Attenuation in western Nevada: Preliminary results from earthquake and explosion sources

Abstract

We present preliminary results from a study of the attenuation of regional seismic waves at frequencies between 1 and 15 Hz and distances up to 250 km in Western Nevada. Following the methods of Anderson and Hough (1984) and Hough et al. (1988), we parameterize the asymptote of the high frequency acceleration spectrum by a two‐parameter model. We relate the model parameters to a two‐layer model for Qi and Qd, the frequency‐independent and the frequency dependent components of the quality factor. We comparing our results to previously published Q studies in the Basin and Range and find that our estimate of total Q, Qt, in the shallow crust is consistent with shear wave Q at close distances as determined by Chavez and Priestley (1985). For depths greater than 5 km, we obtain a Qt which is consistent with previous estimates of coda Q (Singh and Herrmann, 1983) and LgQ (Chavez and Priestley, 1986), suggesting that both coda Q and LgQ are insensitive to near‐surface contributions to attenuation.In addition to our attenuation results, we compare the high frequency content of explosions with that of earthquakes. Our results from S waves are similar to results for Pg waves by Chael et al. (1987), and Chael (1988), who find that the Pg wave spectra from explosions are depleted in high frequency energy with respect to earthquake spectra. Taylor et al. (1988) look at spectral energy at 1–2 Hz compared to energy at 6–8 Hz for earthquakes and explosions and find, especially for Lg waves, relative depletion of the higher frequencies for explosion sources. This result is also consistent with the results from this study.