Structural controls on the Mw 9.0 2011 Offshore-Tohoku earthquake

Date

2011

Authors

Kennett, Brian
Gorbatov, Alexei
Kiser, E.

Journal Title

Journal ISSN

Volume Title

Publisher

Elsevier

Abstract

Joint seismic tomography exploiting P and S wave arrivals conducted before the 2011 Offshore Tohoku earthquake reveals an area comparable to the faulting surface for the 2011 March 11 event with different properties from other areas along the shallow part of the subduction zone. The differences are revealed by using a measure R of the relative variations in shear wavespeed and bulk-sound speed. Within the faulting area there are patches on the subduction zone with slightly reduced S wavespeed, and thus negative R, that appear to separate portions of the rupture with very different character. On the down-dip side there is strong short-period radiation, whilst the largest slip occurs up-dip with most energy release at longer periods. Segmentation of the slip process can be imaged by back projection of seismograms from the US Array; the areas of greatest energy release at short periods lie down-dip from the negative R anomalies. The main seismic moment release from broad-band seismograms lies on the updip side of the same anomalies. The structural variations on the subduction zone thus separate two regions with fundamental differences in the rupture process, stronger long-period radiation up-dip and stronger short-period radiation down-dip. These variations are likely to reflect features brought into the subduction zone, which may have acted as asperities that allowed this event to build up 30-40. m of strain in the near trench zone, making it much bigger than expected. Thus minor changes in the character of the subducted plate can have a significant influence on the behaviour of a great earthquake.

Description

Keywords

Keywords: Back projection; Broad bands; Distribution; Earthquake slip; Energy release; Great earthquake; Japan; Negative R; P- and S-waves; Rupture process; Seismic tomography; Seismic-moment release; Short periods; Structural control; Structural variations; Subduc Distribution; Earthquake slip; Earthquakes; Japan; Joint seismic tomography

Citation

Source

Earth and Planetary Science Letters

Type

Journal article

Book Title

Entity type

Access Statement

License Rights

DOI

10.1016/j.epsl.2011.08.039

Restricted until

2037-12-31