Causes of the discordance in the south-north distribution of the 2017 Jiuzhaigou earthquake sequences

IF 0.7 4区地球科学 Q4 GEOCHEMISTRY & GEOPHYSICS Applied Geophysics Pub Date : 2023-12-27 DOI:10.1007/s11770-023-1048-5

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Abstract

In the 2017 Jiuzhaigou earthquake sequence, the distribution of aftershocks in the north of the main earthquake was scattered, while the distribution of aftershocks in the south of the main earthquake was linear and concentrated. The objective of this inquiry is to analyze the dynamic causes underlying such divergent patterns, relying on the horizontal strain rosette, areal strain (As), and the coefficient of accommodation (Ca) based on the regional strain rate. The following two conclusions are obtained: (1) approximately one-third of the aftershocks with focal mechanisms in the north of the main shock are thrust-type earthquakes. Because the direction of regional tectonic principal compressional strain is perpendicular to the fault trend north of the main shock, generating thrust-type earthquakes on low dip-angle faults is indeed easy. Simultaneously, the overall thrust-type focal mechanism north of the main shock and the poor consistency between plate tectonic movement and fault movement caused by the seismic sequence lead to substantial scattered aftershocks in the north of the main shock. (2) One of the aftershocks with focal mechanisms in the south of the main shock is a reverse strikeslip type, while the other 30 are strike-slip type earthquakes. Moreover, the angle between the regional tectonic principal compressional strain direction and the fault trend in the south of the main shock is large, which makes it easier for faults in the south of the main shock to produce strike-slip-type earthquakes. Simultaneously, the overall strike-slip focal mechanism in the south of the main shock, the good consistency between fault movements caused by the seismic sequence, and plate tectonic movements lead to more linear and concentrated aftershocks in the south of the main shock. The findings are significant for investigations into the seismogenic properties and activity of the Huya Fault located on the northeastern margin of Bayan Har Block.

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2017年九寨沟地震序列南北分布不协调的原因

摘要在2017年九寨沟地震序列中，主震北侧余震分布呈分散状，而主震南侧余震分布呈线状集中分布。本研究的目的是基于区域应变率的水平应变轮纹、面状应变（As）和容纳系数（Ca），分析这种分异格局的动力原因。得出以下两个结论：(1) 在主震北侧的余震中，约有三分之一的余震震源机制为推力型地震。由于区域构造主压应变方向与主震以北的断层走向垂直，在低倾角断层上确实容易产生推力型地震。同时，主震以北的整体推力型聚焦机制以及地震序列引起的板块构造运动与断层运动之间的一致性较差，导致主震以北出现大量分散余震。(2) 在主震南侧的余震中，有 1 个余震的震源机制为逆冲滑动型，其余 30 个余震均为冲滑型地震。此外，区域构造主压应变方向与主震南侧断层走向的夹角较大，使得主震南侧断层更容易产生击滑型地震。同时，主震南部的整体走向滑动聚焦机制、地震序列引起的断层运动与板块构造运动之间的良好一致性，导致主震南部的余震更加线性和集中。这些发现对研究位于巴彦哈尔地块东北边缘的呼亚断层的成震特性和活动具有重要意义。

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来源期刊

Applied Geophysics 地学-地球化学与地球物理

CiteScore

1.50

自引率

14.30%

发文量

912

审稿时长

2 months

期刊介绍： The journal is designed to provide an academic realm for a broad blend of academic and industry papers to promote rapid communication and exchange of ideas between Chinese and world-wide geophysicists. The publication covers the applications of geoscience, geophysics, and related disciplines in the fields of energy, resources, environment, disaster, engineering, information, military, and surveying.