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Physical model of deep low-frequency earthquakes occurred beneath Japan Island Arc

日本岛弧下方深部低频地震的物理模型

基本信息

批准号：
14340127
负责人：
TAKEO Minoru
金额：
$ 4.54万
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：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-14340127/
关键词：
Low-frequency earthquake KM_2O-Langevin equation New algorithm Analysis of time series 震源過程

项目摘要

Since the 1970's, a few earthquakes with depths ranging 20 km to 40 km have been observed just beneath the volcanic front in the northeastern part of Japan Island Arc. Almost all of the deep low-frequency earthquakes (DLF) recognized up to now have had magnitudes less than 2.5, so that we have little information concerning deep low-frequency earthquakes except for their waveforms and the locations of their hypocenters. We develop a new algorithm to estimate an averaged KM_2O-Langevin matrix function for multiple local time series excited by the same source dynamics, and propose the new concept of "Average Dissipation Spectrum". This algorithm was applied in the analysis of DLF occurred in Akita prefecture on 11 July 2001, and we succeeded in separating the characteristics of the source vibration system and the source excitation process into the averaged dissipation term and the fluctuation term, respectively.The continuous seismic tremor called the deep low-frequency tremor (LFT) was f … More ound very recently in the Southwest Japan fore-arc, along the the subducting Philippine Sea Plate. We applied the method of average dissipation spectrum to the LFT data and obtained the characteristic frequency and decay rate of the LFT waveforms. We confirm the several peaks in the dominant frequency range 1-5Hz of the LFT. The decay rate of the LFT is about 0.20 for the data of 2003 and 0.15 to 0.18 for the data of 2002.The major parts of the coda waves of DLF satisfy the stationary property, and the causality values for the linear and odd-degree non-linear transformations are relatively higher than those for the even-degree non-linear transformations. This quantitative property is common among all DLF. A nonlinear process to explain many characteristics of volcanic tremors proposed by Julian (1994) can produce the two kinds of characteristics of causality values represented in DLF and in the deep low-frequency tremor. Of course, this model is not a solitary physical process causing the two kinds of causality value characteristics. However, this physical process is a valid candidate for the source model that is common to DLF and the deep low-frequency tremor. Less

自20世纪70年代以来，在日本岛弧东北部火山锋下观测到几次深度在20公里至40公里之间的地震。迄今所发现的深低频地震震级几乎都在2.5级以下，因此，除了深低频地震的波形和震源位置外，我们对深低频地震的了解很少。本文提出了一种新的估计由同一源动力激励的多个局部时间序列的平均km_20 - langevin矩阵函数的算法，并提出了“平均耗散谱”的新概念。将该算法应用于2001年7月11日秋田地区发生的DLF分析中，成功地将源振动系统的特征和源激励过程的特征分别分离为平均耗散项和波动项。这种被称为深低频地震（LFT）的连续地震是最近在日本西南部沿俯冲的菲律宾海板块的弧前发现的。将平均耗散谱法应用于LFT数据，得到了LFT波形的特征频率和衰减率。我们确认了LFT的主导频率范围为1-5Hz的几个峰值。2003年的LFT衰减率约为0.20,2002年的LFT衰减率为0.15 ~ 0.18。DLF的尾波主要部分满足平稳性质，线性和奇次非线性变换的因果关系值相对高于偶次非线性变换的因果关系值。这种定量性质在所有DLF中都是常见的。Julian（1994）提出的解释火山地震许多特征的非线性过程可以产生DLF和深低频地震所代表的两种因果值特征。当然，这个模型并不是一个单独的物理过程导致这两种因果关系值的特征。然而，这一物理过程是DLF和深低频震颤共同的源模型的有效候选。少