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Characteristics of high-frequency attenuation in the Dead Sea Basin

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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… Click to show full 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 M W  = 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  = 68 f 0.5 . 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 M W  = 3, M W  = 3.3, M W  = 4, and M W  = 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 Q s =80 f 0.81 and Q P  = 41 f 0.84 and Q S / Q P 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.

Keywords: high frequency; frequency; dead sea; characteristics high; frequency attenuation; attenuation

Journal Title: Journal of Seismology
Year Published: 2020

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