough, off Cape Muroto, southwest <span class="hlt">Japan</span>, a phase change from cristobalite to quartz occurs near the depth of the decollement zone, with a prominent seismic reflector marking this diagenetic boundary between the upper and lower Shikoku Basin facies. Outboard of the <span class="hlt">trench</span> this reflector is initially at greater depth than the projected proto-decollement but migrates upward to transgress it before reaching Ocean Drilling Program Site 1173 in the landward direction. This effectively encases the entirety of the decollement in a lithology depleted in cristobalite and enriched in quartz. Creation of a depth section within a three-dimensional seismic reflection volume enabled this diagenetic reflector to be mapped relative to the oceanic basement reflector, the seafloor reflector, and intervening stratigraphic reflectors. Within areas of recent sedimentation in the <span class="hlt">trench</span> the diagenetic reflector diverges from the basement reflector and rises vertically in the section. This upward migration of the diagenetic reflector follows a similar upward migration of the isotherms. Thermal gradients in the Muroto region are increased by proximity to the Shikoku Basin paleo-spreading center axis. At <span class="hlt">subduction</span> regions with lower thermal gradients the cristobalite zone could be expanded to greater depths, allowing sediments untransformed by this diagenetic process to be incorporated into the toe of the prism and potentially altering initial accretionary structures.</p> <div class="credits"> <p class="dwt_author">Zscheile, G.; Moore, J. C.; Bangs, N.; Gulick, S.; Moore, G.</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">273</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=PIA11031&hterms=white&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dwhite"> <span id="translatedtitle">Snow White <span class="hlt">Trench</span> (Animation)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary"><p/> [figure removed for brevity, see original site] Click on image for animation <p/> This animation shows the evolution of the <span class="hlt">trench</span> called 'Snow White' that NASA's Phoenix Mars Lander began digging on the 22nd Martian day of the mission after the May 25, 2008, landing. <p/> The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.</p> <div class="credits"> <p class="dwt_author"></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">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/2013AGUFMDI33A2234Z"> <span id="translatedtitle">Oceanic plate weakened by flexural bending-induced faulting in the outer rise region of the Mariana <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">Strong flexural bending near <span class="hlt">trenches</span> could significantly weaken oceanic plates through development of <span class="hlt">trench</span>-parallel extensional normal faults. We assessed the oceanic plate weakening near the outer rise region of the Mariana <span class="hlt">subduction</span> zone by analyzing and modeling the plate deformation caused by flexural bending. We first obtained a 3-D deformation surface of the <span class="hlt">subducting</span> plate by removing from seafloor bathymetry the topographic effects of sediments, seamounts, and age-related thermal subsidence. We then calculated theoretical models of plate deformation and inverted for along-<span class="hlt">trench</span> changes in the vertical force and bending moment at the <span class="hlt">trench</span> axis, as well as spatial variations in the effective elastic thickness of the <span class="hlt">subducting</span> plate, that best explain the observations. We found that to replicate simultaneously the observed steep slope of the seafloor near the <span class="hlt">trench</span> axis and the long-wavelength flexural profiles seaward of the outer rise region, the effective elastic thickness of the plate must change significantly. The best-fitting models reveal that the effective elastic thickness is about 45-55 km seaward of the outer rise (TeMax), but is reduced to only 19-40 km <span class="hlt">trench</span>-ward of the outer rise region (TeMin); the transition from TeMax to TeMin occurs at Xr =70-120 km away from the <span class="hlt">trench</span> axis. The resultant reduction in the calculated effective elastic thickness, i.e., 1 - (TeMin /TeMax), is in the range of 20-60%, being the greatest near the Challenger Deep area, where the plate deforms significantly within a narrow distance from the <span class="hlt">trench</span> axis and the <span class="hlt">trench</span> axis is the deepest. Our results revealed that reduction in Te along the Mariana <span class="hlt">trench</span> does not exceed 60%, implying that an elastic core remains in the <span class="hlt">subducting</span> plate despite pervasive faulting caused by flexural bending near the <span class="hlt">trench</span> axis.</p> <div class="credits"> <p class="dwt_author">Zhang, F.; Lin, J.; Zhan, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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://www.osti.gov/scitech/biblio/6148863"> <span id="translatedtitle">Model geoid anomalies due to <span class="hlt">subduction</span> of inextensible lithosphere</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">We compute geoid slopes from models of <span class="hlt">subduction</span> in which the <span class="hlt">subducted</span> lithosphere is much stronger than the surrounding mantle. Geoid slope contributions from both the lithospheric slab and mantle boundary deformations are computed from finite element analysis of mantle flow. The finite element model includes a slab of finite length and a depth dependent Newtonian rheology for the surrounding mantle. We find that observed geoid anomalies at <span class="hlt">subduction</span> zones, which are positive, cannot be matched by models with uniform mantle viscosity. However, even with a strong <span class="hlt">subducted</span> lithosphere, the ratio of driving load to boundary deformation is significantly increased by a ten-fold increase of viscosity with depth, resulting in a geoid high. We find that the sign of the geoid slopes within 3000 km of the <span class="hlt">trench</span> are independent of maximum depth of the slab for maximum depths from 700 km to 2800 km. copyright American Geophysical Union 1987</p> <div class="credits"> <p class="dwt_author">Willemann, R.J.; Anderson, C.A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-08-01</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/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 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..12.1209O"> <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">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/2011AGUFM.T13C2387P"> <span id="translatedtitle"><span class="hlt">Subduction</span> seismicity at the global scale</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 framework of the EURYI Project 'Convergent margins and seismogenesis: defining the risk of great earthquakes by using statistical data and modelling', a global collection of recent intraslab seismicity has been performed. Based on EHB hypocenter and CMT Harvard catalogues, the hypocenters, nodal planes and seismic moments of worldwide <span class="hlt">subduction</span>-related earthquakes were extracted for the period 1976 - 2007. Data were collected for centroid depths between sea level and 700 km and for magnitude Mw ? 5.5. For each <span class="hlt">subduction</span> zone, a set of <span class="hlt">trench</span>-normal transects were constructed choosing a 120km width of the cross-section on each side of a vertical plane and a spacing of 1 degree along the <span class="hlt">trench</span>. For each of the 505 resulting transects, the whole <span class="hlt">subduction</span> seismogenic zone was mapped as focal mechanisms projected on to a vertical plane after their faulting type classification according to the Aki-Richards convention. Transect by transect, first the seismicity that can be considered not related to the <span class="hlt">subduction</span> process under investigation was removed, then was selected the upper plate seismicity (i.e. earthquakes generated within the upper plate as a result of the <span class="hlt">subduction</span> process). After deletion from the so obtained event subset of the interplate seismicity as identified in the framework of this project by Heuret et al. (2011), we can be reasonably confident that the remaining seismicity can be related to the <span class="hlt">subducting</span> plate. Among these earthquakes we then selected the intermediate and deep depth seismicity. The upper limit of the intermediate depth seismicity is fixed at 70 km depth in order to avoid possible mixing with interplate seismicity. The ranking of intermediate depth and deep seismicity was referred to earthquakes with focal depth between 70-300 km and with depth exceeding 300 km, respectively. Outer-rise seismicity was also selected. Following Heuret et al. (2011), the 505 transects were merged into 62 larger segments that were ideally homogeneous in terms of their seismogenic zone characteristics. Comparisons between main seismic parameters (e.g. cumulated seismic moment, P- and T-axes distributions, spatial and temporal distribution of largest magnitudes) with relation to both the different categories selected and the different segments have been performed in order to obtain a snapshot on the general behaviour of global <span class="hlt">subduction</span>-related seismicity.</p> <div class="credits"> <p class="dwt_author">Presti, D.; Heuret, A.; Funiciello, 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">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/2014GeoRL..41.1951D"> <span id="translatedtitle">Slab detachment in laterally varying <span class="hlt">subduction</span> zones: 3-D numerical 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">Understanding the three-dimensional (3-D) dynamics of <span class="hlt">subduction</span>-collision systems is a longstanding challenge in geodynamics. We investigate the impact of slab detachment in collision systems that are subjected to along-<span class="hlt">trench</span> variations. High-resolution thermomechanical numerical models, encompassing experimentally derived flow laws and a pseudo free surface, are employed to unravel lithospheric and topographic evolutions. First, we consider coeval <span class="hlt">subduction</span> of adjacent continental and oceanic lithospheres (SCO). This configuration yields to two-stage slab detachment during collision, topographic buildup and extrusion, variable along-<span class="hlt">trench</span> convergence rates, and associated <span class="hlt">trench</span> deformation. The second setting considers a convergent margin, which is laterally limited by a transform boundary (STB). Such collisional system is affected by a single slab detachment, little <span class="hlt">trench</span> deformation, and moderately confined upper plate topography. The effect of initial thermal slab age on SCO and STB models are explored. Similarities with natural analogs along the Arabia-Eurasia collision are discussed.