DEEP, LOW-FREQUENCY MICROEARTHQUAKES IN OR AROUND SEISMIC LOW-VELOCITY ZONES BENEATH ACTIVE VOLCANOS IN NORTHEASTERN JAPAN
DEEP, LOW-FREQUENCY MICROEARTHQUAKES IN OR AROUND SEISMIC LOW-VELOCITY ZONES BENEATH ACTIVE VOLCANOS IN NORTHEASTERN JAPAN
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DOI：
10.1016/0040-1951(94)90243-7
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发表时间：
1994-05-30
期刊：
影响因子：
2.9
通讯作者：
YAMAMOTO, A
中科院分区：
文献类型：
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作者：
HASEGAWA, A;YAMAMOTO, A
通过应用震源区台站校正，对日本东北部浅层板内微地震进行了精确的震源重定位。重新定位的震源分布表明，大多数地震局限于地壳上部15公里，形成了该火山弧的脆性孕震带。它还表明，在日本东北部的12个地点发生了远低于地震-地震边界的异常深的微地震。它们出现在地壳最下部或地幔最上部，在那里岩石的流变学性质被认为是在韧性制度。目前在地壳下部或地幔上部探测到的153个地震，P波和S波的优势频率都非常低（1 ~ 5.5Hz），而在脆性孕震带中的正常浅层地震的优势频率（8-20 Hz）则很低。这些事件的量级很小（M小于或等于2.2）。此外，所有这些事件都位于活火山之下和/或上地幔P波低速带附近。这些事件与活火山的接近性及其它异常特征表明，这些深源低频事件是由地幔底辟的岩浆活动产生的。
Precise hypocenter relocations have been made for shallow intraplate microearthquakes beneath northeastern Japan by applying source-region station corrections. The relocated hypocenter distribution shows that most of the events are confined to the upper 15 km of the crust which forms the brittle seismogenic zone in this volcanic arc. It also shows that exceptionally deep microearthquakes, well below the base of the seismic-aseismic boundary, occur at twelve locations of northeastern Japan. They occur in the lowermost crust or in the uppermost mantle, where rheological properties of rocks are presumed to be in the ductile regime. All the 153 events presently detected in the lowermost crust or in the uppermost mantle have anomalously low predominant frequencies (1-5.5 Hz) both for P and S waves, in contrast to those (8-20 Hz) -of normal shallow events in the brittle seismogenic zone. The magnitudes of these events are small (M less-than-or-equal-to 2.2). Moreover, all of these events are located beneath active volcanoes and/or near P wave low-velocity zones in the uppermost mantle. The proximity of these events' to the active volcanoes and other anomalous features suggest that these deep low-frequency events are generated by magmatic activity of mantle diapirs in the uppermost mantle.