TY - JOUR
T1 - Distribution and characteristics in waveform and spectrum of seismic events associated with the 2000 eruption of Mt. Usu
AU - Matsubara, Wakana
AU - Yomogida, Kiyoshi
AU - Koyama, Junji
AU - Kasahara, Minoru
AU - Ichiyanagi, Makoto
AU - Kawakatsu, Hitoshi
AU - Yamamoto, Mare
N1 - Funding Information:
The authors sincerely thank Takeo Moriya for his help with installing broadband seismometers and Kunikazu Yoshida for his helpful comments on the original draft. Comments by Shigeki Horiuch and one anonymous reviewer are greatly appreciated. We were allowed to use Broadband seismometer systems through the kindness of Yuichi Morita. We used the data of JMA (Japan Meteorological Agency) recorded in and around Mt. Usu. This study was partly supported by the Institute of Seismology and Volcanology, Hokkaido University.
PY - 2004/8/30
Y1 - 2004/8/30
N2 - We installed five broadband seismometers around Mt. Usu, Hokkaido, Japan, just before the first surface eruption on March 31, 2000. By using these broadband data with short-period seismograms recorded by Japan Meteorological Agency and Institute of Seismology and Volcanology of Hokkaido University, we located 590 earthquakes associated with the 2000 eruption of Mt. Usu from March 31, 12:58 to April 5, 2000, including 41 low-frequency earthquakes. Low-frequency earthquakes have clear predominant frequencies of about 1.0-1.5 Hz. While the seismicity of tectonic earthquakes was still active on April 5, there were almost no low-frequency events after April 2. All the low-frequency earthquakes occurred within a vertical and narrow zone near the craters of eruption, and they are shallower than 4 km. In contrast, the active area of tectonic earthquakes spreads out in a large area, particularly deep in the south of the craters. From these temporal and spatial patterns, together with GPS and gravity measurements that support the termination of magma activities before April 2, we suggest that low-frequency earthquakes were caused by magma or hydrothermal activities beneath the volcano while tectonic ones were caused by the regional tectonic stress affected by the intrusion of magma body near the craters. Related to long-term magma activities of this eruption, four deep crustal low-frequency events were identified on October 17, 1998 just in the south of Mt. Usu in the depth range of 20-30 km. As proposed for other active volcanoes, these deep crustal events may represent a part of deep magma activities beneath Mt. Usu.
AB - We installed five broadband seismometers around Mt. Usu, Hokkaido, Japan, just before the first surface eruption on March 31, 2000. By using these broadband data with short-period seismograms recorded by Japan Meteorological Agency and Institute of Seismology and Volcanology of Hokkaido University, we located 590 earthquakes associated with the 2000 eruption of Mt. Usu from March 31, 12:58 to April 5, 2000, including 41 low-frequency earthquakes. Low-frequency earthquakes have clear predominant frequencies of about 1.0-1.5 Hz. While the seismicity of tectonic earthquakes was still active on April 5, there were almost no low-frequency events after April 2. All the low-frequency earthquakes occurred within a vertical and narrow zone near the craters of eruption, and they are shallower than 4 km. In contrast, the active area of tectonic earthquakes spreads out in a large area, particularly deep in the south of the craters. From these temporal and spatial patterns, together with GPS and gravity measurements that support the termination of magma activities before April 2, we suggest that low-frequency earthquakes were caused by magma or hydrothermal activities beneath the volcano while tectonic ones were caused by the regional tectonic stress affected by the intrusion of magma body near the craters. Related to long-term magma activities of this eruption, four deep crustal low-frequency events were identified on October 17, 1998 just in the south of Mt. Usu in the depth range of 20-30 km. As proposed for other active volcanoes, these deep crustal events may represent a part of deep magma activities beneath Mt. Usu.
KW - Deep crustal earthquake
KW - Hypocentral distribution
KW - Low-frequency earthquake
KW - Usu volcano
KW - Volcanic eruption
UR - http://www.scopus.com/inward/record.url?scp=3843146541&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=3843146541&partnerID=8YFLogxK
U2 - 10.1016/j.jvolgeores.2004.05.016
DO - 10.1016/j.jvolgeores.2004.05.016
M3 - Article
AN - SCOPUS:3843146541
VL - 136
SP - 141
EP - 158
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
SN - 0377-0273
IS - 1-2
ER -