The effect of a compliant accretionary wedge on earthquake rupture and tsunamigenesis

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http://meetingorganizer.copernicus.org/EGU2016/EGU2016-2042.pdf
Author(s): Lotto, Gabriel; Jeppson, Tamara; Dunham, Eric; Tobin, Harold
Author Affiliation(s): Primary:
Stanford University, Palo Alto, CA, United States
Other:
University of Wisconsin-Madison, United States
Volume Title: European Geosciences Union general assembly 2016
Source: Geophysical Research Abstracts, Vol.18; European Geosciences Union general assembly 2016, Vienna, Austria, April 17-22, 2016. Publisher: Copernicus GmbH on behalf of the European Geosciences Union (EGU), Katlenburg-Lindau, Germany. ISSN: 1029-7006
Note: In English
Summary: The 11 March 2011 Tohoku megathrust earthquake ruptured through the shallowest part of the subduction zone boundary, resulting in tens of meters of displacement at the seafloor. This extreme shallow slip generated a devastating tsunami. The elastic properties of off-fault materials have an important role in determining slip along a fault. Laboratory ultrasonic velocity measurements performed on samples of rock obtained from the area surrounding the Tohoku earthquake principal fault zone during the Japan Trench Fast Drilling Project (JFAST) have shown that shallow off-fault materials are extremely compliant--P-wave velocities of 2.0-2.4 km/s, S-wave velocities of 0.7-1.0 km/s, and shear moduli ranging from 1.0-2.2 GPa. Seismic imaging around the JFAST drill site corroborates the presence of a compliant, low-velocity frontal prism at the toe of the hanging wall. This compliant wedge is likely a fairly robust feature across the horizontal extent of the Japan Trench and may have contributed to the large amount of displacement recorded. In order to investigate the impact of compliant off fault materials on earthquake rupture and tsunamigenesis, we employ a 2-D finite difference method that models the full seismic and tsunami wavefield associated with dynamic rupture on a dipping fault in a heterogeneous medium. Our numerical method rigorously couples the elastodynamic response of the solid Earth to that of a compressible ocean in the presence of gravity. Idealized models of subduction zone earthquakes show that the presence of a compliant wedge leads to increased slip, greater seafloor displacement, and a larger tsunami. However, preliminary results for a representative Tohoku geometry were not so simple; the compliant wedge enhanced slip and seafloor deformation but only in a localized zone, and tsunami height was not significantly affected. This surprising result indicates that the details of geometry and material structure we observe in real subduction zones are very important to tsunami models. [Copyright Author(s) 2016. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 19 Geophysics, Seismology; 22 Environmental Geology; Accretionary wedges; Asia; Digital simulation; Earthquakes; Far East; Finite difference analysis; Genesis; Geologic hazards; Great earthquakes; Honshu; Integrated Ocean Drilling Program; Japan; Japan Trench; Japan Trench Fast Drilling Project; Megathrust earthquakes; Natural hazards; North Pacific; Northwest Pacific; Numerical models; Pacific Ocean; Rupture; Tohoku-Oki earthquake 2011; Tsunamis; West Pacific
Coordinates: N375619 N375620 E1435449 E1435447
Record ID: 2019065083
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from European Geosciences Union, Munich, Germany