Determining Attenuation Q-Factor Values for Selected Seismic Stations in Iraq

Abstract

The coda wave decay (CWD) method was used to estimate the quality factor from the coda wave amplitude decay rate for the broadband seismic stations (IBDR, MSL, and NSR4) using a single backscattering model. This research aims to calculate the attenuation coefficient and the frequency-dependent coefficient (α) for three stations and compare them to comprehend the details of Earth's crust structure in those stations. Then, to test if they are homogenous or not. Also, investigate how sensitive extracted values to tectonic differences in study stations. The attenuation properties are important for providing information about the medium that seismic waves pass through and can also be applied to areas with seismic activity as initial disaster mitigation. The study used data from the Mesopotamian Network (MP) and the Iraqi Meteorological Organization and Seismology (IMOS) from 2011 to 2021. The selected earthquakes have less than < 100 km epicentral distances, and magnitudes ranging from 3.5 to 5.6. Forty-six earthquakes were recorded by three stations (IBDR, MSL, and NSR4). These earthquakes were analyzed at eight center frequencies (1, 2, 3.5, 6, 8, 10, 12, and 16 Hz) and a 30-sec length window by using the SEISAN Earthquake Analysis Software. The QC values are computed by the frequency-dependent relationship QC= Q0 f α, where Q0 is QC at 1Hz and α denotes frequency dependence degree. The attenuation relationship of the station IBDR is obtained as QC =98 f 1.07, QC = 99 f 1.09 in the MSL station, and QC = 77 f 0.98 in the NSR4 station. The results showed that low Q0 corresponds to high attenuation. The comparison of the estimated QC for these three stations indicates that attenuation is highest at NSR4, followed by other stations.