Coda-Q Estimated from Earthquakes around Unzendake Volcano

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  • 雲仙火山周辺で発生した地震から推定されたコーダQ<sup>-1</sup>
  • 雲仙火山周辺で発生した地震から推定されたコーダQ-1〔英文〕
  • ウンゼン カザン シュウヘン デ ハッセイシタ ジシン カラ スイテイサレタ

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Description

Q-structure around Unzendake volcano, which is on the center of the Shimabara Peninsula in Kyushu, Japan, is investigated using amplitude attenuation of S-coda from earthquake records obtained during the 1991 volcanic activities. Coda-Q-1(Qc-1) value is estimated by assuming a single isotropic scattering approximation. High Qc-1 values are obtained for earthquakes and stations on the western part of the volcano, and for earthquakes under the summit observed by nearby stations. Low Qc-1 values are obtained for the earthquakes in the eastern Shimabara Peninsula. Qc-1 values are also low for the seismograms recorded at stations to the east of the volcano. The observational results are compared with those from Monte Carlo simulation. Attenuation of seismic energy caused by multiple-scattering and intrinsic absorption is simulated assuming media having different characteristics with regard to heterogeneity and anelasticity. It is revealed that the attenuation of seismic waves is remarkable in and near the region of strong heterogeneity and anelasticity that has a high Qc-1 value. It is inferred that the region comprising the western half and the summit of the volcano is characterized by stronger heterogeneity and anelasticity than those under the eastern half of the volcano.

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