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)

Abstract

S U M M A R YWe 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.

QP structure of the accretionary wedge in the Kumano Basin, Nankai Trough, Japan, revealed by long-offset walk-away VSP

“…The spatial distribution of Q in the crust has been drawing attention from seismologists, and a number of studies employing local earthquake tomography techniques to obtain the 3-D distribution of Q have been conducted. 3-D Q tomography is an effective tool for inferring the underground distribution of fracture density and the roles of fluids in the crust (e.g., Rietbrock 2001;Reyners et al 2007;Bennington et al 2008). Matsumoto et al (2009 reported that a high Q P region corresponds to a large-slip fault patch where a large inland shallow earthquake occurred (the 2005 West off-Fukuoka earthquake, Mw 7.0), suggesting a correlation between the frictional strength along the fault and the seismic attenuation of the host rocks.…”

“…In the inversion, we applied a nonnegative least squares method (Lawson and Hanson 1995) because Q −1 P,i cannot take negative values. Note that the first and second integrals (summations) of the observation Equation 5 are evaluated along the ray path from the source at x and along that from the source at x 0 , respectively.…”

The 3D Attenuation Structure of Deception Island (Antarctica)

“…In these media, we may retrieve P-and S-wave attenuation parameters independently of the site and instrumental transfer functions by using the coda normalization method (Aki and Richards 1980;Yoshimoto et al 1993;Sato et al 2012). In recent years, this method has been applied to S-wave attenuation tomography at local scale, exploiting the strong scattering effects produced by strong heterogeneity in volcanic regions (Del Pezzo et al 2006;Matsumoto et al 2009;Sato et al 2012;De Siena et al 2010). The coda normalization method is based on the equation that correlates the ratio between the S-wave direct energy and the coda wave energy to the spatial distribution of the inverse total quality factors calculated along the source-station ray-path (Del Pezzo et al 2006;De Siena et al 2009.…”

Seismic attenuation tomography of the source zone of the 2016 Kumamoto earthquake (M 7.3)

“…Seismic velocity tomography has proven to be a powerful technique to investigate the 3-D crustal and upper mantle structure and seismotectonics [e.g., Zhao et al, 1996;Mishra and Zhao, 2003;Kato et al, 2005;Wang and Zhao, 2006;Wang et al, 2016]. Compared to velocity tomography, seismic attenuation tomography has rarely been applied to large earthquake areas [e.g., Rietbrock, 2001;Matsumoto et al, 2009]. Because seismic attenuation is more sensitive than seismic velocity to some important material properties, such as Journal of Geophysical Research: Solid Earth 10.1002/2016JB013704 temperature, grain size, and water content Toksöz et al, 1979;Jackson et al, 2002;Faul and Jackson, 2005;Aizawa et al, 2008], seismic attenuation tomography is suitable for investigating very heterogeneous regions such as subduction zones [e.g., Eberhart-Phillips and Chadwick, 2002;Schurr et al, 2003;Stachnik et al, 2004;Pozgay et al, 2009;Bohm et al, 2013;Nakajima et al, 2013;Liu et al, 2014;Liu and Zhao, 2015;Saita et al, 2015].…”