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Frequency-dependent Attenuation of High-frequency P and S Waves in the Upper Crust in Western Nagano, Japan |
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| Authors: | K Yoshimoto H Sato Y Iio H Ito T Ohminato M Ohtake |
| Institution: | Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. Fax: +81-22- 217-6783; E-mail: yoshi@zisin.geophys.tohoku.ac.jp, JP National Research Institute for Earth Science and Disaster Prevention, Tennoudai 3-1, Tsukuba 305–0006, Japan., JP Geological Survey of Japan, Higashi 1-1-3, Tsukuba 305–0046, Japan., JP |
| Abstract: | —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 145m 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 P -1? 0.052?-0.66 and Q S -1? 0.0034?-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 P -1/Q S -1 is larger than unity in the entire analyzed frequency range. |
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