Characteristics of high-frequency attenuation in the Dead Sea Basin

Abstract

In this study, we derive the characteristics of high-frequency attenuation and excitation of ground motion for the Dead Sea Basin (DSB) area by regressing the peak amplitudes of narrowband-filtered velocity seismograms measured around the shear wave arrivals. We analyzed about 2000 seismograms from 43 local earthquakes in the magnitude range of MW = 0.9–4.5 that occurred in and around the DSB. The regional crustal attenuation is modeled with a frequency-independent piece-wise continuous linear geometrical spreading function and a frequency-dependent quality parameter Q. Our analysis exhibits that S wave attenuation in the DSB has irregular behavior with the effects of arrivals of supercritical reflections. For distances r ≤ 20 km, the geometrical spreading is 1/r; for distances r ≥ 40 km, the geometric attenuation is r−0.4; and for distances 20 < r <40 km, it is r−0.5. The quality parameter Q is modeled as Q = 68f0.5. The excitation is modeled using the proposed propagation model, increasing stress drop and a high-frequency roll-off parameter κ = 0.03 s. To model the theoretical excitation, we use stress drop values ∆σ = 3 ΜPa, ∆σ = 4 ΜPa, ∆σ = 8 ΜPa, and ∆σ = 9 MPa for earthquakes of MW = 3, MW = 3.3, MW = 4, and MW = 4.5 and site amplification factor of 3. Applying the extended coda normalization method to earthquakes in the DSB area provides quality factors for S and P waves of Qs =80f0.81 and QP = 41f0.84 and QS/QP ratio varying in the range of 1.7–2.9. Anisotropy of seismic wave attenuation in the DSB area is observed. The main direction of anisotropy N20° (110°) is determined based on the model of two orthogonal components producing maximum separation of the attenuation function values.