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Study on seismic wave velocity changes in the crust associated with the 1980 Izu-Hanto-Toho-Oki Earthquake

1980年伊豆阪东东丰冲地震地壳地震波速度变化研究

基本信息

批准号：
15540409
负责人：
FURUMOTO Muneyoshi
金额：
$ 1.41万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2004
项目状态：
已结题

项目摘要

An experiment to detect temporal velocity changes of seismic waves was conducted in 1979-1986 in Kanto and Tokai regions, Japan. Analyzing the travel times observed in the experiment, we have already found that stress variation generated by ocean tides and the tectonic stress accumulation gives rise to the temporal velocity changes in the crust. The Izu-Hanto-Toho-Oki earthquake took place in 1980 within the experiment area. It is supposed that the stress changes associated with the earthquake caused the velocity changes of seismic waves in the crust around the source. We detect the temporal variation of seismic wave velocities, after removing effects of the velocity changes caused by ocean tides and a secular stress accumulation in the crust from the observed travel times. We also investigate the spatial distribution of the stress sensitivity of seismic waves in the crust using the observed velocity changes related the tides, the tectonic stress, and the earthquake. We calculate apparent sensitivities of the velocity to the stress using the observed velocity changes and the relevant stress changes along the wave paths. We compile also apparent stress sensitivities reported by many other researchers. The observed apparent stress sensitivity rapidly decreases with the base line length, which means that the stress sensitivity should sharply decreases with depth. The stress sensitivity is estimated to be about 1 (1/MPa) at the surface and decrease by one order of magnitude every few kilometers.

1979-1986年在日本关东和东海地区进行了一次地震波速度随时间变化的探测试验。通过对实验中观测到的走时进行分析，我们发现海潮引起的应力变化和构造应力的积累引起了地壳速度的时间变化。1980年伊豆-坂东-东邦-冲地震发生在实验区内。据推测，与地震有关的应力变化引起了震源周围地壳中地震波速度的变化。我们检测的地震波速度的时间变化，消除由海洋潮汐引起的速度变化的影响和长期的应力积累在地壳中观察到的旅行时间。我们还调查了地壳中的地震波的应力敏感性的空间分布，利用观测到的速度变化有关的潮汐，构造应力，和地震。利用观测到的速度变化和沿波径沿着的相关应力变化，我们计算了速度对应力的表观灵敏度。我们还汇编了许多其他研究人员报告的明显的应力敏感性。观测到的表观应力敏感性随基线长度迅速减小，这意味着应力敏感性应随深度急剧减小。应力敏感性估计在地表约为1（1/MPa），每隔几公里降低一个数量级。