HR: 1340h
AN: S13B-0192    [Abstracts]
TI: What excites deep low-frequency earthquakes?
AU: * Miyazawa, M
EM: linen@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AU: Mori, J J
EM: mori@eqh.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: We observed that large surface waves from the 2004 Sumatra-Andaman earthquake (M9.2) triggered deep low-frequency (DLF) tremors beneath Shikoku, the Kii peninsula and the Tokai regions in western Japan, where Philippine Sea plate subducts beneath Eurasian plate. Since the source distances are more than about 5000 km, this is a clear example of dynamic triggering. We investigate the relationship between the surface waves and high-frequency components (4-16Hz) of the observed records. During the arrivals of the surface waves, pulse-like features were observed in the high-frequency waveforms, which are identified as DLF tremors. To investigate what phase has triggered the tremor, we determined the hypocenters of the triggered events by use of a modified envelope method. Accurate locations of the triggered earthquakes are important so that we can compare the strain changes in the immediate source area of the triggered events. The tremors are located at depths of about 30 km, where DLF events have been observed. Also, the relationship between the amplitudes of Rayleigh waves and the event magnitudes shows a good correlation. We found the triggering can be correlated with both the phase and amplitude of the arriving Rayleigh waves, but could not find significant excitation during arrivals of S-, SS-, and Love waves. This observation indicates that the triggering is due to volumetric strain changes, and the triggering amplitudes are larger than 10^-9 in the source region.
DE: 7215 Earthquake source observations (1240)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7255 Surface waves and free oscillations
SC: Seismology [S]
MN: Fall Meeting 2005