scholarly journals Deep Investigations of Outer‐Rise Tsunami Characteristics Using Well‐Mapped Normal Faults Along the Japan Trench

2020 ◽  
Vol 125 (10) ◽  
Author(s):  
Toshitaka Baba ◽  
Naotaka Chikasada ◽  
Yasuyuki Nakamura ◽  
Gou Fujie ◽  
Koichiro Obana ◽  
...  
Keyword(s):  
Japan Trench ◽  
Normal Faults ◽  
Outer Rise

scholarly journals Frequency dispersion amplifies tsunamis caused by outer-rise normal faults

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Toshitaka Baba ◽  
Naotaka Chikasada ◽  
Kentaro Imai ◽  
Yuichiro Tanioka ◽  
Shuichi Kodaira
Keyword(s):  
Water Waves ◽  
Frequency Dispersion ◽  
Japan Trench ◽  
Normal Faults ◽  
Ocean Bottom ◽  
Hazard Maps ◽  
Tsunami Height ◽  
Tsunami Inundation ◽  
Outer Rise ◽  
Spatial Dimensions

AbstractAlthough tsunamis are dispersive water waves, hazard maps for earthquake-generated tsunamis neglect dispersive effects because the spatial dimensions of tsunamis are much greater than the water depth, and dispersive effects are generally small. Furthermore, calculations that include non-dispersive effects tend to predict higher tsunamis than ones that include dispersive effects. Although non-dispersive models may overestimate the tsunami height, this conservative approach is acceptable in disaster management, where the goal is to save lives and protect property. However, we demonstrate that offshore frequency dispersion amplifies tsunamis caused by outer-rise earthquakes, which displace the ocean bottom downward in a narrow area, generating a dispersive short-wavelength and pulling-dominant (water withdrawn) tsunami. We compared observational evidence and calculations of tsunami for a 1933 Mw 8.3 outer-rise earthquake along the Japan Trench. Dispersive (Boussinesq) calculations predicted significant frequency dispersion in the 1933 tsunami. The dispersive tsunami deformation offshore produced tsunami inundation heights that were about 10% larger than those predicted by non-dispersive (long-wave) calculations. The dispersive tsunami calculations simulated the observed tsunami inundation heights better than did the non-dispersive tsunami calculations. Contrary to conventional practice, we conclude that dispersive calculations are essential when preparing deterministic hazard maps for outer-rise tsunamis.

Seismicity around the trench axis and outer-rise region of the southern Japan Trench, south of the main rupture area of the 2011 Tohoku-oki earthquake

2021 ◽  
Vol 226 (1) ◽  
pp. 131-145
Author(s):  
Koichiro Obana ◽  
Gou Fujie ◽  
Yojiro Yamamoto ◽  
Yuka Kaiho ◽  
Yasuyuki Nakamura ◽  
...  
Keyword(s):  
Japan Trench ◽  
Normal Faults ◽  
The South ◽  
Plate Interface ◽  
Lower Velocity ◽  
Outer Rise ◽  
Rupture Area ◽  
Trench Axis ◽  
Southern Japan ◽  
Structure Heterogeneity

SUMMARY The 2011 Mw 9.0 Tohoku-oki earthquake ruptured the subduction megathrust fault in the central Japan Trench. We investigated the aftershock activity in the southern Japan Trench to the south of the main rupture area using ocean bottom seismographs deployed both landward and seaward of the trench. In the trench-outer rise region seaward of the trench axis, we identified several ∼100-km-long linear earthquake trends both parallel and oblique to the southern Japan Trench. The earthquake trend oblique to the southern Japan Trench is a southward extension of the trench-parallel linear earthquake trend in the central to northern Japan Trench. The trench-parallel normal-faults in the trench-outer rise region could extend linearly, despite the change of the trench strike from N–S to NNE–SSW to the south of the main rupture area. Normal-faults oblique to the trench should be considered as substantial parts of large intraplate normal-faulting earthquakes. In addition, intraplate seismicity coinciding with the lower velocity oceanic mantle suggest that the structure heterogeneity would be indicative of normal-faults extending into the mantle. In the trench landward area, earthquake activity showed along-trench variations. Earthquakes along the shallow megathrust interface near the trench were observed south of 37°N. These shallow near-trench regular earthquakes, which are located close to the episodic tremors and temporally correlated with the tremor activities, suggest that the afterslip on the plate interface likely extended to the shallow plate interface close to the trench axis. Smaller spatial scale structure heterogeneity, such as the thickness variation in the channel-like low-velocity sedimentary unit, likely relate to the proximity of the regular earthquakes and slow slip which results in the formation of diverse slip behaviours in the shallow subduction zone of the southern Japan Trench.

