Characteristics of isolated hybrid tremor (HBT) during a calm activity period at Aso Volcano |
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| Authors: | Takehiko Mori Yasuaki Sudo Tomoki Tsutsui Shin Yoshikawa |
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| Institution: | 1.Geological Survey of Japan,National Institute of Advanced Industrial Science and Technology,Ibaraki,Japan;2.The Foundation of Aso Volcano Museum,Kumamoto,Japan;3.Faculty of Engineering and Resource Science,Akita University,Akita,Japan;4.Aso Volcanological Laboratory, Graduate School of Science,Kyoto University,Kumamoto,Japan |
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| Abstract: | 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. |
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| Keywords: | Aso Volcano ASO98 experiment Fumarolic activity Volcano seismology Isolated-type tremor Hybrid tremor Volcanic fluid |
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