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A search for silent/slow earthquakes around Japan Islands

搜索日本列岛周围的无声/缓慢地震

基本信息

批准号：
04640399
负责人：
KAWASAKI Ichiro
金额：
$ 1.02万
依托单位：
Toyama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04640399/
关键词：
slow earthquake extensometer strain step time constant 1992 Sanriku earthquake tsunami Earthquake Bayseian model BAYTAP-G スロー・アースクエイクスローアースクエイク日本海溝 BATAP-G 地殻歪 1992年岩手県沖地震

项目摘要

The purpose of this study is to find episodic aseismic faulting at the Japan trench. Subsequently to the July 18, 1992, Sanriku-Oki earthquake (Ms6.9, 39.42ﾟN, 143.33ﾟE), a remarkable quasi-static phase appeared in the crustal strain records by quartz-pipe extensometers of a high resolution of -10^<-11> and low ground noises of -10^<-9> at ESASHI(39.15ﾟN, 141.34ﾟE, r=174km, phi=-99ﾟ), Iwate, Japan. We have decomposed the crustal strains into atmospheric pressure effects, tides and trends by the Baysian tidal analysis method of Ishiguro and Tamura(1985) and Tamura et al.(1991). The EW component of the trend thus extracted displays a clear quasi-static exponential increase of -4Xl0^<-8> with a time constant of about one day. This is about four times greater than a strain step within about one hour subsequent to the seismic event. We have investigated the cause of the quasi-static phase to conclude that this was not due to local disturbances.A similar quasi-static phase of -15X10^<-8> was observed in the EW component of crustal strain records at MIYAKO (39.59ﾟN, 141.98ﾟE, r=117km, phi=-80ﾟ) of the Tohoku University. From the close similarity between the strain waveforms at ESASHI and MlYAKO, we can attribute the quasi-static phase to the ultra-slow faulting subsequent to the seismic event.We have inverted the strain steps to obtain a solution of an interplate low-angle thrusting located about 60 km to the east from the NEIC epicenter and with a moment release of up to (1-4)Xl0^<20> N・m corresponding to that of M_w7.3-7.7 seismic event although the resolution is poor for small number of independent observations.Thus, the possibility is strengthened that the aseismic part of the relative plate motion in the south of the Sanriku region is released episodically with various time constants such as the ultra-slow earthquake.

本研究的目的是寻找日本海沟的幕式活动断层。1992年7月18日日本三陆冲地震（Ms6.9，39.42 <$N，143.33 <$E）后，在日本岩手县<-11><-9>江砂市（39.15 <$N，141.34 <$E，r= 174 km，phi=-99 <$N）的高分辨率石英管应变计记录中出现了一个显著的准静态相。我们利用Ishiguro和Tamura（1985）和Tamura等人的贝叶斯潮汐分析方法，将地壳应变分解为气压效应、潮汐和趋势。（1991年）。由此提取的趋势的EW分量显示出约4X 101的明显准静态指数增加<-8>，时间常数约为一天。这比地震事件之后约一小时内的应变阶跃大约四倍。在<-8>东北大学宫古（39.59 <$N，141.98 <$E，r= 117 km，phi=-80 <$N）的地壳应变记录中，也观测到了类似的东西向分量的-15 × 10 ~（-1）的准静态相位。从ESASHI和MlYAKO的应变波形之间的密切相似性，我们可以将准静态相归因于地震事件之后的超慢速断层。我们反演了应变阶跃，得到了位于NEIC震中以东约60 km处的板间低角度逆冲的解，其力矩释放高达（1-4）X10 ^N·m，对应于M_w7.3 <20>- 7.7地震事件，但独立观测次数少，分辨率低，因此，加强了三陆南部板块相对运动的非活动部分以各种时间常数（如超慢地震）周期性释放的可能性。