</p> <div class="credits"> <p class="dwt_author">Duretz, T.; Gerya, T. V.; Spakman, W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-03-01</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/2011AGUFM.T12A..06T"> <span id="translatedtitle">Friction and stress coupling on the <span class="hlt">subduction</span> interfaces</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 a <span class="hlt">subduction</span> zone, the down-going oceanic plate slides underneath the overriding plate. The frictional resistance to the relative motion between the plates generates great earthquakes along the <span class="hlt">subduction</span> interface, which can cause tremendous damage in the civil life and property. There is a strong incentive to understand the frictional strength of the <span class="hlt">subduction</span> interface. One fundamental question of mechanics of subuction is the degree of coupling between the plates, which is linked to the size of earthquakes. It has been noted that the <span class="hlt">trench</span>-parallel (along-strike) gravity variation correlates positively with the <span class="hlt">trench</span>-parallel topography anomaly and negatively with the activity of great earthquake (Song and Simons, 2003). Regions with a negative <span class="hlt">trench</span>-parallel gravity anomaly are more likely to have great earthquakes. The interpretation of such correlation is that strong coupling along <span class="hlt">subduction</span> interface will drag down the for-arc region of the overriding plate, which generates the gravity and topography anomalies, and could store more strain energy to be released during a great earthquake. We developed a 2D numerical thermo-mechanical code for modeling <span class="hlt">subduction</span>. The numerical method is based on an explicit finite element method similar to the Fast Lagrangian Analysis of Continua (FLAC) technique. The constitutive law is visco-elasti-plastic with strain weakening. The cohesion and friction angle are reduced with increasing plastic strain after yielding. To track different petrologic phases, Lagrangian particles are distributed in the domain. Basalt-eclogite, sediment-schist and peridotite-serpentinite phase changes are included in the model. Our numerical models show that the degree of coupling negatively correlates with the coefficient of friction. In the low friction case, the <span class="hlt">subduction</span> interface has very shallow dipping angle, which helps to elastically couple the downing plate with the overriding plate. The topography and gravity anomalies of the low friction case also indicate strong coupling between plates.</p> <div class="credits"> <p class="dwt_author">Tan, E.; Lavier, L.; van Avendonk, H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</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_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 id="PageLinks" class="pageLinks"> <span> <a onClick='return 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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://www.osti.gov/scitech/biblio/6519485"> <span id="translatedtitle"><span class="hlt">Subduction</span> seismicity and tectonics in the lesser Antilles arc</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">We have studied the mechanisms of 17 earthquakes along the Lesser Antilles <span class="hlt">subduction</span> zone to examine a site where very old lithosphere <span class="hlt">subducts</span> at a slow convergence rate. No large thrust earthquakes occurred during the 1950-1978 study period; the three large (magnitude seven) events are all normal faults. One is a normal faulting event seaward of the <span class="hlt">trench</span>. Its aftershock sequence includes strike slip events on differently oriented faults, probably due to lateral block motion in response to the main shock. A second indicates extension within the slab at depth. These observations suggest that <span class="hlt">subduction</span> in this region is primarily decoupled and aseismic unless the time interval studied is unrepresentative. The third normal fault earthquake occurred within the upper plate with fault planes perpendicular to the arc and <span class="hlt">trench</span>. This unusual geometry may represent a flexural response to the <span class="hlt">subduction</span> of the Barracuda Ridge, a major bathymetric high with uncompensated excess mass at depth which seems analogous to flanking ridges found along some Mid-Atlantic Ridge fracture zones. Thus, the Barracuda Ridge is not buoyant and does not affect Benioff zone dip. Strike slip faulting occurs at depth in the <span class="hlt">subduction</span> zone along a concentration normal to the arc and may indicate a fossil fracture zone. There is no direct evidence in the shallow seismicity for the hypothetical North America-South America-Caribbean triple junction through some of the oceanic 'intraplate' seismicity is consistent with such a boundary.</p> <div class="credits"> <p class="dwt_author">Stein, S.; Engeln, J.F.; Wiens, D.A.; Fujita, K.; Speed, R.C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-10-10</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/2001Tectp.339..311A"> <span id="translatedtitle">Tectonic stress state in NE <span class="hlt">Japan</span> as part of the Okhotsk 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">An existing geodetic flow velocity model, obtained by using an internal free network adjustment technique, is used to derive estimates for various strain rates parameters in NE <span class="hlt">Japan</span>. The greatest shortening rates of the principal strains, trending ˜E-W, are located in regions where much steady, internal, frame-invariant plastic flow deformation is observed to be taking place. The internal geodetic adjustment technique yielded the internal deformation in the Tohoku arc; most of the intraplate deformations, including the much folding deformations observed in the inner zone, are produced from within. An interseismic transient elastic loading at a strongly coupled/locked <span class="hlt">Japan</span> <span class="hlt">trench</span> would not be needed. The observed ongoing extensive ductile folding deformation in the inner zone of Tohoku may mean that the geodetic strain rates, causing shortening at ˜2-3 cm/yr, probably reflect the more correct level of the deformation, which is steady/permanent, in NE <span class="hlt">Japan</span> as compared with seismic/faulting data, which indicate ˜0.5 cm/yr shortening. The calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework. The tectonic stress state in NE <span class="hlt">Japan</span>, as part of the Okhotsk plate, could mostly be influenced by the Okhotsk plate, which is extruding southward to lessen the significant accumulated contractional deformation in NE Asia in the Verkhoyansk-Cherskii mountains. The principal strain rates are ˜N-S extensional essentially everywhere in NE <span class="hlt">Japan</span>, as a result of the southerly extrusion, except in its southernmost leading edge, in the Uetsu/Fossa Magna province, where the <span class="hlt">Japan</span> Alps rampart rises in front of the extrusion. Here an ˜E-W compressional stress state prevails. A second ˜E-W contractional zone is found in north-central Tohoku, extending from the Sanriku province in the outer zone to the inner zone in the <span class="hlt">Japan</span> Sea side, being more prevalent in the latter zone. The calculated rotation rates from the geodetic flow model are clockwise (CW) in both of the ˜E-W contractional regions. NE <span class="hlt">Japan</span>, extruding southward, faces buttresses in (1) the Oga-Ojika Line (OOL), and/or a crustal weakness zone between the northern and the southern halves of Tohoku approx. at ˜38.5°N latitude, and, especially, (2) the Japanese Alps rampart; these obstacles cause the northern and southernmost Tohoku to veer to its right and rotate CW, thereby setting up the ˜E-W-trending compressional deformation in their respective inner zones. Between the OOL (or the 38.5°N boundary) and the Kanto Tectonic Line (KTL), the sense of the differential rotations is counterclockwise (CCW), towards the ocean to the SE. The northern Tohoku (north of the OOL) and the southernmost Tohoku (south of the KTL) cannot rotate CCW towards the ocean because of the Izu block's collision in the south and the relatively strong coupling along the <span class="hlt">subduction</span> interface beneath the <span class="hlt">Japan</span> <span class="hlt">trench</span> in the north off-Sanriku. The relatively stronger long-term coupling between the northern Tohoku and the Pacific plate at the Sanriku coast, with respect to that in off-Fukushima, is due to a flatter <span class="hlt">subduction</span> of the Pacific slab there, increasing the plates' interface contact area; the flattening of the <span class="hlt">subduction</span> dip angle was caused by CCW rotation and shifting of the northern Tohoku along the dextral Honjo-Matsushima Line, roughly corresponding to the OOL, towards the Pacific and overriding of the <span class="hlt">subduction</span> zone during the formation of the <span class="hlt">Japan</span> Sea.