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TitleStatic stress drop in the Mw 9 Tohoku-oki earthquake: heterogeneous distribution and low average value
AuthorBrown, L; Wang, KORCID logo; Sun, T
SourceGeophysical Research Letters vol. 42, issue 24, 2015 p. 1-6, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20150336
Mediapaper; on-line; digital
File formatpdf
AreaTohoku-Oki; Japan
Lat/Long WENS 142.5000 144.0000 38.7500 38.5000
Subjectsgeophysics; mathematical and computational geology; tectonics; faults, thrust; seismic interpretations; seismic models; seismic data; rock stress analyses; stress analyses; stress patterns; stress distribution; earthquake studies; earthquake mechanisms; earthquakes; stress drop
Illustrationsseismic maps; seismic images; location maps; equations; graphs; structural diagrams
ProgramPublic Safety Geoscience Western Canada Geohazards Project
Released2015 12 23
AbstractStatic stress drop distribution and its average value over the rupture area contain important information on the mechanics of large earthquakes. Here we derive static stress drop distributions from 40 published rupture models for the 2011 Mw 9 Tohoku-oki earthquake that are based on various multidisciplinary observations. Average stress drop value over the fault area encompassed by the 5 m coseismic slip contour is not unusually large for each rupture model; the mean for the 40 models is 2.3 ? 1.3 MPa, assuming a uniform rigidity 40 GPa. The value for the entire rupture zone and with a more realistic rigidity structure will be even lower. In the majority of the models, local stress drop in parts of the rupture zone well exceeds 20 MPa. The heterogeneous stress change distribution, with large stress drop being accompanied by large stress increase, leads to the small average for the earthquake.
Summary(Plain Language Summary, not published)
Stress drop is a measure of how much tectonic stress is relieved by an earthquake and therefore is an important parameter for seismic hazard analysis. This paper uses 40 published rupture models for the 2011 magnitude 9 Tohoku-oki earthquake in Japan to constrain its stress drop. The main finding is that the stress drop averaged over the rupture zone is not unusually large because of the heterogeneity of the rupture. A mixture of areas of large stress drop and large stress increase led to the relatively low average value. This work is by far the most comprehensive stress drop study for a single large earthquake, and the results have important implication to understanding rupture mechanics.

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