﻿ 重庆石柱M4.5及武隆M5.0地震前视应力异常对比
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 大地测量与地球动力学  2021, Vol. 41 Issue (3): 249-253  DOI: 10.14075/j.jgg.2021.03.006

引用本文

CHEN Lijuan, GONG Liwen, DONG Di, et al. Comparison of Apparent Stress Anomalies between Shizhu M4.5 Earthquake and Wulong M5.0 Earthquake in Chongqing[J]. Journal of Geodesy and Geodynamics, 2021, 41(3): 249-253.

Foundation support

The Spark Program of Earthquake Technology of CEA, No.XH18036; The Earthquake Tracking Task of CEA, No.2019010126, 2020010129; Project of Chongqing Earthquake Agency in 2020.

第一作者简介

CHEN Lijuan, assistant engineer, majors in digital seismology and earthquake monitoring, E-mail: 517133638@qq.com.

文章历史

1. 重庆市地震局，重庆市红黄路339号，401147

2013-07-18重庆石柱发生M4.5地震，2017-11-23重庆武隆发生M5.0地震，2次地震震中相距约92 km。本文利用地震波形资料反演得到拐角频率、地震矩、地震能量等震源谱参数，计算视应力并分析石柱M4.5及武隆M5.0地震前中小地震视应力的演化过程，对比2次地震前视应力的变化特征，以提取该区显著地震前的视应力异常指标，为渝东南地区地震趋势分析提供判定依据。

1 构造背景及资料选取

 图 1 区域地质资料及地震分布 Fig. 1 Regional geological data and earthquake distribution
2 视应力计算方法

 $\mathit{\Omega }(f)=\frac{\mathit{\Omega }_{0}}{1+\left(\frac{f}{f_{c}}\right)^{2}}$ (1)

 $M_{0}=\frac{4 \pi \rho v^{3}\mathit{\Omega }_{0} d}{\mathscr{R}}$ (2)

 $E_{S}=8 \pi \rho \beta \int_{0}^{\infty} V(f)^{2} \mathrm{~d} f$ (3)

 $\sigma_{\mathrm{app}}=\mu \frac{E_{S}}{M_{0}}$ (4)

3 震源谱参数定标关系

 图 2 研究区地震震源谱参数定标关系 Fig. 2 Calibration relationship between seismic-source spectral parameters in the study area
 $\begin{array}{c} \log M_{0}=1.039\;4 \times M_{L}+10.678\;2, \\ R_{1}=0.946\;8 \end{array}$ (5)
 $\begin{array}{c} \log E_{S}=1.774\;0 \times M_{L}+2.481\;3 \\ R_{2}=0.960\;5 \end{array}$ (6)
 $\begin{array}{c} \log \sigma_{\mathrm{app}}=0.734\;2 \times M_{\mathrm{L}}-2.718\;4, \\ R_{3}=0.842\;5 \end{array}$ (7)
 $\begin{array}{c} \log f_{c}=-0.101\;7 \times M_{L}+0.611\;2, \\ R_{4}=0.410\;4 \end{array}$ (8)

4 视应力随时间变化分析

 图 3 石柱地区ML2.0~2.9地震的视应力及拐角频率随时间变化 Fig. 3 The changes of apparent stress and corner frequency of ML2.0~2.9 earthquakes with time in Shizhu area

 图 4 武隆地区ML2.0~2.9地震的视应力及拐角频率随时间变化 Fig. 4 The changes of apparent stress and corner frequency of ML2.0~2.9 earthquakes with time in Wulong area

 图 5 研究区内114个ML2.0~2.9地震的视应力及拐角频率随时间变化 Fig. 5 The changes of apparent stress and corner frequency of 114 ML2.0~2.9 earthquakes with time in the study area
5 结语

1) 同震级条件下，石柱地区地震的拐角频率低于武隆地区，这可能是因为石柱地区距离长江三峡库区较近，岩体裂隙发育和库水渗透扩散使地壳浅部岩石强度弱化，对地震波的高频成分具有较强的吸收作用，从而导致拐角频率偏小。同等震级条件下，石柱地区地震的视应力低于武隆地区，表明受三峡水库蓄水影响，库水渗透作用使石柱地区地震发震所需的构造应力小于武隆地区。

2) 视应力结果表明，石柱M4.5地震和武隆M5.0地震前视应力均经过长时间上升变化过程，最高异常值达到背景值的2~3倍。这种“震前长时间上升-震前数月略有下降-临震前再次急剧上升”的变化过程，反映研究区内应力的积累释放过程。S波拐角频率在2次地震前的异常变化与视应力基本一致，表明拐角频率也可以反映区域应力大小。武隆地震后研究区内拐角频率、视应力仍较高，说明渝东南片区七曜山-金佛山基底断裂仍承受较高的构造应力。

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Comparison of Apparent Stress Anomalies between Shizhu M4.5 Earthquake and Wulong M5.0 Earthquake in Chongqing
CHEN Lijuan1     GONG Liwen1     DONG Di1     DONG Lei1
1. Chongqing Earthquake Agency, 339 Honghuang Road, Chongqing 401147, China
Abstract: We obtain the seismic-source spectral parameters of seismic energy, corner frequency, seismic moment and apparent stress by spectral analysis of small and medium earthquakes in Shizhu and Wulong areas. We comparatively analyze the differences of seismic-source spectrum parameters of the Shizhu M4.5 earthquake and the Wulong M5.0 earthquake. The results show: 1) Corner frequency and apparent stress in Shizhu area are lower than that in Wulong area under the same magnitude conditions, which may be related to the closer distance from Shizhu to the Three Gorges Reservoir area. 2) The apparent stress in Shizhu area presents two years rising process, decreasing slightly before the main shock, and corner frequency also increasing before the earthquake. 3) The apparent stress in Wulong area presents abnormal changes of "rise-descent-rise" before the Shizhu M4.5 and the Wulong M5.0 earthquakes, and corner frequency also increases before the two earthquakes. 4) The apparent stress of the whole study area has undergone an ascending change process before the Shizhu M4.5 and the Wulong M5.0 earthquakes, and the stress in this area remains high after the earthquakes.
Key words: Three Gorges Reservoir area; Shizhu M4.5 earthquake; Wulong M5.0 earthquake; apparent stress; corner frequency