Spectral characteristics of P-and S-wave quarry blasts in Aswan region, South Egypt

Abstract

The Aswan broadband seismic network, consisting of high-sensitivity sensors with dense stations coverage, provided the opportunity to study and analysed the spectral properties of the quarry blasts in the Aswan region, southern Egypt. We comprehensively analysed 757 digital seismograms from 128 quarry blasts with local magnitude (ML) between 1.7 and 3.1 during time span from 2010 to 2021. A Generalized Inversion Technique (GIT) constrained by a reference site is applied to isolate the attenuation, site responses of the seismic stations, and the source spectra from the observed seismograms by means of iterative least square analysis. The displacement source spectra for P-and S-waves are computed for all quarry blasts based on the theoretical omega-square seismic source model (Brune's model). The spectral analysis demonstrated that both P-and S-waves displacement source spectra of the quarry blasts used in this study have low corner frequency values. The corner frequency of the quarry blasts used in this study ranged from 1.0 to 2.6 Hz and from 1.5 to 4.6 Hz for P-and S-waves, respectively. The P-and S-wave corner frequency ratio (fCP/fCS) is computed for each event. We obtained that the fCP/fCS ratio is less than 1.0 Hz for 106 events (94%) and equal to 1.0 Hz and less than 1.2 Hz for only six selected data events (6%). The analysis indicates that the observed displacement source spectra show discrepancies with the omega-square type spectrum, and they generally have a steep fall off at high frequencies. We also found that the selected quarry blasts have a narrow seismic moment range (from 2.03E+11 to 1.35E+12 Nm), and stress drop values range from 0.001 to 0.023 MPa. The distribution of the used quarry blast stress drop demonstrated a self-similar character.