What Caused the 2011 Tohoku-Oki Earthquake? : Effects of Dynamic Weakening

2014 ◽  
Vol 9 (3) ◽  
pp. 252-263
Author(s):  
Bunichiro Shibazaki ◽  
◽  
Hiroyuki Noda ◽  
Keyword(s):  
Plate Boundary ◽  
Japan Trench ◽  
Plate Interface ◽  
Megathrust Earthquakes ◽  
Shallow Subduction ◽  
Thermal Pressurization ◽  
Dynamic Weakening ◽  
Recurrence Intervals ◽  
Earthquake Effects ◽  
Experimental And Theoretical Studies

Some observational studies have suggested that the 2011 great Tohoku-Oki earthquake (Mw9.0) released a large portion of the accumulated elastic strain on the plate interface owing to considerable weakening of the fault. Recent experimental and theoretical studies have shown that considerable dynamic weakening can occur at high slip velocities because of thermal pressurization or thermal weakening processes. This paper reviews severalmodels of the generation of megathrust earthquakes along the Japan Trench subduction zone, that considers thermal pressurization or a friction law that exhibits velocity weakening at high slip velocities, and it discusses the causes of megathrust earthquakes. To reproduce megathrust earthquakes with recurrence intervals of several hundreds of years, it will be necessary to consider the existence of a region at the shallow subduction plate boundary where significant dynamic weakening occurs due to thermal pressurization or other thermal weakening processes.

scholarly journals Synthetic analysis of the efficacy of the S-net system in tsunami forecasting

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Iyan E. Mulia ◽  
Kenji Satake
Keyword(s):  
Optimization Technique ◽  
Pressure Sensors ◽  
Japan Trench ◽  
Ocean Bottom ◽  
Plate Interface ◽  
Megathrust Earthquakes ◽  
Observation Network ◽  
Tsunami Forecasting ◽  
Seafloor Observation ◽  
Earthquake Size

AbstractThe Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench (S-net) is presently the world’s largest network of ocean bottom pressure sensors for real-time tsunami monitoring. This paper analyzes the efficacy of such a vast system in tsunami forecasting through exhaustive synthetic experiments. We consider 1500 hypothetical tsunami scenarios from megathrust earthquakes with magnitudes ranging from Mw 7.7–9.1. We employ a stochastic slip model to emulate heterogeneous slip patterns on specified 240 subfaults over the plate interface of the Japan Trench subduction zone and its vicinity. Subsequently, the associated tsunamis in terms of maximum coastal tsunami heights are evaluated along the 50-m isobath by means of a Green’s function summation. To produce tsunami forecasts, we utilize a tsunami inversion from virtually observed waveforms at the S-net stations. Remarkably, forecasts accuracy of approximately 99% can be achieved using tsunami data within an interval of 3 to 5 min after the earthquake (2-min length), owing to the exceedingly dense observation points. Additionally, we apply an optimization technique to determine the optimal combination of stations with respect to earthquake magnitudes. The results show that the minimum requisite number of stations to maintain the accuracy attained by the existing network configuration decreases from 130 to 90 when the earthquake size increases from Mw 7.7 to 9.1.

scholarly journals Effects of episodic slow slip on seismicity and stress near a subduction-zone megathrust

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Saeko Kita ◽  
Heidi Houston ◽  
Suguru Yabe ◽  
Sachiko Tanaka ◽  
Youichi Asano ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Fluid Pressure ◽  
Plate Boundary ◽  
Slow Slip ◽  
Plate Interface ◽  
B Values ◽  
Megathrust Earthquakes ◽  
Cyclic Processes ◽  
Stress Orientations ◽  
Oceanic Slab

