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Sample records for japan trench subduction

  1. Subduction of the Daiichi Kashima Seamount in the Japan Trench

    USGS Publications Warehouse

    Lallemand, S.; Culotta, R.; Von Huene, R.

    1989-01-01

    In 1984-1985, the Kaiko consortium collected Seabeam, single-channel seismic and submersible sampling data in the vicinity of the Daiichi-Kashima seamount and the southern Japan trench. We performed a prestack migration of a Shell multichannel seismic profile, that crosses this area, and examined it in the light of this unusually diverse Kaiko dataset. Unlike the frontal structure of the northern Japan trench, where mass-wasting appears to be the dominant tectonic process, the margin in front of the Daiichi-Kashima shows indentation, imbrication, uplift and erosion. Emplacement of the front one-third of the seamount beneath the margin front occurs without accretion. We conclude that the Daiichi-Kashima seamount exemplifies an intermediate stage between the initial collision and subduction of a seamount at a continental margin. ?? 1989.

  2. Forearc slope deformation above the Japan Trench megathrust: Implications for subduction erosion

    NASA Astrophysics Data System (ADS)

    Boston, Brian; Moore, Gregory F.; Nakamura, Yasuyuki; Kodaira, Shuichi

    2017-03-01

    Subduction erosion is a commonly invoked model that is used to explain the tectonic subsidence of the Japan Trench forearc slope, although other models have explained the morphology and history of the margin. New multichannel seismic reflection and bathymetric data collected after the 2011 Tohoku earthquake provide the opportunity to investigate the detailed structure of the overriding plate near the earthquake epicenter and obtain new constraints on tectonic models. We use regional-residual separation of the local bathymetry to constrain fault scarp extents and local landward-dipping forearc basins. Seismic images of these basins clearly show landward-dipping horizons in the shallow section. The strata in these basins imply a different mechanism for formation than the surrounding forearc slope, and we propose that these basins formed from local uplift. A regional basal unconformity mapped ∼150 km along-trench has highly variable relief, indicating that forearc slope subsidence occurs at multiple wavelengths in response to multiple different sources. We characterize the upper to middle slope transition and propose that this region may be the landward limit of major subduction erosion and also the main region for large mass wasting. Normal faults found in this setting have maximum lengths of ∼20 km, limiting their role in margin processes. Our results place constraints on the extent of major subduction erosion at the Japan Trench margin, and indicate that subduction erosion should be revisited as the sole model of formation to include additional tectonic processes.

  3. The effects of plate-bending-related aquifer thickening on temperatures in the Japan Trench subduction zone

    NASA Astrophysics Data System (ADS)

    Spinelli, G. A.

    2015-12-01

    Accurate subduction zone thermal models are necessary to understand a wide range of geophysical and geochemical processes, including: metamorphic reaction progress, mantle wedge hydration, and melt generation. For decades, plate convergence rate and subducting plate age and dip have been recognized as basic factors affecting subduction zone temperatures. Recent discoveries highlight the important effects of fluid circulation in oceanic lithosphere on subduction zone temperatures. However, there are contrasting hypotheses for the distribution of the regions within the oceanic lithosphere that host vigorous fluid circulation: one with a constant thickness aquifer extending both seaward and landward of the trench, one with an aquifer that thickens as it approaches the trench (due to bend-related faulting) but assumes vigorous fluid circulation only occurs prior to subduction, and a hybrid that considers both aquifer thickening seaward of the trench and continued circulation in the subducting plate. I examine the effects of bend-related aquifer thickening on temperatures within the Japan Trench subduction zone with a suite of thermal models. Kawada et al. [2014] hypothesize that plate-bending faults offshore northern Japan increase the thickness of the oceanic crustal aquifer, and therefore influence heat redistribution in the system. Existing models explore the effects of aquifer thickening on heat flux seaward of the trench, but they do not examine the effects of this process on temperatures within the subduction zone; additionally, they treat the aquifer seaward of the trench as completely isolated from the aquifer in the subducted plate. Here, I exploit the fact that aquifer thickening from the outer rise to the trench and continued fluid circulation in subducting crust are expected to produce distinct surface heat flux anomalies, in order to constrain the thermal effects of each process. I find the combinations of the amount of aquifer thickening and the degree of

  4. Distribution of stress state in the Nankai subduction zone, southwest Japan and a comparison with Japan Trench

    NASA Astrophysics Data System (ADS)

    Lin, Weiren; Byrne, Timothy B.; Kinoshita, Masataka; McNeill, Lisa C.; Chang, Chandong; Lewis, Jonathan C.; Yamamoto, Yuzuru; Saffer, Demian M.; Casey Moore, J.; Wu, Hung-Yu; Tsuji, Takeshi; Yamada, Yasuhiro; Conin, Marianne; Saito, Saneatsu; Ito, Takatoshi; Tobin, Harold J.; Kimura, Gaku; Kanagawa, Kyuichi; Ashi, Juichiro; Underwood, Michael B.; Kanamatsu, Toshiya

    2016-12-01

    To better understand the distribution of three dimensional stress states in the Nankai subduction zone, southwest Japan, we review various stress-related investigations carried out in the first and second stage expeditions of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) by the Integrated Ocean Drilling Program (IODP) and compile the stress data. Overall, the maximum principal stress σ1 in the shallower levels (< 1 km) is vertical from near the center of forearc basin to near the trench and; the maximum horizontal stress SHmax (interpreted to be the intermediate principal stress σ2) is generally parallel to the plate convergence vector. The exception to this generalization occurs along the shelf edge of the Nankai margin where SHmax is along strike rather than parallel to the plate convergence vector. Reorientation of the principal stresses at deeper levels (e.g., > 1 km below seafloor or in underlying accretionary prism) with σ1 becoming horizontal is also suggested at all deeper drilling sites. We also make a comparison of the stress state in the hanging wall of the frontal plate-interface between Site C0006 in the Nankai and Site C0019 in the Japan Trench subduction zone drilled after the 2011 Mw 9.0 Tohoku-Oki earthquake. In the Japan Trench, a comparison between stress state before and after the 2011 mega-earthquake shows that the stress changed from compression before the earthquake to extension after the earthquake. As a result of the comparison between the Nankai Trough and Japan Trench, a similar current stress state with trench parallel extension was recognized at both C0006 and C0019 sites. Hypothetically, this may indicate that in Nankai Trough it is still in an early stage of the interseismic cycle of a great earthquake which occurs on the décollement and propagates to the toe (around site C0006).

  5. Paleoseismology Along the Japan Trench Subduction Zone: Deep-Sea Sediment Records of Earthquakes in Tohoku

    NASA Astrophysics Data System (ADS)

    Kanamatsu, T.; Ikehara, K.; Strasser, M.; Usami, K.; McHugh, C. M.; Fink, H. G.; Nakamura, Y.; Kodaira, S.

    2014-12-01

    After the 2011 off the Pacific coast of Tohoku Earthquake, we have intensively explored earthquake-induced records in the deep-sea basins close to rupture zones of the 2011 and past earthquakes in Tohoku, Our study area focuses on small terminal basins near the trench for the following reason. Mass transport deposits from up-slope area down into the Japan Trench axis floor during the 2011 event were documented (e. g. Oguri et al., 2013). Similarly past earthquake-induced turbidites were expected to have been deposited in a number of small basins in the trench floor and in a lower slope terrace. Here we introduce our recent results and future prospects for paleoseismology in the Japan Trench. We collected cores from areas that are generally composed of diatomaceous fine grain sediment and fine-grained turbidites. Occasionally, wide spread tephra patches/layers are intercalated in the sediment. In the trench floor, two thick turbidite units below (older) than the 2011 event deposits were identified in up to 10m long sedimentary cores. An intercalated tephra within these turbidite units indicates that turbidites were triggered by historical earthquakes in Tohoku (Ikehara et al., in prep). On the other hand, frequent occurrence of thin-bedded turbidites was identified in the lower slope terrace. Several turbidite layers can be correlated over a wide area by tephra-correlation and matching of paleomagnetic secular variations (Usami et al., in this session). Turbidite-stratigraphy from both locations, the trench and lower slope terrace shows a similar pattern, and seems to be tied to the onland tsunami deposit stratigraphy straightforwardly. These observations suggest that deep-sea turbidite records are more reliable proxy for paleoseimic-stratigraphy of the Tohoku area. Encouraged by the results obtained so far, we plan extensive investigations in the area over the next few years to document effectively the spatiotemporal distribution of earthquake records of Tohoku.

  6. Seismic heating signatures in the Japan Trench subduction plate-boundary fault zone: evidence from a preliminary rock magnetic `geothermometer'

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Dekkers, Mark J.; Zhang, Bo

    2016-04-01

    Frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation. The amount of annealing varies widely and is, as yet, poorly constrained. Here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature a slip zone has experienced. The case study comprises sheared clay cored from the Japan Trench subduction plate-boundary fault zone (décollement), which accommodated the large slip of the 2011 Mw 9.0 Tohoku-oki earthquake. The décollement was cored during the Integrated Ocean Drilling Program (IODP) Expedition 343, the Japan Trench Fast Drilling Project (JFAST). Heating signatures with estimated maximum temperatures ranging from ˜300 to over 500 °C are determined close to the multiple slip surfaces within the décollement. Since it is impossible to tie a specific slip surface to a certain earthquake, thermal evidence for the cumulative effect of several earthquakes is unveiled. This as yet preliminary rock magnetic `geothermometer' would be a useful tool to detect seismic heating along faults that experienced medium temperature rise, a range which is difficult to assess with other approaches.

  7. Slip to the Trench for Great Subduction Earthquakes

    NASA Astrophysics Data System (ADS)

    Mori, J. J.

    2015-12-01

    The 2011 Tohoku-oki earthquake had the largest ever recorded fault slip (40 to 60 meters) on the shallow portion of the subduction zone close to the trench. This large displacement was largely unexpected for this region and was mainly responsible for the very large and damaging tsunami along the northeast coast of Honshu. We investigate the possibility of large slip to the trench in great earthquakes for other subduction zones around the world. Since the trench region is generally far offshore, it is often difficult to resolve the amount of slip from onshore geodetic and strong-motion data. We use a variety of observations, including slip distribution models, aftershock locations, local coastal deformation, and tsunami heights to determine which events likely had large amounts of slip close to the trench. Tsunami earthquakes, such as 1992 Nicaragua and 2006 Java likely had large shallow slip. Some typical subduction earthquakes, such as 1968 Tokachi-oki and 2003 Tokachi-oki (located in regions north of the source area of the 2011 Tohoku-oki earthquake) likely did not.We will discuss possible factors that influence the slip distribution on the shallow area of subduction megathrusts. Using results from the Japan Trench Fast Drilling Project (JFAST) which sampled the fault in the region of large slip, we can begin to understand the conditions of very large fault slip, such as the characteristic fault zone material and level of friction on the fault.

  8. Subduction trench migration since the Cretaceous

    NASA Astrophysics Data System (ADS)

    Williams, S.; Flament, N. E.; Müller, D.; Butterworth, N. P.

    2015-12-01

    Much of our knowledge about subduction zone processes is derived from analyzing present-day Earth. Several studies of contemporary plate motions have investigated the balance between retreating and advancing trenches and shown that subduction zone kinematics are sensitive to the choice of Absolute Plate Motion (APM) model (or "reference frame"). For past times, the absolute motions of the lithospheric plates relative to the Earth's deep interior over tens of millions of years are commonly constrained using observations from paleomagnetism and age-progressive seamount trails. In contrast, a reference frame linking surface plate motions to subducted slab remnants mapped from seismic tomography has recently been proposed. APM models derived using different methodologies, different subsets of hotspots, or differing assumptions of hotspot motion, have contrasting implications for parameters that describe the long term state of the plate-mantle system, such as the balance between advance and retreat of subduction zones, plate velocities, and net lithospheric rotation. Here we quantitatively compare the subduction zone kinematics, net lithospheric rotation and fit to hotspot trails derived the last 130 Myr for a range of alternative reference frames and a single relative plate motion model. We find that hotspot and tomographic slab-remnant reference frames yield similar results for the last 70 Myr. For the period between 130 and 70 Ma, when hotspot trails become scarce, hotspot reference frames yield a much more dispersed distribution of slab advance and retreat velocities, which is considered geodynamically less plausible. By contrast, plate motions calculated using the slab-remnant reference frame, or using a reference frame designed to minimise net rotation, yield more consistent subduction zone kinematics for times older than 70 Ma. Introducing the global minimisation of trench migration rates as a key criterion in the construction of APM models forms the foundation

  9. Subduction of seamounts at the Java Trench: a view with long-range sidescan sonar

    NASA Astrophysics Data System (ADS)

    Masson, D. G.; Parson, L. M.; Milsom, J.; Nichols, G.; Sikumbang, N.; Dwiyanto, B.; Kallagher, H.

    1990-12-01

    We describe here a 1300 km by 45 km GLORIA long-range sidescan sonar swath along the eastern Java Trench. The swath images the trench axis, a narrow strip of oceanic crust to the south, and the toe of the accretionary wedge to the north, between 108° and 120° E. Sonar images of the ocean crust show a pattern of normal faults typical of the outer wall of trenches. These result from tension related to the bending of the oceanic lithosphere into the subduction zone. A number of sub-circular seamounts are also seen, some of which are currently being subducted. Isolated "ponds" of flat-lying sediments occur in the trench axis, although along much of its length the trench is devoid of such sediment accumulations. On the inner trench wall, the accretionary wedge is recognised by its distinctive "grainy" texture, with the grain aligned sub-parallel to the deformation front. Where subducting seamounts are colliding with the wedge, large crescentic areas of very high backscattering correlate with re-entrants in the deformation front and large indentations in the wedge. The high backscattering within these collision scars is interpreted to arise from outcropping strata and talus covered slopes, resulting from erosion of an inner trench wall shortened and oversteepened by collision with a seamount. All of the sediment ponds in the trench axis occur in close association with collision scars, strongly suggesting localised erosion of the accretionary wedge in the scar areas. However, the volume of the indentations appears to be an order of magnitude greater than the volume of eroded sediments deposited in the trench, indicating that erosion cannot be the primary mechanism by which indentations are created. Most of the "missing" material must be displaced landward by thrusting and folding ahead of the seamount. Our observations at the Java Trench are broadly comparable with those made at the Japan Trench by French and Japanese workers. However, some differences in the detail of

  10. Wide-angle seismic survey in the trench-outer rise region of the central Japan Trench

    NASA Astrophysics Data System (ADS)

    Fujie, G.; Kodaira, S.; Iwamaru, H.; Shirai, T.; Dannowski, A.; Thorwart, M.; Grevemeyer, I.; Morgan, J. P.

    2015-12-01

    Dehydration process within the subducting oceanic plate and expelled water from there affect various subduction-zone processes, including arc volcanism and generation of earthquakes. This implies that the degree of hydration within the incoming oceanic plate just prior to subduction might be a key control factor on the regional variations in subduction zone processes like interplate earthquakes and arc volcanism. Recent advances in seismic structure studies in the trench-outer rise region of the Japan Trench have revealed that seismic velocities within the incoming oceanic plate become lower owing to the plate bending-related faulting, suggesting the hydration of the oceanic plate. If the degree of the oceanic plate hydration is one of key factors controlling the regional variations of the interplate earthquakes, the degree of the oceanic plate hydration just prior to subduction is expected to show the along-trench variation because the interplate seismicity in the forearc region of the Japan Trench show along-trench variations. However, we cannot discuss the along-trench variation of the incoming plate structure because seismic structure studies have been confined only to the northern Japan Trench so far.In 2014 and 2015, JAMSTEC and GEOMAR conducted wide-angle seismic surveys in the trench-outer rise region of the central Japan Trench to reveal the detailed seismic structure of the incoming oceanic plate. The western extension of our survey line corresponds to the epicenter of the 2011 M9 Tohoku earthquakes. We deployed 88 Ocean Bottom Seismometers (OBSs) at intervals of 6 km and shot a tuned air-gun array of R/V Kairei at 200 m spacing. In this presentation, we will show the overview of our seismic survey and present seismic structure models obtained by the data of mainly 2014 seismic survey together with the several OBS data from 2015 survey. The preliminary results show P-wave velocity (Vp) within the oceanic crust and mantle decreases toward the trench axis

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

    USGS Publications Warehouse

    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

    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

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

    NASA Astrophysics Data System (ADS)

    Cadet, Jean-Paul; Kobayashi, Kazuo; Aubouin, Jean; Boulègue, Jacques; Deplus, Christine; Dubois, Jacques; von Huene, Roland; Jolivet, Laurent; Kanazawa, Toshihiko; Kasahara, Junzo; Koizumi, Kinichiro; Lallemand, Serge; Nakamura, Yasuo; Pautot, Guy; Suyehiro, Kiyoshi; Tani, Shin; Tokuyama, Hidekazu; Yamazaki, Toshitsugu

    1987-05-01

    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 km 2 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

  13. Oblique convergence and deformation along the Kuril and Japan trenches

    NASA Technical Reports Server (NTRS)

    Demets, Charles

    1992-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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

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

    NASA Astrophysics Data System (ADS)

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

    2002-12-01

    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

  16. Along strike structural variation in the northern part of the Japan Trench axis region

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Kodaira, S.; Yamashita, M.; Miura, S.; Fujie, G.

    2015-12-01

    Great earthquakes have occurred along the Japan trench subduction zone, and some of them, e.g. Meiji Sanriku earthquake in 1896, could have ruptured the shallow portion of the plate boundary fault similar to the 2011 Tohoku earthquake. Geological/geophysical structure in the vicinity of the trench axis is one of the keys to understand the nature of shallow mega thrust events and tsunamigenesis. We have conducted high resolution seismic surveys in the northern part of the Japan Trench axis region in 38 - 40.5 N to investigate the detailed structure in the trench axis area. Thrust faults and possible slope failures are observed landward of the trench axis, beneath the lowermost landward trench slope. The deformation and evolution styles of the lowermost landward slope show variation along the trench strike. To the south of the survey area in 38 - 39 N, imbricate thrust-and-fold packages is observed but limited within the vicinity of the trench axis. Thickness of the hanging wall sediment is relatively thinner in the lowermost landward slope. These observation could suggest that the lowermost slope has not been well developed in this area. To the north around 40 - 40.5 N, frontal thrusts and imbricate structure are clearly observed on the seismic profiles through ~ 10 - 15 km landward of the trench axis. Thickness of the hanging wall sediment is thicker in this area. The bending-related faults on the subducted plate are generally not located beneath the lowermost slope up to ~ 10 km landward of the trench. These observations suggest that the imbricate structure has been well developed in the last ~ 10 kyr in this area. Around 39.5 N, it is suggested that slope failures have occurred. The trench axis is filled by slump deposits and debris with chaotic acoustic characteristics. Above mentioned variations in the deformation and evolution style in the lowermost landward slope could affect the mechanism of tsunami generation in the northern Japan Trench. The variation on

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

    PubMed

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

    2013-01-01

    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.

  18. 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)

    Casey, J.; Dewey, J. F.

    2013-12-01

    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

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

    NASA Astrophysics Data System (ADS)

    Heki, K.

    2003-12-01

    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 and cause forearc subsidence. Subduction erosion in Northeast Japan (NEJ) has been investigated by many geologists since ocean drilling at the continental slope of the Japan Trench discovered evidence of past erosion, i.e. unconformity over Cretaceous subaerial strata several kilometers deep. Tide gauge data of the last few decades in NEJ forearc also show that both interseismic and coseismic vertical movements are downward, suggesting secular subsidence of the forearc currently goes on. On the other hand, subduction erosion does not take place in Southwest Japan (SWJ); it has a well-developed accretionary prism, and sediment accretion is considered to occur there. Direct observation of the erosion has been difficult as it leaves little geological and geophysical evidence. In the present study, we compare horizontal and vertical velocity profiles across NEJ and SWJ, and investigate geodetic signatures of subduction erosion and accretion with modern satellite geodesy. The horizontal velocities agree well with those predicted by the elastic loading of the subducting slabs. However, vertical velocities in the NEJ forearc show significant negative deviation (subsidence). This may indicate loss of material at the plate interface, due to the erosion of the upper plate by the slab (basal subduction erosion). The estimated rate (15 mm/yr down to 90 km) is somewhat faster than the geological average, and the erosion speed may be variable being controlled by the surface roughness of subducting slabs.

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

    NASA Astrophysics Data System (ADS)

    Burch, Thomas K.; Langseth, Marcus G.

    1981-10-01

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

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

    SciTech Connect

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

    1981-10-10

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

  2. Formation of Island Arc-Trench System due to Plate Subduction on the Basis of Elastic Dislocation Theory

    NASA Astrophysics Data System (ADS)

    Fukahata, Y.; Matsu'ura, M.

    2015-12-01

    The most conspicuous cumulative deformation in subduction zones is the formation of island arc-trench system. A pair of anomalies in topography and free-air gravity, high in the arc and low around the trench, is observed without exceptions all over the world. Since the 1960s, elastic dislocation theory has been widely used to interpret coseismic crustal deformation. For the modeling of longer-term crustal deformation, it is necessary to consider viscoelastic properties of the asthenosphere. By simply applying elastic-viscoelastic dislocation theory to plate subduction, Matsu'ura and Sato (1989, GJI) have shown that some crustal deformation remains after the completion of one earthquake cycle, which means that crustal deformation accumulates with time in a long term due to plate subduction. In fact, by constructing a plate interface model in and around Japan, Hashimoto, Fukui and Matsu'ura (2004, PAGEOPH) have demonstrated that the computed vertical displacements due to steady plate subduction well explain the observed free-air gravity anomaly pattern. Recently, we got a lucid explanation of crustal deformation due to plate subduction. In subduction zones, oceanic plates bend and descend into the mantle. Because the bending of oceanic plates is usually not spontaneous, there exists kinematic interaction between the oceanic and overriding plates, which causes cumulative deformation of the overriding plate. This may be understood based on the law of action and reaction: one is bending of an oceanic plate and the other is deformation of the overriding plate. As a special case, it is useful to consider plate subduction along a part of true circle. In this case, crustal deformation due to steady subduction is solely caused by the effect of gravity, because dislocation along a circle does not cause any intrinsic internal deformation. When an oceanic plate is descending along an arcuate plate interface from the right-hand side, according to dislocation theory, the oceanic

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

    NASA Technical Reports Server (NTRS)

    King, Scott D.; Hager, Bradford H.

    1990-01-01

    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.

  4. Tectonic erosion at the front of the Japan Trench convergent margin

    USGS Publications Warehouse

    Von Huene, R.; Culotta, R.

    1989-01-01

    The imaging of a multichannel seismic record was improved by reprocessing using pre-stack techniques. The reprocessed record shows structures that indicate tectonic erosion and gravity collapse at the front of the Japan Trench margin. Much of the lower slope appears to be underlain by a detached, coherent block of continental crust. The lower slope has failed by mass wasting and the resulting apron of slump debris at the base of the slope has become involved in thrust faulting at the front of the subduction zone. Slumping continues as long as debris is removed from the front of the margin by subduction, and the apron cannot build up sufficiently to stabilize the failing lower slope. Truncated beds at the base of the upper plate indicate subcrustal erosion as well, this probably being the main cause of massive subsidence of the margin. Subsidence was the cause of oversteepening, destabilization and subsequent gravity collapse of the leading edge of the upper plate. ?? 1989.

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

    PubMed

    Kneller, Erik A; van Keken, Peter E

    2007-12-20

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

  6. The Fault Damage Zone of the Shallow Japan Trench Megathrust

    NASA Astrophysics Data System (ADS)

    Keren, T.; Kirkpatrick, J. D.

    2014-12-01

    The Mw 9.0 Tohoku-oki earthquake resulted in an unprecedented coseismic slip of >50 m in the shallow portion of the Japan Trench subduction zone. We present analyses of core recovered during IODP Expedition 343/343T (JFAST) that define structures surrounding the inferred plate boundary décollement, and use the results to constrain the fault's long-term strength. The plate boundary fault is centered at 821.5 m below the sea floor, with a damage zone extending 15.5 m below and 51.5 m above. The damage zone is defined by shear fractures, subsidiary faults, deformation bands, mode I fractures, breccia zones, and sediment-filled veins. Orientations of mutually crosscutting shear fractures decrease in dip angle nearing the fault in the hanging wall, from 67° at 50 m above the fault down to 25°. In the footwall, dips range from 88° at 9.6 m below the fault to 30° at 11 m below. The damage zone characteristics were established using a set of criteria to eliminate drilling-, coring-, and handling-induced damage in core. Core-scale fracture density increases from 21 fractures/m at 51 m above the fault to 247 fractures/m adjacent to the fault in the hanging wall, and from 28 fractures/m at 11 m below the fault to 254 fractures/m adjacent to the fault in the footwall. The fall-off in fracture density is fit by power law functions in the hanging wall and footwall, with decay exponent n values of 0.70 and 1.45, respectively. Microstructures include shear fractures, veins, crystallographic preferred orientation bands, shear zones, and undifferentiated fractures. Microstructure density in the footwall increases from 0.32 fractures/mm 10 m below the fault to 2.04 fractures/mm adjacent to the fault, and is fit by a power law function with n = 1.27. Orientations of shear fractures have attitudes consistent with normal and reverse faults, indicating the stress field underwent significant reorientations multiple times. This is consistent with the inferred stress field changes

  7. An ongoing large submarine landslide at the Japan trench

    NASA Astrophysics Data System (ADS)

    Nitta, S.; Kasaya, T.; Miura, S.; Kawamura, K.

    2013-12-01

    This paper deals with an active submarine landslide on a landward trench slope in the Japan trench. Studied area is located on the upper terrace ranging from 400 to 1200 m in water depth, off Sendai, northeast Japan. We have surveyed in detail the seabed topography using a multi narrow beam (hereafter MBES) and a subbottom profiler (hereafter SBP) during the cruise MR12-E02 of R/V Mirai. The survey lines were 12 lines in N-S, and 3 lines in E-W, and situated in the region from 141°45'E, 37°40'N to 142°33'E, 38°32'N. Moreover, we used multi-channel seismic profile by the cruise KR04-10 of R/V Kairei in the interpretation of the SBP results. In general, horseshoe-shaped depressions of about 100 km wide along the trench slope are arrayed along the Japan trench. It has thought that they were formed by large submarine landslides, but we could not understand critically the relationship between the depressions and the submarine landslides. Based on the survey results, we found signals of an active submarine landslide in the depression as follows. 1) We observed arcuate-shaped lineaments, which are sub-parallel to a horseshoe-shaped depression. The lineaments concentrate in the south region from 38°N at about 20 km wide. These lineaments are formed by deformation structures as anticlines, synclines and normal fault sense displacements. 2) Most of the synclines and anticlines are not buried to form the lineaments. 3) Normal faults cutting about 1 km deep are observed in a multi-channel seismic profile. The normal faults are located just below the arcuate-shaped lineaments, and are tilted eastward being the downslope direction. It indicates a large submarine landslide. We concluded that the arcuate-shaped lineaments were generated by surface sediment movement with the submarine landsliding. We think that the submarine landslide of about 20 km wide and about 1 km thick move continuously down the landward trench slope. This would be the formation process of the horseshoe

  8. Young lava fields on the Cretaceous Pacific Plate in the Japan Trench: Non-hotspot volcanism?

    NASA Astrophysics Data System (ADS)

    Hirano, N.; Haraguchi, S.; Yamamoto, J.; Takahashi, E.; Hirata, T.; Takahashi, A.; Ogawa, Y.

    2004-12-01

    The northwestern part of the Pacific Plate is comprised of Early Cretaceous abyssal oceanic lithosphere and Early to Late Cretaceous seamounts. Until recently, no present-day volcanic activity had been definitively documented on the cool, thick, and old Cretaceous lithosphere; however, Hirano et al. (2001) reported the presence of anomalously young alkali-basalt lavas (5.95±0.31 Ma) on the subducting, ˜130 Ma Pacific Plate. The trench-oceanward slope is characterized by trench-parallel normal faults, resulting from bending of the subducting Pacific Plate. Some hummock structures named the Kaiko Knolls can also be observed on the faulted abyssal plain using seabeam sonar bathymetric mapping. The Kaiko Knolls hummocks and some of the horst and graben fault walls are recognized in the seabeam sonar data by the presence of ocean floor with high acoustic intensity. The newly discovered lava fields include all hummocks in the Kaiko Knolls as well as the underlying sheet flow. The distinct WNW-ESE alignments of knolls are perpendicular to hinge lines of bending plate of the trench and outer-rise system. Composition of the dredged lavas shows the garnet presence in the source because the residual garnet buffered Al2O3 contents with degrees of partial melting and lowered HREE contents. Hirano et al. (2004) demonstrated that the olivine xenocrysts in this rock were entrained from the uppermost mantle. Volcanic eruption occurred ˜600 km ESE off the northern Japan Trench based on the radiometric age and the present absolute motion of the Pacific Plate. Morphological and petrological evidences show that the magma has been brought to the surface along some fissures, which can be interpreted along the direction of the maximum horizontal compression caused by the stress in the downwarping Pacific Plate at eastern edge of the outer-rise.

  9. Large trench-parallel gravity variations predict seismogenic behavior in subduction zones.

    PubMed

    Song, Teh-Ru Alex; Simons, Mark

    2003-08-01

    We demonstrate that great earthquakes occur predominantly in regions with a strongly negative trench-parallel gravity anomaly (TPGA), whereas regions with strongly positive TPGA are relatively aseismic. These observations suggest that, over time scales up to at least 1 million years, spatial variations of seismogenic behavior within a given subduction zone are stationary and linked to the geological structure of the fore-arc. The correlations we observe are consistent with a model in which spatial variations in frictional properties on the plate interface control trench-parellel variations in fore-arc topography, gravity, and seismogenic behavior.

  10. Development of Observatories for the Japan Trench Fast Drilling Project

    NASA Astrophysics Data System (ADS)

    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

    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

  11. Seismological observation in outer-rise of the Japan Trench toward exploring interaction between megathrust and incoming plate

    NASA Astrophysics Data System (ADS)

    Kodaira, S.; Nakamura, Y.; Fujie, G.; Miura, S.; Obana, K.; Takahashi, N.

    2015-12-01

    Previous geophysical, geological and petrological studies suggest a wide range of interactions between tectonic/magmatic processes in a subduction zone and incoming oceanic plate. For example, following a great megathrust earthquake, a large normal-faulting earthquake often occur in an outer- rise region of an incoming plate; the 1933 Meiji-sanriku earthquake (Mw8.1) following the 1896 Meiji-sanriku earthquake (M~8.2) are recognized as typical examples of those doublets in the Japan Trench. Another tectonic process which may control an interaction between processes in subduction interface and incoming plate is hydration/dehydration process of the oceanic plate; i.e., a dehydration process from the subducting oceanic plate is believed to affect various subduction zone processes, including arc volcanism, generation of earthquakes and non-volcanic tremor and inter-plate slow slip. In order to obtain fundamental data for exploring an interaction between a subduction process and an incoming plate, we started a new geophysical project in the outer-rise of the Japan Trench by using an ultra-deep OBS and other active-passive seismological tools. Preliminary results from the outer-rise project show that 1) reduction of Vp and increase of Vp/Vs in the crust and the uppermost mantle from ~150 km seaward of the trench, which is interpreted to be attributed to fluid percolation through bend-related faults, 2) clear Moho reflection of the incoming plate is observed to the trench from the outer-rise with partially obscure Moho reflections, 3) some of clusters of the aftershocks of the 2011 Tohoku-oki earthquake, predominantly normal fault aftershocks, extend to deeper in the mantle (~40 km deep) in an area where the Moho reflection is obscure, and the normal fault earthquake became deeper than earthquakes occurred before the 2011 earthquake. Those observations suggest that growing bend-related normal faults can be a primal mechanism to bring water deeper into the oceanic plate

  12. Sensing of upslope passages of frontal bores across the trench slope break of the Japan Trench

    NASA Astrophysics Data System (ADS)

    Fukao, Yoshio; Sugioka, Hiroko; Ito, Aki; Shiobara, Hajime; Paros, Jerome M.; Furue, Ryo

    2016-05-01

    The circum-Pacific trench slope system is one of the most spectacular topographic features of the Earth. We report the relatively frequent occurrence of upslope passages (˜50 times a year) of internal bores in the Japan Trench system. Observations were made using a triaxial accelerometer, a tiltmeter, and a current meter at the seafloor, ˜3400 m deep, during 10 months from 2013 to 2014. We detected 42 tilt events from the records of the accelerometer and confirmed their consistency with the tiltmeter records. The tilt occurred always landward by 1-10 µrad with a rise time on the order of 1000 s and return to the original with a much longer recovery time. The current and temperature records available for the first two events indicated that landward tilting was associated with an upslope current with a speed of several cm/s and a temperature drop of several tens of m °C. The temperature remained cold even after the current had diminished. All of these observations implied the frontal passages of upslope advancing bores, which caused the instrument to be tilted landward. The observational site was located at the trench slope break, separating the trench slope (sloping supercritically or near critically for the M2 internal tide) from the fore-arc basin (sloping subcritically). This unique locality suggested the internal tide origin of the observed bores, although other possibilities could not be precluded. Bores generated on the trench slope may play a role for upslope transportation of suspended sediments stirred up by deep submarine landslides.

  13. Slow slip near the trench at the Hikurangi subduction zone, New Zealand.

    PubMed

    Wallace, Laura M; Webb, Spahr C; Ito, Yoshihiro; Mochizuki, Kimihiro; Hino, Ryota; Henrys, Stuart; Schwartz, Susan Y; Sheehan, Anne F

    2016-05-06

    The range of fault slip behaviors near the trench at subduction plate boundaries is critical to know, as this is where the world's largest, most damaging tsunamis are generated. Our knowledge of these behaviors has remained largely incomplete, partially due to the challenging nature of crustal deformation measurements at offshore plate boundaries. Here we present detailed seafloor deformation observations made during an offshore slow-slip event (SSE) in September and October 2014, using a network of absolute pressure gauges deployed at the Hikurangi subduction margin offshore New Zealand. These data show the distribution of vertical seafloor deformation during the SSE and reveal direct evidence for SSEs occurring close to the trench (within 2 kilometers of the seafloor), where very low temperatures and pressures exist.

  14. Quantitative Study of Seismogenic Potential Along Manila Trench: Effects of Scaborough Seamount Chain Subduction

    NASA Astrophysics Data System (ADS)

    Yu, H.; Liu, Y.; Li, D.; Ning, J.; Matsuzawa, T.; Shibazaki, B.; Hsu, Y. J.

    2014-12-01

    Modern seismicity record along the Manila Trench shows only infrequent Mw7 earthquakes, the lack of great earthquakes may indicate the subduction fault is either aseismically slipping or is accumulating strain energy toward rapid release in a megathrust earthquake. We conduct numerical simulations of the plate coupling, earthquake nucleation and dynamic rupture propagation processes along the Manila subduction fault (15-19.5ºN), taking into consideration the effects of plate geometry (including subducted seamounts), fault strength, rate-state frictional properties and pore pressure variations. Specifically, we use the bathymetry to depict the outline of Manila trench along its strike, 2681 background seismicity (1970/02/13 to 2013/09/06) from Chinese Earthquake Network Center and 540 focal mechanism solutions (1976/01/01 to 2013/01/27) from Global CMT project to constrain the geometry of the subducting Sunda/Eurasian slab. The compilation of seismicity and focal mechanism indicates the plate dipping angle gradually changes from 28º (south of the Scaborough Seamount Chain) to 12º (north of it). This geometric anomaly may due to the subducted part of the seamount chain. Preliminary modeling results using gabbro gouge friction data show that the Scaborough Seamount Chain could be a barrier to earthquake rupture propagation. Only earthquakes larger than Mw7 can overcome the barrier to rupture the entire Manila trench. Smaller earthquakes would cease rupturing when it encounters the seamount chain. Moreover, we propose that Manila trench subduction zone has the potential of rupturing in a Mw8 megathrust earthquake, if the simulation period is long enough for an Mw8 earthquake cycle and dynamic rupture overcomes the subducted Scaborough Seamount Chain. Our model parameters will be further constrained by laboratory rock mechanics experiments conducted on IODP Expedition 349, South China Sea (SCS), drilling samples (work in progress at China Earthquake Administration

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

    NASA Astrophysics Data System (ADS)

    Fujimoto, H.; Kido, M.

    2012-12-01

    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

  16. P wave anisotropic tomography of the Nankai subduction zone in Southwest Japan

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Zhao, Dapeng

    2012-05-01

    The active subduction of the young Philippine Sea (PHS) plate and the old Pacific plate has resulted in significant seismic heterogeneity and anisotropy in Southwest (SW) Japan. In this work we determined a detailed 3-D P wave anisotropic tomography of the crust and upper mantle beneath SW Japan using ˜540,000 P wave arrival times from 5,249 local earthquakes recorded by 1095 stations. The PHS slab is imaged clearly as a high-velocity (high-V) anomaly which exhibits considerable lateral variations. Significant low-velocity (low-V) anomalies are revealed above and below the PHS slab. The low-V anomalies above the PHS slab may reflect the upwelling flow in the mantle wedge and the PHS slab dehydration, and they form the source zone of the arc volcanoes in SW Japan. The low-V zones under the PHS slab may reflect the upwelling flow in the big mantle wedge above the Pacific slab. The anisotropy in the crust and upper mantle is complex. In Kyushu, the P wave fast velocity direction (FVD) is generally trench-normal in the mantle wedge under the back-arc, which is consistent with the corner flow driven by the PHS slab subduction. The FVD is trench-parallel in the subducting PHS slab under Kyushu. We think that the intraslab seismicity is a potential indicator to the slab anisotropy. That is, the PHS slab with seismicity has kept its original fossil anisotropy formed at the mid-ocean ridge, while the aseismic PHS slab has reproduced the anisotropy according to its current deformation.

  17. Three-dimensional Distribution of Azimuthal and Radial Anisotropy in the Japan Subduction

    NASA Astrophysics Data System (ADS)

    Ishise, M.; Kawakatsu, H.; Shiomi, K.

    2014-12-01

    Seismic anisotropy has close relationships with past and present tectonic and dynamic processes. Therefore, detailed description of seismic anisotropy of subduction zones provides important information for our understanding of the subduction system. The most common method of detecting anisotropy is the S-wave splitting measurement. However, conventional S-wave splitting analysis is not an appropriate way to investigate anisotropy in the mantle and slab because the technique has no vertical resolution. Thus, we have improved common traveltime tomography to estimate three-dimensional anisotropic structures of P-wave, assuming that the modeling space is composed of weakly anisotropic medium with a hexagonal symmetry about a horizontal axis (Ishise & Oda, 2005, JGR; Ishise & Oda, 2008, PEPI). Recently, we extended the anisotropic tomography for P-wave radial anisotropy with vertical hexagonal symmetry axis (Ishise & Kawakatsu, 2012 JpGU). In this study, we expand the study area of our previous regional analyses of P-wave azimuthal and radial anisotropic tomography (Ishise & Oda, 2005; Ishise & Kawakatsu, 2012, JpGU; Ishise et al., 2012, SSJ) using Hi-net arrival time data and examine the subduction system around the Japan islands, where two trenches with different strike directions and plate junction are included. Here are some of the remarkable results associated with the PAC slab and mantle structure. (1) N-S-trending fast axis of P-wave anisotropy is dominant in the PAC slab. (2) the mantle wedge shows trench-normal anisotropy across the trench-trench junction. (3) horizontal velocity (PH) tends to be faster than vertical velocity (PV) in the slab. (4) PV tends to be faster than PH in the mantle wedge. The characteristics of the obtained azimuthal and radial anisotropy of the PAC slab and the mantle wedge qualitatively consistent with heterogeneous plate models (e.g., Furumura & Kennet, 2005) and numerical simulations of mantle flow (Morishige & Honda, 2011; 2013

  18. Fundamental structure model of island arcs and subducted plates in and around Japan

    NASA Astrophysics Data System (ADS)

    Iwasaki, T.; Sato, H.; Ishiyama, T.; Shinohara, M.; Hashima, A.

    2015-12-01

    The eastern margin of the Asian continent is a well-known subduction zone, where the Pacific (PAC) and Philippine Sea (PHS) plates are being subducted. In this region, several island arcs (Kuril, Northeast Japan, Southwest Japan, Izu-Bonin and Ryukyu arcs) meet one another to form a very complicated tectonic environment. At 2014, we started to construct fundamental structure models for island arcs and subducted plates in and around Japan. Our research is composed of 6 items of (1) topography, (2) plate geometry, (3) fault models, (4) the Moho and brittle-ductile transition zone, (5) the lithosphere-asthenosphere boundary, and (6) petrological/rheological models. Such information is basic but inevitably important in qualitative understanding not only for short-term crustal activities in the subduction zone (particularly caused by megathrust earthquakes) but also for long-term cumulative deformation of the arcs as a result of strong plate-arc/arc-arc interactions. This paper is the first presentation of our research, mainly presenting the results of items (1) and (2). The area of our modelling is 12o-54o N and 118o-164o E to cover almost the entire part of Japanese Islands together with Kuril, Ryukyu and Izu-Bonin trenches. The topography model was constructed from the 500-m mesh data provided from GSJ, JODC, GINA and Alaska University. Plate geometry models are being constructed through the two steps. In the first step, we modelled very smooth plate boundaries of the Pacific and Philippine Sea plates in our whole model area using 42,000 earthquake data from JMA, USGS and ISC. For 7,800 cross sections taken with several directions to the trench axes, 2D plate boundaries were defined by fitting to the earthquake distribution (the Wadati-Benioff zone), from which we obtained equi-depth points of the plate boundary. These equi-depth points were then approximated by spline interpolation technique to eliminate shorter wave length undulation (<50-100 km). The obtained

  19. Dynamic effects of plate-buoyancy subduction at Manila Trench, South China Sea

    NASA Astrophysics Data System (ADS)

    Jiang, L.; Zhan, W.; Sun, J.; Li, J.

    2015-12-01

    Bathymetric map of SCS plate shows two subducting buoyancies, the fossil ridge and the oceanic plateau, which are supposed to impact slab segmentation into the north from Taiwan to 18°N, and the south from 17°N to Mindoro. Hypocenter distribution show that slab dip angle turns lower southwards from 45° to 30° in the north segment, and relatively equals ~45° in the south segment at the depth of 100km. Moreover, volcano distribution can be segmented into Miocene WVC, Quaternary EVC in the north and combined SVC in the south (Fig. A). We found that WVC and SVC mostly locate in a parallel belt ~50km apart to Manila trench, however EVC turn father southwards from 50km to 100km (Fig. B). Above characters congruously indicate that SCS plate kept equal dip angle in Miocene; then the north segment shallowed at 18°N and developed northwards in Quaternary, resulting in lower dip angle than the invariant south segment. To check the transformation of slab dip angle from 45° to 30° between 17~18°N, focal mechanism solution nearby 17°N are found 90° in rake and dip angle, strike parallel to the fossil ridge, indicating a slab tear located coincident with the ridge, where is a weak zone of higher heat flow and lower plate coupling ratio than the adjacent zones and slab can be easily tore as an interface for SCS plate segmentation. Subduction of the two buoyancies within SCS plate is supposed as influential dynamic factor: It caused the trench retreat rate reduced, forming a cusp and a flat convex of Manila trench shape; Moreover, the buoyancies resisted subduction, resulting in shear stress heterogeneity of SCS plate, in consequence the fossil ridge as a fragile belt potentially became stress concentration zone that easily tore; Then the buoyant oceanic plateau might lead to shallowing of the northern SCS plate. To examine the hypothesis, dynamic effects of the two subducting buoyancies are being respectively investigated based on numerical models. (Grt. 41376063, 2013

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    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

  1. Hadal disturbance and radionuclide profiles at the deepest Japan Trench, northeastern Japan

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    Four months after the 2011 Tohoku-Oki earthquake, we carried out a video survey and collected sediment core collection from the hadal region (~7,600 m water depth) of the Japan Trench using an autonomous instrument. Fine material remained suspended at ~50 m above the seabed presumably induced by turbidities released during the central earthquake and the following aftershocks. Elevated levels of Cs-137 (T1/2=30 y) and excess Pb-210 (T1/2=22.3 y) concentrations suggested that 30 cm thick sediment layer had accumulated at the trench base (7,553 m) after the mainshock. However, no Cs-134 (T1/2=2 y) fallout from the Fukushima Dai-ichi nuclear disaster was detected. In contract, inspection of a nearby sediment site (7,261 m) 4.9 km away from the central trench site revealed fewer disturbances as reflected by a recent deposition of only 4 cm sediment, but here we encountered recent Cs-134 fallouts from the top 0-1 cm depth. We propose that the apparent lack of Cs-134 in the central trench is coursed by settlement of turbidites containing Cs-137 from past atmospheric fallout and higher excess Pb-210. The fast transport of the Cs-134 to the hadal slope sediment is presumably induced by enhanced scavenging and the vertical transport associated to an intensified diatom blooming occurring just at the time of the Fukushima disaster.

  2. Normal faulting of the Daiichi-Kashima Seamount in the Japan Trench revealed by the Kaiko I cruise, Leg 3

    USGS Publications Warehouse

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

    1987-01-01

    A detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern Japan Trench, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2-4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and single-channel seismic reflection records. Vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported. The northern and southern extensions of the normal fault beyond the flank of the seamount were delineated. Materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount. Canyons observed in the upper landward slope terminate at the mid-slope terrace which has been uplifted since start of subduction of the seamount. Most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern Japan Trench wall. This survey was conducted on R/V "Jean Charcot" as a part of the Kaiko I cruise, Leg 3, in July-August 1984 under the auspices of the French-Japanese scientific cooperative program. ?? 1987.

  3. Physical properties and Consolidation behavior of sediments from the N. Japan subduction zone

    NASA Astrophysics Data System (ADS)

    Valdez, R. D., II; Lauer, R. M.; Ikari, M.; Kitajima, H.; Saffer, D. M.

    2013-12-01

    Sediment hydraulic properties, consolidation state, and ambient pore pressure development are key parameters that affect fluid migration, deformation, and the slip behavior and mechanical strength of subduction zone megathrusts. In order to better understand the dynamics and mechanisms of large subduction earthquakes, Integrated Oceanic Drilling Program (IODP) Expedition 343, drilled into the toe of the Japan Trench subduction zone in a region of large shallow slip in the M 9.0 Tohoku earthquake, as part of the Japan Trench Fast Drilling Project (J-FAST). Here, we report on two constant rate of strain (CRS) uniaxial consolidation experiments and two triaxial deformation experiments on bedded claystone and clayey mudstone core samples collected from the frontal prism and subducted sediment section cored at Site C0019, 2.5 km landward of the Japan Trench, from depths of 697.18 and 831.45 mbsf. The goals of our experiments were: (1) to define the hydraulic and acoustic properties of sediments that host the subduction megathrust fault that slipped in the M 9.0 Tohoku earthquake; and (2) to constrain in-situ consolidation state and its implications for in-situ stress. The permeability-porosity trends are similar for the two samples, and both exhibit permeability that decreases systematically with increasing effective stress and decreasing porosity, and which varies log-linearly with porosity. Permeabilities of material from the frontal prism decrease from 5×10-18 m2 at 5 MPa effective stress, to 3.0×10-19 m2 at 70 MPa, and porosities decrease from 51% to 29%, while permeabilities of the subducted sediment sample decrease from 5×10-18 m2 at 5 MPa to 3.6×10-19 m2 at 90 MPa, and porosities decrease from 49% to 36%. In-situ permeabilities for the prism and underthrust sediment samples, estimated using laboratory defined permeability-porosity relationships, are 4.9×10-18 m2 and 3.7×10-18 m2, respectively. Elastic wavespeeds increase systematically with increasing

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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

  5. Nature and Architecture of the Sedimentary Deposits in the Trench of the Ecuadorian Subduction Margin

    NASA Astrophysics Data System (ADS)

    Gonzalez, Miguel; Proust, Jean-Noel; Michaud, Francois; Pouderoux, Hugo; Ratzov, Gueorgui

    2016-04-01

    The active margin of Ecuador is characterized by strong tectonic erosion that contributes to the formation of a deep trench filled by a complex suite of sedimentary facies. Gravity flow sedimentation is ubiquitous along the margin and facies range from laterally continuous m-thick mass transport deposits to isolated cm-thick turbidites intercalated with hemipelagite and ash layers. However, the nature and architecture of those deposits remain equivocal. This study presents the interpretation of detailed bathymetry, high-resolution seismic profiles and sediment cores recently acquired along the 600 km-long Ecuadorian margin (ATACAMES campaign onboard the R/V L'Atalante, 2012). The margin comprises three morphological segments: (1) the central segment marked by the subduction of the Carnegie Ridge, which induced a narrow (10-30 km wide) and relatively shallow trench (3100-3700 m deep), a steep and gullied continental slope with no canyon and a 20-60 km wide shelf characterized by active subsidence, (2) the northern segment characterized by a wider (~100 km) and deeper (3800-4000 m) trench, a gentler gullied continental slope and similar shelf settings (10-50 km wide), (3) the southern segment presents a wide (20-60 km) and deep (4000-4700 m) trench, a starved continental slope with well-defined canyon systems and a wide subsiding shelf (50-100 km wide). The sedimentary dynamics along the margin is evaluated by the analysis of 15 sediment cores. High-resolution visual description of the cores, X-Ray imagery and the measurement of petrophysical properties (gamma density, magnetic susceptibility, P-wave velocity) led to the identification of 6 sedimentary facies that characterize 6 sedimentary processes: Turbidite beds (turbidity currents), Hemipelagites (continuous marine sedimentation), Tephras (airfall ash layers consecutive to volcanic eruptions), Debris flow deposits (cohesive debris flows), Megaturbidite/Homogenite (large-scale and/or hybrid gravity flows), Mass

  6. GPS/acoustic seafloor geodetic observation in the subduction zone around Japan (Invited)

    NASA Astrophysics Data System (ADS)

    Sato, M.; Kido, M.; Tadokoro, K.; Fujimoto, H.

    2013-12-01

    GPS/acoustic (GPS/A) seafloor geodetic observation is a precise seafloor positioning technique and has made great progress over the last decade. GPS/A observation determines the positions of acoustic mirror-type transponders installed on the seafloor by combining the two techniques of kinematic GPS and acoustic ranging through a ship or a buoy. The original idea was proposed by Prof. Spiess at the Scripps Institution of Oceanography in 1985 and its protocol and hardware were made through research and development of his group by the mid-1990s. In Japan, three research groups, Japan Coast Guard, Tohoku University and Nagoya University, began to develop the GPS/A observation system in the 1990s, established GPS/A observation sites mainly on the landward slope of the plate boundaries around Japan, such as the Japan Trench and the Nankai trough, and have been carrying out campaign observations since around 2000. The primary purpose of our observation is to detect and monitor the crustal deformation caused by the subduction of the oceanic plate near the plate boundary where large interplate earthquakes have repeatedly occurred. By continuous efforts for over a decade, the positioning precision has achieved a few centimeters and seafloor movements such as intraplate deformation and coseismic displacements have been successfully detected. In particular, regarding the 2011 Tohoku-oki earthquake (M9.0), which occurred off northeastern Japan on March 11, 2011, east-southeastward coseismic displacements of up to 31 m were observed above the focal region, especially close to the epicenter, while those detected by on-land GPS measurements over 100 km away from the epicenter, conducted by the Geospatial Information Authority of Japan, was up to 5.3 m. Coseismic slip models on the plate boundary estimated from not only GPS data but also GPS/A results indicate that a huge slip of more than 50 m generated close to the trench axis, which was much larger than that estimated from GPS

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

    PubMed

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

    2013-01-01

    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.

  8. Hadal disturbance in the Japan Trench induced by the 2011 Tohoku–Oki Earthquake

    PubMed Central

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

    2013-01-01

    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. PMID:23715086

  9. Two decades of spatiotemporal variations in subduction zone coupling offshore Japan

    NASA Astrophysics Data System (ADS)

    Loveless, John P.; Meade, Brendan J.

    2016-02-01

    Spatial patterns of interplate coupling on global subduction zones can be used to guide seismic hazard assessment, but estimates of coupling are often constrained using a limited temporal range of geodetic data. Here we analyze ∼19 years of geodetic observations from the GEONET network to assess time-dependent variations in the spatial distribution of coupling on the subduction zones offshore Japan. We divide the position time series into five, ∼3.75-year epochs each decomposed into best-fit velocity, annual periodic signals, coseismic offsets, and postseismic effects following seven major earthquakes. Nominally interseismic velocities are interpreted in terms of a combination of tectonic block motions and earthquake cycle activity. The duration of the inferred postseismic activity covaries with the linear velocity. To address this trade-off, we assume that the nominally interseismic velocity at each station varies minimally from epoch to epoch. This approach is distinct from prior time-series analysis across the earthquake cycle in that position data are not detrended using preseismic velocity, which inherently assumes that interseismic processes are spatially stable through time, but rather the best-fit velocity at each station may vary between epochs. These velocities reveal significant consistency since 1996 in the spatial distribution of coupling on the Nankai subduction zone, with variation limited primarily to the Tokai and Bungo Channel regions, where long-term slow slip events have occurred, and persistently coupled regions coincident with areas that slipped during historic great earthquakes. On the Sagami subduction zone south of Tokyo, we also estimate relatively stable coupling through time. On the Japan-Kuril Trench, we image significant coupling variations owing to effects of the 1994 MW = 7.7 Sanriku-oki, 2003 MW = 8.2 Tokachi-oki, and 2011 MW = 9.0 Tohoku-oki earthquakes. In particular, strong coupling becomes more spatially extensive following

  10. Provenance mixing in an intraoceanic subduction zone: Tonga Trench-Louisville Ridge collision zone, southwest Pacific

    NASA Astrophysics Data System (ADS)

    Cawood, Peter A.

    1990-04-01

    Dredging on the lower slope of the Tonga forearc, at the intersection between the Louisville Ridge hotspot chain and the trench, yielded both Late Tertiary volcaniclastic sediments and Late Cretaceous slightly tuffaceous pelagic sediments. Petrography and phase chemistry of volcanic debris of Tertiary age samples indicates derivation from a low-K tholeiitic arc: volcanic glass has a low K 2O content and shows an Fe enrichment trend; plagioclase grains are high in An and low in Or components; pyroxene grains (calcic clinopyroxene, orthopyroxene and pigeonite) have low TiO 2 contents and show an Fe enrichment trend; alkali feldspar and biotite are absent. The composition of the Tertiary samples is similar to other Tonga forearc sediments and is consistent with their derivation from the adjacent magmatic arc. The character and composition of volcanogenic debris in Cretaceous age samples indicates derivation from an intraplate alkali igneous source: plagioclase compositions show an increasing Or component with increasing Ab; alkali feldspar is a rare additional component of these samples; calcic clinopyroxene has high TiO 2 contents and is titanaugite; amphibole is also rich in TiO 2 and is kaersutite; minor volcanic glass is rich in alkalis. Samples were dredged from the seaward slope of a small terrace on the lower trench slope. A planar reflector, located 2.6 km below the terrace is marked by an abrupt jump in seismic velocity and is interpreted as the top of an essentially undamaged Late Cretaceous guyot of the Louisville chain that was subducted at the Tonga trench about 0.5 Ma. This guyot is the likely source of the Late Cretaceous, intraplate igneous detritus collected at the dredge site. Some dredge samples yielded a mixed volcanic arc/intraplate provenance and/or Late Tertiary/Late Cretaceous ages. This probably represents the mixing of the Cretaceous seamount and Tertiary magmatic arc sources during post-collision slumping of the wedge of lower slope material

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  12. The buoyancy variation of plate coupling from subduction to collision: an example across the northernmost Manila trench

    NASA Astrophysics Data System (ADS)

    Lo, Chung-Liang; Doo, Wen-Bin; Kuo-Chen, Hao; Hsu, Shu-Kun

    2015-04-01

    The Manila trench is the boundary between the South China Sea (SCS) of Eurasian Plate (EU) and Philippine Sea Plate (PSP). The east subducting of SCS is a ceased rifting oceanic crust. To the north, the subduction is obscured and transits to collision extended to the Taiwan orogenesis. The Taiwan Integrated Geodynamics Research (TAIGER) project has implemented several offshore multichannel seismic (MCS) reflection and wide-angle seismic experiments to model the velocity structure of the incipient arc-continental collision. Amongst, along two trench perpendicular transects (MGL0905_23, 25) are associated with ocean bottom seismometer (OBS) deployed in the northern Manila trench. The transect MCS data and tomographic velocity structure provide well constraint on the recognition between the crust and mantle lithosphere that helps to reconstruct synthetic density structure to fit the observation gravity data. The synthetic gravity result along two transects also show that there exists an anomalous high density (~2.97 g/cm3) mass beneath the accretionary prism in the leading edge of overriding plate; however, unfortunately, the MCS and OBS data have no resolution there. Meanwhile, the buoyancies of crust (Hc) and mantle lithosphere (Hm) can be calculated associated with the residual topography based on the isostatic equilibrium. According to the contribution of Hm, the estimation of the plate coupling effect can be approached. Combining two transects data across the northern Manila trench and one profile across the Hengchun Peninsula in southern Taiwan (T29-33, TAICRUST project), a sequence from subduction to collision of plate coupling effect can therefore be evaluated, and also offers the opportunity to examine the lithospheric structure variation in the zone between Taiwan and northernmost Manila trench.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Slip distributions of great and large earthquakes since 1963 along the northern Japan and Kuril trenches are examined to study the recurrence of interplate, intraslab and outer-rise earthquakes. The main findings are that the large earthquakes in 1991 and 1995 reruptured the 1963 great Urup earthquake source, and the 2006, 2007 and 2009 Simshir earthquakes were all different types. We also identify three seismic gaps. The northern Japan to southern Kurile trenches have been regarded as a typical subduction zone with spatially and temporally regular recurrence of great (M>8) interplate earthquakes. The source regions were grouped into six segments by Utsu (1972; 1984). The Headquarters for Earthquake Research Promotion of the Japanese government (2004) divided the southern Kurile subduction zone into four regions and evaluated future probabilities of great interplate earthquakes. Besides great interplate events, however, many large (M>7) interplate, intraslab, outer-rise and tsunami earthquakes have also occurred in this region. Harada, Ishibashi, and Satake (2010, 2011) depicted the space-time pattern of M>7 earthquakes along the northern Japan to Kuril trench, based on the relocated mainshock-aftershock distributions of all types of earthquakes occurred since 1913. The space-time pattern is more complex than that had been considered conventionally. Each region has been ruptured by a M8-class interplate earthquake or by multiple M7-class events. In this study, in order to examine more detail space pattern, or rupture areas, of M>7 earthquakes since 1963 (WWSSN waveform data have been available since this year), we estimated cosiesmic slip distributions by the Kikuchi and Kanamori's (2003) teleseismic body wave inversion method. The WWSSN waveform data were used for earthquakes before 1990, and digital teleseismic waveform data compiled by the IRIS were used for events after 1990. Main-shock hypocenters that had been relocated by our previous study were used as

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

    PubMed

    Peacock; Wang

    1999-10-29

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

  15. Detection of earthquake swarms in subduction zones around Japan

    NASA Astrophysics Data System (ADS)

    Nishikawa, T.; Ide, S.

    2015-12-01

    Earthquake swarms in subduction zones are likely to be related with slow slip events (SSEs) and locking on the plate interface. In the Boso-Oki region in central Japan, swarms repeatedly occur accompanying SSEs (e.g, Hirose et al., 2012). It is pointed out that ruptures of great earthquakes tend to terminate in regions with recurring swarm activity because of reduced and heterogeneous locking there (Holtkamp and Brudzinsiki, 2014). Given these observations, we may be able to infer aseismic slips and spatial variations in locking on the plate interface by investigating swarm activity in subduction zones. It is known that swarms do not follow Omori's law and have much higher seismicity rates than predicted by the ETAS model (e.g., Llenos et al., 2009). Here, we devised a statistical method to detect unexpectedly frequent earthquakes using the space-time ETAS model (Zhuang et al., 2002). We applied this method to subduction zones around Japan (Tohoku, Ibaraki-Boso-oki, Hokkaido, Izu, Tonankai, Nankai, and Kyushu) and detected swarms in JMA catalog (M ≥ 3) from 2001 to 2010. We detected recurring swarm activities as expected in the Boso-Oki region and also in the Ibaraki-Oki region (see Figures), where intensive foreshock activity was found by Maeda and Hirose (2011). In Tohoku, regions with intensive foreshock activity also appear to roughly correspond to regions with recurring swarm activity. Given that both foreshocks and swarms are triggered by SSEs (e.g., Bouchon et al., 2013), these results suggest that the regions with foreshock activity and swarm activity such as the Ibaraki-Oki region are characterized by extensive occurrences of SSEs just like the Boso-Oki region. Besides Ibaraki-Oki and Boso-Oki, we detected many swarms in Tohoku, Hokkaido, Izu, and Kyushu. On the other hand, swarms are rare in the rupture areas of the 1944 Tonankai and 1946 Nankai earthquakes. These variations in swarm activity may reflect variations in SSE activity among subduction zones

  16. On the evolution of Subduction-Transform Edge Propagators (STEPs): application to the Pliny-Strabo 'trenches'

    NASA Astrophysics Data System (ADS)

    Nijholt, Nicolai; Govers, Rob

    2015-04-01

    At the eastern side of the Aegean slab, tomographic evidence shows that a slab edge is present. The subducting African plate needs to tear to permit continued subduction and rollback of the Hellenic trench. This vertical tear is named a Subduction-Transform Edge Propagator (STEP) and is defined as the region of active tearing. At the eastern side of the Hellenic trench, the active STEP is probably located along the Ptolemy 'trench'. The surface expression (deformation zone) of this propagating STEP is observed in bathymetry and seismology, where the Pliny-Strabo 'trenches' are referred to as the STEP fault zone, i.e. the deformation zone in the wake of the active STEP. Due to its immaturity, the plate boundary is a relatively wide zone as strain has not localized yet. A key question is the propagation direction of an active STEP. It is suspected that passive margins may play a critical role in steering a STEP as they represents first order strength contrasts between oceanic and continental lithosphere. Here, we seek to identify the preferred propagation direction for a STEP and also investigate the effect of passive margins on STEP propagation (direction) through mechanical, finite element models. Our model results show that propagation of a STEP along a passive margin-ocean interface is likely for a range of models which show a passive margin-trench orientation within 15 degrees from a perpendicular setup. Passive margins are rarely straight features and with the inclusion of a change in strike of the passive margin ahead of the active STEP, model results show that propagation will occur along the passive margin-ocean interface if this change is less than 25 degrees from a perpendicular setup. Surprisingly, the subduction history and magnitude of the strength(/effective viscosity) contrast across the passive margin are less relevant. The STEP system seems relatively insensitive to small scale details, e.g. so that small, gradual changes in passive margin

  17. Seismic structure related to the Philippine Sea plate subduction beneath the southwestern Nansei-Shoto (Ryukyu) Trench

    NASA Astrophysics Data System (ADS)

    Nishizawa, A.; Kaneda, K.; Oikawa, M.; Horiuchi, D.; Fujioka, Y.

    2013-12-01

    The northwestern part of the Philippine Sea plate (PSP) is subducting beneath the Nansei-Shoto (Ryukyu) Trench. Earthquakes larger than M8 have not been recorded instrumentally in the southwestern part of the Ryukyu Trench. However, there was a large tsunami killed around 12,000 people in 1771 and the position of the source area has not been established. The direction of the PSP subduction is almost perpendicular to the Ryukyu Trench to the northeast of 126.5 E and changes to oblique to the southwest. Seismicity varies along the trench axis and lower seismicity seems to correspond to the free-air gravity anomaly high region in the forearc at around 126 E. On the other hand, the Okinawa-Luzon fracture zone extending from southwest to northeast on the PSP subducts beneath Ryukyu Trench to the northeast of 126 E and seems to relate to the high gravity anomaly. We carried out seismic experiments to elucidate these inhomogeneous crustal structures along the southwestern part of the trench and provide valuable information on potential source areas for large earthquakes and/or tsunamis. We conducted five seismic lines across southwestern Ryukyu Trench region. Multichannel reflection seismic (MCS) data using 240 ch. and 3000 m long hydrophone streamer were collected for airgun shots at an interval of 50 m. We also deployed ocean bottom seismographs (OBSs) as a receiver at an average interval of 5 km along each line. A tri-gun cluster with a volume of 1,050 (350 * 3) cubic inches (17.2 liters) was used for the reflection surveys and a non-tuned airgun array with a volume of 6,000 (1500 * 4) cubic inches (98 liters) was shot at an interval of 200 m (90 sec) for the wide-angle seismic survey. Depth conversion from the MCS time section was carried out using the refraction results. In this paper, we present the seismic structure related to the PSP subduction in the forearc region of the Nansei-Shoto island arc. The subducting Okinawa-Luzon fracture zone was able to be clearly

  18. Estimation of seismic velocity in the subducting crust of the Pacific slab beneath Hokkaido, northern Japan by using guided waves

    NASA Astrophysics Data System (ADS)

    Shiina, T.; Nakajima, J.; Toyokuni, G.; Kita, S.; Matsuzawa, T.

    2014-12-01

    A subducting crust contains a large amount of water as a form of hydrous minerals (e.g., Hacker et al., 2003), and the crust plays important roles for water transportation and seismogenesis in subduction zones at intermediate depths (e.g., Kirby et al., 1996; Iwamori, 2007). Therefore, the investigation of seismic structure in the crust is important to understand ongoing physical processes with subduction of oceanic lithosphere. A guided wave which propagates in the subducting crust is recorded in seismograms at Hokkaido, northern Japan (Shiina et al., 2014). Here, we estimated P- and S-wave velocity in the crust with guided waves, and obtained P-wave velocity of 6.6-7.3 km/s and S-wave velocity of 3.6-4.2 km/s at depths of 50-90 km. Moreover, Vp/Vs ratio in the crust is calculated to be 1.80-1.85 in that depth range. The obtained P-wave velocity about 6.6km/s at depths of 50-70 km is consistent with those estimated in Tohoku, northeast Japan (Shiina et al., 2013), and this the P-wave velocity is lower than those expected from models of subducting crustal compositions, such as metamorphosed MORB model (Hacker et al., 2003). In contrast, at greater depths (>80 km), the P-wave velocity marks higher velocity than the case of NE Japan and the velocity is roughly comparable to those of the MORB model. The obtained S-wave velocity distribution also shows characteristics similar to P waves. This regional variation may be caused by a small variation in thermal regime of the Pacific slab beneath the two regions as a result of the normal subduction in Tohoku and oblique subduction in Hokkaido. In addition, the effect of seismic anisotropy in the subducting crust would not be ruled out because rays used in the analysis in Hokkaido propagate mostly in the trench-parallel direction, while those in Tohoku are sufficiently criss-crossed.

