Body-wave attenuation near the rupture of the 1887 Sonora, México, earthquake (Mw 7.5)

Abstract

We analized body–waves of local and regional earthquakes recorded on the Seismic Network of Northeastern Sonora, México (RESNES) are used to determine empirical attenuation functions for P and S waves in the interval of 0.4–63 Hz. The epicenters are near to the surface rupture of the May 3, 1887 (M_W 7.5) Bavispe, Sonora earthquake. Seismograms of vertical and horizontal components at of ground motion hypocentral distances of 25 to 150 km were used in a nonparametric model. The reported attenuation curves indicate that the spectral amplitudes decay faster in the first 40 km of the path and show different decay rate at approximately 80 km. We found that in the upper crust the exponential dependence of Q with frequency is the same for P and S waves, namely Q ~ f ^1.1, but Q_S is larger by a factor of 3. In the lower crust Q is more complex, showing a strong frequency dependence below 3 Hz and a weaker frequency dependence above 6 Hz.