TY - JOUR
T1 - Tomographic imaging of seismic velocity structure in and around the Onikobe volcanic area, northeastern Japan
T2 - Implications for fluid distribution
AU - Nakajima, Junichi
AU - Hasegawa, Akira
N1 - Funding Information:
We are grateful for fruitful discussions with T. Yoshida and with the members of Research Center for Predictions of Earthquakes and Volcanic Eruptions, Tohoku University. Y. Mitsuhata and M. Mishina provided useful data. M. Mangan, Editor-in-Chief, H. Benz and an anonymous referee provided thoughtful comments that led to improvements in the manuscript. We are deeply grateful for the efforts of N. Tsumura and other members for carrying out temporary observations in 1996 and 1997 in the Onikobe volcanic area. We also thank the staff of Hirosaki University, the University of Tokyo and the Japan Meteorological Agency, as well as the participants in the Joint Seismic Observations in Tohoku in 1997–1999, for allowing us to use their data. All the figures in this paper were plotted using GMT ( Wessel and Smith, 1995 ). This work is partially supported by a grant from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
PY - 2003/9
Y1 - 2003/9
N2 - We estimated three-dimensional P- (Vp) and S-wave velocity (Vs) and Vp/Vs structures in and around the Onikobe volcanic area, northeastern Japan, by local travel time tomography. We used travel time data from source and receiver pairs located within and outside the study area, which plays an important role in obtaining the optimum ray coverage and in elucidating the deeper structure more accurately. Detailed information on deeper structures is essential for imaging the complete volcanic system from the magmatic source zone through areas of shallow hydrothermal circulation. More than 50 000 travel time data for the P-waves and 35 000 for the S-waves were used to image the velocity structure. Our results show the following dominant features: (1) two conduits in the upper crust with low Vp and low Vs indicative of H2O-rich fluid pathways: One lying beneath Naruko volcano, the other beneath the focal area of the 1962 Northern Miyagi earthquake (M6.5); (2) an underlying broad region in the lower crust with low Vp, low Vs and high Vp/Vs, suggestive of a zone of partial melt, from which the fluids in (1) are derived; and (3) low Vp/Vs areas near the surface of the Sanzugawa and Onikobe calderas, suggesting a diffuse vapor-saturated cap.
AB - We estimated three-dimensional P- (Vp) and S-wave velocity (Vs) and Vp/Vs structures in and around the Onikobe volcanic area, northeastern Japan, by local travel time tomography. We used travel time data from source and receiver pairs located within and outside the study area, which plays an important role in obtaining the optimum ray coverage and in elucidating the deeper structure more accurately. Detailed information on deeper structures is essential for imaging the complete volcanic system from the magmatic source zone through areas of shallow hydrothermal circulation. More than 50 000 travel time data for the P-waves and 35 000 for the S-waves were used to image the velocity structure. Our results show the following dominant features: (1) two conduits in the upper crust with low Vp and low Vs indicative of H2O-rich fluid pathways: One lying beneath Naruko volcano, the other beneath the focal area of the 1962 Northern Miyagi earthquake (M6.5); (2) an underlying broad region in the lower crust with low Vp, low Vs and high Vp/Vs, suggestive of a zone of partial melt, from which the fluids in (1) are derived; and (3) low Vp/Vs areas near the surface of the Sanzugawa and Onikobe calderas, suggesting a diffuse vapor-saturated cap.
KW - Caldera
KW - Fluids
KW - NE Japan
KW - Onikobe
KW - Seismic velocity structure
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U2 - 10.1016/S0377-0273(03)00155-0
DO - 10.1016/S0377-0273(03)00155-0
M3 - Article
AN - SCOPUS:0141566230
VL - 127
SP - 1
EP - 18
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
SN - 0377-0273
IS - 1-2
ER -