  19. GPS/Acoustic Observations Along the Japan Trench for Postseismic Deformation After the 2011 Tohoku-Oki Earthquake

    NASA Astrophysics Data System (ADS)

    Kido, M.; Tomita, F.; Osada, Y.; Fujimoto, H.; Hino, R.; Ohta, Y.; Iinuma, T.; Azuma, R.; Wada, I.

    2014-12-01

    After the 2011 Tohoku-Oki Earthquake, we realized that the interplate coupling can be extended to the trench even for subducting slab of great age. Monitoring the recovering process of the coupling after the earthquake may provide important knowledge on the total perspective of this great earthquake. For this purpose, Japanese government decided to strengthen the monitoring systems by means of seafloor geodesy. Constructing a GPS/Acoustic network along the trench is one of these projects. Before the earthquake, only five (Japan Coast Guard) and three (Tohoku Univ.) benchmarks were working off-Tohoku area, however, in 2012, we have newly installed up to 20 benchmarks along the trench, especially close to the trench. We took place GPS/Acoustic surveys after the installation and have carried out four times of campaign surveys until 2013 (FY). Not all the benchmarks were measured in each campaign, however, three times of campaigns were made for most of the benchmarks ranging 1 or 1.5 years. Because of such a short period of data accumulation and hard conditions on the accuracy due to great depth (>5000 m) than before, the estimated errors in the obtained displacement vectors are typically 5-10 cm for most of the benchmarks, which are not enough to clearly address the postseismic deformation. Nevertheless, some benchmarks, one is at relatively close to the coast and the other is on the incoming Pacific plate off-Miyagi, show significant WNW-ward movements up to 17 cm/yr, which is much larger than interseismic subducting rate. This gives a strong constraint to evaluate the viscoelastic relaxation process after the earthquake. More campaign surveys are planned in the next year to accumulate the data for improvement of the total accuracy in the displacement vectors for all the benchmarks. In addition, we are dedicated in improving the analytic technique to reduce error sources, such as acoustic signal processing and sound speed correction to lessen the uncertainty in each

  20. Variations of short-term slow slip events along the Nankai Trough to the Ryukyu Trench, southwest Japan

    NASA Astrophysics Data System (ADS)

    Nishimura, T.

    2013-12-01

    ETSs (Episodic Tremor and Slips) occur at a depth of 30-40 km on the plate interface of the subducting Philippine Sea plate along the Nankai trough, southwest Japan (e.g., Obara, 2010). Low-frequency tremors along the Nankai Trough suddenly disappeared southwest of the Bungo Channel between Shikoku and Kyushu, which is a junction between the southwest Honshu arc along the Nankai Trough and the Ryukyu arc along the Ryukyu Trench. Any short-term SSEs (slow slip events) have never been reported southwest of the Bungo Chanel, though Mw~7 long-term SSEs repeated in the Bungo Channel every ~6 years (e.g., Ozawa et al., 2013). Here, we apply a SSE detection method using continuous GNSS data (Nishimura et al., 2013) to find out SSEs in a region along the Nankai Trough to the Ryukyu Trench. We also compare the detected SSEs with epicenters of low-frequency tremors, very-low-frequency earthquakes (VLFEs), and regular earthquakes and discuss along-trench variations on short-term SSE characteristics. Daily coordinates of ~800 GEONET GNSS stations in southwest Japan were used to detect displacements caused by short-term SSEs. We divided a whole region into three regions for spatial filtering to reduce a noise of GNSS data. We fitted a step function with a linear trend to spatial-filtered daily coordinates to detect significant displacements in a direction opposite to the relative plate motion between the Philippine Sea plate and southwest Japan. If Akaike's information criterion expressing data fits exceeds a threshold, three-dimensional displacements were inverted to estimate a rectangular fault along the plate interface. We found more than 200 probable short-term SSEs in the region over 16 years. In western Shikoku, we detected 49 Mw ~6.0 ETSs. SSEs with a similar magnitude are found at the same depth range in northeast Kyushu without tremors although the number of detected SSEs is only 10. In the further southwest region, we found several shallow SSEs at a depth of 10-40 km

  1. Paleoseismic evidence of earthquakes and tsunamis along the southern part of the Japan Trench

    NASA Astrophysics Data System (ADS)

    Pilarczyk, Jessica; Sawai, Yuki; Horton, Ben; Namegaya, Yuichi; Shinozaki, Tetsuya; Tanigawa, Koichiro; Matsumoto, Dan; Dura, Tina; Fujiwara, Osamu; Shishikura, Masanobu

    2016-04-01

    The northern part of the Japan Trench has frequently generated tsunamigenic-earthquakes with magnitudes up to ~M 8.0. In contrast, the middle and southern parts of the Japan Trench were considered relatively inactive until the 2011 Tohoku (M 9.0) event generated one of the largest tsunamis in recorded history. Geologic evidence from the Sendai plain revealed an event in CE 869 that could have forecast the severity of the Tohoku tsunami in 2011. Seismic models indicate that the Tohoku earthquake may have transferred stress southwards down the fault to the potentially locked southern part of the Japan Trench. This transfer of stress towards a locked section of the trench could produce an earthquake in the near future that would be comparable in magnitude to the Tohoku event. Reconstructing the history of individual great earthquakes and accompanying tsunamis using geological records from the coastal zone adjacent to the southern part of the Japan Trench provides an assessment of the seismic hazard for metropolitan areas in east-central Japan. We have found two anomalous marine sand layers intercalated with muddy peat, which can be traced 3.8 km inland and 5.5 km along the present Kujukuri coastline, approximately 50 km east of Tokyo. Both sand layers have features consistent with tsunami deposits, such as a distinct erosional base, rip-up clasts, normal grading, a mud drape, and marine foraminifera. Results of radiocarbon dating constrain the age of the upper sand to 337 - 299 cal. yrs. BP, which likely corresponds to the only known southern Japan Trench rupture ever recorded, the Empo tsunami of CE 1677. The age of the lower sand is 979 - 903 cal. yrs. BP; marking an event for which there is no historical documentation at present. Preliminary tsunami simulation models indicate that a middle trench (Tohoku-style) rupture is not responsible for significant inundation of the Kujukuri coastline and would likely not have been capable of depositing either sand layer

  2. Effects of Two Subducting Slabs on the Temperature Distribution Along the Subduction Faults in the Kanto Region, Japan

    NASA Astrophysics Data System (ADS)

    Wada, I.; He, J.

    2015-12-01

    In this study, we investigate the thermal effects of subduction of two oceanic plates in the Kanto region of Japan, using a 3-D numerical thermal model. The Kanto region lies in the forearc of a subduction system, where the Pacific (PAC) plate and the Philippine Sea (PHS) plate subduct beneath the North American (NA) plate. In a typical subduction setting with one subducting slab, the motion of the slab drives solid-state mantle flow in the overlying mantle wedge, and the flow brings in hot mantle from the backarc towards the forearc. In the Kanto region, however, the presence of the PHS plate between the overlying NA plate and the subducting PAC plate prevents a typical mantle flow pattern. We developed a 3-D thermal model for the Kanto region to simulate the pattern of mantle wedge flow and to quantify its effect on the thermal structure. The model incorporates realistic slab geometries that were delineated from seismological studies. Mantle wedge flow between the PHS slab and the overlying NA plate is expected to be subdued due to the small space and the relatively slow subduction of the PHS slab. We simplify the model by incorporating the results of a 2-D thermal modeling for the subduction of the PHS slab as part of boundary conditions in the 3-D model to approximate the effect of the subdued mantle wedge flow and the subduction of the PHS slab. We use geophysical observations as constraints for the 3-D thermal model and estimate the temperature distributions along the subduction plate interfaces. The model predicts a particularly cold condition in the central part of the Kanto region where the PAC and PHS slabs are in contact with one another, consistent with the observed deeper extent of seismicity along the subduction faults compared to the neighboring regions.

  3. Revisit of basal effective friction and pore pressure for Japan trench from topographic point of view

    NASA Astrophysics Data System (ADS)

    Koge, H.; Fujiwara, T.; Kodaira, S.; Sasaki, T.; Kameda, J.; Hamahashi, M.; Hamada, Y.; Kimura, G.

    2013-12-01

    2011 Tohoku-oki earthquake (Mw9.0) produced a fault rupture, extending to the shallow part of the Japan Trench. Based on the bathymetry difference before and after the earthquake, it is demonstrated that the seafloor on outermost landward slope moved ~50 m east-southeastward towards the trench and uplifted ~7 to 10 m. Although the mechanism of the fault rupture is not clear, deformation and frictional properties beneath the forearc are the key to elucidate this important issue. Kimura et al (2012) focused on seismic reflection data along one seismic transect at the Japan Trench (name the transect), and calculated the basal effective friction of the plate boundary by using the critical taper theory. Limited profiles from narrow area, however, never represent general friction property of the plate boundary in the Japan trench. Therefore, several profiles are examined to investigate for the better understanding along-trench variation of the basal frictional properties. Bathymetric and seismic reflection data were taken before and after the Tohoku-oki earthquake to obtain the following angles; slope angle of upper surface, basal dip of the outer wedge. Acuired angles are limited to only the lowest trench slope of the Japan Trench. The limitation enables us to treat the wedge as a more uniform body than would have been achieved with the whole range of seismic cross sections. Applying the critical taper theory to the individual seismic cross sections, force balance among the interior and base of the wedge, fluid pressure ratio, and the basal effective friction of the plate boundary are calculated. Additionally, by using "earth pressure theory", we estimated basal effective friction of ~0.15 under the assumption that branching faults act as back-stops in lower slope areas. References Cubas et al., Geophysical Research Letters: DOI:10.1002/grl.50682 Fujiwara et al., Science 2 December 2011: Vol. 334 no. 6060 p. 1240 Wang and Hu, Journal of Geophysical Research, v.111, p1

  4. Fault plane orientations of intermediate-depth and deep-focus earthquakes in the Japan-Kuril-Kamchatka subduction zone

    NASA Astrophysics Data System (ADS)

    Warren, Linda M.; Baluyut, Elena C.; Osburg, Timothy; Lisac, Kristen; Kokkinen, Siiri

    2015-12-01

    In the northwestern Pacific, the Pacific plate subducts to the west at the Japan, Kuril, and Kamchatka trenches. Throughout most of the subduction zone, the subducting slab is planar and dipping at an angle of 30°-60°, with the exception of a fold in the southern Kuril segment. To investigate how the slab deforms in response to the applied forces and which mechanism generates the earthquakes, we analyze the rupture properties of 111 large (MW≥5.7) intermediate-depth and deep-focus earthquakes (60-656 km depth) from 1990 to 2014 in the Japan-Kuril-Kamchatka subduction zone. For each earthquake, we use rupture directivity to estimate rupture direction and rupture speed and to distinguish the fault plane from the auxiliary plane of the focal mechanism. Seventy six percent of the earthquakes with sufficient station coverage are well modeled by unilateral rupture propagation. The estimated rupture speeds range from zero to supershear. The estimated rupture directions allow identification of the fault plane as the more horizontal nodal plane for 30 earthquakes, while an additional 11 earthquakes rupture toward the intersection of the nodal planes, so the fault plane cannot be identified. Combining our newly identified fault planes with previously identified fault planes in the region, we observe that in planar slab segments, most earthquakes slip along a dominant fault orientation. For a steeply dipping slab, this orientation is subhorizontal. In more sharply bent slab segments, such as the Kuril fold, deformation is accommodated along more variable fault orientations, including subvertical faults. The correlation of slab geometry with fault orientation suggests that the local stress field controls fault orientations.

  5. Tectonic implications of Early Miocene OIB magmatism in a near-trench setting: The Outer Zone of SW Japan and the northernmost Ryukyu Islands

    NASA Astrophysics Data System (ADS)

    Kiminami, Kazuo; Imaoka, Teruyoshi; Ogura, Kazuki; Kawabata, Hiroshi; Ishizuka, Hideo; Mori, Yasushi

    2017-03-01

    The Outer Zone of the SW Japan and northernmost Ryukyu arcs was affected by intense igneous activity during the Miocene, characterized by MORB-like basalts, alkaline basalts, and S-type (with subordinate I-type) felsic to intermediate volcano-plutonic complexes. These igneous rocks are inferred to be the products of near-trench magmatism. Early Miocene (∼18 Ma) alkaline basalt dikes from the Shingu-Otoyo area in central northern Shikoku, and an alkaline lamprophyre dike from Tanegashima, one of the northernmost Ryukyu Islands, pre-date the Middle Miocene felsic to intermediate igneous rocks. The basalts and lamprophyre have compositions of basanite, basalt, trachybasalt and phonotephrite. They are characterized by elevated large-ion lithophile elements (LILEs; e.g., Sr, Ba, and Th) and high concentrations of high-field strength elements (HFSEs; e.g., TiO2, Nb, and Zr). The geochemical signatures of the basalts and lamprophyre suggest an ocean island basalt-type (OIB-type) mantle source. The occurrence of alkaline basalts and lamprophyre with OIB-type, intraplate geochemical signatures in a near-trench setting is unusual with regard to plate tectonic processes. We propose that trench-ward motion of the overriding plate during the period around the Early Miocene resulted in a shallowly dipping slab, and interplate coupling between the subducting Philippine Sea Plate (PSP) and the overlying crust beneath most of the Outer Zone in the western part of SW Japan and the northernmost Ryukyu Islands. The OIB-type magmatism in the near-trench environment is most plausibly explained by the upwelling of asthenospheric material from beneath the subducting slab, which migrated through fractures and/or tears in the slab. We envisage two possible scenarios for the formation of these fractures or tears: (1) the shallowing dip angle of the subducted PSP resulted in concave-upwards flexure of the slab, generating fractures in the flexed region; and (2) differential motion within

  6. Depth Limits of Slow Slip Events at the Japan Trench: Insights from Friction Experiments under In-Situ Conditions

    NASA Astrophysics Data System (ADS)

    Sawai, M.; Niemeijer, A. R.; Hirose, T.; Spiers, C. J.

    2014-12-01

    Episodic tremor and slip occurred just before the 2011 Tohoku-oki earthquake on a shallow portion (less than 20 km depth) in the Tohoku subduction zone (Ito et al., 2013). The area where slow slip occurred overlapped with the seismogenic zone. To understand such diverse slip behaviour around the Japan Trench, not only the major earthquakes but also the slow slip events, it is essential to reveal the frictional properties of rocks distributed at the Tohoku subduction zone. We thus conducted friction experiments using a rotary shear apparatus on smectite-rich pelagic sediments retrieved from the plate-boundary thrust during IODP Expedition 343. The sediments were disaggregated and simulated gouges were then sheared at temperatures of 20-200oC, an effective normal stress of 50 MPa and a pore fluid pressure of 50 MPa. We conducted velocity-stepping sequences (0.3 to 100 μm/s) to determine the rate and state parameter (a-b) and investigated the effects of temperature and slip rate on slip stability.Our results show that at low temperatures of 20 and 50oC, the simulated gouges exhibit negative values of (a-b) with a background friction coefficient of 0.38, except at the highest slip rate of 0.1 mm/s. However, the gouges show neutral to positive values of (a-b) at temperatures of >100oC with the same background friction coefficient as at lower temperatures. In addition, the value of parameter (a-b) depends significantly on slip rates: at temperatures of 20 and 50oC it increases from negative to neutral (or slightly positive at 20oC) with increasing slip rates to 0.1 mm/s, whereas it tends to decrease with increasing slip rate at temperatures higher than 100oC. The downdip temperature limit of the slow slip events at Japan Trench (Ito et al., 2013) seems to be in the range between 100 to 150oC. The transition in (a-b) value from neutral to positive, particularly at lower slip rates, occurs at the same temperature range. Hence, this could correspond to the observed downdip

  7. The middle america trench as an example of a subduction zone

    NASA Astrophysics Data System (ADS)

    Aubouin, Jean; Stephan, Jean-François; Roump, Jacqueline; Renard, Vincent

    1982-06-01

    Short Sea-Beam survey cruises were conducted by the R.V. "Jean Charcot" in march 1980 along the Middle America Trench between Panama and Acapulco, with particular emphasis on the IPOD Legs 66 and 67 areas. These detailed mappings have revealed that the Cocos horst- and graben pattern, related to the bending of the oceanic plate, strikes generally 20°-30° oblique to the trench direction. This en-échelon pattern, closely parallel to the magnetic anomalies, is here proposed as being due to the reactivation of inherited fractures generated at the East Pacific Rise. Sea-Beam data, together with UTMSI multichannel seismic reflection profiles and IPOD drilling results, clearly show that at least two distinct geodynamic processes are presently working along the same trench: accretion and no accretion. They also show a relative structural homogeneity of the oceanic side of the trench in contrast to the dual aspect of the continental side.

  8. Sediment Accretion During Horst and Graben Subduction associated with the Tohoku Oki M9 Earthquake, Northern Japan

    NASA Astrophysics Data System (ADS)

    Moore, J. C.; Chester, F. M.

    2015-12-01

    The stratigraphic sequence within the frontal accretionary prism of the Japan Trench, the site of large slip during the Tohoku earthquake, is unique due to horst and graben subduction. Boreholes at IODP Site C0019, penetrating the toe of the Tohoku accretionary prism, document a younger over older intraprism thrust contact with a 9 Ma age gap across the basal plate boundary fault. The anomalously young (Quaternary to Pliocene), fault-bounded sediment package is 130 m thick, of a total of 820 m of sediment above the plate boundary fault. In contrast, typical accretionary prism structure consists of stacked sediment packages on imbricate faults above the basal decollement resulting in an overall increase in age downward. Site C0019 penetrates the prism directly above a horst of the subducting Pacific oceanic crust. Here the plate-boundary fault consists of a thin, weak smectitic pelagic clay that is probably the principal slip surface of ~50 m offset in the 2011 Tohoku earthquake. The fault continues seaward deepening off the seaward edge of the horst and beneath the sediment fill of the adjacent graben, dying out at the landward base of the next incoming horst. The plate boundary fault and its splays in the graben form a narrow-taper protoprism and a small sedimentary basin of trench fill marking the seaward edge of the upper plate. The modern fault and sediment distributions within the graben are used to motivate a viable model for the presence of anomalously young sediments directly above the plate boundary fault. In this model sediments in the trench are thrust over the incoming horst by propagation of the plate boundary thrust up the landward-dipping fault of the incoming horst and along the smectitic clay layer to emplace Quaternary and Pliocene trench deposits directly on top of the incoming horst. These young deposits are in turn overlain by sediments 9 Ma or older that have been transported out of the graben along imbricate faults associated with the

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

    NASA Astrophysics Data System (ADS)

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

    2007-05-01

    Offshore of the Nicoya Gulf at the Middle America Trench, the Cocos Plate is subducting beneath the Caribbean plate at about 84 mm per year. A line of seamounts are entering the trench in this region, causing dramatic deformation of the seafloor landward of the thrust. It has been suggested that these seamounts are being subducted, causing coastal uplift and seismicity. The March 25, 1990 Mw 7.0 Nicoya Gulf earthquake is thought to have occurred as one of these seamounts ruptured. How do these seamounts affect the rupture process? Are they behaving as patches of increased or decreased friction along the seismic interface? How does the subducting topography change the stress field after an earthquake? Can triggered events be explained by static stress changes, or does the rheology down dip from the seismogenic zone influence subsequent events in the region? Using a three dimensional model with patches of variable friction to simulate the seamounts as asperities, we compare the location of aftershocks to the stress changes associated with increased and decreased friction. We compare this to a model of Coulomb static stress change, which displays lobes of static stress increase and decrease due to slip on the fault plane, and the distribution of aftershocks within these lobes. To examine the stress changes associated with a set of delayed inland triggered events, we also vary the rheology of our model, using a linear elastic half space for the seismogenic zone, and viscous creep along the lower, aseismic portion of the fault below 40 kilometers. These models allow us to examine the spatial and temporal relationship of seismicity associated with stress changes due to variable friction and rheology. Our results indicate that stresses increase away from the fault with time if viscous creep is included in the model. These stress increases roughly correspond to inland areas of noted increase in seismicity, suggesting that creep along the down dip, aseismic portion of the

  10. Centrifuge modeling of initial subduction and back-arc extension: suggested tectonics of seawards migration of the Hellenic Trenches

    NASA Astrophysics Data System (ADS)

    Mart, Y.; Aharonov, E.; Mulugeta, G.; Tentler, T.

    2003-04-01

    "brittle continental lithosphere" to be thrust and expand considerably over the "oceanic lithosphere", rifting, and nearly exhuming the "ductile lithosphere" in places. The experiments suggest that in some cases subduction could derive from differential densities between the oceanic and the continental lithospheres, overshadowing the contribution of lateral forces to the subduction process. Furthermore, where friction along the subduction zone is reduced, back-arc basins develop, and the overthrust slab is extended over the sinking oceanic slab, it is rifted and, in places, the ductile continental lithosphere is exhumed. It seems further that the migration of the Hellenic Trenches towards the Ionic Sea, the development of the Aegean Sea as a back-arc basin, and the exhumation of deep segments of the continental crust in the Cyclades are all in overall agreement with this model.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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 we use numerical models in one and two dimensions to evaluate the pore pressure and compaction state of sediments on the subducting Juan de Fuca plate in Cascadia from the trench to the ETS zone. 2-D models allow pressure to diffuse vertically and also laterally normal to strike of the megathrust; 1-D models simulate only vertical diffusion. Model parameters are chosen with reference to two strike-normal profiles: one through central Oregon and one through the Olympic Peninsula of Washington. We examine temporal variations in sediment input to the trench and consider implications for fault strength and permeability as well as the down-dip extent to which compactive dewatering can be considered a significant fluid source. In 1-D, we use a general and fully nonlinear model of sediment compaction derived without making any assumptions regarding stress-strain or porosity-permeability relations and allowing finite strains. In contrast, most previous models of fluid flow in subduction zones have used linear models of diffusion that rely on assumptions of constant sediment permeability and infinitesimal strains for their formulation. Our nonlinear finite-strain model remains valid at greater depths, where stresses and strains are large. Boundary conditions in 1-D are constrained by pore pressure estimates along the megathrust fault that are based on seismic velocities (e.g. Tobin and Saffer, 2010) and data from consolidation tests conducted on sediments gathered during ODP Leg 204 (Tan, 2001). Initial conditions rely on input sediment thickness; while sediment thickness

  12. Direct-path acoustic ranging across the Japan Trench axis, Adjacent to the Large Shallow Thrusting in the 2011 Tohoku-Oki earthquake

    NASA Astrophysics Data System (ADS)

    Osada, Y.; Kido, M.; Ito, Y.; Iinuma, T.; Fujimoto, H.; Hino, R.

    2014-12-01

    Seafloor geodetic data, i.e. GPS/acoustic measurement and continuous seafloor pressure monitoring, brought important evidences showing that the 2011 Tohoku-oki earthquake (Mw 9.0) caused huge (> 50 m) coseismic slip near the Japan Trench. The postseismic behavior of the large slipped area is required to clarify to understand why large amount seismic slip could occur there. We started making direct-path acoustic ranging across the trench axis to reveal the convergence rate between the subducting Pacific and overriding continental plates. We expect the change of the baseline length across the trench axis, the plate boundary, reflects the slip rate at the shallow megathrust, which is difficult to estimate only from other geodetic observations largely affected by intraplate deformation caused by the postseismic viscoelastic relaxation process.  To this end, we developed an ultra-deep seafloor acoustic ranging system. Our previous ranging systems have been designed to measure baseline length ~ 1 km and to be deployed up to 7,000 m water-depth (Osada et al., 2008, 2012). In order to realize the measurement across the Japan Trench, we improved this system to enhance range of acoustic ranging as well as operational depth of instruments. The improved system was designed to allow acoustic ranging up to 3 km and to be durable under the high-pressure equivalent to water depth of 9,000 m. In May 2013, we carried out a test deployment of the new ranging system. The system is composed of three seafloor instruments equipped with precision transponder (PXPs). Two of the PXPs were set on the landward slope of the Japan Trench, where large coseismic slip happened in 2011. Another PXP was deployed on the seaward side of the trench so that the baseline change associated with the slip on the plate boundary fault, if any, can be detected. Continuous records of baseline lengths were successfully obtained for four months. The repeatability of the distance measurements was about 20 mm for

  13. Subduction of a Late Cretaceous Seamount of the Louisville Ridge at the Tonga Trench: A model of normal and accelerated tectonic erosion

    NASA Astrophysics Data System (ADS)

    Ballance, Peter F.; Scholl, David W.; Vallier, Tracy L.; Stevenson, Andrew J.; Ryan, Holly; Herzer, Richard H.

    1989-10-01

    The hotspot-generated Louisville Ridge is a 4000-km chain of seamounts (typically 2-2.5 km high and 10-40 km in diameter) and an underlying crustal swell (1.5 km high and 100+ km wide) trending NNW across the southwestern Pacific. The northwest end of the Ridge collides with the north trending Tonga Trench (26°S) which, just north of that point, is exceptionally deep (10.8 km) and lacks both a turbidite wedge and a bordering accretionary complex. The collision zone is moving rapidly southward. Multichannel seismic reflection data in the collision zone show a west dipping subsurface platform 2-3 km beneath the lower western trench slope, which is interpreted as the flat summit of a subducted guyot, Motuku, of the Louisville chain. Projected eastward, the summit plain passes 1-2 km above the trench floor. Dredging of the nearby inner trench wall recovered uppermost Cretaceous (Maestrichtian) oceanic pelagic sediments interpreted to be fragments of the sedimentary mantle of a subducted Louisville seamount The principal effects of hotspot-ridge collision with a sediment-starved trench are (1) the impacting seamounts are subducted rather than accreted, and (2) although some seamount rocks are temporarily accreted, the inner trench wall is tectonically eroded arcward at rates possibly as high as 50 km/m.y. Accelerated tectonic erosion is related to (1) fracturing, shearing and general weakening of arc substrate rocks as they are lifted by the swell, penetrated by impacting seamounts, and left to collapse as the ridge moves away, (2) a more effective removal of weakened rock in underthrusting grabens which are larger in the crustal swell, (3) a possible elevation of the subduction decollement to account for the removal of as much as 30,000 km³ of material from a 400 km sector of the trench in 1 million years, and (4) a reduction in supply of arc-derived debris resulting from the gap in arc volcanism accompanying subduction of the ridge. "Normal" tectonic erosion in the

  14. Geochemical evidence in the northeast Lau Basin for subduction of the Cook-Austral volcanic chain in the Tonga Trench

    NASA Astrophysics Data System (ADS)

    Price, Allison A.; Jackson, Matthew G.; Blichert-Toft, Janne; Blusztajn, Jerzy; Conatser, Christopher S.; Konter, Jasper G.; Koppers, Anthony A. P.; Kurz, Mark D.

    2016-05-01

    Lau Basin basalts host an array of geochemical signatures that suggest incorporation of enriched mantle source material often associated with intraplate hotspots, but the origin of these signatures remain uncertain. Geochemical signatures associated with mantle material entrained from the nearby Samoan hotspot are present in northwest Lau Basin lavas, and subducted seamounts from the Louisville hotspot track may contribute geochemical signatures to the Tonga Arc. However, lavas in the northeast Lau Basin (NELB) have unique enriched geochemical signatures that cannot be related to these hotspots, but can be attributed to the subduction of seamounts associated with the Cook-Austral volcanic lineament. Here we present geochemical data on a new suite of NELB lavas—ranging in 40Ar/39Ar age from 1.3 Ma to 0.365 ka—that have extreme signatures of geochemical enrichment, including lavas with the highest 206Pb/204Pb (19.580) and among the lowest 143Nd/144Nd (0.512697) encountered in the Lau Basin to date. These signatures are linked to the canonical EM1 (enriched mantle 1) and HIMU (high-μ = 238U/204Pb) mantle end-members, respectively. Using a plate reconstruction model, we show that older portions of the traces of two of the Cook-Austral hotspots that contributed volcanism to the Cook-Austral volcanic lineament—the Rarotonga and Rurutu hotspots—were potentially subducted in the Tonga Trench beneath the NELB. The geochemical signatures of the Rarotonga, Rurutu, and Samoan hotspots provide a compelling match to the extreme geochemical components observed in the new NELB lavas.

  15. Major Existence of Very Low Frequency Earthquakes in Background Seismicity Along Subduction Zone of South-western Japan

    NASA Astrophysics Data System (ADS)

    Ishihara, Y.

    2003-12-01

    The condense, high quality and equalized broadband seismic network provided us to recognize the variety of seismic sources. The active volcanoes excite seismic waves with various frequency characteristics. Some cases show the long period seismic waves greater than 10 sec associates with volcanic activities. The tectonic seismic events originated at the close to trench zone are frequently lack of high frequency, greater than 1 Hz, seismic wave component. Meanwhile, the many low frequency earthquakes and tremors whose sources are not explicated are occurred in lower crust and subcrustal region. The subduction zone of Philippine Sea plate in south-western Japan is actively genetic area of low frequency earthquake group. The broadband seismic array of Japan region observed unknown long period ground motions. The seismograms are higher amplitude between 10 and 30 sec period than ground noise level. The earthquake JMA and USGS catalogues don_ft list about these long period seismograms. The arrival order of wave packet means that these events locate subduction zone around Japan. The hypocenters of unknown events are estimated by arrival times of vertical peak amplitude using the assumption that the ground motion dominates Rayleigh wave. The more detailed determination of major events is performed by combined technique for moment tensor inversion and grid search. The moment magnitude of uncatalogued event is greater than 3.5 because of the detection limitation. The largest event is distributed to about 4.5 Mw level and special event is greater than 5.0. The frequency characteristics show that source time is 7 to 20 sec by comparison with synthetic seismograms. We call these uncatalogued events _gvery low frequency earthquake_h. The hypocenters are located to two kinds of zones along the Philippine Sea subducting plate in south-western Japan. The one zone is very close to the trough. The seismicity listed by earthquake catalogues is low level in the zone and hypocenters are

  16. Anaerobic methanotrophic community of a 5346-m-deep vesicomyid clam colony in the Japan Trench.

    PubMed

    Felden, J; Ruff, S E; Ertefai, T; Inagaki, F; Hinrichs, K-U; Wenzhöfer, F

    2014-05-01

    Vesicomyidae clams harbor sulfide-oxidizing endosymbionts and are typical members of cold seep communities where active venting of fluids and gases takes place. We investigated the central biogeochemical processes that supported a vesicomyid clam colony as part of a locally restricted seep community in the Japan Trench at 5346 m water depth, one of the deepest seep settings studied to date. An integrated approach of biogeochemical and molecular ecological techniques was used combining in situ and ex situ measurements. In sediment of the clam colony, low sulfate reduction rates (maximum 128 nmol mL(-1) day(-1)) were coupled to the anaerobic oxidation of methane. They were observed over a depth range of 15 cm, caused by active transport of sulfate due to bioturbation of the vesicomyid clams. A distinct separation between the seep and the surrounding seafloor was shown by steep horizontal geochemical gradients and pronounced microbial community shifts. The sediment below the clam colony was dominated by anaerobic methanotrophic archaea (ANME-2c) and sulfate-reducing Desulfobulbaceae (SEEP-SRB-3, SEEP-SRB-4). Aerobic methanotrophic bacteria were not detected in the sediment, and the oxidation of sulfide seemed to be carried out chemolithoautotrophically by Sulfurovum species. Thus, major redox processes were mediated by distinct subgroups of seep-related microorganisms that might have been selected by this specific abyssal seep environment. Fluid flow and microbial activity were low but sufficient to support the clam community over decades and to build up high biomasses. Hence, the clams and their microbial communities adapted successfully to a low-energy regime and may represent widespread chemosynthetic communities in the Japan Trench. In this regard, they contributed to the restricted deep-sea trench biodiversity as well as to the organic carbon availability, also for non-seep organisms, in such oligotrophic benthic environment of the dark deep ocean.

  17. Anaerobic methanotrophic community of a 5346-m-deep vesicomyid clam colony in the Japan Trench

    PubMed Central

    Felden, J; Ruff, S E; Ertefai, T; Inagaki, F; Hinrichs, K-U; Wenzhöfer, F

    2014-01-01

    Vesicomyidae clams harbor sulfide-oxidizing endosymbionts and are typical members of cold seep communities where active venting of fluids and gases takes place. We investigated the central biogeochemical processes that supported a vesicomyid clam colony as part of a locally restricted seep community in the Japan Trench at 5346 m water depth, one of the deepest seep settings studied to date. An integrated approach of biogeochemical and molecular ecological techniques was used combining in situ and ex situ measurements. In sediment of the clam colony, low sulfate reduction rates (maximum 128 nmol mL−1 day−1) were coupled to the anaerobic oxidation of methane. They were observed over a depth range of 15 cm, caused by active transport of sulfate due to bioturbation of the vesicomyid clams. A distinct separation between the seep and the surrounding seafloor was shown by steep horizontal geochemical gradients and pronounced microbial community shifts. The sediment below the clam colony was dominated by anaerobic methanotrophic archaea (ANME-2c) and sulfate-reducing Desulfobulbaceae (SEEP-SRB-3, SEEP-SRB-4). Aerobic methanotrophic bacteria were not detected in the sediment, and the oxidation of sulfide seemed to be carried out chemolithoautotrophically by Sulfurovum species. Thus, major redox processes were mediated by distinct subgroups of seep-related microorganisms that might have been selected by this specific abyssal seep environment. Fluid flow and microbial activity were low but sufficient to support the clam community over decades and to build up high biomasses. Hence, the clams and their microbial communities adapted successfully to a low-energy regime and may represent widespread chemosynthetic communities in the Japan Trench. In this regard, they contributed to the restricted deep-sea trench biodiversity as well as to the organic carbon availability, also for non-seep organisms, in such oligotrophic benthic environment of the dark deep ocean. PMID

  18. Seismological detection of low-velocity anomalies surrounding the mantle transition zone in Japan subduction zone

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Park, Jeffrey; Karato, Shun-ichiro

    2016-03-01

    In the Japan subduction zone, a locally depressed 660 discontinuity has been observed beneath northeast Asia, suggesting downwelling of materials from the mantle transition zone (MTZ). Vertical transport of water-rich MTZ materials across the major mineral phase changes could lead to water release and to partial melting in surrounding mantle regions, causing seismic low-velocity anomalies. Melt layers implied by low-velocity zones (LVZs) above the 410 discontinuity have been detected in many regions, but seismic evidence for partial melting below the 660 discontinuity has been limited. High-frequency migrated Ps receiver functions indicate LVZs below the depressed 660 discontinuity and above the 410 discontinuity in the deep Japan subduction zone, suggesting dehydration melting induced by water transport out of the MTZ. Our results provide insights into water circulation associated with dynamic interactions between the subducted slab and surrounding mantle.

  19. Variable Holocene deformation above a shallow subduction zone extremely close to the trench

    NASA Astrophysics Data System (ADS)

    Thirumalai, Kaustubh; Taylor, Frederick W.; Shen, Chuan-Chou; Lavier, Luc L.; Frohlich, Cliff; Wallace, Laura M.; Wu, Chung-Che; Sun, Hailong; Papabatu, Alison K.

    2015-06-01

    Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. Moreover, past abrupt motions are proxies for potential tsunamigenic earthquakes and benefit hazard assessment. Well-dated records are required to understand the relationship between past earthquakes and Holocene vertical deformation. Here we measure elevations and 230Th ages of in situ corals raised above the sea level in the western Solomon Islands to build an uplift event history overlying the seismogenic zone, extremely close to the trench (4-40 km). We find marked spatiotemporal heterogeneity in uplift from mid-Holocene to present: some areas accrue more permanent uplift than others. Thus, uplift imposed during the 1 April 2007 Mw 8.1 event may be retained in some locations but removed in others before the next megathrust rupture. This variability suggests significant changes in strain accumulation and the interplate thrust process from one event to the next.

  20. Variable Holocene deformation above a shallow subduction zone extremely close to the trench.

    PubMed

    Thirumalai, Kaustubh; Taylor, Frederick W; Shen, Chuan-Chou; Lavier, Luc L; Frohlich, Cliff; Wallace, Laura M; Wu, Chung-Che; Sun, Hailong; Papabatu, Alison K

    2015-06-30

    Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. Moreover, past abrupt motions are proxies for potential tsunamigenic earthquakes and benefit hazard assessment. Well-dated records are required to understand the relationship between past earthquakes and Holocene vertical deformation. Here we measure elevations and (230)Th ages of in situ corals raised above the sea level in the western Solomon Islands to build an uplift event history overlying the seismogenic zone, extremely close to the trench (4-40 km). We find marked spatiotemporal heterogeneity in uplift from mid-Holocene to present: some areas accrue more permanent uplift than others. Thus, uplift imposed during the 1 April 2007 Mw 8.1 event may be retained in some locations but removed in others before the next megathrust rupture. This variability suggests significant changes in strain accumulation and the interplate thrust process from one event to the next.

  1. Hydrothermal Heat Transport within an Abruptly Formed Permeable Slot: An Application to Heat Flow Peaks Observed at the Japan Trench Offshore of Sanriku

    NASA Astrophysics Data System (ADS)

    Kawada, Y.; Yamano, M.

    2015-12-01

    Anomalous heat flow has been observed within 150 km seaward of the trench axis at the Japan Trench offshore of Sanriku, northeast Japan [Yamano et al., 2008, 2014]. The average heat flow is ~70 mW/m2 (50 mW/m2 is expected for the plate age), and small-scale (2 to 3 km) variations, whose peak value is >100 mW/m2, are embedded. In the area of high heat flow, a high Vp/Vs layer in the oceanic crust has been detected [Fujie et al., 2013]. The layer thickness is increased toward the trench axis. Fujie et al.[2013] interpreted this layer as a result of fracturing due to bending of the subducting plate. This layer may work as an aquifer in which heat is transported by fluid circulation. In a previous study [Kawada et al., 2014], we constructed a model for aquifer thickening in order to explain the observed anomalous heat flow: a 500-m-thick aquifer 150 km seaward of the trench axis is gradually thickened to 3000 m toward the trench axis. We found that hydrothermal circulation within the thickening aquifer mines heat beneath its underlying part, and heat flow is elevated accordingly. Although the model can explain the observed high heat flow in an average sense, the origin of the small-scale heat flow variations remains to be solved. This study expands the previous model by incorporating abrupt thickening of the aquifer to account for the small-scale heat flow. Typically, we consider a situation in which a permeable slot of 2000 m wide and 3000 m deep suddenly appears. This model results in a high heat flow peak of 100 mW/m2 above the permeable slot, which persists over hundreds of thousand years. Heat outside the slot is transported horizontally toward the slot by thermal conduction and then is transported vertically due to hydrothermal circulation within the slot. Because the volume of the permeable slot is smaller than its surrounding region, high heat flow above the slot lasts for a long time.

  2. Crustal structure and seismicity associated with seamount subduction: A synthesis of results from the Tonga-Kermadec Trench - Louisville Ridge collision zone

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    The Tonga-Kermadec plate boundary is the most linear, fastest converging and most seismically active subduction 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 subducting 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 subduction. 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 trench depth and a 15° anticlockwise rotation of the trench 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 subducting 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 subduction interface. This latter observation is interpreted as subducting 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

  3. Variable Holocene deformation above a shallow subduction zone extremely close to the trench

    PubMed Central

    Thirumalai, Kaustubh; Taylor, Frederick W.; Shen, Chuan-Chou; Lavier, Luc L.; Frohlich, Cliff; Wallace, Laura M.; Wu, Chung-Che; Sun, Hailong; Papabatu, Alison K.

    2015-01-01

    Histories of vertical crustal motions at convergent margins offer fundamental insights into the relationship between interplate slip and permanent deformation. Moreover, past abrupt motions are proxies for potential tsunamigenic earthquakes and benefit hazard assessment. Well-dated records are required to understand the relationship between past earthquakes and Holocene vertical deformation. Here we measure elevations and 230Th ages of in situ corals raised above the sea level in the western Solomon Islands to build an uplift event history overlying the seismogenic zone, extremely close to the trench (4–40 km). We find marked spatiotemporal heterogeneity in uplift from mid-Holocene to present: some areas accrue more permanent uplift than others. Thus, uplift imposed during the 1 April 2007 Mw 8.1 event may be retained in some locations but removed in others before the next megathrust rupture. This variability suggests significant changes in strain accumulation and the interplate thrust process from one event to the next. PMID:26123872

  4. Recurrence of postseismic coastal uplift, Kuril subduction zone, Japan

    USGS Publications Warehouse

    Kelsey, H.; Satake, K.; Sawai, Y.; Sherrod, B.; Shimokawa, K.; Shishikura, M.

    2006-01-01

    Coastal stratigraphy of eastern Hokkaido indicates that decimeters of coastal uplitt occurred repeatedly m the late Holocene. Employing radiocarbon dating and tephrochronology, we identify along a 100 km length of the Kuril subduction zone six uplift events since ???2,800 years B.P. Uplift events occur at the same frequency as unusually high tsunamis. Each coastal uplift event, which occurs on average every 500 years, is the product of decade-long post seismic deep slip on the down dip extension of the seismogenic plate boundary following an offshore multi-segment earthquake that generates unusually high tsunamis. Copyright 2006 by the American Geophysical Union.

  5. Variation of interplate fault zone properties with depth in the japan subduction zone

    PubMed

    Bilek; Lay

    1998-08-21

    The depth dependence of physical properties along the Japan subduction zone interface was explored using teleseismic recordings of earthquake signals. Broadband body waves were inverted to determine the duration of rupture and source depth for 40 interplate thrust earthquakes located offshore of Honshu between 1989 and 1995. After scaling for differences in seismic moment, there is a systematic decrease in rupture duration with increasing depth along the subducting plate interface. This indicates increases in rupture velocity or stress drop with depth, likely related to variation in rigidity of sediments on the megathrust.

  6. Thermal Studies at the Middle America Trench Offshore Costa Rica and Nankai Trough, Japan

    NASA Astrophysics Data System (ADS)

    Harris, R. N.; Solomon, E. A.; Spinelli, G. A.; Scientific Team of IODP Drilling Expedition 334

    2011-12-01

    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 subduction. Fluid flow advects heat from deeper along the subduction 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 trench. Heat flow and geochemical results are consistent with basement fluid flow at the Muroto transect but are more ambiguous at the NanTroSEIZE transect.

  7. First measurement of the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using GPS/acoustic technique

    NASA Astrophysics Data System (ADS)

    Tomita, Fumiaki; Kido, Motoyuki; Osada, Yukihito; Hino, Ryota; Ohta, Yusaku; Iinuma, Takeshi

    2015-10-01

    The subduction rate of an oceanic plate may accelerate after large earthquakes rupture the interplate coupling between the oceanic and overriding continental plates. To better understand postseismic deformation processes in an incoming oceanic plate, we directly measured the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using a GPS/acoustic technique over a period of 2 years (September 2012 to September 2014). The displacement rate was measured to be 18.0 ± 4.5 cm yr-1 (N302.0°E) relative to the North American Plate, which is almost twice as fast as the predicted interseismic plate motion. Because the sum of steady plate motion and viscoelastic response to the Tohoku-Oki earthquake roughly accounts for the observed displacement rate, we conclude that viscoelastic relaxation is the primary mechanism responsible for postseismic deformation of the Pacific Plate and that significant subduction acceleration did not occur at least not during the observation period.

  8. The 2000 Nemuro-Hanto-Oki earthquake, off eastern Hokkaido, Japan, and the high intraslab seismic activity in the southwestern Kuril Trench

    USGS Publications Warehouse

    Takahashi, H.; Hirata, K.

    2003-01-01

    The 2000 Nemuro-Hanto-Oki earthquake (Mw6.8) occurred in the southwestern part of the Kuril Trench. The hypocenter was located close to the aftershock region of the great 1994 Kuril earthquake (Mw8.3), named "the 1994 Hokkaido-Toho-Oki earthquake" by the Japan Meteorological Agency, for which the fault plane is still in debate. Analysis of the 2000 event provides a clue to resolve the fault plane issue for the 1994 event. The hypocenters of the 2000 main shock and aftershocks are determined using arrival times from a combination of nearby inland and submarine seismic networks with an improved azimuthal coverage. They clearly show that the 2000 event was an intraslab event occurring on a shallow-dipping fault plane between 55 and 65 km in depth. The well-focused aftershock distribution of the 2000 event, the relative location of the 1994 event with respect to the 2000 event, and the similarity between their focal mechanisms strongly suggest that the faulting of the great 1994 earthquake also occurred on a shallow-dipping fault plane in the subducting slab. The recent hypocenter distribution around the 1994 aftershock region also supports this result. Large intraslab earthquakes occuring to the southeast of Hokkaido may occur due to a strong coupling on the plate boundary, which generates relatively large stress field within the subducting Pacific plate.

  9. Geology of the Gorny Altai subduction accretion complex, southern Siberia: Tectonic evolution of an Ediacaran Cambrian intra-oceanic arc-trench system

    NASA Astrophysics Data System (ADS)

    Ota, Tsutomu; Utsunomiya, Atsushi; Uchio, Yuko; Isozaki, Yukio; Buslov, Mikhail M.; Ishikawa, Akira; Maruyama, Shigenori; Kitajima, Koki; Kaneko, Yoshiyuki; Yamamoto, Hiroshi; Katayama, Ikuo

    2007-07-01

    Japan Islands in East Asia and the Cordillera in western North America. The Cryogenian boninite-bearing arc volcanism indicates that the initial stage of arc development occurred in a transient setting from a transform zone to an incipient subduction zone. The less abundant of terrigenous clastics from mature continental crust and thick deep-sea chert in the Ediacaran-Early Cambrian AC may suggest that the southern Gorny Altai region evolved in an intra-oceanic arc-trench setting like the modern Mariana arc, rather than along the continental arc of a major continental margin. Based on geological, petrochemical, and geochronological data, we synthesize the Late Neoproterozoic to Early Paleozoic tectonic history of the Gorny Altai region in the western CAOB.

  10. Three Dimensional Seismic Velocity Structure of the Subducted Pacific Slab Beneath NE Japan

    NASA Astrophysics Data System (ADS)

    Tsuji, Y.; Nakajima, J.; Okada, T.; Matsuzawa, T.; Hasegawa, A.

    2006-12-01

    The occurrence of earthquakes in the subducting 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 subduction principally through infiltration of seawater via normal or transform faulting [e.g. Kirby et al., 1996] and/or through hot-spot magmatism [Seno and Yamanaka, 1996]. During subduction, the fluids released by dehydration reactions induce in situ mechanical instability and brittle deformation by increasing pore pressure. Mishra and Zhao [2004] revealed the existence of low-velocity zone around the hypocenter of the 2003 Miyagi- Oki intraslab earthquake (M7.1). Nakajima and Hasegawa [2006] detected a linear alignment of seismicity and a narrow low-velocity zone along it within the Pacific slab beneath Kanto, Japan. These results suggest that the occurrence of intraslab earthquakes is closely associated with the heterogeneous structure in the subducted slab. This study is the first attempt to investigate 3D seismic velocity structure in the subducted Pacific slab for the entire NE Japan. A detailed investigation of heterogeneous structure is essential to understand the mechanism for triggering intraslab earthquake. We apply the Double-Difference Tomogaphy method (Zhang and Thurber, 2003) to arrival-time data of 208,026 and 142,259 P and S waves, respectively, obtained from 3131 earthquakes that occurred from October 1997 to March 2006. The total number of stations used in this study is 206. We adopted a grid spacing of 10km-40km in the horizontal direction and 5-30km in the vertical direction. At the first inversion, we used only absolute travel-time data and determine large scale velocity structure, and then differential travel-time data were added to the absolute data to investigate slab structure in detail. The obtained results show

  11. Aftereffects of Subduction-Zone Earthquakes: Potential Tsunami Hazards along the Japan Sea Coast.

    PubMed

    Minoura, Koji; Sugawara, Daisuke; Yamanoi, Tohru; Yamada, Tsutomu

    2015-01-01

    The 2011 Tohoku-Oki Earthquake is a typical subduction-zone earthquake and is the 4th largest earthquake after the beginning of instrumental observation of earthquakes in the 19th century. In fact, the 2011 Tohoku-Oki Earthquake displaced the northeast Japan island arc horizontally and vertically. The displacement largely changed the tectonic situation of the arc from compressive to tensile. The 9th century in Japan was a period of natural hazards caused by frequent large-scale earthquakes. The aseismic tsunamis that inflicted damage on the Japan Sea coast in the 11th century were related to the occurrence of massive earthquakes that represented the final stage of a period of high seismic activity. Anti-compressive tectonics triggered by the subduction-zone earthquakes induced gravitational instability, which resulted in the generation of tsunamis caused by slope failing at the arc-back-arc boundary. The crustal displacement after the 2011 earthquake infers an increased risk of unexpected local tsunami flooding in the Japan Sea coastal areas.

  12. Controls on intrusion of near-trench magmas of the Sanak-Baranof Belt, Alaska, during Paleogene ridge subduction, and consequences for forearc evolution

    USGS Publications Warehouse

    Kusky, Timothy M.; Bradley, Dwight C.; Donely, D. Thomas; Rowley, David; Haeussler, Peter J.

    2003-01-01

    A belt of Paleogene near-trench plutons known as the Sanak-Baranof belt intruded the southern Alaska convergent margin. A compilation of isotopic ages of these plutons shows that they range in age from 61 Ma in the west to ca. 50 Ma in the east. This migrating pulse of magmatism along the continental margin is consistent with North Pacific plate reconstructions that suggests the plutons were generated by migration of a trench-ridge-trench triple junction along the margin. On the Kenai Peninsula the regional lower greenschist metamorphic grade of the turbiditic host rocks, texture of the plutons, contact-metamorphic assemblage, and isotopic and fluid inclusion studies suggest that the plutons were emplaced at pressures of 1.5–3.0 kbars (5.2–10.5 km) into a part of the accretionary wedge with an ambient temperature of 210–300 °C. The presence of kyanite, garnet, and cordierite megacrysts in the plutons indicates that the melts were generated at a depth greater than 20 km and minimum temperature of 650 °C. These megacrysts are probably xenocrystic remnants of a restitic or contact metamorphic phase entrained by the melt during intrusion. However, it is also possible that they are primary magmatic phases crystallized from the peraluminous melt.Plutons of the Sanak-Baranof belt serve as time and strain markers separating kinematic regimes that predate and postdate ridge subduction. Pre-ridge subduction structures are interpreted to be related to the interaction between the leading oceanic plate and the Chugach terrane. These include regional thrust faults, NE-striking map-scale folds with associated axial planar foliation, type-1 mélanges, and an arrayof faults within the contact aureole indicating shortening largely accommodated by layer-parallel extension. Syn-ridge subduction features include the plutons, dikes, and ductile shear zones within contact aureoles with syn-kinematic metamorphic mineral growth and foliation development. Many of the studied plutons

  13. Three-dimensional electromagnetic imaging of upwelling fluids in the Kyushu subduction zone, Japan

    NASA Astrophysics Data System (ADS)

    Hata, Maki; Oshiman, Naoto; Yoshimura, Ryokei; Tanaka, Yoshikazu; Uyeshima, Makoto

    2015-01-01

    A three-dimensional (3-D) lithospheric-scale electrical resistivity model, developed using network-magnetotelluric (network-MT) data, contains structures associated with arc magmatism beneath Kyushu Island in the Southwest Japan arc. Kyushu Island, where the Philippine Sea Plate (PSP) subducts beneath the Eurasian plate, can be divided into northern and southern volcanic regions separated by a nonvolcanic region. Many active Quaternary volcanoes occur along the volcanic front (VF) associated with the PSP in the two volcanic regions. Our 3-D electrical resistivity model shows three different shapes of upwelling fluid-like conductive anomalies, indicative of either slab-derived aqueous fluid and/or partial melt beneath the volcanic and nonvolcanic regions. A conductive anomaly in the northern volcanic region, located at some distance from the subducting PSP, extends from the surface to depths of <100 km, whereas another conductive anomaly in the southern volcanic region, located along the subducting PSP at >70 km depth, extends from the surface to depths of >100 km. In the nonvolcanic region, the upper region of a relatively conductive anomaly extends upward to a depth of ~50 km along the subducting plate. The degrees of magmatism and the relative contribution of slab-derived fluids to the magmatism vary spatially in the one nonvolcanic and two volcanic regions.

  14. Fast Identification of Near-Trench Earthquakes Along the Mexican Subduction Zone Based on Characteristics of Ground Motion in Mexico City

    NASA Astrophysics Data System (ADS)

    Perez-Campos, X.; Singh, S. K.; Arroyo, D.; Rodríguez, Q.; Iglesias, A.

    2015-12-01

    The disastrous 1985 Michoacan earthquake gave rise to a seismic alert system for Mexico City which became operational in 1991. Initially limited to earthquakes along the Guerrero coast, the system now has a much wider coverage. Also, the 2004 Sumatra earthquake exposed the need for a tsunami early warning along the Mexican subduction zone. A fast identification of near-trench earthquakes along this zone may be useful in issuing a reliable early tsunami alert. The confusion caused by low PGA for the magnitude of an earthquake, leading to "missed" seismic alert, would be averted if its near-trench origin can be quickly established. It may also help reveal the spatial extent and degree of seismic coupling on the near-trench portion of the plate interface. This would lead to a better understanding of tsunami potential and seismic hazard along the Mexican subduction zone. We explore three methods for quick detection of near-trench earthquakes, testing them on recordings of 65 earthquakes at station CU in Mexico City (4.8 ≤Mw≤8.0; 270≤R≤615 km). The first method is based on the ratio of total to high-frequency energy, ER (Shapiro et al., 1998). The second method is based on parameter Sa*(6) which is the pseudo-acceleration response spectrum with 5% damping, Sa, at 6 s normalized by the PGA. The third parameter is the PGA residual, RESN, at CU, with respect to a newly-derived ground motion prediction equation at CU for coastal shallow-dipping thrust earthquakes following a bayesian approach. Since the near-trench earthquakes are relatively deficient in high-frequency radiation, we expect ER and Sa*(6) to be relatively large and RESN to be negative for such events. Tests on CU recordings show that if ER ≥ 100 and/or Sa*(6) ≥ 0.70, then the earthquake is near trench; for these events RESN ≤ 0. Such an event has greater tsunami potential. Few misidentifications and missed events are most probably a consequence of poor location, although unusual depth and source

  15. Middle Miocene near trench volcanism in northern Colombia: A record of slab tearing due to the simultaneous subduction of the Caribbean Plate under South and Central America?

    NASA Astrophysics Data System (ADS)

    Lara, M.; Cardona, A.; Monsalve, G.; Yarce, J.; Montes, C.; Valencia, V.; Weber, M.; De La Parra, F.; Espitia, D.; López-Martínez, M.

    2013-08-01

    Field, geochemical, geochronological, biostratigraphical and sedimentary provenance results of basaltic and associated sediments northern Colombia reveal the existence of Middle Miocene (13-14 Ma) mafic volcanism within a continental margin setting usually considered as amagmatic. This basaltic volcanism is characterized by relatively high Al2O3 and Na2O values (>15%), a High-K calc-alkaline affinity, large ion lithophile enrichment and associated Nb, Ta and Ti negative anomalies which resemble High Al basalts formed by low degree of asthenospheric melting at shallow depths mixed with some additional slab input. The presence of pre-Cretaceous detrital zircons, tourmaline and rutile as well as biostratigraphic results suggest that the host sedimentary rocks were deposited in a platform setting within the South American margin. New results of P-wave residuals from northern Colombia reinforce the view of a Caribbean slab subducting under the South American margin. The absence of a mantle wedge, the upper plate setting, and proximity of this magmatism to the trench, together with geodynamic constraints suggest that the subducted Caribbean oceanic plate was fractured and a slab tear was formed within the oceanic plate. Oceanic plate fracturing is related to the splitting of the subducting Caribbean Plate due to simultaneous subduction under the Panama-Choco block and northwestern South America, and the fast overthrusting of the later onto the Caribbean oceanic plate.

  16. A zone of anomalously low b-values within the subducting slab prior to the September 26, 2003 Tokachi-oki, Japan, earthquake (M=8.0)

    NASA Astrophysics Data System (ADS)

    Nakaya, S.

    2004-12-01

    The M=8.0 26 September 2003 Tokachi-oki earthquake occurred in the southern Kuril Trench southeast of Hokkaido, Japan, 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 subduction 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 subduction [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 subducting slab along the Kuril Trench 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 subducting slab prior to the mainshock provide seismological evidence for high stress concentrations associated with

  17. Microbial Diversity in Sediments Collected from the Deepest Cold-Seep Area, the Japan Trench.

    PubMed

    Li; Kato; Horikoshi

    1999-07-01

    : The Japan Trench land slope at a depth of 6,400 m is the deepest cold-seep environment with Calyptogena communities. Sediment samples from inside and beside the Calyptogena communities were collected, and the microbial diversity in the sediment samples was studied by molecular phylogenetic techniques. From DNA extracted directly from the sediment samples, 16S rDNAs were amplified by the polymerase chain reaction method. The sequences of the amplified 16S rDNAs selected by restriction fragment length polymorphism analysis were determined and compared with sequences in DNA databases. The results showed that 33 different bacterial 16S rDNA sequences from the two samples analyzed fell into similar phylogenetic categories, the alpha-, gamma-, delta-, and varepsilon-subdivisions of Proteobacteria, Cytophaga, and gram-positive bacteria; some of the 16S rDNA sequences were common to both samples. delta- and varepsilon-Proteobacteria-related sequences were abundant in both sediments. These sequences are mostly related to sulfate-reducing or sulfur-reducing bacteria and epibionts, respectively. Eight different archaeal 16S rDNA sequences were cloned from the sediments. The majority of the archaeal 16S rDNA sequences clustered in Crenarchaeota and showed high similarities to marine group I archaeal rDNA. A Methanococcoides burtonii-related sequence obtained from the sediment clustered in the Euryarchaeota indicating that M. burtonii-related strains in the area of Calyptogena communities may contribute to production of methane in this environment. From these results, we propose a possible model of sulfur circulation within the microbial community and that of Calyptogena clams in the cold-seep environment.

  18. Japan trench studies on earthquake, mass-wasting deposits and related tsunami based on most recent submarine survey

    NASA Astrophysics Data System (ADS)

    Kawamura, K.; Kasaya, T.; Sasaki, T.; Kanamatsu, T.; Sakaguchi, A.; Tsuji, T.

    2011-12-01

    On 11 March 2011, Tohoku, northeast Japan, 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 Japan Trench 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 Japan trench. The Japan Trench 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

  19. Spatial variation of attenuation factor in subduction zone of Philippine Sea slab around Kyushu Island Japan

    NASA Astrophysics Data System (ADS)

    Parithusta, Rizkita; Matsumoto, Satoshi; Shimizu, Hiroshi

    2010-05-01

    Kyushu Island, in south-western part of Japan is characterized by subduction from Philippine Sea Slab and Eurasian Plate (Amurian); volcanic front seen in islands arcs runs through the central part of Kyushu Island. In Kyushu, shallow and intermediate-depth earthquakes occur robustly through a depth of about 200 km. We estimated attenuation structure beneath Southern Part of Japan, at subduction zone of Philippine Sea Slab by applying modified coda normalization method (Eq.1) proposed by Parithusta, et.al. (2008*). The method estimates relative source spectra by taking spectral ratio in coda waves between two events at first. From a lot of the spectral data, those can be estimated with higher stability through singular value decomposition. After that, the relative source effect between event pair can be eliminated by the solution from ratios between direct wave spectra for many event pairs. We confirmed the estimation of source factor by assessment with empirical method, the result show that estimates of source factor almost satisfy empirical relation between magnitude and energy relation. The attenuation factor can be obtained from a relation below; ( ) Edij(tij,?-)- -1 dn = ln Edi'j(ti'j,?) = - ?Q(?) (tij - ti'j)+ const.... (1) Where: Ed denotes Direct S-wave power spectrum and Q is attenuation factor at target area; t is lapse time from origin time. Subscript i,jdenote identification number for event and station, respectively. Q-1 factor can be estimated from decay with ?tii'j(= tij - ti'j). By using this method, we obtained frequency dependent Q-1 value with smaller estimation error than previous study carried by Matsumoto et.al (2007). We used waveform data from earthquakes occurred in Philippine Sea Slab, recorded by Hi-net and Kyushu University seismic networks. Window length adopted here is 2.5 seconds for taking spectrum. The results shows the Q-1 values around Bungo-Suido area, northern part of Kyushu. Q-1 values are plotted in seven depth ranges as a

  20. Evolution of a trench-slope basin within the Cascadia subduction margin: the Neogene Humboldt Basin, California

    USGS Publications Warehouse

    McCrory, P.A.

    1995-01-01

    The Neogene Humboldt (Eel River) Basin is located along the north-eastern margin of the Pacific Ocean within the Cascadia subduction zone. This sedimentary basin originated near the base of the accretionary prism in post-Eocene time. Subduction 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

  1. Documenting large earthquakes similar to the 2011 Tohoku-oki earthquake from sediments deposited in the Japan Trench over the past 1500 years

    NASA Astrophysics Data System (ADS)

    Ikehara, Ken; Kanamatsu, Toshiya; Nagahashi, Yoshitaka; Strasser, Michael; Fink, Hiske; Usami, Kazuko; Irino, Tomohisa; Wefer, Gerold

    2016-07-01

    The 2011 Tohoku-oki earthquake and tsunami was the most destructive geohazard in Japanese history. However, little is known of the past recurrence of large earthquakes along the Japan Trench. Deep-sea turbidites are potential candidates for understanding the history of such earthquakes. Core samples were collected from three thick turbidite units on the Japan Trench floor near the epicenter of the 2011 event. The uppermost unit (Unit TT1) consists of amalgamated diatomaceous mud (30-60 cm thick) that deposited from turbidity currents triggered by shallow subsurface instability on the lower trench slope associated with strong ground motion during the 2011 Tohoku-oki earthquake. Older thick turbidite units (Units TT2 and TT3) also consist of several amalgamated subunits that contain thick sand layers in their lower parts. Sedimentological characteristics and tectonic and bathymetric settings of the Japan Trench floor indicate that these turbidites also originated from two older large earthquakes of potentially similar to the 2011 Tohoku-oki earthquake. A thin tephra layer between Units TT2 and TT3 constrains the age of these earthquakes. Geochemical analysis of volcanic glass shards within the tephra layer indicates that it is correlative to the Towada-a tephra (AD 915) from the Towada volcano in northeastern Japan. The stratigraphy of the Japan Trench turbidites resembles that of onshore tsunami deposits on the Sendai and Ishinomaki plains, indicating that the cored uppermost succession of the Japan Trench comprises a 1500-yr-old record that includes the sedimentary fingerprint of the historical Jogan earthquake of AD 869.

  2. A New View on the Space-Time Pattern of M>7 Earthquakes in the Northern Japan to Kurile Subduction Zones

    NASA Astrophysics Data System (ADS)

    Harada, T.; Satake, K.

    2012-04-01

    The northern Japan to southern Kurile trenches have been regarded as a typical subduction zone with spatially and temporally regular recurrence of great (M>8) interplate earthquakes. The source regions were grouped into six segments by Utsu (1972; 1984). The Headquarters for Earthquake Research Promotion of the Japanese government (2004) divided the southern Kurile subduction zone into four regions and evaluated future probabilities of great interplate earthquakes. Besides great interplate events, however, many large (M>7) interplate, intraslab, outer-rise and tsunami earthquakes have also occurred in this region. First, we depicted the space-time pattern of M>7 earthquakes along the northern Japan to Kuril trench, based on the relocated mainshock-aftershock distributions of all types of earthquakes occurred since 1913. We relocated the hypocenters reported in the ISC, ISS, and BCIS bulletins by using the HYPOSAT (Schweitzer, 2003) and the Modified JHD method (Hurukawa, 1995). Then, in order to examine more detail space pattern, or rupture areas, of M>7 earthquakes since 1963, we estimated coseismic slip distributions by the Kikuchi and Kanamori's (2003) teleseismic body wave inversion method. The WWSSN waveform data were used for earthquakes between 1963 and 1990, and digital teleseismic waveform data compiled by the IRIS were used for events after 1990. Mainshock hypocenters relocated by us were used as initial rupture points. As a result, we found that the more complex feature of earthquake occurrence. Each region has been ruptured by a M8-class interplate earthquake or by multiple M7-class events. Offshore Urup Is. is source region of the 1963 Urup earthquake (M 8.5). Large interplate earthquakes occurred in the eastern and western part of the 1963 source region in 1991 (M 7.6) and 1995 (M 7.9), respectively. Their aftershock areas almost re-occupied the 1963 aftershock area. The 1963, 1991, and 1995 coseismic slip distributions show that the southwestern

  3. Reconstruction of ocean plate stratigraphy in the Gwna Group, NW Wales: Implications for the subduction-accretion process of a latest Proterozoic trench-forearc

    NASA Astrophysics Data System (ADS)

    Asanuma, Hisashi; Okada, Yoshihiro; Fujisaki, Wataru; Suzuki, Kazue; Sato, Tomohiko; Sawaki, Yusuke; Sakata, Shuhei; Yamamoto, Shinji; Hirata, Takafumi; Maruyama, Shigenori; Windley, Brian F.

    2015-11-01

    The Gwna Group in Anglesey island and Lleyn peninsula, Wales consists of a latest Proterozoic volcano-sedimentary trench mélange, which has a complicated accretionary structure, and is poorly constrained by isotopic ages. The mélange contains oceanic-trench rocks including pillow basalts, cherts, mudstones and sandstones, which have not previously been interpreted as ocean plate stratigraphy (OPS). We reconstructed imbricated OPS at 5 localities in the coastal Lleyn peninsula. In order to constrain the depositional U-Pb age of the upper clastic sediments, detrital zircons, separated from 9 clastic sediments, were analyzed with a Nu AttoM single-collector inductively-coupled plasma-mass spectrometer. The ages indicate that there are two Gwna Groups (maximum depositional ages of: 1 at 608-601 Ma, and 2 at 564-539 Ma) that were deposited between the late Neoproterozoic and the Middle Cambrian contemporaneously with dated calc-alkaline arc magmatism and regional metamorphism in the Anglesey-Lleyn complex. The age spectra of the detrital zircons show a prominent peak at ca. 650-600 Ma, and several Proterozoic and Archean ages. To account for the older ages, we integrated our new isotopic data with published radiometric and fossil ages, and conclude that the clastic sediments at the top of the OPS were deposited in a trench on the western active margin of Avalonia when it was close to the Amazonian craton, and that the Gwna Group OPS began to be incorporated into an accretionary wedge in an active subduction zone in the latest Proterozoic.

