Lower crustal fluid distribution in the northeastern Japan arc revealed by high-resolution 3D seismic tomography |
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| Authors: | Makoto Matsubara Naoshi Hirata Hiroshi Sato Shin'ichi Sakai |
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| Institution: | aNational Research Institute for Earth Science and Disaster Prevention 3-1, Tennodai, Tsukuba, Ibaraki 305-0006, Japan;bThe Earthquake Research Institute, the University of Tokyo 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan |
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| Abstract: | The Ou Backbone Range strikes northwards through the central northeastern Japan arc and is bounded on both sides by the active reverse Uwandaira and Sen'ya faults. We have applied a traveltime inversion method (seismic tomography) with spatial velocity correlation to active and passive seismic data in order to investigate a three-dimensional (3-D) velocity structure. The data set contains 33,993 P- and 18,483 S-wave arrivals from 706 natural sources and 40 blasts, as well as 2803 P-wave traveltime data from 10 explosions detonated during the 1997 controlled source experiment. The traveltime inversion reveals a zone beneath the Ou Backbone Range in which P-wave velocities (VP) are approximately 6–8% lower than the average velocity at equivalent depths. The low VP and a low VP to S-wave velocity (VS) ratio (VP/VS) of about 1.65 suggest the presence of aqueous fluids in the middle crust. |
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| Keywords: | Island arc Volcanic front Middle crustal aqueous fluids Tomographic method Northeastern Japan arc |
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