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Journal: |
Journal of Geophysical Research 2019 No.8
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Title:
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Author:
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Qing-Yu Wang1 , Michel Campillo1, Florent Brenguier1 , Albanne Lecointre1, Tetsuya Takeda2, and Akinori Hashima |
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Adress: |
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Abstract:
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Studies of mechanical responses of the Earth crust to large earthquakes can provide us with
unique insights into the processes of stress buildup and release. As a complement to geodetic methods that
derive crustal strain dynamics from surface observations (e.g., GPS, InSAR), noise-based seismic velocity
monitoring directly probes the mechanical state of the crust, at depth and continuously in time. We
investigate the responses of the crust to the Mw 9.0, 2011 Tohoku-oki earthquake. In addition to the Hi-net
short-period sensors, we use Hi-net tiltmeters as long-period seismometers (8–50 s) to sample the crust
below 5 km in depth. The spatial distribution of the strong velocity decreases at short periods appears to be
limited to the region of strong ground shaking induced by the 2011 Tohoku-oki earthquake, while the
long-period velocity changes correlate well with the modeled static strain induced by viscoelastic
relaxation and afterslip at depth. Amplitudes of coseismic velocity changes decrease with increasing depth.
The temporal evolution of velocity changes in different period bands shows that the maximum drops in the
velocity at long periods are delayed in time with respect to the occurrence of the Tohoku-oki earthquake.
The inversion of seismic velocity changes at depth illustrates how S wave velocities evolve down to 40 km
at a regional scale after a major earthquake. |
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