Attenuation characteristics of coda wave in southern Arabian Shield

Abstract

This study aims to estimate regional attenuation of coda wave in the southernmost part of the Arabian Shield. The decay rate of the time-domain coda envelope was analyzed and used for the estimation of coda wave quality factor (Qc) following the single isotropic-scattering model. The dataset comprises of a total number of 78 earthquakes of magnitude ranges from 1.5 to 4.5 recorded by 13 seismic stations within a hypocentral distance of 11 to 205 km and a lapse time between 10 and 40 s. Seismograms from vertical and two horizontal components have been analyzed at central frequencies of 3, 6, 9, 12, 18, 21, and 24 Hz, obtaining frequency-dependent attenuation relationships in the form of Qc=(36 ± 10)f(0.98±0.1), Qc=(53 ± 13)f(0.89±0.1), Qc=(63 ± 12)f(0.86±0.1), and Qc=(75 ± 13)f(0.81±0.14) at lapse time 10, 20, 30, and 40 s respectively. The regional frequency-dependent relationship is approximated by the power law of Qc=57±11f0.88±0.1 for the study area. For 10 sec lapse time, the average Qc ranges between 124 ± 41 at 3 Hz and 890 ± 193 at 24 Hz, while for 40 sec lapse time it varies from 200 ± 51 at 3 Hz to 1077 ± 130 at 24 Hz, implying a continuous increase in Qc with lapse time as a consequence of subsurface homogeneity with depth. The relationship between Qc and frequency shows that the coda quality factor is frequency dependent. The low attenuation characteristics can be attributed to the geodynamic process that causes a thin lithosphere beneath the study area due to active rifting in the Red Sea combined with magma flow and migration into the Arabian Shield.

Keywords

• Coda wave attenuation
• Lapse time
• Frequency dependent
• Red Sea
• Arabian Shield