  4. High-Resolution Subduction Zone Seismicity and Velocity Structure in Ibaraki, Japan

    NASA Astrophysics Data System (ADS)

    Shelly, D. R.; Beroza, G. C.; Zhang, H.; Thurber, C. H.; Ide, S.

    2004-12-01

    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 subduction zone under Ibaraki Prefecture of north-central Honshu, Japan. 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 subduction 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, subduction 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 subduction

  5. Automated Monitoring of Non-Volcanic Tremors in Southwest Japan Subduction Zone

    NASA Astrophysics Data System (ADS)

    Suda, N.; Ishihara, Y.; Nakata, R.; Kusumi, T.

    2005-12-01

    Activities of low-frequency tremors, which occur in the non-volcanic region of southwest Japan along the subduction zone of the Philippine Sea plate, often show slow migration of tremor sources with a speed of about 10 km/day and quasi-periodicity of occurrence with an interval of 2--6 months. Such characteristics seem to be related to fluid liberated from the subducting slab. Monitoring of tremor activities therefore may lead us to elucidation of fluid property and its role in the subduction zone. To monitor activities of low-frequency tremors in real-time, we have developed the automatic detection and hypocenter determination system using real-time data from the commutation-satellite seismic telemetry system. We divide the tremor region into 6 subregions, and use 8--12 vertical-component seismic data to monitor the tremor activity in each subregion. Before applying the detection method, we preprocess real-time data by applying the bandpass filter with a frequency band of 1--10 Hz, resampling them from 100 Hz to 20 Hz, calculating their envelopes, and finally applying the moving average with a time window of 3 seconds. The automatic detection method is based on a two-step numerical statistical test: the first test is for examining whether given two envelopes with a length of 2 minutes are correlated or not, and the second for examining whether an event occur or not in this time window using results of the first test. If an event is detected then the automatic hypocenter determination method is applied. In this method time lags for the maximum cross-correlations obtained in the detection method are utilized as traveltime difference data, and hypocenters are determined by minimizing the absolute residual using the simplex method. The results obtained by the automatic detection method are consistent to those determined by visual inspection of waveforms, and also the results obtained by the automatic hypocenter determination are consistent to those determined by the

  6. Rockmagnetic characterization of event deposits induced by March 2011 Tohoku-oki Earthquake in the Japan Trench

    NASA Astrophysics Data System (ADS)

    Kanamatsu, T.; Ikehara, K.; Arai, K.; Sato, T.

    2012-12-01

    -currents occurred during the event. A combination of trench 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 trench 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 Japan trench.

  7. The Mariana Trench: A new view based on multibeam echosounding

    NASA Astrophysics Data System (ADS)

    Gardner, J. V.; Armstrong, A. A.

    2011-12-01

    The entire Mariana Trench, from its northern end at Dutton Ridge to the southwestern terminus at the Yap Trench, was mapped in 2010 using a Kongsberg EM122 12-kHz multibeam echosounder. The region ranges in depths from the shoreline at Guam to almost 11,000 m at the Challenger Deep. The northern part of the trench is receiving seamounts and guyots of the Magellan Seamount chain, whereas the southern section is receiving seafloor that carries the Caroline Ridge to the trench. The area immediately seaward of the trench where the Pacific Plate has bent downward toward the subduction zone has been broken by a series of subparallel horst and graben structures generated by extension on the bending upper surface of the Pacific Plate. Four bathymetric "bridges" span across the trench axis and extend from the Pacific Plate to the inner wall of the trench. The bridges stand as much as 2500 m above the trench axis and are composed of Latest Jurassic to Early Cretaceous accreted seamounts and guyots of the Magellan Seamount chain that are in the process of breaking up and being subducted beneath the Philippine Plate. Only two seamounts of the Caroline Ridge are in the vicinity of the trench and they both presently reside on the outer trench wall. The faults of the horsts and grabens have fractured the seamounts and guyots within the trench depression seaward from the axis outward for about 80 km, but within ~5 km of the trench axis the faults have reactivated to compressional thrust faults. The faults tend to parallel the axis of the trench until the immediate vicinity of an accreting seamount or guyot where the faults bend inward toward the trench axis, as has been observed in many other trenches. Most of the accreted seamounts and guyots are not associated with embayments or reentrants on the inner trench wall, as has been documented in the Middle America and Japan Trenches, perhaps because there is not a large accretionary prism that extends seaward of the forearc. The one

  8. The mechanics of subduction zone tremor and transient slip in Japan

    NASA Astrophysics Data System (ADS)

    Shelly, David R.

    2007-12-01

    Subduction zones produce a wide array of seismicity including the planet's largest earthquakes. Recently, modern geodetic instruments have illuminated transient slip events in subduction zones (and elsewhere) with durations ranging from days to years. These events appear to be relatively common on the portion of the plate interface downdip of the region that generates earthquakes. Such events are of particular interest because they likely increase the stress on the shallower more brittle portion of the fault and therefore could trigger a large earthquake. Although these slow events do not generate strong shaking, they are often accompanied by a weak semi-continuous seismic signal that has been termed non-volcanic tremor. A variety of mechanisms have been proposed to explain this tremor and its association with slow slip, often involving fluid flow. By utilizing seismic data from a dense borehole network in southwest Japan, I demonstrate that tremor is instead generated by a sequence of small shear failures on the plate interface. These failures likely occur under very low shear stresses and may be enabled by high pore fluid pressures interpreted to exist in this zone. Added together, these shear events form the semi-continuous tremor signal, usually during much larger-scale slow slip events. In addition, I present precise locations of tremor, obtained using a matched filter technique with previously recorded "template events," which allow slip to be tracked with unprecedented resolution. These locations reveal a complex evolution of slow slip, with smaller, shorter duration subevents exhibiting along-dip migration rates of 20-150 km/hour in repeated rupture episodes over the several-day course of an event. Tremor may be generated primarily at plate interface heterogeneities that stick and slip while driven to repeated failure by slip on neighboring portions of the fault.

  9. Early Paleozoic subduction initiation volcanism of the Iwatsubodani Formation, Hida Gaien belt, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Tsukada, Kazuhiro; Yamamoto, Koshi; Gantumur, Onon; Nuramkhaan, Manchuk

    2017-01-01

    In placing Japanese tectonics in an Asian context, variation in the Paleozoic geological environment is a significant issue. This paper investigates the geochemistry of the lower Paleozoic basalt formation (Iwatsubodani Formation) in the Hida Gaien belt, Japan, to consider its tectonic setting. This formation includes the following two types of rock in ascending order: basalt A with sub-ophitic texture and basalt B with porphyritic texture. Basalt A has a high and uniform FeO*/MgO ratio, moderate TiO2, high V, and low Ti/V. The HFSE and REE are nearly the same as those in MORB, and all the data points to basalt A being the "MORB-like fore-arc tholeiitic basalt (FAB)" reported, for example, from the Izu-Bonin-Mariana arc. By contrast, basalt B has a low FeO*/MgO ratio, low TiO2, and low V and Ti/V. It has an LREE-enriched trend and a distinct negative Nb anomaly in the MORB-normalized multi-element pattern and a moderately high LREE/HREE. All these factors suggest that basalt B is calc-alkaline basalt. It is known that FAB is erupted at the earliest stage of arc formation—namely, subduction initiation—and that boninitic/tholeiitic/calc-alkaline volcanism follows at the supra-subduction zone (SSZ). Thus, the occurrence of basalts A (FAB) and B (calc-alkaline rock) is strong evidence of early Paleozoic arc-formation initiation at an SSZ. Evidence for an early Paleozoic SSZ arc is also recognized from the Oeyama, Hayachine-Miyamori, and Sergeevka ophiolites. Hence, both these ophiolites and the Iwatsubodani Formation probably coexisted in a primitive SSZ system in the early Paleozoic.

  10. Small-scale spatial variation in near-surface turbidites around the JFAST site near the Japan Trench

    NASA Astrophysics Data System (ADS)

    Yoshikawa, Shuro; Kanamatsu, Toshiya; Kasaya, Takafumi

    2016-03-01

    This paper aims to improve our understanding of the depositional processes associated with turbidites related to recent earthquake events. A series of short sediment cores (ca. 20-30 cm long) were recovered from the landward slope of the Japan Trench around JFAST (Japan Trench Fast Drilling Project) site C0019 by a remotely operated vehicle, KAIKO 7000 II, and the sample sites were accurately located using an LBL (long base line) acoustic navigation system. The properties of the cores were analyzed using visual observations, soft X-ray radiographs, smear slides, measurement of anisotropy of magnetic susceptibility, and analysis of radioactive elements (134Cs, 137Cs, and excess 210Pb). For the first time, small-scale (ca. 200-1000 m) spatial variations in recent earthquake-triggered deep-sea turbidites, the formation of which was probably linked to the 2011 Tohoku-oki earthquake, are described. We also examine the submarine landslide that probably generated the sediment unit below the turbidites, which is thought to be an important process in the study area. The spatial distribution and characteristics of the near-surface seismoturbidite obtained immediately after the earthquake, presented here, will enable precise calibration of offshore evidence of recent earthquakes, and thus facilitate the use of the sedimentary archive for paleoseismic interpretations. Furthermore, although sampling for turbidite seismology on steep slopes has not been widely performed previously, our results suggest that the recent event deposits may be continuously tracked from the slope to the basin using a combination of the present sampling method and conventional large-scale investigation techniques.

  11. Activity of Small Repeating Earthquakes along Izu-Bonin and Ryukyu Trenches

    NASA Astrophysics Data System (ADS)

    Hibino, K.; Matsuzawa, T.; Uchida, N.; Nakamura, W.; Matsushima, T.

    2014-12-01

    There are several subduction systems near the Japanese islands. The 2011 Mw9.0 Tohoku-oki megathrust earthquake occurred at the NE Japan (Tohoku) subduction zone. We have revealed a complementary relation between the slip areas for huge earthquakes and small repeating earthquakes (REs) in Tohoku. Investigations of REs in these subduction zones and the comparison with Tohoku area are important for revealing generation mechanism of megathrust earthquakes. Our target areas are Izu-Bonin and Ryukyu subduction zones, which appear to generate no large interplate earthquake. To investigate coupling of plate boundary in these regions, we estimated spatial distribution of slip rate by using REs. We use seismograms from the High Sensitivity Seismograph Network (Hi-net), Full Range Seismograph Network of Japan (F-net), and permanent seismic stations of Japan Meteorological Agency (JMA), Tohoku University, University of Tokyo, and Kagoshima University from 8 May 2003 (Izu-Bonin) and 14 July 2005 (Ryukyu) to 31 December 2012 to detect REs along the two trenches, by using similarity of seismograms. We mainly follow the procedure adopted in Uchida and Matsuzawa (2013) that studied REs in Tohoku area to compare our results with the REs in Tohoku. We find that the RE distribution along the Ryukyu trench shows two bands parallel to the trench axis. This feature is similar to the pattern in Tohoku where relatively large earthquakes occur between the bands. Along the Izu-Bonin trench, on the other hand, we find much fewer REs than in Tohoku or Ryukyu subduction zones and only one along-trench RE band, which corresponds to the area where the subducting Pacific plate contacts with the crust of the Philippine Sea plate. We also estimate average slip rate and coupling coefficient by using an empirical relationship between seismic moment and slip for REs (Nadeau and Johnson, 1998) and relative plate motion model. As a result, we find interplate slip rate in the deeper band is higher than

  12. Deep seismic reflection profiling of the subduction megathrust across the Sagimi trough and Tokyo bay, Japan

    NASA Astrophysics Data System (ADS)

    Sato, Hiroshi; Iwasaki, Takaya; Abe, Susumu; Saito, Hideo; Kawanaka, Taku; Hirata, Naoshi

    2010-05-01

    Beneath the metropolitan Tokyo, the Philippine Sea plate, in particular the fore arc portion of the Izu-Bonin island arc, has been subducted. Subduction megathrust beneath Tokyo generated M-8 class earthquakes, such as the 1923 Kanto (M7.9) and 1703 Genroku (M8.0) earthquakes. Due to the buyant subduction of the Izu-Bonin arc, the megathrust lies very shallow part of the crust. The Kozu-Matsuda fault, probable spray fault from the megathrust, emerged at the surface. In 2009, we acquired the deep seismic reflection data across the toe of the thrust system to reveal the connectivity of the probable spray fault to the megathrust. Together with the deep seismic section acquired in 2003, we show a 120-km-long deep seismic reflection profile from the front to 30 km in depth and discuss the geometry and characteristics of the thrust system. We performed deep seismic profiling across the Sagami trough for a 70-km-long seismic line in September 2009, using two ships for offshore seismic data acquisition: a gun-ship with a 3020 cu. inch air-gun and a cable-ship with a 2-km-long, streamer cable and a 480 cu. inch air-gun. The seismic signals were recorded at Miura and Izu peninsulas located both ends of the seismic line. At both sides of the onshore line, off-line recorders were deployed along total 20-km-long seismic lines at a 50m interval. Seismic reflection data were acquired by different offset of ships making large-offset gathers. The northeast end of the seismic line connected with the 2003 Tokyo bay seismic line (Sato et al., 2005: Science). The obtained seismic sections portray the detailed geometry of the spray faults, suggesting an emergent thrust with 4 km thick landward dipping strata. It merges to the megathrust at 6-7 sec (TWT). Judging from the geometry of fault-related fold in the trough fill sediments, the tip of the megathrust is located at 3 sec (TWT) beneath the trough axis. According to the co-seismic crustal deformation, the slip of the 1923 Kanto

  13. Prediction of long-period ground motions from huge subduction earthquakes in Osaka, Japan

    NASA Astrophysics Data System (ADS)

    Kawabe, H.; Kamae, K.

    2008-04-01

    There is a high possibility of reoccurrence of the Tonankai and Nankai earthquakes along the Nankai Trough in Japan. It is very important to predict the long-period ground motions from the next Tonankai and Nankai earthquakes with moment magnitudes of 8.1 and 8.4, respectively, to mitigate their disastrous effects. In this study, long-period (>2.5 s) ground motions were predicted using an earthquake scenario proposed by the Headquarters for Earthquake Research Promotion in Japan. The calculations were performed using a fourth-order finite difference method with a variable spacing staggered-grid in the frequency range 0.05 0.4 Hz. The attenuation characteristics ( Q) in the finite difference simulations were assumed to be proportional to frequency ( f) and S-wave velocity ( V s) represented by Q = f · V s / 2. Such optimum attenuation characteristic for the sedimentary layers in the Osaka basin was obtained empirically by comparing the observed motions during the actual M5.5 event with the modeling results. We used the velocity structure model of the Osaka basin consisting of three sedimentary layers on bedrock. The characteristics of the predicted long-period ground motions from the next Tonankai and Nankai earthquakes depend significantly on the complex thickness distribution of the sediments inside the basin. The duration of the predicted long-period ground motions in the city of Osaka is more than 4 min, and the largest peak ground velocities (PGVs) exceed 80 cm/s. The predominant period is 5 to 6 s. These preliminary results indicate the possibility of earthquake damage because of future subduction earthquakes in large-scale constructions such as tall buildings, long-span bridges, and oil storage tanks in the Osaka area.

  14. Detection of the structure near the 410 km and 660 km discontinuities in Japan subduction zone from the waveform triplication

    NASA Astrophysics Data System (ADS)

    Cui, H.; Zhou, Y.

    2015-12-01

    Slab subduction plays an important role in the mantle material circulation [Stern, 2002], and can also affect the feature of the 410 km and 660 km seismic discontinuities (410 and 660) [Lebedev et al., 2002]. Japan subduction zone is a natural laboratory for studying the mantle composition and velocity structure associated with the deep subduction of the Pacific plate. In this study, triplicated waveforms of an intermediate-depth earthquake at the Hokkaido of Japan (2011/10/21, 08:02:37.62, 142.5315°E, 43.8729°N, Mb6.0, relocated depth: 188 km) are retrieved from the dense Chinese Digital Seismic Network (CDSN). P and S waveforms are filtered with the band of 0.05-1.0 Hz and 0.02-0.5 Hz, respectively, and then integrated into the displacement data. The relative traveltime and synthetic waveform fitting is applied to mapping the deep structure. The best fitting models are obtained through the trial and error tests. We find a 15 km uplift of the 410 and a 25 km depression of the 660, indicating the cold environment caused by the subduction slab; both the 410 and 660 show the sharp discontinuity, but a smaller velocity contrast than the IASP91 model [Kennett and Engdahl, 1991]. Atop the 410 and 660, there are high-velocity layers associated with the subduction (or stagnant) slab. We also find a low-velocity anomaly with the thickness of ~65 km below the 660, which may relate to the slab dehydration or the hot upwelling at the top of the lower mantle. The seismic velocity ratio (VP/VS) shows a lower zone at the depth of ~210-395 km, showing the consistency with the low Poisson's ratio signature of the oceanic plate; a higher zone at the depth of ~560-685 km, implying the hydrous mantle transition zone.

  15. Progressive enrichment of arc magmas caused by the subduction of seamounts under Nishinoshima volcano, Izu-Bonin Arc, Japan

    NASA Astrophysics Data System (ADS)

    Sano, Takashi; Shirao, Motomaro; Tani, Kenichiro; Tsutsumi, Yukiyasu; Kiyokawa, Shoichi; Fujii, Toshitsugu

    2016-06-01

    The chemical composition of intraplate seamounts is distinct from normal seafloor material, meaning that the subduction of seamounts at a convergent margin can cause a change in the chemistry of the mantle wedge and associated arc magmas. Nishinoshima, a volcanic island in the Izu-Bonin Arc of Japan, has been erupting continuously over the past 2 years, providing an ideal opportunity to examine the effect of seamount subduction on the chemistry of arc magmas. Our research is based on the whole-rock geochemistry and the chemistry of minerals within lavas and air-fall scoria from Nishinoshima that were erupted before 1702, in 1973-1974, and in 2014. The mineral phases within the analyzed samples crystallized under hydrous conditions (H2O = 3-4 wt.%) at temperatures of 970 °C-990 °C in a shallow (3-6 km depth) magma chamber. Trace element data indicate that the recently erupted Nishinoshima volcanics are much less depleted in the high field strength elements (Nb, Ta, Zr, Hf) than other volcanics within the Izu-Bonin Arc. In addition, the level of enrichment in the Nishinoshima magmas has increased in recent years, probably due to the addition of material from HIMU-enriched (i.e., high Nb/Zr and Ta/Hf) seamounts on the Pacific Plate, which is being subducted westwards beneath the Philippine Sea Plate. This suggests that the chemistry of scoria from Nishinoshima volcano records the progressive addition of components derived from subducted seamounts.

  16. Distribution and Niche Separation of Planktonic Microbial Communities in the Water Columns from the Surface to the Hadal Waters of the Japan Trench under the Eutrophic Ocean.

    PubMed

    Nunoura, Takuro; Hirai, Miho; Yoshida-Takashima, Yukari; Nishizawa, Manabu; Kawagucci, Shinsuke; Yokokawa, Taichi; Miyazaki, Junichi; Koide, Osamu; Makita, Hiroko; Takaki, Yoshihiro; Sunamura, Michinari; Takai, Ken

    2016-01-01

    The Japan Trench is located under the eutrophic Northwestern Pacific while the Mariana Trench that harbors the unique hadal planktonic biosphere is located under the oligotrophic Pacific. Water samples from the sea surface to just above the seafloor at a total of 11 stations including a trench axis station, were investigated several months after the Tohoku Earthquake in March 2011. High turbidity zones in deep waters were observed at most of the sampling stations. The small subunit (SSU) rRNA gene community structures in the hadal waters (water depths below 6000 m) at the trench axis station were distinct from those in the overlying meso-, bathy and abyssopelagic waters (water depths between 200 and 1000 m, 1000 and 4000 m, and 4000 and 6000 m, respectively), although the SSU rRNA gene sequences suggested that potential heterotrophic bacteria dominated in all of the waters. Potential niche separation of nitrifiers, including ammonia-oxidizing archaea (AOA), was revealed by quantitative PCR analyses. It seems likely that Nitrosopumilus-like AOAs respond to a high flux of electron donors and dominate in several zones of water columns including shallow and very deep waters. This study highlights the effects of suspended organic matter, as induced by seafloor deformation, on microbial communities in deep waters and confirm the occurrence of the distinctive hadal biosphere in global trench environments hypothesized in the previous study.

  17. Distribution and Niche Separation of Planktonic Microbial Communities in the Water Columns from the Surface to the Hadal Waters of the Japan Trench under the Eutrophic Ocean

    PubMed Central

    Nunoura, Takuro; Hirai, Miho; Yoshida-Takashima, Yukari; Nishizawa, Manabu; Kawagucci, Shinsuke; Yokokawa, Taichi; Miyazaki, Junichi; Koide, Osamu; Makita, Hiroko; Takaki, Yoshihiro; Sunamura, Michinari; Takai, Ken

    2016-01-01

    The Japan Trench is located under the eutrophic Northwestern Pacific while the Mariana Trench that harbors the unique hadal planktonic biosphere is located under the oligotrophic Pacific. Water samples from the sea surface to just above the seafloor at a total of 11 stations including a trench axis station, were investigated several months after the Tohoku Earthquake in March 2011. High turbidity zones in deep waters were observed at most of the sampling stations. The small subunit (SSU) rRNA gene community structures in the hadal waters (water depths below 6000 m) at the trench axis station were distinct from those in the overlying meso-, bathy and abyssopelagic waters (water depths between 200 and 1000 m, 1000 and 4000 m, and 4000 and 6000 m, respectively), although the SSU rRNA gene sequences suggested that potential heterotrophic bacteria dominated in all of the waters. Potential niche separation of nitrifiers, including ammonia-oxidizing archaea (AOA), was revealed by quantitative PCR analyses. It seems likely that Nitrosopumilus-like AOAs respond to a high flux of electron donors and dominate in several zones of water columns including shallow and very deep waters. This study highlights the effects of suspended organic matter, as induced by seafloor deformation, on microbial communities in deep waters and confirm the occurrence of the distinctive hadal biosphere in global trench environments hypothesized in the previous study. PMID:27559333

  18. Basalts erupted along the Tongan fore arc during subduction initiation: Evidence from geochronology of dredged rocks from the Tonga fore arc and trench

    NASA Astrophysics Data System (ADS)

    Meffre, Sebastian; Falloon, Trevor J.; Crawford, Tony J.; Hoernle, Kaj; Hauff, Folkmar; Duncan, Robert A.; Bloomer, Sherman H.; Wright, Dawn J.

    2012-12-01

    A wide variety of different rock types were dredged from the Tonga fore arc and trench between 8000 and 3000 m water depths by the 1996 Boomerang voyage. 40Ar-39Ar whole rock and U-Pb zircon dating suggest that these fore arc rocks were erupted episodically from the Cretaceous to the Pliocene (102 to 2 Ma). The geochemistry suggests that MOR-type basalts and dolerites were erupted in the Cretaceous, that island arc tholeiites were erupted in the Eocene and that back arc basin and island arc tholeiite and boninite were erupted episodically after this time. The ages generally become younger northward suggesting that fore arc crust was created in the south at around 48-52 Ma and was extended northward between 35 and 28 Ma, between 9 and 15 Ma and continuing to the present-day. The episodic formation of the fore arc crust suggested by this data is very different to existing models for fore arc formation based on the Bonin-Marianas arc. The Bonin-Marianas based models postulate that the basaltic fore arc rocks were created between 52 and 49 Ma at the beginning of subduction above a rapidly foundering west-dipping slab. Instead a model where the 52 Ma basalts that are presently in a fore arc position were created in the arc-back arc transition behind the 57-35 Ma Loyalty-Three Kings arc and placed into a fore arc setting after arc reversal following the start of collision with New Caledonia is proposed for the oldest rocks in Tonga. This is followed by growth of the fore arc northward with continued eruption of back arc and boninitic magmas after that time.

  19. Psychromonas kaikoae sp. nov., a novel from the deepest piezophilic bacterium cold-seep sediments in the Japan Trench.

    PubMed

    Nogi, Yuichi; Kato, Chiaki; Horikoshi, Koki

    2002-09-01

    Two strains of obligately piezophilic bacteria were isolated from sediment collected from the deepest cold-seep environment with chemosynthesis-based animal communities within the Japan Trench, at a depth of 7434 m. The isolated strains, JT7301 and JT7304T, were closely affiliated with members of the genus Psychromonas on the basis of 16S rDNA sequence analysis. Hybridization values for DNA-DNA relatedness between these strains and the Psychromonas antarctica reference strain were significantly lower than that accepted as the phylogenetic definition of a species. The optimal temperature and pressure for growth of the isolates were 10 degrees C and 50 MPa and they produced both eicosapentaenoic acid (C20:5omega3) and docosahexaenoic acid (C22:6) in the membrane layer. Based on the taxonomic differences observed, the isolated strains appear to represent a novel obligately piezophilic Psychromonas species. The name Psychromonas kaikoae sp. nov. (type strain JT7304T = JCM 11054T = ATCC BAA-363T) is proposed. This is the first proposed obligately piezophilic species of the genus Psychromonas.

  20. Triangulation Scale Error as a Possible Cause for Overlooking Seismic Potential Along the Japan Trench

    NASA Astrophysics Data System (ADS)

    Sagiya, T.; Matta, N.; Meneses, A.; Nomura, S.; Suzuki, S.; Ohta, Y.

    2012-12-01

    The 2011 M9.0 Tohoku earthquake was not anticipated before its occurrence. One of the reasons of this overlook was that crustal strain during the 20th century did not show significant strain accumulation associated with the subduction of the Pacific plate. On the other hand, GPS data after 1990's clearly showed E-W shortening of the Tohoku area with an average strain rate over 0.1 ppm/year. However, since no strain accumulation was observed for a longer term, it was expected that the short-term strain be released through aseismic processes like a slow slip or afterslip. The length scale of the triangulation network was determined by baseline surveys. 15 baselines with a length from 3 to 10 km were distributed over the national triangulation network and measured with a steel baseline rod. We found that one baseline, the Shionohara baseline (5172m) located in Yamagata prefecture of the Tohoku district, was measured in 1894, and the M7.0 Shonai earthquake occurred just after this survey. The Shonai earthquake was considered as a thrust type earthquake under E-W compression, and its hypocenter was located about 30 km west of the Shionohara baseline. Fault model calculation shows that the baseline could be coseismically elongated by as much as 10 ppm, causing a scale error for the triangulation network. The Shionohara baseline was the only baseline in the middle Tohoku area. So the triangulation network in the surrounding area might be isotropically downscaled. In addition to the absence of E-W contraction in the strain distribution for 100 years, significant N-S extension in the same area supports the existence of the scale bias.

  1. Some aspects of the tectonics of subduction zones

    NASA Astrophysics Data System (ADS)

    Aubouin, Jean

    1989-03-01

    The main structures of a subduction zone are as follows. (1) On the outer wall: faults, formed either by reactivation of the structural grain of the oceanic plate, when the latter is slightly oblique to the trench, or by a new fault network parallel to the trench, or both. The width of the faulted zone is about 50 miles. (2) On the inner wall: either an accretionary prism or an extensional fault network, or both; collapsed structures and slumps are often associated, sometimes creating confusion with the accretionary structures. (3) The overall structure of the trench itself is determined by the shape of the edge of the continental crust or of the island arc. Its detailed structure, however, is related to the oceanic plate, namely when the structural grain of the latter is slightly oblique to the trench, which then takes an "en echelon" form. Collapsed units can fill up the trench which is, in that case, restricted to an irregular narrow depression; the tectonic framework of the trench can be buried under a sedimentary blanket when the sedimentation rate is high and the trench bottom is a large, flat area. Two extreme types of active margins can be distinguished: convergent compressive margins, when the accretionary mechanism is strongly active; and convergent extensional margins where the accretionary mechanism is absent or only weakly active. The status of a given margin between these two extreme types is related to the convergence rate of the plates, the dip of the subduction zone, the sedimentation activity and the presence of a continental obstacle, because oceanic seamounts and aseismic ridges are easily subducted. Examples are taken from the Barbados, Middle America, Peru, Kuril, Japan, Nankai, Marianna, Manila, New Hebredes and Tonga trenches.

  2. Development of Real-time Tsunami Inundation Forecast Using Ocean Bottom Tsunami Networks along the Japan Trench

    NASA Astrophysics Data System (ADS)

    Aoi, S.; Yamamoto, N.; Suzuki, W.; Hirata, K.; Nakamura, H.; Kunugi, T.; Kubo, T.; Maeda, T.

    2015-12-01

    In the 2011 Tohoku earthquake, in which huge tsunami claimed a great deal of lives, the initial tsunami forecast based on hypocenter information estimated using seismic data on land were greatly underestimated. From this lesson, NIED is now constructing S-net (Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench) which consists of 150 ocean bottom observatories with seismometers and pressure gauges (tsunamimeters) linked by fiber optic cables. To take full advantage of S-net, we develop a new methodology of real-time tsunami inundation forecast using ocean bottom observation data and construct a prototype system that implements the developed forecasting method for the Pacific coast of Chiba prefecture (Sotobo area). We employ a database-based approach because inundation is a strongly non-linear phenomenon and its calculation costs are rather heavy. We prepare tsunami scenario bank in advance, by constructing the possible tsunami sources, and calculating the tsunami waveforms at S-net stations, coastal tsunami heights and tsunami inundation on land. To calculate the inundation for target Sotobo area, we construct the 10-m-mesh precise elevation model with coastal structures. Based on the sensitivities analyses, we construct the tsunami scenario bank that efficiently covers possible tsunami scenarios affecting the Sotobo area. A real-time forecast is carried out by selecting several possible scenarios which can well explain real-time tsunami data observed at S-net from tsunami scenario bank. An advantage of our method is that tsunami inundations are estimated directly from the actual tsunami data without any source information, which may have large estimation errors. In addition to the forecast system, we develop Web services, APIs, and smartphone applications and brush them up through social experiments to provide the real-time tsunami observation and forecast information in easy way to understand toward urging people to evacuate.

  3. Non-elastic Plate Weakening at Tonga, Costa Rica and Japanese Subduction Zones

    NASA Astrophysics Data System (ADS)

    Arredondo, K.; Billen, M. I.

    2010-12-01

    Traditionally studies of plate bending in subduction zones have utilized elastic, viscous or elastic-plastic rheologies to model the deformation of subducting plates, yet they are based on averaged plate properties and do not take into account variations in plate strength. Direct measurements of plate strength at subduction zones could permit more detailed models of how plates deform during subduction and may allow differentiation between the elastic and viscous or plastic rheologies. Additionally, weakening of the subducting plate is important for understanding the degree of coupling of the surface plate to the negative buoyancy of descending slabs. To obtain quantitative measurements of changes in plate strength along profiles parallel to the trench, we use analysis of the gravity-topography admittance in three subduction zones: Tonga, Costa Rica and Japan. We show that the plate flexural rigidity decreases near and inside the trench of the Tonga and Japan subduction zones, in agreement with previous results for the Kermadec subduction zone (1). Near the trench the flexural rigidity values are consistently smaller than those predicted by an elastic rheology and the plate age (2). This degree of weakening, by up to 3 orders magnitude, suggests that the plate does not act elastically as it is subducted, possibly due to lithospheric-scale weakening by extensional faulting and plastic yielding at depth. In contrast lithospheric-scale weakening in the Costa Rica subduction zone is less clear. This may be due to the younger age of the subducting plate and the small age difference between the seamounts and surrounding plate, which limits the sensitivity of the gravity field to changes in the non-isostatic support of topographic feature. These results suggest that this technique is only applicable to older plates with large seamounts that are appreciably younger than the subducting plate. Comparison of the flexural rigidity results to the tectonic characteristics of all

  4. Earthquake-induced submarine sliding on the trench-slope basin within the Late Pliocene to Pleistocene Chikura Group, Central Japan

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Suzuki, K.

    2004-12-01

    Fossil example of large-scale sediment mass wasting occurred on the trench-slope-basin was identified. A large-scale chaotic sedimentary body within Late Pliocene to Pleistocene trench-slope cover sediments of the Chikura Group, Central Japan, can be traced E×W over a distance of 5 km. A recently excavated road cutting has exposed a cross-section through the entire chaotic sedimentary body, including its upper and lower contacts with coherent sediments. Evidence of sand intrusions and block rotation within the body indicates that the chaotic nature of the sediments arose from earthquake-induced liquefaction and subsequent submarine sliding (liquefied sediment flow). It is possible that the formation of such a large-scale submarine slide body generated a large tsunami. We will report a detailed description of the occurrence and structural characteristics of this recently exposed outcrop of chaotically mixed sediments.

  5. Earthquake-induced submarine sliding on the trench-slope basin within the Late Pliocene to Pleistocene Chikura Group, Central Japan

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Suzuki, K.

    2007-12-01

    Fossil example of large-scale sediment mass wasting occurred on the trench-slope-basin was identified. A large-scale chaotic sedimentary body within Late Pliocene to Pleistocene trench-slope cover sediments of the Chikura Group, Central Japan, can be traced E-W over a distance of 5 km. A recently excavated road cutting has exposed a cross-section through the entire chaotic sedimentary body, including its upper and lower contacts with coherent sediments. Evidence of sand intrusions and block rotation within the body indicates that the chaotic nature of the sediments arose from earthquake-induced liquefaction and subsequent submarine sliding (liquefied sediment flow). It is possible that the formation of such a large-scale submarine slide body generated a large tsunami. We will report a detailed description of the occurrence and structural characteristics of this recently exposed outcrop of chaotically mixed sediments.

  6. Internal structure of the shallow Japan Trench décollement: insights into the long-term evolution of the margin and coseismic slip processes

    NASA Astrophysics Data System (ADS)

    Kirkpatrick, J. D.; Ujiie, K.; Mishima, T.; Chester, F. M.; Rowe, C. D.; Regalla, C.; Remitti, F.; Moore, J. C.; Toy, V. G.; Kameda, J.; Bose, S.; Wolfson-Schwehr, M.

    2013-12-01

    The 2011 MW 9.0 Tohoku-oki earthquake ruptured to the Japan Trench, with largest coseismic slip occurring on the shallow part of the décollement. To better understand the controls on rupture propagation and slip, the structure and composition of the décollement near the trench were investigated during Integrated Ocean Drilling Project Expedition 343 (the JFAST project). The plate boundary décollement is localized upon a ≤4.86 m thick layer of smectite-rich pelagic clay. Stratigraphic discontinuities at the base of the hangingwall, top of the footwall and surrounding a horse of intra-décollement mudstone suggest that the fault contains multiple slip surfaces, although most of these were not recovered. The décollement damage zone is <10 m wide in both the overlying frontal prism and down-going Pacific plate showing that long-term displacement on the plate boundary fault near the Japan Trench is extremely localized and in turn suggesting the fault is weak relative to the bounding sediments. A pervasive composite foliation, or scaly fabric, defined by striated, lustrous surfaces enclosing lenses of less fissile phacoids is distributed throughout the décollement clay. The asymmetry of phacoids is consistent with top-to-the-trench shear sense. Several narrow, planar discontinuities crosscut the scaly fabric, truncating or disrupting the foliation and in one case juxtaposing domains of the clay with different foliation orientation and intensity, indicating relative displacement. The scaly fabric is indicative of distributed shear across the recovered interval (~1 m), and may represent deformation at interseismic strain rates. The sharp discontinuities within the décollement clay, however, resulted from slip localization. They are similar to structures produced in friction experiments conducted at coseismic slip rates suggesting they may record earthquake deformation.

  7. On the initiation of subduction

    NASA Technical Reports Server (NTRS)

    Mueller, Steve; Phillips, Roger J.

    1991-01-01

    Estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation. Three environments proposed as preferential sites of incipient subduction are investigated: passive continental margins, transform faults/fracture zones, and extinct ridges. None of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses. Subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins. The attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates. This is the only tectonic force sufficient to trigger the nucleation of a new subduction zone. The ubiquitous distribution of transform faults and fracture zones, combined with the common proximity of these features to mature subduction complexes, suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere.

  8. On the initiation of subduction

    SciTech Connect

    Mueller, S.; Phillips, R.J. )

    1991-01-10

    Estimates of shear resistance associated with lithospheric thrusting and convergence represent lower bounds on the force necessary to promote trench formation. Three environments proposed as preferential sites of incipient subduction are investigated: passive continental margins, transform faults/fracture zones, and extinct ridges. None of these are predicted to convert into subduction zones simply by the accumulation of local gravitational stresses. Subduction cannot initiate through the foundering of dense oceanic lithosphere immediately adjacent to passive continental margins. The attempted subduction of buoyant material at a mature trench can result in large compressional forces in both subducting and overriding plates. This is the only tectonic force sufficient to trigger the nucleation of a new subduction zone. The ubiquitous distribution of transform faults and fracture zones, combined with the common proximity of these features to mature subduction complexes, suggests that they may represent the most likely sites of trench formation if they are even marginally weaker than normal oceanic lithosphere.

  9. Across-arc variations of isotope and trace element compositions from Quaternary basaltic volcanic rocks in northeastern Japan: Implications for interaction between subducted oceanic slab and mantle wedge

    NASA Astrophysics Data System (ADS)

    Shibata, Tomoyuki; Nakamura, Eizo

    1997-04-01

    Isotopic compositions of Pb, Sr, and Nd and concentrations of trace elements were determined for Quaternary island arc basaltic rocks from northeastern Japan. Sr and Pb isotopic ratios decrease, and Nd isotopic ratios increase from the volcanic front toward the back arc. The isotopic compositions nearest the back arc side are nearly identical to those of mid-ocean ridge basalt (MORB). The high field strength elements and heavy rare earth elements show homogeneous and MORB-like characteristics. These observations indicate that the mantle wedge beneath northeastern Japan originally had a MORB-type mantle composition that was homogeneous across the arc. Pb isotope compositions show a mixing relationship between mantle wedge and oceanic sediments reflecting the introduction of subduction component into the mantle wedge, Across-arc isotopic variations were caused by interaction between MORB-type mantle wedge and the subducting slab, and the amount of subduction component correlates with the depth to the slab. The isotopic compositions of subduction component are expressed by bulk mixing of 15 wt % of oceanic sediment and 85 wt % of altered MORB. Inversion analyses of isotopic compositions using two-component mixing relationships show that the Sr/Nd and Pb/Nd ratios in subduction component decrease with increasing depth to the slab, while the Sr/Pb ratio is nearly constant. These changes can be explained only by a preferential discharge of the elements into the wedge mantle associated with continuous dehydration of the subducting slab. The present study further demonstrates that a very wide range of isotopic and elemental compositions in island arc magmas is a consequence of the interaction between subducting slab and mantle wedge without the involvement of an oceanic island basalts component, and the slab can carry water and supply a subduction component as a fluid to the overlying mantle wedge to depths exceeding 150 km.

  10. Slow slip and aseismic deformation episodes associated with the subducting Pacific plate offshore Japan, revealed by changes in seismicity (Invited)

    NASA Astrophysics Data System (ADS)

    Marsan, D.; Reverso, T.; Helmstetter, A.; Enescu, B.

    2013-12-01

    Aseismic phenomena, including slow slip, can alter the surrounding seismicity. We here investigate how seismicity can be used in order to reveal episodes of aseismic deformation: transient anomalous increases of seismicity activity are searched for, as signatures of episodic aseismic deformation in a fault zone. An objective method is proposed, that accounts for both earthquake interactions and transient loading. Applying it to the 1990 - 2011 (pre-Tohoku) seismicity of the Japan subduction zone, we find several significant instances of aseismic transients. Small scale and short duration transients are favored updip of the subducting plate.Large scale transients are mostly observed off-shore Ibaraki prefecture, in a partly decoupled zone that extends downdip. The four most intense of such transients have occurred periodically every 5.9 years, and are likely due to slow slip episodes. Other aseismic phenomena, including possible fluid intrusion in the outer-rise, are also detected. Finally, the seismicity in January and February 2011, close to the epicenter of the mega-thrust Tohoku earthquake, is found to be due to aseismic loading, confirming previous studies, although this transient is only one among others, and is not the most intense nor the most significant for the 21 year-long period studied here.

  11. Slow slip and aseismic deformation episodes associated with the subducting Pacific plate offshore Japan, revealed by changes in seismicity

    NASA Astrophysics Data System (ADS)

    Marsan, D.; Reverso, T.; Helmstetter, A.; Enescu, B.

    2013-09-01

    Aseismic phenomena, including slow slip, can alter the surrounding seismicity. We here investigate how seismicity can be used in order to reveal episodes of aseismic deformation. An objective method is proposed that accounts for both earthquake interactions and transient loading. Applying it to the 1990-2011 (pre-Tohoku) seismicity of the Japan subduction zone, we find several significant instances of aseismic transients. Small-scale and short-duration transients are favored updip of the subducting plate. Large-scale transients are mostly observed offshore Ibaraki prefecture, in a partly decoupled zone that extends downdip. The four most intense of such transients have occurred periodically every 5.9years and are likely due to slow-slip episodes. Other aseismic phenomena, including possible fluid intrusion in the outer rise, are also detected. Finally, the seismicity in January and February 2011, close to the epicenter of the megathrust Tohoku earthquake, is found to be due to aseismic loading, confirming previous studies, although this transient is only one among others and is not the most intense nor the most significant for the 21year long period studied here.

  12. Determination of fault plane orientations from rupture directivity of intermediate and deep earthquakes in the northeastern Japan subduction zone

    NASA Astrophysics Data System (ADS)

    Osburg, Tim

    Earthquakes occur at intermediate (≥ 70 km) and deep (≥ 300 km) depths within the Earth. Since their discovery, the cause of intermediate and deep-focus earthquakes has remained a fundamental problem in seismology. While several physical mechanisms have been theorized to explain the occurrence of deep earthquakes, the mechanism may be constrained by determining the fault plane orientation. I used rupture directivity of 52 events in the northeastern Japan subduction zone to determine each event's fault plane orientation. With adequate station coverage, in both azimuth and distance, rupture can be identified along a single nodal plane signifying the fault plane. P-wave duration is shortest in the direction of rupture propagation and greatest in the opposite direction. Measuring the differential rupture duration between seismic stations allows for the determination of rupture direction, rupture velocity relative to the background seismic velocity, and the fault plane for each event. Rupture directivity is determined for a total of 20 events. Results indicate that rupture at intermediate and deep focus depths occur along the subhorizontal nodal plane. While fault plane orientation is apparently uniform in the subducting slab, rupture direction appears scattered. These results suggest multiple mechanisms are responsible for the orientation and azimuthal direction of rupture.

  13. Three-dimensional numerical modeling of thermal regime and slab dehydration beneath Kanto and Tohoku, Japan

    NASA Astrophysics Data System (ADS)

    Ji, Yingfeng; Yoshioka, Shoichi; Manea, Vlad Constantin; Manea, Marina; Matsumoto, Takumi

    2017-01-01

    Although the thermal regime of the interface between two overlapping subducting plates, such as those beneath Kanto, Japan, is thought to play an important role in affecting the distribution of interplate and intraslab earthquakes, the estimation of the thermal regime remains challenging to date. We constructed a three-dimensional (3-D) thermal convection model to simulate the subduction of the Pacific plate along the Japan Trench and Izu-Bonin Trench, including the subduction of the Philippine Sea beneath Kanto and investigated the slab thermal regime and slab water contents in this complex tectonic setting. Based on the subduction parameters tested in generic models with two flat oceanic plates, a faster or thicker plate subducting in a more trench-normal direction produces a colder slab thermal regime. The interplate temperature of the cold anomaly beneath offshore Kanto was approximately 300°C colder than that beneath offshore Tohoku at a same depth of 40 km and approximately 600°C colder at a depth of 70 km. The convergence between the two subducting plates produces an asymmetric thermal structure in the slab contact zone beneath Kanto, which is characterized by clustered seismicity in the colder southwestern half. The thermo-dehydration state of the mid-ocean ridge basalt near the upper surface of the subducted Pacific plate controls the interplate seismicity beneath the Kanto-Tohoku region according to the spatial concurrence of the thermo-dehydration and seismicity along the megathrust fault zone of the subducted Pacific plate.

  14. Micro-seismicity survey of a seismic gap caused by the subduction of the Louisville seamount chain in the Tonga trench, 25°30’S to 28°S

    NASA Astrophysics Data System (ADS)

    Grevemeyer, I.; Dannowski, A.; Flueh, E. R.; Moeller, S.

    2009-12-01

    The distribution of teleseismically recorded earthquakes in the Kermadec-Tonga subduction zone reveals a major seismic gap centered roughly at 26°S. The gap parallels the trench axis and stretches for approximately 250 km. The seismic gap coincides with the area, where the Louisville hotspot chain enters the Tonga trench. Subducting seamounts may therefore control seismic coupling and hence define seismogenic asperities in subduction zones. Louisville seamounts rise 3 to 4 km above the regional seafloor. Seamounts and guyots are between 10 to 40 km in diameter and hence smaller than the width of the seismic gap, suggesting that other features - like the hotspot swell, crustal underplating or the flexural may contribute or control seismic locking. We deployed a network of 21 ocean-bottom-seismometers (OBS) and 2 ocean-bottom-hydrophones (OBH), including 9 broadband OBS with Guralp CMG-40T sensors. The network covered the southern portion of the seismic gap and the transition zone to “normal” seismic behavior. The ocean bottom seismic stations provided data from July 9, 2007 to December 31, 2007. For the earthquake location procedure we derived a minimum 1-D velocity model from active seismic wide-angle profiling in the uppermost 6 km of the fore-arc crust and earthquake arrival time data at greater depths. In total 1523 local and regional earthquake could be located. Within the network, 383 events have been recorded with a gap of <230 degree at 4 stations, and 160 events with a gap of <180 degree at 6 stations. It is interesting to note that local earthquakes (M < 4) did not mimic the teleseismic gap. Overall, seismicity seems to be randomly distributed within the network. Furthermore, in contrast to other subduction zones, where earthquakes occur predominantly along the subduction megathrust fault, we observed only a few events along the plate boundary. Thus, most local earthquakes occur in the uppermost mantle, perhaps caused by extension related to the slab

  15. Long-Term Seismic Quiescences and Great Earthquakes in and Around the Japan Subduction Zone Between 1975 and 2012

    NASA Astrophysics Data System (ADS)

    Katsumata, Kei

    2016-10-01

    An earthquake catalog created by the International Seismological Center (ISC) was analyzed, including 3898 earthquakes located in and around Japan between January 1964 and June 2012 shallower than 60 km with the body wave magnitude of 5.0 or larger. Clustered events such as earthquake swarms and aftershocks were removed from the ISC catalog by using a stochastic declustering method based on Epidemic-Type Aftershock Sequence (ETAS) model. A detailed analysis of the earthquake catalog using a simple scanning technique (ZMAP) shows that the long-term seismic quiescences lasting more than 9 years were recognized ten times along the subduction zone in and around Japan. The three seismic quiescences among them were followed by three great earthquakes: the 1994 Hokkaido-toho-oki earthquake (M w 8.3), the 2003 Tokachi-oki earthquake (M w 8.3), and the 2011 Tohoku earthquake (M w 9.0). The remaining seven seismic quiescences were followed by no earthquake with the seismic moment M 0 ≥ 3.0 × 1021 Nm (M w 8.25), which are candidates of the false alarm. The 2006 Kurile Islands earthquake (M w 8.3) was not preceded by the significant seismic quiescence, which is a case of the surprise occurrence. As a result, when limited to earthquakes with the seismic moment of M 0 ≥ 3.0 × 1021 Nm, four earthquakes occurred between 1976 and 2012 in and around Japan, and three of them were preceded by the long-term seismic quiescence lasting more than 9 years.

  16. On the Possibility of Slip-to-trench Rupture in Cascadia Megathrust Earthquakes

    NASA Astrophysics Data System (ADS)

    Gao, D.; Wang, K.; Riedel, M.; Sun, T.; Insua, T. L.; Goldfinger, C.; Priest, G. R.

    2015-12-01

    Tsunamis may be generated by subduction zone earthquakes in four ways: (1) elastic seafloor deformation of the upper plate induced by a buried rupture, (2) enhanced seafloor uplift due to splay faulting, (3) seaward motion of the sloping seafloor due to slip-to-trench rupture, and (4) activation of multiple thrusts and back-thrusts due to sudden shortening of the frontal accretionary prism. Cascadia megathrust rupture models previously developed for tsunami hazard assessment include the first two scenarios. The 2011 Mw 9.0 Tohoku-oki earthquake which exhibited dramatic coseismic slip at the trench raised a new question. Can the shallowest portion of the Cascadia megathrust also slip to trench in great earthquakes as in the Tohoku-oki earthquake or would it normally resist coseimic rupture but creep aseismically after the earthquake as in the 2005 Mw 8.7 Nias earthquake? We reanalyzed seismic images from marine multichannel seismic surveys conducted in 1985 and 1989 with a new focus on the accretionary wedge deformation front. The incoming plate at Cascadia is blanketed by ~3km sediment near the deformation front. Off Vancouver Island, deformation style varies along the subduction margin. In a southern portion there are multiple thrusts dipping landward. Half-way north the vergence changes to dominantly back-thrusting. Farther north, in the Explorer segment, both seaward and landward vergent thrusts are present. This is in sharp contrast to the sediment-starved Japan trench where one continuous decollement extends all the way to the trench, a structure style that facilitates slip-to-trench rupture. Given the complex structure at Cascadia's deformation front, slip-to-trench rupture appears to be much less likely. Scenarios (1) and (4) may be the more likely source scenarios for Cascadia. However, for tsunami hazard assessment, all the rupture scenarios should be considered even for the low probability slip-to-trench rupture scenario involving frontal thrusts with

  17. Global correlations between maximum magnitudes of subduction zone interface thrust earthquakes and physical parameters of subduction zones

    NASA Astrophysics Data System (ADS)

    Schellart, W. P.; Rawlinson, N.

    2013-12-01

    The maximum earthquake magnitude recorded for subduction zone plate boundaries varies considerably on Earth, with some subduction zone segments producing giant subduction zone thrust earthquakes (e.g. Chile, Alaska, Sumatra-Andaman, Japan) and others producing relatively small earthquakes (e.g. Mariana, Scotia). Here we show how such variability might depend on various subduction zone parameters. We present 24 physical parameters that characterize these subduction 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 subduction zone segments in the period 1900-June 2012. The investigations were done for one dataset using a geological subduction 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 subduction segments with MW > 8.5 and the observed ranges for all subduction segments gives more useful insight into the spatial distribution of giant subduction thrust earthquakes. For segments with MW > 8.5 distinct (narrow) ranges are observed for several parameters, most notably the trench-normal overriding plate deformation rate (vOPD⊥, i.e. the relative velocity between forearc and stable far-field backarc), trench-normal absolute trench rollback velocity (vT⊥), subduction partitioning ratio (vSP⊥/vS⊥, the fraction of the subduction velocity that is accommodated by subducting plate motion), subduction thrust dip angle (δST), subduction thrust curvature (CST), and trench curvature angle (

  18. Seismic interferometry imaging of subducting Philippine Sea plate and crustal structure in Tokai region, central Japan using natural earthquakes

    NASA Astrophysics Data System (ADS)

    Totani, M.; Watanabe, T.; Yamaoka, K.; Kato, A.; Iidaka, T.; Ikuta, R.; Tsumura, N.; Okubo, M.; Suzuki, S.

    2013-12-01

    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 Japan. 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 subducting 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

  19. Three-dimensional numerical modeling of temperature and mantle flow fields associated with subduction of the Philippine Sea plate, southwest Japan

    NASA Astrophysics Data System (ADS)

    Ji, Yingfeng; Yoshioka, Shoichi; Matsumoto, Takumi

    2016-06-01

    We investigated temperature and mantle flow distributions associated with subduction of the Philippine Sea (PHS) plate beneath southwest Japan, by constructing a three-dimensional parallelepiped model incorporating a past clockwise rotation, the bathymetry of the Philippine Sea plate, and distribution of the subducting velocity within its slab. The geometry of the subducting plate was inferred from contemporary seismic studies and was used as a slab guide integrated with historical plate rotation into the 3-D simulation. Using the model, we estimated a realistic and high-resolution temperature field on the subduction plate interface, which was constrained by a large number of heat flow data, and attempted to clarify its relationship with occurrences of megathrust earthquakes, long-term slow slip events (L-SSEs), and nonvolcanic low-frequency earthquakes (LFEs). Results showed that the oblique subduction coupled with the 3-D geometry of subducting PHS plate was a key factor affecting the interplate and intraplate temperature distributions, leading to a cold anomaly in the plate interface beneath western Shikoku, the Bungo Channel, and the Kii Peninsula. Temperatures in the slab core in these regions at a depth near the continental Moho were nearly 200°C lower than that in eastern Shikoku, indicating a high thermal lateral heterogeneity within the subducting plate. The geothermal control of the LFEs beneath western Shikoku was estimated to be within a range from 400 to 700°C, and the interplate temperature for the L-SSEs with a slip larger than 15 cm beneath the Bungo Channel was estimated to be approximately 350-500°C. A large horizontal temperature gradient of 2.5 ~ °C/km was present where the LFEs occurred repeatedly. The steep temperature change was likely to be related to the metamorphic phase transformation from lawsonite or blueschist to amphibolite of hydrous minerals of the mid-ocean ridge basalt of the subducting PHS plate.

  20. The geological and petrological studies of the subduction boundaries and suggestion for the geological future work in Japan - How to avoid ultra-mega-earthquakes -

    NASA Astrophysics Data System (ADS)

    Ishii, T.

    2015-12-01

    The Pacific plate is surrounded by circum-Pacific active margin, along which volcanic and seismic activities are very high. Ultra-Mega-Earthquakes (=UMEs, M>9.0) are occasionally observed along the margin, where sedimentary rocks of subducting slaves contact with the accreted sedimentary rocks of subducted slaves. But, those UME have never been occured along western Pacific islandarc-trench system including Izu-Ogasawara (=Bonin)-Mariana-Yap-Palau-Philippine-Tonga-Kermadec Trenches. I assume that the geological and petrological characteristics of the subduction boundaries are very important to understand those different seismic activities. Along the above mentioned trench inner wall, especially in the southern Mariana, mantle peridotites are widely distributed. Subducting slave contacts directly with the olivine dominant mantle peridotites of subducted slave, serpentinite layer can be deposited easily under hydrous oceanic sub-bottom environment and very slippery subduction boundaries are left along the subduction zone.On the other hand, those geological evidences give us some ideas on how to avoid UMEs in the Japanese Islands along Japan Trench and Nankai Trough in future. We will be able to change artificially from normal subduction boundaries with asperity zone into slippery subduction boundaries with serpentine layer, by means of serpentine mud injection toward the subduction boundaries interior by combining the following improved drilling technologies A and B. (A) Deep Sea Drilling Vessel CHIKYU has a drilling ability to reach subduction boundary with asperity zone in the Nankai Trough. (B) Advanced drilling technology in the shale gas industry is tremendous, that is, after one vertical deep drilling, horizontal drilling towards several direction are performed, then shale gas is collected by hydraulic fracturing method. I hope that, after several generations, our posterity will be able to avoid UMEs by continuous serpentine mud injection.

  1. A global view of shear wave splitting and mantle flow in subduction systems

    NASA Astrophysics Data System (ADS)

    Long, Maureen; Silver, Paul; Hanna, Jenny; Wirth, Erin; Kincaid, Chris; Montesi, Laurent

    2010-05-01

    The character of the mantle flow field in subduction zone regions remains poorly understood, despite its importance for our understanding of subduction dynamics. Observations of seismic anisotropy, which manifests itself in shear wave splitting, can shed light on the geometry of mantle flow in subduction zones, but placing constraints on anisotropy in various parts of the subduction system (including the overriding plate, the mantle wedge, the subducting slab, and the sub-slab mantle) remains challenging from an observational point of view. In order to identify dynamic processes that make first-order contributions to the pattern of mantle flow in subduction zones, we analyze a global compilation of shear wave splitting measurements for a variety of ray paths, including SK(K)S and teleseismic S phases as well as local S and source-side splitting from slab earthquakes. Key challenges associated with assembling such a compilation include correctly assessing and accounting for any dependence of local S splitting parameters on frequency and correctly characterizing any contribution to SKS splitting measurements from anisotropy within the subducting slab that is unrelated to active mantle flow. We present local case studies from the Japan and Izu-Bonin-Marianas subduction zones that explore frequency-dependent splitting due to heterogeneous anisotropy in the mantle wedge and that use a variety of raypath combinations to isolate the contribution from anisotropy within the slab. Keeping these results in mind, we have compiled shear wave splitting measurements from subduction zones globally from the literature and from our own work to produce estimates of average shear wave splitting parameters - and their spatial variation - for the mantle wedge and the sub-wedge region for individual subduction segments. These estimates are then compared to other parameters that describe subduction. The sub-wedge splitting signal is relatively simple and is dominated by trench

  2. Modeling the effects of 3-D slab geometry and oblique subduction on subduction zone thermal structure

    NASA Astrophysics Data System (ADS)

    Wada, I.; Wang, K.; He, J.

    2013-12-01

    In this study, we revisit the effects of along-strike variation in slab geometry and oblique subduction on subduction zone thermal structures. Along-strike variations in slab dip cause changes in the descending rate of the slab and generate trench-parallel pressure gradients that drive trench-parallel mantle flow (e.g., Kneller and van Keken, 2007). Oblique subduction also drives trench-parallel mantle flow. In this study, we use a finite element code PGCtherm3D and examine a range of generic subduction 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 Japan, 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 subducting slabs in the forearc and arc regions are well delineated at these three subduction zones. Further, relatively large compilations of surface heat flow data at these subduction zones make them excellent candidates for this study. At NE Japan, 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 subduction thrust earthquake for the purpose of disaster prevention. Temperature influences the slip behavior of subduction 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 subduction thrust earthquakes, the thermal structure is affected strongly by the pattern of mantle wedge flow. This flow is driven by viscous coupling between the subducting slab and the overriding mantle, and it brings in hot flowing mantle into the wedge. The trench-ward (up-dip) extent of the slab-mantle coupling is thus a key factor that controls the thermal structure. Slab-mantle decoupling at shallow

  3. Paleostress analysis of a subduction zone megasplay fault - An example from the Nobeoka Thrust, Japan

    NASA Astrophysics Data System (ADS)

    Kawasaki, R.; Hamahashi, M.; Hashimoto, Y.; Otsubo, M.; Yamaguchi, A.; Kitamura, Y.; Kameda, J.; Hamada, Y.; Fukuchi, R.; Kimura, G.

    2014-12-01

    The megasplay faults in subduction zones, branching from plate boundary thrusts, are thought to have a potential to generate earthquakes and accompany tsunamis. Paleo-splay faults exposed on land often preserve clear deformation features of the seismogenic zone and provide information on the fault mechanisms at depth. One of the important information that can be obtained from exhumed faults is paleo-stress field. Here we investigated the Nobeoka Thrust, a fossilized megasplay fault in the Shimanto Belt in Kyushu, which consists of phyllite and sandstone-shale mélanges that have experienced maximum burial temperatures of ~250 -320°C, [Kondo et al., 2005, Tectonics 24.6(2005)]. Kondo et al. (2005) described two orientations of slickensides from the outcrop, suggesting the existence of flexural gentle fold in kilometer scale. The paleo-stress fields preserved in the Nobeoka Thrust is likely to represent multiple stages occurring during burial and uplift, enabling the reconstruction of fault motions along the fault. In this study, we analyzed paleo-stress from slip vectors on small faults observed in the drilled cores of the Nobeoka Thrust obtained from scientific drilling performed in 2011. Small faults are expected to be less-reactivated and their population is much larger than that of large faults, providing high statistical reliability. Multiple inverse method [MIM; Yamaji, 2000, Journal of Structural Geology, 22, 441-452] was applied to the small faults. K-means clustering [Otsubo et al. , 2006, Journal of Structural Geology, 28, 991-997] was applied to stress tensors detected by the MIM for estimating optimal solutions. The results reveal stress solution of four directions existing throughout the drilled range. The stress solution is applied to faults distributed among different lithology, and therefore the paleo-stress is thought to have acted on the whole cores. By drawing the stress polygon from the direction of the stress solution and the stress rate, we

  4. Gravity anomalies, forearc morphology and seismicity in subduction zones

    NASA Astrophysics Data System (ADS)

    Bassett, D.; Watts, A. B.; Das, S.

    2012-12-01

    We apply spectral averaging techniques to isolate and remove the long-wavelength large-amplitude trench-normal topographic and free-air gravity anomaly "high" and "low" associated with subduction zones. The residual grids generated illuminate the short-wavelength structure of the forearc. Systematic analysis of all subduction 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 trench, isolated residual anomalies with amplitudes of up to 2.5 km and 125 mGal are generally interpreted as accreted/subducting 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 Japan and Java appear to have influenced the nucleation and/or propagation of large magnitude earthquakes. Long-wavelength (500 - >1000 km) trench-parallel forearc ridges with residual anomalies of up to 1.5 km and 150 mGal are identified in approximately one-third of the subduction 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 trench-parallel forearc ridges is explained through the identification and tracking of pre-existing structure on the over-riding and subducting plates into the seismogenic portion of the plate boundary. Spatial correlations between regions with well-defined trench-parallel forearc ridges and the occurrence of large magnitude interplate earthquakes, in addition to the uncompensated state of these ridges, suggest links

  5. Acceleration of regional plate subduction beneath Kanto, Japan, after the 2011 Tohoku-oki earthquake

    NASA Astrophysics Data System (ADS)

    Uchida, Naoki; Asano, Youichi; Hasegawa, Akira

    2016-09-01

    Two oceanic plates (the Pacific (PA) and Philippine Sea (PH)) subduct beneath the land plate, and they forms deeper (PH-PA) and shallower (land-PH) plate boundaries beneath Kanto. Remarkably enhanced seismicity was observed in the densely populated area after the 2011 Tohoku-oki earthquake, which cannot simply be explained by the southern expansion of the postseismic slip of the earthquake. We examine interplate repeating earthquakes to constrain the relative plate motion across aseismically slipping faults. The repeater slip rates show creep rates in the deeper and shallower boundaries, respectively, increased to 2.4-6.6 times and 1.3-6.2 times the pre-Tohoku-oki rates. In addition, the repeater slip directions show no change larger than 4° in the deeper boundary. The interplate creep rates and slip directions suggest that regional movements of both the two plates had accelerated. They probably caused the seismicity increase, frequent slow slips on the shallower boundary, and enhanced probability of larger earthquakes.

  6. Multiscale seismic imaging of the Western-Pacific subduction zone

    NASA Astrophysics Data System (ADS)

    Zhao, D.

    2011-12-01

    We used multiscale seismic tomography to determine the detailed 3-D structure of the crust and mantle under the Western-Pacific subduction zone. The subducting Pacific and Philippine Sea (PHS) slabs are imaged clearly from their entering the mantle at the oceanic trenches to their reaching the mantle transition zone and finally to the core-mantle boundary (CMB). High-resolution local tomography of Northeast Japan has imaged the shallow portion of the slab from the Japan Trench down to about 200 km depth under Japan Sea. The 3-D Vp and Vs structures of the forearc region under the Pacific Ocean are constrained by locating suboceanic events precisely with sP depth phases. Strong structural heterogeneity is revealed in the megathrust zone under the forearc region, and there is a good correlation between the heterogeneity and the distribution of large thrust earthquakes including the great 2011 Tohoku-oki earthquake (Mw 9.0). A joint inversion of local and teleseismic data imaged the subducting Pacific slab down to 670 km depth under the Japan Islands and the Japan Sea. The PHS slab is detected down to 500 km depth under SW Japan. A mantle upwelling is found under SW Japan that rises from about 400 km depth right above the Pacific slab up to the PHS slab. Regional and global tomography revealed the Pacific slab that is stagnant in the mantle transition zone under Eastern China. A big mantle wedge (BMW) has formed in the upper mantle above the stagnant slab. Convective circulations in the BMW and deep dehydration of the stagnant slab may have caused the intraplate volcanoes in NE Asia, such as the Changbai and Wudalianchi volcanoes. The active Tengchong volcanism in SW China is caused by a similar process in the BMW above the subducting Burma (or Indian) slab. Global tomography shows pieces of fast anomalies in the middle and lower mantle as well as in the D" layer above the CMB, suggesting that the stagnant slab finally collapses down to the lower mantle and CMB as a

  7. Repeatability of high-speed migration of tremor along the Nankai subduction zone, Japan

    NASA Astrophysics Data System (ADS)

    Kato, A.; Tsuruoka, H.; Nakagawa, S.; Hirata, N.

    2015-12-01

    Tectonic tremors have been considered to be a swarm or superimposed pulses of low-frequency earthquakes (LFEs). To systematically analyze the high-speed migration of tremor [e.g., Shelly et al., 2007], we here focus on an intensive cluster hosting many low-frequency earthquakes located at the western part of Shikoku Island. We relocated ~770 hypocenters of LFEs identified by the JMA, which took place from Jan. 2008 to Dec. 2013, applying double differential relocation algorithm [e.g., Waldhauser and Ellsworth, 2000] to arrival times picked by the JMA and those obtained by waveform cross correlation measurements. The epicentral distributions show a clear alignment parallel to the subduction of the Philippine Sea plate, as like a slip-parallel streaking. Then, we applied a matched-filter technique to continuous seismograms recorded near the source region using relocated template LFEs during 6 years (between Jan. 2008 and Dec. 2013). We newly detected about 60 times the number of template events, which is fairly larger than ones obtained by conventional envelope cross correlation method. Interestingly, we identified many repeated sequences of tremor migrations along the slip-parallel streaking (~350 sequences). Front of each or stacked migration of tremors can be modeled by a parabolic envelope, indicating a diffusion process. The diffusivity of parabolic envelope is estimated to be around 105 m2/s, which is categorized as high-speed migration feature (~100 km/hour). Most of the rapid migrations took place during occurrences of short-term slow slip events (SSEs), and seems to be triggered by ocean and solid Earth tides. The most plausible explanation of the high-speed propagation is a diffusion process of stress pulse concentrated within a cluster of strong brittle patches on the ductile shear zone [Ando et al., 2012]. The viscosity of the ductile shear zone within the streaking is at least one order magnitude smaller than that of the slow-speed migration. This

  8. P and S wave tomography of Japan subduction zone from joint inversions of local and teleseismic travel times and surface-wave data

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Zhao, Dapeng

    2016-03-01

    We determined P and S wave velocity tomography of the Japan subduction zone down to a depth of 700 km by conducting joint inversions of a large number of high-quality arrival-time data of local earthquakes and teleseismic events which are newly collected for this study. We also determined 2-D phase-velocity images of fundamental mode Rayleigh waves at periods of 20-150 s beneath Japan and the surrounding oceanic regions using amplitude and phase data of teleseismic Rayleigh waves. A detailed 3-D S-wave tomography of the study region is obtained by jointly inverting S-wave arrival times of local and teleseismic events and the Rayleigh-wave phase-velocity data. Our inversion results reveal the subducting Pacific and Philippine Sea slabs clearly as dipping high-velocity zones from a 1-D starting velocity model. Prominent low-velocity (low-V) anomalies are revealed in the mantle wedge above the slabs and in the mantle below the Pacific slab. The distinct velocity contrasts between the subducting slabs and the surrounding mantle reflect significant lateral variations in temperature as well as water content and/or the degree of partial melting. The low-V anomalies in the mantle wedge are attributed to slab dehydration and corner flows in the mantle wedge. A sheet-like low-V zone is revealed under the Pacific slab beneath NE Japan, which may reflect hot upwelling from the deeper mantle and subduction of a plume-fed asthenosphere as well. Our present results indicate that joint inversions of different seismic data are very effective and important for obtaining robust tomographic images of the crust and mantle.