scholarly journals Deep Investigations of Outer-Rise Tsunami Characteristics using Well-Mapped Normal Faults along the Japan Trench

2020 ◽  
Author(s):  
Toshitaka Baba ◽  
Naotaka Yamamoto Chikasada ◽  
Yasuyuki Nakamura ◽  
Gou Fujie ◽  
Koichiro Obana ◽  
...  
Keyword(s):  
Japan Trench ◽  
Normal Faults ◽  
Outer Rise

scholarly journals Mantle-derived helium released through the Japan trench bend-faults

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jin-Oh Park ◽  
Naoto Takahata ◽  
Ehsan Jamali Hondori ◽  
Asuka Yamaguchi ◽  
Takanori Kagoshima ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Large Scale ◽  
Japan Trench ◽  
Helium Isotope ◽  
Normal Faults ◽  
Circulation System ◽  
Deep Penetration ◽  
Oceanic Plate ◽  
Seismic Reflection Data ◽  
Reflection Data

AbstractPlate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.

scholarly journals Along‐trench variations in the seismic structure of the incoming Pacific plate at the outer rise of the northern Japan Trench

2016 ◽  
Vol 43 (2) ◽  
pp. 666-673 ◽  
Author(s):  
Gou Fujie ◽  
Shuichi Kodaira ◽  
Takeshi Sato ◽  
Tsutomu Takahashi
Keyword(s):  
Pacific Plate ◽  
Japan Trench ◽  
Seismic Structure ◽  
Outer Rise ◽  
Northern Japan

Active sediment creep deformation on a deep-sea terrace in the Japan Trench

2018 ◽  
Vol 158 (1) ◽  
pp. 39-46 ◽  
Author(s):  
Sayaka Nitta ◽  
Takafumi Kasaya ◽  
Kiichiro Kawamura
Keyword(s):  
Active Region ◽  
Creep Deformation ◽  
Deep Sea ◽  
Japan Trench ◽  
Normal Faults ◽  
Tectonic Erosion ◽  
Active Folds ◽  
Sequence Unit ◽  
Water Depths ◽  
Rising Sea Level

AbstractEighty-six new acoustic survey lines along and across the Japan Trench revealed active sediment creep deformation on a deep-sea terrace at water depths of 400–1200 m in an area of arcuate-shaped depressions that are probably associated with tectonic erosion. The most active region of creep is located on the top at the surface of the depression south of 38° N. The area of creep deformation is characterized by arcuate-shaped topographic lineaments with active folds and active normal faults stepping down trenchward. In contrast to the southern region, normal faults at the top of the depression north of 38° N cut a sedimentary sequence (Unit 1) that is acoustically transparent with continuous weak reflectors, and this is covered by the undeformed layered sediment sequence of Unit 2. Unit 2 corresponds to the period of rising sea level that extended from the latest Pleistocene to the early Holocene (14–6 ka). Thus, creep is ongoing at the top of the depression south of 38° N in the surface layer, whereas it stopped north of the depression between 14 and 6 ka. These observations might indicate that the active region jumped from north to south due to probably retrogressive sliding.

scholarly journals Dynamic slab segmentation due to brittle-ductile damage interactions in the outer rise

2020 ◽  
Author(s):  
Taras Gerya ◽  
David Bercovici ◽  
Thorsten Becker
Keyword(s):  
Plate Tectonics ◽  
Potential Temperature ◽  
Ductile Deformation ◽  
Ductile Damage ◽  
Normal Faults ◽  
Prior History ◽  
Outer Rise ◽  
Slab Breakoff ◽  
Subducting Plate ◽  
Oceanic Plates

