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)

A set of 43 microearthquakes of the Granada Basin with magnitude duration MD 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 5.45×1017 dyne cm to 1.53×1020 dyne cm. The source radii are between 0.13 and 0.39 km. The seismic energy ranges from 7.17×103 J to 1.13×108 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.