Crustal 1-D Q-Structure In The Southern Korean Peninsula

Recently, many works for the seismic wave attenuation have been performed in the Korean Peninsula. The frequency dependent Q-values for S wave studied by several authors are not concordant with each other. It is thought that the discrepancies between them are thought to be arised from two factors. The one is the treatment of the geometrical spreading coefficient in estimating Q-value. The another is relevant to data sets to be used. Since the estimated Q-values are dependent on the distance, the inverted Q-values from the different composition of data sets become different. Accordingly the geometrical spreading coefficient was directly determined from the ray approximation method and eliminated from the unknown parameters in this work. Assuming that the Q-value varies with the depth, a three-layer model of frequency-dependent Q with uniformity in each layer was also inverted using the method of separation of source, path, and site effects in terms of the central frequencies of 1.5, 3, 5, 10, 15, and 25 Hz. The 780 seismograms recorded at 29 seismic stations by 68 earthquakes occurring in the period from 1996 to June 2005 in the Gyeongsang Basin, southeastern Korean Peninsula, were selected for this study. The model for Q-value corresponding to the seismic wave velocity structure in the crust determined from the least square inversion was presented. The estimated Q-values revealed a tendency to increase with the increment of the frequency in each layer. The Q-values in the 2nd layer are larger than those in the 1st layer. However, the values in the 3rd layer showed to decrease rather than those in the 2nd layer in the high frequency range above 5 Hz.