HR: 1340h
AN: S23B-0322    [Abstracts]
TI: Non-uniform spatial distribution of the S-coda-wave energy in Japan estimated from the seismograms of local earthquakes
AU: * Yoshimoto, K
EM: k\_yoshi@yokohama-cu.ac.jp
AF: Graduate School of Integrated Science, Yokohama City University, 22-2 Seto, Kanazawa, Yokohama, 236-0027 Japan
AB: Seismic coda waves of local earthquakes had been considered as the multiple scattered waves that distribute uniformly in space at large lapse times. However, the analysis using data from the dense seismic network in northeastern Honshu, Japan had revealed that the coda-wave energy in the forearc is much larger in magnitude than that in the backarc (Yoshimoto et al, 2003). Is such non-uniform spatial distribution of coda-wave energy common and observed in other regions? This study analyzed the spatial distribution of coda-wave energy of 9 local earthquakes (magnitude 4.7-7.1) occurred in Japan. We selected the earthquakes with very few aftershocks to accurately investigate the coda-wave characteristics of the single event. The velocity seismograms recorded by the Hi-net, which is operating by the National Research Institute for Earth Science and Disaster Prevention and consists of about 700 borehole seismometers, were used in our analysis. We calculated the coda-wave energy as the squared sum of the coda-wave amplitudes on horizontal components. In the high-frequency range of 16-32 Hz, the spatial distribution of coda-wave energy shows clear regional variations, except for the random scatter due to the effect of site amplification. The magnitude of coda-wave energy is systematically small in the area where the Quaternary volcanoes exist. The difference in magnitude reaches up to one-hundred times. This tendency is observed in the whole area studied. Our result shows that the S-coda-wave energy does not distribute uniformly in space in the tectonically active region. From the spatial correlation between the Quaternary volcanoes and the high heat flux, it is suggested that the structure of the intrinsic attenuation in the crust and the uppermost mantle characterizes the regional variation in coda-wave energy.
DE: 7200 SEISMOLOGY
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2004 AGU Fall Meeting