Abstract

The seismicity of the Yangsan fault in southeastern S. Korea has received increasing attention recently because the fault lies in an industrial area. For this fault region, we first measured

\(Q_{P}^{-1}\)
and
\(Q_{S}^{-1}\)
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
\(Q_{P}^{-1}\)
and
\(Q_{S}^{-1}\)
values decrease from (7 ± 2) × 10–3 and (5 ± 4) × 10–3 at 1.5 Hz to (5 ± 4) × 10–4 and (5 ± 2) × 10–4 at 24 Hz, respectively. By fitting power-law frequency dependence to the estimated values over the whole stations, we obtained 0.009 f–1.05 for
\(Q_{P}^{-1}\)
and 0.004 f–0.70 for
\(Q_{S}^{-1}\)
, where f is frequency in Hz. These results indicate that
\(Q_{P}^{-1}\)
and
\(Q_{S}^{-1}\)
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.

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