</p> <div class="credits"> <p class="dwt_author">Altis, Sungat</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-09-01</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://adsabs.harvard.edu/abs/2014EGUGA..16.3144B"> <span id="translatedtitle">Intrinsic and Extrinsic Factors in <span class="hlt">Subduction</span> Dynamics</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 realization that tectonic plates sink into the mantle, in a process we now call <span class="hlt">subduction</span>, our understanding of this process has improved dramatically through the combined application of observations, theory and modeling. During that time independent research groups focusing on different aspects of <span class="hlt">subduction</span> have identified factors with a significant impact on <span class="hlt">subduction</span>, such as three-dimensionality, slab rollback, rheology of the slab and mantle and magnitude of phase changes. However, as each group makes progress we often wonder how these different factors interact as we all strive to understand the real world <span class="hlt">subduction</span> system. These factors can be divided in two groups: intrinsic factors, including the age of the slab, its thermal structure, composition, and rheology, and extrinsic factors including others forces on plates, overall mantle flow, structure of the overriding plate, rheology of the mantle and phase changes. In addition, while modeling has been a powerful tool for understanding <span class="hlt">subduction</span>, all models make important (but often necessary) approximations, such as using two dimensions, imposed boundary conditions, and approximations of the conservation equations and material properties. Here we present results of a study in which the "training wheels" are systematically removed from 2D models of <span class="hlt">subduction</span> to build a more realistic model of <span class="hlt">subduction</span> and to better understand how combined effects of intrinsic and extrinsic factors contribute to the dynamics. We find that a change from the Boussinesq to the extended Boussinesq form of the conservation equations has a dramatic effect on slab evolution in particular when phase changes are included. Allowing for free (dynamically-driven) <span class="hlt">subduction</span> and <span class="hlt">trench</span> motion is numerically challenging, but also an important factor that allows for more direct comparison to observations of plate kinematics. Finally, compositional layering of the slab and compositionally-controlled phase changes also have a strong effect on the rate of <span class="hlt">subduction</span> and small-scale buckling and folding of the slab. These studies suggest that the evolution of slabs can differ significantly from more simplified models, and therefore a better understanding of the underlying physical controls on slab dynamics requires more realistic models.</p> <div class="credits"> <p class="dwt_author">Billen, Magali; Arredondo, Katrina</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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://www.terrapub.co.jp/journals/EPS/pdf/2001/5309/53090861.pdf"> <span id="translatedtitle">Dehydration of serpentinized slab mantle: Seismic evidence from 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 seismicity in the <span class="hlt">subducting</span> Philippine Sea slab (PHS) beneath southwest <span class="hlt">Japan</span> shows a variety of modes of occurrence. We try to explain this variety on the basis of dehydration embrittlement in the <span class="hlt">subducting</span> oceanic crust and\\/or mantle. The PHS <span class="hlt">subducting</span> along the Nankai Trough shows commonly a single narrow seismic zone shallower than 60 km, which may reflect dehydration</p> <div class="credits"> <p class="dwt_author">Tetsuzo Seno; Dapeng Zhao; Yoji Kobayashi; Masao Nakamura</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">285</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 " 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/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 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/2005JGRB..110.2304B"> <span id="translatedtitle">Magnitude and location of historical earthquakes in <span class="hlt">Japan</span> and implications for the 1855 Ansei Edo 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"><span class="hlt">Japan</span> Meteorological Agency (JMA) intensity assignments IJMA are used to derive intensity attenuation models suitable for estimating the location and an intensity magnitude Mjma for historical earthquakes in <span class="hlt">Japan</span>. The intensity for shallow crustal earthquakes on Honshu is equal to -1.89 + 1.42MJMA - 0.00887?h - 1.66log?h, where MJMA is the JMA magnitude, ?h = (?2 + h2)1/2, and ? and h are epicentral distance and focal depth (km), respectively. Four earthquakes located near the <span class="hlt">Japan</span> <span class="hlt">Trench</span> were used to develop a <span class="hlt">subducting</span> plate intensity attenuation model where intensity is equal to -8.33 + 2.19MJMA -0.00550?h - 1.14 log ?h. The IJMA assignments for the MJMA7.9 great 1923 Kanto earthquake on the Philippine Sea-Eurasian plate interface are consistent with the <span class="hlt">subducting</span> plate model; Using the <span class="hlt">subducting</span> plate model and 226 IJMA IV-VI assignments, the location of the intensity center is 25 km north of the epicenter, Mjma is 7.7, and MJMA is 7.3-8.0 at the 1? confidence level. Intensity assignments and reported aftershock activity for the enigmatic 11 November 1855 Ansei Edo earthquake are consistent with an MJMA 7.2 Philippine Sea-Eurasian interplate source or Philippine Sea intraslab source at about 30 km depth. If the 1855 earthquake was a Philippine Sea-Eurasian interplate event, the intensity center was adjacent to and downdip of the rupture area of the great 1923 Kanto earthquake, suggesting that the 1855 and 1923 events ruptured adjoining sections of the Philippine Sea-Eurasian plate interface.</p> <div class="credits"> <p class="dwt_author">Bakun, William H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-02-01</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://academic.research.microsoft.com/Publication/48935935"> <span id="translatedtitle">Forearc 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://academic.research.microsoft.com/">Microsoft Academic Search </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</p> <div class="credits"> <p class="dwt_author">Mark K. Reagan; Osamu Ishizuka; Robert J. Stern; Katherine A. Kelley; Yasuhiko Ohara; Janne Blichert-Toft; Sherman H. Bloomer; Jennifer Cash; Patricia Fryer; Barry B. Hanan; Rosemary Hickey-Vargas; Teruaki Ishii; Jun-Ichi Kimura; David W. Peate; Michael C. Rowe; Melinda Woods</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">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/1988JGR....93.8911M"> <span id="translatedtitle">Mechanisms of sediment accretion in the Middle America <span class="hlt">Trench</span> off 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">High-resolution seismic reflection and Sea Beam bathymetrie data provide insights into the processes of sediment offscraping and accretion in the Middle America <span class="hlt">Trench</span> off southern Mexico. Thick terrigenous sediments that are transported down Ometepec Canyon and accumulate along the <span class="hlt">trench</span> floor are scraped off the oceanic plate and accreted in thrust packets to the lower <span class="hlt">trench</span> slope. The packets offscraped represent most of the <span class="hlt">trench</span> strata. Underlying hemipelagic deposits that accumulate on the seafloor seaward of the <span class="hlt">trench</span> are <span class="hlt">subducted</span> landward of the toe of the slope. Horizontal displacement on the thrusts is less than 1 km. Leading edge folds are the surface expressions of the thrusts and strike subparallel to the base of the <span class="hlt">trench</span> slope. The folds are continuous for as much as 10 km and have amplitudes as high as 200 m and wavelengths of 0.5 to 2 km. Folds are best developed along sections of the <span class="hlt">trench</span> with interbedded silly turbidite and mud deposits. Folds are absent where thick coarse-grained fan deposits occur. Thickening of the thrust packets occurs by large-scale thrust duplication, by layer-parallel shortening, and by deposition of material that slumps off the leading edge of older upslope thrust blocks.</p> <div class="credits"> <p class="dwt_author">Moore, Gregory F.; Shipley, Thomas H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-08-01</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://www.agu.org/journals/gl/gl0409/2004GL019489/2004GL019489.pdf"> <span id="translatedtitle">Seismic evidence for dehydration embrittlement of the <span class="hlt">subducting</span> Pacific 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">We determined a fine 3-D P-wave velocity structure of the <span class="hlt">subducting</span> Pacific slab by inverting a large number of high-quality P-arrival times to better understand the genesis of the 26 May 2003 Miyagi-oki earthquake (Mw 7.0) and its aftershock sequence, which occurred within the <span class="hlt">subducting</span> Pacific slab beneath northeast (NE) <span class="hlt">Japan</span>. Lateral and depth-ward heterogeneities are imaged up to several</p> <div class="credits"> <p class="dwt_author">O. P. Mishra; Dapeng Zhao</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">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/2014JAESc..88...62F"> <span id="translatedtitle">Age spectra of detrital zircon of the Jurassic clastic rocks of the Mino-Tanba AC belt in SW <span class="hlt">Japan</span>: Constraints to the provenance of the mid-Mesozoic <span class="hlt">trench</span> in East Asia</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">U-Pb ages of detrital zircon grains were determined from an upper Middle Jurassic siliceous mudstone and two lower Upper Jurassic sandstones of the Mino-Tanba belt, Southwest <span class="hlt">Japan</span>, by Laser-ablation ICPMS. The age spectra of detrital zircon grains of the three analyzed samples show multiple age clusters: 175-198 Ma (Early Jurassic), 202-284 Ma (Permian to Triassic), 336-431 Ma (Silurian to Carboniferous), and 1691-2657 Ma (Neoarchean to Paleoproterozoic). As per the Precambrian grains, the prominent peak exists around 1800-2000 Ma in all analyzed samples. The age clusters of 175-198 Ma, 202-284 Ma, and 336-431 Ma suggest that pre-Middle Jurassic <span class="hlt">Japan</span> has exposed older granitic batholiths. The corresponding batholiths occur in the Cathaysian part of South China block. In contrast, the absence of them in modern <span class="hlt">Japan</span> suggests that these batholiths were totally consumed by post-Jurassic tectonic erosion. The Neoarchean to Paleoproterozoic detrital zircon grains were derived from South China, North China, or possibly both of them; nonetheless, the circumstantial geologic lines of evidence point to South China, in particular to Cathaysia, rather than North China.</p> <div class="credits"> <p class="dwt_author">Fujisaki, Wataru; Isozaki, Yukio; Maki, Kenshi; Sakata, Shuhei; Hirata, Takafumi; Maruyama, Shigenori</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-07-01</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://dx.doi.org/10.1111/j.1365-246X.2008.04035.x"> <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://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</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, G. P.; Wald, D. J.</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">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/2012AGUFM.S31A2483P"> <span id="translatedtitle">Characterization of <span class="hlt">Subduction</span> Seismicity at the Global Scale</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 framework of the EURYI Project 'Convergent margins and seismogenesis: defining the risk of great earthquakes by using statistical data and modelling', a global collection of recent <span class="hlt">subduction</span> seismicity - partitioned between interplate, intraslab and upper plate events - has been performed. Based on EHB hypocenter and CMT Harvard catalogues, the hypocenters, nodal planes and seismic moments of worldwide <span class="hlt">subduction</span>-related earthquakes were extracted for the period 1976 - 2007. Data were collected for centroid depths between sea level and 700 km and for magnitude Mw ? 