  9. Deformation and veining processes on the subduction zone; example from the Cretaceous Shimanto accretionary complex in Japan

    NASA Astrophysics Data System (ADS)

    Tokiwa, T.; Kageyama, N.; Yoshida, H.

    2015-12-01

    In this study, the authors discuss the relationship between deformation and veining stages in the accretionary complex in order to understand the deformation and fluid flow process during the subduction. This study deals with the Miyama Formation in the Cretaceous Shimanto accretionary complex located in the Kii Peninsula of Japan. The deformation can be divided three types with four types of vein. Based on the differences, the process can be divided four stage by their cutting relationship as follow. Stage 1; the deformation (D1) in this stage is characterized by the aspect ratio of the deformed clasts with range from 0.1 to 0.4, and pinch-and-swell structure and budinaged structures of the sandstone are developed. The veins (V1) are recognized only within the sandstone, and the veins are cut by muddy matrix. Stage 2; the deformation (D2) is characterized by the aspect ratio is more than 0.4, and is distributed along the unit boundary. The clasts such as sandstone and chert are strongly sheared, and random fabric is often recognized. The vein (V2) in this stage cut the D1, and the V2 and D2 are cut by each other. Stage 3; outcrop-scale faults (D3) cutting D1 and D2 has been progressed in this stage. The vein (V3) is recognized along D3. Stage 4; the vein (V4) cutting D1 to D3 is developed in this stage. From the above-mentioned occurrence and data shown by previous studies of the Miyama Formation, process of each Stage interpreted as follows; Stage 1 developed underthrusting, Stages 2 and 3 correspond to underplating of subducted sediments. In addition, it is considered that Stage 4 is in later stage of underplating. The main components of the V1 to V3 veins are calcite and/or quartz. On the other hand, the V4 vein consists mainly of siderite and ankerite, and contain an abundance of Fe than the other veins. Morphological feature of V1 and V3 veins also show blocky texture suggesting higher rate growth than fracture opening, and V2 vein indicate syn-taxial growth

  10. Seismic reflection imaging of the Juan de Fuca plate from ridge to trench: New constraints on the distribution of faulting and evolution of the crust prior to subduction

    NASA Astrophysics Data System (ADS)

    Han, Shuoshuo; Carbotte, Suzanne M.; Canales, Juan Pablo; Nedimović, Mladen R.; Carton, Hélène; Gibson, James C.; Horning, Greg W.

    2016-03-01

    We present prestack time-migrated multichannel seismic images along two cross-plate transects from the Juan de Fuca (JdF) Ridge to the Cascadia deformation front (DF) offshore Oregon and Washington from which we characterize crustal structure, distribution and extent of faults across the plate interior as the crust ages and near the DF in response to subduction bending. Within the plate interior, we observe numerous small offset faults in the sediment section beginning 50-70 km from the ridge axis with sparse fault plane reflections confined to the upper crust. Plate bending due to sediment loading and subduction initiates at ~120-150 km and ~65-80 km seaward of the DF, respectively, and is accompanied by increase in sediment fault offsets and enhancement of deeper fault plane reflectivity. Most bend faulting deformation occurs within 40 km from the DF; on the Oregon transect, bright fault plane reflections that extend through the crust and 6-7 km into the mantle are observed. If attributed to serpentinization, ~0.12-0.92 wt % water within the uppermost 6 km of the mantle is estimated. On the Washington transect, bending faults are confined to the sediment section and upper-middle crust. The regional difference in subduction bend-faulting and potential hydration of the JdF plate is inconsistent with the spatial distribution of intermediate-depth intraslab seismicity at Cascadia. A series of distinctive, ridgeward dipping (20°-40°) lower crustal reflections are imaged in ~6-8 Ma crust along both transects and are interpreted as ductile shear zones formed within the ridge's accretionary zone in response to temporal variations in mantle upwelling, possibly associated with previously recognized plate reorganizations at 8.5 Ma and 5.9 Ma.

  11. Paleomagnetic records of core samples of the plate-boundary thrust drilled during the IODP Japan Trench Fast Drilling Project (JFAST)

    NASA Astrophysics Data System (ADS)

    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.

    2013-12-01

    IODP Expedition 343, Japan Trench Fast Drilling Project (JFAST), drilled across the plate-boundary décollement zone near the Japan Trench 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

  12. Three-dimensional Thermal Model of the Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Rosas, J. C.; Pimentel, F. D. C.; Currie, C. A.; He, J.; Harris, R. N.

    2015-12-01

    Along the Mexican section of the Middle America Trench (MAT), the Cocos plate subducts beneath the North American plate. The most important feature of this subduction zone is the flat-slab section below central Mexico, extending approximately 250 km landward from the trench at a depth of 50 km. Further west, the dip changes to 45-50º. This particular geometry has several unique consequences, such as a volcanic arc that is not aligned with the trench and very shallow slab seismicity. For the mantle wedge, the abrupt change in slab geometry could lead to a three-dimensional (3D) mantle wedge flow that departs from the classical 2D subduction-driven corner flow. Evidence of 3D flow in the region comes from seismic anisotropy studies, which show that olivine fast-direction axes have a component that is parallel to the MAT. In other subduction zones, such as Costa Rica-Nicaragua and Japan, 3D flow has been observed to increase temperatures by >50º C relative to corner flow models.For this study, we have created the first 3D finite-element model of the Mexican subduction zone in order to analyze its thermal structure. Our objective is to assess the effects of 3D mantle flow and hydrothermal circulation (HC) in the subducting slab. In this region, low surface heat flow values near the trench indicate that HC may remove heat from the oceanic plate. Our model incorporates the effect of HC through conductivity proxies in the subducting crust and a 2D oceanic geotherm that includes the age variations of the Cocos plate along the MAT. For an isoviscous mantle, our model shows that the slab dip variations induce a flow that departs from 2D corner flow near the transition between the flat-slab and normal-dipping sections. The mantle flows in eastward direction toward the flat slab, and its orientation is consistent with seismic anisotropy studies. The maximum along-margin flow rate is nearly 2 cm/yr, which is >30% of the convergence rate. Temperatures at the location of this

  13. Detailed structure of the Philippine Sea plate subducting along the Nankai Trough, western Japan, inferred from high-frequency seismic wave analysis

    NASA Astrophysics Data System (ADS)

    Furumura, T.; Padhy, S.; Maeda, T.

    2012-12-01

    A detailed structure of the subducting Philippine Sea plate (PHP) along the Nankai trough in western Japan was studied by analyzing waveforms recorded at dense Hi-net stations in Japan. It is well recognized that the waveforms from intraplate earthquakes dominate in high-frequency (f >1 Hz) signals due to the waveguide effect of the subducting slab (Furumura and Kennett, 2005; 2008). This results in distorted pattern of intensity and peak ground acceleration (PGA) above the hypocenter with a substantial elongation of isoseismic contours correlated with the configuration of the isodepth contours of the subducting PHP beneath western Japan. A detailed analysis of the dense Hi-net waveform data from the intermediate-depth PHP event shows that the high-frequency S-wave signals suddenly disappear as the waves propagate the zone away from the Kii Channel to the boundary of Hyogo and Okayama prefectures and large S-to-P conversion occurs before the arrival of S-wave. Such anomalies do not occur for shallow and deep earthquakes occurring outside the PHP. These observations support the recent debate on the complexities of the configuration of the PHP subducting beneath western Japan such as that shown by Shiomi et al. (2008) based on receiver function images and the PHP-split model beneath the Kii channel shown by Ide et al.(2010) based on the analysis of comprehensive geophysical data. In order to explain the observations associated with sudden lateral change in the PHP structure, we conducted finite difference method (FDM) simulations of seismic wave propagation taking the detailed PHP model into account. It is confirmed that high-frequency guided wave energy decouple from waveguide where the shape of the PHP is suddenly deformed, which results in dramatic attenuation of high-frequency signals associating with large S-to-P conversions developed at sharp plate boundary. The present results also support the recently proposed complicated PHP-split model, however, further

  14. Identification and genomic analysis of temperate Pseudomonas bacteriophage PstS-1 from the Japan trench at a depth of 7000 m.

    PubMed

    Yoshida, Mitsuhiro; Yoshida-Takashima, Yukari; Nunoura, Takuro; Takai, Ken

    2015-11-01

    Viruses play important roles in aquatic ecosystems, but deep-sea bacteriophages remain largely unexplored. A temperate bacteriophage (termed vB_PstS-1) was identified from the psychrotolerant gammaproteobacterium Pseudomonas stutzeri 1-1-1b, which was isolated from hadopelagic water (depth of 7000 m) of the Japan Trench in the Northwest Pacific Ocean. The genome size of PstS-1 was 48,666 bp; its genome displayed a 59.8% G + C content and a total of 79 coding sequences were identified in its genome. The PstS-1 phage belongs to the family Siphoviridae, but its genomic sequence and organization are distinct from those of any other well-known Siphoviridae phage. The mosaic genomic structure of PstS-1 suggests the occurrence of genetic exchange between distinct temperate phages in deep-sea Pseudomonas populations. The PstS-1 genome also harbors three distinct sequence regions corresponding to spacers within a single clustered regularly interspaced short palindromic repeat (CRISPR) locus in the rhizosphere-associated diazotrophic P. stutzeri A1501 genome. The extension of these spacers to the soil environment and the presence of many homologs of both the hadal deep-sea phage PstS-1 and terrestrial Pseudomonas phages suggest the early co-evolution of temperate phages and their host genus Pseudomonas prior to the divergence of their habitational and physiological adaptation.

  15. Substrate-specific pressure-dependence of microbial sulfate reduction in deep-sea cold seep sediments of the Japan Trench

    PubMed Central

    Vossmeyer, Antje; Deusner, Christian; Kato, Chiaki; Inagaki, Fumio; Ferdelman, Timothy G.

    2012-01-01

    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 Japan Trench. 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. PMID:22822404

  16. C sub 1 -C sub 8 hydrocarbons in sediments from Guaymas Basin, Gulf of California: Comparison to Peru margin, Japan Trench and California borderlands

    SciTech Connect

    Whelan, J.K.; Tarafa, M.E. ); Simoneit, B.R.T. )

    1988-01-01

    Surface sea floor sediments, hydrothermal vent samples, and Deep Sea Drilling Project sediments (Hole 481 A) from the Guaymas Basin were examined for C{sub 1}-C{sub 8} hydrocarbons. The proportions of various classes of compounds were examined and compared to those from other geographic areas (Peru upwelling region and Japan Trench) to gain insight into the relative importance of thermal generation, migration and biodegradation. Concentrations of C{sub 2}-C{sub 7} hydrocarbons were about 10-10,000 times higher in geothermally warm Guaymas Basin sediments in comparison to the low concentrations (0.1-10 ppb per compound) typical of geothermally cold sea floor and DSDP diatomaceous sediments. Alkene/alkane ratios of 0.1 or greater were typical of both geothermally cold sediments and also of very hydrocarbon-rich Alvin samples recovered from the sea floor. Because little or no alkene was generally detected in buried sediments exposed to geothermal temperatures greater than 30C, it is suggested that the alkenes are produced by biogenic processes. Normal alkanes predominated over cyclic and branched structures in geothermally cooler (<20{degree}C) sediments, with the proportion of cyclic and branched compounds increasing in hotter sediments. Similarities in compositions of branched and cyclic compounds were observed in some pairs of bitumen-rich Guaymas sea floor samples recovered from different areas, suggesting common mechanisms of light hydrocarbon generation and/or migration. 76 refs.

  17. Substrate-specific pressure-dependence of microbial sulfate reduction in deep-sea cold seep sediments of the Japan Trench.

    PubMed

    Vossmeyer, Antje; Deusner, Christian; Kato, Chiaki; Inagaki, Fumio; Ferdelman, Timothy G

    2012-01-01

    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 Japan Trench. 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.

  18. Salty Trench

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image taken by the panoramic camera on the Mars Exploration Rover Spirit shows a trench dug by the rover on its way toward the 'Columbia Hills.' Measurements taken of the soil contained in the trench by Spirit's alpha particle X-ray spectrometer showed the presence of sulfur and magnesium. Concentrations of those two elements varied in parallel at different locations in the trench, suggesting that they may be paired as a magnesium-sulfate salt. One possible explanation for these findings is that water percolated through underground material and dissolved out minerals, then as the water evaporated near the surface, it left concentrated salts behind.

  19. Backarc spreading and mantle wedge flow beneath the Japan Sea: insight from Rayleigh-wave anisotropic tomography

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Zhao, Dapeng

    2016-10-01

    We present the first high-resolution Rayleigh-wave phase-velocity azimuthal anisotropy tomography of the Japan subduction zone at periods of 20-150 s, which is determined using a large number of high-quality amplitude and phase data of teleseismic fundamental-mode Rayleigh waves. The obtained 2-D anisotropic phase-velocity models are then inverted for a 3-D shear-wave velocity azimuthal anisotropy tomography down to a depth of ˜300 km beneath Japan. The subducting Pacific slab is imaged as a dipping high-velocity zone with trench-parallel fast-velocity directions (FVDs) which may indicate the anisotropy arising from the normal faults produced at the outer-rise area near the Japan trench axis, overprinting the slab fossil fabric, whereas the mantle wedge generally exhibits lower velocities with trench-normal FVDs which reflect subduction-driven corner flow and anisotropy. Depth variations of azimuthal anisotropy are revealed in the big mantle wedge beneath the Japan Sea, which may reflect past deformations in the Eurasian lithosphere related to backarc spreading during 21 to 15 Ma and complex current convection in the asthenosphere induced by active subductions of both the Pacific and Philippine Sea plates.

  20. Geometry and lithofacies of coarse-grained injectites and extrudites in a late Pliocene trench-slope basin on the southern Boso Peninsula, Japan

    NASA Astrophysics Data System (ADS)

    Ito, Makoto; Ishimoto, Sakumi; Ito, Kento; Kotake, Nobuhiro

    2016-10-01

    This study investigates the geometry and internal structures of coarse- to very coarse-grained volcanic sandstones and volcanic breccias with many siltstone clasts (interpreted to be sill-like injectites and extrudites) occurring in an upper Pliocene trench-slope basin succession on the southern Boso Peninsula, Japan. The injectites occur in the uppermost Shiramazu Formation, and pinch out laterally into siltstone-dominated deposits of the Mera Formation. Their thicknesses vary from a few centimeters to 2 m. The basal and upper contacts of the injectites with host muddy deposits are sharp and/or erosional, and are locally discordant with the bedding of the host deposits. Siltstone clasts, which were ripped up or ripped down from the host muddy deposits, are commonly incorporated into the injectites, although some siltstone clasts have geological ages older than those of the host deposits. Seven lithofacies have been identified in the injectites based on the internal structures. The combinations of internal structures are different from those of high-density turbidity current deposits and debrites, and suggest that injection was promoted by a combination of turbulent and laminar flow conditions. The extrudites show an overall convex-up geometry and possess lithological features similar to those of the injectites. They have been identified in the Rendaiji Conglomerate Member, which is encased in the Mera Formation, and which rests on the uppermost Shiramazu Formation. The extrudites are characterized by gently undulating waveforms that show upstream migration and climbing stacking patterns similar to the cross-sectional geometry of cyclic steps or upstream-migrating antidunes. The active eruption of solid-liquid mixtures onto the seafloor and sedimentary piles may have subsequently collapsed to produce supercritical high-density gravity currents down the flanks of a neptunian volcano. The injectites and extrudites locally contain Calyptogena shells and shell

  1. Seismicity of the Earth 1900-2007, Japan and Vicinity

    USGS Publications Warehouse

    Rhea, Susan; Tarr, Arthur C.; Hayes, Gavin P.; Villaseñor, Antonio; Benz, Harley

    2010-01-01

    This map shows details of Japan and vicinity not visible in an earlier publication, U.S. Geological Survey Scientific Investigations Map 3064. Japan and its island possessions lie across four major tectonic plates: Pacific plate, North America plate; Eurasia plate; and Philippine Sea plate. The Pacific plate is subducted into the mantle, beneath Hokkaido and northern Honshu, along the eastern margin of the Okhotsk microplate, a proposed subdivision of the North America plate (Bird, 2003). Farther south, the pacific plate is subducted beneath volcanic islands along the eastern margin of the Philippine Sea plate. This 2,200 km-long zone of subduction of the Pacific plate is responsible for the creation of the deep offshore Ogasawara and Japan trenches as well as parallel chains of islands and volcanoes, typical of the Circumpacific island arcs. Similarly, the Philippine Sea plate is itself subducting under the Eurasia plate along a zone, extending from Taiwan to southern Honshu, that comprises the Ryuku Islands and the Nansei-Shonto trench.

  2. Relationship between temperatures and fault slips on the upper surface of the subducting Philippine Sea plate beneath the Kanto district, central Japan

    NASA Astrophysics Data System (ADS)

    Yoshioka, Shoichi; Takagi, Rumi; Matsumoto, Takumi

    2015-05-01

    To elucidate the relationship between interplate temperatures and generation mechanisms for megathrust earthquakes and slow slip events (SSEs) in the Kanto district, central Japan, we performed numerical simulations on the thermal state. For this purpose, we newly developed a 2-D box-type thermal convection model that is able to handle the subduction of two oceanic plates: the young oceanic Philippine Sea (PHS) plate subducts following subduction of the old oceanic Pacific (PAC) plate beneath it. To constrain temperatures on the upper surface of the PHS plate, we used high-density Hi-net heat flow data on land. We found that low heat flow in the Kanto district was caused mostly by subduction of the cold PHS plate. To explain the heat flow distribution in the Kanto district in more detail, we needed to incorporate 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 associated with crustal deformation during the Quaternary on land into the models. The most suitable pore pressure ratio to explain the heat flow data was 0.98. The thermally estimated seismogenic zone corresponded well to the fault planes of the 1923 Taisho Kanto earthquake and the western half of the 1707 Genroku Kanto earthquake. The eastern half of the fault plane of the 1707 Genroku Kanto earthquake could be divided into two areas; the northwestern fault plane corresponded to the thermally estimated seismogenic zone, whereas the relationship between the southeastern fault plane and interplate temperatures was ambiguous. The off-Boso SSEs occurred on the plate interface at temperatures lower than approximately 250 °C, and the slipped region passed through the 150 °C isotherm, corresponding to the clay mineral phase transformation from smectite to illite. This might suggest that the SSEs occurred in relation to a dehydration process.

  3. Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust

    USGS Publications Warehouse

    Von Huene, R.; Scholl, D. W.

    1991-01-01

    At ocean margins where two plates converge, the oceanic plate sinks or is subducted beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The subduction 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 subducting lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment subduction, and terrestrial matter can be removed from the upper plate by processes of subduction erosion. Sediment subduction occurs where sediment remains attached to the subducting oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment subduction 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 subducted beneath the massif of basement or framework rocks forming the landward trench slope. At accreting or type 1 margins, sediment subduction 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% subducts 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 trench floor section is

  4. Hydration of the incoming plate in the Kuril subduction zone

    NASA Astrophysics Data System (ADS)

    Fujie, G.; Kodaira, S.; Yamashita, M.; Sato, T.; Takahashi, T.; Takahashi, N.; Noguchi, N.

    2010-12-01

    Water supplied from the subducting oceanic plate by dehydration is inferred to cause seismicity and magmatism in subduction zones. It is important, therefore, to reveal the distribution of water within the incoming plate for understanding seismic and volcanic activities in subduction zones. In 2009 and 2010, to reveal the detailed seismic structure and hydration process within the incoming plate, we conducted a wide-angle seismic survey in the Kuril subduction zone, where the old Pacific plate formed in the eastern Pacific ridge is subducting from south to north beneath the island arc of Japan. We designed a north-south 500km-long seismic experimental line to be perpendicular to the Kuril trench. The northern end of our line is located at about 30km south of the trench axis and well-developed horst and graben structure is observed around the northern end. We deployed 80 Ocean Bottom Seismometers (OBSs) at intervals of 6km and shot a large tuned airgun array towed by R/V Kairei. In addition, we obtained MCS reflection data using a 444-channel hydrophone streamer (6km long) along the same line. We modelled both P-wave and S-wave velocity structures by the traveltime inversion using refraction, reflection and PS-conversion traveltimes. Our results show that P-wave velocity beneath the well-developed horst and graben structure is about 5% lower than that in the south of outer rise. This is consistent with a previous structure study in the Chili subduction zone that shows the P-wave velocity in the vicinity of the trench axis is lower than that of normal oceanic plate. More notable feature of our results is the regional variations of Vp/Vs. The S-wave velocity, as well as P-wave velocity, gradually decreases toward the trench axis. However Vp/Vs is not uniform; Vp/Vs immediately beneath the sediments is remarkably high beneath the well-developed horst and graben structure, and Vp/Vs decreases with depth (high Vp/Vs is confined to the top of the oceanic plate). Since the

  5. Near-trench slip potential of megaquakes evaluated from fault properties and conditions

    PubMed Central

    Hirono, Tetsuro; Tsuda, Kenichi; Tanikawa, Wataru; Ampuero, Jean-Paul; Shibazaki, Bunichiro; Kinoshita, Masataka; Mori, James J.

    2016-01-01

    Near-trench slip during large megathrust earthquakes (megaquakes) is an important factor in the generation of destructive tsunamis. We proposed a new approach to assessing the near-trench slip potential quantitatively by integrating laboratory-derived properties of fault materials and simulations of fault weakening and rupture propagation. Although the permeability of the sandy Nankai Trough materials are higher than that of the clayey materials from the Japan Trench, dynamic weakening by thermally pressurized fluid is greater at the Nankai Trough owing to higher friction, although initially overpressured fluid at the Nankai Trough restrains the fault weakening. Dynamic rupture simulations reproduced the large slip near the trench observed in the 2011 Tohoku-oki earthquake and predicted the possibility of a large slip of over 30 m for the impending megaquake at the Nankai Trough. Our integrative approach is applicable globally to subduction zones as a novel tool for the prediction of extreme tsunami-producing near-trench slip. PMID:27321861

  6. Near-trench slip potential of megaquakes evaluated from fault properties and conditions.

    PubMed

    Hirono, Tetsuro; Tsuda, Kenichi; Tanikawa, Wataru; Ampuero, Jean-Paul; Shibazaki, Bunichiro; Kinoshita, Masataka; Mori, James J

    2016-06-20

    Near-trench slip during large megathrust earthquakes (megaquakes) is an important factor in the generation of destructive tsunamis. We proposed a new approach to assessing the near-trench slip potential quantitatively by integrating laboratory-derived properties of fault materials and simulations of fault weakening and rupture propagation. Although the permeability of the sandy Nankai Trough materials are higher than that of the clayey materials from the Japan Trench, dynamic weakening by thermally pressurized fluid is greater at the Nankai Trough owing to higher friction, although initially overpressured fluid at the Nankai Trough restrains the fault weakening. Dynamic rupture simulations reproduced the large slip near the trench observed in the 2011 Tohoku-oki earthquake and predicted the possibility of a large slip of over 30 m for the impending megaquake at the Nankai Trough. Our integrative approach is applicable globally to subduction zones as a novel tool for the prediction of extreme tsunami-producing near-trench slip.

  7. Magmatic and metasomatic imprints in a long-lasting subduction zone: Evidence from zircon in rodingite and serpentinite of Kochi, SW Japan

    NASA Astrophysics Data System (ADS)

    Hu, Chao-Nan; Santosh, M.; Yang, Qiong-Yan; Kim, S. W.; Nakagawa, M.; Maruyama, S.

    2017-03-01

    Southwest Japan, as an active convergent margin, is one of the world's natural laboratories to investigate magmatic and metasomatic processes associated with a long-lived subduction zone. Rocks that carry the imprints of mantle metasomatism in this region include serpentinite, jadeitite, omphacitite, albitite, and rodingite. Here we investigate rodingites, serpentinites and pyroxenites from the accretionary complex of Kochi in the Shikoku island from within the Kurosegawa serpentinite mélange. We present petrology, zircon U-Pb geochronology, rare earth element (REE) geochemistry and Lu-Hf isotope data which indicate multiple pulses of magmatism and metasomatism. The zircon grains in these rocks yield major age peaks at 485 Ma and 469 Ma, marking the timing of formation of the protoliths. The wide range of minor age peaks including those at 152 Ma and 104 Ma suggest continuous fluid- and melt-induced mantle metasomatism in an active subduction zone from Cambrian to Paleogene associated with subduction of the Pacific plate. Our data suggest that the serpentinite-rodingite association might belong to various stages of subduction with the 450 Ma marking the initial phase. This is also close to the serpentinite zircon age of ca. 490 Ma. The REE patterns of zircons in all the rocks analyzed in this study show a distinct negative Eu-anomaly, particularly in the case of hydrothermal zircons. However, few zircons show only a slight negative Eu-anomaly suggesting that they might have crystallised from melts with high H2O content generated by partial melting of mantle wedge during the interaction of fluids released by the downgoing slab and the overlying sediments. Although the εHf(t) values of zircons in our samples show wide variation from - 9 to 18, most zircon grains that are younger than 485 Ma are typically characterised by positive εHf(t) values (ranging from 2 to18). This feature indicates that the zircon grains crystallised during serpentinisation and

  8. Dynamic Simulation of the 2011 M9.0 Tohoku Earthquake with Geometric Complexity on a Rate- and State-dependent Subduction Plane

    NASA Astrophysics Data System (ADS)

    Luo, B.; Duan, B.

    2015-12-01

    The Mw 9.0 Tohoku megathrust earthquake on 11 March 2011 is a great surprise to the scientific community due to its unexpected occurrence on the subduction zone of Japan Trench where earthquakes of magnitude ~7 to 8 are expected based on historical records. Slip distribution and kinematic slip history inverted from seismic data, GPS and tsunami recordings reveal two major aspects of this big event: a strong asperity near the hypocenter and large slip near the trench. To investigate physical conditions of these two aspects, we perform dynamic rupture simulations on a shallow-dipping rate- and state-dependent subduction plane with topographic relief. Although existence of a subducted seamount just up-dip of the hypocenter is still an open question, high Vp anomalies [Zhao et al., 2011] and low Vp/Vs anomalies [Yamamoto et al., 2014] there strongly suggest some kind of topographic relief exists there. We explicitly incorporate a subducted seamount on the subduction surface into our models. Our preliminary results show that the subducted seamount play a significant role in dynamic rupture propagation due to the alteration of the stress state around it. We find that a subducted seamount can act as a strong barrier to many earthquakes, but its ultimate failure after some earthquake cycles results in giant earthquakes. Its failure gives rise to large stress drop, resulting in a strong asperity in slip distribution as revealed in kinematic inversions. Our preliminary results also suggest that the rate- and state- friction law plays an important role in rupture propagation of geometrically complex faults. Although rate-strengthening behavior near the trench impedes rupture propagation, an energetic rupture can break such a barrier and manage to reach the trench, resulting in significant uplift at seafloor and hence devastating tsunami to human society.

  9. The reasons why the M9 earthquake in the northeastern Japan subduction zone could not be anticipated and why it really occurred

    NASA Astrophysics Data System (ADS)

    Matsuzawa, T.; Iio, Y.

    2011-12-01

    The M9 Tohoku earthquake on 11 March 2011 had a great impact on the seismologists all over the world. This is because the northeastern Japan subduction zone was one of the most investigated subduction 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 subducting beneath the subduction 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, Japan) (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 Japan. (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

  10. Characterizing Mega-Earthquake Related Tsunami on Subduction Zones without Large Historical Events

    NASA Astrophysics Data System (ADS)

    Williams, C. R.; Lee, R.; Astill, S.; Farahani, R.; Wilson, P. S.; Mohammed, F.

    2014-12-01

    Due to recent large tsunami events (e.g., Chile 2010 and Japan 2011), the insurance industry is very aware of the importance of managing its exposure to tsunami risk. There are currently few tools available to help establish policies for managing and pricing tsunami risk globally. As a starting point and to help address this issue, Risk Management Solutions Inc. (RMS) is developing a global suite of tsunami inundation footprints. This dataset will include both representations of historical events as well as a series of M9 scenarios on subductions zones that have not historical generated mega earthquakes. The latter set is included to address concerns about the completeness of the historical record for mega earthquakes. This concern stems from the fact that the Tohoku Japan earthquake was considerably larger than had been observed in the historical record. Characterizing the source and rupture pattern for the subduction zones without historical events is a poorly constrained process. In many case, the subduction zones can be segmented based on changes in the characteristics of the subducting slab or major ridge systems. For this project, the unit sources from the NOAA propagation database are utilized to leverage the basin wide modeling included in this dataset. The length of the rupture is characterized based on subduction zone segmentation and the slip per unit source can be determined based on the event magnitude (i.e., M9) and moment balancing. As these events have not occurred historically, there is little to constrain the slip distribution. Sensitivity tests on the potential rupture pattern have been undertaken comparing uniform slip to higher shallow slip and tapered slip models. Subduction zones examined include the Makran Trench, the Lesser Antilles and the Hikurangi Trench. The ultimate goal is to create a series of tsunami footprints to help insurers understand their exposures at risk to tsunami inundation around the world.

  11. Marine electromagnetics: A new tool for mapping fluids at subduction zones

    NASA Astrophysics Data System (ADS)

    Key, K.; Naif, S.; Constable, S.; Evans, R. L.

    2013-12-01

    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 subduction 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 subducted, and fluids escaping through the overlying forearc crust. Since water also plays an important role in regulating subduction earthquake processes and frictional behavior along the plate boundary, EM data have the potential to reveal new insights on the causes of large subduction 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 subduction zone, carried out at the Middle America Trench 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 trench 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 trench outer rise and images a continuous zone of low resistivity porous sediments being carried down with the subducting plate to at least 10 km down dip from the trench. Further landward at about 25 km from the trench, a sub-vertical low-resistivity zone extending from the plate boundary

  12. Oceanic Plate Bending Along the Manila Trench

    NASA Astrophysics Data System (ADS)

    Zhang, F.; Lin, J.; Zhan, W.

    2014-12-01

    We quantify along-trench variations in plate flexural bending along the Manila trench in the South China Sea. A 3-D interpreted flexural deformation surface of the subducting South China Sea Plate was obtained by removing from the observed bathymetry the effects of sediment loading, isostatically-compensated topography based on gravity modeling, age-related lithospheric thermal subsidence, and residual short-wavelength features. We analyzed flexural bending of 21 across-trench profile sections along the Manila trench and then calculated five best-fitting tectonic and plate parameters that control the flexural bending for each of the across-trench profile sections. Results of analysis revealed significant along-trench variations: The trench relief of the Manila trench varies from 0.8 to 2.2 km, trench-axis vertical loading (-V0) from -0.4x1012 to 1.21x1012 N/m, and axial bending moment (-M0) from 0.005x1017 to 0.6x1017 N. The effective elastic plate thickness seaward of the Manila outer-rise region (TeM) ranges from 30 to 40 km, while that trench-ward of the outer-rise (Tem) ranges from 11 to 30 km. This corresponds to a reduction in Te of 26-63% for the Manila trench. The transition from TeM to Tem occurs at a breaking distance of 50-120 km from the Manila trench axis. The axial vertical loading, bending moment, and the effective elastic thickness of the Manila trench are much smaller than the Mariana trench (Zhang et al., 2014). The contrast in the flexural bending between the Mariana and Manila trenches might be related to the difference in the ages of the subducting plates and other tectonic variables. Zhang, F., Lin, J., Zhan, W., 2014. Variations in oceanic plate bending along the Mariana trench, Earth Planet. Sci. Lett. 401, 206-214. doi: 10.1016/j.epsl.2014.05.032

  13. A Detailed 3D Seismic Velocity Structure of the Subducting Pacific Slab Beneath Hokkaido, Tohoku and Kanto, Japan, by Double-Difference Tomography

    NASA Astrophysics Data System (ADS)

    Tsuji, Y.; Nakajima, J.; Kita, S.; Okada, T.; Matsuzawa, T.; Hasegawa, A.

    2007-12-01

    Three-dimensional heterogeneous structure beneath northeastern (NE) Japan 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 subducting 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 to understand the whole process of water transportation from the slab to the surface. Here we show a detailed 3D seismic velocity structure within the subducted Pacific slab around Japan and propose a water-transportation path from the slab to the mantle wedge. In this study, we estimated 3D velocity structure within the Pacific slab by the double-difference tomography (Zhang and Thurber, 2003). We divided the study area, from Hokkaido to Kanto, into 6 areas due to the limitation of memory and computation time. In each area, arrival-time data of 7,500-17,000 events recorded at 70-170 stations were used in the analysis. The total number of absolute travel-time data was about 140,000-312,000 for P wave and 123,000-268,000 for S wave, and differential data were about 736,000-1,920,000 for P wave and 644,000-1,488,000 for S wave. Horizontal and vertical grid separations are 10-25 km and 6.5 km, respectively. RMS residuals of travel times for P wave decreased from 0.23s to 0.09s and for S wave from 0.35s to 0.13s. The obtained results are as follows: (1) a remarkable low-Vs zone exists in the uppermost part of the subducting slab, (2) it extends down to a depth of about 80 km, (3) the termination of this low-Vs zone almost corresponds to the "seismic belt" recently detected in the upper plane of the double seismic zone (Kita et al.,2006; Hasegawa et al., 2007), (4) at depths deeper than 80 km, a low-Vs and high-Vp/Vs zone is apparently distributed in the mantle wedge, immediately above the slab crust. We consider that these features reflect water-transportation processes

  14. Genetic relations between the central and southern Philippine Trench and the Sangihe Trench

    NASA Astrophysics Data System (ADS)

    Lallemand, Serge E.; Popoff, Michel; Cadet, Jean-Paul; Bader, Anne-Gaelle; Pubellier, Manuel; Rangin, Claude; Deffontaines, Benoã®T.

    1998-01-01

    We surveyed the junction between the central and southern Philippine Trench and the Sangihe Trench near 6°N using swath bathymetry, gravity, and magnetics. These data, along with seismicity, allow us to discuss the genetic relations between these trenches and the forces acting on converging plates. Our final model favors the northern extension of the Halmahera Arc up to 8°N, with three segments offset left-laterally along NW-SE transform faults. Accretion of the northern segment to Mindanao Island 4 to 5 m.y. ago resulted in the failure within the Philippine Sea Plate east of the arc. Initiation of the Philippine Trench between 7°N and 10°N agrees with the maximum recorded depth of the Philippine Trench floor (10,000 m below sea-level) and Philippine Sea slab (200 km). South of 6°N (trench junction), another segment of the arc is being subducted beneath the Sangihe margin, while south of 3°N, the southern segment of the Halmahera Arc is still active. The rapid southward shallowing of the trench floor along the southern Philippine Trench, the type of faulting affecting both sides of the trench, the lack of significant interplate seismicity, and the concentration of the seismicity beneath the Miangas-Talaud Ridge are interpreted as a slowing down of the subduction along this branch of the Philippine Trench compared with the rest of the subduction zone. The Sangihe deformation front has been recognized up to 7°N but seems active only south of 6°N.

  15. Trench Visualization

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image shows oblique views of NASA's Phoenix Mars Lander's trench visualized using the NASA Ames Viz software package that allows interactive movement around terrain and measurement of features. The Surface Stereo Imager images are used to create a digital elevation model of the terrain. The trench is 1.5 inches deep. The top image was taken on the seventh Martian day of the mission, or Sol 7 (June 1, 2008). The bottom image was taken on the ninth Martian day of the mission, or Sol 9 (June 3, 2008).

    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.

  16. Phoenix Trenches

    NASA Technical Reports Server (NTRS)

    2008-01-01

    [figure removed for brevity, see original site] Annotated Version

    [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

    This image is a stereo, panoramic view of various trenches 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).

    In figure 1, the trenches 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.

    For scale, the 'Pet Donkey' trench 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.

    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.

  17. Evidence for retrograde lithospheric subduction on Venus

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.; Schubert, Gerald

    1992-01-01

    Annular moats and outer rises around large Venus coronas such as Artemis, Latona, and Eithinoha are similar in arcuate planform and topography to the trenches and outer rises of terrestrial subduction zones. On earth, trenches and outer rises are modeled as the flexural response of a thin elastic lithosphere to the bending moment of the subducted slab; this lithospheric flexure model also accounts for the trenches and outer rises outboard of the major coronas on Venus. Accordingly, it is proposed that retrograde lithospheric subduction 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 trenches or chasmata on Venus such as those in the Dali-Diana chasmata area of aestern Aphrodite Terra.

  18. Building a Subduction Zone Observatory

    USGS Publications Warehouse

    Gomberg, Joan S.; Bodin, Paul; Bourgeois, Jody; Cashman, Susan; Cowan, Darrel; Creager, Kenneth C.; Crowell, Brendan; Duvall, Alison; Frankel, Arthur; Gonzalez, Frank; Houston, Heidi; Johnson, Paul; Kelsey, Harvey; Miller, Una; Roland, Emily C.; Schmidt, David; Staisch, Lydia; Vidale, John; Wilcock, William; Wirth, Erin

    2016-01-01

    Subduction zones contain many of Earth’s most remarkable geologic structures, from the deepest oceanic trenches to glacier-covered mountains and steaming volcanoes. These environments formed through spectacular events: Nature’s largest earthquakes, tsunamis, and volcanic eruptions are born here.

  19. Japan.

    ERIC Educational Resources Information Center

    Geiger, Rita; And Others

    The document offers practical and motivating techniques for studying Japan. Dedicated to promoting global awareness, separate sections discuss Japan's geography, history, culture, education, government, economics, energy, transportation, and communication. Each section presents a topical overview; suggested classroom activities; and easily…

  20. Approximate General Coulomb Model for Accretionary Prisms: An Integrated Study of the Kumano Transect, Nankai Subduction Zone, Southwest Japan

    NASA Astrophysics Data System (ADS)

    Skarbek, Rob; Ikari, Matt; Hüpers, Andre; Rempel, Alan; Wilson, Dean; Kitajima, Hiroko

    2014-05-01

    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 trench. 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 trench. 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.

  1. Buoyant subduction on Venus: Implications for subduction around coronae

    NASA Astrophysics Data System (ADS)

    Burt, J. D.; Head, J. W.

    1993-03-01

    Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven subduction 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 subduction zones in planform and topographic cross-section were described, including trenches 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 subduction was explored and the conditions which would lead to under thrusting versus those allowing the formation of trenches and self-perpetuating subduction were defined. Applying a finite element code to assess the effects of buoyant forces on slabs subducting into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences subduction angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease subduction angle to near an under thrusting position when the subducting lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, subduction 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 subduction. 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.

  2. Buoyant subduction on Venus: Implications for subduction around coronae

    NASA Technical Reports Server (NTRS)

    Burt, J. D.; Head, J. W.

    1993-01-01

    Potentially low lithospheric densities, caused by high Venus surface and perhaps mantle temperatures, could inhibit the development of negative buoyancy-driven subduction 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 subduction zones in planform and topographic cross-section were described, including trenches 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 subduction was explored and the conditions which would lead to under thrusting versus those allowing the formation of trenches and self-perpetuating subduction were defined. Applying a finite element code to assess the effects of buoyant forces on slabs subducting into a viscous mantle, it was found that mantle flow induced by horizontal motion of the convergent lithosphere greatly influences subduction angle, while buoyancy forces produce a lesser effect. Induced mantle flow tends to decrease subduction angle to near an under thrusting position when the subducting lithosphere converges on a stationary overriding lithosphere. When the overriding lithosphere is in motion, as in the case of an expanding corona, subduction 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 subduction. 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.

  3. Space-time Renewal Model for Repeating Earthquakes and Slow Slip before and after the Major Earthquakes in the Northeastern Japan Subduction Zone

    NASA Astrophysics Data System (ADS)

    Nomura, S.; Ogata, Y.; Uchida, N.

    2014-12-01

    Repeating earthquake sequences on the plate subduction zone represent the slip-rate histories around their fault patches. So they are useful resources for monitoring precursory aseismic slip of major earthquakes on plate boundaries. Repeating earthquakes are often modeled by renewal processes, point processes whose recurrence intervals are independent and identically distributed. However, their repeating intervals are greatly influenced by larger seismic events or aseismic slow slip, and hence we need to model such non-stationary behavior of repeating earthquakes. In this study, we propose a non-stationary space-time model for repeating earthquakes based on the model in Nomura et al. (2014) applied to the Parkfield catalog. We used the empirical relation between magnitudes and slip sizes of repeating earthquakes by Nadeau and Johnson (1998) to estimate the slip-rate histories in repeating sequences. The proposed model can estimate spatio-temporal variation in slip rate with smoothness restriction adjusted to optimize its Bayesian likelihood.We apply the proposed model to the large catalog of repeating earthquakes in Uchida and Matsuzawa (2013) on subduction zone of Pacific Plate in the northeastern Japan from 1993 to 2011 and estimate slip-rate history of the plate boundary. From this analysis, we discuss the characteristic changes in slip rate before and after the major earthquakes such as Sanriku-Haruka-Oki (1994 Mw7.6), Tokachi-Oki (2003 Mw8.0), Kushiro-Oki (2004 Mw7.1), Fukushima-Oki (2008 Mw6.9), Ibaraki-Oki (2008 Mw7.0) and Tohoku-Oki (2011 Mw9.0).

  4. Middle Miocene swift migration of the TTT triple junction and rapid crustal growth in southwest Japan: A review

    NASA Astrophysics Data System (ADS)

    Kimura, Gaku; Hashimoto, Yoshitaka; Kitamura, Yujin; Yamaguchi, Asuka; Koge, Hiroaki

    2014-07-01

    We review recent progress in geological and geophysical investigation in SW Japan, Nankai Trough, and Philippine Sea Plate (PSP), and propose a hypothesis for the Miocene tectonics in SW Japan driven by middle Miocene swift migration of the TTT (trench-trench-trench) triple junction. The new hypothesis is based on the new interpretations as follows. Near-trench magmatism in the outer zone of SW Japan is ascribed to a collision of proto-Izu arc in addition to the previous model of an oceanic ridge of the Shikoku Basin and hot PSP subduction. The indentation structures at Capes Ashizuri, Muroto in Shikoku, and Shiono on the Kii Peninsula were previously explained by "kink folding" due to recent E-W compression. We alternatively suppose the collision of the active arc or topographic peaks such as seamounts inferred from geological and experimental observations. The main crustal component in SW Japan is suggested to be of igneous plutonic rocks rather than the previous interpretation of Cretaceous to Tertiary accretionary complexes. This is typically illustrated in the outer zone to the north of Capes Ashizuri, Muroto, and Shiono from geophysical observation of gravity anomalies, velocity and resistivity, together with geological estimations of caldera age and the size of its root pluton. Episodic crustal growth due to intrusion of igneous rock and subduction of the PSP may have stopped after approximately 12 Ma and restarted at approximately 6 Ma. Our emphasis for this gap is a cessation and resurgence of subduction rather than the previous interpretation, i.e., decreasing of subduction rate.

  5. A Hybrid Tsunami Risk Model for Japan

    NASA Astrophysics Data System (ADS)

    Haseemkunju, A. V.; Smith, D. F.; Khater, M.; Khemici, O.; Betov, B.; Scott, J.

    2014-12-01

    Around the margins of the Pacific Ocean, denser oceanic plates slipping under continental plates cause subduction earthquakes generating large tsunami waves. The subducting Pacific and Philippine Sea plates create damaging interplate earthquakes followed by huge tsunami waves. It was a rupture of the Japan Trench subduction zone (JTSZ) and the resultant M9.0 Tohoku-Oki earthquake that caused the unprecedented tsunami along the Pacific coast of Japan on March 11, 2011. EQECAT's Japan Earthquake model is a fully probabilistic model which includes a seismo-tectonic model describing the geometries, magnitudes, and frequencies of all potential earthquake events; a ground motion model; and a tsunami model. Within the much larger set of all modeled earthquake events, fault rupture parameters for about 24000 stochastic and 25 historical tsunamigenic earthquake events are defined to simulate tsunami footprints using the numerical tsunami model COMCOT. A hybrid approach using COMCOT simulated tsunami waves is used to generate inundation footprints, including the impact of tides and flood defenses. Modeled tsunami waves of major historical events are validated against observed data. Modeled tsunami flood depths on 30 m grids together with tsunami vulnerability and financial models are then used to estimate insured loss in Japan from the 2011 tsunami. The primary direct report of damage from the 2011 tsunami is in terms of the number of buildings damaged by municipality in the tsunami affected area. Modeled loss in Japan from the 2011 tsunami is proportional to the number of buildings damaged. A 1000-year return period map of tsunami waves shows high hazard along the west coast of southern Honshu, on the Pacific coast of Shikoku, and on the east coast of Kyushu, primarily associated with major earthquake events on the Nankai Trough subduction zone (NTSZ). The highest tsunami hazard of more than 20m is seen on the Sanriku coast in northern Honshu, associated with the JTSZ.

  6. Modelling guided waves in the Alaskan-Aleutian subduction zone

    NASA Astrophysics Data System (ADS)

    Coulson, Sophie; Garth, Thomas; Reitbrock, Andreas

    2016-04-01

    Subduction zone guided wave arrivals from intermediate depth earthquakes (70-300 km depth) have a huge potential to tell us about the velocity structure of the subducting oceanic crust as it dehydrates at these depths. We see guided waves as the oceanic crust has a slower seismic velocity than the surrounding material, and so high frequency energy is retained and delayed in the crustal material. Lower frequency energy is not retained in this crustal waveguide and so travels at faster velocities of the surrounding material. This gives a unique observation at the surface with low frequency energy arriving before the higher frequencies. We constrain this guided wave dispersion by comparing the waveforms recorded in real subduction zones with simulated waveforms, produced using finite difference full waveform modelling techniques. This method has been used to show that hydrated minerals in the oceanic crust persist to much greater depths than accepted thermal petrological subduction zone models would suggest in Northern Japan (Garth & Rietbrock, 2014a), and South America (Garth & Rietbrock, in prep). These observations also suggest that the subducting oceanic mantle may be highly hydrated at intermediate depth by dipping normal faults (Garth & Rietbrock 2014b). We use this guided wave analysis technique to constrain the velocity structure of the down going ~45 Ma Pacific plate beneath Alaska. Dispersion analysis is primarily carried out on guided wave arrivals recorded on the Alaskan regional seismic network. Earthquake locations from global earthquake catalogues (ISC and PDE) and regional earthquake locations from the AEIC (Alaskan Earthquake Information Centre) catalogue are used to constrain the slab geometry and to identify potentially dispersive events. Dispersed arrivals are seen at stations close to the trench, with high frequency (>2 Hz) arrivals delayed by 2 - 4 seconds. This dispersion is analysed to constrain the velocity and width of the proposed waveguide

  7. Average slip rate at the transition zone on the plate interface in the Nankai subduction zone, Japan, estimated from short-term SSE catalog

    NASA Astrophysics Data System (ADS)

    Itaba, S.; Kimura, T.

    2013-12-01

    Short-term slow slip events (S-SSEs) in the Nankai subduction zone, Japan, have been monitored by borehole strainmeters and borehole accelerometers (tiltmeters) mainly. The scale of the S-SSE in this region is small (Mw5-6), and therefore there were two problems in S-SSE identification and estimation of the fault model. (1) There were few observatories that can detect crustal deformation associated with S-SSEs. Therefore, reliability of the estimated fault model was low. (2) The signal associated with the S-SSE is relatively small. Therefore, it was difficult to detect the S-SSE only from strainmeter and tiltmeter. The former problem has become resolvable to some extent by integrating the data of borehole strainmeter, tiltmeter and groundwater (pore pressure) of the National Institute of Advanced Industrial Science and Technology, tiltmeter of the National Research Institute for Earthquake Science and Disaster Prevention and borehole strainmeter of the Japan Meteorological Agency. For the latter, by using horizontal redundant component of a multi-component strainmeter, which consists generally of four horizontal extensometers, it has become possible to extract tectonic deformation efficiently and detect a S-SSE using only strainmeter data. Using the integrated data and newly developed technique, we started to make a catalog of S-SSE in the Nankai subduction zone. For example, in central Mie Prefecture, we detect and estimate fault model of eight S-SSEs from January 2010 to September 2012. According to our estimates, the average slip rate of S-SSE is 2.7 cm/yr. Ishida et al. [2013] estimated the slip rate as 2.6-3.0 cm/yr from deep low-frequency tremors, and this value is consistent with our estimation. Furthermore, the slip deficit rate in this region evaluated by the analysis of GPS data from 2001 to 2004 is 1.0 - 2.6 cm/yr [Kobayashi et al., 2006], and the convergence rate of the Philippine Sea plate in this region is estimated as 5.0 - 7.0 cm/yr. The difference

  8. The effect of a power-law mantle viscosity on trench retreat rate

    NASA Astrophysics Data System (ADS)

    Holt, Adam F.; Becker, Thorsten W.

    2017-01-01

    The subduction of lithospheric plates is partitioned between subducting plate motion and lateral slab migration (i.e. trench retreat and advance). We use 3-D, dynamic models of subduction to address the role of a power-law mantle viscosity on subduction dynamics and, in particular, rates of trench retreat. For all numerical models tested, we find that a power-law rheology results in reduced rates of trench retreat, and elevated slab dip angles, relative to the equivalent isoviscous mantle model. We analyse the asthenospheric pressure distribution and the style of mantle flow, which exhibits only limited variability as a function of mantle rheology, in order to compute estimates of the mantle forces associated with subduction. The inclusion of a power-law rheology reduces the mantle shear force (which resists subducting plate motion) to a greater degree than it reduces the dynamic pressure gradient across the slab (which resists trench retreat). Therefore, the inclusion of a power-law mantle rheology favours a shift towards a subduction mode with a reduced trench retreat component, typically a relative reduction of order 25 per cent in our 3-D models. We suggest that this mechanism may be of importance for reducing the high trench retreat rates observed in many previous models to levels more in line with the average subduction partitioning observed on Earth at present (i.e. trench velocity ≤ plate velocity), for most absolute plate motion reference frames.

  9. Trench Connection

    PubMed Central

    Jamieson, Alan J.; Fujii, Toyonobu

    2011-01-01

    Trench Connection’ was the first international symposium focusing primarily on the hadal zone (depths greater than 6000 m). It was held at the University of Tokyo's Atmosphere and Ocean Research Institute in November 2010. The symposium was successful in having attracted an international collective of scientists and engineers to discuss the latest developments in the exploration and understanding of the deepest environments on Earth. The symposium sessions were categorized into three themes: (i) new deep-submergence technology; (ii) trench ecology and evolution; and (iii) the physical environment. Recent technological developments have overcome the challenges of accessing the extreme depths, which have in turn prompted an international renewed interest in researching physical and biological aspects of the hadal ecosystems. This bringing together of international participants from different disciplines led to healthy discussions throughout the symposium, providing potential opportunities and realizations of where the future of unravelling hadal ecology lies. Hadal science is still at relatively rudimentary levels compared with those of shallower marine environments; however, it became apparent at the symposium that it is now an ever-expanding scientific field. PMID:21450723

  10. Trench connection.

    PubMed

    Jamieson, Alan J; Fujii, Toyonobu

    2011-10-23

    'Trench Connection' was the first international symposium focusing primarily on the hadal zone (depths greater than 6000 m). It was held at the University of Tokyo's Atmosphere and Ocean Research Institute in November 2010. The symposium was successful in having attracted an international collective of scientists and engineers to discuss the latest developments in the exploration and understanding of the deepest environments on Earth. The symposium sessions were categorized into three themes: (i) new deep-submergence technology; (ii) trench ecology and evolution; and (iii) the physical environment. Recent technological developments have overcome the challenges of accessing the extreme depths, which have in turn prompted an international renewed interest in researching physical and biological aspects of the hadal ecosystems. This bringing together of international participants from different disciplines led to healthy discussions throughout the symposium, providing potential opportunities and realizations of where the future of unravelling hadal ecology lies. Hadal science is still at relatively rudimentary levels compared with those of shallower marine environments; however, it became apparent at the symposium that it is now an ever-expanding scientific field.

  11. Japan.

    PubMed

    1987-02-01

    Japan is composed of 4 main islands and more than 3900 smaller islands and has 317.7 persons/square kilometer. This makes it one of the most densely populated nations in the world. Religion is an important force in the life of the Japanese and most consider themselves Buddhists. Schooling is free through junior high but 90% of Japanese students complete high school. In fact, Japan enjoys one of the highest literacy rates in the world. There are over 178 newspapers and 3500 magazines published in Japan and the number of new book titles issued each year is greater than that in the US. Since WW1, Japan expanded its influence in Asia and its holdings in the Pacific. However, as a direct result of WW2, Japan lost all of its overseas possessions and was able to retain only its own islands. Since 1952, Japan has been ruled by conservative governments which cooperate closely with the West. Great economic growth has come since the post-treaty period. Japan as a constitutional monarchy operates within the framework of a constitution which became effective in May 1947. Executive power is vested in a cabinet which includes the prime minister and the ministers of state. Japan is one of the most politically stable of the postwar democracies and the Liberal Democratic Party is representative of Japanese moderate conservatism. The economy of Japan is strong and growing. With few resources, there is only 19% of Japanese land suitable for cultivation. Its exports earn only about 19% of the country's gross national product. More than 59 million workers comprise Japan's labor force, 40% of whom are women. Japan and the US are strongly linked trading partners and after Canada, Japan is the largest trading partner of the US. Foreign policy since 1952 has fostered close cooperation with the West and Japan is vitally interested in good relations with its neighbors. Relations with the Soviet Union are not close although Japan is attempting to improve the situation. US policy is based on

  12. Environmental Acoustic Considerations for Passive Detection of Maritime Targets by Hydrophones in a Deep Ocean Trench

    DTIC Science & Technology

    2010-06-01

    63 ix LIST OF FIGURES Figure 1. Subduction zone area with related features (from [7...shows the subduction zone cutting along the north shore of Puerto Rico, Hispaniola, and Cuba. The surrounding topography consists of various undersea...representing a symmetrical canyon. .............................22 Figure 14. Trench B bathymetry representing a subduction zone

  13. Brucite as an important phase of the shallow mantle wedge: Evidence from the Shiraga unit of the Sanbagawa subduction zone, SW Japan

    NASA Astrophysics Data System (ADS)

    Kawahara, Hirokazu; Endo, Shunsuke; Wallis, Simon R.; Nagaya, Takayoshi; Mori, Hiroshi; Asahara, Yoshihiro

    2016-06-01

    Large parts of the shallow mantle wedge are thought to be hydrated due to release of fluids from the subducting slab and serpentinization of the overlying mantle rocks. If serpentinization proceeds under low SiO2 activity, brucite can be a major phase in the low-temperature (< 450 °C) part of the serpentinized mantle wedge, but only very few natural examples have been documented. A combined petrological, geochemical, and geological study shows that brucite is widely distributed in the wedge mantle-derived Shiraga metaserpentinite body in the Sanbagawa metamorphic belt of SW Japan. Thermodynamic modeling combined with bulk rock composition and point counting indicates that the original fully hydrated shallow parts of the Sanbagawa mantle wedge contained ~ 10-15 vol.% brucite before the onset of exhumation of the Shiraga body and before peak metamorphic conditions. A distinct zone of brucite-free essentially monomineralic antigorite serpentinite occurs limited to a 100-m-thick marginal zone of the body. This indicates a limited degree of Si-metasomatism by slab-derived fluids in the shallow mantle wedge. The presence of brucite may strongly affect the H2O budget and mechanical properties of serpentinite; these should be taken into consideration when examining the behavior of the shallow mantle wedge.

  14. Japan.

    ERIC Educational Resources Information Center

    Jones, Savannah C.

    Materials for a secondary level, interdisciplinary social studies course on Japan are divided into introductory information, 14 classroom units, and study and evaluation materials. Introductory material includes lists of objectives and skills, an outline of Japanese history, and an explanation of Japan's name and flag. The units cover the…

  15. Japan

    ERIC Educational Resources Information Center

    Hawkins, John N.

    1986-01-01

    Analyzes the intergroup relations in Japanese society and Japan's educational system. Challenges the view that Japan 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)

  16. Crustal structure and configuration of the subducting Philippine Sea plate beneath the Pacific coast industrial zone in Japan inferred from receiver function analysis

    NASA Astrophysics Data System (ADS)

    Igarashi, T.; Iidaka, T.; Sakai, S.; Hirata, N.

    2012-12-01

    We apply receiver function (RF) analyses to estimate the crustal structure and configuration of the subducting Philippine Sea (PHS) plate beneath the Pacific coast industrial zone stretching from Tokyo to Fukuoka in Japan. 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 subducting 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

  17. Geophysics. Migrating tremor off southern Kyushu as evidence for slow slip of a shallow subduction interface.

    PubMed

    Yamashita, Y; Yakiwara, H; Asano, Y; Shimizu, H; Uchida, K; Hirano, S; Umakoshi, K; Miyamachi, H; Nakamoto, M; Fukui, M; Kamizono, M; Kanehara, H; Yamada, T; Shinohara, M; Obara, K

    2015-05-08

    Detection of shallow slow earthquakes offers insight into the near-trench part of the subduction interface, an important region in the development of great earthquake ruptures and tsunami generation. Ocean-bottom monitoring of offshore seismicity off southern Kyushu, Japan, recorded a complete episode of low-frequency tremor, lasting for 1 month, that was associated with very-low-frequency earthquake (VLFE) activity in the shallow plate interface. The shallow tremor episode exhibited two migration modes reminiscent of deep tremor down-dip of the seismogenic zone in some other subduction zones: a large-scale slower propagation mode and a rapid reversal mode. These similarities in migration properties and the association with VLFEs strongly suggest that both the shallow and deep tremor and VLFE may be triggered by the migration of episodic slow slip events.

  18. Resolving depth-dependent subduction zone viscosity and afterslip from postseismic displacements following the 2011 Tohoku-oki, Japan earthquake

    NASA Astrophysics Data System (ADS)

    Freed, Andrew M.; Hashima, Akinori; Becker, Thorsten W.; Okaya, David A.; Sato, Hiroshi; Hatanaka, Yuki

    2017-02-01

    We developed a 3-D, viscoelastic finite element model of the M9 2011 Tohoku-oki, Japan earthquake capable of predicting postseismic displacements due to viscoelastic relaxation and afterslip. We consider seismically inferred slab geometries associated with the Pacific and Philippine Sea Plate and a wide range of candidate viscoelastic rheologies. For each case, we invert for afterslip based on residual surface displacements (observed GPS minus that predicted due to viscoelastic relaxation) to develop combined viscoelastic relaxation and afterslip models. We are able to find a mechanical model that fully explains all observed geodetic on-land and seafloor horizontal and vertical postseismic displacements. We find that postseismic displacements are in about equal parts due to viscoelastic relaxation and afterslip, but their patterns are spatially distinct. Accurately predicting both horizontal and vertical on-land postseismic displacements requires a mantle wedge viscosity structure that is depth dependent, reflecting the manner in which temperature, pressure, and water content influence viscosity. No lateral heterogeneities within the mantle wedge viscosity structure beneath northern Honshu are required. Westward-directed postseismic seafloor displacements may be due flow via low-temperature, plastic creep within the lower half of a Pacific lithosphere weakened by plate bending. The distribution of afterslip is controlled by the location of coseismic slip from the Tohoku-oki and other regional historic earthquakes. The paradigm by which afterslip is thought of as the dominant postseismic mechanism immediately following earthquakes, with viscoelastic relaxation to follow in later years, is shown to no longer be valid.

  19. A critical assessment of viscous models of trench topography and corner flow

    NASA Technical Reports Server (NTRS)

    Zhang, J.; Hager, B. H.; Raefsky, A.

    1984-01-01

    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 trench topography it is essential to use realistic geometries. Topography and seismicity data from northern Hoshu, Japan, 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 trench topography and gravity anomalies. There is poor agreement. Purely viscous models of subducting 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 subduction process.

  20. Origin of back-arc basins and effects of western Pacific subduction systems on eastern China geology

    NASA Astrophysics Data System (ADS)

    Niu, Y.

    2013-12-01

    Assuming that subduction initiation is a consequence of lateral compositional buoyancy contrast within the lithosphere [1], and recognizing that subduction initiation within normal oceanic lithosphere is unlikely [1], we can assert that passive continental margins that are locations of the largest compositional buoyancy contrast within the lithosphere are the loci of future subduction zones [1]. We hypothesize that western Pacific back-arc basins were developed as and evolved from rifting at passive continental margins in response to initiation and continuation of subduction zones. This hypothesis can be tested by demonstrating that intra-oceanic island arcs must have basement of continental origin. The geology of the Islands of Japan supports this. The highly depleted forearc peridotites (sub-continental lithosphere material) from Tonga and Mariana offer independent lines of evidence for the hypothesis [1]. The origin and evolution of the Okinawa Trough (back-arc basin) and Ryukyu Arc/Trench systems represents the modern example of subduction initiation and back-arc basin formation along a (Chinese) continental margin. The observation why back-arc basins exit behind some subduction zones (e.g., western Pacific) but not others (e.g., in South America) depends on how the overlying plate responds to subduction, slab-rollback and trench retreat. In the western Pacific, trench retreat towards east results in the development of extension in the upper Eurasian plate and formation of back-arc basins. In the case of South America, where no back-arc basins form because trench retreat related extension is focused at the 'weakest' South Mid-Atlantic Ridge. It is thus conceptually correct that the South Atlantic is equivalent to a huge 'back-arc basin' although its origin may be different. Given the negative Clayperon slope of the Perovskite-ringwoodite phase transition at the 660 km mantle seismic discontinuity (660-D), slab penetration across the 660-D is difficult and

  1. Analysis of past recurrent methane seep activity using radiocarbon dating of Calyptogena spp. shells in the eastern Nankai subduction zone, Japan

    NASA Astrophysics Data System (ADS)

    Yagasaki, Kazuhiro; Ashi, Juichiro; Yokoyama, Yusuke; Miyairi, Yosuke; Kuramoto, Shin'ichi

    2016-04-01

    Fault activity around subduction zones have been widely studied and monitored through drilling of oceanic plates, studying piston cores, use of monitoring equipment or through visual analysis using submersible vehicles. Yet the understanding of how small scale faults near shallow regions of the seabed behave in relation to cold seep vent activity is still vague, especially determining when they were active in the past. In tectonically active margins such as the Nankai and Tokai regions off Japan, dense methane hydrate reservoirs have been identified. Cold seeps releasing methane rich hydrocarbon fluids are common here, supporting a wide variety of biological species that hold a symbiotic relationship with the chemosynthetic bacteria. In 1998 a large dead Calyptogena spp. bivalve colony (over 400m2 in size) was discovered off Tokai, Japan. It is unusual for a bivalve colony this size to mostly be dead, raising questions as to what caused their death. In this study we document the radiocarbon 14C age of these bivalve shells to attempt analysing the possible methane seep bahaviour in the past. The measured 14C age ranged in three age groups of 1396±36-1448±34, 1912±31-1938±35 and 5975±34. The 14C age of shells that were alive upon collection and the dissolved inorganic carbon (DIC) in seawater show little difference (˜100 14C age) indicating that shells are not heavily affected by the dead carbon effect from cold seeps that is of biogenic or thermogenic origin, which can make the age to become considerably older than the actual age. Thus the novel calibration model used was based on the seawater DIC collected above the Calyptogena spp. colony site (1133±31), which resulted in the dead shells to be clustered around 1900 Cal AD. This proves to be interesting as the predicted epicenter of the Ansei-Tokai earthquake (M 8.4) in 1854 is extremely close to the bibalve colony site. Using geological data obtained using visual analysis and sub-seafloor structural

  2. Seismic attenuation structure associated with episodic tremor and slip zone beneath Shikoku and the Kii peninsula, southwestern Japan, in the Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Kita, Saeko; Matsubara, Makoto

    2016-03-01

    The three-dimensional seismic attenuation structure (frequency-independent Q) beneath southwestern Japan was analyzed using t* estimated by applying the S coda wave spectral ratio method to the waveform data from a dense permanent seismic network. The seismic attenuation (Qp-1) structure is clearly imaged for the region beneath Shikoku, the Kii peninsula, and eastern Kyushu at depths down to approximately 50 km. At depths of 5 to 35 km, the seismic attenuation structure changes at the Median tectonic line and other geological boundaries beneath Shikoku and the southwestern Kii peninsula. High-Qp zones within the lower crust of the overlying plate are found just above the slip regions at the centers of the long-term slow-slip events (SSEs) beneath the Bungo and Kii channels and central Shikoku. Beneath central Shikoku, within the overlying plate, a high-Qp zone bounded by low-Qp zones is located from the land surface to the plate interface of the subducting plate. The high-Qp zone and low-Qp zones correspond to high-Vp and low-Vp zones of previous study, respectively. The boundaries of the high- and low-Qp zones are consistent with the segment boundaries of tremors (segment boundaries of short-term SSEs). These results indicated that the locations of the long- and short-term SSEs could be limited by the inhomogeneous distribution of the materials and/or condition of the overlying plate, which is formed due to geological and geographical process. The heterogeneity of materials and/or condition within the fore-arc crust possibly makes an effect on inhomogeneous rheological strength distribution on the interface.

