Q-values for P and S waves in the southern Korean Peninsula based on the coda-normalization method

Abstract

The attenuation of seismic waves can be measured by the quality factorQ, which is an important parameter of the physical properties of the Earth's interior. Using the extended coda-normalization method, we estimatedQ-values for P waves (Q _P) and S waves (Q _S) in the southern Korean Peninsula as well as for the three sub-tectonic provinces (the Gyeonggi Massif, the Ogcheon Belt and the Yeongnam Massif, and the Gyeongsang Basin) in it. We chose 675 seismograms from 189 earthquakes that occurred in Korea from January 2001 to October 2003. Most earthquakes had small magnitudes (M_L≤3.0) and shallow focal depths (≤15 km). Assuming thatQ is independent of frequency, theQ-value and geometric spreading factor (γ) were calculated simultaneously using least squares inversion. The resulting values for the southern Korean Peninsula wereQ _P=1384 andQ _S=2036. The Gyeongsang Basin had the lowest value, indicating that its crustal structure is relatively heterogeneous and might be highly fractured. The γ values varied from 0.73 to 0.87. Assuming thatQ is dependent on frequency and γ has a constant value of 1.0, the values ofQ at the central frequencies of 1, 2, 3, 5, 10, 20, and 30 Hz yieldedQ _P=188.6f ^0.8110 andQ _S=201.4f ^0.7509 for the southern Korean Peninsula. We analyzed the variation ofQ _S for two hypocentral distance ranges: 0–90 km and 90–180 km, respectively. The estimatedQ-values for both P and S waves in the Gyeongsang Basin are the lowest, except for the case ofQ _S(f), in the low frequency range. The frequency-dependentQ _S for the hypocentral distance range of 90 to 180 km, appeared to be the larger than that for the shorter distance range. The values ofQ _S(f) estimated in this study were comparatively higher than for a seismically active area.