Frequency-dependent Attenuation of High-frequency P and S Waves in the Upper Crust in Western Nagano, Japan

Borehole seismograms from local earthquakes in the aftershock region of the 1984 western Nagano Prefecture, Japan earthquake were analyzed to measure the frequency-dependent characteristics of P- and S-wave attenuation in the upper crust. The records from a three-component velocity seismometer at the depth of 145 m exhibit high S:N-ratio in a wide frequency range up to 100 Hz. Extended coda normalization methods were applied to bandpass-filtered seismograms of frequencies from 25 to 102 Hz. For the attenuation of high-frequency P and S waves, our measurements show Q 1 P #0.052f 0.66 and Q 1 S #0.0034f 0.12, respectively. The frequency dependence of the quality factor of S waves is very weak as compared with that of P waves. The ratio of Q 1 P :Q 1 S is larger than unity in the entire analyzed frequency range.