Attenuation of High-Frequency P and S Waves in the Crust of Southeastern South Korea

The seismicity of the Yangsan fault in southeastern S. Korea has re-ceived increasing attention recently because the fault lies in an industrial area. For this fault region, we first measured QP − 1 and QS − 1 simultaneously by applying the extended coda-normalization method to seismograms at nine stations of a network deployed by the Korea Institute of Geology, Mining, and Materials. We analyzed 707 seismograms of local earthquakes that occurred between December 1994 and February 2000. From velocity seismograms, bandpass-filtered traces were made by applying a phaseless four-pole butterworth filter with five octave-width frequency bands, 1–2, 2–4, 4–8, 8–16, and 16–32 Hz. Estimated QP − 1 and QS − 1 values decrease from (7 2) 103 and (5 4) 103 at 1.5 Hz to (5 4) 104 and (5 2) 104 at 24 Hz, respectively. By fitting power-law frequency dependence to the estimated values over the whole stations, we obtained 0.009 f1.05 for QP − 1 and 0.004 f0.70 for QS − 1, where f is frequency in Hz. These results indicate that QP − 1 and QS − 1 in the crust of southeastern S. Korea are the lowermost of the reported values in the world, although the exponent values agree well with those in the other areas.