Abstract The recycling of oceanic plates by means of subduction represents the major plate driving force and subducting plate strength controls many aspects of the thermo-chemical evolution of Earth. Regardless of its prior history, each subducting plate experiences intense normal faulting1-11 during bending that accommodates the transition from horizontal to downward motion at the outer rise at subduction trenches. Here, we investigate the consequences of this bending-induced plate damage using new numerical, thermomechanical subduction models in which both brittle and ductile deformation, as well as grain size evolution, are tracked and coupled self-consistently. Pervasive slab weakening and pronounced segmentation can occur at the outer rise region due to the strong feedback between brittle and ductile damage localization. The “memory” of bending varies from segmentation to broadly-distributed damage depending on the age of the subducting plate, mantle potential temperature, and the magnitude of strain-induced weakening of outer rise normal faults. This new slab damage phenomenon explains the development of large-offset normal faults8,9, the occurrence of deep compressional thrust-faulting earthquakes12, and the appearance of localized areas of reduced effective viscosity13 observed at subduction trenches. Furthermore, brittle-viscously damaged slabs show a strong tendency for slab breakoff at elevated mantle temperatures. Given Earth’s planetary cooling history14, this implies that intermittent subduction with frequent slab breakoff episodes15,16 may have been characteristic for terrestrial plate tectonics until more recent times than expected from memory-free rheologies17.

scholarly journals Outer-rise normal fault development and influence on near-trench décollement propagation along the Japan Trench, off Tohoku

2014 ◽  
Vol 66 (1) ◽  
pp. 135 ◽  
Author(s):  
Brian Boston ◽  
Gregory F Moore ◽  
Yasuyuki Nakamura ◽  
Shuichi Kodaira
Keyword(s):  
Normal Fault ◽  
Japan Trench ◽  
Outer Rise

scholarly journals Outer trench slope flexure and faulting at Pacific basin subduction zones

2019 ◽  
Vol 218 (1) ◽  
pp. 708-728 ◽  
Author(s):  
Emmanuel Soliman M Garcia ◽  
David T Sandwell ◽  
Dan Bassett
Keyword(s):  
Subduction Zones ◽  
Gravity Data ◽  
Bending Moment ◽  
Normal Faults ◽  
Nonlinear Inversion ◽  
Outer Rise ◽  
Trench Axis ◽  
Effective Elastic Thickness ◽  
Age Model ◽  
Trench Slope

SUMMARY Flexure and fracturing of the seafloor on the outer trench wall of subduction zones reflect bending of the lithosphere beyond its elastic limit. To investigate these inelastic processes, we have developed a full nonlinear inversion approach for estimating the bending moment, curvature and outer trench wall fracturing using shipboard bathymetry and satellite altimetry-derived gravity data as constraints. Bending moments and downward forces are imposed along curved trench axes and an iterative method is used to calculate the nonlinear response for 26 sites in the circum-Pacific region having seafloor age ranging from 15 to 148 Ma. We use standard thermal and yield strength envelope models to develop the nonlinear moment versus curvature relationship. Two coefficients of friction of 0.6 and 0.3 are considered and we find that the lower value provides a better overall fit to the data. The main result is that the lithosphere is nearly moment saturated at the trench axis. The effective elastic thickness of the plate on the outer trench slope is at least three times smaller than the elastic thickness of the plate before bending at the outer rise in agreement with previous studies. The average seafloor depth of the unbent plate in these 26 sites matches the Parsons & Sclater depth versus age model beyond 120 Ma. We also use the model to predict the offsets of normal faults on the outer trench walls and compare this with the horst and graben structures observed by multibeam surveys. The model with the lower coefficient of friction fits the fault offset data close to the trench axis. However, the model predicts significant fracturing of the lithosphere between 75 and 150 km away from the trench axis where no fracturing is observed. To reconcile these observations, we impose a thermoelastic pre-stress in the lithosphere prior to subduction. This pre-stress delays the onset of fracturing in better agreement with the data.

Sign in / Sign up

Export Citation Format

Share Document