AbstractSlow slip phenomena deep in subduction zones reveal cyclic processes downdip of locked megathrusts. Here we analyze seismicity within a subducting oceanic slab, spanning ~50 major deep slow slip with tremor episodes over 17 years. Changes in rate, b-values, and stress orientations of in-slab seismicity are temporally associated with the episodes. Furthermore, although stress orientations in the slab below these slow slips may rotate slightly, in-slab orientations 20–50 km updip from there rotate farther, suggesting that previously-unrecognized transient slow slip occurs on the plate interface updip. We infer that fluid pressure propagates from slab to interface, promoting episodes of slow slip, which break mineral seals, allowing the pressure to propagate tens of km further updip along the interface where it promotes transient slow slips. The proposed methodology, based primarily on in-slab seismicity, may help monitor plate boundary conditions and slow slip phenomena, which can signal the beginning stages of megathrust earthquakes.

scholarly journals Effects of episodic slow slip on seismicity and stress near a subduction-zone megathrust

2021 ◽  
Author(s):  
Saeko Kita ◽  
Heidi Houston ◽  
Suguru Yabe ◽  
Sachiko Tanaka ◽  
Youichi Asano ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Plate Boundary ◽  
Slow Slip ◽  
Plate Interface ◽  
Kii Peninsula ◽  
B Values ◽  
Megathrust Earthquakes ◽  
Cyclic Processes ◽  
Stress Orientations ◽  
Oceanic Slab

Abstract Slow slip phenomena deep in subduction zones reveal cyclic processes downdip of locked megathrusts. Here we analyze seismicity within a subducting oceanic slab under Kii Peninsula, Japan, spanning nearly 50 major deep slow slip and tremor episodes over 17 years. Changes in rate, b-values, and stress orientations of inslab seismicity are temporally associated with the slow slip episodes. Furthermore, although stress orientations in the slab below these slow slips may rotate slightly, inslab orientations 20 to 50 km updip from there rotate significantly, suggesting previously-unrecognized transient slow slip occurs on the plate interface updip. We infer that fluid migrates from slab to interface, promoting episodes of slow slip, which break mineral seals, letting fluid migrate 10’s of km further updip along the interface where it promotes transient slow slips. The proposed methodology, based primarily on inslab seismicity, may help monitor plate boundary conditions and slow slip phenomena, which can signal the beginning stages of megathrust earthquakes.

scholarly journals Structure and lithology of the Japan Trench subduction plate boundary fault

Tectonics ◽  
2015 ◽  
Vol 34 (1) ◽  
pp. 53-69 ◽  
Author(s):  
James D. Kirkpatrick ◽  
Christie D. Rowe ◽  
Kohtaro Ujiie ◽  
J. Casey Moore ◽  
Christine Regalla ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Japan Trench ◽  
Boundary Fault

scholarly journals New constraints on the 1922 Atacama, Chile, earthquake from Historical seismograms

2019 ◽  
Vol 219 (1) ◽  
pp. 645-661 ◽  
Author(s):  
Hiroo Kanamori ◽  
Luis Rivera ◽  
Lingling Ye ◽  
Thorne Lay ◽  
Satoko Murotani ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Source Region ◽  
Plate Boundary ◽  
Spatial Proximity ◽  
Motion Data ◽  
Megathrust Earthquakes ◽  
Great Earthquakes ◽  
Chile Earthquake ◽  
Earthquake Research ◽  
Earthquake Research Institute

SUMMARY We recently found the original Omori seismograms recorded at Hongo, Tokyo, of the 1922 Atacama, Chile, earthquake (MS = 8.3) in the historical seismogram archive of the Earthquake Research Institute (ERI) of the University of Tokyo. These recordings enable a quantitative investigation of long-period seismic radiation from the 1922 earthquake. We document and provide interpretation of these seismograms together with a few other seismograms from Mizusawa, Japan, Uppsala, Sweden, Strasbourg, France, Zi-ka-wei, China and De Bilt, Netherlands. The 1922 event is of significant historical interest concerning the cause of tsunami, discovery of G wave, and study of various seismic phase and first-motion data. Also, because of its spatial proximity to the 1943, 1995 and 2015 great earthquakes in Chile, the 1922 event provides useful information on similarity and variability of great earthquakes on a subduction-zone boundary. The 1922 source region, having previously ruptured in 1796 and 1819, is considered to have significant seismic hazard. The focus of this paper is to document the 1922 seismograms so that they can be used for further seismological studies on global subduction zones. Since the instrument constants of the Omori seismographs were only incompletely documented, we estimate them using the waveforms of the observed records, a calibration pulse recorded on the seismogram and the waveforms of better calibrated Uppsala Wiechert seismograms. Comparison of the Hongo Omori seismograms with those of the 1995 Antofagasta, Chile, earthquake (Mw = 8.0) and the 2015 Illapel, Chile, earthquake (Mw = 8.3) suggests that the 1922 event is similar to the 1995 and 2015 events in mechanism (i.e. on the plate boundary megathrust) and rupture characteristics (i.e. not a tsunami earthquake) with Mw = 8.6 ± 0.25. However, the initial fine scale rupture process varies significantly from event to event. The G1 and G2, and R1 and R2 of the 1922 event are comparable in amplitude, suggesting a bilateral rupture, which is uncommon for large megathrust earthquakes.

