Determination of source parameters for local and regional earthquakes in Israel

We have investigated earthquake source parameters and seismic moment-magnitude relations from 103 regional and local earthquakes with moment magnitude 2.6 to 7.2, which occurred in a distance range from 4.5 to 550 km during 1995–2012 by applying Brune’s seismic source model (J Geophys Res 75:4997–5009, 1970, J Geophys Res 76:5002, 1971) for P- and S/L_g-wave displacement spectra. Considering P- and S-wave data separately, we first studied the empirical dependence of the Fourier spectral amplitudes Ω due to the geometrical spreading and the inelastic attenuation and of the corner frequency, f₀, with the epicentral distances, R. We found the distance correction parameters, Re^0.0042R and R^0.8333e^0.00365R for the low-frequency spectral amplitudes and f₀ = f₀ ^′e^0.00043R and f₀ = f₀ ^′e^0.00044R for the corner frequency at the source, f₀, and observed at the station, f₀ ^′, from P-wave and S-wave spectra, respectively. Applying the distance correction procedure, we determined the source displacement spectrum of P and S waves for each earthquake to estimate the seismic moment, M₀; the moment magnitude, M_W; the source radius, r; and the stress drop, Δσ. The seismic moments range from 1.06 × 10¹³ to 7.67 × 10¹⁹ N m, and their corresponding moment magnitudes are in the range of 2.6–7.2. Values of stress drop Δσ vary from 0.1 to 44 MPa. It was found that the stress drop increases with the increasing seismic moment in the range of 10¹³–10¹⁶ N m and possibly becomes constant at higher magnitudes, reaching a maximum value of about 40–45 MPa. We demonstrate that the values of the M₀ and M_W estimated from P-wave and S-wave analysis are consistent and confirmed by the results of waveform inversions, i.e., centroid moment tensor (CMT) solution.