TY - JOUR
T1 - Seismic imaging of arc magma and fluids under the central part of northeastern Japan
AU - Nakajima, Junichi
AU - Matsuzawa, Toru
AU - Hasegawa, Akira
AU - Zhao, Dapeng
N1 - Funding Information:
We appreciate the fruitful discussions with T. Yoshida, M. Wyss, I.S. Sacks and N. Umino and all the members at Research Center for Prediction of Earthquakes and Volcanic Eruptions, Tohoku University. We are also grateful to the members who have participated in the 1997–1999 Joint Seismic Observations in Tohoku for their efforts in the field work. We also thank the staffs of JMA for allowing us to use some of the data recorded by their seismic network. We benefited from the comments of two anonymous referees provided thoughtful reviews, which improved the manuscript. All the figures in this paper are plotted using the GMT (Wessel and Smith, 1995) . This research was partially supported by a grant from the Ministry of Education, Science and Culture of Japan.
PY - 2001
Y1 - 2001
N2 - A dense seismic network was temporarily deployed during 1997-1999 in the central part of northeastern Japan by Japanese university research groups. Using the local earthquake arrival time data recorded by the network, we have determined high-resolution three-dimensional images of P-wave velocity (Vp), S-wave velocity (Vs) and Vp/Vs ratio in this area. Our results show that low Vp, low Vs and high Vp/Vs areas are extensively distributed in the uppermost mantle along the volcanic front. In the lower crust, low Vp, low Vs and high Vp/Vs areas are visible but they are confined to the individual volcanic areas. In contrast, the upper crust of volcanic areas shows low Vp, low Vs and low Vp/Vs rather than high Vp/Vs. These observations suggest that partial melting materials exist in the uppermost mantle along the volcanic front and they spread up to the midcrust of the volcanic areas. Low Vp, low Vs and low Vp/Vs in the upper crust of the volcanic areas suggest the presence of H2O (rather than melt) there. Deep low-frequency microearthquakes, perhaps caused by the rapid movement of fluids, are located mostly at the edge of partial melting zones, particularly at their upper surface. Distinct S-wave reflectors (bright spots) with large reflection coefficients are distributed in the midcrust with slightly low Vp/Vs, suggesting that most of them are filled with H2O.
AB - A dense seismic network was temporarily deployed during 1997-1999 in the central part of northeastern Japan by Japanese university research groups. Using the local earthquake arrival time data recorded by the network, we have determined high-resolution three-dimensional images of P-wave velocity (Vp), S-wave velocity (Vs) and Vp/Vs ratio in this area. Our results show that low Vp, low Vs and high Vp/Vs areas are extensively distributed in the uppermost mantle along the volcanic front. In the lower crust, low Vp, low Vs and high Vp/Vs areas are visible but they are confined to the individual volcanic areas. In contrast, the upper crust of volcanic areas shows low Vp, low Vs and low Vp/Vs rather than high Vp/Vs. These observations suggest that partial melting materials exist in the uppermost mantle along the volcanic front and they spread up to the midcrust of the volcanic areas. Low Vp, low Vs and low Vp/Vs in the upper crust of the volcanic areas suggest the presence of H2O (rather than melt) there. Deep low-frequency microearthquakes, perhaps caused by the rapid movement of fluids, are located mostly at the edge of partial melting zones, particularly at their upper surface. Distinct S-wave reflectors (bright spots) with large reflection coefficients are distributed in the midcrust with slightly low Vp/Vs, suggesting that most of them are filled with H2O.
KW - Active volcano
KW - Fluids
KW - Northeastern Japan
KW - Seismic velocity structure
KW - Travel-time tomography
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U2 - 10.1016/S0040-1951(01)00181-0
DO - 10.1016/S0040-1951(01)00181-0
M3 - Article
AN - SCOPUS:0035669102
VL - 341
SP - 1
EP - 17
JO - Tectonophysics
JF - Tectonophysics
SN - 0040-1951
IS - 1-4
ER -