Determination of near-surface attenuation, with κ parameter, to obtain the seismic moment, stress drop, source dimension and seismic energy for microearthquakes in the Granada Basin (Southern Spain)

Abstract

A set of 43 microearthquakes of the Granada Basin with magnitude duration M D from 1.4 to 3.5, have been spectrally analysed. The digital data used in this study was recorded by two short-period digital seismic network, five permanent stations using Andalusian Seismic Network (Red Sı́smica de Andalucı́a, RSA) and three stations of a portable digital seismic network (Red Sı́smica Portátil, RSP). The displacement spectra for P- and S-waves were analysed with Brune’s [J. Geophys. Res. 75 (1970) 4997; J. Geophys. Res. 76 (1971) 5002] source model and the spectra parameters were determined by Snoke’s model. To correct spectra from path attenuation coda- Q was used. For the spectra correction from near-surface attenuation κ parameter was calculated, obtaining it from acceleration spectra. The values of κ parameter range from 0.01 to 0.04 s for P-waves and from 0.006 to 0.04 s to S-waves. Once the spectra of these attenuation effects was corrected, we obtained the seismic moments that range from 5.45×10 17 dyne cm to 1.53×10 20 dyne cm. The source radii are between 0.13 and 0.39 km. The seismic energy ranges from 7.17×10 3 J to 1.13×10 8 J. The stress drop values were below 4 bars. The scaling relations between seismic moment and stress drop indicated decreasing stress drop with decreasing seismic moment.