火山性地震とその発生機構モデル

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Volcanic earthquakes are the earthquakes originating from some magmatism. In this paper, the characteristics of these earthquakes and their source models are reviewed in relation to the volcanic eruptions. Volcanic earthquakes are classified in several ways. The classification of A-type earthquake, Btype earthquake, explosion earthquake and volcanic tremor follows the recorded features of earthquake-motions and their relation to volcanic eruption. Recently, people prefer to give more emphasis on the frequency components of the seismic wave, and to classify volcanic earthquakes into low frequency and high frequency earthquakes. The last decade development of advanced seismometric and other geophysical surveillance networks around several volcanoes in Japan has made it possible to infer source mechanisms of volcanic earthquakes. Such study has revealed the relation between the volcanic activities and the volcanic earthquakes little by little. Source models of explosion earthquakes so far proposed could be divided into two categories. The first is the model that the seismic wave is excited by the rapid increase of pressure in the volcanic conduit. The second model assumes that the wave is excited by a single force applied in the direction opposite to the blast direction. The second model was successfully applied to the explosion earthquakes at Mount St. Helens volcano and Asama volcano, and used to obtain their magnitudes and source time functions from long-period seismograms. Some new ideas on source models for volcanic tremor have been recently proposed such as the jerky extension of fluid-driven crack and the unsteady fluid flow in volcanic conduits. Since dominant frequencies of volcanic earthquakes are variable over wide frequency range, the broad-band and wide dynamic range seismographs installed near the volcanoes are desirable for more advanced interpretation of volcanic earthquakes.
特定非営利活動法人日本火山学会の論文
1986-03-31

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武尾実
気象研究所

火山性地震とその発生機構モデル

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