5.5. For each <span class="hlt">subduction</span> zone, a set of <span class="hlt">trench</span>-normal transects were constructed choosing a 120km width of the cross-section on each side of a vertical plane and a spacing of 1 degree along the <span class="hlt">trench</span>. For each of the 505 resulting transects, the whole <span class="hlt">subduction</span> seismogenic zone was mapped as focal mechanisms projected on to a vertical plane after their faulting type classification according to the Aki-Richards convention. Transect by transect, was defined a "<span class="hlt">subduction</span> box" identifying the spatial limits of the seismicity strictly related to the <span class="hlt">subduction</span> zone under investigation, then the seismicity considered not related to the <span class="hlt">subduction</span> process under investigation was removed. For each transect, the events previously identified by Heuret et al (2011) as <span class="hlt">subduction</span> interface earthquakes were removed from the "<span class="hlt">subduction</span> box". Upper plate seismicity (i.e. earthquakes generated within the upper plate as a result of the <span class="hlt">subduction</span> process) was then extracted from the remaining events. We can be reasonably confident that the remaining seismicity can be related to the <span class="hlt">subducting</span> plate. In this way the <span class="hlt">subduction</span> seismicity has been properly classified in three categories: interpolate-, intraslab- and upper plate-seismicity. Following Heuret et al. (2011), the 505 transects have been merged into 62 larger segments that were ideally homogeneous in terms of their seismogenic zone characteristics. Several checks were performed, in order both to remove duplicate events, often occurring in these catalogues due to their marginal location relative to the boundary of adjacent transects and to verify if, due to the <span class="hlt">trench</span> curvature and/or to the huge event clustering typical of some <span class="hlt">subduction</span> zones, the same event is classified as belonging both to the upper plate and the intraslab category. Comparisons between main seismic parameters (e.g. maximum magnitude, number of events, cumulated seismic moment, recurrence time) with relation to both the different categories selected and the different segments have been performed and the correlation with a wide range of <span class="hlt">subduction</span>-related parameters taken from the literature (e.g. plates/slab kinematics, thermal parameters) have been evaluated. This allowed to highlight possible cause-effect relationships and to obtain a snapshot on the general behavior of global <span class="hlt">subduction</span>-related seismicity.</p> <div class="credits"> <p class="dwt_author">Presti, D.; Funiciello, F.; Heuret, A.; Piromallo, C.</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">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/2013AGUFM.T43I..02R"> <span id="translatedtitle"><span class="hlt">Subduction</span> and break-off controls on Indentation tectonics 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">Large deformations of the Asian continent and drastic change in the geometry of the plate boundary are the result of the interaction between the <span class="hlt">subduction</span> of Tethys followed by the <span class="hlt">subduction</span> of India continent and the Asian upper plates during convergence. The link between Asian tectonics, oceanic and continental <span class="hlt">subductions</span> and the breakoff episodes has been explored by comparing global tomographic images showing remnants of slabs and Asian tectonics reconstruction. It allows formulating hypotheses on how deep <span class="hlt">subduction</span> and indentation tectonics are coupled, and constrains self-consistent three-dimensional numerical models of coupled <span class="hlt">subducting</span> - upper plates in an ambient mantle that we perform. 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>, as evidenced for India using global tomography, 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. It is similar to the geometry of the indian lithosphere, underthrusting to the west the Asian lithosphere early in the collision time, then <span class="hlt">subducts</span> lately far north of the front beneath the Hindu-Kush, while more to the east India <span class="hlt">subducts</span> much earlier and more to the south. The breakoff episodes evidenced using global tomography 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, A.; capitanio, F. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</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/2012EGUGA..14.5640G"> <span id="translatedtitle">Deformation and topography above the lateral transition from continental to oceanic <span class="hlt">subduction</span> in three-dimensional laboratory models: what can we learn on the Hellenic <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">We use three-dimensional dynamically self-consistent laboratory models to analyze relationships between surface evolution and deep dynamics at convergent margins. Our models are setup with a viscous plate of silicone (lithosphere) <span class="hlt">subducting</span> under negative buoyancy in a viscous layer of glucose syrup (upper mantle). We focus on the <span class="hlt">subduction</span> of a laterally heterogeneous lithosphere characterized by an abrupt transition of density using negatively and positively buoyant silicone to reproduce oceanic and continental <span class="hlt">subduction</span>, respectively. We quantify and establish relationships between the <span class="hlt">subduction</span> dynamics and resulting slab geometry, <span class="hlt">trench</span> kinematics and pattern of horizontal/vertical deformation for both the overriding plate and the upper mantle. Assuming that our modeling results can be representative of the natural behavior of <span class="hlt">subduction</span> zones, we compare them to the Neogene to Quaternary evolution of the Hellenic <span class="hlt">subduction</span> zone. We more particularly focus on the deformation and topography of the Hellenic upper plate, which may have been influenced by the difference in <span class="hlt">subduction</span> dynamics north and south of the Kephalonia Transform Zone, with a slowly <span class="hlt">subducting</span> Adriatic continental lithosphere in the north and a rapidly <span class="hlt">subducting</span> Ionian oceanic lithosphere in the south.</p> <div class="credits"> <p class="dwt_author">Guillaume, B.; Funiciello, F.; Faccenna, C.; Husson, L.; Royden, L. H.</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">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/2013EGUGA..15.1259K"> <span id="translatedtitle">Tsunami generation near <span class="hlt">Japan</span> by Earthquakes Along-strike Single Segmentation and Along-dip Double 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">After the 2011 Tohoku-oki megathrust earthquake of Mw9.0, we have proposed a hypothesis that megathrust earthquakes worldwide occur Along-dip Double Segmentation (ADDS) or Along-strike Single Segmentation (ASSS). The former is characterized by the apparent absence of earthquakes in the aligned seismic segments along the <span class="hlt">Japan</span> <span class="hlt">trench</span> as opposed to those along the <span class="hlt">Japan</span> Islands that generate repeated smaller earthquakes (ADDS), where the 2011 Tohoku-oki megathrust occurred. Meanwhile, the latter is by a weak seismic activity before the main event all over the <span class="hlt">subduction</span> zone, where we find aligned seismic segments along the <span class="hlt">subduction</span> zone from the <span class="hlt">trench</span> to the island-arc (ASSS). A typical example of ASSS is the Nankai trough, <span class="hlt">Japan</span>, where future great earthquakes are expected. The 1960 and 2010 Chile megathrusts occurred in ASSS. In and near <span class="hlt">Japan</span>, ADDS earthquake activity is restrictively found along the Pacific side of Hokkaido and Tohoku regions and the Hyuganada, Kyushu. The rest of seismic activity near <span class="hlt">Japan</span> is classified into ASSS. Comparing tsunami magnitude m from local tsunami-wave heights and seismic moment Mo from long-period surface-waves of 61 earthquakes from 1923 in and near <span class="hlt">Japan</span>, we found that tsunami-wave heights of ASSS earthquakes are almost two times larger than those of ADDS's. This is also confirmed by studying tsunami magnitude Mt evaluated from teleseismic tsunami-wave heights. The reason of this different excitation between ADDS and ASSS is considered to be due to either (1) shallower focal depths for ASSS give rise to larger ocean bottom deformation, resulting in larger tsunami excitation, (2) larger dip-angles of fault planes for ASSS, (3) three dimensional ocean-bottom structures, such as troughs, <span class="hlt">trenches</span> and continental shelves, or (4) ocean bottom topography nearby causes the focusing of tsunami waves. (1) is the conclusion that we would like to derive. (2) Speaking about the effect of dip angles to the maximum ocean bottom deformations, the difference is about 30% in cases of reverse faults with dip angles of 30 and 60 degrees. (3) Both of earthquakes along the passive margin of the back-arc basin of the <span class="hlt">Japan</span> sea and along the Nankai trough are classified into ASSS. (4) Both of local and teleseismic tsunami-wave heights do suggest the similar result, rejecting the local tsunami focusing. Therefore, we conclude that the larger tsunami excitation for ASSS earthquakes is due to larger amount of ocean bottom deformations than those for ADDS earthquakes or by the reason of (1) or by both the effects. Asperity for ADDS locates in the shallow part of the <span class="hlt">subduction</span> zone along the <span class="hlt">trench</span>, and it ruptures only in the case of megathrust events like as the 2011 Tohoku-oki earthquake. In estimating tsunami wave heights for future earthquakes, we have to take into account of this difference in tsunami excitations in the ADDS or ASSS zone.