Report on DELP 1986 Cruises in the Northwestern Pacific : Part III: Seismic Structure Revealed by Explosion Experiments
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概要
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Several interesting features of the crust to upper mantle structure beneath the Northwest Pacific Basin were revealed by a seismic explosion experiment conducted during the DELP cruises in 1986. A large lateral heterogeneity was found both in the configuration of the crust/mantle structure and in the sub-Moho lithosphere. The data from the long range explosion experiment along the WSW-ENE survey line do not support the speculation of large scale anisotropy in this region. The lateral heterogeneities in the crust/mantle structure are indicated by variations of the velocity gradients within oceanic layer 3 and in the velocity transitions from layer 3 to the upper mantle. Wide-angle reflections from inside the sub-Moho lithosphere are clearly recorded with a good signal to noise ratio by small explosions of only 20kg at distances as far as 450km. However, the appearance of these phases differs from place to place. In some places, they are not observed. Lateral heterogeneity of this reflective layer seems to be related to such tectonic features as the fracture zone as well as Nakwe deepsea channel.1986年度夏に実施されたDELPによる北西太平洋海域の発破を利用した地震波構造探査によって,この海域の海底地殻下部から上部マントルの地震波速度構造に関して,いくつかの特徴的な解析結果が得られたので報告する.海洋地殻内部及びモホへの漸移形態のみならず,モホ以深に於ける速度構造にも地域的に非一様性がみられる. WSW-ENE方向の長距離発破測線から得られた記録からは,上部マントルにおける,大規模な速度異方性の存在を支持するような結果は見られなかった.モホ・マントルに関わる地域的非一様性は,海洋地殻第3層に於ける速度の勾配と,モホ面に於ける速度の跳びによって特徴づけられる.モホ以深のリソスフェア内部の何等かの層構造によると思われる広角反射波が,小薬量の発破に依っても450km先まで記録されている.この際だった反射面の存在様式は地震波速度構造の大規模な地域的非一様性と,地磁気によって示されているような破砕帯の存在に深く関係していると考えられる.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,Hawaii Institute of Geophysics, University of Hawaii,Department of Earth Science, Kobe Universityの論文
- 1990-06-30
著者
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Kato Aitaro
Univ. Tokyo Tokyo Jpn
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Kuwano Asako
Univ. Tokyo Tokyo Jpn
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Katao H
Kyoto Univ. Kyoto Jpn
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Ouchi T
Kobe Univ.
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Nagumo S
Univ. Hawaii
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