  3. Unusually large earthquakes inferred from tsunami deposits along the Kuril trench

    USGS Publications Warehouse

    Nanayama, F.; Satake, K.; Furukawa, R.; Shimokawa, K.; Atwater, B.F.; Shigeno, K.; Yamaki, S.

    2003-01-01

    The Pacific plate converges with northeastern Eurasia at a rate of 8-9 m per century along the Kamchatka, Kuril and Japan trenches. Along the southern Kuril trench, which faces the Japanese island of Hokkaido, this fast subduction 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 trench. We infer that such multi-segment earthquakes persistently recur among a larger number of single-segment events.

  4. What really causes flat slab subduction?

    NASA Astrophysics Data System (ADS)

    Manea, V. C.; Perez-Gussinye, M.; Manea, M.

    2014-12-01

    How flat slab geometries are generated has been long debated. It has been suggested thattrenchward motion of thick cratons in some areas of South America and Cenozoic NorthAmerica progressively closed the asthenospheric wedge and induced flat subduction. Here wedevelop time-dependent numerical experiments to explore how trenchward motion of thickcratons may result in flat subduction. We find that as the craton approaches the trench andthe wedge closes, two opposite phenomena control slab geometry: the suction between oceanand continent increases, favoring slab flattening, while the mantle confined within the closingwedge dynamically pushes the slab backward and steepens it. When the slab retreats, as inthe Peru and Chile flat slabs, the wedge closure rate and dynamic push are small and suctionforces generate, in some cases, flat subduction. We model the past 30 m.y. of subduction in theChilean flat slab area and demonstrate that trenchward motion of thick lithosphere, 200-300km, currently ~700-800 km away from the Peru-Chile Trench, reproduces a slab geometrythat fits the stress pattern, seismicity distribution, and temporal and spatial evolution ofdeformation and volcanism in the region. We also suggest that varying trench kinematics mayexplain some differing slab geometries along South America. When the trench is stationaryor advances, the mantle flow within the closing wedge strongly pushes the slab backward andsteepens it, possibly explaining the absence of flat subduction in the Bolivian orocline.

  5. Geodynamics of flat subduction: Seismicity and tomographic constraints from the Andean margin

    NASA Astrophysics Data System (ADS)

    Gutscher, Marc-André; Spakman, Wim; Bijwaard, Harmen; Engdahl, E. Robert

    2000-10-01

    The cause and geodynamic impact of flat subduction are investigated. First, the 1500 km long Peru flat slab segment is examined. Earthquake hypocenter data image two morphologic highs in the subducting Nazca Plate which correlate with the positions of subducted oceanic plateaus. Travel time tomographic images confirm the three-dimensional slab geometry and suggest a lithospheric tear may bound the NW edge of the flat slab segment, with possible slab detachment occurring down dip as well. Other flat slab regions worldwide are discussed: central Chile, Ecuador, NW Colombia, Costa Rica, Mexico, southern Alaska, SW Japan, and western New Guinea. Flat subduction is shown to be a widespread phenomenon, occuring in 10% of modern convergent margins. In nearly all these cases, as a spatial and temporal correlation is observed between subducting oceanic plateaus and flat subduction, we conclude that flat subduction is caused primarily by (1) the buoyancy of thickened oceanic crust of moderate to young age and (2) a delay in the basalt to eclogite transition due to the cool thermal structure of two overlapping lithospheres. A statistical analysis of seismicity along the entire length of the Andes demonstrates that seismic energy release in the upper plate at a distance of 250-800 km from the trench is on average 3-5 times greater above flat slab segments than for adjacent steep slab segments. We propose this is due to higher interplate coupling and the cold, strong rheology of the overriding lithosphere which thus enables stress and deformation to be transmitted hundreds of kilometers into the heart of the upper plate.

  6. A Crustal Structure Study of the Southern Ryukyu Subduction Zone by Using the Aftershock Data

    NASA Astrophysics Data System (ADS)

    Cho, Y.; Lin, J.; Lee, C.

    2011-12-01

    The region along the Ryukyu subduction zone is known as a tsunami disaster zone. The biggest tsunami (85 m) of Japan 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 subduction 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 subduction 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 Trench. 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 Japan subduction 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 Trench. This group may represent the ridge structure relate to the Taitung canyon fault. The front of Ryukyu Trench was being as a locked subduction zone where it is easily to

  7. Strong Quake Strikes Japan

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2011-03-01

    As Eos was about to go to press, a powerful earthquake with a preliminary estimated magnitude of 8.9 shook the northeast coast of Japan on 11 March at 05:46:23 UTC. It is the largest known earthquake along the Japan Trench subduction 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.

  8. Link between ridge subduction and gold mineralization in southern Alaska

    USGS Publications Warehouse

    Haeussler, Peter J.; Bradley, Dwight C.; Goldfarb, Richard; Snee, Lawrence W.; Taylor, Cliff D.

    1995-01-01

    40Ar/39Ar geochronology reveals that turbidite-hosted gold deposits in the southern Alaska accretionary prism are the same age as nearby near-trench plutons. These early Tertiary plutons and gold lodes formed above a slab window during subduction of an oceanic spreading center. Ridge subduction is a previously unrecognized tectonic process for the generation of lode gold.

  9. GPS Monitoring of Subduction Zone Deformation in Costa Rica

    NASA Technical Reports Server (NTRS)

    Lundgren, Paul

    1997-01-01

    The subduction of the Cocos plate beneath Costa Rica is among the highest convergence rates in the world. The high subduction rate and nearness of the Nicoya Peninsula, Costa Rica to the Middle America Trench (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.

  10. The Dynamics of Double Slab Subduction

    NASA Astrophysics Data System (ADS)

    Holt, A. F.; Royden, L. H.; Becker, T. W.

    2017-01-01

    We use numerical models to investigate the dynamics of two interacting slabs with parallel trenches. Cases considered are: a single slab reference, outward dipping slabs (out-dip), inward dipping slabs (in-dip), and slabs dipping in the same direction (same-dip). Where trenches converge over time (same-dip and out-dip systems), large positive dynamic pressures in the asthenosphere are generated beneath the middle plate, and large trench-normal extensional forces are transmitted through the middle plate. This results in slabs that dip away from the middle plate at depth, independent of trench geometry. The single slab, the front slab in the same-dip case, and both out-dip slabs undergo trench retreat and exhibit stable subduction. However, slabs within the other double subduction systems tend to completely overturn at the base of the upper mantle, and exhibit either trench advance (rear slab in same-dip), or near-stationary trenches (in-dip). For all slabs, the net slab-normal dynamic pressure at 330 km depth is nearly equal to the slab normal force induced by slab buoyancy. For double subduction, the net outward force on the slabs due to dynamic pressure from the asthenosphere is effectively counterbalanced by the net extensional force transmitted through the middle plate. Thus, dynamic pressure at depth, inter-plate coupling, and lithospheric stresses are closely linked and their effects cannot be isolated. Our results provide insights into both the temporal evolution of double slab systems on Earth and, more generally, how the various components of subduction systems, from mantle flow/pressure to inter-plate coupling, are dynamically linked.

  11. Seismic evidence of the change in the physical properties of the subducting slabs in the Western Pacific region.

    NASA Astrophysics Data System (ADS)

    Gorbatov, A.; Kennett, B. L. N.

    2003-04-01

    Analysis of bulk-sound and shear wave speed variations in the Earth's interior provides valuable information about the tectonic fabric of the subduction zones because the results can be directly compared with the elastic properties of the subducting material determined in the laboratory experiments. A detailed regional tomographic inversion for the Western Pacific region has been carried out using the arrival times for P and S wave ray paths with comparable coverage. The inversion was performed directly for bulk-sound and shear wave speed variations in the Earth's mantle. The study region was parameterized by cells with sides from of 0.5 to 2 degrees and 19 layers to a depth of 1500 km, while the surrounding whole mantle was parameterized by cells of 5x5 degrees and 16 layers. A simultaneous inversion was undertaken for both the regional and global structures to minimize the influence of surrounding structures on the regional image. The nonlinearity of the inverse problem was taken into account by using a scheme which iteratively applied three-dimensional ray tracing and linearized inversion. The results of the joint inversion show the penetration of subducted slabs below the 660 km discontinuity below the Kurile-Kamchatka, Bonin, Mariana, Phillipine, Talaud, New Guinea, Java, Solomon and Tonga convergence boundaries while the flattening of slabs above this depth is observed in the Japan, Ryukyu, and Izu-Bonin subduction zones on both the bulk-sound and shear images. Low-amplitude high-velocity zones are observed below the flattened part of the subducted slabs at the Ryukyu and Izu-Bonin subduction zones for both the bulk and shear modulus, but their relation to the subducted slab is not obvious. The shear wave speed perturbations of the subducted slab is distinctively higher than the bulk-sound perturbations for all these subduction zones in the uppermost mantle, except the Philippines, Talaud, New Guinea, and Solomon subduction zones, which are characterized by

  12. Age of the subducting Pacific slab beneath East Asia and its geodynamic implications

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Zhao, Dapeng; Li, Sanzhong; Wei, Wei

    2017-04-01

    We study the age of the subducting Pacific slab beneath East Asia using a high-resolution model of P-wave tomography and paleo-age data of ancient seafloor. Our results show that the lithosphere age of the subducting slab becomes younger from the Japan Trench (∼130 Ma) to the slab's western edge (∼90 Ma) beneath East China, and the flat (stagnant) slab in the mantle transition zone (MTZ) is the subducted Pacific plate rather than the proposed Izanagi plate which should have already collapsed into the lower mantle. The flat Pacific slab has been in the MTZ for no more than ∼10-20 million years, considerably less than the age of the big mantle wedge beneath East Asia (>110 million years). Hence, the present flat Pacific slab in the MTZ has contributed to the Cenozoic destruction of the East Asian continental lithosphere with extensive intraplate volcanism and back-arc spreading, whereas the destruction of the North China Craton during the Early Cretaceous (∼140-110 Ma) was caused by the subduction of the Izanagi (or the Paleo-Pacific) plate.

  13. Scenarios of tsunamigenic earthquakes generated along the Hellenic subduction zone and impact along the French coastlines

    NASA Astrophysics Data System (ADS)

    Gailler, Audrey; Hébert, Hélène; Schindelé, François

    2016-04-01

    The Hellenic subduction is an active deformation zone characterized by a sustained day-to-day seismicity (magnitude < 4.5) among the strongest in Europe. The last significant earthquake along the Hellenic subduction zone detected and characterized by the French tsunami warning center (CENALT) occurred on 16th April 2015 (Mw = 6.0) along the southeastern coasts of Crete, without any tsunami risk for the French coastlines. Even if great subduction earthquakes (magnitude > 7.5) are less frequent than in Chile or Japan, the Hellenic area experienced several strong events by the past, the biggest being associated with major tsunamis (e.g., in 551, in 1303). The last known sequence dates the end of the 19th beginning of the 20th century with a seismic gap located along the South Peloponnese - West Crete segment. The legendary 365 AD great earthquake (magnitude 8 to 8.5) is assumed to have ruptured along a major inverse fault parallel to the trench in this area, generating a large tsunami observed up to the Adriatic. In this work we investigate the tsunami potential of earthquakes localized along the Hellenic subduction zone, especially the minimum magnitude required to generate a tsunami that would be able to cross from Eastern to Western Mediterranean. The impact along Corsica coastlines is discussed through the modeling of a set of tsunami scenarios (magnitude ranging from 8.0 to 8.5) established from historical events parameters.

  14. Subduction zone tectonic studies to develop concepts for the occurrence of sediment subduction (Phase I). Final technical report

    SciTech Connect

    Hilde, T.W.C.

    1984-08-01

    The objective was to determine the fate of sediments at convergent lithospheric plate boundaries. The study focuses on the structures of the Circum-Pacific trenches and shallow portions of the associated subduction zones. Sediment distribution and the nature of sediment deformation was defined through the various stages of plate convergence to determine if the sediments are subducted or accreted. The controlling factors for sediment subduction and/or accretion were determined. 50 figs. (ACR)

  15. Evidence for retrograde lithospheric subduction on Venus

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.; Schubert, Gerald

    1992-01-01

    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 subduction and back-arc spreading. The perimeters of several large coronae (e.g., Latona, Artemis, and Eithinoha) resemble Earth subduction zones in both their planform and topographic profile. The planform of arcuate structures in Eastern Aphrodite were compared with subduction zones of the East Indies. The venusian structures have radii of curvature that are similar to those of terrestrial subduction zones. Moreover, the topography of the venusian ridge/trench structures is highly asymmetric with a ridge on the concave side and a trough on the convex side; Earth subduction zones generally display the same asymmetry.

  16. Subduction dynamics: Constraints from gravity field observations

    NASA Technical Reports Server (NTRS)

    Mcadoo, D. C.

    1985-01-01

    Satellite systems do the best job of resolving the long wavelength components of the Earth's gravity field. Over the oceans, satellite-borne radar altimeters such as SEASAT provide the best resolution observations of the intermediate wavelength components. Satellite observations of gravity contributed to the understanding of the dynamics of subduction. Large, long wavelength geoidal highs generally occur over subduction zones. These highs are attributed to the superposition of two effects of subduction: (1) the positive mass anomalies of subducting slabs themselves; and (2) the surface deformations such as the trenches convectively inducted by these slabs as they sink into the mantle. Models of this subduction process suggest that the mantle behaves as a nonNewtonian fluid, its effective viscosity increases significantly with depth, and that large positive mass anomalies may occur beneath the seismically defined Benioff zones.

  17. Numerical modeling of mantle wedge processes and exhumation of UHP mantle in subduction zones

    NASA Astrophysics Data System (ADS)

    Gorczyk, W.; Gerya, T. V.; Guillot, S.; Connolly, J. A.; Yuen, D.

    2007-12-01

    The upwelling of subduction generated partially molten rocks is potentially a mechanism for the exhumation of UHP rocks through the mantle wedge. We investigated this processes using a 2-D coupled petrological- thermomechanical model that incorporates slab dehydration and water transport as well as partial melting of mantle and crustal rocks. This approach allows us to study the dynamics of mantle wedge processes including evolution of partially molten plumes and their interaction with surrounding dry mantle. To study the internal structure of the plumes we used ultra-high resolution numerical simulations with 10 billion active markers to detail the internal structure of natural plumes originating from the slab. The plumes consist of partially molten hydrated peridotite, dry solid mantle and subducted oceanic crust, which may comprise up to 12 volume % of the plume. As the plumes grow and mature these materials mix chaotically resulting in attenuation and duplication of the original layering on scales of 1-1000 m. Comparison of numerical results with geological observations from the Horoman ultramafic complex in Japan suggests that mixing and differentiation processes related to development of partially molten plumes above slabs may be responsible for strongly layered lithologically mixed (marble cake) structure of asthenospheric mantle wedges. The recent discovery of garnet bearing peridotites in the subduction zone of the Great Antilles in Hispaniola has raised questions about the process that leads to their exhumation. To evaluate whether upwelling plumes are a plausible exhumation mechanism we investigated the dynamics of subduction of slow spreading ridges. The results show that subduction of strongly serpentinized oceanic plate causes strong dehydration of the slab and leads to a rheological weakening of the interface between subducting and overriding plate. This weakening triggers trench retreat and massive asthenospheric upwelling into the gap between the

  18. Development of Forearcs of Intraoceanic Subduction Zones

    NASA Astrophysics Data System (ADS)

    Lundberg, Neil

    1983-02-01

    The uplifted Costa Rican forearc landward of the Middle America Trench and the Mariana forearc drilled on IPOD leg 60 both lack the thick clastic sequences, complex deformation, and abundant evidence of accretion which characterize more widely known forearcs that border continents. Both regions contain significant in situ accumulations of pelagic and hemipelagic sediments in place of thick trench and trench slope basin sequences composed of terrigenous turbidites. The Nicoya Peninsula of Costa Rica contains no significant melange terranes. Deformation of the mafic igneous basement and its thin cover of pelagic, hemipelagic, and first-cycle volcanogenic material is mild overall, with discrete zones of intense deformation disrupting otherwise well-preserved stratigraphic sections. Intraoceanic subduction zones lacking longitudinal trench feed are sites of little or no accretion of sediments, and recently suggested experimental and theoretical models of subduction zone processes involving flow melanges are inappropriate for intraoceanic forearcs. Intraoceanic forearcs generally lack high-grade exotic components such as blueschist and eclogite tectonically incorporated as blocks in lower-grade matrix, although uplift and erosion of the forearc basement may provide detritus of amphibolite and ultramafic rock to the trench and trench slope.

  19. Earthquake hazards on the cascadia subduction zone

    SciTech Connect

    Heaton, T.H.; Hartzell, S.H.

    1987-04-10

    Large subduction earthquakes on the Cascadia subduction zone pose a potential seismic hazard. Very young oceanic lithosphere (10 million years old) is being subducted beneath North America at a rate of approximately 4 centimeters per year. The Cascadia subduction zone shares many characteristics with subduction zones in southern Chile, southwestern Japan, and Colombia, where comparably young oceanic lithosphere is also subducting. Very large subduction earthquakes, ranging in energy magnitude (M/sub w/) between 8 and 9.5, have occurred along these other subduction zones. If the Cascadia subduction 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 subduction 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 subduction 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.

  20. Earthquake hazards on the cascadia subduction zone.

    PubMed

    Heaton, T H; Hartzell, S H

    1987-04-10

    Large subduction earthquakes on the Cascadia subduction zone pose a potential seismic hazard. Very young oceanic lithosphere (10 million years old) is being subducted beneath North America at a rate of approximately 4 centimeters per year. The Cascadia subduction zone shares many characteristics with subduction zones in southern Chile, southwestern Japan, and Colombia, where comparably young oceanic lithosphere is also subducting. Very large subduction earthquakes, ranging in energy magnitude (M(w)) between 8 and 9.5, have occurred along these other subduction zones. If the Cascadia subduction zone is also storing elastic energy, a sequence of several great earthquakes (M(w) 8) or a giant earthquake (M(w) 9) would be necessary to fill this 1200-kilometer gap. The nature of strong ground motions recorded during subduction earthquakes of M(w) less than 8.2 is discussed. Strong ground motions from even larger earthquakes (M(w) up to 9.5) are estimated by simple simulations. If large subduction 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.

  1. Variations in oceanic plate bending along the Mariana trench

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Lin, Jian; Zhan, Wenhuan

    2014-09-01

    We quantify along-trench variations in plate flexural bending along the Mariana trench in the western Pacific Ocean. A 3-D interpreted flexural deformation surface of the subducting Pacific Plate was obtained by removing from the observed bathymetry the effects of sediment loading, isostatically-compensated topography based on gravity modeling, age-related lithospheric thermal subsidence, and residual short-wavelength features. We analyzed flexural bending of 75 across-trench profile sections and calculated five best-fitting tectonic and plate parameters that control the flexural bending. Results of analysis revealed significant along-trench variations: the trench relief varies from 0.9 to 5.7 km, trench-axis vertical loading (-V0) from -0.73×1012 to 3.17×1012 N/m, and axial bending moment (-M0) from 0.1×1017 to 2.7×1017 N. The effective elastic plate thickness seaward of the outer-rise region (TeM) ranges from 45 to 52 km, while that trench-ward of the outer-rise (Tem) ranges from 19 to 40 km. This corresponds to a reduction in Te of 21-61%. The transition from TeM to Tem occurs at a breaking distance of 60-125 km from the trench axis, which is near the outer-rise and corresponds to the onset of observed pervasive normal faults. The Challenger Deep area is associated with the greatest trench relief and axial vertical loading, while areas with seamounts at the trench axis are often associated with more subtle trench relief, smaller axial vertical loading, and greater topographic bulge at the outer-rise.

  2. Great (≥Mw8.0) megathrust earthquakes and the subduction of excess sediment and bathymetrically smooth seafloor

    USGS Publications Warehouse

    Scholl, David W.; Kirby, Stephe H.; von Huene, Roland; Ryan, Holly F.; Wells, Ray E.; Geist, Eric L.

    2015-01-01

    However, large Mw8.0–9.0 IPTs commonly (n = 23) nucleated at thin-sediment trenches. These earthquakes are associated with the subduction of low-relief ocean floor and where the debris of subduction erosion thickens the plate-separating subduction channel. The combination of low bathymetric relief and subduction erosion is inferred to also produce a smooth trench-parallel distribution of coupling posited to favor the characteristic lengthy rupturing of high-magnitude IPT earthquakes. In these areas subduction of a weak sedimentary sequence further enables rupture continuation.

  3. Simulation of tectonic evolution of the Kanto basin of Japan since 1 Ma due to subduction of the Pacific and Philippine sea plates and collision of the Izu-Bonin arc

    NASA Astrophysics Data System (ADS)

    Hashima, Akinori; Sato, Toshinori; Sato, Hiroshi; Asao, Kazumi; Furuya, Hiroshi; Yamamoto, Shuji; Kameo, Koji; Miyauchi, Takahiro; Ito, Tanio; Tsumura, Noriko; Kaneda, Heitaro

    2015-04-01

    The Kanto basin, the largest lowland in Japan, developed by flexure as a result of (1) the subduction of the Philippine Sea (PHS) and the Pacific (PAC) plates and (2) the collision of the Izu-Bonin arc with the Japanese island arc. Geomorphological, geological, and thermochronological data on long-term vertical movements over the last 1 My suggest that subsidence initially affected the entire Kanto basin after which the area of subsidence gradually narrowed until, finally, the basin began to experience uplift. In this study, we modelled the tectonic evolution of the Kanto basin following the method of Matsu'ura and Sato (1989) for a kinematic subduction model with dislocations, in order to quantitatively assess the effects of PHS and PAC subduction. We include the steady slip-rate deficit (permanent locking rate at the plate interface) in our model to account for collision process. We explore how the arc-arc collision process has been affected by a westerly shift in the PHS plate motion vector with respect to the Eurasian plate, thought to have occurred between 1.0-0.5 Ma, using long-term vertical deformation data to constrain extent of the locked zone on the plate interface. We evaluated the change in vertical deformation rate for two scenarios: (1) a synchronous shift in the orientation of the locked zone as PHS plate motion shifts and (2) a delayed shift in the orientation of the locked zone following a change in plate motion. Observed changes in the subsidence/uplift pattern are better explained by scenario (2), suggesting that recent (<1 My) deformation in the Kanto basin shows a lag in crustal response to the shift in plate motion. We also calculated recent stress accumulation rates and found a good match with observed earthquake mechanisms, which shows that intraplate earthquakes serve to release stress accumulated through long-term plate interactions.

  4. Simulation of tectonic evolution of the Kanto Basin of Japan since 1 Ma due to subduction of the Pacific and Philippine Sea plates and the collision of the Izu-Bonin arc

    NASA Astrophysics Data System (ADS)

    Hashima, Akinori; Sato, Toshinori; Sato, Hiroshi; Asao, Kazumi; Furuya, Hiroshi; Yamamoto, Shuji; Kameo, Koji; Miyauchi, Takahiro; Ito, Tanio; Tsumura, Noriko; Kaneda, Heitaro

    2016-06-01

    The Kanto Basin, the largest lowland in Japan, developed by flexure as a result of (1) the subduction of the Philippine Sea (PHS) and the Pacific (PAC) plates and (2) the repeated collision of the Izu-Bonin arc fragments with the Japanese island arc. Geomorphological, geological, and thermochronological data on vertical movements over the last 1 My suggest that subsidence initially affected the entire basin after which the area of subsidence gradually narrowed until, finally, the basin began to experience uplift. In this study, we modeled the tectonic evolution of the Kanto Basin following the method of Matsu'ura and Sato (1989) for a kinematic subduction model with dislocations, in order to quantitatively assess the effects of PHS and PAC subduction. We include the steady slip-rate deficit (permanent locking rate at the plate interface) in our model to account for collision process. We explore how the latest collision of the Izu Peninsula block has been affected by a westerly shift in the PHS plate motion vector with respect to the Eurasian plate, thought to have occurred between 1.0-0.5 Ma, using long-term vertical deformation data to constrain extent of the locked zone on the plate interface. We evaluated the change in vertical deformation rate for two scenarios: (1) a synchronous shift in the orientation of the locked zone as PHS plate motion shifts and (2) a delayed shift in the orientation of the locked zone following the shift in plate motion. Observed changes in the uplift/subsidence pattern are better explained by scenario (2), suggesting that recent (< 1 My) deformation in the Kanto Basin shows a lag in crustal response to the plate motion shift. We also calculated stress accumulation rates and found a good match with observed earthquake mechanisms, which shows that intraplate earthquakes serve to release stress accumulated through long-term plate interactions.

  5. Spirit Digs a Trench

    NASA Technical Reports Server (NTRS)

    2004-01-01

    A view from the front hazard avoidance camera of NASA's Spirit rover on its 47th sol shows a trench excavated by the rover's left front wheel within the 'Laguna Hollow' area. The trench, dubbed 'Road Cut,' is 7 centimeters (3 inches) deep. The soil at this location is more cohesive than the material where Spirit's twin, Opportunity, dug its first trench at Meridiani. Spirit made 11 back-and-forth passes to dig this trench, and still did not produce as deep a hole as Opportunity dug in 6 passes. Scientists and engineers plan to begin up-close inspection of the soil in this trench on sol 48 by placing the microscopic imager on the floor and the walls before conducting Moessbauer and alpha particle x-ray spectrometer readings on some of the same points.

  6. Saline Fluids in Subduction Channels and Mantle Wedge

    NASA Astrophysics Data System (ADS)

    Kawamoto, T.; Hertwig, A.; Schertl, H. P.; Maresch, W. V.; Shigeno, M.; Mori, Y.; Nishiyama, T.

    2015-12-01

    Saline fluids can transport large-ion-lithophile elements and carbonate. Subduction-zone fluids contain salts with various amounts of NaCl equivalent similar to that of the present and/or Phanerozoic seawater (about 3.5 wt% NaCl). The salinity of aqueous fluids in the mantle wedge decreases from trench side to back-arc side, although available data have been limited. Such saline fluids from mantle peridotite underneath Pinatubo, a frontal volcano of the Luzon arc, contain 5.1 wt% NaCl equivalent and CO2 [Kawamoto et al., 2013 Proc Natl Acad Sci USA] and in Ichinomegeta, a rear-arc volcano of the Northeast Japan arc, contain 3.7 wt% NaCl equivalent and CO2 [Kumagai et al., Contrib Mineral Petrol 2014]. Abundances of chlorine and H2O in olivine-hosted melt inclusions also suggest that aqueous fluids to produce frontal basalts have higher salinity than rear-arc basalts in Guatemala arc [Walker et al., Contrib Mineral Petrol 2003]. In addition to these data, quartz-free jadeitites contain fluid inclusions composed of aqueous fluids with 7 wt% NaCl equivalent and quartz-bearing jadeitite with 4.6 wt% NaCl equivalent in supra-subduction zones in Southwest Japan [Mori et al., 2015, International Eclogite Conference] and quartz-bearing jadeitite and jadeite-rich rocks contain fluid inclusions composed of aqueous fluids with 4.2 wt% NaCl equivalent in Rio San Juan Complex, Dominica Republic [Kawamoto et al., 2015, Goldschmidt Conference]. Aqueous fluids generated at pressures lower than conditions for albite=jadeite+quartz occurring at 1.5 GPa, 500 °C may contain aqueous fluids with higher salinity than at higher pressures.

  7. The earthquake cycle in subduction zones

    NASA Technical Reports Server (NTRS)

    Melosh, H. J.; Fleitout, L.

    1982-01-01

    A simplified model of a subduction zone is presented, which incorporates the mechanical asymmetry induced by the subducted slab to anchor the subducting plate during post-seismic rebound and thus throw most of the coseismic stream release into the overthrust plate. The model predicts that the trench moves with respect to the deep mantle toward the subducting 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.

  8. Osmium Recycling in Subduction Zones

    PubMed

    Brandon; Creaser; Shirey; Carlson

    1996-05-10

    Peridotite xenoliths from the Cascade arc in the United States and in the Japan arc have neodymium and osmium isotopic compositions that are consistent with addition of 5 to 15 percent of subducted material to the present-day depleted mantle. These observations suggest that osmium can be partitioned into oxidized and chlorine-rich slab-derived fluids or melts. These results place new constraints on the behavior of osmium (and possibly other platinum group elements) during subduction of oceanic crust by showing that osmium can be transported into the mantle wedge.

  9. Unrevealing the History of Earthquakes and Tsunamis of the Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Ramirez-Herrera, M. T.; Castillo-Aja, M. D. R.; Cruz, S.; Corona, N.; Rangel Velarde, V.; Lagos, M.

    2014-12-01

    The great earthquakes and tsunamis of the last decades in Sumatra, Chile, and Japan remind us of the need for expanding the record of history of such catastrophic events. It can't be argued that even countries with extensive historical documents and tsunami sand deposits still have unsolved questions on the frequency of them, and the variables that control them along subduction zones. We present here preliminary results of a combined approach using historical archives and multiple proxies of the sedimentary record to unrevealing the history of possible great earthquakes and their tsunamis on the Mexican Subduction zone. The Mexican subduction zone extends over 1000 km long and little is known if the entire subduction zone along the Middle American Trench behaves as one enormous unit rather than in segments that rupture at different frequencies and with different strengths (as the short instrumental record shows). We searched on historical archives and earthquake databases to distinguish tsunamigenic events registered from the 16th century to now along the Jalisco-Colima and Guerrero-Oaxaca coastal stretches. The historical data referred are mostly from the 19th century on since the population on the coast was scarce before. We found 21 earthquakes with tsunamigenic potential, and of those 16 with doubtful to definitive accompanying tsunami on the Jalisco-Colima coast, and 31 tsunamigenic earthquakes on the Oaxaca-Guerrero coast. Evidence of great earthquakes and their tsunamis from the sedimentary record are scarce, perhaps due poor preservation of tsunami deposits in this tropical environment. Nevertheless, we have found evidence for a number of tsunamigenic events, both historical and prehistorical, 1932 and 1400 AD on Jalisco, and 3400 BP, 1789 AD, 1979 ad, and 1985 AD on Guerrero-Oaxaca. We continue working and a number of events are still to be dated. This work would aid in elucidating the history of earthquakes and tsunamis on the Mexican subduction zone.

  10. Tsunami Numerical Simulation for Hypothetical Giant or Great Earthquakes along the Izu-Bonin Trench

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    We performed tsunami numerical simulations from various giant/great fault models along the Izu-Bonin trench 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 Japan. 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 trench (Ishibashi and Harada, 2013, SSJ Fall Meeting abstract). The Izu-Bonin subduction zone has been regarded as so-called 'Mariana-type subduction 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 Japan 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 trench 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 trench and check the Ishibashi and Harada's hypothesis, we performed tsunami numerical simulations from fault models along the Izu-Bonin trench

  11. Overriding plate deformation and variability of fore-arc deformation during subduction: Insight from geodynamic models and application to the Calabria subduction zone

    NASA Astrophysics Data System (ADS)

    Chen, Zhihao; Schellart, Wouter P.; Duarte, João. C.

    2015-10-01

    In nature, subducting slabs and overriding plate segments bordering subduction zones are generally embedded within larger plates. Such large plates can impose far-field boundary conditions that influence the style of subduction and overriding plate deformation. Here we present dynamic laboratory models of progressive subduction in three-dimensional space, in which the far-field boundary conditions at the trailing edges of the subducting plate (SP) and overriding plate (OP) are varied. Four configurations are presented: Free (both plates free), SP-Fixed, OP-Fixed, and SP-OP-Fixed. We investigate their impact on the kinematics and dynamics of subduction, particularly focusing on overriding plate deformation. The results indicate that the variation in far-field boundary conditions has an influence on the slab geometry, subduction partitioning, and trench migration partitioning. Our models also indicate that in natural (narrow) subduction zones, assuming a homogeneous overriding plate, the formation of back-arc basins (e.g., Tyrrhenian Sea, Aegean Sea, and Scotia Sea) is generally expected to occur at a comparable location (250-700 km from the trench), irrespective of the boundary condition. In addition, our models indicate that the style of fore-arc deformation (shortening or extension) is influenced by the mobility of the overriding plate through controlling the force normal to the subduction zone interface (trench suction). Our geodynamic model that uses the SP-OP-Fixed setup is comparable to the Calabria subduction zone with respect to subduction kinematics, slab geometry, trench curvature, and accretionary configuration. Furthermore, the model can explain back-arc and fore-arc extension at the Calabria subduction zone since the latest middle Miocene as a consequence of subduction of the narrow Calabrian slab and the immobility of the subducting African plate and overriding Eurasian plate. This setting induced strong trench suction, driving fore-arc extension, and

  12. Frictional properties of fault rocks along the shallow part of the Japan Trench décollement: insights from samples recovered during the Integrated Ocean Drilling Project Expedition 343 (the JFAST project)

    NASA Astrophysics Data System (ADS)

    Remitti, Francesca; Smith, Steven; Gualtieri, Alessandro; Di Toro, Giulio; Nielsen, Stefan

    2014-05-01

    The Japan Trench 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 (μ, shear stress/normal stress) at all investigated velocities of 0.04<μ<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

  13. Relationships among temperature, dehydration of the subducting Philippine Sea plate, and the occurrence of a megathrust earthquake, low-frequency earthquakes, and a slow slip event in the Tokai district, central Japan

    NASA Astrophysics Data System (ADS)

    Suenaga, Nobuaki; Yoshioka, Shoichi; Matsumoto, Takumi

    2016-11-01

    In this study, we performed two-dimensional numerical simulations of temperature distribution associated with subduction of the Philippine Sea (PHS) plate, and estimated the dehydration process of hydrous mid-ocean-ridge basalt (MORB) in the oceanic crust in the Tokai district, central Japan. We discuss the relationship among temperature, dehydration, and a seismogenic zone of an expected megathrust Tokai earthquake, and the occurrence of a slow slip event (SSE) and deep low-frequency earthquakes (LFEs). The depth range of the seismogenic zone for the megathrust earthquake was estimated to be 8-22 km, narrowing toward the east. The most suitable value of the pore pressure ratio on the plate interface was estimated to be 0.97, indicating minimal frictional heating there. The temperatures of the upper surface of the PHS plate, where the Tokai SSE occurred from 2000 to 2005, were estimated to be 350-450 °C. Therefore, the Tokai SSE is considered to have occurred at the transition zone between unstable and stable sliding. In addition, hydrous MORB was transformed from blueschist into greenschist near the region where the Tokai SSE occurred. The temperatures of the upper surface of the PHS plate, where LFEs occur, were estimated to be 450-500 °C. Therefore, LFEs are considered to occur near the down-dip limit of the transition zone. The amount of dehydration from the oceanic crust of the subducting PHS plate near the region where LFEs are distributed in a belt-like form decreases toward the east with deepening of the hypocenters of the LFEs. Thus, the mechanisms of generation of LFEs in the Tokai district might differ from those in southwest and central Japan where LFEs generally occur at depths between 27 and 35 km. In summary, we consider that the occurrence of LFEs is related to both temperature conditions and dehydration process. However, there is an exceptional area in the eastern part of the Tokai district where the occurrence of LFEs is restricted by

  14. Subduction zone tectonic studies to develop concepts for the occurrence of sediment subduction (Phase 2): Volume 3

    SciTech Connect

    Payne, J.; Bandy, B.; Altis, S.; Lee, M.C.; Dwan, S.F.; Ku, K.; Hilde, T.W.C.

    1989-02-01

    The objectives of this study represent a continuation and refinement of the objectives addressed in Phase 1. This study focuses on trying to define the tectonics of sediment subduction at the trench axis through the use of accepted plate tectonic principles and the application of new subduction theory. The fundamental methods include: (1) compilation of all available bathymetric data from our Global Marine Geophysical Data Collection for all major ocean trenches, (2) generation of stacked bathymetric profiles and corresponding navigational maps, and structural maps, (3) selection and analysis of appropriate seismic reflection and refraction profiles and additional supporting data such as side-scan sonar, SEABEAM, magnetic, gravity and drilling data, and (4) detailed study of selected trench regions in which data quality and/or quantity is exceptional. Phase 2 of this project represents a unique compilation and synthesis of existing data for the world's deep ocean trenches. The analysis of data and discussion of results in the context of current literature aids our understanding of the sediment distribution and nature of sediment deformation through various stages of plate convergence, the determination of whether sediments are subducted or accreted, and the evaluation of the controlling factors for sediment subduction and/or accretion. A major emphasis in our analysis of the data was to try and map the seaward-of-the-trench distribution of faults and associated surface roughness. Illustrations and an extensive bibliography are included in the report.

  15. Geological and historical evidence of irregular recurrent earthquakes in Japan.

    PubMed

    Satake, Kenji

    2015-10-28

    Great (M∼8) earthquakes repeatedly occur along the subduction zones around Japan and cause fault slip of a few to several metres releasing strains accumulated from decades to centuries of plate motions. Assuming a simple 'characteristic earthquake' model that similar earthquakes repeat at regular intervals, probabilities of future earthquake occurrence have been calculated by a government committee. However, recent studies on past earthquakes including geological traces from giant (M∼9) earthquakes indicate a variety of size and recurrence interval of interplate earthquakes. Along the Kuril Trench off Hokkaido, limited historical records indicate that average recurrence interval of great earthquakes is approximately 100 years, but the tsunami deposits show that giant earthquakes occurred at a much longer interval of approximately 400 years. Along the Japan Trench off northern Honshu, recurrence of giant earthquakes similar to the 2011 Tohoku earthquake with an interval of approximately 600 years is inferred from historical records and tsunami deposits. Along the Sagami Trough near Tokyo, two types of Kanto earthquakes with recurrence interval of a few hundred years and a few thousand years had been recognized, but studies show that the recent three Kanto earthquakes had different source extents. Along the Nankai Trough off western Japan, recurrence of great earthquakes with an interval of approximately 100 years has been identified from historical literature, but tsunami deposits indicate that the sizes of the recurrent earthquakes are variable. Such variability makes it difficult to apply a simple 'characteristic earthquake' model for the long-term forecast, and several attempts such as use of geological data for the evaluation of future earthquake probabilities or the estimation of maximum earthquake size in each subduction zone are being conducted by government committees.

  16. Sediment Pathways Across Trench Slopes: Results From Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Cormier, M. H.; Seeber, L.; McHugh, C. M.; Fujiwara, T.; Kanamatsu, T.; King, J. W.

    2015-12-01

    Until the 2011 Mw9.0 Tohoku earthquake, the role of earthquakes as agents of sediment dispersal and deposition at erosional trenches was largely under-appreciated. A series of cruises carried out after the 2011 event has revealed a variety of unsuspected sediment transport mechanisms, such as tsunami-triggered sheet turbidites, suggesting that great earthquakes may in fact be important agents for dispersing sediments across trench slopes. To complement these observational data, we have modeled the pathways of sediments across the trench slope based on bathymetric grids. Our approach assumes that transport direction is controlled by slope azimuth only, and ignores obstacles smaller than 0.6-1 km; these constraints are meant to approximate the behavior of turbidites. Results indicate that (1) most pathways issued from the upper slope terminate near the top of the small frontal wedge, and thus do not reach the trench axis; (2) in turn, sediments transported to the trench axis are likely derived from the small frontal wedge or from the subducting Pacific plate. These results are consistent with the stratigraphy imaged in seismic profiles, which reveals that the slope apron does not extend as far as the frontal wedge, and that the thickness of sediments at the trench axis is similar to that of the incoming Pacific plate. We further applied this modeling technique to the Cascadia, Nankai, Middle-America, and Sumatra trenches. Where well-defined canyons carve the trench slopes, sediments from the upper slope may routinely reach the trench axis (e.g., off Costa Rica and Cascadia). In turn, slope basins that are isolated from the canyons drainage systems must mainly accumulate locally-derived sediments. Therefore, their turbiditic infill may be diagnostic of seismic activity only - and not from storm or flood activity. If correct, this would make isolated slope basins ideal targets for paleoseismological investigation.

  17. Structural Responses to the Chile Ridge Subduction, Southern South America

    NASA Astrophysics Data System (ADS)

    Rodriguez, E. E.; Russo, R. M.; Mocanu, V. I.; Gallego, A.; Murdie, R.; Comte, D.

    2015-12-01

    The Nazca-Antarctic plate boundary, the Chile spreading ridge, subducts beneath South America, forming the northward-migrating Chile Triple Junction (CTJ), now at ~46.5°S, where an actively spreading segment is currently in the Nazca trench. Ridge subduction is associated with diachronously developed variable structure and magmatism of overriding South America. To assess the effects of ridge subduction, we deployed a network of 39 broadband seismometers in southern Chile between 43 - 49°S and 71 - 76°W from Dec. 2004 - Feb. 2007, recording 102 earthquakes suitable for receiver function analyses, i.e., M > 5.9, of various backazimuths, and at epicentral distances of 30 - 90°. The network encompassed onland portions of the current triple junction and ridge subduction, areas to the south of the CTJ where ridge segments subducted during the last 6 m.y., and regions north of the CTJ not yet affected by ridge subduction, allowing the assessment of the effects of ridge subduction on crustal structure of overriding South America. We constructed 551 teleseismic receiver functions to estimate crustal thicknesses, H, and average compressional to shear wave velocity ratios, Vp/Vs = k, using the iterative time deconvolution method of Ligorria and Ammon (1999). H and k were calculated using the grid search method of Zhu and Kanamori (2000). Beneath stations closest to the trench, where the Nazca plate subducts, we found Moho depths between 28 and 55 km, thickening northward. At the locus of current ridge subduction, in the Taitao Pennisula, thinner crust ranges from 27 - 36 km. H is 36-38 km where the Antarctic plate subducts and the Chile ridge recently subducted. The direct effect of the subducting ridge on South America can be seen in H differences between forearc regions that have sustained ridge subduction versus those that have not. South American forearc crust above the subducted Nazca plate is as much as 28 km thicker than forearc crust recently affected by ridge

  18. Elastic Properties of Subduction Zone Materials in the Large Shallow Slip Environment for the Tohoku 2011 Earthquake: Laboratory data from JFAST Core Samples

    NASA Astrophysics Data System (ADS)

    Jeppson, T.; Tobin, H. J.

    2014-12-01

    The 11 March 2011 Tohoku-Oki earthquake (Mw=9.0) produced large displacements of ~50 meters near the Japan Trench. In order to understand earthquake propagation and slip stabilization in this environment, quantitative values of the real elastic properties of fault zones and their surrounding wall rock material is crucial. Because elastic and mechanical properties of faults and wallrocks are controlling factors in fault strength, earthquake generation and propagation, and slip stabilization, an understanding of these properties and their depth dependence is essential to understanding and accurately modeling earthquake rupture. In particular, quantitatively measured S-wave speeds, needed for estimation of elastic properties, are scarce in the literature. We report laboratory ultrasonic velocity measurements performed at elevated pressures, as well as the calculated dynamic elastic moduli, for samples of the rock surrounding the Tohoku earthquake principal fault zone recovered by drilling during IODP Expedition 343, Japan Trench Fast Drilling Project (JFAST). We performed measurements on five samples of gray mudstone from the hanging wall and one sample of underthrust brown mudstone from the footwall. We find P- and S-wave velocities of 2.0 to 2.4 km/s and 0.7 to 1.0 km/s, respectively, at 5 MPa effective pressure. At the same effective pressure, the hanging wall samples have shear moduli ranging from 1.4 to 2.2 GPa and the footwall sample has a shear modulus of 1.0 GPa. While these values are perhaps not surprising for shallow, clay-rich subduction zone sediments, they are substantially lower than the 30 GPa commonly assumed for rigidity in earthquake rupture and propagation models [e.g., Ide et al., 1993; Liu and Rice, 2005; Loveless and Meade, 2011]. In order to better understand the elastic properties of shallow subduction zone sediments, our measurements from the Japan Trench are compared to similar shallow drill core samples from the Nankai Trough, Costa Rica

  19. Geochemical variations in Japan Sea back-arc basin basalts formed by high-temperature adiabatic melting of mantle metasomatized by sediment subduction components

    NASA Astrophysics Data System (ADS)

    Hirahara, Yuka; Kimura, Jun-Ichi; Senda, Ryoko; Miyazaki, Takashi; Kawabata, Hiroshi; Takahashi, Toshiro; Chang, Qing; Vaglarov, Bogdan S.; Sato, Takeshi; Kodaira, Shuichi

    2015-05-01

    The Yamato Basin in the Japan Sea is a back-arc basin characterized by basaltic oceanic crust that is twice as thick as typical oceanic crust. Two types of ocean floor basalts, formed during the opening of the Japan Sea in the Middle Miocene, were recovered from the Yamato Basin during Ocean Drilling Program Legs 127/128. These can be considered as depleted (D-type) and enriched (E-type) basalts based on their incompatible trace element and Sr-Nd-Pb-Hf isotopic compositions. Both types of basalts plot along a common mixing array drawn between depleted mantle and slab sediment represented by a sand-rich turbidite on the Pacific Plate in the NE Japan fore arc. The depleted nature of the D-type basalts suggests that the slab sediment component is nil to minor relative to the dominant mantle component, whereas the enrichment of all incompatible elements in the E-type basalts was likely caused by a large contribution of bulk slab sediment in the source. The results of forward model calculations using adiabatic melting of a hydrous mantle with sediment flux indicate that the melting conditions of the source mantle for the D-type basalts are deeper and hotter than those for the E-type basalts, which appear to have formed under conditions hotter than those of normal mid-oceanic ridge basalts (MORB). These results suggest that the thicker oceanic crust was formed by greater degrees of melting of a hydrous metasomatized mantle source at unusually high mantle potential temperature during the opening of the Japan Sea.

  20. Heterogeneous interplate coupling along the Nankai Trough, Japan, detected by GPS-acoustic seafloor geodetic observation

    NASA Astrophysics Data System (ADS)

    Yokota, Yusuke; Ishikawa, Tadashi; Sato, Mariko; Watanabe, Shun-ichi; Saito, Hiroaki; Ujihara, Naoto; Matsumoto, Yoshihiro; Toyama, Shin-ichi; Fujita, Masayuki; Yabuki, Tetsuichiro; Mochizuki, Masashi; Asada, Akira

    2015-12-01

    The recurring devastating earthquake that occurs in the Nankai Trough subduction zone between the Philippine Sea plate and the Eurasian plate has the potential to cause an extremely dangerous natural disaster in the foreseeable future. Many previous studies have assumed interplate-coupling ratios for this region along the trench axis using onshore geodetic data in order to understand this recursive event. However, the offshore region that has the potential to drive a devastating tsunami cannot be resolved sufficiently because the observation network is biased to the land area. Therefore, the Hydrographic and Oceanographic Department of Japan constructed a geodetic observation network on the seafloor along the Nankai Trough using a GPS-acoustic combination technique and has used it to observe seafloor crustal movements directly above the Nankai Trough subduction zone. We have set six seafloor sites and cumulated enough data to determine the displacement rate from 2006 to January 2011. Our seafloor geodetic observations at these sites revealed a heterogeneous interplate coupling that has three particular features. The fast displacement rates observed in the easternmost area indicate strong interplate coupling (>75%) around not only the future Tokai earthquake source region but also the Paleo-Zenisu ridge. The slow displacement rates near the trench axis in the Kumano-nada Sea, a shallow part of the 1944 Tonankai earthquake source region, show a lower coupling ratio (50% to 75%). The slow displacement rate observed in the area shallower than the 1946 Nankaido earthquake source region off Cape Muroto-zaki reflects weakening interplate coupling (about 50%) probably due to a subducting seamount. Our observations above the subducting ridge and seamount indicate that the effect of a subducting seamount on an interplate-coupling region depends on various conditions such as the geometry of the seamount and the friction parameters on the plate boundary.

  1. Methane and propane micro-inclusions in olivine in titanoclinohumite-bearing dunites from the Sanbagawa high-P metamorphic belt, Japan: Hydrocarbon activity in a subduction zone and Ti mobility

    NASA Astrophysics Data System (ADS)

    Arai, Shoji; Ishimaru, Satoko; Mizukami, Tomoyuki

    2012-11-01

    Micro-inclusions of methane and propane were examined in olivine and titanoclinohumite in dunite from Fujiwara, Sanbagawa high-P/T metamorphic belt, Japan, in order to understand the behavior of hydrocarbons in the subduction zone and mantle wedge. In the Fujiwara dunite, olivines coexist with magnetite and exhibit a wide range of chemical compositions (Fo88-96 and 0.2-0.6 wt% NiO), possibly indicating a deserpentinization origin for the dunite. The primary chromian spinel shows an intermediate Cr/(Cr+Al) atomic ratio, 0.5-0.6, and 1-3 wt% TiO2, and are enclosed by its alteration phases (ferritechromite and magnetite) that contain less than 0.8 wt% TiO2. Titanoclinohumite is frequently accompanied with the altered spinels, suggesting its Ti was provided by spinel alteration. Thin (<1 cm) titanoclinohumite veinlets are commonly found, indicating Ti was mobile during the metamorphic formation of the Fujiwara meta-dunite. Hydrocarbons are usually associated with serpentine and brucite, almost free of magnetite, in individual micro-inclusions, suggesting initial entrapment of hydrocarbon-rich aqueous fluids and subsequent reaction only between their water component and the wall olivine. The primary dunite of Fujiwara, originally formed as a cumulate from intra-plate magma, and was serpentinized and brecciated to contain carbonaceous matter in the matrix part before incorporation in the subduction zone. The hydrocarbons possibly formed with maturation of the carbonaceous matter in the process of subduction. The continuously formed hydrocarbons mobilized Ti from chromian spinel to leave low-Ti ferritechromite and magnetite in the Fujiwara dunite, and finally stabilized as titanoclinohumite and other Ti-rich minerals during deserpentinization at high pressures. The titanoclinohumite veinlet formation suggests the Ti mobility, although in a short distance in this specific case. Ti is possibly mobile within the mantle wedge if hydrocarbons are available from the slab, but

  2. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga-Kermadec arc

    NASA Astrophysics Data System (ADS)

    Timm, Christian; Bassett, Daniel; Graham, Ian J.; Leybourne, Matthew I.; de Ronde, Cornel E. J.; Woodhead, Jon; Layton-Matthews, Daniel; Watts, Anthony B.

    2013-04-01

    Subduction of intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in subduction 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 trench intersection, to provide new insights into the effects of Louisville seamount subduction. Elevated 206Pb/204Pb, 208Pb/204Pb, 86Sr/87Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of subducted alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the subducted Louisville seamount chain that, combined with estimates of the timing of fluid release from the subducting slab, suggests primarily trench-normal mantle flow beneath the central Tonga-Kermadec arc system.

  3. Louisville seamount subduction and its implication on mantle flow beneath the central Tonga-Kermadec arc.

    PubMed

    Timm, Christian; Bassett, Daniel; Graham, Ian J; Leybourne, Matthew I; de Ronde, Cornel E J; Woodhead, Jon; Layton-Matthews, Daniel; Watts, Anthony B

    2013-01-01

    Subduction of intraplate seamounts beneath a geochemically depleted mantle wedge provides a seldom opportunity to trace element recycling and mantle flow in subduction 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 trench intersection, to provide new insights into the effects of Louisville seamount subduction. Elevated (206)Pb/(204)Pb, (208)Pb/(204)Pb, (86)Sr/(87)Sr in lavas from the central Tonga-Kermadec arc front are consistent with localized input of subducted alkaline Louisville material (lavas and volcaniclastics) into sub-arc partial melts. Furthermore, absolute Pacific Plate motion models indicate an anticlockwise rotation in the subducted Louisville seamount chain that, combined with estimates of the timing of fluid release from the subducting slab, suggests primarily trench-normal mantle flow beneath the central Tonga-Kermadec arc system.

  4. From subduction to collision: results of French POP2 program on Taiwan-Philippine festoon

    SciTech Connect

    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.

    1986-07-01

    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 Trench and its junction with the Taiwan tectonic prism; and (3) southern termination of Manila Trench in front of Mindoro Island. Transitions between active subduction along the Manila Trench and collision of Taiwan and Mindoro, and relations between active subduction and extension in the Okinawa-Ryukyu and the northeastern Taiwan systems are particularly studied.

  5. A consistent model for fluid distribution, viscosity distribution, and flow-thermal structure in subduction zone

    NASA Astrophysics Data System (ADS)

    Horiuchi, Shun-suke; Iwamori, Hikaru

    2016-05-01

    Water plays crucial roles in the subduction zone dynamics affecting the thermal-flow structure through the fluid processes. We aim to understand what controls the dynamics and construct a model to solve consistently fluid generation, fluid transport, its reaction with the solid and resultant viscosity, and thermal-flow structure. We highlight the effect of mechanical weakening of rocks associated with hydration. The viscosity of serpentinite (ηserp) in subduction zones critically controls the flow-thermal structure via extent of mechanical coupling between the subducting slab and overlying mantle wedge. When ηserp is greater than 1021 Pa s, the thermal-flow structure reaches a steady state beneath the volcanic zone, and the melting region expands until Cin (initial water content in the subducting oceanic crust) reaches 3 wt %, and it does not expand from 3 wt %. On the other hand, when ηserp is less than 1019 Pa s, the greater water dependence of viscosity (expressed by a larger fv) confines a hot material to a narrower channel intruding into the wedge corner from a deeper part of the back-arc region. Consequently, the overall heat flux becomes less for a larger fv. When ageba (age of back-arc basin as a rifted lithosphere) = 7.5 Ma, the increase in fv weakens but shifts the melting region toward the trench side because of the narrow channel flow intruding into the wedge corner, where as it shuts down melting when ageba=20 Ma. Several model cases (particularly those with ηserp=1020 to 1021 Pa s and a relatively large fv for Cin=2 to 3 wt %) broadly account for the observations in the Northeast Japan arc (i.e., location and width of volcanic chain, extent of serpentinite, surface heat flow, and seismic tomography), although the large variability of surface heat flow and seismic tomographic images does not allow us to constrain the parameter range tightly.

  6. Metamorphic Perspectives of Subduction Zone Volatiles Cycling

    NASA Astrophysics Data System (ADS)

    Bebout, G. E.

    2008-12-01

    Field study of HP/UHP metamorphic rocks provides "ground-truthing" for experimental and theoretical petrologic studies estimating extents of deep volatiles subduction, and provides information regarding devolatilization and deep subduction-zone fluid flow that can be used to reconcile estimates of subduction inputs and arc volcanic outputs for volatiles such as H2O, N, and C. Considerable attention has been paid to H2O subduction in various bulk compositions, and, based on calculated phase assemblages, it is thought that a large fraction of the initially structurally bound H2O is subducted to, and beyond, subarc regions in most modern subduction zones (Hacker, 2008, G-cubed). Field studies of HP/UHP mafic and sedimentary rocks demonstrate the impressive retention of volatiles (and fluid-mobile elements) to depths approaching those beneath arcs. At the slab-mantle interface, high-variance lithologies containing hydrous phases such as mica, amphibole, talc, and chlorite could further stabilize H2O to great depth. Trench hydration in sub-crustal parts of oceanic lithosphere could profoundly increase subduction inputs of particularly H2O, and massive flux of H2O-rich fluids from these regions into the slab-mantle interface could lead to extensive metasomatism. Consideration of sedimentary N concentrations and δ15N at ODP Site 1039 (Li and Bebout, 2005, JGR), together with estimates of the N concentration of subducting altered oceanic crust (AOC), indicates that ~42% of the N subducting beneath Nicaragua is returned in the corresponding volcanic arc (Elkins et al., 2006, GCA). Study of N in HP/UHP sedimentary and basaltic rocks indicates that much of the N initially subducted in these lithologies would be retained to depths approaching 100 km and thus available for addition to arcs. The more altered upper part of subducting oceanic crust most likely to contribute to arcs has sediment-like δ15NAir (0 to +10 per mil; Li et al., 2007, GCA), and study of HP/UHP eclogites

  7. 'Snow White' Trench

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image was acquired by NASA's Phoenix Mars Lander's Surface Stereo Imager on Sol 43, the 43rd Martian day after landing (July 8, 2008). This image shows the trench informally called 'Snow White.'

    Two samples were delivered to the Wet Chemistry Laboratory, which is part of Phoenix's Microscopy, Electrochemistry, and Conductivity Analyzer (MECA). The first sample was taken from the surface area just left of the trench and informally named 'Rosy Red.' It was delivered to the Wet Chemistry Laboratory on Sol 30 (June 25, 2008). The second sample, informally named 'Sorceress,' was taken from the center of the 'Snow White' trench and delivered to the Wet Chemistry Laboratory on Sol 41 (July 6, 2008).

    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.

  8. Track-and-Trench

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image shows the tracks and trench marks made by the Mars Exploration Rover Opportunity at Meridiani Planum, Mars. The rover can be seen to the lower left of the lander. The trench is visible to the upper left of the rover, which has traveled a total of 35.3 meters (116 feet) since leaving the lander on sol 7 (January 31, 2004). On sol 23 (February 16, 2004), the rover used one of its wheels to dig a trench measuring approximately 10 centimeters (4 inches) deep, 50 centimeters (20 inches) long, and 20 centimeters (8 inches) wide. This vertically projected image was created using a combination of images from the rover's navigation camera and hazard-avoidance cameras.

  9. Offset trench isolation

    NASA Astrophysics Data System (ADS)

    Roth, S. S.; Cooper, K. J.; Ray, W.; Kirsch, H. C.; Grove, Charlotte

    1994-08-01

    Feasibility of a new, recessed isolation technique that utilizes an offset, shallow trench in combination with thermal oxidation for achieving near zero final encroachment with excellent planarity is demonstrated. Etch of the shallow trench is offset from the original hardmask by an oxide sidewall spacer. After trench etch, HF is used to remove the hardmask oxide and sidewall spacers and to form a cavity which is self-aligned to the nitride edge. Exposed silicon regions are then reoxidized and encapsulated with polysilicon. Field oxide is then grown. The final field oxide profile exhibits steep sidewall angles without inducing substrate defects as evidenced by low diode leakage. Other isolation sensitive device parametrics such as gate oxide quality and metal oxide semiconductor field effect transistor threshold voltage stability are presented and exhibit good characteristics.

  10. Subduction Variability Along the Active Chilean Margin

    NASA Astrophysics Data System (ADS)

    Reichert, C. J.; Barckhausen, U.; Bartsch, H.; Block, M.; Boennemann, C.; Diaz-Naveas, J. L.; Flueh, E. R.; Delisle, G.; Gaedicke, C.; Kopp, H.; Krawczyk, C. M.; Kus, J.; Ladage, S.; Ranero, C.; Schreckenberger, B.; Stoll, J. B.; Urbina, O.; Wiedicke-Hombach, M.

    2002-12-01

    The presence of different subduction modes in the convergence process between the Nazca and South-American plates along the Chilean margin is known from previous investigations. In order to study this variability in detail a comprehensive combined off- and onshore geo-scientific survey (SPOC) was recently conducted between Coquimbo and Valdivia in collaboration between a number of German and Chilean institutions. Major focus was also put on the structure of the sedimentary forearc basins and the distribution of gas hydrates along the slope. SPOC is the successor project to a similar experiment named CINCA that was earlier performed in the far north of Chile between Arica and Taltal. The SPOC results clearly show a change in subduction mode at about 33 deg S where the Juan Fernandez Ridge presently strikes the margin. North of that latitude, structural features such as extensional fracturing of the continental slope, very little or almost no sedimentary trench fill, intensive block faulting of the oceanic crust, a missing accretionary wedge, a very narrow shelf and other facts provide evidence for subduction erosion in that region. South of 33 deg S, we observed significantly steeper frontal slope angles and much less inclination of the oceanic crust toward the trench. In general, the topography of the oceanic crust is relatively smooth with the exception of several seamounts and fracture zones. Moreover, the width of the trench and of the shelf significantly widens toward the south, and pronounced forearc basins developed. Compared to the thick sedimentary trench fill of up to 2 km a very narrow accretionary wedge was encountered. Preliminary mass balancing combined with the assumption that the high present convergence rate occurred also in the past suggests that the bulk of the trench sediments is removed by subduction. Thus, accretionary processes can play only a subordinate or intermittent role. Geological seafloor samples support the assumption that small- to

  11. Phoenix's Snow White Trench

    NASA Technical Reports Server (NTRS)

    2008-01-01

    A soil sample taken from the informally named 'Snow White' trench at NASA's Phoenix Mars Lander work site produced minerals that indicate evidence of past interaction between the minerals and liquid water.

    This image was taken by the Surface Stereo Imager on Sol 103, the 103rd day since landing (Sept. 8, 2008).

    The trench is approximately 23 centimeters (9 inches) long.

    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.

  12. Interplate coupling along the Java trench from CGPS observation

    NASA Astrophysics Data System (ADS)

    Meilano, I.; Kuncoro, H.; Susilo, S.; Efendi, J.; Abidin, H. Z.; Nugraha, A. D.; Widiyantoro, S.

    2014-12-01

    Interplate seismogenic zones along the Java trench were estimated by using continuous GPS observation from South of Lampung in the west to Lombok Island in the east. The observation period starting from 2010 to 2013 with more than 60 CGPS observation stations. The GPS analysis indicates that present-day deformation of Java Island is controlled by rotation of Sunda land, extension in the southern Strait of Sunda, postseismic deformation of the 2006 earthquake and the coupling between Indo-Australian plate and Sunda land. Strain rate solutions indicate compression in the south of Java Island. Using elastic dislocation theory the estimated interplate seismozonic coupling in the Java trench is about 50 percent in the sunda strait, smaller in the south west java and become larger to the east. Slip deficit on subduction interface has important implication for seismic hazard of Java Island. Keywords: CGPS observation, Interplate Seismogenic, Java Trench

  13. Late Permian/early Triassic orogeny in Japan: piling up of nappes, transverse lineation and continental subduction of the Honshu block

    NASA Astrophysics Data System (ADS)

    Faure, Michel; Charvet, Jacques

    1987-07-01

    Field surveys in the Oga-Atetsu and Yamaguchi areas of Southwest Japan have been conducted in order to precise the structure of the Permian orogen. A stack of nappes is recognized comprising from top to bottom: (1) the Oga nappe which is considered to be a seamount complex, (2) HP Sangun metamorphics, (3) the Permian Yakuno ophiolite, and (4) the Permian detrital Maizuru group which is interpreted as the sedimentary cover of a continental block, called here the Honshu block, outcropping as the Older Granite. This stack of nappes is overthrust by the Paleozoic Hida basement consisting of HT gneisses, granites and late Carboniferous shallow-water sediments. Microtectonic analysis of the Sangun schists shows that the subhorizontal schistosity bearing a submeridian lineation was formed during the synmetamorphic phase. Asymmetric pressure shadows, shear bands and sigmoidal minerals show that the synmetamorphic deformation corresponds to a ductile shear from north to south. The Permian/early Triassic orogeny is interpreted as the result of a collision between the Hida gneiss (or South China block) and the Honshu block, the intervening oceanic area gave rise to southward directed nappes. The Permian orogenic belt extends at least from Taiwan to central Japan.

  14. Subduction zone tectonic studies to develop concepts for the occurrence of sediment subduction (Phase 2): Volume 2

    SciTech Connect

    Payne, J.; Bandy, B.; Altis, S.; Lee, M.C.; Dwan, S.F.; Ku, K.; Hilde, T.W.C.

    1989-02-01

    The objectives of this study represent a continuation and refinement of the objectives addressed in Phase 1. This study focuses on trying to define the tectonics of sediment subduction at the trench axis through the use of accepted plate tectonic principles and the application of new subduction theory. The fundamental methods include: (1) compilation of all available bathymetric data from our Global Marine Geophysical Data Collection for all major ocean trenches, (2) generation of stacked bathymetric profiles and corresponding navigational maps, and structural maps, (3) selection and analysis of appropriate seismic reflection and refraction profiles and additional supporting data such as side-scan sonar, SEABEAM, magnetic, gravity and drilling data, and (4) detailed study study of selected trench regions in which data quality and/or quantity is exceptional. Phase 2 of this project represents a unique compilation and synthesis of existing data for the world's deep ocean trenches. The analysis of data and discussion of results in the context of current literature aids our understanding of the sediment distribution and nature of sediment deformation through various stages of plate convergence, the determination of whether sediments are subducted or accreted, and the evaluation of the controlling factors for sediment subduction and/or accretion. A discussion on petroleum and natural gas hydrate resource potential is included.

  15. Subduction zone tectonic studies to develop concepts for the occurrence of sediment subduction (Phase 2): Volume 1

    SciTech Connect

    Payne, J.; Bandy, B.; Altis, S.; Lee, M.C.; Dwan, S.F.; Ku, K.; Hilde, T.W.C.

    1989-02-01

    This is volume one of three volumes. The objectives of this study represent a continuation and refinement of the objectives addressed in Phase I. This study focuses on trying to define the tectonics of sediment subduction at the trench axis through the use of accepted plate tectonic principles and the application of new subduction theory. The fundamental methods include: (1) compilation of all available bathymetric data from our Global Marine Geophysical Data Collection for all major ocean trenches, (2) generation of stacked bathymetric profiles and corresponding navigational maps, and structural maps, (3) selection and analysis of appropriate seismic reflection and refraction profiles and additional supporting data such as side-scan sonar, SEABEAM, magnetic, gravity and drilling data, and (4) detailed study of selected trench regions in which data quality and/or quantity is exceptional. Phase II of this project represents a unique compilation and synthesis of existing data for the world's deep ocean trenches. The analysis of data and discussion of results in the context of current literature aids our understanding of the sediment distribution and nature of sediment deformation through various stages of plate convergence, the determination of whether sediments are subducted or accreted, and the evaluation of the controlling factors for sediment subduction and/or accretion. A discussion is included on forearc petroleum and natural gas hydrate resource potential. 128 figs.

  16. Snow White 5 Trench

    NASA Technical Reports Server (NTRS)

    2008-01-01

    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 trench informally called 'Snow White 5.' The trench 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.

    Snow White 5 is Phoenix's current active digging area after additional trenching, grooming, and scraping by Phoenix's Robotic Arm in the last few sols to trenches 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.

    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.'

    This image has been enhanced to brighten shaded areas.

    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.

  17. Alternative Trench Disposal Concepts

    SciTech Connect

    Wilhite, E.

    2001-09-05

    During Fiscal Year 2000, a number of activities were conducted to expand the use of trenches for disposal of low-level waste in the E-Area Low-Level Waste Facility (LLWF). This document presents a summary and interpretation of these activities in the context of future work.

