Depth-dependent Postseismic Response of the Mw 9.0, 2011 Tohoku-oki Earthquake from Seismic Noise-based Monitoring.
Abstract
Studying the mechanical response of the crust to large earthquakes provides unique insight into the processes of deformation in preparation for future earthquakes. Noise-based seismic velocity monitoring can directly probe the mechanical state of the crust at depth continuously in time. In this work, we study the response of the crust to the Mw 9.0, 2011 Tohoku-oki earthquake. In addition to the Hi-net short period sensors, we employ here for the first time for the noise-based monitoring the very dense network of Hi-net tiltmeters as long period (8 - 50 s) seismometers to sample the crust below 5 km depth. Spatial distribution of strong velocity decreases at short periods can be limited to strong ground shaking induced by the 2011 Tohoku-oki earthquake, while the long period velocity changes correlate well with modelled static strain induced by viscoelastic relaxation and afterslip at depth. This observation indicates that the variations at depth are not a spurious effect of changes in the shallow layers. The amplitudes of coseismic velocity changes diminish with increasing depth. The temporal evolution of velocity changes at different depths shows that the maximum drops of velocity at depth are delayed with respect to the date of the earthquake. This delay could find its origin in both the visco-elastic response of the crust to large strain changes or a complex response of crustal seismic velocities to transient deformation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S12A..08W
- Keywords:
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- 7203 Body waves;
- SEISMOLOGYDE: 7255 Surface waves and free oscillations;
- SEISMOLOGYDE: 7260 Theory;
- SEISMOLOGYDE: 7270 Tomography;
- SEISMOLOGY