</p> <div class="credits"> <p class="dwt_author">Koyama, Junji; Tsuzuki, Motohiro</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">297</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19920060789&hterms=connell&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3D%2522o%2527connell%2522"> <span id="translatedtitle">Ablative <span class="hlt">subduction</span> - A two-sided alternative to the conventional <span class="hlt">subduction</span> model</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The plausibility of a two-sided fluid-based model of lithospheric <span class="hlt">subduction</span> that is based upon current views of lithospheric structure is examined. In this model the viscous lower lithosphere flows downward, and the brittle upper lithosphere deforms in passive response. This process is potentially double-sided, since it is found that even a buoyant plate can be dragged downward by a dense descending neighbor. Thus an apparent overriding plate may be worn away by a process of viscous ablation, with the rate of ablation a function of plate buoyancy. This process, called 'ablative <span class="hlt">subduction</span>,' makes it possible to simply interpret observations concerning slab profiles, interplate seismicity, back arc tectonics, and complex processes such as double <span class="hlt">subduction</span> and <span class="hlt">subduction</span> polarity reversal. When experiments modeling the evolution of simple fluid 'slabs' are performed, slab profile is found to be strongly influenced by ablation in the overriding plate. When ablation is weak, as when a buoyant continent borders the <span class="hlt">trench</span>, deformable slabs adopt shallow Andean-style profiles.</p> <div class="credits"> <p class="dwt_author">Tao, Winston C.; O'Connell, Richard J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</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/2012AGUFMDI33B..01C"> <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 maximised 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, F. A.; Faccenda, M.</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">299</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/2014EGUGA..16.2908G"> <span id="translatedtitle">Downgoing plate controls on overriding plate deformation 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">Although <span class="hlt">subduction</span> zones are convergent margins, deformation in the upper plate can be extensional or compressional and tends to change through time, sometimes in repeated episodes of strong deformation, e.g, phases of back-arc extension. It is not well understood what factors control this upper plate deformation. We use the code Fluidity, which uses an adaptive mesh and a free-surface formulation, to model a two-plate <span class="hlt">subduction</span> system in 2-D. The model includes a composite temperature- and stress-dependent rheology, and plates are decoupled by a weak layer, which allows for free <span class="hlt">trench</span> motion. We investigate the evolution of the state of stress and topography of the overriding plate during the different phases of the <span class="hlt">subduction</span> process: onset of <span class="hlt">subduction</span>, free-fall sinking in the upper mantle and interaction of the slab with the transition zone, here represented by a viscosity contrast between upper and lower mantle. We focus on (i) how overriding plate deformation varies with <span class="hlt">subducting</span> plate age; (ii) how spontaneous and episodic back-arc spreading develops for some <span class="hlt">subduction</span> settings; (iii) the correlation between overriding plate deformation and slab interaction with the transition zone; (iv) whether these trends resemble observations on Earth.</p> <div class="credits"> <p class="dwt_author">Garel, Fanny; Davies, Rhodri; Goes, Saskia; Davies, Huw; Kramer, Stephan; Wilson, Cian</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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/2012AGUFM.T13B2602S"> <span id="translatedtitle">High-Velocity Frictional Behavior of Incoming Pelagic Sediments to the Tohoku <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 2011 Tohoku earthquake (Mw 9.0) off the Pacific coast of <span class="hlt">Japan</span> produced huge slip (~50 m) on the shallow part of the fault close to the toe of the megathrust (e.g., Fujiwara et al., 2011), resulting in destructive tsunamis. Although the multiple causes of such large slip at shallow depths is expected, the frictional property of sediments around the fault, especially at coseismic slip velocities, may significantly contribute to large slip along the fault. We thus investigate the frictional properties of pelagic sediments to be <span class="hlt">subducting</span> beneath the Tohoku region at high velocities and large displacement toward understanding the rupture processes to cause large slip at the shallow portion of <span class="hlt">subduction</span> zone. We have conducted friction experiments on incoming pelagic sediment on the Pacific plate (DSDP, Site 436, Leg56, 378 mbsf) that consider as simulated fault gouge. The site locates about 100 km northeast from the Hole C0019E drilled during the IODP Expedition 343 (J-FAST). The sediment contains mainly montmorillonite and its blackish color is quite similar to the sheared sediments in the plate boundary fault recovered during the Expedition 343. Experiments are performed at slip velocities of 2.5 x 10-4 to 1.3 m/s, normal stresses of 0.5 to 2.0 MPa and slip displacement of about 16 m under brine saturated conditions, using a rotary-shear friction apparatus. One gram of gouge was placed between rock cylinders of sandstone or gabbro of 25 mm diameter with Teflon sleeve outside to contain gouge. Both gouge sample and host rock were saturated with brine. At slip velocity of 1.3 m/s and normal stresses of 0.5 to 2.0 MPa, a typical slip weakening behavior is observed; friction coefficient of the sediment rapidly increases 0.1 - 0.3 at the onset of sliding and subsequently decreases to 0.06 - 0.15 over the displacement of > 1 m. However, peak friction and frictional work during slip-weakening (fracture energy) are markedly lower as compared to similar studies conducted on other fault gouge (e.g., Mizoguchi et al., 2007; Ujiie and Tsutsumi, 2010). In addition, steady-state friction coefficient at normal stress of 1 MPa is less than 0.2 over a wide range of slip velocity from 0.25 mm/s to 1.3 m/s. These results suggest that the incoming pelagic sediments to the <span class="hlt">Japan</span> <span class="hlt">Trench</span> are energetically very easy for earthquake ruptures to propagate at shallow portion of the Tohoku <span class="hlt">subduction</span> zone.</p> <div class="credits"> <p class="dwt_author">Sawai, M.; Hirose, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</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_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" 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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_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/2002AGUFM.T22C..03O"> <span id="translatedtitle">Depth Distribution of The <span class="hlt">Subduction</span> Zone Earthquakes and Devolatilization Phase Equilibria of <span class="hlt">Subducting</span> Slab</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 present study, we show a close link between the depth distribution of <span class="hlt">subduction</span>-zone earthquakes and that of dehydration reactions in hydrated slab peridotite. The depth distribution of world <span class="hlt">subduction</span>-zone earthquakes is known to show bimodal distribution. Frequency of mantle earthquakes is high in shallow to intermediate-depth (0-300 km) and in mantle transition zone (450-650 km). A depth range from 300 to 450 km has less number of seismicity. However, the depth distribution of hypocenters in individual <span class="hlt">subduction</span> zone varies from area to area. We classified the world <span class="hlt">subduction</span>-zones into three types on the basis of the mode of distribution of hypocenters with depth; type 1 is for the <span class="hlt">subduction</span> zones having only shallow to intermediate-depth earthquakes (e.g. SW-<span class="hlt">Japan</span>, Alaska, Kyushu); type 2 is for the <span class="hlt">subduction</span> zones showing clear bimodal depth-distribution (e.g. northern Chile, Sunda, a part of Izu-Mariana); and, type 3 is for the <span class="hlt">subduction</span> zones having deep earthquakes, but without obvious bimodal depth-distribution (e.g._@Tonga, NE-<span class="hlt">Japan</span>, a part of Izu-Mariana). We constructed a phase diagram up to 30 GPa in the MgO-CaO-Al2O3-SiO2-CO2-H2O system by combination of thermodynamic calculation and the Schreinemakers analysis on the previous experimental data. In the intermediate-depth (<250 km), devolatilizations including antigorite, talc, brucite, clinochlore, and Mg-sursassite occur. In the range of 250-400 km depth, only dehydration of Mg-sursassite is possible. And dehydrations of dense hydrous Mg-silicates (phase E and superhydrous phase B) occur in the mantle transition zone. Such depth dependences of dehydration reactions are consistent to the depth distribution of earthquakes. The variations of individual seismic zones are explained by the difference of thermal structure depending on the age of <span class="hlt">subducting</span> plate, <span class="hlt">subducting</span> speed and angle. In previous studies, it was shown that the dehydration hypothesis explains the mesoscopic structure of intermediate-depth seismic zone, i.e. double seismic zone and organized interplane earthquakes (Omori et al. 2000, 2002). Therefore, the dehydration hypothesis should be a unique model that explains the earthquakes from intermediate-depth to mantle transition zone. And we may see the site of devolatilizations and temperature in <span class="hlt">subduction</span> zone by the hypocenter distribution.</p> <div class="credits"> <p class="dwt_author">Omori, S.; Komabayashi, T.; Maruyama, S.