﻿ 尼泊尔地区季节性水文负荷对地震活动性的调制作用
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 大地测量与地球动力学  2020, Vol. 40 Issue (6): 596-600, 633  DOI: 10.14075/j.jgg.2020.06.010

### 引用本文

WANG Chenxu, XIONG Yongliang, ZHANG Lupeng, et al. Modulation of Seismic Activity by Seasonal Hydrological Load in Nepal[J]. Journal of Geodesy and Geodynamics, 2020, 40(6): 596-600, 633.

### Foundation support

National Natural Science Foundation of China, No. 41674028.

### Corresponding author

XIONG Yongliang, PhD, professor, majors in GNSS theory and application research, E-mail: ylxiong@sina.com.

### 文章历史

1. 西南交通大学地球科学与环境工程学院，成都市犀安路999号，611756;
2. 台湾中央研究院地球科学研究所，台北市研究院路二段128号，11529

1 数据和方法 1.1 季节性信号提取

 $\begin{array}{l} y\left( {{t_i}} \right) = {y_0} + v{t_i} + A\sin \left( {2{\rm{ \mathsf{ π} }}{t_i}} \right) + B\cos \left( {2{\rm{ \mathsf{ π} }}{t_i}} \right) + \\ C\sin \left( {{\rm{4 \mathsf{ π} }}{t_i}} \right) + D\cos \left( {{\rm{4 \mathsf{ π} }}{t_i}} \right) + \sum\limits_{j = 1}^k {{O_j}H\left( {{t_i} - {t_{{O_j}}}} \right)} + \\ {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} {\kern 1pt} \sum\limits_{j = 1}^m {H\left( {{t_i} - {t_{{q_j}}}} \right)\left( {{c_j} + {p_j}\ln \left( {1 + \frac{{\left( {{t_i} - {t_{{q_j}}}} \right)}}{{\tau _j^{\log }}}} \right)} \right)} + {\varepsilon _i} \end{array}$ (1)

 $y\left( {{t_i}} \right) = {\rm{Amp}} \cdot \sin \left( {2{\rm{ \mathsf{ π} }}{t_i} + {\rm{Pha}}} \right)$ (2)

 ${\rm{Amp}} = \sqrt {{A^2} + {B^2}} , {\rm{Pha}} = \arctan \left( {B/A} \right)$

1.2 季节性降水和地震目录的去震群处理

 图 1 尼泊尔地区的月降水量时间序列及去震群算法处理结果对比 Fig. 1 Time series of monthly rainfall in Nepal, and comparison of processing results of the declustering algorithms

2 结果分析 2.1 季节性位移与降水的相关性

 图 2 1个年周期内测站最大季节性位移出现的月份 Fig. 2 The month in which the maximum seasonal displacement of the station occurs in an annual cycle

 图 3 尼泊尔地区4个季节内的月平均降水量 Fig. 3 Monthly average rainfall over the four seasons in Nepal

 图 4 尼泊尔地区月平均降水量及垂直位移变化 Fig. 4 The monthly average rainfall and the changes of vertical displacement in Nepal
2.2 地壳形变机制的季节性变化

 $\Delta {\rm{CFS}} = \Delta {\tau _S} + \mu '\Delta {\sigma _n}$ (3)

 图 5 尼泊尔地区月平均降水量、面应变和库仑应力的变化 Fig. 5 The monthly average rainfall and the changes of vertical displacement, surface strain and Coulomb stress in Nepal
2.3 地震活动的水文调节机制

 图 6 3种去震群方法在不同月份中地震事件的数量 Fig. 6 The number of earthquake events in different months by three declustering methods

 图 7 水文负荷对应变产生影响示意图 Fig. 7 Sketch map of the effect of hydrologic load on strain
3 结语

1) 尼泊尔地区降水的季节性变化显著，垂直位移与季节性降水区域存在明显的时空相关性，季节性降水可能是导致地表垂直位移出现季节性变化的主要原因。

2) 面应变与水文负荷之间存在着相关性，在月平均降水量最大的7月，面应变收缩出现最大值，进而推断水文负荷是导致地表季节性形变的主要驱动因素。

3) 将应变转换为与喜马拉雅主前缘断裂(MFT)平行的垂直断层上的库仑应力，面应变和库仑应力在相位和相对振幅上存在一致性，库仑应力的季节性变化与水文负荷造成的地表形变有关。

4) 尼泊尔地区冬季地震的数量较夏季季风期多，结合库仑应力的变化推测，夏季季风期的降水对断层的长期运动趋势产生扰动，使库仑应力得到一定程度的释放，进而对地震活动产生抑制作用，影响了地震发生的时间。

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Modulation of Seismic Activity by Seasonal Hydrological Load in Nepal
WANG Chenxu1     XIONG Yongliang1     ZHANG Lupeng1     JIANG Zhongshan1,2     ZHANG Rui1     QIAO Jiayuan1
1. Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, 999 Xi'an Road, Chengdu 611756, China;
2. Institute of Earth Sciences, Academia Sinica, 128 Section 2 of Yanjiuyuan Road, Taipei 11529, China
Abstract: The study of the disturbance process of hydrologic load on crustal stress is helpful in clarifying the relationship between hydrologic load and seismic activity. Using the seasonal signal of GPS time series in Nepal, the seasonal three-dimensional displacement field and stress-strain field model in this region is constructed. The modulation effect of seasonal hydrological load on seismicity in this area is studied by combining rainfall and seismic catalogue. The results show that: 1) there is a strong spatiotemporal correlation between seasonal surface displacement and rainfall; 2) the rainfall in monsoon period disturbs the long-term movement trend of the fault and releases the Coulomb stress to a certain extent, thus inhibiting the seismic activity and affecting the time of the earthquake.
Key words: GPS time series; hydrological load; seasonal displacement; stress and strain; seismic activity