  18. Stress interaction between subduction earthquakes and forearc strike-slip faults: Modeling and application to the northern Caribbean plate boundary

    USGS Publications Warehouse

    ten Brink, U.; Lin, J.

    2004-01-01

    Strike-slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers. We explore the interaction between thrust events on the subduction interface and strike-slip faults within the forearc region using three-dimensional models of static Coulomb stress change. Model results reveal that subduction earthquakes with slip vectors subparallel to the trench axis enhance the Coulomb stress on strike-slip faults adjacent to the trench but reduce the stress on faults farther back in the forearc region. In contrast, subduction events with slip vectors perpendicular to the trench axis enhance the Coulomb stress on strike-slip faults farther back in the forearc, while reducing the stress adjacent to the trench. 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 subduction interface. We argue that although Coulomb stress changes from individual subduction 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 subduction zone. Subduction earthquakes with slip vectors nearly perpendicular to the Caribbean trench axis is dominant in the Hispaniola segment, where the strike-slip faults are more than 60 km inland from the trench. In contrast, subduction slip motion is nearly parallel to the Caribbean trench axis along the Puerto Rico segment, where the strike-slip fault is less than 15 km from the trench. This observed jump from a strike-slip fault close to the trench 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

  19. Near-trench aftershocks of the 2011 Tohoku-oki earthquake based on ocean bottom seismograph obserbations

    NASA Astrophysics Data System (ADS)

    Obana, K.; Shinohara, M.; Yamada, T.; Uehira, K.; Hino, R.; Shiobara, H.; Nakahigashi, K.; Sugioka, H.; Ito, A.; Nakamura, Y.; No, T.; Miura, S.; Kodaira, S.; Takahashi, N.

    2012-12-01

    After the 2011 Mw 9.0 Tohoku-Oki Earthquakes, aftershocks with a normal-faulting focal mechanism have been activated both in the overriding plate and incoming/subducting Pacific plate near the trench axis [e.g., Asano et al., 2011]. We conducted ocean bottom seismograph (OBS) observations using short-period and broad-band OBSs near the Japan Trench from August to October 2011. These OBSs were deployed on the landward slope including the area, where the several tens of meters co-seismic displacement was observed [e.g., Fujiwara et al., 2011], with approximately 10 to 20 km separation in horizontal. Earthquakes were detected from continuous seismograms obtained by the OBSs. The phase arrival times were picked manually. We determined the hypocenters by using a grid search method in a 2-D velocity model based on the active seismic survey [Ito et al., 2005]. Focal mechanisms were also estimated from polarities of the first motion of P-wave arrivals. The obtained results show that normal-faulting earthquakes occurred within the overriding plate. These earthquakes likely relate to the normal fault system in the overriding plate. On the other hand, no earthquakes have been observed within the toe of the overriding plate, where the several tens of meters of co-seismic slip displacement along the plate interface occurred during the 2011 Tohoku-oki Earthquake. Earthquakes located within the subducting plate have a strike-slip faulting focal mechanism. These earthquakes are considered to be an aftershock activity of the Mw 7.0 strike slip event occurred on July 10, 2011.

  20. Significant foreshock activities of M>7.5 earthquakes in the Kuril subduction zone

    NASA Astrophysics Data System (ADS)

    Harada, T.; Yokoi, S.; Satake, K.

    2014-12-01

    In the Kuril subduction zone, some M>7.5 earthquakes are accompanied by significant foreshock activities, providing a good opportunity to understand the characteristics of foreshocks for large interplate events such as occur along the Japan Trench and Nankai Trough etc. Some preliminary results from our examination of the foreshock sequences are as follows. Relocated foreshocks tend to migrate with time toward the trench axis. Foreshock distributions of the interplate earthquakes do not overlap with the large coseismic slips (asperities) of the mainshocks. Foreshocks of the 2007 northern Kuril outer-rise event, however, were distributed on the entire rupture area. Foreshock sequences seem to be limited in the regions where the background seismicity rates are relatively high. The foreshock activities were found in the examination of the space-time pattern of M>7 events along the northern Japan to Kuril trench since 1913 (e.g. Harada, Satake, and Ishibashi, 2011:AGU, 2012:AOGS). The large earthquakes preceded by active foreshock sequences are: the 2006 (M8.3), 2007 (M8.1) offshore Simushir earthquakes, the 1963 (M8.5), 1991 (M7.6), 1995 (M7.9) offshore Urup events, the 1978 (M7.8) offshore Iturup events, the 1969 (M8.2) offshore Shikotan event. In contrast, M>7.5 interplate earthquakes offshore Hokkaido (1952 (M8.1), 1973 (M7.8), 2003 (M8.1)) and intraslab earthquakes (1958 (M8.3), 1978 (M7.8), 1993 (M7.6), 1994 (M8.3)) had few or no foreshocks. In the examination of the active foreshocks, we relocated foreshocks by the Modified JHD method (Hurukawa, 1995), compared relocated foreshock areas with mainshock coseismic slip distributions estimated by the teleseismic body-wave inversion (Kikuchi and Kanamori, 2003), and examined the relation between active foreshock sequences and regional background seismicity. This study was supported by the MEXT's "New disaster mitigation research project on Mega thrust earthquakes around Nankai/Ryukyu subduction zones".

  1. Formation of the Yakuno ophiolite; accretionary subduction under medium-pressure-type metamorphic conditions

    NASA Astrophysics Data System (ADS)

    Osozawa, Soichi; Takeuchi, Hiroshi; Koitabashi, Toru

    2004-11-01

    The notion that the Yakuno ophiolite and overlying Maizuru Group represents an accretionary prism formed during the Permian evolution of Japan on the Yakuno eruptive sequence, association of hemipelagic mudstone with silicic tuff, exotic fossiliferous limestones derived from previously accreted sea-mounts, upward coarsening of sequences terrigenous sandstone and conglomerate, and mildly deformed Permian and Triassic forearc basin formations. The most important indicator, however, is the seaward imbrication and repetition observed in both the Maizuru Group and the ophiolite itself. D1 deformation structures include axial-planar foliations (pressure-solution cleavage for the Maizuru Group and granulite-amphibolite metamorphic layering in the ophiolite), flattening type strain, symmetric pressure shadows and fringes, and isoclinal folds showing axial-planar foliations and thrust faulting at their overturned limb. The exceptional asymmetry observed indicates seaward-directed shearing near the thrust, while D1 structures in the Maizuru zone are explained by off-scraping, above the basal decollement. The later Jurassic D2 kink fold structure includes a first-order asymmetric kink with a brittle thrust at its overturned limb, more-or-less coeval with M2 retrograde metamorphism. Medium-pressure M1 prograde metamorphism in the Yakuno ophiolite produced layering of granulite and amphibolite, and in the Maizuru Group, formation of illite along pressure-solution cleavage of mudstones. The metamorphic grade is controlled by the stratigraphic relationships and appears typical of that in ocean floor regions. However, there was only one episode of M1 prograde metamorphism which occurred contemporaneously with D1 off-scraping. Given that subduction zones are normally characterized by high P/ T metamorphic regimes, the observed P/ T history appears to reflect relatively unusual conditions. Such high thermal gradients may plausibly reflect the approach of a young, hot oceanic plate

  2. Trench migration, net rotation and slab mantle coupling

    NASA Astrophysics Data System (ADS)

    Funiciello, F.; Faccenna, C.; Heuret, A.; Lallemand, S.; Di Giuseppe, E.; Becker, T. W.

    2008-07-01

    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 subduction dynamics over geological time scales. Our models are set up with a viscous plate of silicone (lithosphere) subducting 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 subduction 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 subduction 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 trench/subducting plate velocity ratios as well as the variability of subduction styles observed in nature.

  3. Subduction Drive of Plate Tectonics

    NASA Astrophysics Data System (ADS)

    Hamilton, W. B.

    2003-12-01

    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. Subduction-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 subduction drive. All trenches roll back when allowance is made for back-arc spreading and intracontinental deformation. Africa rotates slowly toward subduction 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 subduction 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.

  4. Evolution and diversity of subduction zones controlled by slab width.

    PubMed

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

    2007-03-15

    Subducting 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 subduction-induced flow. Most previous geodynamic studies treat subduction zones as either infinite in trench-parallel extent (that is, two-dimensional) or finite in width but fixed in space. Subduction 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 subduction zones and their tendency to retreat backwards with time. Using three-dimensional numerical simulations of free subduction, we show that trench 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 trench retreat increases towards concave-shaped edges. Additionally, we identify periods (5-10 Myr) of slow trench 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.

  5. A runaway slip to the trench due to breaking through abnormally pressurized megathrust under the middle trench slope - The tsunamigenesis of the 2011 Tohoku earthquake -

    NASA Astrophysics Data System (ADS)

    Kimura, G.; Hina, S.; Hamada, Y.; Kameda, J.; Tsuji, T.; Kinoshita, M.; Yamaguchi, A.

    2011-12-01

    The rupture and slip by the 2011 Tohoku Earthquake on March 11 along the plate boundary megathrust propagated upward, broke through the ordinal up-dip limit of the seismogenic zone at a depth of ~15 km, and reached the trench. The extremely large tsumani caused by rapid uplift of the middle to lower slope more than 10 m took place at ~60s after the rise of the earthquake as a result of the runaway slip along the megathrust more than a few tens of meters The 2011 Tohoku earthquake is examined from the point of view of the structure of the forearc before the earthquake, the reflection property of the megathrust around the ordinal up-dip limit of the seismogenic zone, thermal state of the shallow portion of subduction zone, and dehydration process of underthrust sediment. The Pacific plate subducts westward at a dip angle of 4.6°. Middle and lower slopes dip eastward at angles of ~2.5° and ~8.0°, respectively. The prisms beneath the middle and lower slopes are inferred to be under extenionally and compressively critical states, respectively because of clear internal deformation features and aftershock earthquakes. Rapid uplift causing the tsunami during the 2011 earthquake might have associated with the internal deformation of the prism. The critical states of the prisms suggest that effective basal frictions of the plate boundary megathrust might be μb'<0,03 for the middle prism and μb'>0.08 for the lower prism. The megathrust under the middle slope is characterized by a reflector with negative polarity, of which amplitude increases landward. Such seismic character suggests that the megathrust includes abnormally pressurized fluid. Underthrust sediments in this part of the Japan Trench are dominated by pelagic and siliceous diatomaceous silt with clay. Dehydration kinetics of Opal A to quartz, clay transformation of smectite-illite, and thermal condition suggests that maximum dehydration from the sediments would take place from ~50 km to 60 km from the

  6. 3D Numerical simulations of oblique subduction

    NASA Astrophysics Data System (ADS)

    Malatesta, C.; Gerya, T.; Scambelluri, M.; Crispini, L.; Federico, L.; Capponi, G.

    2012-04-01

    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 subduction 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 trench-normal component of velocity. Several present and past subduction zones worldwide are however driven by oblique convergence between the plates, where trench-normal motion of the subducting slab is coupled with trench-parallel displacement of the plates. Can the exhumation mechanism and the exhumation rates of high-pressure rocks be affected by the shear component of subduction? 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 subduction. 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 subduction 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 subduction 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

  7. Geophysical signature of hydration-dehydration processes in active subduction zones

    NASA Astrophysics Data System (ADS)

    Reynard, Bruno

    2013-04-01

    Seismological and magneto-telluric tomographies are potential tools for imaging fluid circulation when combined with petrophysical models. Recent measurements of the physical properties of serpentine allow refining hydration of the mantle and fluid circulation in the mantle wedge from geophysical data. In the slab lithospheric mantle, serpentinization caused by bending at the trench is limited to a few kilometers below the oceanic crust (<5 km). Double Wadati-Benioff zones, 20-30 km below the crust, are explained by deformation of dry peridotites, not by serpentine dehydration. It reduces the required amount of water stored in solid phases in the slab (Reynard et al., 2010). In the cold (<700°C) fore-arc mantle wedge above the subducting slab, serpentinization is caused by the release of large amounts of hydrous fluids in the cold mantle above the dehydrating subducted plate. Low seismic velocities in the wedge give a time-integrated estimate of hydration and serpentinization. Serpentinization reaches 50-100% in hot subduction, while it is below 10% in cold subduction (Bezacier et al., 2010; Reynard, 2012). Electromagnetic profiles of the mantle wedge reveal high electrical-conductivity bodies. In hot areas of the mantle wedge (> 700°C), water released by dehydration of the slab induces melting of the mantle under volcanic arcs, explaining the observed high conductivities. In the cold melt-free wedge (< 700°C), high conductivities in electromagnetic profiles provide "instantaneous" images of fluid circulation because the measured electrical conductivity of serpentine is below 0.1 mS/m (Reynard et al., 2011). A small fraction (ca. 1% in volume) of connective high-salinity fluids accounts for the highest observed conductivities. Low-salinity fluids (≤ 0.1 m) released by slab dehydration evolve towards high-salinity (≥ 1 m) fluids during progressive serpentinization in the wedge. These fluids can mix with arc magmas at depths and account for high-chlorine melt

  8. The Pliny-Strabo trench region: A large shear zone resulting from slab tearing

    NASA Astrophysics Data System (ADS)

    Özbakır, Ali D.; Şengör, A. M. C.; Wortel, M. J. R.; Govers, R.

    2013-08-01

    The eastern part of the Hellenic subduction zone is composed of the Pliny and Strabo "trenches" that have been regarded as a zone of convergence between the subducting African lithosphere and the overriding Anatolian-Aegean plate. In the Pliny and Strabo "trenches", the oblique relative plate motion is generally thought to be accommodated by a typical strain partitioning consisting of strike-slip and convergence components. Notwithstanding the occurrence of strike-slip motion parallel with the Pliny-Strabo "trenches", trench-normal thrusting is not observed so far. Therefore, we conducted a detailed analysis to investigate the deformation mechanisms of the eastern part of the Hellenic Trench system. Our analyses of offshore faulting and mechanisms of earthquakes in the overriding Aegean lithosphere show that the region of the Pliny and Strabo "trenches" obeys the mechanics of the sinistral shear zone model of Tchalenko (1970). We propose that the trench perpendicular convergence is taken up by the Rhodes fold and thrust belt, which has been postulated off the southeast coast of Rhodes. Several regional P-wave tomography results give indications of a slow seismic anomaly under this zone, which is interpreted as a tear between the Hellenic and Cyprus subduction zones. The primary reason for such tear and its propagation is the ongoing rollback of the subducted part of the African lithosphere, also referred to as "the Aegean slab". Our work elucidates the surface expression of this tearing process in the form of the development of a shear zone between the Aegean lithosphere in the NW and the African lithosphere in the SE, the Pliny-Strabo Shear Zone.

  9. Geologic signature of early Tertiary ridge subduction in Alaska

    USGS Publications Warehouse

    Bradley, Dwight C.; Kusky, Timothy M.; Haeussler, Peter J.; Goldfarb, Richard J.; Miller, Marti L.; Dumoulin, Julie A.; Nelson, Steven W.; Karl, Susan M.

    2003-01-01

    A mid-Paleocene to early Eocene encounter between an oceanic spreading center and a subduction zone produced a wide range of geologic features in Alaska. The most striking effects are seen in the accretionary prism (Chugach–Prince William terrane), where 61 to 50 Ma near-trench granitic to gabbroic plutons were intruded into accreted trench sediments that had been deposited only a few million years earlier. This short time interval also saw the genesis of ophiolites, some of which contain syngenetic massive sulfide deposits; the rapid burial of these ophiolites beneath trench turbidites, followed immediately by obduction; anomalous high-T, low-P, near-trench metamorphism; intense ductile deformation; motion on transverse strike-slip and normal faults; gold mineralization; and uplift of the accretionary prism above sea level. The magmatic arc experienced a brief flare-up followed by quiescence. In the Alaskan interior, 100 to 600 km landward of the paleotrench, several Paleocene to Eocene sedimentary basins underwent episodes of extensional subsidence, accompanied by bimodal volcanism. Even as far as 1000 km inboard of the paleotrench, the ancestral Brooks Range and its foreland basin experienced a pulse of uplift that followed about 40 million years of quiescence.All of these events - but most especially those in the accretionary prism - can be attributed with varying degrees of confidence to the subduction of an oceanic spreading center. In this model, the ophiolites and allied ore deposits were produced at the soon-to-be subducted ridge. Near-trench magmatism, metamorphism, deformation, and gold mineralization took place in the accretionary prism above a slab window, where hot asthenosphere welled up into the gap between the two subducted, but still diverging, plates. Deformation took place as the critically tapered accretionary prism adjusted its shape to changes in the bathymetry of the incoming plate, changes in the convergence direction before and after

  10. The Role of Slab Windows in Subduction Cycles

    NASA Astrophysics Data System (ADS)

    Thorkelson, D. J.; Breitsprecher, K.

    2011-12-01

    Active continental margins are enduring features which commonly record a history of subduction spanning tens of millions of years. A subduction history is commonly divisible into distinct intervals of subduction activity separated by periods of non-subduction. The intervals of non-subduction are dominated by transform, transtensional or transpressional regimes. The recognition of subduction 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 subduction are varied, and include collision of island arcs or oceanic plateaus, swerves in the motions of large plates, plate deformation and microplate formation, and subduction of oceanic spreading ridges. These processes punctuate subduction 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 subduction zone brings two distinctive tectono-magmatic systems together at the same location. The style of ridge-subduction zone interaction varies considerably, depending on factors such as the obliquity of ridge-trench intersection, relative plate motions, plate integrity and thermal conditions. Where the ridge intersects the trench, 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 subducted slab, termed a slab window, will develop beneath the continent in the

  11. Phoenix's 'Dodo' Trench

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image was taken by NASA's Phoenix Mars Lander's Robotic Arm Camera (RAC) on the ninth Martian day of the mission, or Sol 9 (June 3, 2008). The center of the image shows a trench informally called 'Dodo' after the second dig. 'Dodo' is located within the previously determined digging area, informally called 'Knave of Hearts.' The light square to the right of the trench is the Robotic Arm's Thermal and Electrical Conductivity Probe (TECP). The Robotic Arm has scraped to a bright surface which indicated the Arm has reached a solid structure underneath the surface, which has been seen in other images as well.

    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.

  12. Phoenix's La Mancha Trench

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This false color image, taken by NASA's Phoenix Mars Lander's Surface Stereo Imager, was taken on the 131st Martian day, or sol, of the mission (Oct. 7, 2008). The image shows color variations of the trench, informally named 'La Mancha,' and reveals the ice layer beneath the soil surface. The trench's depth is about 5 centimeters deep.

    The color outline of the shadow at the bottom of the image is a result of sun movement with the combined use of infrared, green, and blue filters.

    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.

  13. Snow White Trenches

    NASA Technical Reports Server (NTRS)

    2008-01-01

    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 trenches informally called 'Snow White 1' (left) and 'Snow White 2' (right). The trench is about 5 centimeters (2 inches) deep and 30 centimeters (12 inches) long.

    '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 trench, the side farthest away from the lander, and has been dubbed 'Croquet Ground.' The digging site has been named 'Wonderland.'

    This image has been enhanced to brighten shaded areas.

    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.

  14. Earth Sphericity Effects on Subduction Morphology

    NASA Astrophysics Data System (ADS)

    Morra, G.; Chatelain, P.; Tackley, P.; Koumoutsakos, P.

    2007-12-01

    We present here the first application in Geodynamics of a Multipole accelerated Boundary Element Method (FMM- BEM) for Stokes Flow. The approach offers the advantage of a reduced number of computational elements and linear scaling with the problem size. We show that this numerical mehod can be fruitfully applied to the simulation of several geodynamic systems at the planetary scale in spheical coordinates and we suggest a general appraoch for modeling combined mantle convection and plate tectonics. The potentialities of the approach are shown investigating the effect played by Earth sphericity on the subduction of a very wide oceanic lithosphere , comparing the morphology of the subducted lithosphere in a spherical and in flat setting. The results show a striking difference between the two models: while the slab on a "flat Earth" shows slight undulation, the same subducting plate on a spherical Earth-like setting presents a distinct folding below the trench far from the edges, with wavelength of (1000km-2000km) as Pacific trenches.

  15. 3D Finite-Difference Modeling of Scattered Teleseismic Wavefields in a Subduction Zone

    NASA Astrophysics Data System (ADS)

    Morozov, I. B.; Zheng, H.

    2005-12-01

    For a teleseismic array targeting subducting crust in a zone of active subduction, scattering from the zone underlying the trench result in subhorizontally-propagating waves that could be difficult to distinguish from converted P- and S- wave backscattered from the surface. Because back-scattered modes often provide the most spectacular images of subducting slabs, it is important to understand their differences from the arrivals scattered from the trench zone. To investigate the detailed teleseismic wavefield in a subduction zone environment, we performed a full-waveform, 3-D visco-elastic finite-difference modeling of teleseismic wave propagation using a Beowulf cluster. The synthetics show strong scattering from the trench zone, dominated by the mantle and crustal P-waves propagating at 6.2-8.1.km/s and slower. These scattered waves occupy the same time and moveout intervals as the backscattered modes, and also have similar amplitudes. Although their amplitude decay characters are different, with the uncertainties in the velocity and density structure of the subduction zone, unambiguous distinguishing of these modes appears difficult. However, under minimal assumptions (in particular, without invoking slab dehydration), recent observations of receiver function amplitudes decreasing away from the trench favor the interpretation of trench-zone scattering.

  16. Accretionary processes along the Middle America Trench off Costa Rica

    SciTech Connect

    Shipley, T.H.; Stoffa, P.L. ); McIntosh, K.; Silver, E.A. )

    1990-06-01

    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 Trench. 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 Trench. So far in the analysis, these data illustrate the relationships between the basement, the prism shape, and overlying slope sedimentary deposits. For instance, the subducted 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 trench creating a small pile of sediments at the base of the trench. How this offscraped sediment is incorporated into the prism is still being investigated. Underplating of parts of the 400 m thick subducted section begin: at a very shallow structural level, 4 to 10 km arcward of the trench. 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.

  17. Numerical modeling of the deformations associated with large subduction earthquakes through the seismic cycle

    NASA Astrophysics Data System (ADS)

    Fleitout, L.; Trubienko, O.; Garaud, J.; Vigny, C.; Cailletaud, G.; Simons, W. J.; Satirapod, C.; Shestakov, N.

    2012-12-01

    A 3D finite element code (Zebulon-Zset) is used to model deformations through the seismic cycle in the areas surrounding the last three large subduction earthquakes: Sumatra, Japan and Chile. The mesh featuring a broad spherical shell portion with a viscoelastic asthenosphere is refined close to the subduction zones. The model is constrained by 6 years of postseismic data in Sumatra area and over a year of data for Japan and Chile plus preseismic data in the three areas. The coseismic displacements on the subduction 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 trench 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 subduction 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 trench 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 μKelvin=μelastic/3. A second Kelvin-Voigt element with very limited amplitude may explain some characteristics of the short time-scale signal. The postseismic subsidence is

  18. Subslab seismic anisotropy and mantle flow in the western Pacific subduction zones

    NASA Astrophysics Data System (ADS)

    Peng, C. C.; Kuo, B. Y.; Chen, C. W.

    2014-12-01

    We present source-side anisotropy for a few subduction zones in an attempt to map the mantle flow beneath the slab. Shear-wave splitting parameters of S were measured at stations towards the back of the subduction with the receiver-side anisotropy removed. We examined the observed fast directions against tilting/rotation of olivine fabric relative to the geometry of the subduction. We found that at the SW edge of the Ryukyu subduction zone the olivine fabric in the subslab mantle must rotate clockwise by 25 degrees from the slab subduction trajectory to explain the observed pattern of shear-wave splitting. This rotation echoes the deformation model of the slab when it is impinging against the Eurasian lithosphere. In the Vanuatu (New Hebrides) subduction zone, the olivine fabric may rotate dramatically to accommodate the rapid retreat of the trench and flipping of subduction polarity in the past a few Mys.

  19. Precise hypocenter distribution and earthquake generating and stress in and around the upper-plane seismic belt in the subducting Pacific slab beneath NE Japan

    NASA Astrophysics Data System (ADS)

    Kita, S.; Okada, T.; Nakajima, J.; Matsuzawa, T.; Uchida, N.; Hasegawa, A.

    2007-12-01

    1. Introduction We found an intraslab seismic belt (upper-plane seismic belt) in the upper plane of the double seismic zone within the Pacific slab, running interface at depths of 70-100km beneath the forearc area. The location of the deeper limits of this belt appears to correspond to one of the facies boundaries (from jadeite lawsonite blueschist to lawsonite amphibole eclogite) in the oceanic crust [Kita et al., 2006, GRL]. In this study, we precisely relocated intraslab earthquakes by using travel time differences calculated by the waveform cross-spectrum analysis to obtain more detailed distribution of the upper plane-seismic belt within the Pacific slab beneath NE Japan. We also discuss the stress field in the slab by examining focal mechanisms of the earthquakes. 2. Data and Method We relocated events at depths of 50-00 km for the period from March 2003 to November 2006 from the JMA earthquake catalog. We applied the double-difference hypocenter location method (DDLM) by Waldhauser and Ellsworth (2000) to the arrival time data of the events. We use relative earthquake arrival times determined both by the waveform cross-spectrum analysis and by the catalog-picking data. We also determine focal mechanisms using the P wave polarity. 3. Spatial distribution of relocated hypocenters In the upper portion of the slab crust, seismicity is very active and distributed relatively homogeneously at depths of about 70-100km parallel to the volcanic front, where the upper-plane seismic belt has been found. In the lower portion of slab crust and/or the uppermost portion of the slab mantle, seismicity is spatially very limited to some small areas (each size is about 20 x 20km) at depths around 65km. Two of them correspond to the aftershock area of the 2003 Miyagi (M7.1) intraslab earthquake and that of the 1987 Iwaizumi (M6.6) intraslab earthquake, respectively. Based on the dehydration embrittelment hypothesis, the difference of the spatial distribution of the seismicity in

  20. Spirit Shadow over Laguna Trench

    NASA Technical Reports Server (NTRS)

    2004-01-01

    NASA's Mars Exploration Rover Spirit casts a shadow over the trench that the rover is examining with tools on its robotic arm. Spirit took this image with its front hazard-avoidance camera on Feb. 21, 2004, during the rover's 48th martian day, or sol. It dug the trench with its left front wheel the preceding sol. Plans call for Spirit to finish examining the trench on sol 50.

  1. Trench Left By Sampler Scoop

    NASA Technical Reports Server (NTRS)

    1976-01-01

    A shallow 12-inch-long trench was dug by Viking 2 s surface sampler scoop yesterday (September 12) on Mars. The trench is difficult to see in this photo because it is in the shadow of a rock (out of view to the right). The sampler scoop stopped operating sometime after soil was excavated from the trench and delivered to Viking 2 s biology instrument.

  2. Geoscience: Subduction undone

    NASA Astrophysics Data System (ADS)

    Hodges, Kip V.

    2017-03-01

    Rocks are subjected to increased pressure as they are buried during subduction. Contrary to general belief, a study suggests that peak pressures recorded in subducted rocks might not reflect their maximum burial depths.

  3. Present-day chaotic formations around the Japanese trenches: Comparison to the on land examples from the Shimanto and Miura-Boso, and from the Franciscan, Mineoka and Ankara

    NASA Astrophysics Data System (ADS)

    Ogawa, Yujiro; Kawamura, Kiichiro; Tsunogae, Toshiaki; Mori, Ryota; Chiba, Tae; Sasaki, Tomoyuki

    2010-05-01

    Four different types of chaotic formations were recognized by the submersible observation around the Japanese trenches, including the Nankai and Sagami troughs, Boso triple junction, Japan trench, 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 trench landward slope toe of the Nankai and Sagami troughs and Boso triple junction area as well as the Japan trench 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 subduction 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 subduction to the trench, 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 Japan trench. In all cases on land and under the sea in the trench landward slope, some calcareous breccias are associated with methane

  4. Seismic Characterization of the Transition from Continental to Oceanic Subduction along the western Hellenic Subduction Zone

    NASA Astrophysics Data System (ADS)

    Pearce, F. D.; Rondenay, S.; Zhang, H.; Sachpazi, M.; Charalampakis, M.; Royden, L.

    2010-12-01

    The Hellenic subduction zone is located in the east-central Mediterranean region and exhibits large variations in convergence rate along its western edge. Differences in the lithosphere entering the subduction zone are believed to drive the different rates of convergence. While seismic reflection data has shown a transition from continental to oceanic lithosphere along the foreland, no detailed images of the mantle-wedge structure have been available to test this hypothesis. Here, we use high-resolution seismic images across northern and southern Greece to investigate differences in the subducted crust along the western Hellenic subduction zone. We deployed 40 broadband seismometers from the IRIS PASSCAL pool across Greece in a northern line (NL, across Northern Greece) and southern line (SL, across Peloponnesus, Attica, and Evia), each roughly perpendicular to the trench axis. We recorded over 50 high-quality teleseismic events with good azimuthal coverage from each line. We processed them using a 2D teleseismic migration algorithm based on the Generalized Radon Transform and a 3D receiver function algorithm that includes dipping interfaces. In addition, we constructed a 3D velocity model by applying double-difference tomography to ~5000 local earthquakes. The 3D velocity model was used to construct an optimal background model for the teleseismic imaging. Migration and RF images reveal N60E dipping low-velocity layers beneath both NL and SL. From high-resolution migration images, we interpret an ~8 km thick low-velocity layer beneath SL as subducted oceanic crust and a ~20 km thick low-velocity layer beneath NL as subducted continental crust. Relocated earthquakes show that the NL subducted crust is seismically active near the foreland down to 50 km depth presumably as a result of slab flexure. Beyond this region, the subducted crust is aseismic until its signal disappears at ~70 km depth. In contrast, the SL subducted crust is marked by seismicity that extends

  5. Collapse of the northern Jalisco continental slope:Subduction erosion, forearc slivering, or subduction beneath the Tres Marias escarpment?

    NASA Astrophysics Data System (ADS)

    Bandy, W. L.; Mortera-Gutierrez, C. A.; Ortiz-Zamora, G.; Ortega-Ramirez, J.; Galindo Dominguez, R. E.; Ponce-Núñez, F.; Pérez-Calderón, D.; Rufino-Contreras, I.; Valle-Hernández, S.; Pérez-González, E.

    2010-12-01

    The Jalisco subduction zone exhibits several interesting characteristics. Among these is that convergence between the Rivera and North American plate is highly oblique, especially north of 20N, the obliquity progressively increasing to the NW. By analogy to other better studied subduction zones, this distribution of forces should produce a NW-SE extension in the overriding plate, especially north of 20N. This has led to the proposal that the trench perpendicular Bahia de Banderas is an expression of this extension [Kostoglodov and Bandy, JGR, vol. 100, 1995]. To further investigate this proposal, multibeam bathymetric data and seafloor backscatter images, seismic reflection sub-bottom profiles and marine magnetic data were collected during the MORTIC08 campaign of the B.O. EL PUMA in March 2009. The bathymetric data provides for 100% coverage (20 to 200 meter spacing of the actual measured depth value depending on the water depth) of the continental slope and trench areas north of 20N. These data indicate that a marked change occurs in the morphology of the continental slope at 20N. To the north the slope consists of a broad, fairly flat plain lying between a steep lower inner trench slope to the west and a steep, concave seaward, escarpment to the east. In contrast, to the south the continental slope exhibits a more gradual deepening until the steep lower inner trench slope. A prominent submarine canyon deeply incises the continental slope between these two morphotectonic domains. This canyon appears to represent the boundary between two NW-SE diverging forearc blocks or slivers, consistent with the presence of oblique convergence. In contrast, the broad, fairly flat plain is better explained by subsidence induced by subduction erosion (i.e. erosion of the base of the overriding plate underneath the continental slope area). The shoaling of the trench axis northward towards the Puerto Vallarta Graben and subsequent deepening may be related to subduction of the

  6. Snow White Trench (Animation)

    NASA Technical Reports Server (NTRS)

    2008-01-01

    [figure removed for brevity, see original site] Click on image for animation

    This animation shows the evolution of the trench 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.

    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.

  7. Model geoid anomalies due to subduction of inextensible lithosphere

    SciTech Connect

    Willemann, R.J.; Anderson, C.A.

    1987-08-01

    We compute geoid slopes from models of subduction in which the subducted 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 subduction zones, which are positive, cannot be matched by models with uniform mantle viscosity. However, even with a strong subducted 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 trench are independent of maximum depth of the slab for maximum depths from 700 km to 2800 km. copyright American Geophysical Union 1987

  8. An ocean bottom seismometer study of shallow seismicity near the Mid- America Trench offshore Guatemala ( Pacific).

    USGS Publications Warehouse

    Ambos, E.L.; Hussong, D.M.; Holman, C.E.

    1985-01-01

    Five ocean bottom seismometers recorded seismicity near the Mid-America Trench offshore Guatemala for 27 days in 1979. The array was emplaced in the lower slope region, just above the topographic trench. Approximately 170 events were recorded by 3 or more seismometers, and almost half were located with statistical hypocentral errors of <10 km. Most epicenters were located immediately landward of the trench axis, and many were further confined to a zone NW of the array. In terms of depth, most events were located within the subducting Cocos plate rather than in the overlying plate or at the plate-plate boundary. Most magnitudes ranged between 3.0 and 4.0 mb, and the threshold magnitude of locatable events was about 2.8 mb. Two distinct composite focal mechanisms were determined. One appears to indicate high- angle reverse faulting in the subducting plate, in a plane parallel to trench axis strike. The other, constructed for some earthquakes in the zone NW of the array, seems to show normal faulting along possible fault planes oriented quasi-perpendicular to the trench axis. Projection of our seismicity sample and of well-located WWSSN events from 1954 to 1980 onto a plane perpendicular to the trench axis shows a distinct gap between the shallow seismicity located by our array, and the deeper Wadati-Benioff zone seismicity located by the WWSSN. We tentatively ascribe this gap to inadequate sampling.-from Authors

  9. Slow slip events in plate-rate laboratory experiments on samples from shallow regions of subduction megathrusts

    NASA Astrophysics Data System (ADS)

    Ikari, M.; Ito, Y.; Ujiie, K.; Kopf, A.

    2015-12-01

    It is now recognized that slow slip events on plate-boundary fault zones occur not only downdip of the seismogenic zone, but also updip within several km from the seafloor. These shallower events are advantageous because the fault material can be sampled by drilling, and in-situ conditions can be replicated in the laboratory. We report here on results of laboratory friction experiments investigating fault zone material sampled during Ocean Drilling Program and International Ocean Drilling Program expeditions to subduction zones in Japan and Costa Rica. We employ laboratory conditions of 7-16 MPa effective stress and ~20 °C simulating ~1-2.5 km burial depth. Additionally, we shear the samples at plate convergence rates of less than 10 cm/yr. When driven at plate convergence rates, friction perturbations analogous to slow slip events are sometimes observed. In plate-boundary fault zone samples from the Tohoku region at the Japan Trench, these events exhibit stress drops of 3-7% over several hours with a maximum slip rate of 10-25 cm/yr under 7 MPa effective normal stress. Increasing the effective normal stress to 16 kPa results in a corresponding increase in stress drop up to 15% and slip rates up to 57 cm/yr, consistent with critical stiffness theory which predicts that increasing effective normal stress decreases frictional stability. A sample from the plate boundary décollement from the Costa Rica margin exhibited similar slow slip behavior, with stress drops of 3-12% and maximum slip velocities up to 16 cm/yr. This sample is described as a hemipelagic clay, whereas a sample of nannofossil chalk from the same region did not exhibit such behavior. For the Nankai Trough offshore Japan, samples from the megasplay fault zone and décollement did not exhibit the slow slip events observed in the Japan Trench and Costa Rica samples. Analyses of velocity-stepping data from these tests indicate a propensity for velocity-weakening frictional behavior at slow rates

  10. The subduction zone flow field from seismic anisotropy: a global view.

    PubMed

    Long, Maureen D; Silver, Paul G

    2008-01-18

    Although the morphologies of subducting slabs have been relatively well characterized, the character of the mantle flow field that accompanies subduction remains poorly understood. To analyze this pattern of flow, we compiled observations of seismic anisotropy, as manifested by shear wave splitting. Data from 13 subduction zones reveal systematic variations in both mantle-wedge and subslab anisotropy with the magnitude of trench migration velocity |V(t)|. These variations can be explained by flow along the strike of the trench induced by trench motion. This flow dominates beneath the slab, where its magnitude scales with |V(t)|. In the mantle wedge, this flow interacts with classical corner flow produced by the convergence velocity V(c); their relative influence is governed by the relative magnitude of |V(t)| and V(c).

  11. Opal-CT in chert beneath the toe of the Tohoku margin and its influence on the seismic aseismic transition in subduction zones

    NASA Astrophysics Data System (ADS)

    Kameda, Jun; Okamoto, Atsushi; Sato, Kiminori; Fujimoto, Koichiro; Yamaguchi, Asuka; Kimura, Gaku

    2017-01-01

    Thick accumulation of chert is a ubiquitous feature of old oceanic plates at convergent margins. In this study, we investigate chert fragments recovered by the Integrated Ocean Drilling Program expedition 343 at the Japan Trench where the 2011 Tohoku-Oki earthquake (Mw 9.0) occurred. This sample provides a unique opportunity to investigate in situ chert diagenesis at an active subduction margin and its influence on the kinematics of megathrust faulting. Our mineralogical analyses revealed that the chert is characterized by hydrous opal-CT and may therefore be highly deformable via pressure solution creep and readily accommodate shear strain between the converging plates at driving stresses of kilopascal order. As chert diagenesis advances, any further deformation requires stresses of >100 MPa, given the increasing transport distances for solutes as represented in cherts on land. The chert diagenesis is thus related to the mechanical transition from a weakly to strongly coupled plate interface at this margin.

  12. Tectonic stress state in NE Japan as part of the Okhotsk plate

    NASA Astrophysics Data System (ADS)

    Altis, Sungat

    2001-09-01

    latter zone. The calculated rotation rates from the geodetic flow model are clockwise (CW) in both of the ˜E-W contractional regions. NE Japan, 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 subduction interface beneath the Japan trench 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 subduction of the Pacific slab there, increasing the plates' interface contact area; the flattening of the subduction 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 subduction zone during the formation of the Japan Sea.

  13. Slab detachment in laterally varying subduction zones: 3-D numerical modeling

    NASA Astrophysics Data System (ADS)

    Duretz, T.; Gerya, T. V.; Spakman, W.

    2014-03-01

    Understanding the three-dimensional (3-D) dynamics of subduction-collision systems is a longstanding challenge in geodynamics. We investigate the impact of slab detachment in collision systems that are subjected to along-trench 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 subduction of adjacent continental and oceanic lithospheres (SCO). This configuration yields to two-stage slab detachment during collision, topographic buildup and extrusion, variable along-trench convergence rates, and associated trench 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 trench 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.

  14. Friction and stress coupling on the subduction interfaces

    NASA Astrophysics Data System (ADS)

    Tan, E.; Lavier, L.; van Avendonk, H.

    2011-12-01

    At a subduction 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 subduction interface, which can cause tremendous damage in the civil life and property. There is a strong incentive to understand the frictional strength of the subduction 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 trench-parallel (along-strike) gravity variation correlates positively with the trench-parallel topography anomaly and negatively with the activity of great earthquake (Song and Simons, 2003). Regions with a negative trench-parallel gravity anomaly are more likely to have great earthquakes. The interpretation of such correlation is that strong coupling along subduction 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 subduction. 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 subduction 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

  15. Nationwide tsunami hazard assessment project in Japan

    NASA Astrophysics Data System (ADS)

    Hirata, K.; Fujiwara, H.; Nakamura, H.; Osada, M.; Ohsumi, T.; Morikawa, N.; Kawai, S.; Aoi, S.; Yamamoto, N.; Matsuyama, H.; Toyama, N.; Kito, T.; Murashima, Y.; Murata, Y.; Inoue, T.; Saito, R.; Akiyama, S.; Korenaga, M.; Abe, Y.; Hashimoto, N.

    2014-12-01

    In 2012, we began a project of nationwide Probabilistic Tsunami Hazard Assessment (PTHA) in Japan to support various measures (Fujiwara et al., 2013, JpGU; Hirata et al., 2014, AOGS). The most important strategy in the nationwide PTHA is predominance of aleatory uncertainty in the assessment but use of epistemic uncertainty is limited to the minimum, because the number of all possible combinations among epistemic uncertainties diverges quickly when the number of epistemic uncertainties in the assessment increases ; we consider only a type of earthquake occurrence probability distribution as epistemic uncertainty. We briefly show outlines of the nationwide PTHA as follows; (i) we consider all possible earthquakes in the future, including those that the Headquarters for Earthquake Research Promotion (HERP) of Japanese Government, already assessed. (ii) We construct a set of simplified earthquake fault models, called "Characterized Earthquake Fault Models (CEFMs)", for all of the earthquakes by following prescribed rules (Toyama et al., 2014, JpGU; Korenaga et al., 2014, JpGU). (iii) For all of initial water surface distributions caused by a number of the CEFMs, we calculate tsunamis by solving a nonlinear long wave equation, using FDM, including runup calculation, over a nesting grid system with a minimum grid size of 50 meters. (iv) Finally, we integrate information about the tsunamis calculated from the numerous CEFMs to get nationwide tsunami hazard assessments. One of the most popular representations of the integrated information is a tsunami hazard curve for coastal tsunami heights, incorporating uncertainties inherent in tsunami simulation and earthquake fault slip heterogeneity (Abe et al., 2014, JpGU). We will show a PTHA along the eastern coast of Honshu, Japan, based on approximately 1,800 tsunami sources located within the subduction zone along the Japan Trench, as a prototype of the nationwide PTHA. This study is supported by part of the research

  16. Large fault slip peaking at trench in the 2011 Tohoku-oki earthquake.

    PubMed

    Sun, Tianhaozhe; Wang, Kelin; Fujiwara, Toshiya; Kodaira, Shuichi; He, Jiangheng

    2017-01-11

    During the 2011 magnitude 9 Tohoku-oki earthquake, very large slip occurred on the shallowest part of the subduction megathrust. Quantitative information on the shallow slip is of critical importance to distinguishing between different rupture mechanics and understanding the generation of the ensuing devastating tsunami. However, the magnitude and distribution of the shallow slip are essentially unknown due primarily to the lack of near-trench constraints, as demonstrated by a compilation of 45 rupture models derived from a large range of data sets. To quantify the shallow slip, here we model high-resolution bathymetry differences before and after the earthquake across the trench axis. The slip is determined to be about 62 m over the most near-trench 40 km of the fault with a gentle increase towards the trench. This slip distribution indicates that dramatic net weakening or strengthening of the shallow fault did not occur during the Tohoku-oki earthquake.

  17. Large fault slip peaking at trench in the 2011 Tohoku-oki earthquake

    NASA Astrophysics Data System (ADS)

    Sun, Tianhaozhe; Wang, Kelin; Fujiwara, Toshiya; Kodaira, Shuichi; He, Jiangheng

    2017-01-01

    During the 2011 magnitude 9 Tohoku-oki earthquake, very large slip occurred on the shallowest part of the subduction megathrust. Quantitative information on the shallow slip is of critical importance to distinguishing between different rupture mechanics and understanding the generation of the ensuing devastating tsunami. However, the magnitude and distribution of the shallow slip are essentially unknown due primarily to the lack of near-trench constraints, as demonstrated by a compilation of 45 rupture models derived from a large range of data sets. To quantify the shallow slip, here we model high-resolution bathymetry differences before and after the earthquake across the trench axis. The slip is determined to be about 62 m over the most near-trench 40 km of the fault with a gentle increase towards the trench. This slip distribution indicates that dramatic net weakening or strengthening of the shallow fault did not occur during the Tohoku-oki earthquake.

  18. Large fault slip peaking at trench in the 2011 Tohoku-oki earthquake

    PubMed Central

    Sun, Tianhaozhe; Wang, Kelin; Fujiwara, Toshiya; Kodaira, Shuichi; He, Jiangheng

    2017-01-01

    During the 2011 magnitude 9 Tohoku-oki earthquake, very large slip occurred on the shallowest part of the subduction megathrust. Quantitative information on the shallow slip is of critical importance to distinguishing between different rupture mechanics and understanding the generation of the ensuing devastating tsunami. However, the magnitude and distribution of the shallow slip are essentially unknown due primarily to the lack of near-trench constraints, as demonstrated by a compilation of 45 rupture models derived from a large range of data sets. To quantify the shallow slip, here we model high-resolution bathymetry differences before and after the earthquake across the trench axis. The slip is determined to be about 62 m over the most near-trench 40 km of the fault with a gentle increase towards the trench. This slip distribution indicates that dramatic net weakening or strengthening of the shallow fault did not occur during the Tohoku-oki earthquake. PMID:28074829

  19. Magnitude and location of historical earthquakes in Japan and implications for the 1855 Ansei Edo earthquake

    USGS Publications Warehouse

    Bakun, W.H.

    2005-01-01

    Japan 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 Japan. 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 Japan Trench were used to develop a subducting 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 subducting plate model; Using the subducting 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.

  20. Seismic velocity structure and deformation due to the collision of the Louisville Ridge with the Tonga-Kermadec Trench

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    New marine geophysical data recorded across the Tonga-Kermadec subduction zone are used to image deformation and seismic velocity structures of the forearc and Pacific Plate where the Louisville Ridge seamount chain subducts. Due to the obliquity of the Louisville Ridge to the trench and the fast 128 mm yr-1 south-southwest migration of the ridge-trench collision zone, post-, current and pre-seamount subduction deformation can be investigated between 23°S and 28°S. We combine our interpretations from the collision zone with previous results from the post- and pre-collision zones to define the along-arc variation in deformation due to seamount subduction. In the pre-collision zone the lower-trench slope is steep, the mid-trench slope has ˜3-km-thick stratified sediments and gravitational collapse of the trench slope is associated with basal erosion by subducting horst and graben structures on the Pacific Plate. This collapse indicates that tectonic erosion is a normal process affecting this generally sediment starved subduction system. In the collision zone the trench-slope decreases compared to the north and south, and rotation of the forearc is manifest as a steep plate boundary fault and arcward dipping sediment in a 12-km-wide, ˜2-km-deep mid-slope basin. A ˜3 km step increase in depth of the middle and lower crustal isovelocity contours below the basin indicates the extent of crustal deformation on the trench slope. At the leading edge of the overriding plate, upper crustal P-wave velocities are ˜4.0 km s-1 and indicate the trench fill material is of seamount origin. Osbourn Seamount on the outer rise has extensional faulting on its western slope and mass wasting of the seamount provides the low Vp material to the trench. In the post-collision zone to the north, the trench slope is smooth, the trench is deep, and the crystalline crust thins at the leading edge of the overriding plate where Vp is low, ˜5.5 km s-1. These

  1. Developing framework to constrain the geometry of the seismic rupture plane on subduction interfaces a priori - A probabilistic approach

    USGS Publications Warehouse

    Hayes, G.P.; Wald, D.J.

    2009-01-01

    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 subducting 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 trench in the source region of the Mw 8.6 Southern Sumatra earthquake of March 2005, and for the Northern Chile Trench 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 Japan and Kamchatka Trenches. 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

  2. Subduction of fracture zones

    NASA Astrophysics Data System (ADS)

    Constantin Manea, Vlad; Gerya, Taras; Manea, Marina; Zhu, Guizhi; Leeman, William

    2013-04-01

    Since Wilson proposed in 1965 the existence of a new class of faults on the ocean floor, namely transform faults, the geodynamic effects and importance of fracture zone subduction is still little studied. It is known that oceanic plates are characterized by numerous fracture zones, and some of them have the potential to transport into subduction zones large volumes of water-rich serpentinite, providing a fertile water source for magma generated in subduction-related arc volcanoes. In most previous geodynamic studies, subducting plates are considered to be homogeneous, and there is no clear indication how the subduction of a fracture zone influences the melting pattern in the mantle wedge and the slab-derived fluids distribution in the subarc mantle. Here we show that subduction of serpentinized fracture zones plays a significant role in distribution of melt and fluids in the mantle wedge above the slab. Using high-resolution tree-dimensional coupled petrological-termomechanical simulations of subduction, we show that fluids, including melts and water, vary dramatically in the region where a serpentinized fracture zone enters into subduction. Our models show that substantial hydration and partial melting tend to concentrate where fracture zones are being subducted, creating favorable conditions for partially molten hydrous plumes to develop. These results are consistent with the along-arc variability in magma source compositions and processes in several regions, as the Aleutian Arc, the Cascades, the Southern Mexican Volcanic Arc, and the Andean Southern Volcanic Zone.

  3. Subduction zone decoupling/retreat modeling explains south Tibet (Xigaze) and other supra-subduction zone ophiolites and their UHP mineral phases

    NASA Astrophysics Data System (ADS)

    Butler, Jared P.; Beaumont, Christopher

    2017-04-01

    The plate tectonic setting in which proto-ophiolite 'oceanic' lithosphere is created remains controversial with a number of environments suggested. Recent opinions tend to coalesce around supra-subduction zone (SSZ) forearc extension, with a popular conceptual model in which the proto-ophiolite forms during foundering of oceanic lithosphere at the time of spontaneous or induced onset of subduction. This mechanism is favored in intra-oceanic settings where the subducting lithosphere is old and the upper plate is young and thin. We investigate an alternative mechanism; namely, decoupling of the subducting oceanic lithosphere in the forearc of an active continental margin, followed by subduction zone (trench) retreat and creation of a forearc oceanic rift basin, containing proto-ophiolite lithosphere, between the continental margin and the retreating subduction zone. A template of 2D numerical model experiments examines the trade-off between strength of viscous coupling in the lithospheric subduction channel and net slab pull of the subducting lithosphere. Three tectonic styles are observed: 1) C, continuous subduction without forearc decoupling; 2) R, forearc decoupling followed by rapid subduction zone retreat; 3) B, breakoff of subducting lithosphere followed by re-initiation of subduction and in some cases, forearc decoupling (B-R). In one case (BA-B-R; where BA denotes backarc) subduction zone retreat follows backarc rifting. Subduction zone decoupling is analyzed using frictional-plastic yield theory and the Stefan solution for the separation of plates containing a viscous fluid. The numerical model results are used to explain the formation of Xigaze group ophiolites, southern Tibet, which formed in the Lhasa terrane forearc, likely following earlier subduction and not necessarily during subduction initiation. Either there was normal coupled subduction before subduction zone decoupling, or precursor slab breakoff, subduction re-initiation and then decoupling

  4. Interplate deformation at early-stage oblique subduction: 3-D thermomechanical numerical modeling

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    Oblique subduction zones are complex settings where the simultaneous action of trench-normal and trench-parallel components of convergence can produce heterogeneous deformational pattern of the upper plate and affect the accretional/erosional behavior of the plate margin. Here we present three-dimensional thermomechanical numerical models that highlight some processes occurring in the early history (15-20 Myr) of intraoceanic oblique subduction zones, which so far represent the less studied case. These models have been compared with a simulation of a slab sinking under a continental plate. We test subduction starting in oceans floored by two classes of lithosphere: layered (fast spreading oceans) and serpentinite rich (slow to ultraslow spreading oceans). Two main domains develop along the margin of both type of oceanic plates: (a) a domain with a mostly stable trench, a shortening upper plate, characterized by the formation of a topographic relief, and (b) a domain with retreating trench and extending upper plate. In general, we observed that varying the subduction obliquity, the margin could either (i) record an erosional to a balanced accretion/erosion regime or (ii) be characterized by a predominant balanced accretion/erosion regime. In both cases, even where the sediment amount in the trench is high, the upper plate experiences tectonic erosion. We suggest that the formation of topographic reliefs on the fore arc is possibly related to the low amount of sediment in the trench, affecting interplate friction and promoting the upper plate indentation against the slab. The Puysegur subduction zone and the central Andes can be possibly natural examples of such a regime.

  5. Phoenix Deepens Trenches on Mars

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The Surface Stereo Imager on NASA's Phoenix Mars Lander took this false color image on Oct. 21, 2008, during the 145th Martian day, or sol, since landing. The white areas seen in these trenches are part of an ice layer beneath the soil.

    The trench on the upper left, called 'Upper Cupboard,' is about 60 centimeters (24 inches) long and 3 centimeters (1 inch) deep. The trench in the middle, called 'Ice Man,' is about 30 centimeters (12 inches) long and 3 centimeters (1 inch) deep. The trench on the right, called 'La Mancha,' is about 31 centimeters (12 inches) and 5 centimeters (2 inches) deep.

    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.

  6. Phoenix Deepens Trenches on Mars

    NASA Technical Reports Server (NTRS)

    2008-01-01

    The Surface Stereo Imager on NASA's Phoenix Mars Lander took this false color image on Oct. 21, 2008, during the 145th Martian day, or sol, since landing. The bluish-white areas seen in these trenches are part of an ice layer beneath the soil.

    The trench on the upper left, called 'Dodo-Goldilocks,' is about 38 centimeters (15 inches) long and 4 centimeters (1.5 inches) deep. The trench on the right, called 'Upper Cupboard,' is about 60 centimeters (24 inches) long and 3 centimeters (1 inch) deep. The trench in the lower middle is called 'Stone Soup.'

    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.

  7. 'Dodo' and 'Baby Bear' Trenches

    NASA Technical Reports Server (NTRS)

    2008-01-01

    NASA's Phoenix Mars Lander's Surface Stereo Imager took this image on Sol 11 (June 5, 2008), the eleventh day after landing. It shows the trenches dug by Phoenix's Robotic Arm. The trench on the left is informally called 'Dodo' and was dug as a test. The trench on the right is informally called 'Baby Bear.' The sample dug from Baby Bear will be delivered to the Phoenix's Thermal and Evolved-Gas Analyzer, or TEGA. The Baby Bear trench is 9 centimeters (3.1 inches) wide and 4 centimeters (1.6 inches) deep.

    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.

  8. Opportunity Trenches Martian Soil

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The Mars Exploration Rover Opportunity dragged one of its wheels back and forth across the sandy soil at Meridiani Planum to create a hole (bottom left corner) approximately 50 centimeters (19.7 inches) long by 20 centimeters (7.9 inches) wide by 9 centimeters (3.5 inches) deep. The rover's instrument deployment device, or arm, will begin studying the fresh soil at the bottom of this trench later today for clues to its mineral composition and history. Scientists chose this particular site for digging because previous data taken by the rover's miniature thermal emission spectrometer indicated that it contains crystalline hematite, a mineral that sometimes forms in the presence of water. The brightness of the newly-exposed soil is thought to be either intrinsic to the soil itself, or a reflection of the Sun. Opportunity's lander is in the center of the image, and to the left is the rock outcrop lining the inner edge of the small crater that encircles the rover and lander. This mosaic image is made up of data from the rover's navigation and hazard-avoidance cameras.

  9. Offshore double-planed shallow seismic zone in the NE Japan forearc region revealed by sP depth phases recorded by regional networks

    USGS Publications Warehouse

    Gamage, S.S.N.; Umino, N.; Hasegawa, A.; Kirby, S.H.

    2009-01-01

    We detected the sP depth phase at small epicentral distances of about 150 km or more in the seismograms of shallow earthquakes in the NE Japan forearc region. The focal depths of 1078 M > 3 earthquakes that occurred from 2000 to 2006 were precisely determined using the time delay of the sP phase from the initial P-wave arrival. The distribution of relocated hypocentres clearly shows the configuration of a double-planed shallow seismic zone beneath the Pacific Ocean. The upper plane has a low dip angle near the Japan Trench, increasing gradually to ???30?? at approximately 100 km landward of the Japan Trench. The lower plane is approximately parallel to the upper plane, and appears to be the near-trench counterpart of the lower plane of the double-planed deep seismic zone beneath the land area. The distance between the upper and lower planes is 28-32 km, which is approximately the same as or slightly smaller than that of the double-planed deep seismic zone beneath the land area. Focal mechanism solutions of the relocated earthquakes are determined from P-wave initial motion data. Although P-wave initial motion data for these offshore events are not ideally distributed on the focal sphere, we found that the upper-plane events that occur near the Japan Trench are characterized by normal faulting, whereas lower-plane events are characterized by thrust faulting. This focal mechanism distribution is the opposite to that of the double-planed deep seismic zone beneath the land area. The characteristics of these focal mechanisms for the shallow and deep doubled-planed seismic zones can be explained by a bending-unbending model of the subducting Pacific plate. Some of relocated earthquakes took place in the source area of the 1933 Mw8.4 Sanriku earthquake at depths of 10-23 km. The available focal mechanisms for these events are characterized by normal faulting. Given that the 1933 event was a large normal-fault event that occurred along a fault plane dipping landward, the

  10. High-Velocity Frictional Behavior of Incoming Pelagic Sediments to the Tohoku Subduction zone

    NASA Astrophysics Data System (ADS)

    Sawai, M.; Hirose, T.

    2012-12-01

    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 Japan Trench are energetically very easy for earthquake ruptures to propagate at shallow portion of the Tohoku subduction zone.

  11. Crustal structure around the asperity regions of large earthquakes along the southernmost Kuril trench revealed by two Airgun-OBS seismic profilings

    NASA Astrophysics Data System (ADS)

    Machida, Y.; Takanami, T.; Murai, Y.; Amamiya, S.; Nishimura, Y.; Shinohara, M.; McHizuki, K.; Yamada, T.; Nakahigashi, K.; Kuwano, A.; Kanazawa, T.; Hino, R.; Azuma, R.

    2007-12-01

    In the southeast off Hokkaido, Japan, large earthquakes have occurred repeatedly with temporal and spatial regularities along the Kuril trench due to the subduction of Pacific plate at a rate of 80 mm/year (DeMets et al., 1990) [e.g. the 1952 Tokachi-oki earthquake (Mw=8.2), the 1973 Nemuro-oki earthquake (Mw=7.8) and the 2003 Tokachi-oki earthquake (Mw=8.2)]. It is considered that the next large earthquake will occur at the source region of the 1973 Nemuro-oki earthquake in the near future because a low seismic activity has been found in the off shore region of the Nemuro peninsula. In order to clarify the relation between asperity and the recurrence of large earthquake, it is necessary to determine a detailed crustal structure running across the two asperities of the 2003 Tokachi-oki earthquake and 1973 Nemuro-oki earthquake. Therefore we conducted a wide-angle survey across the coseismic rupture areas of the 2003 Tokachi-oki and 1973 Nemuro-oki earthquakes and the afterslip area of the 2003 Tokachi-oki earthquake parallel (profile-A) and perpendicular (profile-B) to the Kuril trench using Ocean Bottom Seismometers (OBSs). In profile-A, 19 OBSs were deployed at a spacing of about 10km and three 25 liter air-guns were fired every 90 seconds which corresponds to a shot interval of about 230m. In profile-B, 11 OBSs were deployed at a spacing of about 11km and two 25 liter airguns were fired every 60 seconds which corresponds to a shot interval of about 150m. In this presentation, we report on the crustal structure using the data obtained in the profile A and B and compare our results with past researches around this region. This study is founded by the Ministry of Education, Culture, Sports, Science and Technology, Japan.

  12. Velocities of Subducted Sediments and Continents

    NASA Astrophysics Data System (ADS)

    Hacker, B. R.; van Keken, P. E.; Abers, G. A.; Seward, G.

    2009-12-01

    The growing capability to measure seismic velocities in subduction zones has led to unusual observations. For example, although most minerals have VP/ VS ratios around 1.77, ratios <1.7 and >1.8 have been observed. Here we explore the velocities of subducted sediments and continental crust from trench to sub-arc depths using two methods. (1) Mineralogy was calculated as a function of P & T for a range of subducted sediment compositions using Perple_X, and rock velocities were calculated using the methodology of Hacker & Abers [2004]. Calculated slab-top temperatures have 3 distinct depth intervals with different dP/dT gradients that are determined by how coupling between the slab and mantle wedge is modeled. These three depth intervals show concomitant changes in VP and VS: velocities initially increase with depth, then decrease beyond the modeled decoupling depth where induced flow in the wedge causes rapid heating, and increase again at depth. Subducted limestones, composed chiefly of aragonite, show monotonic increases in VP/ VS from 1.63 to 1.72. Cherts show large jumps in VP/ VS from 1.55-1.65 to 1.75 associated with the quartz-coesite transition. Terrigenous sediments dominated by quartz and mica show similar, but more-subdued, transitions from ~1.67 to 1.78. Pelagic sediments dominated by mica and clinopyroxene show near-monotonic increases in VP/ VS from 1.74 to 1.80. Subducted continental crust that is too dry to transform to high-pressure minerals has a VP/ VS ratio of 1.68-1.70. (2) Velocity anisotropy calculations were made for the same P-T dependent mineralogies using the Christoffel equation and crystal preferred orientations measured via electron-backscatter diffraction for typical constituent phases. The calculated velocity anisotropies range from 5-30%. For quartz-rich rocks, the calculated velocities show a distinct depth dependence because crystal slip systems and CPOs change with temperature. In such rocks, the fast VP direction varies from slab

  13. Downgoing plate controls on overriding plate deformation in subduction zones

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    Although subduction 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 subduction 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 trench motion. We investigate the evolution of the state of stress and topography of the overriding plate during the different phases of the subduction process: onset of subduction, 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 subducting plate age; (ii) how spontaneous and episodic back-arc spreading develops for some subduction settings; (iii) the correlation between overriding plate deformation and slab interaction with the transition zone; (iv) whether these trends resemble observations on Earth.

  14. An Examination of Seismicity Linking the Solomon Islands and Vanuatu Subduction Zones

    NASA Astrophysics Data System (ADS)

    Neely, J. S.; Furlong, K. P.

    2015-12-01

    The Solomon Islands-Vanuatu composite subduction zone represents a tectonically complex region along the Pacific-Australia plate boundary in the southwest Pacific Ocean. Here the Australia plate subducts under the Pacific plate in two segments: the South Solomon Trench and the Vanuatu Trench. The two subducting sections are offset by a 200 km long, transform fault - the San Cristobal Trough (SCT) - which acts as a Subduction-Transform Edge Propagator (STEP) fault. The subducting segments have experienced much more frequent and larger seismic events than the STEP fault. The northern Vanuatu trench hosted a M8.0 earthquake in 2013. In 2014, at the juncture of the western terminus of the SCT and the southern South Solomon Trench, two earthquakes (M7.4 and M7.6) occurred with disparate mechanisms (dominantly thrust and strike-slip respectively), which we interpret to indicate the tearing of the Australia plate as its northern section subducts and southern section translates along the SCT. During the 2013-2014 timeframe, little seismic activity occurred along the STEP fault. However, in May 2015, three M6.8-6.9 strike-slip events occurred in rapid succession as the STEP fault ruptured east to west. These recent events share similarities with a 1993 strike-slip STEP sequence on the SCT. Analysis of the 1993 and 2015 STEP earthquake sequences provides constraints on the plate boundary geometry of this major transform fault. Preliminary research suggests that plate motion along the STEP fault is partitioned between larger east-west oriented strike-slip events and smaller north-south thrust earthquakes. Additionally, the differences in seismic activity between the subducting slabs and the STEP fault can provide insights into how stress is transferred along the plate boundary and the mechanisms by which that stress is released.

  15. Scientists Examine Challenges and Lessons From Japan's Earthquake and Tsunami

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2011-03-01

    A week after the magnitude 9.0 great Tohoku earthquake and the resulting tragic and damaging tsunami of 11 March struck Japan, 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 Japan's damaged Fukushima Daiichi Nuclear Power Station, about 225 kilometers northeast of Tokyo, where radiation was leaking. The earthquake offshore of Honshu in northeastern Japan (see Figure 1) was a plate boundary rupture along the Japan Trench subduction 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.

  16. The forearc extension in the Central Kuril Islands and the trench rollback

    NASA Astrophysics Data System (ADS)

    Baranov, B. V.; Lobkovsky, L. I.; Dozorova, K. A.

    2016-07-01

    On the basis of bathymetric and seismic data, obtained during cruises 37 (2005) and 41 (2006) of R/V Akademik M.A. Lavrentiev, a new structural scheme of transverse faults in the forearc of the Central Kuril Islands was compiled, the fault kinematics was studied, and a model of the extension zone in the structural pattern of the study area was proposed. According to this model, the trench rollback and development of back-arc basins resulted from the continuous supply of material into the upper mantle convection cell owing to subduction and an increase in the dynamic pressure that pushes the subducting plate, causing it to migrate toward the ocean.

  17. Seafloor Geodesy for Approaching Great Earthquakes Around Japan

    NASA Astrophysics Data System (ADS)

    Fujita, M.; Sato, M.; Ishikawa, T.; Watanabe, S. I.; Yokota, Y.

    2014-12-01

    Seafloor geodesy has been developed as an application of space geodetic technique for the purpose of investigating geodynamic phenomena having their major information in offshore regions. One of such targets is the occurrence of disastrous earthquakes in plate subduction areas. Japan, among others, has repeatedly experienced offshore megathrust earthquakes because of its tectonic location, where multiple plates interact with each other. Most recently, an earthquake of M9.0 occurred off the Pacific coast of east Japan in 2011 with a subsequent huge tsunami, which totally devastated coastal areas and claimed nearly 20,000 lives including those still missing. We, the group of Japan Coast Guard (JCG), have developed a seafloor geodetic technique combining the GPS positioning and underwater acoustic ranging, which is able to measure the position of the seafloor reference point consisting of multiple acoustic transponders with a precision of a few centimeters. We have deployed our seafloor reference points over two regions on the Pacific side of Japan; one is the region along the Japan trench off the eastern coast where the huge 2011 event occurred and another is the region along the Nankai Trough off the southern coast where earthquakes of around M8 have repeated every 100-150 years. With these measurements, we have so far successfully obtained important results providing exclusive information for elucidating the plate boundary behavior causing huge earthquakes. In particular, in the region off east Japan, we have revealed different phases of seafloor movements during the period between several years before and after the 2011 event. They include linear intraplate movements with several centimeters per year before the event, which were the first significant offshore geodetic signals detected around Japan, as well as the coseismic displacements of unprecedentedly huge amount over 20 m close to the epicenter and subsequent postseismic movements with various characteristics

  18. Multi-beam surveys of the Michelson Ridge guyots: Subduction or obduction

    NASA Astrophysics Data System (ADS)

    Christian Smoot, N.

    1983-12-01

    This is the first graphic presentation of the Michelson Ridge in its entirety from a total coverage, multi-beam survey. The ridge splits the Izu and Bonin Trenches, is comprised of four guyots, and is anomalous to the strike of all other ridges heretofore discovered in the Pacific Ocean. The ridge is obducting/offscraping onto the Philippine plate instead of subducting.

