Qs-values in the Southern Korean Peninsula Area

Abstract:

There are Q_s-values independently determined in the Southern Korean Peninsula area. The results of previous studies showed that some were frequency dependent while others were frequency independent. They used different methods and limited digital earthquake data. We analyzed seismograms of 400 earthquakes recorded at seismic stations operated by Korea Institute of Geoscience and Mineral Resources, Korea Meteorological Administration, and Korea Electric Power Research Institute from January 2001 to June 2014. The magnitudes (M_L) were between 2.0 and 5.1, the hypocentral distances between 20 and 120 km. We used ground velocities by removing the instrument response for the safety purpose. Seismograms of 1-2, 2-4, 4-8, 8-16, and 16-32 Hz frequency bands were analyzed to determine frequency dependent Q_s-values. Coda normalization technique was employed. To avoid the polarization effect, we utilized the vectorial amplitude of an equation (1), where A_E, A_N, and A_Z are EW, NS, and vertical components of a seismogram, respectively. If the root-mean-square (rms) amplitude of coda waves is less than twice of the noise rms amplitude, the data were ignored. The Q_s-values were determined 143, 572, 1214, 1694, and 1856 at frequency bands of 1.5, 3, 6, 12, and 24 Hz, respectively as preliminary results. The best fitting frequency dependent Q_s-value presentation was Q_s = 318.2f ^0.53.