Separation of scattering and intrinsic attenuation for the Kanto-Tokai region, Japan, using measurements ofS-wave energy versus hypocentral distance

Abstract

S U M M A R YDetermining the relative amount of attenuation caused by scattering and intrinsic absorption is important to the understanding of wave propagation and attenuation in the heterogeneous lithosphere. A recently developed model based on radiative transfer theory provides a method for quantifying the ratio of scattering loss to total attenuation, which is called seismic albedo. The basic assumption of this model is that the medium is composed of a uniform distribution of isotropic scatterers. The method is based on a theoretical result showing that the variation with sourcereceiver distance in the seismic energy integrated over time is directly related to albedo and total attenuation, Q;'. We introduce an improvement in the previously used method which results in more reliable estimates of seismic albedo and Q;', which can be used to calculate the losses due to scattering and intrinsic absorption. We call our new method multiple lapse-time window analysis. The improvement is based on the observation that the relationship between integrated energy and distance is strongly dependent on the time duration over which energy is integrated. We show that parameters describing media attenuation can be estimated from measurements of two ratios from the integrated energy versus distance relations compiled using two time windows for integration. One ratio is the energy integrated from 0 to 15 s after the S-wave arrival observed at 50 km source-receiver distance divided by the energy in the same time interval observed at 150 km distance. The second ratio is the energy integrated from 0 to 15 s observed at 150 km divided by that from 30 to 100 s observed at the same source-receiver distance.Integrated energy calculated for many source-receiver pairs may be corrected for relative site amplification and relative source amplitude determined using the coda-wave method. These corrections allow us to use data from many sourcereceiver pairs to find a well-constrained energy versus distance relation. Site amplifications relative to a reference station are calculated for three frequency bands by determining the ratio of the spectral amplitude in each band at one station for a 10s time window to that at the reference station in the same 10s time window. Ratios are calculated for many 10s time windows for each of 10 events. For each station, we found little scatter in the ratios among the windows and events used. The average of all the ratios obtained for each station was taken to be the site amplification relative to the reference station.We applied the multiple lapse-time window analysis method and source-site correction procedures to data from the Kanto-Tokai region of Japan and found that intrinsic attenuation Q;' is larger than scattering attenuation Q;' over three frequency bands; 1-2, 2-4, and 4-8Hz. We found that estimates of coda-wave attenuation Q,' made using the coda-wave decay method, are similar to the 787 788 M. Fehler et al intrinsic attenuation Q;' for the frequency range of 2-8Hz. We were unable to fit data for ...

Multiple scattering and mode conversion revealed by an active seismic experiment at Asama volcano, Japan

“…We also demonstrated that we could estimate the scattering coefficients and the intrinsic absorption separately by using the different time windows in a manner slightly different from the multiple lapse time analysis [e.g., Fehler et al, 1992;Hoshiba, 1991]. The estimated isotropic scattering coefficient in the 8-16 Hz band for P-to-P scattering is 0.24 km −1 and those of S-to-S and P-to-S scattering are 3 and 2.8 times larger than that of P-to-P scattering.…”

Temporal variations of coda Q: An attenuation-coefficient view

“…Scattering certainly represents the principal mechanism of seismic coda generation, and numerous efforts have been made for developing scattering-based coda models (Aki, 1969;Aki and Chouet, 1975;Dainty and Toksöz, 1977;Aki, 1980;Roecker et al, 1982;Aki, 1991;Hoshiba et al, 1991;Zeng et al, 1991;Fehler et al, 1992;Hoshiba, 1993;Paasschens, 1997;Chouet, 2003;Carcolé and Ugalde, 2008). However, in the author's opinion, model-based approaches will unlikely reach the accuracy required for unambiguous inversion for the in situ Q, and even more so -of its frequency dependence.…”

“…The apparent Q c is conventionally inverted for the in situ elastic (scattering, Q s ) and anelastic (intrinsic, Q i ) quality factors, which are associated with the properties of velocity/density fluctuations and anelastic energy dissipation, respectively (e.g., Jin and Aki, 1986;Aki, 1991). This inversion is usually based on the single-scattering (Aki and Chouet, 1975) or multiple-scattering models (e.g., Dainty and Toksöz, 1977;Fehler et al, 1992). All of these models use a number of strong assumptions and simplifications, such as the uniform or smooth velocity background, perfectly-known geometrical spreading (GS), absence of free-surface effects and layered reflectivity, and isotropic and often uniformly-distributed scattering.…”

Direct simulation Monte Carlo method with a focal mechanism algorithm

“…The main cause of this scatter is known to be the different radiation pattern of each earthquake (e.g. Fehler et al, 1992). The regional alteration of local structure has also been thought of as one of the causes of the observational scatter (e.g.…”

“…The most widely used approach to the separation into Q i -1 and Q s -1 is multiple lapse time window analysis (MLTWA), introduced almost simultaneously by Hoshiba et al (1991) and Fehler et al (1992). Based on the observations that the early portion of a seismogram is dominated by the direct S-wave whose amplitude is reduced by Q t -1 , whereas the S-coda is composed entirely by scattered S-waves whose amplitude is reduced by Q i , MLTWA simulates the integral of the observed energy from multiple earthquakes in three successive time windows.…”