On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake

2020 ◽  
Author(s):  
Mario D'Acquisto ◽  
Matthew Herman ◽  
Rob Govers
Keyword(s):  
Subduction Zones ◽  
Relaxation Times ◽  
Underlying Mechanism ◽  
Rupture Zone ◽  
Elastic Response ◽  
Postseismic Deformation ◽  
Plate Interface ◽  
Mechanical Coupling ◽  
Megathrust Earthquakes ◽  
Viscous Relaxation

<div> <p>During and after a large megathrust earthquake, the overriding plate above the rupture zone moves oceanward. Enigmatically, the post-seismic motion of the overriding plate after several recent large earthquakes, further along strike from the rupture zone, was faster in the landward direction than before the event. Previous studies interpreted these changes as the result of increased mechanical coupling along the megathrust interface, transient slab acceleration, or bulk postseismic deformation with elastic bending mentioned as a possible underlying mechanism. Before invoking additional mechanisms, it is important to understand the contribution of postseismic deformation processes that are inherent features of megathrust earthquakes. We thus aim to quantify and analyse the deformation that produces landward motion during afterslip and viscous relaxation. </p> </div><div> <p>We use velocity-driven 3D mechanical finite element models, in which large megathrust earthquakes occur periodically on the finite plate interface. The model geometry is similar to most present-day subduction zones, but does not exactly match any specific subduction zone. </p> </div><div> <p>The results show increased post-seismic landward motion at (trench-parallel) distances greater than 450 km from the middle of the ruptured asperity. Similar patterns of landward motion are generated by viscous relaxation in the mantle wedge and by deep afterslip on the shear zone downdip of the brittle megathrust interface. Landward displacement due to postseismic relaxation largely accumulates at exponentially decaying rates until ~6 Maxwell relaxation times after the earthquake. The spatial distribution and magnitude of the velocity changes is broadly consistent with observations related to both the 2010 Maule and the 2011 Tohoku-oki earthquakes.  </p> </div><div> <p>Further model experiments show that patterns of landward motion due to afterslip and to viscous relaxation are insensitive to the locking pattern of the megathrust. However, the locking distribution does affect the magnitudes of the displacements and velocities. Results show that the increased landward displacement due to postseismic deformation scales directly proportionally to seismic moment. </p> </div><div> <p>We conclude that the landward motion results from in-plane horizontal bending of the overriding plate and mantle. This bending is an elastic response to oceanward tractions near the base of the plate around the ruptured asperity, causing extension locally and compression further away along-trench. This elastic in-plate bending consistently contributes to earthquake-associated changes in surface velocities for the biggest megathrust earthquakes, producing landward motion along strike from the rupture zone.</p> </div>

Tsunamigenic potential of the shallow subduction plate boundary inferred from slow seismic slip

2012 ◽  
Vol 5 (6) ◽  
pp. 414-418 ◽  
Author(s):  
Hiroko Sugioka ◽  
Taro Okamoto ◽  
Takeshi Nakamura ◽  
Yasushi Ishihara ◽  
Aki Ito ◽  
...  
Keyword(s):  
Plate Boundary ◽  
Seismic Slip ◽  
Shallow Subduction
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