Determination of source parameters for local and regional earthquakes in Israel
G. Ataeva, A. Shapira & A. Hofstetter
Journal of Seismology ISSN 1383-4649 J Seismol DOI 10.1007/s10950-014-9472-x
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Author's personal copy J Seismol DOI 10.1007/s10950-014-9472-x
ORIGINAL ARTICLE
Determination of source parameters for local and regional earthquakes in Israel G. Ataeva & A. Shapira & A. Hofstetter
Received: 13 April 2014 / Accepted: 19 November 2014 # Springer Science+Business Media Dordrecht 2014
Abstract 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/Lg-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, Re0.0042R and R0.8333e0.00365R for the lowfrequency spectral amplitudes and f0 =f′0e0.00043R and f0 =f′0e0.00044R for the corner frequency at the source, f0, and observed at the station, f′0, 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, MW; 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 G. Ataeva : A. Hofstetter (*) Geophysical Institute of Israel, Lod, Israel e-mail:
[email protected] A. Shapira National Steering Committee for Earthquake Preparedness, Jerusalem, Israel
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 MW 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. Keywords Seismic moment . Spectra . Earthquakes . Magnitude
1 Introduction Seismologists consider the seismic moment M0 and moment magnitude MW (i.e., Kanamori 1977; Hanks and Kanamori 1979; Hanks and Boore 1984) as reliable measures of earthquake size that represents the total deformation at the source and correlates with the seismic energy release. The earthquake source parameters have been widely used for computing scaling laws applicable for seismic hazard assessments (Hanks and Wyss 1972; Thatcher and Hanks 1973; Rebollar 1985; Shapira and Hofstetter 1993; Baumbach and Bormann 1999, 2012; Tan and Helmberger 2007; Tusa and Gresta 2008; Tusa et al. 2012). Therefore, defining the seismic moment M0 and other source parameters and developing a reliable relationship between them and magnitude are of fundamental importance.
Author's personal copy J Seismol
In this study, we use earthquakes that occurred along the Dead Sea Fault and in the Eastern Mediterranean region (Fig. 1). The Dead Sea Fault, which is about 1200 km long, connects the Taurus-Zagros compressional front in the north to the extensional zone of the Red Sea in the south, accommodating the left-lateral motion between the Sinai subplate and the Arabian plate (several out of many, van Eck and Hofstetter 1990, Salamon et al. 1996, 2003; Ben-Avraham et al. 2008; Garfunkel 2013; and references therein). The Dead Sea Fault and the Eastern Mediterranean region are seismically active with several strong earthquakes, based on historical accounts and instrumental records. The earthquake on 11 July 1927, M 6.2, occurred in the northern part of the Dead Sea basin causing 285 deaths, 940 wounded, and extensive damage in many towns and villages on both sides of the Dead Sea Transform (Ben-Menahem et al. 1976; Shapira et al. 1992; Avni 1998). Several other widely felt earthquakes occurred along the Dead Sea Fault in 1903, 1928, 1956, 1970, 1979, 1995, and 2004, with magnitudes M∼5.0–7.2, causing no or minor damage (i.e., Ben-Menahem et al. 1976; Arieh et al. 1982; Amiran et al. 1994; Salamon et al. 1996; Klinger et al. 1999; Ken-Tor et al. 2001; Hofstetter et al. 2003, 2008; Migowski et al. 2004; AlTarazi et al. 2006; Shamir et al. 2006). The use of P-wave data can be of particular interest when the S-wave data are clipped or when trying to estimate magnitudes in real time. Hanks and Wyss (1972) and Baumbach and Bormann (1999, 2012) demonstrated the use of P-wave spectrum for estimation of seismic moment M0, corner frequency f0, and source radius r. Watanabe et al. (1996) investigated the source characteristics from P and S waves for earthquakes with magnitudes ranging from 3.3 to 6.0 and confirmed that the seismic moments determined are consistent. Ottemoller and Havskov (2003) presented good results of the method to automatically determine the moment magnitude from the source spectra of P and S or Lg waves of local and regional earthquakes. Tusa and Gresta (2008) and Tusa et al. (2012) had used displacement spectra of P wave to estimate source parameters for events of magnitude less than 4.6 and for microearthquakes (ML
