open access

https://hdl.handle.net/2115/57958

High resolutionQ−1estimation based on extension of coda normalization method and its application toP-wave attenuation structure in the aftershock area of the 2005 West Off Fukuoka Prefecture Earthquake (M7.0)

英語

Wave scattering and diffraction

2009-11

Oxford University Press

Geophysical Journal International

179(2)

1039-1054

We developed a method for estimating the seismic-wave attenuation (1/Q) in a seismically active region such as an aftershock area. To estimate the attenuation factor between two adjacent hypocentres, we employed two seismograms recorded at a station and calculate the ratio between two power spectra of direct waves normalized by those in the coda for both the events. The coda normalization of the spectrum and the ratio between the two events minimize the possible influences of sources, sites, instruments and attenuation from the station to the hypocentral area. The 1/Q value can be estimated from the variation of the ratios of event pairs calculated at many stations for various traveltime differences between the even pairs. This method involves double-difference (DD) estimation from the logarithmic power spectra for estimating the 1/Q structure, employing a concept similar to the recently developed ‘DD tomography’ for velocity structures. We applied this method to the aftershock area of the 2005 West Off Fukuoka Prefecture Earthquake (M7.0) in order to investigate the 1/Q structure of P waves. By using the spectra of the seismograms of 1781 events recorded at a dense seismic network deployed around the aftershock area, we obtained the spatial variation of the 1/Q value in this region. The 1/Q distribution thereby obtained suggests that there exists a high-attenuation region around the edge of the main shock fault, which could correspond to the segment boundary between the earthquake fault and the adjacent faults. In addition, we found that the initiation points of the main shock and aftershocks were located in a low-attenuation region.

学術雑誌論文

Version of Record

This article has been accepted for publication in Geophysical Journal International ©:The Authors 2009 Published by Oxford University Press on behalf of The Royal Astronomical Society All rights reserved.

0956-540X

1365-246X