Physics
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012georl..3902302r&link_type=abstract
Geophysical Research Letters, Volume 39, Issue 2, CiteID L02302
Physics
Seismology: Earthquake Dynamics (1242), Seismology: Earthquake Source Observations (1240), Seismology: Surface Waves And Free Oscillations
Scientific paper
We study the rupture process of the 2011 Tohoku megathrust by analyzing 384 regional strong-motion records using a novel back-projection method for Rayleigh waves with periods between 13 and 100 s. The proposed approach is based on isolating the signal at the selected period with a continuous wavelet transform, and generating the stack using arrival times predicted from detailed fundamental mode Rayleigh wave group velocity maps. We verify the method by back-projecting synthetic time series representing a point source off the coast of Tohoku, which we generate with a 3D finite difference method and a mesh based on the Japan Integrated Velocity Structure Model. Application of the method to K-NET/KiK-net records of the Mw 9.1 Tohoku earthquake reveals several Rayleigh wave emitters, which we attribute to different stages of rupture. Stage 1 is characterized by slow rupture down-dip from the hypocenter. The onset of stage 2 is marked by energetic Rayleigh waves emitted from the region between the JMA hypocenter and the trench within 60 s after hypocentral time. During stage 3 the rupture propagates bilaterally towards the north and south at rupture velocities between 3 and 3.5 km · s-1, reaching Iwate-oki 65 s and Ibaraki-oki 105 s after nucleation. In contrast to short-period back-projections from teleseismic P-waves, which place radiation sources below the Honshu coastline, Rayleigh wave emitters identified from our long-period back-projection are located 50-100 km west of the trench. This result supports the interpretation of frequency-dependent seismic wave radiation as suggested in previous studies.
Koketsu Kazuki
Miyake Hiroe
Roten Daniel
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