Broadband Seismic Observation of 1995 Explosion Experiment in the Unzen Volcano

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概要

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• We conducted broadband seismic observation of six artificial explosions on November 30, 1995, in the Unzen volcanic region. We installed three broadband seismometers (STS-2) and two short-period vertical seismometers (L-22D) at three obsenation points to study the shallow structure of the Unzen volcanic region. At all the three observation points, seismograms could be recorded for all the six explosions. By comparison of waveforms and spectral data at the three observation points, we identify a highly attenuating area of P wave at frequency higher than 6 Hz in the west of Fugendake. Comparing seismograms recorded by STS-2 with those by L-22D, the difference in the response of both seismometers at frequency lower than 2 Hz has little effect on the recorded wavefoms. Apparent P-wave velocity is slow around Fugendake but high in the west of Fugendake, compared with other areas in the Shimabara Peninsula. The value of Q^<-1>, which represents the attenuation of amplitude of direct P wave with propagation distance, is large in the frequency range of 4-10 Hz in the whole Shimabara Peninsula. Dividing the Shimabara Peninsula into three subregions and comparing Q^<-1> in each region, the value of Q^<-1> is remarkably large only around Fugendake but not in the west of it. In a wide frequency range, temporal decaying factor of S-coda wave (Q^<-1>_c) around Fugendake is larger than that in other areas. The above regional variations express very compelex geological structure, particularly in the west of Fugendake where a magma ascent path is proposed undemeath. We suggest that the metamorphosis, due to the magma rising from deep in a western shore of the Shimabara Peninsula to the summit of Fugendake, attenuates seismic waves propagating deep in this area while P-wave velocity is rather high and the attenuation is not necessarily strong near the surface. Meanwhile, around the summit of Fugendake the velocity is low and the attenuation is large even near the surface.

• 特定非営利活動法人日本火山学会の論文
• 1997-11-25

著者

• Matsushima Takeshi

  Shimabara Earthquake And Volcano Observatory Faculty Of Science Kyushu University

• MAEDA Mitoshi

  Department of Earth and Planetary Systems Science, Hiroshima University,

• YOMOGIDA Kiyoshi

  Department of Earth and Planetary Systems Science, Hiroshima University

• UMAKOSHI Kodo

  Shimabara Earthquake and Volcano Observatory, Faculty of Science, Kyushu University

• OKAMATSU Norikazu

  Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University,

• FUJII Yushiro

  Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University

• Yomogida Kiyoshi

  Department Of Earth And Planetary Systems Science Hiroshima University

• Yomogida Kiyoshi

  Department Of Earth And Planetary Systems Science Faculty Of Science Hiroshima University

• Fujii Yushiro

  Department Of Earth And Planetary Sciences Faculty Of Science Kyushu University

• Maeda Mitoshi

  Department Of Earth And Planetary Systems Science Hiroshima University :(present) Nagoya Branch Pasc

• Umakoshi Kodo

  Shimabara Earthquake And Volcano Observatory Faculty Of Science Kyushu University

• Okamatsu Norikazu

  Department Of Earth And Planetary Sciences Faculty Of Science Kyushu University :(present) Yame Seni

関連論文

• Coda Q^ in Awaji Island Estimated from the Aftershock Records of the 1995 Hyogo-ken Nanbu Earthquake
• Broadband Seismic Observation of 1995 Explosion Experiment in the Unzen Volcano
• Complex Scattering at the Core-Mantle Boundary Observed in Short-Period Diffracted P-Waves
• Spatial variation of coda wave amplitude in media with a localized heterogeneous region
• Seismograms Explained by the Slip Distribution of the 1995 Hyogo-ken Nanbu Earthquake
• RELATION BETWEEN SEISMIC OBSERVATIONS AND THE FAULT COMPLEXITY OF THE 1995 HYOGOKEN-NAMBU EARTHQUAKE
• Group Velocity Measurement of Surface Waves by the Wavelet Transform
• Spatial variation of coda wave amplitude in media with a localized heterogeneous region

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