Forerunners of ScS Waves from Nearby Deep Earthquakes and Upper Mantle Structure in Hokkaido
Forerunners of ScS Waves from Nearby Deep Earthquakes and Upper Mantle Structure in Hokkaido
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来自北海道附近深部地震和上地幔结构的 SCS 波的先驱
DOI：
10.4294/zisin1948.24.3_228
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发表时间：
1971
期刊：
影响因子：
--
通讯作者：
H. Okada
中科院分区：
文献类型：
--
作者：
H. Okada
1967年8月14日，福井县西南部发生深源地震。这次地震在北海道URA和KMU站的正常ScS震相之前约8秒产生了一个明显的纵向震相。在仔细检查KMU附近其他深源地震的地震记录时，发现多个地震记录上也记录了类似的前兆。这些先行者可能不会被解释为PKiKP阶段，因为它们的时间差异。一种可能的解释是在上地幔的某个不连续面从ScS转换为ScSp。假设ScS波垂直入射，在不连续处存在速度对比（上层的速度比下层的速度小10%），根据ScSp入射角、时间差和振幅比确定转换平面可能所在的区域。转换面倾角约为35-39 °，与深部地震带几乎平行。转换面位于深地震带的上边界附近，可能与倾斜的高Q、高V带和陆侧低Q、低V带的边界重合。有趣的是，地震活动在这个转换平面之下是低的，而地表火山活动在这个平面之上。
A deep earthquake occurred in the SW part of Fukui Prefecture on 14 August 1967. This shock produced a clear longitudinal phase about 8 sec before the normal ScS phase at stations URA and KMU, Hokkaido. On careful examination of seismograms of other nearby deep earthquakes at KMU, it was found that similar forerunners were recorded on several seismograms. These forerunners may not be interpreted as PKiKP phases because of their time differences. A possible interpretation is the conversion from ScS to ScSp at some plane of discontinuity in the upper mantle. Assuming the vertical incidence of ScS waves and a velocity contrast at the discontinuity (the upper layer has a velocity 10% smaller than that of the lower layer), a region in which the conversion plane may be located is determined from the ScSp incident angle, the time difference, and the amplitude ratio. The conversion plane has a dip of about 35-39 and is nearly parallel to the deep seismic zone. The conversion plane is located near the upper boundary of the deep seismic zone and may coincide with the boundary between the dipping high-Q, high-V zone and the landside low-Q, low-V zone. It is interesting that the seismic activity is low under this conversion plane, while the surface volcanism is present above this plane.