基于弹性位错理论的2004年Mw 6.0 Parkfield地震断层应力降分布

doi:10.7523/j.ucas.2021.0041

摘要/Abstract

摘要： 地震的发生伴随着区域应力状态调整，地震学上通常采用应力降表征震源区的应力释放水平。作为重要震源参数之一，应力降被广泛用于地震类型判断、震后应力状态分析及破裂扩展预测。目前，地震学家们常常根据拐角频率给出一个平均应力降结果，但是，一方面，发震区域和断层面岩石强度及应力状态存在不均匀性，单一的平均值难以呈现出空间变化，很难反映整个断层面上的应力调整情况；另一方面，由于观测台网限制、各个台站场地、射线路径等震源谱数据及相关计算参数获取方式和精确度不同而往往导致不同研究结果存在较大差异。为此，从力学角度出发，利用Okada静力学方法计算断层错动所引起的断层面上的剪应力变化，即基于位错滑动模型得到断层面上的地震应力降分布。数值计算结果表明，地震的发生虽然释放了断层面上的集中应力，但由于断层面上存在障碍体或者滑动量不均匀分布，断层面上位错量大的局部区域应力释放反而会使得其邻近区域应力集中，呈现出地震应力降非均匀分布现象，增大了断层面局部段落再次破裂的风险。应力降的非均匀性分布和断层几何形状的变化一定程度上也决定了断层的非均匀滑移行为。以2004年M_w 6.0 Parkfield地震为例，计算其断层面上应力降分布：主震最大错动区域地震应力降约9.2MPa，但是在发震断层上部分段落的应力反而增加，可达-3.5MPa。相较于单一的平均地震应力降，基于位错模型获取应力降分布可更好地反映出震源破裂过程及对余震发展的分析预测。

关键词: 滑动模型, Okada位错理论, 应力降, Parkfield地震

Abstract: The occurrence of earthquakes is accompanied by regional stress state adjustment. In seismology, stress drop is usually used to characterize the stress release level after an earthquake. As one of the important parameters, stress drop is widely used to judge the type of earthquake, analyze the stress state after earthquake, and predict the rupture propagation. At present, seismologists often give an average stress drop value based on the earthquake corner frequency. However, the rock strength and stress state of the seismic fault plane are inhomogeneities in real terms. Besides, a single average value is difficult to show the spatial variation in stress changes, which could not reflect the stress adjustment across fault plane. Meanwhile, there are great differences among different researches due to the limited observation stations or different source spectrum data or other related calculation parameters. In this paper, from the point of view of mechanics, we propose the method of adoption the Okada's dislocation theory to calculate the shear stress change of the fault plane, that is, based on the slip model to obtained the distribution of fault plane. From the results of numerical calculation, it is found that the occurrence of an earthquake releases the concentrated stress of fault plane, due to the presence of obstacles on fault or uneven slip distribution, the stress release in the local area with large dislocation will increase the stress concentration in the adjacent area, showing the phenomenon of non-uniform distribution of stress drop, and increasing the rupture tendency of local section. Moreover, the non-uniformity distribution of stress drop and the uneven fault geometry determine the non-uniform slip behavior of fault. Taking the 2004 M_w 6.0 Parkfield earthquake as an example, the stress drop distribution of the fault plane was calculated. The maximum stress drop was about 9.2MPa, which near the source. But the stress drop increased in some sections of the fault plane, reaching -3.5MPa. Compared with the average stress drop, the distribution of stress drop on fault plane calculated by the dislocation model can better reflect the source rupture process and predict the aftershock evolution.

Key words: slip model, Okada's dislocation theory, stress drop, parkfield earthquake

中图分类号:

P315.0

窦甜甜, 程惠红, 石耀霖. 基于弹性位错理论的2004年M_w 6.0 Parkfield地震断层应力降分布[J]. 中国科学院大学学报, 2023, 40(2): 179-190.

DOU Tiantian, CHENG Huihong, SHI Yaolin. Stress drop distribution of 2004 M_w 6.0 Parkfield earthquake based on the elastic dislocation theory[J]. Journal of University of Chinese Academy of Sciences, 2023, 40(2): 179-190.

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