Characteristics of isolated hybrid tremor (HBT) during a calm activity period at Aso Volcano
Characteristics of isolated hybrid tremor (HBT) during a calm activity period at Aso Volcano
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阿苏火山平静活动期孤立混合震颤（HBT）特征
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发表时间：
2008
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通讯作者：
S. Yoshikawa
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作者：
Takehiko Mori;Y. Sudo;T. Tsutsui;S. Yoshikawa
具有两个不同主频率事件的孤立型地震是在阿苏火山喷发活动阶段观测到的典型地震现象。这些孤立的震颤被称为混合震颤（HBT），由两部分组成：最初的部分称为“高频部分”，其主导频率在高频区域（约10赫兹），接下来的部分称为“低频部分”，其主导频率在低频区域（约2赫兹）。低频部分发生在高频部分之后，高频部分伴有长周期震颤（LPT）。震源和震源参数的估计是利用在Nakadake火山口周围64个站点记录的地震记录。各高频部分的振幅分布几乎具有相似的趋势。同样，所有lf部分的振幅分布几乎具有相似的趋势。然而，高频部分和低频部分的振幅分布并不相似。根据这些结果，我们提出HF-和lf -零件的震源和震源参数并不相同，但它们各自具有相同的震源和震源参数。估计hf部分震源区位于第1火山口以南的喷气孔区下方，体积波动是主要震源因素。LF-parts的震源区域估计在第一个火山口下方约300 m的深度，走滑分量是主要的震源参数。lf -零件的震源深度位于估计为lpt源的裂缝的上端。lpt和hpt几乎同时被观察到。我们认为火山流体参与了HBT和LPT的成因机制。
Isolated-type tremors having two events with different dominant frequencies are characteristic seismological phenomena observed during the fumarolic activity stage at Aso Volcano. These isolated tremors are called hybrid tremors (HBT) and comprise two parts: an initial part named the “HF-part” with a dominant frequency in the high-frequency region (approximately 10 Hz) and the following part named the “LF-part” with a dominant frequency in the low-frequency region (approximately 2 Hz). The LF-part is observed after the HF-part, and the HBT is accompanied by a long-period tremor (LPT). Hypocenters and source parameters are estimated using seismograms recorded at 64 stations around Nakadake crater. The amplitude distributions of all HF-parts have almost similar trends. Similarly, the amplitude distributions of all LF-parts have almost similar trends. However, the amplitude distributions of HF- and LF-parts are not similar. From these results, we proposed that the hypocenters and source parameters of HF- and LF-parts are not common, but each of them have common hypocenters and source parameters. The hypocenter region of HF-parts was estimated to be just beneath the fumarole region south of the 1st crater: the volume fluctuation is the major source factor. The hypocenter region of LF-parts is estimated to be at a depth of approximately 300 m beneath the first crater: the strike–slip component is the major source parameter. The hypocentral depth of LF-parts is located at the upper end of the crack estimated to be the source of the LPTs. The LPTs and HBTs are observed almost simultaneously. We consider that volcanic fluid is involved in the source mechanisms of both HBT and LPT.