</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">302</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.T13A2174S"> <span id="translatedtitle">An oceanic plateau <span class="hlt">subduction</span> offshore Eastern 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 area offshore Java represents one of a few places globally where the early stage of <span class="hlt">subduction</span> of an oceanic plateau is observed. We study the little investigated Roo Rise oceanic plateau on the Indian plate, <span class="hlt">subducting</span> beneath Eurasia.Our study area is located south of eastern Java and covers the edge of the Roo Rise plateau, the Java <span class="hlt">trench</span> and the entire forearc section. For the first time the detailed deep structure of the Roo Rise is studied, <span class="hlt">subduction</span> of which has a significant effect on the forearc dynamics and evolution and the increase of the geohazards risks. The tsunamogenic earthquakes of 1994 and 2006 are associated with the oceanic plateau edge been <span class="hlt">subducted</span>. We present integrated results of a refraction/wide-angle reflection tomography, gravity modeling, and multichannel reflection seismic imaging using data acquired in 2006 along a corridor centered around 113°E and composed of a 340 km long N-S profile and a 130 km long E-W oriented profile. The composite structural models reveal the previously unresolved deep geometry of the collision zone and the structure of the oceanic plateau. The crustal thickness of the Roo Rise plateau is ranging from 18 to 12 km. The structure of the upper crust of the incoming oceanic plate shows the extreme degree of fracturing in its top section, and is associated with a plate bending. The forearc Moho has a depth range from 16 to 20 km. The gravity modeling requires a sharp crustal thickness increase below Java. Within our profiles we do not recover any direct evidence for the presence of the bathymetric features on the oceanic plate currently present below the accretionary prism, responsible for the tsunamogenic earthquake triggering. However vertical variations of the forearc basement edge are observed on the <span class="hlt">trench</span>-parallel profile, which opens a discussion on the origin of such basement undulations, together with a localized patchy uplift character of the forearc high.The complex geometry of the backstop suggests two models for the structural formation within this segment of the margin. The <span class="hlt">subducting</span> plateau is affecting the stress field within the accretionary complex and the backstop edge, which favors the initiation of large, potentially tsunamogenic earthquakes such as the 1994 Mw=7.8 tsunamogenic event.</p> <div class="credits"> <p class="dwt_author">Shulgin, A.; Kopp, H.; Mueller, C.; Planert, L.; Lueschen, E.; Flueh, E. R.; Djajadihardja, Y.</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">303</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">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/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">305</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/49306821"> <span id="translatedtitle">Metastable olivine wedge and deep dry cold slab beneath 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">Oceanic plates <span class="hlt">subducted</span> at <span class="hlt">trenches</span> penetrate into the deep mantle, and encounter a structural boundary at a depth of 410km where olivine, the dominant element of mantle rocks, transforms into a higher density form wadsleyite. This transformation may be delayed within the coldest core of <span class="hlt">subducting</span> plates (slabs) due to kinetic effects, and it has been suggested that metastable olivine</p> <div class="credits"> <p class="dwt_author">Hitoshi Kawakatsu; Shoichi Yoshioka</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">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/2012AGUFM.G21B..02H"> <span id="translatedtitle">Accelerated <span class="hlt">subduction</span> of the Pacific Plate after mega-thrust earthquakes: evidence from GPS and GRACE</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">Interplate thrust earthquakes are often followed by afterslips (Heki et al., 1997; Miyazaki et al., 2004; Ozawa et al., 2012). They let the fore-arc move slowly trenchward and accelerate plate convergence. Accelerated convergence of the oceanic side (including ocean floor and slab) has been suggested by changes of focal mechanisms of earthquakes within oceanic plates after mega-thrust events, i.e. change from <span class="hlt">trench</span>-normal compression to tension in outer rise regions, and from down-dip tension to compression in intermediate depths (Lay et al., 1989). However, landward acceleration of the oceanic plate has never been observed geodetically due to the scarcity of appropriate islands on oceanic plates near <span class="hlt">trenches</span>. The westward velocity of GPS stations in NE <span class="hlt">Japan</span> show gradient decreasing from east to west reflecting the E-W compressional stress built up by the inter-plate coupling. We found that such coupling significantly enhanced after the 2003 Tokachi-Oki earthquake (Mw8.0), Hokkaido, in the segments adjacent to the ruptured fault. The coupling was further enhanced after the 2011 Tohoku-Oki earthquake (Mw9.0). Movement of the ocean floor benchmark after the 2011 event suggests that the current (i.e. 2011-2012) <span class="hlt">subduction</span> of the Pacific Plate is about three times as fast as the geological average, e.g. NUVEL-1 (DeMets et al., 1990). Such a temporary acceleration of the <span class="hlt">subduction</span> would be a response of the <span class="hlt">subducting</span> slab to the sudden decrease of interplate coupling (decoupling); because slab-pull and ridge-push cannot change, viscous traction has to increase to recover the force balance. We will present a simple physical model assuming a thin low-viscosity layer on the slab surface that has enabled such a rapid adjustment. The accelerated <span class="hlt">subduction</span> would account for high regional interplate seismicity after mega-thrust earthquakes, especially successive ruptures of remote segments, e.g. the 2003 Tokachi-Oki, 2006 Kuril, and 2011 Tohoku-Oki earthquakes. GRACE satellite gravimetry revealed coseismic gravity drops in the back-arc regions due to the dilatation of island arc lithosphere for the 2004 Sumatra-Andaman (Han et al., 2005), 2010 Maule (Heki and Matsuo, 2010), and 2011 Tohoku-oki (Matsuo and Heki, 2011) earthquakes. Postseismic slow gravity increase centered in the fore-arc region was first found for the 2004 Sumatra-Andaman earthquake (Ogawa and Heki, 2007). Here we show that similar postseismic gravity increases also followed the other two mega-thrust earthquakes. We assume that they also reflect accelerating <span class="hlt">subduction</span> of oceanic plates, i.e. episodic convergence at the boundary propagates into oceanic plate interior by stress diffusion (Bott and Dean, 1973), and postseismic thickening of the coseismically thinned lithosphere causes the on-going gravity increases.</p> <div class="credits"> <p class="dwt_author">Heki, K.; Mitsui, Y.; Matsuo, K.; Tanaka, Y.</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">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/2011EOSTr..92...97S"> <span id="translatedtitle">Scientists Examine Challenges and Lessons From <span class="hlt">Japan</span>'s Earthquake and Tsunami</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 week after the magnitude 9.0 great Tohoku earthquake and the resulting tragic and damaging tsunami of 11 March struck <span class="hlt">Japan</span>, the ramifications continued, with a series of major aftershocks (as Eos went to press, there had been about 4 dozen with magnitudes greater than 6); the grim search for missing people—the death toll was expected to approximate 10,000; the urgent assistance needed for the more than 400,000 homeless and the 1 million people without water; and the frantic efforts to avert an environmental catastrophe at <span class="hlt">Japan</span>'s damaged Fukushima Daiichi Nuclear Power Station, about 225 kilometers northeast of Tokyo, where radiation was leaking. The earthquake offshore of Honshu in northeastern <span class="hlt">Japan</span> (see Figure 1) was a plate boundary rupture along the <span class="hlt">Japan</span> <span class="hlt">Trench</span> <span class="hlt">subduction</span> zone, with the source area of the earthquake estimated at 400-500 kilometers long with a maximum slip of 20 meters, determined through various means including Global Positioning System (GPS) and seismographic data, according to Kenji Satake, professor at the Earthquake Research Institute of the University of Tokyo. In some places the tsunami may have topped 7 meters—the maximum instrumental measurement at many coastal tide gauges—and some parts of the coastline may have been inundated more than 5 kilometers inland, Satake indicated. The International Tsunami Information Center (ITIC) noted that eyewitnesses reported that the highest tsunami waves were 13 meters high. Satake also noted that continuous GPS stations indicate that the coast near Sendai—which is 130 kilometers west of the earthquake and is the largest city in the Tohoku region of Honshu—moved more than 4 meters horizontally and subsided about 0.8 meter.</p> <div class="credits"> <p class="dwt_author">Showstack, Randy</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-03-01</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://academic.research.microsoft.com/Publication/14897850"> <span id="translatedtitle">Measuring the onset of locking in the Peru-Chile <span class="hlt">trench</span> with GPS and acoustic measurements</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> zone off the west coast of South America marks the convergence of the oceanic Nazca plate and the continental South America plate. Nazca-South America convergence over the past 23 million years has created the 6-km-deep Peru-Chile <span class="hlt">trench</span>, 150km offshore. High pressure between the plates creates a locked zone, leading to deformation of the overriding plate. The surface area</p> <div class="credits"> <p class="dwt_author">Katie Gagnon; C. David Chadwell; Edmundo Norabuena</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">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/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 " 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://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">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/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 " 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://adsabs.harvard.edu/abs/2014EGUGA..1610343M"> <span id="translatedtitle">Interplate coupling at oblique <span class="hlt">subduction</span> zones: influence on upper plate 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">In active <span class="hlt">subduction</span> zones, when the converging plates cannot slip freely past each other, "plate coupling" occurs. The moving <span class="hlt">subducting</span> slab and therefore the coupling/decoupling relationship between plates control both short- and long-term deformation of the upper plate. Short-term deformation is dominantly elastic, occurs at human timescales and can be directly associated with earthquakes. Long-term deformation is cumulative, permanent and prevails at the geological timescale (Hoffman-Rothe et al., 2006, Springer Berlin Heidelberg). Here we used 3D numerical simulations to test oblique <span class="hlt">subduction</span> zones and to investigate: 1) how long-term deformation and coupling relationship vary along the <span class="hlt">trench</span>-axis; 2) how this relationship influences erosion and down-drag of upper plate material. Our models are based on thermo-mechanical equations solved with finite differences method and marker-in-cell