地震研究

针对相对重力观测过程中可能受到环境等因素影响而出现高频信号和局部异常的情况,以2021年漾濞6.4级地震前重力变化为例,通过时空平滑约束重构重力变化数据,对比重构前后重力变化情况。基于球坐标系下六面体模型模拟场源体介质,反演场源视密度变化,分析场源区介质密度演化特征。结果显示:观测数据经过时空平滑重构后,在不改变总体变化趋势的情况下,标准差由17.86×10^-8 m/s²降到8.99×10^-8 m/s²,变化值区间从(-74.20～66.28)×10^-8 m/s²降到(-21.79～27.70)×10^-8 m/s²,数据离散程度得到有效压缩,并能压制高频信号和局部噪声,孕震区域内重力变化时空演化趋势更加连续,便于异常特征的识别。场源区视密度变化显示有一个明显的NW-SE向物质迁移过程,在经过震中位置后逐渐收缩,在震中位置形成一个“孤岛”形态。孕震过程中正负变化分界线从SW-NE向转为NW-SE向,在分界线与构造走向一致后随即发震。

In response to the possibility of high-frequency signals and local anomalies caused by environmental factors during relative gravity observation,spatio-temporal smoothing constraints are introduced to reconstruct the data change,and then the gravity changes before and after reconstruction is compared.Further,the field source medium is simulated based on a hexahedral model in spherical coordinates,and the apparent density changes of the field source is inverted,to analyze the evolution characteristics of the medium density in the field source area.The results show that after spatio-temporal smoothing reconstruction,the standard deviation of the observed data decreased from 17.86×10^-8 m/s² to 8.99×10^-8 m/s² without changing the overall trend.The range of variation values decreased from(-74.20-66.28)×10^-8 m/s² to(-21.79-27.70)×10^-8 m/s²; this effectively compressed the degree of data dispersion and suppressed high-frequency signals and noise in some areas.Thus,the relative gravity spatio-temporal evolution trend in the seismogenic region became more continuous,which facilitated the identification of abnormal features.The change in apparent density in the source area reveals an obvious NW-SE migration process of the underground material.The material gradually contracted after passing through the epicentral area,forming an “island” at the epicenter.During the seismogenic process,the boundary between positive variation and negative variation shifted from SW-NE to NW-SE direction,and earthquakes occurred immediately after the boundary became in line with the structural direction.

引言
1 数据与方法
2 重力变化数据重构结果
3 视密度反演
4 讨论
5 结论

图1 漾濞6.4级地震孕震区域内相对重力测点分布<br/>Fig.1 The distribution of the relative-gravity-measurement stations in the seismogenic zoneof the Yangbi MS6.4 earthquake

图1 漾濞6.4级地震孕震区域内相对重力测点分布
Fig.1 The distribution of the relative-gravity-measurement stations in the seismogenic zoneof the Yangbi MS6.4 earthquake

表1 重构前后重力变化极值及标准差对比<br/>Tab.1 Comparison of extreme values and standard deviations before and after reconstruction

表1 重构前后重力变化极值及标准差对比
Tab.1 Comparison of extreme values and standard deviations before and after reconstruction

图2 原始数据及重构数据变化量值分布对比<br/>Fig.2 Distribution of observed and reconstructeddata in different value ranges

图2 原始数据及重构数据变化量值分布对比
Fig.2 Distribution of observed and reconstructeddata in different value ranges

图3 不同空间域范围内重构前后重力均值变化对比<br/>Fig.3 Comparison of the variation of average gravity data before and after reconstruction in different ranges

图3 不同空间域范围内重构前后重力均值变化对比
Fig.3 Comparison of the variation of average gravity data before and after reconstruction in different ranges

图4 累计重力变化重构结果<br/>Fig.4 Forward reconstruction results of cumulative gravity changes

图4 累计重力变化重构结果
Fig.4 Forward reconstruction results of cumulative gravity changes

图5 0.50°×0.50°(a)和0.25°×0.25°(b)不同分辨率检测结果<br/>Fig.5 Results from the detection with different resolutions of 0.50 °×0.50 °(a)and 0.25 °×0.25 °(b)

图5 0.50°×0.50°(a)和0.25°×0.25°(b)不同分辨率检测结果
Fig.5 Results from the detection with different resolutions of 0.50 °×0.50 °(a)and 0.25 °×0.25 °(b)

图6 累计重力变化视密度反演结果<br/>Fig.6 Apparent density inversion of cumulative gravity changes

图6 累计重力变化视密度反演结果
Fig.6 Apparent density inversion of cumulative gravity changes

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备注

引言

1 数据与方法

2 重力变化数据重构结果

3 视密度反演

4 讨论

5 结论

期刊信息