Regional waveform inversion of 2004 February 11 and 2007 February 09 Dead Sea earthquakes

Abstract

SUMMARY Two felt moderate size earthquakes with local magnitudes 5.2 on 2004 February 11 and 4.4 on 2007 February 09 occurred to the east of the Dead Sea and along the northern part of the Arava/Araba fault (ARF), respectively. Being well recorded by the national seismic networks operating on the Dead Sea region, they offer a good opportunity to update the crustal model, revealing the tectonic process and present-day stress field on the Dead Sea region. The observed group velocity dispersion of Rayleigh and Love waves picked from the broad-band records for the 2004 and 2007 main shocks are used to update the Jordan Seismological Observatory model, which shows a good match between the observed and theoretical dispersion. Our updated model shows small traveltime residuals during our location process and yields a high variance reduction for our regional waveform inversion. The earthquake hypocentre, determined from the observed P- and S-wave traveltime data, and regional waveform inversion indicate a source depth of ∼14 and ∼12 km for the 2004 and 2007 main shocks, respectively. Focal mechanism obtained from both first motion polarities of local-regional observations and moment tensor inversion of regional observations of 2004 earthquake reveal a mainly normal faulting, with minor strike-slip component, along WNW–ESE fault, whose orientation is nearly consistent with the transverse Zarqa Ma'in fault. However, the focal mechanism of 2007 main shock shows left-lateral, strike-slip faulting along a near-vertical, near-NNE–SSW striking fault plane whose orientation is in good agreement with the surface expression of the observed northern ARF. The focal mechanism for a felt foreshock of 2007 earthquake indicates a similar left-lateral strike-slip fault with a slight normal component. Moment tensors estimated from regional waveforms indicate predominantly double-couple mechanisms for the three studied events. These results can be used to calibrate ground motions, evaluate 3-D velocity models for simulation of large scenario earthquakes and seismic risk assessment along the Dead Sea Fault.