techniques combined with a multigrid approach (Gerya, 2010, Cambridge Univ. Press). The reference model simulates an intraoceanic <span class="hlt">subduction</span> close to the continental margin (Malatesta et al., 2013, Nature Communications, 4:2456 DOI:10.1038/ncomms3456). The oceanic crust is layered with a 5-km-thick layer of gabbro overlain by a 3-km-thick layer of basalt. The ocean floor is covered by 1-km-thick sediments. Plates move with a total velocity of 3.15 cm/yr; the oblique convergence is obtained using velocity vectors that form an angle of 45° with the initial starting point of <span class="hlt">subduction</span> (weak zone in the lithosphere). After initiation of plate convergence, part of sediments on top of the incoming plate enters the <span class="hlt">subduction</span> zone and is buried; another part is suddenly transferred along strike at shallow depths and along the <span class="hlt">subducting</span> slab according to the direction of the along-<span class="hlt">trench</span> velocity component of <span class="hlt">subduction</span>. The lateral migration of sediment causes the evolution of the <span class="hlt">trench</span> along its strike from sediment-poor to sediment-rich. As soon as <span class="hlt">subduction</span> starts, where the sedimentary infill of the <span class="hlt">trench</span> is almost nonexistent, short-term shallow coupling occurs and friction between the frontal sector of the overriding plate and the downgoing plate triggers upper-plate bending. In this sector, after the early short-term coupling, the overriding plate is hereafter decoupled from the <span class="hlt">subducting</span> slab. Moving along <span class="hlt">trench</span>-strike, where sediments amount increases, the upper plate couples with the <span class="hlt">subducting</span> plate and is dragged coherently downwards. If a large amount of sediments is stored in the <span class="hlt">trench</span> the overriding plate is scraped off and incorporated as fragments along the plate interface. Our results suggest that a) one main parameter controlling coupling at convergent plate margins is the occurrence and the amount of sediment at the <span class="hlt">trench</span>; b) the upper plate margin is dragged to depth or destroyed only where sediments thickness at the <span class="hlt">trench</span> is large enough to promote interplate coupling, suggesting that a variation of sediment amount along the <span class="hlt">trench</span>-axis influences the amount and style of transport of upper-plate material in the mantle.</p> <div class="credits"> <p class="dwt_author">Malatesta, Cristina; Gerya, Taras; Crispini, Laura; Federico, Laura; Scambelluri, Marco; Capponi, Giovanni</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</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://www.ncbi.nlm.nih.gov/pubmed/19847262"> <span id="translatedtitle"><span class="hlt">Trench</span>-parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge.</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 anisotropy is a powerful tool for detecting the geometry and style of deformation in the Earth's interior, as it primarily reflects the deformation-induced preferred orientation of anisotropic crystals. Although seismic anisotropy in the upper mantle is generally attributed to the crystal-preferred orientation of olivine, the strong <span class="hlt">trench</span>-parallel anisotropy (delay time of one to two seconds) observed in several <span class="hlt">subduction</span> systems is difficult to explain in terms of olivine anisotropy, even if the entire mantle wedge were to act as an anisotropic source. Here we show that the crystal-preferred orientation of serpentine, the main hydrous mineral in the upper mantle, can produce the strong <span class="hlt">trench</span>-parallel seismic anisotropy observed in <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 during deformation; 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 is an order of magnitude greater than that for olivine, and therefore 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 also consistent with the presence of a hydrous phase in the mantle wedge, as inferred from anomalously low seismic-wave velocities. PMID:19847262</p> <div class="credits"> <p class="dwt_author">Katayama, Ikuo; Hirauchi, Ken-ichi; Michibayashi, Katsuyoshi; Ando, Jun-ichi</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-10-22</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/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">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/1986E%26PSL..80..145V"> <span id="translatedtitle">Opening of the Okinawa basin and collision in Taiwan: a retreating <span class="hlt">trench</span> model with lateral anchoring</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">Using a two-dimensional finite element model with an elasto-plastic behavior, we show that the opening of the Okinawa basin behind the Ryukyu <span class="hlt">trench</span> since about 6 Ma can be explained by a retreating <span class="hlt">trench</span> model with lateral anchoring due to the collision in Taiwan. We assume that a suction force is applied to the edge of the overriding plate. This force corresponds to the difference between the mean lithospheric pressure in the overriding lithosphere and the normal pressure applied to its edge. It results in an outward motion of the edge of the continental margin (retreating <span class="hlt">trench</span>) and in the opening of the Okinawa basin. If, on the contrary, no suction force is applied, the collision in Taiwan does not result in any extension in the Okinawa area. On both extremities of the Ryukyu <span class="hlt">trench</span>, this outward motion is locked by the collision in Taiwan and the buoyant <span class="hlt">subduction</span> of the Palau-Kyushu ridge. It results in the arcuate shape of the Ryukyu arc. In order to explain the actual amount of extension in the Okinawa basin, it is however necessary to take into account the presence of the Miocene volcanic arc which results in a weakened lithosphere. In our model, this weak zone is simulated by a lower yield condition. Finally, the dissymmetry of the Ryukyu arc and Okinawa basin can be explained by a lateral variation of the suction force related to the variation of the length of the <span class="hlt">subducting</span> slab, thus of the slab pull force.</p> <div class="credits"> <p class="dwt_author">Viallon, C.; Huchon, P.; Barrier, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-10-01</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/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">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/2013Tectp.600...91Y"> <span id="translatedtitle">Stress states at the <span class="hlt">subduction</span> input site, Nankai <span class="hlt">Subduction</span> Zone, using anelastic strain recovery (ASR) data in the basement basalt and overlying sediments</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 three-dimensional orientations of stress and stress magnitudes in the basement basalt and overlying sediments at the <span class="hlt">subduction</span> input site, IODP Site C0012, have been determined using anelastic strain recovery (ASR) analyses. The ASR results in the sedimentary sequence indicate that ?1 is nearly vertical. The magnitudes of ?2 and ?3 are very similar, indicating that the stress state in the sedimentary sequence is "at rest". On the other hand, ASR analyses in the basement basalt show that ?1 is nearly horizontal and oriented NE-SW, almost parallel (or slightly oblique) to the <span class="hlt">trench</span> axis. ?3 plunges moderately to the NW. The stress state of the basement basalts suggests a strike-slip or thrust (reverse fault) regime, which is very different from a "state at rest" condition, which is the theoretical stress condition for the ocean floor far from a <span class="hlt">subduction</span> zone. The basement basalt at the <span class="hlt">subduction</span> input site (C0012) has experienced <span class="hlt">trench</span>-parallel compression and <span class="hlt">trench</span>-normal extension, consistent with the focal mechanisms of earthquakes in the vicinity. The estimated stress magnitudes show only small variations between the principal stresses, implying that the directions of principal stress could be easily rotated in association with any tectonically induced local stress variation. The stress orientation in the basement basalt seems to be the result of hinge extension during bending of the Philippine Sea Plate, either in association with <span class="hlt">subduction</span> or with the formation of an anticline during intraoceanic thrusting.</p> <div class="credits"> <p class="dwt_author">Yamamoto, Yuzuru; Lin, Weiren; Oda, Hirokuni; Byrne, Timothy; Yamamoto, Yuhji</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">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.ntis.gov/search/product.aspx?ABBR=PB85118743"> <span id="translatedtitle">Deformation of Ground Near Tunnels and <span class="hlt">Trenches</span>.</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">Contents: Finite elements and Cam-clay; Application of Critical State Soil Mechanics to tunnels and <span class="hlt">trenches</span>; Undrained deformations (theory of plasticity); Stability numbers for tunnels; Collapse mechanisms for tunnels; Stability numbers for <span class="hlt">trenches</span>; Co...