  19. Control of paleoshorelines by trench forebulge uplift, Loyalty Islands

    NASA Astrophysics Data System (ADS)

    Dickinson, William R.

    2013-07-01

    Unlike most tropical Pacific islands, which lie along island arcs or hotspot chains, the Loyalty Islands between New Caledonia and Vanuatu owe their existence and morphology to the uplift of pre-existing atolls on the flexural forebulge of the New Hebrides Trench. The configuration and topography of each island is a function of distance from the crest of the uplifted forebulge. Both Maré and Lifou are fully emergent paleoatolls upon which ancient barrier reefs form highstanding annular ridges that enclose interior plateaus representing paleolagoon floors, whereas the partially emergent Ouvea paleoatoll rim flanks a drowned remnant lagoon. Emergent paleoshoreline features exposed by island uplift include paleoreef flats constructed as ancient fringing reefs built to past low tide levels and emergent tidal notches incised at past high tide levels. Present paleoshoreline elevations record uplift rates of the islands since last-interglacial and mid-Holocene highstands in global and regional sea levels, respectively, and paleoreef stratigraphy reflects net Quaternary island emergence. The empirical uplift rates vary in harmony with theoretical uplift rates inferred from the different positions of the islands in transit across the trench forebulge at the trench subduction rate. The Loyalty Islands provide a case study of island environments controlled primarily by neotectonics.

  20. Novel trench gate field stop IGBT with trench shorted anode

    NASA Astrophysics Data System (ADS)

    Xudong, Chen; Jianbing, Cheng; Guobing, Teng; Houdong, Guo

    2016-05-01

    A novel trench field stop (FS) insulated gate bipolar transistor (IGBT) with a trench shorted anode (TSA) is proposed. By introducing a trench shorted anode, the TSA-FS-IGBT can obviously improve the breakdown voltage. As the simulation results show, the breakdown voltage is improved by a factor of 19.5% with a lower leakage current compared with the conventional FS-IGBT. The turn off time of the proposed structure is 50% lower than the conventional one with less than 9% voltage drop increased at a current density of 150 A/cm2. Additionally, there is no snapback observed. As a result, the TSA-FS-IGBT has a better trade-off relationship between the turn off loss and forward drop. Project supported by the National Natural Science Foundation of China (No. 61274080) and the Postdoctoral Science Foundation of China (No. 2013M541585).

  1. Vertical motions of the Puerto Rico Trench and Puerto Rico and their cause

    USGS Publications Warehouse

    ten Brink, U.

    2005-01-01

    The Puerto Rico trench exhibits great water depth, an extremely low gravity anomaly, and a tilted carbonate platform between (reconstructed) elevations of +1300 m and -4000 m. I argue that these features are manifestations of large vertical movements of a segment of the Puerto Rico trench, its forearc, and the island of Puerto Rico that took place 3.3 m.y. ago over a time period as short as 14-40 kyr. I explain these vertical movements by a sudden increase in the slab's descent angle that caused the trench to subside and the island to rise. The increased dip could have been caused by shearing or even by a complete tear of the descending North American slab, although the exact nature of this deformation is unknown. The rapid (14-40 kyr) and uniform tilt along a 250 km long section of the trench is compatible with scales of mantle flow and plate bending. The proposed shear zone or tear is inferred from seismic, morphological, and gravity observations to start at the trench at 64.5??W and trend southwestwardly toward eastern Puerto Rico. The tensile stresses necessary to deform or tear the slab could have been generated by increased curvature of the trench following a counterclockwise rotation of the upper plate and by the subduction of a large seamount.

  2. Mw 8.6 Sumatran earthquake of 11 April 2012: rare seaward expression of oblique subduction

    USGS Publications Warehouse

    Ishii, Miaki; Kiser, Eric; Geist, Eric L.

    2013-01-01

    The magnitude 8.6 and 8.2 earthquakes off northwestern Sumatra on 11 April 2012 generated small tsunami waves that were recorded by stations around the Indian Ocean. Combining differential travel-time modeling of tsunami waves with results from back projection of seismic data reveals a complex source with a significant trench-parallel component. The oblique plate convergence indicates that ~20-50 m of trench-parallel displacement could have accumulated since the last megathrust earthquake, only part of which has been taken up by the Great Sumatran fault. This suggests that the remaining trench-parallel motion was released during the magnitude 8.6 earthquake on 11 April 2012 within the subducting plate. The magnitude 8.6 earthquake is interpreted to be a result of oblique subduction as well as a reduction in normal stress due to the occurrence of the Sumatra-Andaman earthquake in 2004.

  3. Propagation of back-arc extension in the arc of the southern New Hebrides Subduction Zone (South West Pacific) and possible relation to subduction initiation.

    NASA Astrophysics Data System (ADS)

    Fabre, M.; Patriat, M.; Collot, J.; Danyushevsky, L. V.; Meffre, S.; Falloon, T.; Rouillard, P.; Pelletier, B.; Roach, M. J.; Fournier, M.

    2015-12-01

    Geophysical data acquired during three expeditions of the R/V Southern Surveyor allows us to characterize the deformation of the upper plate at the southern termination of the New Hebrides subduction zone where it bends 90° eastward along the Hunter Ridge. As shown by GPS measurements and earthquake slip vectors systematically orthogonal to the trench, this 90° bend does not mark a transition from subduction to strike slip as usually observed at subduction termination. Here the convergence direction remains continuously orthogonal to the trench notwithstanding its bend. Multibeam bathymetric data acquired in the North Fiji Basin reveals active deformation and fragmentation of the upper plate. It shows the southward propagation of a N-S back-arc spreading ridge into the pre-existing volcanic arc, and the connection of the southern end of the spreading axis with an oblique active rift in the active arc. Ultimately the active arc lithosphere is sheared as spreading progressively supersedes rifting. Consequently to such incursion of back-arc basin extension into the arc, peeled off and drifted pieces of arc crust are progressively isolated into the back-arc basin. Another consequence is that the New Hebrides arc is split in two distinct microplates, which move independently relative to the lower plate, and thereby define two different subduction systems. We suggest arc fragmentation could be a consequence of the incipient collision of the Loyalty Ridge with the New Hebrides Arc. We further speculate that this kinematic change could have resulted, less than two million year ago, in the initiation of a new subduction orthogonal to the New Hebrides Subduction possibly along the paleo STEP fault. In this geodynamic setting, with an oceanic lithosphere subducting beneath a sheared volcanic arc, a particularly wide range of primitive subduction-related magmas have been produced including adakites, island arc tholeiites, back-arc basin basalts, and medium-K subduction

  4. Deformation of Japan as measured by improved analysis of GEONET data

    NASA Astrophysics Data System (ADS)

    Owen, S. E.; Dong, D.; Webb, F. H.; Newport, B. J.; Simons, M.

    2006-12-01

    The Japan subduction zone represents a complex set of plate interfaces with significant trench-parallel variability in great earthquakes and transient deep slip events. Within the Japan arc the Nankai segment of the Eurasian-Philippine plate boundary is one of the classic subduction zone segments that last produced a set of temporally linked great earthquakes in the 1940's. Recently, down-dip of the Nankai seismogenic portion of the plate interface, transient slip events and seismic tremor events were observed. Through analysis of the GEONET GPS data, the spatial and higher frequency temporal characteristics of transient slip events can be captured. We describe our analysis methods, the spatial filtering technique that has been developed for use on large networks, a periodic signal filtering method that improves on commonly-used sinusoidal function models, and the resultant velocities and time series. Our newly developed analysis method, the GPS Network Processor, gives us the ability to process large volumes of data extremely fast. The basis of the GPS Network Processor is the JPL-developed GIPSY-OASIS GPS analysis software and the JPL-developed precise point positioning technique. The Network Processor was designed and developed to efficiently implement precise point positioning and bias fixing on a 1000-node (2000 cpu) Beowulf cluster. The entire 10 year ~1000-station GEONET data set can be reanalyzed using the Network Processor in a matter of days. This permits us to test different processing strategies, each with potentially large influence on our ability to detect strain transients from the subduction zones. For example, we can test different ocean loading models, which can effect the diurnal positions of coastal GPS sites by up to 2 cm. We can also test other potentially important factors such as using reprocessed satellite orbits and clocks, the parameterization of the tropospheric delay, or the implementation of refined solid body tide estimates. We will

  5. Dynamic modelling of the subduction zone of central Mexico

    NASA Astrophysics Data System (ADS)

    Gardi, A.; Cocco, M.; Negredo, A. M.; Sabadini, R.; Singh, S. K.

    2000-12-01

    In central Mexico some significant normal faulting events have occurred within the subducted oceanic Cocos plate, just below or near the down-dip edge of the strongly coupled interface. These normal faulting shocks followed large shallow thrust earthquakes. In other subduction zones such events generally precede the up-dip thrust events. A vertical 2-D finite element modelling has been used to simulate the subduction of the Cocos plate beneath the North American plate when the slab is driven by an active convergence velocity or slab pull. We find that the latter mechanism plays only a minor role due to shallow subduction. The modelling results show that the stress pattern is very sensitive to the geometry of the plates. In particular, normal faulting earthquakes that follow large thrust events can be explained on the basis of the flexural response of the overriding and subducting plates to the peculiar geometry of this subduction zone, where the subducting slab becomes horizontal at about 100km from the trench. This horizontal part of the subducting plate, down-dip with respect to the main thrust zone, is under an extensional stress field. This provides an alternative explanation to the slab pull for the occurrence of normal faulting intraplate earthquakes. In order for normal faulting earthquakes to occur in the early part of the seismic cycle, it is necessary that the large up-dip thrust events have a partial stress drop. We find that for small fractional stress drop, a wide region of extension remains below the down-dip edge of the main fault plane following a large thrust earthquake. Thus, the main thrust earthquakes do not invert the polarity of the active stress field, which is compressional and extensional up-dip and down-dip, respectively, with respect to the main thrust fault. Larger fractional stress drops result in larger delays in the occurrence of normal faulting events after the main thrust events.

  6. The role of deep subduction in supercontinent breakup

    NASA Astrophysics Data System (ADS)

    Capitanio, Fabio; Dal Zilio, Luca; Faccenda, Manuele

    2016-04-01

    The breakup of continents is a crucial stage of the episodic aggregation and dispersal of tectonic plates. In particular, the transition from a stable supercontinent to its rifting, breakup and subsequent drifting is one of the least understood aspects of plate tectonics. Over the last decades, several works have highlighted the potential role of pre-existing weaknesses or that of raising mantle plumes in assisting the localization of strain. However, to sustain large-scale divergent regime over geological time, extensional stresses are strictly required. Here we present results from 2-D thermo-mechanical numerical experiments and we show that rifting and drifting of continents result from lithospheric subduction at convergent margins, when this extends to lower mantle depths. We quantify the drag exerted by subduction-induced mantle flow along the basal surface of continental plates, comparing models where lithospheric slabs stagnate above the upper-lower mantle boundary with those where slabs penetrate into the lower mantle. When subduction is upper mantle-confined, divergent basal tractions localize at distances comparable to the effective upper mantle thickness (~500 km), causing the breakup of a microcontinent and opening of a marginal basin. Instead, when the descending lithosphere subducts deeper, extensional stresses localize at greater distances from the trench (≥ 2900 km), are higher and are sustained over a longer time. Although relatively low, basal shear stresses integrated over large plates generate tension forces that may exceed the strength of the continental lithosphere, eventually leading to breakup and opening of an intervening distal basin. The models illustrate that the mechanism leading to the formation of back-arc basins above upper mantle-confined subduction provides a viable explanation for the opening of larger basins above deeper subduction. Examples include the Atlantic Ocean formation and the South and North American plates drifting

  7. Track-and-Trench 2

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image shows the tracks and trench marks made by the Mars Exploration Rover Opportunity at Meridiani Planum, Mars. The rover can be seen to the lower left of the lander. The trench is visible to the upper left of the rover, which has traveled a total of 35.3 meters (116 feet) since leaving the lander on sol 7 (January 31, 2004). On sol 23 (February 16, 2004), the rover used one of its wheels to dig a trench measuring approximately 10 centimeters (4 inches) deep, 50 centimeters (20 inches) long, and 20 centimeters (8 inches) wide. This polar-projected image showing the horizon was created using a combination of images from the rover's navigation camera and hazard-avoidance cameras.

  8. [Adrian Stokes and 'trench jaundice'].

    PubMed

    Wever, Peter C

    2015-01-01

    On the day that Great Britain declared war on Germany in 1914, the Irish physician and bacteriologist Adrian Stokes travelled to London to volunteer. One week later he left for France with the first British troops as an officer with the Royal Army Medical Corps. He spent most of the First World War attached to No. 1 Mobile Bacteriological Laboratory at the Remy Siding British-Canadian field hospital in Flanders. In April 1916, he was confronted with an outbreak of trench jaundice, also known as epidemic jaundice (Weil's disease). Conditions in the trenches contributed to the hundred cases identified by Stokes in a short period. In 1917, he was the first to publish (in The Lancet) the finding that the bacterium Spirochaeta icterohaemorrhagiae, the causative agent of epidemic jaundice, could be isolated from the kidneys of rats. A subsequent rat control campaign in the trenches successfully curbed the disease.

  9. Exploring a Link Between Great and Giant Megathrust Earthquakes and Relative Thickness of Sediment and Eroded Debris in the Subduction Channel to Roughness of Subducted Relief

    NASA Astrophysics Data System (ADS)

    Scholl, D. W.; Kirby, S. H.; von Huene, R.

    2011-12-01

    SEDIMENT SUBDUCTION AND SEISMICITY: At sediment-nourished (>1-2 km) subduction 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 trenches (<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 trench 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 subduction zone constructs a laterally homogenous layer within the plate-separating subduction channel where seismogenic rupturing occurs. The layer of subducted sediment works to even the trench-parallel distribution of coupling strength (asperities) by smothering the roughness or rugosity of subducted sea-floor relief. In doing so sediment subduction contributes to the lengthy (>300-500 km) rupturing of great and giant megathrust Eqs. Larger Mw Eqs do not correlate with increasing thickness of subducted 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

  10. Sedimentation and deformation in the Amlia Fracture Zone sector of the Aleutian Trench

    USGS Publications Warehouse

    Scholl, D. W.; Vallier, T.L.; Stevenson, A.J.

    1982-01-01

    subducting oceanic crust. Up-to-arc extensional faulting can be attributed to the downbending of the Pacific plate into the Aleutian subduction zone. The rupturing direction and dip is controlled by zones of crustal weakness that parallel north Pacific magnetic anomalies, which were formed south of a late Cretaceous-early Tertiary spreading center (Kula-Pacific Ridge). The strike of these anomalies is fortuitously nearly parallel to the Amlia sector. The up-to-arc fracturing style may locally assist in elevating blocks of trench deposits to form the toe of the trench's landward slope, which is in part underlain by a compressionally thickened accretionary mass of older trench deposits. Compressional structures that can be related to underthrusting are only indistinctly recorded in the turbidite wedge that underlies the trench floor. ?? 1982.

  11. Structural and thermal control of seismic activity and megathrust rupture dynamics in subduction zones: Lessons from the Mw 9.0, 2011 Tohoku earthquake

    NASA Astrophysics Data System (ADS)

    Satriano, Claudio; Dionicio, Viviana; Miyake, Hiroe; Uchida, Naoki; Vilotte, Jean-Pierre; Bernard, Pascal

    2014-10-01

    The 2011 Tohoku megathrust earthquake ruptured a vast region of the northeast Japan Trench subduction zone in a way that had not been enough anticipated by earthquake and tsunami risk scenarios. We analyzed the Tohoku rupture combining high-frequency back-projection analysis with low frequency kinematic inversion of the co-seismic slip. Results support the to-day well-accepted broadband characteristics of this earthquake. Most of the seismic moment is released during the first 100 s, with large co-seismic slip (up to 55 m) offshore Miyagi in a compact region on the landward side of the trench. Coherent high-frequency radiation areas and relatively low co-seismic slip are a distinctive signature of the slab-mantle interface. The broadband characteristics of the Tohoku rupture are interpreted, integrating the seismic activity and structure information on the NE Japan forearc region, as a signature of along-dip segmentation and segment interactions, that result from thermal structure, plate geometry, material composition and fracture heterogeneities along the plate boundary interface. Deep mantle corner flow and low dehydration rates along the cold subduction slab interface lead to an extended seismogenic slab-mantle interface, with strong bi-material contrast controlling larger propagation distance in the downdip preferred rupture direction. Off Miyagi, plate bending below the mantle wedge, ∼142.3°E at ∼25 km depth, is associated with the eastern limit of the deep M7-8-class thrust-earthquakes, and of the strongest coherent high-frequency generation areas. The region of the slab-crust interface between the mantle wedge limit, ∼142.7°E at ∼20 km depth, and a trenchward plate bending, ∼143.2°E at ∼15 km, acted as an effective barrier resisting for many centuries to stress-loading gradient induced by deep stable sliding and large earthquakes along the slab-mantle interface. The 2011 Tohoku earthquake, whose hypocenter is located on the east side of the

  12. Trench-parallel anisotropy produced by serpentine deformation in the hydrated mantle wedge.

    PubMed

    Katayama, Ikuo; Hirauchi, Ken-ichi; Michibayashi, Katsuyoshi; Ando, Jun-ichi

    2009-10-22

    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 trench-parallel anisotropy (delay time of one to two seconds) observed in several subduction 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 trench-parallel seismic anisotropy observed in subduction 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 trench-parallel seismic anisotropy in the case of a steeply subducting 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.

  13. Active Subduction on Both Coasts of Costa Rica Does not Represent an Important Tsunami Hazard

    NASA Astrophysics Data System (ADS)

    Protti, M.; Gonzalez, V.

    2007-05-01

    Costa Rica, on the southern terminus of the Middle American Trench is being affected by active subduction on both, along the Pacific coast as well as on its Caribbean coast. Three main subduction segments can be recognized along the Pacific coast: 1) under northwestern Costa Rica, off Papagayo Gulf and Nicoya peninsula, the Cocos plate is subducting under the Caribbean plate; 2) under southern Costa Rica (Osa and Burica peninsulas) the Cocos plate subducts under the Panama Block and 3) in the central Pacific coast (between Nicoya and Osa peninsulas) the Cocos plate subducts under a shear zone that marks the transition between the Caribbean and the Cocos plate. Along the Caribbean coast, south of Puerto Limon, the Caribbean plate subducts under the Panama block. Large subduction earthquakes occur under the Nicoya peninsula, Osa peninsula and south of Limon. Most of the rupture area of these large events lies below land so the deformation of the ocean floor is minimal and therefore the tsunamis they generate are small. No large subduction earthquakes occur under the central Pacific coast of Costa Rica due to the subduction of small sea mounts that act as small asperities without potential to accumulate large amounts of slip. For this reason the region between Nicoya and Osa peninsulas is not an important tsunamigenic zone.

  14. Comparing slip behavior and hydromechanical properties of fault systems in the Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Ikari, M.; Saffer, D. M.; Marone, C.; Knuth, M. W.

    2010-12-01

    At subduction zones, the plate boundary system includes several active faults, including the master décollement and splay faults that branch from it and cut the overriding margin wedge. The partitioning of strain accumulation and slip on these structures may provide important information about the mechanical behavior of the plate boundary, and for earthquake rupture and tsunamigenesis. We conducted laboratory experiments to measure the frictional and hydrologic properties of fault and wall rock from three distinct fault zone systems sampled during IODP Expedition 316 and ODP Leg 190 to the Nankai Trough offshore Japan. These fault zones are: (1) a major out-of-sequence thrust fault that terminates ~25 km landward of the trench and extends for >120 km along-strike, termed the “megasplay”; (2) the frontal thrust, comprising a region of diffuse thrust faulting near the trench; and (3) the décollement zone sampled 2 km from the trench. We observe predominantly low friction (µ ≤ 0.46), and low permeability (k ≤ 7.00x10-19 m2) consistent with the clay-rich composition of the samples. Samples from the décollement zone are both consistently weaker (µ ≤ 0.30) and less permeable than those from the megasplay area and the frontal thrust system. Fault zone material from the megasplay is both significantly weaker and less permeable than the surrounding wall rocks, a pattern not observed in the frontal thrust and décollement. All samples exhibit velocity-strengthening frictional behavior over most of the experimental conditions we explored, consistent with aseismic slip at shallow depths. Slip stability does not vary between fault zone and wall rock in any of the three settings. A previously observed minimum in the friction rate parameter a-b at sliding velocities of ~1-3 µm/s (~0.1-0.3 m/d) for samples from the megasplay fault zone is also observed for both the frontal thrust and décollement, and our data suggests that this phenomenon may be controlled

  15. Monitoring of seafloor crustal deformation using GPS/Acoustic technique along the Nankai Trough, Japan

    NASA Astrophysics Data System (ADS)

    Yasuda, K.; Tadokoro, K.; Ikuta, R.; Watanabe, T.; Fujii, C.; Matsuhiro, K.; Sayanagi, K.

    2014-12-01

    Seafloor crustal deformation is crucial for estimating the interplate locking at the shallow subduction zone and has been carried out at subduction margins in Japan, e.g., Japan Trench and Nankai Trough [Sato et al., 2011; Tadokoro et al., 2012]. Iinuma et al. [2012] derived slip distributions during the 2011 Tohoku-Oki earthquake using GPS/Acoustic data and on-land GPS data. The result showed that maximum slip is more than 85 m near the trench axis. The focal area along the Nankai trough extended to the trough axis affected this earthquake by cabinet office, government of Japan.  We monitored seafloor crustal deformation along the Nankai trough, Japan. Observation regions are at the eastern end of Nankai trough (named Suruga trough) and at the central Nankai trough. We established and monitored by two sites across the trough at each region. In the Suruga trough region, we repeatedly observed from 2005 to 2013. We observed 13 and 14 times at a foot wall side (SNE) and at a hanging wall side (SNW), respectively. 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 N94±3˚W direction and 39±11 mm/y to N84±9˚W 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 4 mm/y between SNW and on-land GPS stations at hanging wall side of the Suruga Trough. This result shows that the plate interface at the northernmost Suruga trough is strongly locked. In the central Nankai trough region, we established new two stations across the central Nankai trough (Both stations are about 15km distance from trough) and observed only three times, August 2013, January 2014, and June 2014. We report the results of monitoring performed in this year.

  16. Role of H2O in Generating Subduction Zone Earthquakes

    NASA Astrophysics Data System (ADS)

    Hasegawa, A.

    2017-03-01

    A dense nationwide seismic network and high seismic activity in Japan have provided a large volume of high-quality data, enabling high-resolution imaging of the seismic structures defining the Japanese subduction zones. Here, the role of H2O in generating earthquakes in subduction zones is discussed based mainly on recent seismic studies in Japan using these high-quality data. Locations of intermediate-depth intraslab earthquakes and seismic velocity and attenuation structures within the subducted slab provide evidence that strongly supports intermediate-depth intraslab earthquakes, although the details leading to the earthquake rupture are still poorly understood. Coseismic rotations of the principal stress axes observed after great megathrust earthquakes demonstrate that the plate interface is very weak, which is probably caused by overpressured fluids. Detailed tomographic imaging of the seismic velocity structure in and around plate boundary zones suggests that interplate coupling is affected by local fluid overpressure. Seismic tomography studies also show the presence of inclined sheet-like seismic low-velocity, high-attenuation zones in the mantle wedge. These may correspond to the upwelling flow portion of subduction-induced secondary convection in the mantle wedge. The upwelling flows reach the arc Moho directly beneath the volcanic areas, suggesting a direct relationship. H2O originally liberated from the subducted slab is transported by this upwelling flow to the arc crust. The H2O that reaches the crust is overpressured above hydrostatic values, weakening the surrounding crustal rocks and decreasing the shear strength of faults, thereby inducing shallow inland earthquakes. These observations suggest that H2O expelled from the subducting slab plays an important role in generating subduction zone earthquakes both within the subduction zone itself and within the magmatic arc occupying its hanging wall.

  17. Nonvolcanic tremors in the Mexican subduction zone

    NASA Astrophysics Data System (ADS)

    Payero, J. S.; Kostoglodov, V.; Mikumo, T.; Perez-Campos, X.; Iglesias, A.; Clayton, R.

    2007-05-01

    Nonvolcanic low frequency tremors (NVT) have been discovered and studied recently in Japan and Cascadia subduction zones and deep beneath the San Andreas Fault. The tremors activity is increasing during so-called silent earthquakes (SQ) in Japan and Cascadia. NVT clusters also migrate following the propagation of the SQ. The origin of the NVT is still unclear. The studies of NVT and SQ in different subduction zones are required to understand the cause for these phenomena. We discovered a number of NVT from daily spectrograms of continuous broad band records at seismic stations of Servicio Seismológico Nacional (SSN) an MASE project. The analyzed data cover a period of 2001-2004 (SSN) when in 2002 a large SQ has occurred in the Guerrero- Oaxaca region, and a steady-state interseismic epoch of 2005 and a new large SQ in 2006 (MASE). NVT occurred in the central part of the Mexican subduction zone (Guerrero) at approximately 200 km from the coast. We can not accurately localize the tremors because of sparse station coverage in 2001-2004. The MASE data of 2005-2006 show that NVT records in Mexico are very similar to those obtained in Cascadia subduction zone. The tremors duration is of 10-60 min, and they appear to travel at S-wave velocities. More than 100 strong NVT were recorded by most of the MASE stations with the epicenters clustered in the narrow band of ~40x150 km to the south of Iguala city and parallel to the coast line. NVT depths are poorly constrained but seem to be less than 40 km deep. We noticed a some increase of NVT activity during the 2001-2002 and 2006 SQs compared with an NVT activity for the "SQ quiet" period of 2003-2004 nevertheless. A lack of NVT for the period of 2-3 months after the SQ is apparent in 2002 and 2006.

  18. Slab pull and the seismotectonics of subducting lithosphere

    USGS Publications Warehouse

    Spence, William

    1987-01-01

    earthquakes of northern Japan. The slab pull model explains the lower layer of double seismic zones as due to tension from the deeper, sinking plate and the upper layer as due to localized in-plate compression, as plate motion is resisted by the bounding mantle. Just downdip of the interface thrust zone, there occurs an aseismic 20°–50° dip increase of subducted plate. This slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change. Resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone.

  19. Intensive hydration of the wedge mantle at the Kuril arc - NE Japan arc junction: implications from mafic lavas from Usu Volcano, northern Japan

    NASA Astrophysics Data System (ADS)

    Kuritani, T.; Tanaka, M.; Yokoyama, T.; Nakagawa, M.; Matsumoto, A.

    2015-12-01

    The southwestern part of Hokkaido, northern Japan, is located at the junction of the NE Japan arc and the Kuril arc. The subducting Pacific plate under this region shows a hinge-like shape due to the dip change of the subducting plate along the trench. Because of the interest in this unique tectonic setting, this arc-arc junction has been the focus of extensive geophysical studies (e.g. Kita et al., 2010, Morishige and van Keken, 2014; Wada et al., 2015). This region is also known as an area in which magmatism has been intense; there are many active volcanoes such as Usu, Tarumae, and Komagatake, and large calderas including Toya, Shikotsu, and Kuttara. In this region, the temporal and spatial evolution of the volcanism and the chemical compositions of the volcanic rocks are well characterized (e.g. Nakagawa, 1992). However, the generation conditions of magmas have not been estimated for these volcanoes, probably because of the scarcity of basaltic products. Therefore, a possible link between the tectonic setting and the intense magmatism is still unclear. In this study, we carried out a petrological and geochemical study on mafic lavas (49.6-51.3 wt.% SiO2) from Usu Volcano, and estimated the conditions under which the magmas were generated. By application of a plagioclase-melt hygrometer to the plagioclase and the host magma, the water content of ~6.5 wt.% was obtained for the basaltic magma. Using this information, as well as the olivine maximum fractionation model (Tatsumi et al., 1983), the composition of the primary magma is estimated to be 47.9 wt.% SiO2, 15.1 wt.% MgO, and 4.1 wt.% H2O. Analyses using the multi-component thermodynamics suggest that the primary magma was generated in the source mantle with 0.9 wt.% H2O at 1310ºC and at 1.6 GPa. The water content of 0.9 wt.% of the source mantle is significantly higher than the estimates for the source mantle in the main NE Japan arc (<0.7 wt.% H2O); this implies that the flux of slab-derived fluids is

  20. Geoid anomalies in the vicinity of subduction zones

    NASA Technical Reports Server (NTRS)

    Mcadoo, D. C.

    1980-01-01

    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 subduction 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, subducting slabs can be expected to produce primarily intermediate and longer wavelength variations. Gravimetric profiles across trench/island arc complexes resolve primarily short wavelengths. The model represents subducting 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 trench 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.

  1. A close link between serpentinization and seismogenesis in the Philippine Sea slab beneath Kanto, Japan

    NASA Astrophysics Data System (ADS)

    Nakajima, J.; Hasegawa, A.; Umino, N.; Demachi, T.

    2010-12-01

    The Kanto district in central Japan, 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 trench-trench-trench (TTT) triple junction with two obliquely subducting oceanic plates, the Philippine Sea (PHS) and Pacific (PAC) plates. Recent studies have shown that the bottom of the PHS slab is in contact with the upper surface of the Pacific slab beneath Kanto (Uchida et al., 2009, EPSL; Nakajima et al., 2009, JGR). As a result of the subduction of the two slabs, many disastrous M~8 and numerous M~7 earthquakes have struck the Tokyo metropolitan area. For example, the 1923 Kanto earthquake (M7.9), one of the most destructive earthquakes in the 20th century, caused severe damage to the Tokyo metropolitan area, along with 105,000 fatalities. We perform travel-time tomography beneath Kanto, Japan, to obtain detailed structures of the subducting PHS slab and to discuss the seismogenesis of interplate and intraplate earthquakes in terms of the contact of the two slabs. We detected a wedge-shaped prominent low-velocity zone with high Vp/Vs at the easternmost portion of the PHS slab. The western boundary of the low-velocity zone is sub-vertical, and seismic velocities vary by 15-20% across it over a short distance of ~10 km. This low-velocity zone is interpreted as serpentinized mantle of the PHS slab because serpentinization of the mantle of the PHS plate is observed along the Izu-Bonin trench before its subduction (Kamimura et al., 2002, PEPI). We found two clear relation between serpentinization and seismicity around the PHS slab. First, thrust earthquakes between the bottom of the PHS slab and the upper surface of the PAC slab occur inhomogenously in space and are almost absent along the PHS-PAC interface overlain by the serpentinized PHS-slab mantle. This observation strongly suggests that low viscosity of the serpentine prevents the plate interface from slipping seismically

  2. Dynamic buckling of subducting slabs reconciles geological and geophysical observations

    NASA Astrophysics Data System (ADS)

    Lee, Changyeol; King, Scott D.

    2011-12-01

    Ever since the early days of the development of plate tectonic theory, subduction zones have been engrained in geological thinking as the place where steady, linear slabs descend into the mantle at a constant, uniform dip angle beneath volcanic arcs. However, growing evidence from geological and geophysical observations as well as analog and numerical modeling indicates that subducting slabs buckle in a time-dependent manner, in contrast to the steady-state, linear cartoons that dominate the literature. To evaluate the implication of time-dependent slab buckling of geological events, we conduct a series of 2-D numerical dynamic/kinematic subduction experiments by varying the viscosity increase across the 660 km discontinuity and the strength of the subducting slab. Our results show that slab buckling is a universal figure in all the experiments when rate of the trench migration ( Vtrench) is relatively slow ( Vtrench| < 2 cm/a) and viscosity increases across the 660 km discontinuity are greater than a factor of 30. Slab buckling is expressed as alternate shallowing and steepening dip of the subducting slab (from ~ 40 to ~ 100°) which is correlated with increasing and decreasing convergent rate of the incoming oceanic plate toward the trench. Further, the slab buckling in our experiments is consistent with the previously developed scaling laws for slab buckling; using reasonable parameters from subducted slabs the buckling amplitude and period are ~ 400 km and ~ 25 Myr, respectively. The slab buckling behavior in our experiments explains a variety of puzzling geological and geophysical observations. First, the period of slab buckling is consistent with short periodic variations (~ 25 Myr) in the motions of the oceanic plates that are anchored by subduction zones. Second, the scattered distributions of slab dips (from ~ 20 to ~ 90°) in the upper mantle are snapshots of time-dependent slab dip. Third, the current compressional and extensional stress environments in

  3. Seismic structure off the Kii Peninsula, Japan, deduced from passive- and active-source seismographic data

    NASA Astrophysics Data System (ADS)

    Yamamoto, Yojiro; Takahashi, Tsutomu; Kaiho, Yuka; Obana, Koichiro; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki

    2017-03-01

    We conduct seismic tomography to model subsurface seismicity between 2010 and 2012 and structural heterogeneity off the Kii Peninsula, southwestern Japan, and to investigate their relationships with segmentation of the Nankai and Tonankai seismogenic zones of the Nankai Trough. In order to constrain both the shallow and deep structure of the offshore seismogenic segments, we use both active- and passive-source data recorded by both ocean-bottom seismometers and land seismic stations. The relocated microearthquakes indicate a lack of seismic activity in the Tonankai seismogenic segment off Kumano, whereas there was active intraslab seismicity in the Kii Channel area of the Nankai seismogenic segment. Based on comparisons among the distribution of seismicity, age, and spreading rate of the subducting Philippine Sea plate, and the slip-deficit distribution, we conclude that seismicity in the subducting slab under the Kii Channel region nucleated from structures in the Philippine Sea slab that pre-date subduction and that fluids released by dehydration are related to decreased interplate coupling of these intraslab earthquakes. Our velocity model clearly shows the areal extent of two key structures reported in previous 2-D active-source surveys: a high-velocity zone beneath Cape Shionomisaki and a subducted seamount off Cape Muroto, both of which are roughly circular and of 15-20 km radius. The epicenters of the 1944 Tonankai and 1946 Nankai earthquakes are near the edge of the high-velocity body beneath Cape Shionomisaki, suggesting that this anomalous structure is related to the nucleation of these two earthquakes. We identify several other high- and low-velocity zones immediately above the plate boundary in the Tonankai and Nankai seismogenic segments. In comparison with the slip-deficit model, some of the low-velocity zones appear to correspond to an area of strong coupling. Our observations suggest that, unlike the Japan Trench subduction zone, in our study area

  4. Strength and survival of subducted lithosphere during the Laramide orogeny

    SciTech Connect

    Spencer, J.E. )

    1993-04-01

    The strength of subducted ocean lithosphere is influenced primarily by two competing processes. During subduction 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 subduction 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 subducted 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 subduction beneath southwestern North America, using slab ages and subduction rates for the Farallon plate from Engebretson et al., suggests that the subducted 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 trench because much rock remains in the brittle regime and is under high confining pressure.

  5. Influence of subduction history on South American topography

    NASA Astrophysics Data System (ADS)

    Flament, Nicolas; Gurnis, Michael; Müller, R. Dietmar; Bower, Dan J.; Husson, Laurent

    2015-11-01

    The Cenozoic evolution of South American topography is marked by episodes of large-scale uplift and subsidence not readily explained by lithospheric deformation. The drying up of the inland Pebas system, the drainage reversal of the Amazon river, the uplift of the Sierras Pampeanas and the uplift of Patagonia have all been linked to the evolution of mantle flow since the Miocene in separate studies. Here we investigate the evolution of long-wavelength South American topography as a function of subduction history in a time-dependent global geodynamic model. This model is shown to be consistent with these inferred changes, as well as with the migration of the Chaco foreland basin depocentre, that we partly attribute to the inboard migration of subduction resulting from Andean mountain building. We suggest that the history of subduction along South America has had an important influence on the evolution of the topography of the continent because time-dependent mantle flow models are consistent with the history of vertical motions as constrained by the geological record at four distant areas over a whole continent. Testing alternative subduction scenarios reveals flat slab segments are necessary to reconcile inferred Miocene shorelines with a simple model paleogeography. As recently suggested, we find that the flattening of a subduction zone results in dynamic uplift between the leading edge of the flat slab segment and the trench, and in a wave of dynamic subsidence associated with the inboard migration of the leading edge of flat subduction. For example, the flattening of the Peruvian subduction contributed to the demise of Pebas shallow-water sedimentation, while continental-scale tilting also contributed to the drainage reversal of the Amazon River. The best correlation to P-wave tomography models for the Peruvian flat slab segment is obtained for a case when the asthenosphere, here considered to be 150 km thick and 10 times less viscous than the upper mantle, is

  6. Seismic properties of the Nazca oceanic crust in southern Peruvian subduction system

    NASA Astrophysics Data System (ADS)

    Kim, YoungHee; Clayton, Robert W.

    2015-11-01

    The horizontal Nazca slab, extending over a distance of ∼800 km along the trench is one of enigmatic features in Peruvian subduction zone. Increased buoyancy of the oceanic lithosphere alone due to the subduction of Nazca Ridge is insufficient to fully explain such a lengthy segment. We use data from the recent seismic experiment in southern Peru to find that the subduction-related hydration plays a major role in controlling shear wave velocities within the upper part of the oceanic crust and overlying materials. We observe substantial velocity reductions of ∼20-40% near the top plate interface along- and perpendicular-to the trench from ∼40-120 km depths. In particular, significant shear wave velocity reductions and subsequently higher P-to-S velocity ratio (exceeding 2.0) at the flat slab region suggest that the seismically probed layer is fluid-rich and mechanically weak. The dominant source of fluid comes from metasediments and subducted crust (Nazca Ridge). Long-term supply of fluid from the southward migrating Nazca Ridge provides additional buoyancy of the subducting oceanic lithosphere and also lowers the viscosity of the overlying mantle wedge to drive and sustain the flat plate segment of ∼800 km along the trench. Also, by comparing calculated seismic velocities with experimentally derived mineral physics data, we additionally provide mechanical constraints on the possible changes in frictional behavior across the subduction zone plate interface. Observed low seismic velocities in the seismogenic zone suggest a presence of low strength materials that may be explained by overpressured pore fluids (i.e., accreted sediment included in the subduction channel).

  7. Seismic properties of the Nazca oceanic crust in southern Peruvian subduction system

    NASA Astrophysics Data System (ADS)

    Kim, Y.; Clayton, R. W.

    2015-12-01

    The horizontal Nazca slab, extending over a distance of ~800 km along the trench is one of enigmatic features in Peruvian subduction zone. Increased buoyancy of the oceanic lithosphere alone due to the subduction of Nazca Ridge is insufficient to fully explain such a lengthy segment. We use data from the recent seismic experiment in southern Peru to find that the subduction-related hydration plays a major role in controlling shear wave velocities within the upper part of the oceanic crust and overlying materials. We observe substantial velocity reductions of ~20-40% near the top plate interface along- and perpendicular-to the trench from ~40-120 km depths. In particular, significant shear wave velocity reductions and subsequently higher P-to-S velocity ratio (exceeding 2.0) at the flat slab region suggest that the seismically probed layer is fluid-rich and mechanically weak. The dominant source of fluid comes from metasediments and subducted crust (Nazca Ridge). Long-term supply of fluid from the southward migrating Nazca Ridge provides additional buoyancy of the subducting oceanic lithosphere and also lowers the viscosity of the overlying mantle wedge to drive and sustain the flat plate segment of ~800 km along the trench. Also, by comparing calculated seismic velocities with experimentally derived mineral physics data, we additionally provide mechanical constraints on the possible changes in frictional behavior across the subduction zone plate interface. Observed low seismic velocities in the seismogenic zone suggest a presence of low strength materials that may be explained by overpressured pore fluids (i.e., accreted sediment included in the subduction channel).

  8. Shallow subduction, ridge subduction, and the evolution of continental lithosphere

    SciTech Connect

    Helmstaedt, H.; Dixon, J.M.; Farrar, E.; Carmichael, D.M.

    1985-01-01

    Subduction of oceanic lithosphere beneath continental crust at a shallow angle has occurred throughout the Phanerozoic Eon. Ridge subduction often follows shallow subduction and causes bimodal volcanism and crustal rifting, forming back-arc basins. Recent models for Archean plate tectonics propose very fast rates of spreading (400-800 km/Ma) and convergence, and sinking rates comparable to or slower (<10 km/Ma) than those of today. As faster convergence and slower sinking correspond to subduction at shallower angles, shallow subduction and ridge subduction must have been ubiquitous during the Archean permobile regime. This is compatible with a back-arc-basin origin for Archean greenstone belts. The common coexistence of tholeiitic and calc-alkaline igneous rocks in Archean greenstone belts, also implies ridge subduction. The authors envisage a transition, between 2.4 and 1.8 Ga., from a regime dominated by shallow subduction and repeated ridge subduction to one of normal plate tectonics with steeper subduction. Spreading rates decreased; continental plates became larger and stable shelves could develop at trailing margins. Shallow subduction became the exception, restricted to episodes of abnormally fast convergence; nevertheless, the long span of post-Archean time makes it unlikely that any part of the continental crust has escaped shallow subduction and ridge subduction. These processes recycle much volatile-rich oceanic crust into the sub-continental upper mantle, thereby underplating the crust, effecting upper-mantle metasomatism and affecting intraplate magmatism.

  9. The dynamics of double slab subduction from numerical and semi-analytic models

    NASA Astrophysics Data System (ADS)

    Holt, A.; Royden, L.; Becker, T. W.

    2015-12-01

    Regional interactions between multiple subducting slabs have been proposed to explain enigmatic slab kinematics in a number of subduction zones, a pertinent example being the rapid pre-collisional plate convergence of India and Eurasia. However, dynamically consistent 3-D numerical models of double subduction have yet to be explored, and so the physics of such double slab systems remain poorly understood. Here we build on the comparison of a fully numerical finite element model (CitcomCU) and a time-dependent semi-analytic subduction models (FAST) presented for single subduction systems (Royden et. al., 2015 AGU Fall Abstract) to explore how subducting slab kinematics, particularly trench and plate motions, can be affected by the presence of an additional slab, with all of the possible slab dip direction permutations. A second subducting slab gives rise to a more complex dynamic pressure and mantle flow fields, and an additional slab pull force that is transmitted across the subduction zone interface. While the general relationships among plate velocity, trench velocity, asthenospheric pressure drop, and plate coupling modes are similar to those observed for the single slab case, we find that multiple subducting slabs can interact with each other and indeed induce slab kinematics that deviate significantly from those observed for the equivalent single slab models. References Jagoutz, O., Royden, L. H., Holt, A. F. & Becker, T. W., 2015, Nature Geo., 8, 10.1038/NGEO2418. Moresi, L. N. & Gurnis, M., 1996, Earth Planet. Sci. Lett., 138, 15-28. Royden, L. H. & Husson, L., 2006, Geophys. J. Int. 167, 881-905. Zhong, S., 2006, J. Geophys. Res., 111, doi: 10.1029/2005JB003972.

  10. Seismicity, topography, and free-air gravity of the Aleutian-Alaska subduction zone

    NASA Astrophysics Data System (ADS)

    Wells, R. E.; Blakely, R. J.; Scholl, D. W.; Ryan, H. F.

    2011-12-01

    The Aleutian-Alaska subduction zone, extending 3400 km from the Queen Charlotte Fault to Kamchatka, has been the source of six great megathrust earthquakes in the 20th Century. Four earthquakes have ruptured the 2000-km-long Aleutian segment, where the Cenozoic Aleutian arc overlies the subducting Pacific plate. These include the 1946 M 8.6 earthquake off Unimak Is., the 1957 M 8.6 and 1986 M 8.0 earthquakes off the Andreanoff Is., and the 1965 M 8.7 Rat Is. earthquake. The source regions of these earthquakes inferred from waveform inversions underlie the well-defined Aleutian deep-sea terrace. The deep-sea terrace is about 4 km deep and is underlain by Eocene arc framework rocks, which extend nearly to the trench. It is bounded on its seaward and landward margins by strong topographic and fee-air gravity gradients. The main asperities (areas of largest slip) for the great earthquakes and nearly all of the Aleutian thrust CMT solutions lie beneath the Aleutian terrace, between the maximum gradients. Similar deep-sea terraces are characteristic of non-accretionary convergent margins globally (75% of subduction zones), and, where sampled by drilling (e.g., Japan, Peru, Tonga, Central America), are undergoing sustained subsidence. Sustained subsidence requires removal of arc crust beneath the terrace by basal subduction erosion (BSE). BSE is in part linked to the seismic cycle, as it occurs in the same location as the megathrust earthquakes. Along the eastern 1400 km of the Alaskan subduction zone, the Pacific plate subducts beneath the North American continent. The boundary between the Aleutian segment and the continent is well defined in free-air gravity, and the distinctive deep-sea terrace observed along the Aleutian segment is absent. Instead, the Alaskan margin consists of exhumed, underplated accretionary complexes forming outer arc gravity highs. Superimposed on them are broad topographic highs and lows forming forearc basins (Shumagin, Stevenson) and islands

  11. KSC Launch Pad Flame Trench Environment Assessment

    NASA Technical Reports Server (NTRS)

    Calle, Luz Marina; Hintze, Paul E.; Parlier, Christopher R.; Curran, Jerome P.; Kolody, Mark R.; Sampson, Jeffrey W.

    2010-01-01

    This report summarizes conditions in the Launch Complex 39 (LC-39) flame trenches during a Space Shuttle Launch, as they have been measured to date. Instrumentation of the flame trench has been carried out by NASA and United Space Alliance for four Shuttle launches. Measurements in the flame trench 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 trench and to provide data used to improve models of the launch environment in the flame trench.

  12. Quaternary Sediment Accumulation in the Aleutian Trench: Implications for Dehydration Reaction Progress and Pore Pressure Development Offshore Alaska

    NASA Astrophysics Data System (ADS)

    Meridth, L. N.; Screaton, E.; Jaeger, J. M.; James, S. R.; Villaseñor, T. G.

    2015-12-01

    Sediment inputs to subduction zones impart a significant control on diagenetic reaction progress, fluid production and pore pressure development and thus affect hydrologic and tectonic behavior during subduction. Intensified glaciation following the mid-Pleistocene transition increased sediment flux to the Gulf of Alaska. Rapid sediment accumulation (>1 km/my) in the Aleutian Trench increases overburden and should accelerate dehydration of hydrous sedimentary components by elevating temperatures in the incoming sediment column. These processes have the potential to generate fluid overpressures in the mud-dominated, low permeability sediments deposited on the incoming plate, offshore SE Alaska. Mineralogical analyses on incoming sediments from Deep Sea Drilling Project Leg 18 and Integrated Ocean Drilling Program Expedition 341 show that both smectite and Opal-A are present as hydrous mineral phases. A 1-D numerical model was developed to track dehydration reaction progress and pore pressures in the incoming sediment column from the abyssal plain to the Aleutian Trench. Simulated temperatures in the incoming column increase due to the insulating effect of trench sediments. As a result, trench sedimentation causes smectite dehydration to begin and Opal-A dehydration to nearly reach completion at the deformation front. Simulated excess pore pressures in the proto-decollement zone increase from nearly hydrostatic to almost half of lithostatic due to the rapid deposition of trench sediments. The 1-D modeling results were incorporated into a 2-D model that follows the underthrust column at the deformation front into the subduction zone. Simulated results of the 2-D flow model illustrate the effects of lateral flow on pore pressure distribution following subduction.

  13. Vertical slab sinking and westward subduction offshore of Mesozoic North America

    NASA Astrophysics Data System (ADS)

    Sigloch, Karin; Mihalynuk, Mitchell G.

    2013-04-01

    Subducted slabs in the mantle, as imaged by seismic tomography, preserve a record of ancient subduction zones. Ongoing debate concerns how direct this link is. How long ago did each parcel of slab subduct, and where was the trench located relative to the imaged slab position? Resolving these questions will benefit paleogeographic reconstructions, and restrict the range of plausible rheologies for mantle convection simulations. We investigate one of the largest and best-constrained Mesozoic slab complexes, the "Farallon" in the transition zone and lower mantle beneath North America. We quantitatively integrate observations from whole-mantle P-wave tomography, global plate reconstructions, and land geological evidence from the North American Cordillera. These three data sets permit us to test the simplest conceivable hypothesis for linking slabs to paleo-trenches: that each parcel of slab sank only vertically shortly after entering the trench That is, we test whether within the limits of tomographic resolution, all slab material lies directly below the location where it subducted beneath its corresponding arc. Crucially and in contrast to previous studies, we do not accept or impose an Andean-style west coast trench (Farallon-beneath-continent subduction) since Jurassic times, as this scenario is inconsistent with many geological observations. Slab geometry alone suggests that trenches started out as intra-oceanic because tomography images massive, linear slab "walls" in the lower mantle, extending almost vertically from about 800 km to 2000+ km depth. Such steep geometries would be expected from slabs sinking vertically beneath trenches that were quasi-stationary over many tens of millions of years. Intra-oceanic trenches west of Mesozoic North America could have been stationary, whereas a coastal Farallon trench could not, because the continent moved westward continuously as the Atlantic opened. Overlap of North American west-coast positions, as reconstructed in a

  14. Revisiting the physical characterisitics of the subduction interplate seismogenic zones

    NASA Astrophysics Data System (ADS)

    Heuret, Arnauld; Lallemand, Serge; Funiciello, Francesca; Piromallo, Claudia

    2010-05-01

    Based on the Centennial earthquake catalog, the revised 1964-2007 EHB hypocenters catalog and the 1976-2007 CMT Harvard catalog, we have extracted the hypocenters, nodal planes and seismic moments of worldwide subduction earthquakes for the 1900-2007 period. For the 1976-2007 period, we combine the focal solutions provided by Harvard and the revised hypocenters from Engdahl et al. (1998). Older events are extracted from the Centennial catalogue (Engdahl and Villasenor, 2002) and they are used to estimate the cumulated seismic moment only. The selection criteria for the subduction earthquakes are similar to those used by Mc Caffrey (1994), i.e., we test if the focal mechanisms are consistent with 1/ shallow thrust events (depth > 70 km, positive slips, and at least one nodal plane gets dip < 45°), and, 2/ the plate interface local geometry and orientation (one nodal plane is oriented toward the volcanic arc, the azimuth of this nodal plane ranges between ± 45° with respect to the trench one, its dip ranges between ± 20° with respect to the slab one and the epicentre is located seaward of the volcanic arc). Our study concerns segments of subduction zones that fit with estimated paleoruptures associated with major events (M > 8). We assume that the seismogenic zone coincides with the distribution of 5.5 < M < 7 subduction earthquakes. We provide a map of the interplate seismogenic zones for 80% of the trench systems including dip, length, downdip and updip limits, we revisit the statistical study done by Pacheco et al. (1993) and test some empirical laws obtained for example by Ruff and Kanamori (1980) in light of a more complete, detailed, accurate and uniform description of the subduction interplate seismogenic zone. Since subduction earthquakes result from stress accumulation along the interplate and stress depends on plates kinematics, subduction zone geometry, thermal state and seismic coupling, we aim to isolate some correlations between parameters. The

  15. Magnesium Isotopic Composition of Subducting Marine Sediments

    NASA Astrophysics Data System (ADS)

    Hu, Y.; Teng, F. Z.; Plank, T. A.; Huang, K. J.

    2015-12-01

    Subducted marine sediments have recently been called upon to explain the heterogeneous Mg isotopic composition (δ26Mg, ‰) found in mantle wehrlites (-0.39 to +0.09 [1]) in the context of a homogeneous mantle (-0.25 ± 0.07 [2]). However, no systematic measurements of δ26Mg on marine sediments are currently available to provide direct support to this model. To characterize the Mg inputs to global subduction zones, we measured δ26Mg data for a total of 90 marine sediments collected from 12 drill sites outboard of the world's major subduction zones. These sediments span a 1.73‰ range in δ26Mg. The detritus-dominated sediments have δ26Mg (-0.59 to +0.53) comparable to those of weathered materials on continents (e.g. -0.52 to +0.92 [3]), while the calcareous oozes yield δ26Mg (as light as -1.20) more similar to the seawater value (-0.83 [4]). The negative correlation between δ26Mg and CaO/Al2O3 in these sediments indicates the primary control of mineralogy over the Mg isotopic distribution among different sediment types, as carbonates are enriched in light Mg isotopes (-5.10 to -0.40 [5]) whereas clay-rich weathering residues generally have heavier δ26Mg (e.g. up to +0.65 in saprolite [6]). In addition, chemical weathering and grain-size sorting drive sediments to a heavier δ26Mg, as indicated by the broad positive trends between δ26Mg with CIA (Chemical Index of Alteration [7]) and Al2O3/SiO2, respectively. Collectively, the arc systems sampled in this study represent ~30% of global arc length and the extrapolated global Mg flux of subducting marine sediments accounts for ~9% of the yearly Mg riverine input with a flux-weighted average δ26Mg at -0.26. Subduction of these heterogeneous sediments may not cause significant mantle heterogeneity on a global scale, but the highly variable Mg fluxes and δ26Mg of sediments delivered to different trenches are capable of producing local mantle variations. Volcanic rocks sourced from these mantle domains are thus

  16. Inside the Subduction Factory

    NASA Astrophysics Data System (ADS)

    Eiler, John

    Subduction zones helped nucleate and grow the continents, they fertilize and lubricate the earth's interior, they are the site of most subaerial volcanism and many major earthquakes, and they yield a large fraction of the earth's precious metals. They are obvious targets for study—almost anything you learn is likely to impact important problems—yet arriving at a general understanding is notoriously difficult: Each subduction zone is distinct, differing in some important aspect from other subduction zones; fundamental aspects of their mechanics and igneous processes differ from those in other, relatively well-understood parts of the earth; and there are few direct samples of some of their most important metamorphic and metasomatic processes. As a result, even first-order features of subduction zones have generated conflict and apparent paradox. A central question about convergent margins, for instance—how vigorous magmatism can occur where plates sink and the mantle cools—has a host of mutually inconsistent answers: Early suggestions that magmatism resulted from melting subducted crust have been emphatically disproved and recently just as emphatically revived; the idea that melting is fluxed by fluid released from subducted crust is widely held but cannot explain the temperatures and volatile contents of many arc magmas; generations of kinematic and dynamic models have told us the mantle sinks at convergent margins, yet strong evidence suggests that melting there is often driven by upwelling. In contrast, our understanding ofwhy volcanoes appear at ocean ridges and "hotspots"—although still presenting their own chestnuts—are fundamentally solved problems.

  17. Constraining Cretaceous subduction polarity in eastern Pacific from seismic tomography and geodynamic modeling

    NASA Astrophysics Data System (ADS)

    Liu, Lijun

    2014-11-01

    Interpretation of recent mantle seismic images below the America ignited a debate on the Cretaceous subduction polarity in the eastern Pacific Ocean. The traditional view is that the massive vertical slab wall under eastern North America resulted from an eastward Farallon subduction. An alternative interpretation attributes this prominent seismic structure to a westward subduction of the North American Plate against a stationary intraoceanic trench. Here I design quantitative subduction models to test these two scenarios, using their implied plate kinematics as velocity boundary conditions. Modeling results suggest that the westward subduction scenario could not produce enough slab volume as seismic images reveal, as is due to the overall slow subduction rate (~2.5 cm/yr). The results favor the continuous eastward Farallon subduction scenario, which, with an average convergence rate of >10 cm/yr prior to the Eocene, can properly generate both the volume and the geometry of the imaged lower mantle slab pile. The eastward subduction model is also consistent with most Cretaceous geological records along the west coast of North America.

  18. A review of the geodynamic evolution of flat slab subduction in Mexico, Peru, and Chile

    NASA Astrophysics Data System (ADS)

    Manea, V. C.; Manea, M.; Ferrari, L.; Orozco-Esquivel, T.; Valenzuela, R. W.; Husker, A.; Kostoglodov, V.

    2017-01-01

    Subducting plates around the globe display a large variability in terms of slab geometry, including regions where smooth and little variation in subduction parameters is observed. While the vast majority of subduction slabs plunge into the mantle at different, but positive dip angles, the end-member case of flat-slab subduction seems to strongly defy this rule and move horizontally several hundreds of kilometers before diving into the surrounding hotter mantle. By employing a comparative assessment for the Mexican, Peruvian and Chilean flat-slab subduction zones we find a series of parameters that apparently facilitate slab flattening. Among them, trench roll-back, as well as strong variations and discontinuities in the structure of oceanic and overriding plates seem to be the most important. However, we were not able to find the necessary and sufficient conditions that provide an explanation for the formation of flat slabs in all three subduction zones. In order to unravel the origin of flat-slab subduction, it is probably necessary a numerical approach that considers also the influence of surrounding plates, and their corresponding geometries, on 3D subduction dynamics.

  19. 'Snow White' Trench After Scraping

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This view from the Surface Stereo Imager on NASA's Phoenix Mars Lander shows the trench informally named 'Snow White.' This image was taken after a series of scrapings by the lander's Robotic Arm on the 58th Martian day, or sol, of the mission (July 23, 2008). The scrapings were done in preparation for collecting a sample for analysis from a hard subsurface layer where soil may contain frozen water.

    The trench is 4 to 5 centimeters (about 2 inches) deep, about 23 centimeters (9 inches) wide and about 60 centimeters (24 inches) long.

    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.

  20. Structure and deformation of the Tonga-Kermadec subduction system in the Louisville Ridge pre-collision zone

    NASA Astrophysics Data System (ADS)

    Funnell, M. J.; Peirce, C.; Stratford, W. R.; Paulatto, M.; Watts, A. B.

    2013-12-01

    New multichannel seismic data collected ~200 km south of the collision between the Tonga-Kermadec Trench and the Louisville Ridge show normal subduction zone structures indicating that the effects of the collision decay rapidly along-arc. Due to the obliqueness of plate convergence at the Tonga-Kermadec Trench, the collision zone is migrating rapidly southwards at 180 mm yr-1. Consequently, the along-arc transition from ridge-trench deformation to normal subduction zone deformation is rapid. To determine the 'normal' stratigraphy and structure of the subducting plate and forearc prior to Louisville Ridge collision, a 250 km-long multichannel seismic profile was shot perpendicular to the Kermadec Trench at ~28°S. Interpretation of coincident swath bathymetry and multichannel seismic data shows horst and graben structures on the down-going plate that offset the seafloor on large-scale, steeply-listric normal faults. These faults accommodate bending-induced extensional stresses generated as the trenchward plate dip increases. The graben have accumulated thin sedimentary deposits but are largely unfilled. Background sediment influx along the length of the 2700 km long subduction system is largely due to pelagic sedimentation and volcaniclastics from the arc, with regional sediment thicknesses in the trench of <400 m. However, a 50% increase in trench sediment thickness is observed, and is inferred to be due to increased sediment influx from an uplifting and eroding forearc. Trench and forearc structure are typical for a subduction system. However, the forearc mid-slope basin shows both arcward rotation of sedimentary sequences and extensional collapse on km-scale faults. A fresh fault scarp with ~400 m of throw leave exposed sedimentary sections indicating that extensional deformation of the forearc is both large-scale and recent. We propose that these faults accommodate the majority of forearc extension. Sediments on the upper trench slope document depositional

  1. Subducting-slab transition-zone interaction: Stagnation, penetration and mode switches

    NASA Astrophysics Data System (ADS)

    Agrusta, Roberto; Goes, Saskia; van Hunen, Jeroen

    2017-04-01

    Seismic tomography shows that subducting slabs can either sink straight into the lower mantle, or lie down in the mantle transition zone. Moreover, some slabs seem to have changed mode from stagnation to penetration or vice versa. We investigate the dynamic controls on these modes and particularly the transition between them using 2D self-consistent thermo-mechanical subduction models. Our models confirm that the ability of the trench to move is key for slab flattening in the transition zone. Over a wide range of plausible Clapeyron slopes and viscosity jumps at the base of the transition zone, hot young slabs (25 Myr in our models) are most likely to penetrate, while cold old slabs (150 Myr) drive more trench motion and tend to stagnate. Several mechanisms are able to induce penetrating slabs to stagnate: ageing of the subducting plate, decreasing upper plate forcing, and increasing Clapeyron slope (e.g. due to the arrival of a more hydrated slab). Getting stagnating slabs to penetrate is more difficult. It can be accomplished by an instantaneous change in the forcing of the upper plate from free to motionless, or a sudden decrease in the Clapeyron slope. A rapid change in plate age at the trench from old to young cannot easily induce penetration. On Earth, ageing of the subducting plate (with accompanying upper plate rifting) may be the most common mechanism for causing slab stagnation, while strong changes in upper plate forcing appear required for triggering slab penetration.

  2. Collapse risk of buildings in the Pacific Northwest region due to subduction earthquakes

    USGS Publications Warehouse

    Raghunandan, Meera; Liel, Abbie B; Luco, Nicolas

    2015-01-01

    Subduction earthquakes similar to the 2011 Japan and 2010 Chile events will occur in the future in the Cascadia subduction zone in the Pacific Northwest. In this paper, nonlinear dynamic analyses are carried out on 24 buildings designed according to outdated and modern building codes for the cities of Seattle, Washington, and Portland, Oregon. The results indicate that the median collapse capacity of the ductile (post-1970) buildings is approximately 40% less when subjected to ground motions from subduction, as compared to crustal earthquakes. Buildings are more susceptible to earthquake-induced collapse when shaken by subduction records (as compared to crustal records of the same intensity) because the subduction motions tend to be longer in duration due to their larger magnitude and the greater source-to-site distance. As a result, subduction earthquakes are shown to contribute to the majority of the collapse risk of the buildings analyzed.

  3. Sedimentation in the central segment of the Aleutian Trench: Sources, transport, and depositional style

    SciTech Connect

    Stevenson, A.J.; Scholl, D.W.; Vallier, T.L. ); Underwood, M.B. )

    1990-05-01

    The central segment of the Aleutian Trench (162{degree}W to 175{degree}E) is an intraoceanic subduction zone that contains an anomalously thick sedimentary fill (4 km maximum). The fill is an arcward-thickening and slightly tilted wedge of sediment characterized acoustically by laterally continuous, closely spaced, parallel reflectors. These relations are indicative of turbidite deposition. The trench floor and reflection horizons are planar, showing no evidence of an axial channel or any transverse fan bodies. Cores of surface sediment recover turbidite layers, implying that sediment transport and deposition occur via diffuse, sheetlike, fine-grained turbidite flows that occupy the full width of the trench. The mineralogy of Holocene trench sediments document a mixture of island-arc (dominant) and continental source terranes. GLORIA side-scan sonar images reveal a westward-flowing axial trench channel that conducts sediment to the eastern margin of the central segment, where channelized flow cases. Much of the sediment transported in this channel is derived from glaciated drainages surrounding the Gulf of Alaska which empty into the eastern trench segment via deep-sea channel systems (Surveyor and others) and submarine canyons (Hinchinbrook and others). Insular sediment transport is more difficult to define. GLORIA images show the efficiency with which the actively growing accretionary wedge impounds sediment that manages to cross a broad fore-arc terrace. It is likely that island-arc sediment reaches the trench either directly via air fall, via recycling of the accretionary prism, or via overtopping of the accretionary ridges by the upper parts of thick turbidite flows.

  4. Subduction zones: Not relevant to present-day problems of waste disposal

    USGS Publications Warehouse

    Silver, E.A.

    1972-01-01

    SUBDUCTION zones are considered to be sites of disposal for vast areas of the Earth's surface1, while new surface is generated simultaneously at rise crests2. Bostrom and Sherif3 suggest that the world's industrial and domestic waste be dumped into subduction zones at deep sea trenches to allow nature to complete the recycling process at geologically rapid rates of 5 to 10 cm/yr. They also point out that trenches are often sites of rapid rates of deposition and suggest that the dumped wastes would, speaking geologically, soon be buried. Francis4 suggests that canisters of toxic chemical and radioactive wastes could be dumped onto trench sediments and be expected to sink at rates of 20 m/yr, assuming that the mass of turbidites in the trench fill often spontaneously liquefies on shaking by earthquakes. The assumption is based on the supposed lack of evidence for deformed sediment in trenches. I will argue that the suggestion of Bostrom and Sherif3 is not useful for the next few dozen generations of human populations and will point out observational evidence to show that Francis's4 assumption is incorrectly founded. ?? 1972 Nature Publishing Group.

  5. Continental Subduction and Subduction Initiation Leading to Extensional Exhumation of Ultra-High Pressure Rocks During Ongoing Plate Convergence in Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Buck, W. R.; Petersen, K. D.

    2014-12-01

    Subduction of continental rocks is necessary to produce ultra-high pressure (UHP) rocks but the mechanism bringing them to the surface is disputed. A major question is whether this involves fairly small diapirs of crust that move up through the mantle or it involves an entire subducted plate that undergoes coherent 'reverse subduction' (sometimes called 'eduction'). Both mechanisms have been invoked to explain the only known region of on-going exhumation of UHP rocks, on the D'Entrecasteaux Islands of Papua New Guinea. Ductile flow fabrics in the island rocks have been used to argue for a diapiric model while constraints on the plate kinematics of the region require relatively large (>100 km) amounts of recent (>6 Myr) extension, supporting eduction as a primary mechanism. A self-consistent thermo-mechanical model of continental subduction shows that eduction can be accompanied by some ductile flow within the crust. Also we show, that subduction and stacking of continental crust can cause a subduction zone to lock up and lead to subduction initiation elsewhere. When this happens the region of earlier continental subduction can reverse direction causing exhumation of rocks from depth of ~100 km followed by localized extension and plate spreading. This can occur even if a region is in overall convergence. Applied to New Guinea our results are consistent with earlier suggestions that extension of the Woodlark Basin was caused by the initiation of the New Britain Trench, as indicated on the attached figure. We suggest that this subduction initiation event triggered eduction that led to exposure of the D'Entrcasteaux Islands and exhumation of the UHP rocks there. Our numerical results are broadly consistent with the recently refined seismic structure of the region around the islands. The model implies that the present-day basement of the ~70 km wide Goodenough Bay, south of the islands, was subducted then exhumed. This can be tested by drilling.

  6. New insights on the tectonics along the New Hebrides subduction zone based on GPS results

    NASA Astrophysics Data System (ADS)

    Calmant, StéPhane; Pelletier, Bernard; Lebellegard, Pierre; Bevis, Michael; Taylor, Frederick W.; Phillips, David A.

