Abstract

We quantify the attenuation of ground motion with distance in southern Spain using 6052 velocity recordings from 1107 local and regional earthquakes registered by the Andalusian vertical-component short-period network. Epicentral distances and magnitudes range from 3 to 500 km and from 1.0 to 5.1, respectively. The observed peak velocity and the root mean square (rms). Fourier velocity amplitudes with distance are parameterized by excitation, distance, and site terms for a set of frequencies ranging from 1 to 12 Hz. We obtain these terms by performing an iterative-damped least-squares regression. From the excitation term, we extract its scaling law with magnitude by using Brune’s source model. The distance terms are fitted by analytic functions that depend on geometrical spreading coefficients and a frequency-dependent attenuation parameter. Apart from the analysis of the entire data set, we perform two separate analyses of two subdata sets: offshore earthquakes (Alboran data set) and inland earthquakes (Betic data set). These data sets have differences in their probed earth structures, showing distance terms clearly distinct, with higher attenuation in the Alboran area (Q0∼100) compared to the Betic area (Q0∼200). Random vibration theory proved to be a suitable tool to simulate observed peak amplitudes from the obtained spectral scaling laws and signal durations.

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