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Study on detailed rupture processes and generation mechanism of strong ground motions by dense array observations in an earthquake swarm area

震群区强地震动详细破裂过程及产生机制的密集阵观测研究

基本信息

批准号：
10490010
负责人：
KOKETSU Kazuki
金额：
$ 7.68万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2001
项目状态：
已结题

项目摘要

For investigating detailed rupture processes and generation mechanism of strong ground motions, we deployed a dense strong-motion observation array in the off-Ito area of the Izu peninsula region, where earthquake swarm activities were repeated and another one can be expected during the term of this project. However, any activity has not yer occurred in these four years after the previous swarm from March to June 1998, and so we also carried out mobile observations in the northern Izu islands region, where the eruption of Miyakejima induced a swarm of earthquakes in 2000. They brought us a huge dataset of strong motion records for many middle-size earthquakes including thirty-one M5 events and five M6 events.For the off-Ito area of the Izu peninsula region, we analyze the strong motion records observed at 384 stations in the Kanto basin for the 1998 Izu Toho Oki earthquake (M5.7) immediately before the project term. Such a strike-slip event in Izu or the Sagami bay as this earthquake often generates dominant surface waves called Love waves for rather long-period strong motions in the Kanto basion, and their generation and propagation are controlled by the three-dimensional structure of the basin. We then carry out moment tensor inversions and tomographic analyzes for the observed seismograms from the earthquake swarm induced by the Miyakejima eruption. Spatio-temporal variations in the earthquake source mechanism are found in the seismically active zone, and the three-dimensional attenuation structure in the zone is also derived from the spectral amplitudes of the observed records. The analysis of the seismic motions associated with the caldera collapse indicates slow inflation and some phenomenon represented by a single force beneath the crater.

为了研究详细的破裂过程和强地震动的产生机制，我们在伊豆半岛地区的伊东外地区部署了密集的强震动观测阵列，该地区经常发生地震群活动，并且在本项目期间预计还会发生另一次地震群活动。然而，自1998年3月至6月的上一次群震之后的四年里，我们还没有发生过任何活动，因此我们还在伊豆群岛北部地区进行了流动观测，2000年三宅岛喷发引发了群震，为我们带来了包括31次M5事件和5次M6事件在内的许多中型地震的巨大强震记录数据集。在伊豆半岛地区，我们分析了项目期前 1998 年伊豆东丰冲地震（M5.7）在关东盆地 384 个台站观测到的强震记录。像本次地震这样的伊豆或相模湾走滑事件，在关东基底的相当长周期的强烈运动中，常常会产生称为洛夫波的主导面波，其产生和传播受到盆地三维结构的控制。然后，我们对三宅岛喷发引发的地震群观测到的地震图进行矩张量反演和层析成像分析。在地震活动区发现了震源机制的时空变化，并且根据观测记录的谱振幅推导出该区域的三维衰减结构。对与火山口塌陷相关的地震运动的分析表明，缓慢的膨胀和火山口下方的单一力所代表的一些现象。