</p> <div class="credits"> <p class="dwt_author">M. J. Gunn</p> <p class="dwt_publisher"></p> <p class="publishDate">1984-01-01</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://academic.research.microsoft.com/Publication/11681964"> <span id="translatedtitle">B-type olivine fabric in the mantle wedge: Insights from high-resolution non-Newtonian <span class="hlt">subduction</span> zone 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">Several hypotheses have been proposed to explain <span class="hlt">trench</span>-parallel shear wave splitting in the mantle wedge of <span class="hlt">subduction</span> zones. These include 3-D flow effects, parallel melt filled cracks, and B-type olivine fabric. We predict the distribution of B-type and other fabrics with high-resolution thermal and stress models of <span class="hlt">subduction</span> zones. A composite viscous rheology is used that incorporates wet diffusion creep,</p> <div class="credits"> <p class="dwt_author">Erik A. Kneller; Peter E. van Keken; Shun-ichiro Karato; Jeffrey Park</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">320</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 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 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</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://adsabs.harvard.edu/abs/2010PEPI..178...92Z"> <span id="translatedtitle"><span class="hlt">Subduction</span> of the Western Pacific Plate underneath Northeast China: Implications of numerical studies</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 geodynamic process of the deep <span class="hlt">subduction</span> of the western Pacific Plate underneath Northeast China is critical for understanding the extensional events and volcanism in Northeast China. Understanding of this process depends on: (1) the initial time of the <span class="hlt">subduction</span>, (2) the <span class="hlt">trench</span> retreat velocity during the <span class="hlt">subduction</span> process, (3) the contribution of Indian-Eurasian collision and Pacific-Eurasian <span class="hlt">subduction</span> to extensional events in the northeast of China. However, information on these three issues is very limited. We use several regional models to gain insight into these three issues. Each of the models includes temperature-dependent viscosity structures, and distinct velocity patterns at the surface. Our results show that the <span class="hlt">subduction</span> of the Pacific Plate under the Eurasian plate started most probably around 70 Ma. To be consistent with the tomography under Northeast China, <span class="hlt">trench</span> retreat must be included in the models, with a rate less than 45 km/Ma that has been estimated in the past. We suggest that the extension events in the northeast China are attributed to Indian-Eurasian collision and Pacific-Eurasian <span class="hlt">subduction</span> according to the velocity evolution in our models.</p> <div class="credits"> <p class="dwt_author">Zhu, Guizhi; Shi, Yaolin; Tackley, Paul</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">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/2013AGUSMNS32A..01K"> <span id="translatedtitle">Central Andean Giant Ore Deposits: Links to Forearc <span class="hlt">Subduction</span> Erosion, Shallowing <span class="hlt">Subduction</span> and Thickening Crust</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">An outstanding question on the Central Andean margin is the relationship between tectonic processes like ebbing arc volcanism, shallowing of the <span class="hlt">subducting</span> slab and crustal thickening, and the origin of giant porphyry and epithermal Cu, Au and Ag deposits. Another potentially important factor in forming these major mineral deposits is forearc <span class="hlt">subduction</span> erosion, which is postulated to have removed up to ~250 km of Central Andean forearc crust since the Jurassic. Geochemical and geophysical studies provide insights into possible links. Evidence for partial melts of removed and <span class="hlt">subducted</span> forearc crust reaching the arc magma source and thus the magmas that host the ore deposits comes from the chemistry of late Neogene volcanic rocks on both the northern and southern margin of the Chilean-Pampean flat-slab (28°-33°S), where the frontal arc was displaced ~50 km into the foreland between ~10 and 3 Ma. This chemical evidence consists of transient ultra-steep REE patterns, elevated Mg, Cr and Ni contents and steps in isotopic ratios that are particularly notable in the glassy adakitic 8-3 Ma (Pircas Negras) andesites on the northern flat-slab margin at 27°-28°S. Well constrained reconstructions of the margin near 26-28°S that assume a sustained 300 km wide arc-<span class="hlt">trench</span> gap and ~50 km of forearc removal suggest an accelerated average forearc <span class="hlt">subduction</span> erosion rate over 150 km3/my/km between 8 and 3 Ma. Noting that the late Miocene arc is now at least ~ 260 km from the <span class="hlt">trench</span> from 26°S to 34°S and that the active arc extrapolates through the amagmatic flat-slab region (28°-33°S) at 300 km from the <span class="hlt">trench</span>, accelerated forearc removal could be inferred from ~34°S to 26°S at ~10 to 3 Ma. Geophysical evidence for forearc crust entering the mantle wedge as the flatslab shallowed could come from low Vp/Vs seismic ratios in the mantle wedge under the flatslab, which Wagner et al. (2010) attribute to orthopyroxene. Formation of this orthopyroxene could be explained by forearc crust reacting with the mantle wedge. Thus, the slab shallowing, crustal thickening and forearc <span class="hlt">subduction</span> erosion in the flatslab region, which began at ca 20-18 Ma and accelerated after 11-10 Ma could have set the stage for the formation of the Los Pelambres, Rio Blanco and El Teniente giant Cu porphyries between ~ 11-4 Ma. The backarc 8-6 Ma Bajo de la Alumbrera Cu-Au district near 27°S, also formed east of the migrating volcanic arc on the northern flatslab margin at this time. This deposit is notable for now being above a high Qp mantle seismic anomaly overlying the slab, which is at a depth of ~150 km. Elsewhere, Ag-Zn mineralization in the ~14-12 Ma Potosi district near 19.5°S in the Altiplano backarc, which has been suggested to have occurred in the early stages of steepening of a shallow slab, would potentially predate flushing of eroded forearc material from an expanding mantle wedge. In the same vein, a lack of known big Cu-Au-Ag deposits associated with the late Neogene giant plateau ignimbrite complexes, considered to be fomed over steepening <span class="hlt">subduction</span> zones characterized by low Vp and Vs and high Qp tomographic seismic anomalies, could also partially reflect loss of forearc <span class="hlt">subducted</span> components from an expanding wedge.</p> <div class="credits"> <p class="dwt_author">Kay, S. M.; Mpodozis, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</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://ntrs.nasa.gov/search.jsp?R=19800019231&hterms=North+Island+New+Zealand&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522North%2BIsland%2BNew%2BZealand%2522"> <span id="translatedtitle">Geoid anomalies in the vicinity of <span class="hlt">subduction</span> zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The regional geoid of the southwest Pacific is matched reasonably well by results from a model of the upper mantle density structure (including slabs) associated with <span class="hlt">subduction</span> zones of the region. Estimates of the geoid are obtained from Geos-3 and Seasat radar altimeter data. These data are very well suited to the task of detecting intermediate wavelength (600-4000 km) geopotential variations. Actually, <span class="hlt">subducting</span> slabs can be expected to produce primarily intermediate and longer wavelength variations. Gravimetric profiles across <span class="hlt">trench</span>/island arc complexes resolve primarily short wavelengths. The model represents <span class="hlt">subducting</span> slabs as thin surfaces of anomalous mass per unit area. These surfaces are positioned using published seismicity results which detail the configuration of the Benioff zones. Crustal effects are ignored. Effects due to the contrast between the young thermal lithosphere of the behind-arc regions (marginal basins) and the older lithosphere seaward of the <span class="hlt">trench</span> are modelled. Results indicate that the New Hebrides slab possesses an average areal density anomaly of about 300,000 gm/sq cm. This is about three times that which is estimated for the Tonga-Kermadec slab. Additional modelling suggests that slabs worldwide may be an important source of large, long wavelength gravity highs; i.e., they may contribute substantially to geopotential power of harmonic degree as low as three or four up to twenty or more.</p> <div class="credits"> <p class="dwt_author">Mcadoo, D. C.</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">324</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 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://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">326</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 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://ntrs.nasa.gov/search.jsp?R=20110005480&hterms=Second+Life+environment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3DSecond%2BLife%25C2%25AE%2Benvironment"> <span id="translatedtitle">KSC Launch Pad Flame <span class="hlt">Trench</span> Environment Assessment</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">This report summarizes conditions in the Launch Complex 39 (LC-39) flame <span class="hlt">trenches</span> during a Space Shuttle Launch, as they have been measured to date. Instrumentation of the flame <span class="hlt">trench</span> has been carried out by NASA and United Space Alliance for four Shuttle launches. Measurements in the flame <span class="hlt">trench</span> are planned to continue for the duration of the Shuttle Program. The assessment of the launch environment is intended to provide guidance in selecting appropriate test methods for refractory materials used in the flame <span class="hlt">trench</span> and to provide data used to improve models of the launch environment in the flame <span class="hlt">trench</span>.</p> <div class="credits"> <p class="dwt_author">Calle, Luz Marina; Hintze, Paul E.; Parlier, Christopher R.; Curran, Jerome P.; Kolody, Mark R.; Sampson, Jeffrey W.</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">328</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/2013AGUFM.T51F2529H"> <span id="translatedtitle">Dynamics of 3-D thermo-mechanical <span class="hlt">subduction</span> with an overriding 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">Characterizing the role of the upper plate in dynamic <span class="hlt">subduction</span> models is of paramount importance in understanding the <span class="hlt">subduction</span> system as a whole. We investigate the effect of the overriding plate on <span class="hlt">subduction</span> dynamics in a 3D, purely dynamic thermo-mechanical setup of the finite element code, CitcomCU (Moresi & Gurnis, 1996; Zhong, 2006). The reference models are purely Newtonian with a temperature dependent viscosity. <span class="hlt">Subduction</span> is initiated by an asymmetric notch in the down going plate, and the two plates are decoupled by a weak, 15 km thick crustal layer, along shear is localized. As observed in previous 2D modeling studies the presence of an overriding plate decreases the vertical extent of the poloidal flow, resulting in reduced vertical <span class="hlt">subduction</span> velocity, reduced <span class="hlt">trench</span> retreat and a larger dip angle. This increased dip angle results in preferential slab folding, as opposed to flattening, at the 660-km discontinuity when the overriding plate is included. It has recently been suggested that toroidal flow, due to slab rollback, creates <span class="hlt">trench</span>-perpendicular gradients in basal traction below the overriding lithosphere which can cause back-arc extension (Schellart & Moresi, 2013; Duarte et al., 2013). In our models, we also observe long wavelength back-arc extensional stresses, an