    2003-06-01

    At the New Hebrides (NH) subduction zone, ridges born by the subducting Australia plate enter the trench and collide with the overriding margin. Results from GPS surveys conducted on both sides of the trench and new bathymetry maps of the NH archipelago bring new light on the complex tectonics of this area. Convergence vectors present large variations that are not explained by Australia/Pacific (A/P) poles and that define four segments. Vectors remain mostly perpendicular to the trench and parallel to the earthquake slip vectors. Slow convergence (i.e., 30-40 mm/yr) is found at the central segment facing the D'Entrecasteaux Ridge. The southern segment moves faster than A/P motion predicts (89 to 124 mm/yr). Relatively to a western North Fiji basin (WNFB) reference, the northern and southern segments rotate in opposite directions, consistently with the extension observed in the troughs east of both segments. Both rotations combine in Central Vanuatu into an eastward translation that "bulldozes" the central segment into the WNFB at ˜55 mm/yr. That model suggests that the motion of the central segment, forced by the subduction/collision of the D'Entrecasteaux ridge, influences the motion of the adjoining segments. The New Caledonia archipelago is motionless with respect to the rest of the Australia plate despite the incipient interaction between the Loyalty ridge and the NH margin. Southeast of the interaction area, convergence is partitioned into a ˜50 mm/yr trench-normal component accommodated at the trench and a ˜90 mm/yr trench-parallel component, close to the A/P convergence, and presumably accommodated by a transform boundary at the rear of the NH arc.

  7. RETRACTED: Signatures of downgoing plate-buoyancy driven subduction in motions and seismic coupling at major subduction zones

    NASA Astrophysics Data System (ADS)

    Capitanio, F. A.; Goes, S.; Morra, G.; Giardini, D.

    2007-10-01

    This article has been retracted at the request of the Editor-in-Chief and Authors. Please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy). Reason: after publication, errors were discovered in the plate-motion database that it was based on. This dataset was an updated version of the dataset presented in Sdrolias and Muller (2006), provided to us by the first author. The errors in this version were in the away-from-trench/towards-trench assignment for subduction zones with back-arcs and also due to the fact that the next generation plate model had only partially been completed. These errors affect the conclusions about seismic coupling. They also change some of the points in most of the other plots, and although this does not invalidate the other conclusions, the discussion to reach them would be altered.

  8. Evidence for a large-scale remnant of subducted lithosphere beneath Fiji.

    PubMed

    Chen, W P; Brudzinski, M R

    2001-06-29

    We combine spatial variations of P- and S-wave speeds, 1000 fault plane solutions, and 6600 well-determined hypocenters to investigate the nature of subducted lithosphere and deep earthquakes beneath the Tonga back-arc. We show that perplexing patterns in seismicity and fault plane solutions can be accounted for by the juxtaposition of a steep-dipping Wadati-Benioff zone and a subhorizontal remnant of slab that is no longer attached to the actively subducting lithosphere. The detached slab may be from a previous episode of subduction along the fossil Vitiaz trench about 5 to 8 million years ago. The juxtaposition of slabs retains a large amount of subducted material in the transition zone of the mantle. Such a configuration, if common in the past, would allow the preservation of a primordial component in the lower mantle.

  9. Subducted slabs beneath the eastern Indonesia-Tonga region: insights from tomography

    NASA Astrophysics Data System (ADS)

    Hall, Robert; Spakman, Wim

    2002-07-01

    Tomographic images of mantle structure beneath the region north and northeast of Australia show a number of anomalously fast regions. These are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems. Several strong anomalies are related to current subduction. The inferred slab lengths and positions are consistent with Neogene subduction beneath the New Britain and Halmahera arcs, and at the Tonga and the New Hebrides trenches where there has been rapid rollback of subduction hinges since about 10 Ma. There are several deeper flat-lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by Australia since 25 Ma. Beneath the Bird's Head and Arafura Sea is an anomaly interpreted to be due to north-dipping subduction beneath the Philippines-Halmahera arc between 45 and 25 Ma. A very large anomaly extending from the Papuan peninsula to the New Hebrides, and from the Solomon Islands to the east Australian margin, is interpreted to be the remnant of south-dipping subduction beneath the Melanesian arc between 45 and 25 Ma. This interpretation implies that a flat-lying slab can survive for many tens of millions of years at the bottom of the upper mantle. In the lower mantle there is a huge anomaly beneath the Gulf of Carpentaria and east Papua New Guinea. This is located above the position where the tectonic model interprets a change in polarity of subduction from north-dipping to south-dipping between 45 and 25 Ma. We suggest this deep anomaly may be a slab subducted beneath eastern Australian during the Cretaceous, or subducted north of Australia during the Cenozoic before 45 Ma. The tomography also supports the tectonic interpretation which suggests little Neogene subduction beneath western New Guinea since no slab is imaged south of the New Guinea trench. However, one subduction zone in the tectonic model and many others, that associated with the Trobriand

  10. The 2011 Tohoku-Oki earthquake: displacement reaching the trench axis.

    PubMed

    Fujiwara, Toshiya; Kodaira, Shuichi; No, Tetsuo; Kaiho, Yuka; Takahashi, Narumi; Kaneda, Yoshiyuki

    2011-12-02

    We detected and measured coseismic displacement caused by the 11 March 2011 Tohoku-Oki earthquake [moment magnitude (M(W)) 9.0] by using multibeam bathymetric surveys. The difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the Japan Trench, suggesting that the fault rupture reached the trench axis. The sea floor on the outermost landward area moved about 50 meters horizontally east-southeast and ~10 meters upward. The large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement.

  11. Seismic evidence for a slab tear at the Puerto Rico Trench

    USGS Publications Warehouse

    Meighan, Hallie E.; Pulliam, Jay; Brink, Uri ten; López-Venegas, Alberto M.

    2013-01-01

    The fore-arc region of the northeast Caribbean plate north of Puerto Rico and the Virgin Islands has been the site of numerous seismic swarms since at least 1976. A 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms, along with additional events. Joint analyses of the ocean bottom seismographs and land-based seismic data reveal that the swarms are located at depths of 50–150 km. Focal mechanism solutions, found by jointly fitting P wave first-motion polarities and S/P amplitude ratios, indicate that the broadly distributed events outside the swarm generally have strike- and dip-slip mechanisms at depths of 50–100 km, while events at depths of 100–150 km have oblique mechanisms. A stress inversion reveals two distinct stress regimes: The slab segment east of 65°W longitude is dominated by trench-normal tensile stresses at shallower depths (50–100 km) and by trench-parallel tensile stresses at deeper depths (100–150 km), whereas the slab segment west of 65°W longitude has tensile stresses that are consistently trench normal throughout the depth range at which events were observed (50–100 km). The simple stress pattern in the western segment implies relatively straightforward subduction of an unimpeded slab, while the stress pattern observed in the eastern segment, shallow trench-normal tension and deeper trench-normal compression, is consistent with flexure of the slab due to rollback. These results support the hypothesis that the subducting North American plate is tearing at or near these swarms. The 35 year record of seismic swarms at this location and the recent increase in seismicity suggest that the tear is still propagating.

  12. Farallon plate dynamics prior to the Laramide orogeny: Numerical models of flat subduction

    NASA Astrophysics Data System (ADS)

    Liu, Sibiao; Currie, Claire A.

    2016-01-01

    The Laramide orogeny (~ 80-50 Ma) was an anomalous period of mountain-building in the western United States that occurred more than 1000 km inboard of the Farallon Plate subduction margin. It is widely believed that this orogeny is coincident with a period of flat (subhorizontal) subduction. However, the factors that caused the Farallon Plate to evolve from a normal (steep) geometry to flat subduction are not well understood. Three proposed factors are: (1) a westward (trenchward) increase in North America motion, (2) an increased slab suction force owing to the presence of thick Colorado Plateau lithosphere, and (3) subduction of a low-density oceanic plateau. This study uses 2D upper mantle scale numerical models to investigate these factors. The models show that trenchward continental motion is the primary control on subduction geometry, with decreasing slab dip as velocity increases. However, this can only create low-angle subduction, as the Farallon Plate was old (> 100 Myr) and denser than the mantle. A transition to flat subduction requires: (1) subduction of a buoyant oceanic plateau that includes an 18-km-thick crust that does not undergo metamorphic densification and an underlying depleted harzburgite layer, and (2) a slab break-off at the landward side of the plateau. The break-off removes the dense frontal slab, and flat subduction develops as the buoyant plateau deflects the slab upward. The slab suction force has only a minor effect on slab flattening, but the thickness of the Colorado Plateau lithosphere controls the depth of the flat slab. With a continental velocity of 4 cm/yr and a 400-km-wide oceanic plateau, flat subduction develops within 15 Ma after plateau subduction. The flat slab underthrusts the continent at ~ 200 km depth, eventually extending > 1500 km inboard of the trench.

  13. Organochemical characteristics of carbonaceous materials as indicators of heat recorded on an ancient plate-subduction fault

    NASA Astrophysics Data System (ADS)

    Kaneki, S.; Hirono, T.; Mukoyoshi, H.; Sampei, Y.; Ikehara, M.

    2016-07-01

    Coseismic shear stress and slip distance affect subduction-related earthquake processes. They need to be understood to evaluate the earthquake's mechanism and the tsunami generation potential near trenches. The amount of frictional heat generated depends on the shear stress and slip distance, which are therefore able to be derived from the temperature recorded in the fault. Here we developed a new temperature proxy for carbonaceous materials by performing spectroscopic, thermogravimetric, and organic elemental analyses in conjunction with heating experiments. We found marked anomalies in the infrared and Raman spectra and atomic compositions of carbonaceous materials retrieved from the slip zone of an ancient megasplay fault in the Cretaceous Shimanto accretionary complex, Japan: the infrared spectra show extinction of aliphatic C-H bonding and very weak aromatic C=C bonding, and the Raman spectra show a slightly elevated ratio of disordered band intensity to graphitic band intensity and relatively low H/C and O/C ratios. These correlate well with the spectral and elemental features of host-rock carbonaceous materials after heating to 600°C. Thus, we conclude that the slip zone experienced a temperature of 600°C during a past earthquake event, indicating coseismic slip of 2-9 m, which could have generated a large tsunami if the ruptures propagated to the seafloor.

  14. Formation of forearc basins by collision between seamounts and accretionary wedges: an example from the New Hebrides subduction zone

    USGS Publications Warehouse

    Collot, J.-Y.; Fisher, M.A.

    1989-01-01

    Seabeam data reveal two deep subcircular reentrants in the lower arc slope of the New Hebrides island arc that may illustrate two stages in the development of a novel type of forearc basin. The Malekula reentrant lies just south of the partly subducted Bougainville seamount. This proximity, as well as the similarity in morphology between the reentrant and an indentation in the lower arc slope off Japan, suggests that the Malekula reentrant formed by the collision of a seamount with the arc. An arcuate fold-thrust belt has formed across the mouth of the reentrant, forming the toe of a new accretionary wedge. The Efate reentrant may show the next stage in basin development. This reentrant lies landward of a lower-slope ridge that may have begun to form as an arcuate fold-thrust belt across the mouth of a reentrant. This belt may have grown by continued accretion at the toe of the wedge, by underplating beneath the reentrant, and by trapping of sediment shed from the island arc. These processes could result in a roughly circular forearc basin. Basins that may have formed by seamount collision lie within the accretionary wedge adjacent to the Aleutian trenches. -Authors

  15. Arc-arc Collision Structure in the Southernmost Part of the Kuril Trench Region -Results from Integrated Analyses of the 1998-2000 Hokkaido Transect Seismic Data-

    NASA Astrophysics Data System (ADS)

    Iwasaki, Takaya; Tsumura, Noriko; Ito, Tanio; Sato, Hiroshi; Kurashimo, Eiji; Hirata, Naoshi; Arita, Kazunori; Noda, Katsuya; Fujiwara, Akira; Abe, Susumu; Kikkuchi, Shunsuke; Suzuki, Kazuko

    2015-04-01

    The Hokkaido Island, located in the southernmost part of the Kuril trench region, has been under a unique tectonic environment of arc-arc collision. Due to the oblique subduction of the Pacific (PAC) plate, the Kuril forearc sliver started to collide against Northeast (NE) Japan arc from the east at the time of middle Miocene to form complicated structures in the Hidaka collision zone (HCZ), as characterized by the westward obduction of the crustal rocks of the Kuril arc (the Hidaka metamorphic belt (HMB)) along the Hidaka main thrust (HMT) and a thick foreland fold-and-thrust belt. In and around the HCZ, a series of seismic reflection/refraction experiments were undertaken from 1994 to 2000, which provided important structural features including crustal delamination in the southern HCZ and a thick fold-and-thrust belt with velocity reversals (low velocity layers) in the northern HCZ. Reprocessing/reinterpretation for these data sets, which started in 2012, is aimed to construct a more detailed collision model through new processing and interpretation techniques. A multi-disciplinary project of the 1998-2000 Hokkaido Transect, crossing the northern part of the HCZ in EW direction, collected high-quality seismic data on a 227-km seismic refraction/wide-angle reflection profile and three seismic reflection lines. Our reanalyses revealed interesting collision structure ongoing in the northern part of the HCZ. The westward obduction of the Kuril arc crust was clearly imaged along the HMT. This obduction occurs at a depth of 27-30 km, much deeper than in the southern HCZ (23-25 km). The CRS/MDRS processing to the reflection data firstly succeeded in imaging clear reflection events at a 30-45 km depth below the obducted Kuril arc crust. These events show an eastward dip, probably corresponding to the lower crust/Moho within the NE Japan arc descending down to the east under the collision zone. Gently eastward dipping structures above these events (in a depth range of 5

  16. Subduction modelling with ASPECT

    NASA Astrophysics Data System (ADS)

    Glerum, Anne; Thieulot, Cédric; Spakman, Wim; Quinquis, Matthieu; Buiter, Susanne

    2013-04-01

    ASPECT (Advanced Solver for Problems in Earth's ConvecTion) is a promising new code designed for modelling thermal convection in the mantle (Kronbichler et al. 2012). The code uses state-of-the-art numerical methods, such as high performance solvers and adaptive mesh refinement. It builds on tried-and-well-tested libraries and works with plug-ins allowing easy extension to fine-tune it to the user's specific needs. We make use of the promising features of ASPECT, especially Adaptive Mesh Refinement (AMR), for modelling lithosphere subduction in 2D and 3D geometries. The AMR allows for mesh refinement where needed and mesh coarsening in regions less important to the parameters under investigation. In the context of subduction, this amounts to having very small grid cells at material interfaces and larger cells in more uniform mantle regions. As lithosphere subduction modelling is not standard to ASPECT, we explore the necessary adaptive grid refinement and test ASPECT with widely accepted benchmarks. We showcase examples of mechanical and thermo-mechanical oceanic subduction in which we vary the number of materials making up the overriding and subducting plates as well as the rheology (from linear viscous to more complicated rheologies). Both 2D and 3D geometries are used, as ASPECT easily extends to three dimensions (Kronbichler et al. 2012). Based on these models, we discuss the advection of compositional fields coupled to material properties and the ability of AMR to trace the slab's path through the mantle. Kronbichler, M., T. Heister and W. Bangerth (2012), High Accuracy Mantle Convection Simulation through Modern Numerical Methods, Geophysical Journal International, 191, 12-29.

  17. Seismicity and Geometry Properties of the Hellenic Subduction Zone

    NASA Astrophysics Data System (ADS)

    Papadimitriou, E. E.; Karakostas, V. G.; Vallianatos, F.; Makropoulos, C.; Drakatos, G.

    2014-12-01

    Recent seismicity and fault plane solutions of earthquakes that occurred along the Hellenic Arc-Trench system are engaged for approximating the geometry of the subducted oceanic plate. Seismicity and focal mechanisms confirm the gentle subduction (~15o-20o) of the oceanic crust reaching a depth of 20 km at a distance of 100 km from the trench. The slab is then bending at larger angles, and in particular at ~45o up to the depth of 80 km and at ~65o up to the depth of 180 km, when seismicity ceased. This geometry of the slab is shown in a bunch of cross sections normal to the convergence strike, up to ~25o (east Crete Island). To the east the sparse inslab seismicity reveals an almost vertical dipping of the lower part (from 80 km downdip) of the descending slab. The slab interface that accommodates hazardous earthquakes is clearly nonplanar with the main seismic moment release taking place on its up-dip side. The fore-arc, upper plate seismicity, is remarkably low in comparison with both subduction and back arc seismicity, and confined inside a seismogenic layer having a width not exceeding the 20km. Offshore seismicity is spatially variable forming distinctive streaks thus revealing that parts of the oceanic crust are probably slipped aseismically. This observation along with the fact that coupling in the Hellenic arc is only about a tenth of the plate motion, imply the presence of areas of lower and higher coupling across the subduction interface. Areas of high coupling imply areas of the slab interface subjected to high normal forces and correlate with earthquake asperities. Although asperity distributions vary substantially through time, identification of such characteristics in the seismogenesis can have a significant impact in the seismic hazard assessment. This research has been co-funded by the European Union (European Social Fund) and Greek national resources under the framework of the "THALES Program: SEISMO FEAR HELLARC" project.

  18. Seismic Anisotropy and SKS Splitting in the Sangihe Subduction Zone Predicted from 3-D Mantle Flow Models

    NASA Astrophysics Data System (ADS)

    Di Leo, J. F.; Li, Z.; Walker, A. M.; Wookey, J.; Kendall, J.; Ribe, N. M.; Tommasi, A.

    2012-12-01

    Observations of shear wave splitting are often interpreted as being due to strain-induced crystal alignment of olivine in the convecting upper mantle, and the polarization of the fast shear wave is frequently taken to directly indicate the direction of mantle flow. Caution must be exercised when making such inferences, as the relationship between olivine lattice-preferred orientation (LPO) and fast direction is dependent on many factors, including the entire deformation history. This is especially the case in regions where complex time-dependent mantle flow is expected, e.g., subduction zones. Observations of shear wave splitting at subduction zones are varied, ranging from trench-perpendicular to -parallel fast directions, or a combination of both. Rigorously interpreting this variety of observations requires modeling which properly accounts for LPO development in the near-slab mantle environment. To this end, we simulate olivine LPO evolution caused by defomation of polycrystalline aggregates as they deform and move along pathlines extracted from a 3-D mantle flow model at a subduction zone (Li & Ribe, 2012). The model is based on 3-D boundary-element numerical simulations of a dense fluid sheet (representing the slab) with a geometry approximating that of the Sangihe subduction zone in Indonesia, where trench-parallel fast directions have recently been measured and ascribed to trench-parallel sub-slab mantle flow (Di Leo et al., 2012). This subduction zone is unique in that it is part of the only double-sided subduction system on Earth. At the Sangihe trench, the Molucca Sea plate is subducting westwards beneath the Eurasian plate. However, this microplate is also subducting eastwards at the nearby Halmahera trench. To test whether the measured trench-parallel fast directions are due to sub-slab mantle flow, and whether this is only possible due to the double-sided geometry, we use two different flow models: one with single- and one with double-sided subduction

  19. Laboratory models of the thermal evolution of the mantle during rollback subduction.

    PubMed

    Kincaid, C; Griffiths, R W

    2003-09-04

    The subduction of oceanic lithosphere plays a key role in plate tectonics, the thermal evolution of the mantle and recycling processes between Earth's interior and surface. Information on mantle flow, thermal conditions and chemical transport in subduction zones come from the geochemistry of arc volcanoes, seismic images and geodynamic models. The majority of this work considers subduction as a two-dimensional process, assuming limited variability in the direction parallel to the trench. In contrast, observationally based models increasingly appeal to three-dimensional flow associated with trench migration and the sinking of oceanic plates with a translational component of motion (rollback). Here we report results from laboratory experiments that reveal fundamental differences in three-dimensional mantle circulation and temperature structure in response to subduction with and without a rollback component. Without rollback motion, flow in the mantle wedge is sluggish, there is no mass flux around the plate and plate edges heat up faster than plate centres. In contrast, during rollback subduction flow is driven around and beneath the sinking plate, velocities increase within the mantle wedge and are focused towards the centre of the plate, and the surface of the plate heats more along the centreline.

  20. Trenching in the New Madrid seismic zone

    SciTech Connect

    Not Available

    1990-01-01

    Trenching studies of the San Andreas fault have been of great value to geologists in California for determining not only the prehistoric occurrences of earthquakes on the fault but also the age of these movements. In the New Madrid seismic zone, US Geological Survey scientists have been trenching across suspected faults to try to assess earthquake frequency in the Central US. The following photographs document these trenching studies.

  1. Coseismic seafloor deformation in the trench region during the Mw8.8 Maule megathrust earthquake.

    PubMed

    Maksymowicz, A; Chadwell, C D; Ruiz, J; Tréhu, A M; Contreras-Reyes, E; Weinrebe, W; Díaz-Naveas, J; Gibson, J C; Lonsdale, P; Tryon, M D

    2017-04-05

    The Mw 8.8 megathrust earthquake that occurred on 27 February 2010 offshore the Maule region of central Chile triggered a destructive tsunami. Whether the earthquake rupture extended to the shallow part of the plate boundary near the trench remains controversial. The up-dip limit of rupture during large subduction zone earthquakes has important implications for tsunami generation and for the rheological behavior of the sedimentary prism in accretionary margins. However, in general, the slip models derived from tsunami wave modeling and seismological data are poorly constrained by direct seafloor geodetic observations. We difference swath bathymetric data acquired across the trench in 2008, 2011 and 2012 and find ~3-5 m of uplift of the seafloor landward of the deformation front, at the eastern edge of the trench. Modeling suggests this is compatible with slip extending seaward, at least, to within ~6 km of the deformation front. After the Mw 9.0 Tohoku-oki earthquake, this result for the Maule earthquake represents only the second time that repeated bathymetric data has been used to detect the deformation following megathrust earthquakes, providing methodological guidelines for this relatively inexpensive way of obtaining seafloor geodetic data across subduction zone.

  2. Coseismic seafloor deformation in the trench region during the Mw8.8 Maule megathrust earthquake

    PubMed Central

    Maksymowicz, A.; Chadwell, C. D.; Ruiz, J.; Tréhu, A. M.; Contreras-Reyes, E.; Weinrebe, W.; Díaz-Naveas, J.; Gibson, J. C.; Lonsdale, P.; Tryon, M. D.

    2017-01-01

    The Mw 8.8 megathrust earthquake that occurred on 27 February 2010 offshore the Maule region of central Chile triggered a destructive tsunami. Whether the earthquake rupture extended to the shallow part of the plate boundary near the trench remains controversial. The up-dip limit of rupture during large subduction zone earthquakes has important implications for tsunami generation and for the rheological behavior of the sedimentary prism in accretionary margins. However, in general, the slip models derived from tsunami wave modeling and seismological data are poorly constrained by direct seafloor geodetic observations. We difference swath bathymetric data acquired across the trench in 2008, 2011 and 2012 and find ~3–5 m of uplift of the seafloor landward of the deformation front, at the eastern edge of the trench. Modeling suggests this is compatible with slip extending seaward, at least, to within ~6 km of the deformation front. After the Mw 9.0 Tohoku-oki earthquake, this result for the Maule earthquake represents only the second time that repeated bathymetric data has been used to detect the deformation following megathrust earthquakes, providing methodological guidelines for this relatively inexpensive way of obtaining seafloor geodetic data across subduction zone. PMID:28378757

  3. Towards a new thermomechanical model of subduction channel

    NASA Astrophysics Data System (ADS)

    Quinteros, J.; Sobolev, S. V.

    2009-04-01

    Subduction is known to be a major process in most collision zones, and the subduction channel is one of the key elements in the subduction process. In the last years the key-role of the subduction channel was thoroughly studied by many authors. From a mechanical point of view, its properties are highly determined by the friction coefficient, which depends on many factors, and the rheology that is set up. Despite of being a few kilometers wide, and small compared to the big subduction picture, its effects can propagate far away from the trench. For example, that was demonstrated by Sobolev and Babeyko (Geology, 2005) by means of a numerical model focused at the evolution of the Central Andean Subduction Zone. The model was based on a finite-element/finite-difference explicit code called LAPEX-2D (Babeyko et al., EPSL, 2002). Here, we present a new and enhanced 2-D thermomechanical model developed to study this type of tectonic setting. The main ideas of the technical implementation are based on the work published by Popov and Sobolev (PEPI, 2008). The domain is modeled by means of the Finite Elements Method with an implicit approach. The rheology is considered to be elasto-visco-plastic and the viscosity is temperature- and stress-dependent. Diffusion, Dislocation and Peierls types of creep and Mohr-Coulomb plasticity are included. Topography evolution is naturally tracked by a Lagrangian mesh. A particle technique similar to the particle-in-cell method was used to minimize diffusion during remeshing. One of the improvements added in this work, compared to the previous models, is a non-uniform mesh, which allows two main benefits. First, the study of specified regions of interest with more detail by means of the concentration of elements (like subduction channel), and second, the capability to define more realistic and smooth interfaces between different materials without distorsions related to mesh orientation. Also, the remeshing process includes basic automatic

  4. A model for the termination of the Ryukyu subduction zone against Taiwan: A junction of collision, subduction/separation, and subduction boundaries

    USGS Publications Warehouse

    Wu, F.T.; Liang, W.-T.; Lee, J.-C.; Benz, H.; Villasenor, A.

    2009-01-01

    The NW moving Philippine Sea plate (PSP) collides with the Eurasian plate (EUP) in the vicinity of Taiwan, and at the same time, it subducts toward the north along SW Ryukyu. The Ryukyu subduction zone terminates against eastern Taiwan. While the Ryukyu Trench is a linear bathym??trie low about 100 km east of Taiwan, closer to Taiwan, it cannot be clearly identified bathymetrically owing to the deformation related to the collision, making the location of the intersection of the Ryukyu with Taiwan difficult to decipher. We propose a model for this complex of boundaries on the basis of seismicity and 3-D velocity structures. In this model the intersection is placed at the latitude of about 23.7??N, placing the northern part of the Coastal Range on EUP. As PSP gets deeper along the subduction zone it collides with EUP on the Taiwan side only where they are in direct contact. Thus, the Eurasian plate on the Taiwan side is being pushed and compressed by the NW moving Philippine Sea plate, at increasing depth toward the north. Offshore of northeastern Taiwan the wedge-shaped EUP on top of the Ryukyu subducting plate is connected to the EUP on the Ryukyu side and coupled to the NW moving PSP by friction at the plate interface. The two sides of the EUP above the western end of the subduction zone are not subjected to the same forces, and a difference in motions can be expected. The deformation of Taiwan as revealed by continuous GPS measurements, geodetic movement along the east coast of Taiwan, and the formation of the Hoping Basin can be understood in terms of the proposed model. Copyright 2009 by the American Geophysical Union.

  5. Naval Trench 94 soils report

    SciTech Connect

    Carlos, W.C.

    1992-10-01

    This document is submitted in accordance with Westinghouse Hanford Company Order No. MLW-SW-037106, Task Order E-91-23. This report responds to direction given to Ebasco by Westinghouse Hanford Company on September 26, 1991. The sail tests results provided herein are applicable to the 100 year design life and 26 year design life passive cathodic protection designs for the SRC`s in Trench 94. These test results are also applicable to the 100 year design life and 26 year design life active cathodic protection systems presently being designed.

  6. Naval Trench 94 soils report

    SciTech Connect

    Carlos, W.C. )

    1992-10-01

    This document is submitted in accordance with Westinghouse Hanford Company Order No. MLW-SW-037106, Task Order E-91-23. This report responds to direction given to Ebasco by Westinghouse Hanford Company on September 26, 1991. The sail tests results provided herein are applicable to the 100 year design life and 26 year design life passive cathodic protection designs for the SRC's in Trench 94. These test results are also applicable to the 100 year design life and 26 year design life active cathodic protection systems presently being designed.

  7. Digging in 'Snow White' Trench

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image was acquired by NASA's Phoenix Mars Lander's Surface Stereo Imager on the 44th Martian day of the mission, or Sol 43 (July 7, 2008), after the May 25, 2008, landing, showing the current sample scraping area in the trench informally called 'Snow White.'

    The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is led by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.

  8. Recent Results of Hadal Investigations in the Southern Mariana Trench

    NASA Astrophysics Data System (ADS)

    Fryer, P. B.; Hellebrand, E.; Sharma, S. K.; Acosta-Maeda, T.; Jicha, B. R.; Cameron, J.

    2014-12-01

    The deepest parts of the southern Mariana Trench have variously been interpreted to 1) indicate strike-slip motion along the trench, 2) contain a series of 3 sediment ponds at greater than 10,900 m depth separated from one another by fault-controlled ridges on the subducting plate, and 3) have an even deeper feature in the western-most pond (Vitiaz Deep). Recent lander deployments in all three ponds and the Deepsea Challenger submersible dive by J. Cameron in 2012 showed that the deepest ponds within the Challenger Deep area have nearly unbroken, flat surfaces. One point explored showed veined serpentinite at a depth of 10,800+ m. The potential for active serpentinite-hosted seeps and vent communities was demonstrated for the Shinkai Vent Field at 5,800m depth. Rocks collected using the Wood Hole Oceanographic Institution's hybrid remotely operated vehicle, Nereus, in 2009 from deep (10,879 m) on the incoming plate south of the Challenger Deep, were recovered from the base of a fault scarp where large, columnar-jointed blocks are draped with sediment. Optical microscopy, electron-microprobe and Raman analysis show that they are partially altered massive diabase with altered interstitial glass and containing microbial tubules in vug-filling secondary phases. The chain of seamounts striking NNW, colinear with the Lyra Trough, has been interpreted as a boundary between the Pacific Plate and the seafloor north of the Caroline Ridge. Sediments, drilled from above postulated basement north of the Caroline Ridge are no older that Oligocene. Ar/Ar age dates completed for one rock collected by Nereus in 2009 give a weighted mean plateau age, based on two experiments, of 24.6 +/- 3.2 Ma. Thus, the igneous basement of the subducting plate south of the Challenger Deep is, far younger than the Jurassic Pacific Plate subducting further east. This represents a previously unidentified tectonic plate. With new vehicles and technologies the future for hadal exploration is ripe.

  9. Global analysis of the effect of fluid flow on subduction zone temperatures

    NASA Astrophysics Data System (ADS)

    Rotman, Holly M. M.; Spinelli, Glenn A.

    2013-08-01

    Knowledge of the controls on temperature distributions at subduction zones is critical for understanding a wide range of seismic, metamorphic, and magmatic processes. Here, we present the results of ˜220 thermal model simulations covering the majority of known subduction zone convergence rates, incoming plate ages, and slab dips. We quantify the thermal effects of fluid circulation in the subducting crust by comparing results with and without advective heat transfer in the oceanic crustal aquifer. We find that hydrothermal cooling of a subduction zone is maximized when the subducting slab is young, slowly converging, steeply dipping, and the crustal aquifer is ventilated near the trench. Incoming plate age is one of the primary controls on the effectiveness of advective heat transfer in the aquifer, and the greatest temperature effects occur with an incoming plate <50 Ma. The thermal effects of fluid circulation decrease dramatically with increasing age of the incoming plate. Temperatures in the Cascadia, Nankai, southern Chile, Colombia/Ecuador, Mexico, and Solomon Islands subduction zones are likely strongly affected by fluid circulation; for these systems, only thermal models of Cascadia and Nankai have included fluid flow in subducting crust.

  10. Introduction: Subduction's sharpest arrow

    NASA Astrophysics Data System (ADS)

    Eichelberger, John C.

    In the center of the 6000-km reach of Kurile-Kamchatka-Aleutian-Alaska subduction is arguably Earth's most remarkable subduction cusp. The Kamchatka-Aleutian junction is a sharp arrowhead mounted on the shaft of the Emperor Seamount Chain. This collection of papers provides context, definition, and suggestions for the origin of the junction, but a comprehensive understanding remains elusive, in part because of the newness of international collaborations. Necessary cross-border syntheses have been impeded by the adversarial international relations that characterized the 20th century. For much of this period, Kamchatka and the Kurile Islands were part of the Soviet Union, a mostly closed country. The entire region was swept by World War II, abundant remnants of which are wrecked ships and planes, unexploded ordnance, and Rommel stakes.

  11. Tomography and Dynamics of Western-Pacific Subduction Zones

    NASA Astrophysics Data System (ADS)

    Zhao, D.

    2012-01-01

    We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V/low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under

  12. Cascadia Subduction Zone

    USGS Publications Warehouse

    Frankel, Arthur D.; Petersen, Mark D.

    2008-01-01

    The geometry and recurrence times of large earthquakes associated with the Cascadia Subduction Zone (CSZ) were discussed and debated at a March 28-29, 2006 Pacific Northwest workshop for the USGS National Seismic Hazard Maps. The CSZ is modeled from Cape Mendocino in California to Vancouver Island in British Columbia. We include the same geometry and weighting scheme as was used in the 2002 model (Frankel and others, 2002) based on thermal constraints (Fig. 1; Fluck and others, 1997 and a reexamination by Wang et al., 2003, Fig. 11, eastern edge of intermediate shading). This scheme includes four possibilities for the lower (eastern) limit of seismic rupture: the base of elastic zone (weight 0.1), the base of transition zone (weight 0.2), the midpoint of the transition zone (weight 0.2), and a model with a long north-south segment at 123.8? W in the southern and central portions of the CSZ, with a dogleg to the northwest in the northern portion of the zone (weight 0.5). The latter model was derived from the approximate average longitude of the contour of the 30 km depth of the CSZ as modeled by Fluck et al. (1997). A global study of the maximum depth of thrust earthquakes on subduction zones by Tichelaar and Ruff (1993) indicated maximum depths of about 40 km for most of the subduction zones studied, although the Mexican subduction zone had a maximum depth of about 25 km (R. LaForge, pers. comm., 2006). The recent inversion of GPS data by McCaffrey et al. (2007) shows a significant amount of coupling (a coupling factor of 0.2-0.3) as far east as 123.8? West in some portions of the CSZ. Both of these lines of evidence lend support to the model with a north-south segment at 123.8? W.

  13. Trench Outer Rise Flexure Models with Laterally Variable Plate Rigidity Derived from Oceanic Lithosphere Strength Profiles

    NASA Astrophysics Data System (ADS)

    Garcia, E. S. M.; Sandwell, D. T.; Bassett, D.

    2015-12-01

    We generate model bathymetry and free-air gravity grids for the seafloor seaward of subduction zones that capture the broad trends of deformation due to lithospheric flexure. By using a thin elastic plate formulation with rigidity variations along both horizontal dimensions and which accounts for the effects of plastic yielding, our models are able to reproduce the observed rapid change in curvature at the outer trench wall. Forward models for flexural deflection and plate rigidity are fitted to satellite altimetry-derived marine gravity anomalies jointly with shipboard sonar soundings and swath bathymetry data sets. The estimated parameters are the applied vertical shear and bending moment at the trench axis, and the data misfits are minimized with respect to the L1-norm subject to Tikhonov regularization for smooth variation of the load parameters along the strike of the trench. We perform pre-processing of the input data to enhance the recovery of the flexural signal. Short-wavelength features such as seamounts are isolated using a directional median filter and then excluded from the parameter estimation process. The advantage of adopting anisotropic filtering over similar methods that separate local scale topography from regional swells is that it provides consistent performance in feature detection with minimal user supervision. Our preliminary results from several examples show that the plate rigidity progressively decreases with increasing proximity to the trench axis. These zones of plate weakening correspond to the occurrence of trench-parallel seafloor fractures at the outer trench wall as seen in high-resolution bathymetry data. We seek to determine whether a correlation exists between the distribution or morphology of these fractures and the amount or trend in the reduction of plate rigidity for outer rise regions across the Pacific Rim.

  14. Slab Roll-Back and Trench Retreat As Controlling Factor for Island-Arc Related Basin Evolution: A Case Study from Southern Central America

    NASA Astrophysics Data System (ADS)

    Brandes, C.; Winsemann, J.

    2014-12-01

    Slab roll-back and trench retreat are important factors for basin subsidence, magma generation and volcanism in arc-trench systems. From the sedimentary and tectonic record of the Central American island-arc it is evident that repeated slab roll-back and trench retreats occurred since the Late Cretaceous. These trench retreats were most probably related to the subduction of oceanic plateaus and seamounts. Evidence for trench retreats is given by pulses of uplift in the outer-arc area, followed by subsidence in both the fore-arc and back-arc basins. The first slab roll-back probably occurred during the Early Paleocene indicated by the collapse of carbonate platforms, and the re-deposition of large carbonate blocks into deep-water turbidites. At this time the island-arc was transformed from an incipient non-extensional stage into an extensional stage. A new pulse of uplift or decreased subsidence, respectively during the Late Eocene is attributed to subduction of rough crust, a subsequent slab detachment and the establishment of a new subduction zone further westward. Strong uplift especially affected the outer arc of the North Costa Rican arc segment. In the Sandino Fore-arc basin very coarse-grained deep-water channel-levee complexes were deposited. These deposits contain large well-rounded andesitic boulders and are rich in reworked shallow-water carbonates pointing to uplift of the inner fore-arc. Evidence for the subsequent trench retreat is given by an increased subsidence during the early Oligocene in the Sandino Fore-arc Basin and the collapse of the Barra Honda platform in North Costa Rica. Another trench retreat might have occurred in Miocene times. A phase of higher subsidence from 18 to 13 Ma is documented in the geohistory curve of the North Limon Back-arc Basin. After a short pulse of uplift the subsidence increased to approx. 300 m/myr.

  15. Slab-Dip Variability and Trench-Parallel Flow beneath Non-Uniform Overriding Plates: Insights form 3D Numerical Models

    NASA Astrophysics Data System (ADS)

    Rodríguez-González, J.; Billen, M. I.; Negredo, A. M.

    2012-12-01

    Forces driving plate tectonics are reasonably well known but some factors controlling the dynamics and the geometry of subduction processes are still poorly understood. The effect of the thermal state of the subducting and overriding plates on the slab dip have been systematically studied in previous works by means of 2D and 3D numerical modeling. These models showed that kinematically-driven slabs subducting under a cold overriding plate are affected by an increased hydrodynamic suction, due to the lower temperature of the mantle wedge, which leads to a lower subduction angle, and eventually to the formation of flat slab segments. In these models the subduction is achieved by imposing a constant velocity at the top of the overriding plate, which may lead to unrealistic results. Here we present the results of 3D non-Newtonian thermo-mechanical numerical models, considering a dynamically-driven self-sustained subduction, to test the influence of a non-uniform overriding plate. Variations of the thermal state of the overriding plate along the trench cause variation in the hydrodynamic suction, which lead to variations of the slab dip along strike (Fig. 1) and a significant trench-parallel flow. When the material can flow around the edges of the slab, through the addition of lateral plates, the trench parallel flow is enhanced (Fig. 2), whereas the variations on the slab dip are diminished.; Effect of a non-uniform overriding plate on slab-dip. 3D view of the 1000 C isosurface. ; Effect of a non-uniform overriding plate on trench-parallel flow. Map view of the slab at different depths and times, showing the viscosity (colormap) and the velocity (arrows).

  16. Melt Inclusion Evidence for Subduction-modified Mantle Beneath the Woodlark Spreading Center, Solomon Islands

    NASA Astrophysics Data System (ADS)

    Chadwick, J.; Turner, A.; Collins, E.

    2015-12-01

    The Woodlark Spreading Center (WSC) to the east of Papua New Guinea separates the Indo-Australian plate and Solomon Sea microplate. At its eastern terminus, the WSC is being subducted at the New Britain trench, forming a triple junction near the New Georgia Group arc in the Solomon Islands. Previous studies have shown that lavas recovered from greater than 100 km from the trench on the WSC are N-MORB, but closer to the trench they have arc-like Sr-Nd-Pb isotopic ratios, enrichments in LILE, and depletions in HFSE. In the complex triple junction area of the WSC on the Simbo and Ghizo Ridges, island arc tholeiites to medium-K calc-alkaline andesites and dacites have been recovered, many with trace element and isotopic characteristics that are similar to the true arc lavas in the New Georgia Group on the other side of the trench. We suggest that subduction-modified arc mantle migrates through slab windows created by the subduction of the WSC as the plates continue to diverge after subduction. This transfer of mantle across the plate boundary leads to variable mixing between arc and N-MORB end-members, forming the hybrid to arc-like lavas recovered on the WSC. To test this hypothesis and to characterize the end-member compositions, we have analyzed melt inclusions in olivine, pyroxene, and plagioclase phenocrysts in Simbo and Ghizo Ridge lava samples. Major elements were analyzed using the electron microprobe facility at Fayetteville State University and volatiles were analyzed on the ion probe facility at Woods Hole Oceanographic Institution. The melt inclusions show a wide diversity of magmas from basalts to dacites, and mixing modeling shows that most Woodlark Spreading Center lava compositions are explained by mixing between the most extreme mafic (MORB) and felsic (arc) inclusion compositions.

  17. Advancing Subduction Zone Science After a Big Quake

    NASA Astrophysics Data System (ADS)

    Beck, Susan; Rietbrock, Andreas; Tilmann, Frederik; Barrientos, Sergio; Meltzer, Anne; Oncken, Onno; Bataille, Klause; Roecker, Steven; Vilotte, Jean-Pierre; Russo, Raymond M.

    2014-06-01

    After a long quiet period for earthquake activity with magnitude greater than 8.5, several great subduction megathrust earthquakes occurred during the past decade: Sumatra in 2004 and 2005, Chile in 2010, and Japan in 2011. Each of these events caused loss of life and damage to critical infrastructure on an enormous scale. And, in April, a Mw 8.2 earthquake occurred off the Chilean coast.

  18. Seismic structure of the northwestern Japan convergent margin: A synthesis

    NASA Astrophysics Data System (ADS)

    Hasegawa, Akira; Horiuchi, Shigeki; Umino, Norihito

    1994-11-01

    Many studies recently made on the basis of seismic observations have revealed a detailed structure of the crust and the upper mantle beneath the northeastern Japan arc and its relationship to seismic and volcanic activity. Spatial distributions of the depths to the Conrad and the Moho discontinuities, estimated from shallow earthquake data and seismic explosion data, show that both discontinuities are deep in the middle of the land area and shallow toward the coastlines of the Japan Sea and the Pacific Ocean. The Pn velocity has a lateral variation; it is as low as approximately 7.5 km/s beneath the land area, while that beneath the Japan Sea and the Pacific Ocean is 8.0-8.2 km/s. It changes abruptly at the transition zones, which are located along the coastlines. Precise structure and location of the subducted Pacific plate beneath the land area is inferred from converted or reflected seismic waves at the top or bottom of the plate. The Pacific plate is composed of a thin (approximately 5 km) low-velocity upper layer and a thick high-velocity lower layer, its total thickness being 80-90 km. The upper plane seismicity of the double seismic zone is confined to the thin low-velocity upper layer, which probably corresponds to the subducted former oceanic crust. The lower plane seismicity lies at the middle of the high-velocity lower layer, and the lower half of the plate below it is incapable of generating earthquakes. The shallower portion of the upper surface of the plate beneath the Pacific Ocean, along which major seismicity with low-angle thrust faultings is actually occurring, is also located by seismic observations on land and in the sea. The Pacific plate subducts at an extremely low angle of approximately 5 deg for the first approximately 25-km depth, and then the dip steepens rather abruptly to approximately 30 deg. Normal-fault type events at the top of the plate have not been detected in the portion where the downward-bending is the largest, but have been

  19. Distribution and origin of igneous rocks from the landward slopes of the Mariana Trench: Implications for its structure and evolution

    SciTech Connect

    Bloomer, S.H.

    1983-09-10

    The landward slope of the Mariana Trench is composed largely of igneous rocks. Serpentinites and serpentinized ultramafic rocks occur at nearly all structural levels on the slope from depths of 8000 to 1200 m. Seamountlike features on the trench slope break are the surface expression of serpentinite diapirs. Cumulate and massive gabbros are found; several varieties of volcanic rocks are common including boninites, altered and metamorphosed basalts, andesites, and dacites. The chemical characteristics of the volcanic rocks indicate that nearly all are products of island arc volcanism. Together with the gabbros, these volcanic rocks represent what is probably a late Eocene arc complex. These rocks were probably the first volcanic products to result from the subduction of the Pacific plate beneath the Phillippine Sea plate; their exposure on the trench slope today implies a significant amount of tectonic erosion of the landward slope since Eocene time. Most of this removal of material appears to have occurred during the early stages of subduction. There are isolated occurrences on the landward slope of rock assemblages including alkalic basalts, chert, hyaloclastites, upper Cretaceous siliceous sediments, and shallow water limestones. These assemblages are very similar to rocks dredged from seamounts on the offshore flank of the trench, and their presence on the landward slope suggests that since the cessation of vigorous tectonic erosion, there has been episodic accretion of seamount fragments to the landward slope.

  20. Upper plate deformation and seismic barrier in front of Nazca subduction zone: The Chololo Fault System and active tectonics along the Coastal Cordillera, southern Peru

    NASA Astrophysics Data System (ADS)

    Audin, Laurence; Lacan, Pierre; Tavera, Hernando; Bondoux, Francis

    2008-11-01

    The South America plate boundary is one of the most active subduction zone. The recent Mw = 8.4 Arequipa 2001 earthquake ruptured the subduction plane toward the south over 400 km and stopped abruptly on the Ilo Peninsula. In this exact region, the subduction seismic crisis induced the reactivation of continental fault systems in the coastal area. We studied the main reactivated fault system that trends perpendicular to the trench by detailed mapping of fault related-geomorphic features. Also, at a longer time scale, a recurrent Quaternary transtensive tectonic activity of the CFS is expressed by offset river gullies and alluvial fans. The presence of such extensional fault systems trending orthogonal to the trench along the Coastal Cordillera in southern Peru is interpreted to reflect a strong coupling between the two plates. In this particular case, stress transfer to the upper plate, at least along the coastal fringe, appears to have induced crustal seismic events that were initiated mainly during and after the 2001 earthquake. The seafloor roughness of the subducting plate is usually thought to be a cause of segmentation along subduction zones. However, after comparing and discussing the role of inherited structures within the upper plate to the subduction zone segmentation in southern Peru, we suggest that the continental structure itself may exert some feedback control on the segmentation of the subduction zone and thus participate to define the rupture pattern of major subduction earthquakes along the southern Peru continental margin.

  1. Ophiolites of the deep-sea trenches of the western Pacific

    SciTech Connect

    Chudaev, O.

    1990-06-01

    Igneous and metamorphic rocks of ophiolites are widespread in the basement of the Izu-Bonin, Volcano, Mariana, Philippine, Yap, Palau, New Hebrides, West Melanesian, Tonga, and Mussau trenches. Ophiolite in the trenches includes (1) metamorphic rocks ranging from low-T and low P to high-T and moderate P; (2) serpentinites after harzburgite; (3) ultramafic-mafic layered series; (4) tholeiitic basalts, dolerites, and their metamorphosed varieties; and (5) rocks of the boninitic series. Two geodynamic stages could be distinguished in the formation of the ophiolites of the Western Pacific. At the rifting stage, mantle diapir ascended during rifting and magmatic series were formed. In this period, rocks underwent intense low-temperature metasomatic alterations in the zones of heated seawater circulation. At the compression stage (subduction zone) regional pressure metamorphism of the ophiolites superimposed on the low-temperature metasomatic processes.

  2. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

    NASA Astrophysics Data System (ADS)

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-07-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface.

  3. New seafloor map of the Puerto Rico Trench helps assess earthquake and tsunami hazards

    USGS Publications Warehouse

    ten Brink, Uri S.; Danforth, William; Polloni, Christopher; Andrews, Brian D.; Llanes Estrada, Pilar; Smith, Shepard; Parker, Eugene; Uozumi, Toshihiko

    2004-01-01

    The Puerto Rico Trench, the deepest part of the Atlantic Ocean, is located where the North American (NOAM) plate is subducting under the Caribbean plate (Figure l). The trench region may pose significant seismic and tsunami hazards to Puerto Rico and the U.S.Virgin Islands, where 4 million U.S. citizens reside. Widespread damage in Puerto Rico and Hispaniola from an earthquake in 1787 was estimated to be the result of a magnitude 8 earthquake north of the islands [McCann et al., 2004]. A tsunami killed 40 people in NW Puerto Rico following a magnitude 7.3 earthquake in 1918 [Mercado and McCann, 1998]. Large landslide escarpments have been mapped on the seafloor north of Puerto Rico [Mercado et al., 2002; Schwab et al., 1991],although their ages are unknown.

  4. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench.

    PubMed

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-07-22

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15-18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface.

  5. Structure of the tsunamigenic plate boundary and low-frequency earthquakes in the southern Ryukyu Trench

    PubMed Central

    Arai, Ryuta; Takahashi, Tsutomu; Kodaira, Shuichi; Kaiho, Yuka; Nakanishi, Ayako; Fujie, Gou; Nakamura, Yasuyuki; Yamamoto, Yojiro; Ishihara, Yasushi; Miura, Seiichi; Kaneda, Yoshiyuki

    2016-01-01

    It has been recognized that even weakly coupled subduction zones may cause large interplate earthquakes leading to destructive tsunamis. The Ryukyu Trench is one of the best fields to study this phenomenon, since various slow earthquakes and tsunamis have occurred; yet the fault structure and seismic activity there are poorly constrained. Here we present seismological evidence from marine observation for megathrust faults and low-frequency earthquakes (LFEs). On the basis of passive observation we find LFEs occur at 15–18 km depths along the plate interface and their distribution seems to bridge the gap between the shallow tsunamigenic zone and the deep slow slip region. This suggests that the southern Ryukyu Trench is dominated by slow earthquakes at any depths and lacks a typical locked zone. The plate interface is overlaid by a low-velocity wedge and is accompanied by polarity reversals of seismic reflections, indicating fluids exist at various depths along the plate interface. PMID:27447546

  6. Gravity and Flexure Modelling of Subducting Plates

    NASA Astrophysics Data System (ADS)

    Hunter, J. A.; Watts, A. B.; SO 215 Shipboard Scientific Party

    2012-04-01

    The long-term strength of the lithosphere is determined by its flexural rigidity, which is commonly expressed through the effective elastic thickness, Te. Flexure studies have revealed a dependence of Te on thermal age. In the oceans, loads formed on young (70 Ma) seafloor. In the continents, loads on young (1000 Ma) lithosphere. Recent studies have questioned the relationship of Te with age, especially at subduction zones, where oceanic and continental lithosphere are flexed downwards by up to ~6 km over horizontal distances of up to ~350 km. We have therefore used free-air gravity anomaly and topography profile data, combined with forward and inverse modelling techniques, to re-assess Te in these settings. Preliminary inverse modelling results from the Tonga-Kermadec Trench - Outer Rise system, where the Pacific plate is subducting beneath the Indo-Australian plate, show large spatial variations in Te that are unrelated to age. In contrast to the southern end of the system, where Te is determined by the depth to the 600° C and 900° C isotherms, the northern end of the system shows a reduction in strength. Results also suggest a reduction in Te trenchward of the outer rise that is coincident with a region of pervasive extensional faulting visible in swath bathymetry data. In a continental setting, the Ganges foreland basin has formed by flexure of the Indo-Australian plate in front of the migrating loads of the Himalaya. Preliminary forward modelling results, using the Himalaya as a known surface topographic load, suggest that Te is high - consistent with the great age of Indian cratonic lithosphere. However, results from inverse modelling that solves for unknown loads (vertical shear force and bending moment) show significant scatter and display trade-offs between Te and these driving loads.

  7. Recent Intermediate Depth Earthquakes in El Salvador, Central Mexico, Cascadia and South-West Japan

    NASA Astrophysics Data System (ADS)

    Lemoine, A.; Gardi, A.; Gutscher, M.; Madariaga, R.

    2001-12-01

    We studied occurence and source parameters of several recent intermediate depth earthquakes. We concentrated on the Mw=7.7 salvadorian earthquake which took place on January 13, 2001. It was a good example of the high seismic risk associated to such kind of events which occur closer to the coast than the interplate thrust events. The Salvadorian earthquake was an intermediate depth downdip extensional event which occured inside the downgoing Cocos plate, next to the downdip flexure where the dip increases sharply before the slab sinks more steeply. This location corresponds closely to the position of the Mw=5.7 1996 and Mw=7.3 1982 downdip extensional events. Several recent intermediate depth earthquakes occured in subduction zones exhibiting a ``flat slab'' geometry with three distinct flexural bends where flexural stress may be enhanced. The Mw=6.7 Geiyo event showed a downdip extensional mechanism with N-S striking nodal planes. This trend was highly oblique to the trench (Nankai Trough), yet consistent with westward steepening at the SW lateral termination of the SW Japan flat slab. The Mw=6.8 Olympia earthquake in the Cascadia subduction zone occured at the downdip termination of the Juan de Fuca slab, where plate dip increases from about 5o to over 30o. The N-S orientation of the focal planes, parallel to the trench indicated downdip extension. The location at the downdip flexure corresponds closely to the estimated positions of the 1949 M7.1 Olympia and 1965 M6.5 Seattle-Tacoma events. Between 1994 and 1999, in Central Mexico, an unusually high intermediate depth seismicity occured where several authors proposed a flat geometry for the Cocos plate. Seven events of magnitude between Mw=5.9 and Mw=7.1 occured. Three of them were downdip compressional and four where down-dip extensional. We can explain these earthquakes by flexural stresses at down-dip and lateral terminations of the supposed flat segment. Even if intermediate depth earthquakes occurence could

  8. Subduction on long time scales: Tighter constraints on mantle rheologies require cross-disciplinary engagement with subduction histories.

    NASA Astrophysics Data System (ADS)

    Sigloch, Karin; Mihalynuk, Mitchell G.

    2016-04-01

    Two observational records constrain subduction on long timescales: accretionary mountain belts at the surface and subducted lithosphere in the subsurface. Subducted slabs represent paleo-oceans and can be imaged by seismic tomography. Mountain belts consist of crustal slivers that were produced and aggregated near paleo-trenches but escaped subduction (arc terranes, accretionary complexes, ophiolites). They are mapped by regional geologists and further constrained by lab-based rock analysis methods. The strength of seismic tomography consists in relatively comprehensive spatial coverage of the mantle's slab inventory, together with established methods for probing uncertainties (image resolution). Unfortunately, subsurface imaging provides no direct constraints on slabs' ages and their deformation histories from rigid oceanic plates to lumpy velocity anomalies. Convection modelling by itself cannot remedy this shortcoming because independent observational constraints on mantle rheologies are lacking. Through dating of accretionary orogens, geology can in principle provide the subduction and slab ages that geophysics is missing. This requires a testable strategy for associating slabs with major accretionary events, and synthesis of geological inputs across vast spatial scales (1000 to 10,000 km) and time scales (10-100 million years). Orogens provide only limited spatial constraints on paleo-trenches because they record several generations of accreted terranes, usually heavily deformed, overprinted, and translated with the migrating continent. The interpretational uncertainties produced by these complexities are very nonlinear: Miss a suture in the field, and you may be missing an entire paleo-ocean - while also incorrectly attributing the associated slab. This danger is real, as we demonstrate for North American slabs and Cordilleran geology. Prevailing paleo-geographic interpretations for the Cordillera arguably miss a Jura-Cretaceous ocean, and slab geometries in

  9. The variations of long time period slow slip events along the Ryukyu subduction zone

    NASA Astrophysics Data System (ADS)

    Tu, Y. T.; Heki, K.

    2014-12-01

    Slow slip events (SSEs) are a type of slow earthquakes that can be observed with Global Positioning System (GPS) networks in the world. Those events are detected on intensely coupled plate boundaries such as Cascadia subduction zone (Dragert et al., 2001), western North America, Mexico (Kostoglodov et al., 2003), Alaska (Ohta et al., 2007) and Tokai and Boso areas (Ozawa et al., 2002, 2003), central Japan and are considered to have relations to large subduction thrust earthquakes. However, in southwestern Ryukyu trench where most of researchers believe that it should be a decoupled plate boundary, SSEs recur regularly and are located at a patch that is as deep as 20 to 40 km (Heki and Kataoka, 2008). For comprehending the characteristics and time variations of SSEs in this area, the GEONET GPS data of 16 years are used in this study. During 1997 to 2014, more than thirty SSEs are identified near Hateruma Island, Ryukyu. The average recurrence interval is calculated to be 6.3 months and release seismic moment is Mw 6.6 on average. However, the values of recurrence interval are not invariable. From 1997 to 2002, interval period of SSEs is 7.5 months, but during 2002 to 2008, the interval period decreases suddenly to 5.5 months. After 2008, the value restores to 7.2 months again. Furthermore, the slip amount of SSEs in this area varies with time. From 1997 to 2002, the slip is 9.5 cm/year; and during 2002 to 2008, the value slightly increases to 10.5 cm/year. However, in 2008 to 2013, the slip drops to 6.6 cm/year, but accord to the trend of cumulative slip, the slip value would increase in 2014. Considering these data, we find the slip values increase conspicuously in 2002 and 2013. Coincidentally, one Mw 7.1 thrust earthquake occurred in 2002 and earthquake swarm activity started in the Okinawa trough approximately 50km north of the SSE patch. In 2013, another earthquake swarm activity occurred in nearly the same area as the 2002 activity. This suggests that the

  10. 3-D simulation of temporal change in tectonic deformation pattern and evolution of the plate boundary around the Kanto Region of Japan due to the collision of the Izu-Bonin Arc

    NASA Astrophysics Data System (ADS)

    Hashima, A.; Sato, T.; Ito, T.; Miyauchi, T.; Furuya, H.; Tsumura, N.; Kameo, K.; Yamamoto, S.

    2010-12-01

    The Kanto region of Japan is in a highly complex tectonic setting with four plates interacting with each other: beneath Kanto, situated on the Eurasian and North American plates, the Philippine sea plate subducts and the Pacific plate further descends beneath the North American and Philippine sea plates, forming the unique trench-trench-trench triple junction on the earth. In addition, the Izu-Bonin (Ogasawara) arc on the Philippine sea plate is colliding with the Japan islands, which is considered to be a significant effect on the tectonics of Kanto. To reveal the present crustal structure and the present internal stress fields in such a complex tectonic setting, it is essential to comprehend them through the long-term tectonic evolution process. In this study, we estimate the temporal change in tectonic deformation pattern along with the geometry of the plate boundary around Kanto by numerical simulation with a kinematic plate subduction model based on the elastic dislocation theory. This model is based on the idea that mechanical interaction between plates can rationally be represented by the increase of the displacement discontinuity (dislocation) across plate interfaces. Given the 3-D geometry of plate interfaces, the distribution of slip rate vectors for simple plate subduction can be obtained directly from relative plate velocities. In collision zones, the plate with arc crust cannot easily descend because of its buoyancy. This can be represented by giving slip-rate deficit. When crustal deformation occurs, it also causes change in geometry of the plate boundary itself. This geometry change sensitively affects mechanical interaction at the plate boundary. Then the renewed plate-to-plete interaction alters crustal deformation rates. This feedback system has a large effect on collision zones. Indeed, the plate boundary around the Izu peninsula, the northernmost end of the Izu-Bonin arc, intends landward as large as 100 km. Iterating this effect sequentially

  11. Mantle plumes in the vicinity of subduction zones

    NASA Astrophysics Data System (ADS)

    Mériaux, C. A.; Mériaux, A.-S.; Schellart, W. P.; Duarte, J. C.; Duarte, S. S.; Chen, Z.

    2016-11-01

    We present three-dimensional deep-mantle laboratory models of a compositional plume within the vicinity of a buoyancy-driven subducting plate with a fixed trailing edge. We modelled front plumes (in the mantle wedge), rear plumes (beneath the subducting plate) and side plumes with slab/plume systems of buoyancy flux ratio spanning a range from 2 to 100 that overlaps the ratios in nature of 0.2-100. This study shows that 1) rising side and front plumes can be dragged over thousands of kilometres into the mantle wedge, 2) flattening of rear plumes in the trench-normal direction can be initiated 700 km away from the trench, and a plume material layer of lesser density and viscosity can ultimately almost entirely underlay a retreating slab after slab/plume impact, 3) while side and rear plumes are not tilted until they reach ∼600 km depth, front plumes can be tilted at increasing depths as their plume buoyancy is lessened, and rise at a slower rate when subjected to a slab-induced downwelling, 4) rear plumes whose buoyancy flux is close to that of a slab, can retard subduction until the slab is 600 km long, and 5) slab-plume interaction can lead to a diversity of spatial plume material distributions into the mantle wedge. We discuss natural slab/plume systems of the Cascadia/Bowie-Cobb, and Nazca/San Felix-Juan Fernandez systems on the basis of our experiments and each geodynamic context and assess the influence of slab downwelling at depths for the starting plumes of Java, Coral Sea and East Solomon. Overall, this study shows how slab/plume interactions can result in a variety of geological, geophysical and geochemical signatures.

  12. Potential for generation of natural gas in sediments of the convergent margin of the Aleutian Trench Area

    SciTech Connect

    Kvenvolden, K.A.; von Huene, R.

    1983-01-01

    Sediment being subducted in the eastern part of the convergent margin of the Aleutian Trench has a potential to generate large volumes of natural gas, perhaps as much as 2.8 x 10/sup 6/ m/sup 3/ of methane per km/sup 3/ of sediment, even though the content of organic carbon in the sediment is very low, averaging about 0.4%. This high potential for gas generation results primarily from the enormous volume of sediment undergoing subduction. Along the eastern Aleutian Arc-Trench system a 3-km thick sheet of sediment is being subducted at a rate of about 60 km per million years. We estimate, based on considerations of the stability requirements for gas hydrates observed as anomalous reflectors in some of our seismic records, and on one measurement in a deep well, that the geothermal gradient in this region is about 30/sup 0/C/km. Such a gradient suggests a temperature regime in which the maximum gas generation in the subducting sediment occurs beneath the upper slope. Thus the sediment of the upper slope, as opposed to that of the shelf and lower slope, could be the most prospective for gas accumulation if suitable reservoirs are present. 40 refs., 11 figs., 3 tabs.

  13. A new model of slab tear of the subducting Philippine Sea Plate associated with Kyushu-Palau Ridge subduction

    NASA Astrophysics Data System (ADS)

    Cao, Lingmin; Wang, Zhi; Wu, Shiguo; Gao, Xiang

    2014-12-01

    We suggest that the Kyushu-Palau Ridge (KPR) plays a key role in the subduction process of the Philippine Sea Plate (PSP) and the origin of the Abu volcano in the southwestern Japan. The 3-D P-wave velocity structure was imaged to approximately 300 km beneath the Abu volcano using a large number of P-wave arrivals from local earthquakes and teleseismic events. Our results indicate that a high-velocity anomaly beneath the Abu volcano is associated with the subducting PSP; however, the anomaly is not continuous, being interrupted apparently by a low-velocity anomaly zone extending northwestwards from 80 km to great depth. The PSP appears to be tearing and then forms a 'slab window' corresponding to KPR subduction at ca. 2 Ma. The low-velocity anomaly may indicate hot upper mantle material rising through the slab window and causing partial melting both of the lower crust of the overriding plate and the oceanic crust of the subducted KPR. A new model is presented for slab tearing of the PSP associated with the subduction of the buoyant, wide and thick KPR and directional change in the motion of the plate, contributing to better understanding of the Abu volcanism.

  14. Coseismic and interseismic displacements at a subduction zone - a parameter study using finite-element modelling

    NASA Astrophysics Data System (ADS)

    Li, Tao; Hampel, Andrea

    2013-04-01

    Tide-gauge and geodetic measurements of coseismic and interseismic displacements in the forearc of subduction zones showed that the coastal region undergoes uplift during the interseismic phase and subsidence during the coseismic phase, while opposite vertical movements are observed in the neighbouring regions (e.g., Savage & Thatcher 1992; Hyndman & Wang 1995). Horizontal displacements during the interseismic phase are typically directed landward, whereas the forearc moves seaward during the earthquake (e.g., Klotz et al. 1999). Here we use two-dimensional finite-element modelling to evaluate how the friction coefficient along the plate interface, the length and the position of the downdip end of the locked zone affect the coseismic and interseismic displacements. Our model consists of a deformable, rheologically stratified upper plate and an undeformable oceanic plate, which rotates at a prescribed angular velocity (cf. Cailleau & Oncken, 2008). The frictional plate interface is divided - from the trench to the base of the continental lithosphere - into a seismogenic zone, a transition zone and a landward free slip zone. During an initial phase, the seismogenic zone is locked, which leads to the accumulation of elastic strain in the forearc. During the subsequent coseismic phase, the strain is released and causes sudden slip of several meters on the plate interface. During the next interseismic phase, the seismogenic zone is locked again. Our model results show patterns of vertical and horizontal displacements that are in general agreement with geodetically observed patterns. A sensitivity analysis reveals that the magnitude of the vertical displacements is strongly influenced by the friction coefficients of the seismogenic zone and the transition zone. The location of the zones of maximum interseismic uplift and coseismic subsidence in the coastal regions depends on the length and position of the locked zone. Preliminary results from three-dimensional models

  15. Plate interface strength and the flexural rigidity of subducting oceanic plates

    NASA Astrophysics Data System (ADS)

    Naliboff, J.; Billen, M. I.; Faccenda, M.; Gerya, T.

    2015-12-01

    Flexural rigidity estimates across a wide range of subduction zones reveal that oceanic plates rapidly weaken as they bend and pass through the outer-rise region into the trench. Inherently, the magnitude of weakening reflects the forces acting on the plate, which drive deformation through plastic yielding and brittle faulting. These forces include those acting to drive (slab pull) or resist (bending, plate coupling) subduction, which vary significantly through long-term (millions of years) changes in slab structure and dynamics. The forces also vary on seismic time-scales as indicated by changes in outer-rise seismicity characteristics before and after great earthquakes in many regions. As the rheology of the downgoing-overriding plate interface plays a first-order role in governing great earthquake seismicity, a quantifiable relationship may exist between large-scale slab weakening and the strength of the subduction interface. Here, we assess this relationship using high-resolution, thermal-mechanical models of the Tonga subduction zone. Rather than developing subduction through time-dependent processes, these models use a cross-sectional slice (2-D) through the Tonga subduction zone as an initial condition in order to approximate the modern forces driving and resisting subduction. Consequently, deformation patterns develop over short (< 0.1 Myr) time-scales, allowing a direct comparison to measurements of flexural rigidity. We define a rheologically distinct, 1 km thick zone between the downgoing and overriding plate. The properties of this zone are varied to examine a range of interface strengths, including fixed (Von Mises), pressure (Mohr-Coulomb) and velocity-dependent rheologies. We then quantify the relationship between variations in subduction interface strength on these time-scales and the corresponding changes in the flexural rigidity of the subducting plate.

  16. Kinematics of the Hellenic Trench System from Earthquake Seismology and Field Observations

    NASA Astrophysics Data System (ADS)

    Howell, A.; Jackson, J. A.; England, P. C.; Synolakis, C.

    <