Broadband analysis of the extended foreshock sequence of the Miyagi-Oki earthquake of 12 June 1978
Broadband analysis of the extended foreshock sequence of the Miyagi-Oki earthquake of 12 June 1978
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1978 年 6 月 12 日宫城冲地震扩展前震序列的宽带分析
DOI：
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发表时间：
1982
影响因子：
3
通讯作者：
J. Boatwright
中科院分区：
文献类型：
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作者：
G. L. Choy;J. Boatwright
1978年6月12日发生的宫城-冲地震是一次大的（Ms 7.8）板间逆冲事件，发生在一个自1938年以来没有经历过7级以上地震的地区。在主震发生前的2年时间里，宫城冲地震破裂带周围发生了4次中等规模（5.4 < mb < 6.1）地震序列。分析了全球数字地震台网台站数字记录的体波宽频带位移和速度记录，以确定序列的静态和动态特征。这些特征包括力矩、辐射能、动、静态应力降和视应力。对速度波形进行的持续时间测量的反演允许量化事件的复杂性以及约束其破裂几何形状。
前三次事件间隔7至8个月;主要休克发生在第三次事件后4个月。第三个事件的破裂过程相对复杂;该事件的动态应力降（175巴）也比前两个事件的应力降（分别为9巴和10巴）高得多。这些观测结果表明，第三次地震是主震的中期前兆。第四个事件是主震的短期前兆，发生在主震前8分钟左右。其动态应力降（20巴）低于第三次事件，但高于前两次事件。
The Miyagi-Oki earthquake of 12 June 1978, a large ( Ms 7.8) interplate thrust event, occurred in a region which had not experienced earthquakes of magnitude greater than 7 since 1938. A sequence of four moderate-sized (5.4 < mb < 6.1) earthquakes encircled the rupture zone of the Miyagi-Oki earthquake over a period of 2 yr before the main shock. Broadband displacement and velocity records of body waves recorded digitally by stations of the Global Digital Seismograph Network are analyzed to determine the static and dynamic characteristics of the sequence. These characteristics include moment, radiated energy, dynamic and static stress drop, and apparent stress. Inversions of duration measurements made on the velocity waveforms permit quantifying the complexity of an event as well as constraining its rupture geometry.
Intervals of 7 to 8 months separated the first three events; the main shock occurred 4 months after the third event. The rupture process of the third event was relatively complex; the event also had a substantially higher dynamic stress drop (175 bars) than did the stress drops of the first two events (9 and 10 bars, respectively). These observations suggest that the third event was an interme-diate-term precursor to the main shock. The fourth event, a short-term precursor to the main shock, occurred about 8 min before the main shock. Its dynamic stress drop (20 bars) was lower than that of the third event but higher than that of the first two events.