Data & Methods

The dataset consists of 158 earthquakes recorded at 16 broadband (20 sps) three-component stations of the BDSN between 1992 and 2004. The wide distribution of data parameters allows for sensitivity testing. We calculate $Q_{Lg}$ by fitting the power-law model, $Q_0f^\eta$ using five different methods. The first two methods use the seismic coda to correct for the source effect. The last three methods use a spectral ratio technique to correct for source, and possibly site effects.

The coda normalization (CN) method uses the local shear-wave coda as a proxy for the source and site effects, thus amplitude ratios remove these two effects from the S-wave spectrum ( Aki, 1980; Yoshimoto et al., 1993). The coda-source normalization (CS) method uses the stable, coda-derived source spectra to isolate the path attenuation component of the $Lg$ spectrum ( Walter et al., 2007). The two-station (TS) method takes the ratio of $Lg$ recorded at two different stations along the same narrow path from the same event in order to remove the common source term (e.g., Chavez and Priestley, 1986; Xie and Mitchell, 1990). The reverse two-station (RTS) method uses two TS setups, where a source is on either side of the station pair in a narrow azimuthal window ( Chun et al., 1987). The two ratios are combined to remove the common source and site terms. The source-pair/receiver-pair (SPRP) method is the RTS method with a relaxation on the narrow azimuthal window requirement ( Shih et al., 1994).