| 四川地区流动重力资料的位场 分离与异常特征提取 |
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| 引用本文： | 李大虎,丁志峰,梁明剑,李,军,苏,琴.四川地区流动重力资料的位场 分离与异常特征提取[J].地震学报,2014,36(2):261-274. |
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| 作者姓名： | 李大虎 丁志峰 梁明剑 李 军 苏 琴 |
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| 作者单位： | 1.中国北京 100081 中国地震局地球物理研究所 |
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| 基金项目： | 中国地震局地震科技星火计划项目(XH12041Y)和四川省地震局地震科技专项(LY1312)联合资助. |
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| 摘 要： | 用于监测四川地区重力场随时间变化的流动重力测网于2008年5月12日汶川MS8.0地震后进行了全面改造， 形成了新的闭合环线并对整网点位每年实施2次重力观测工作. 该文以2010—2012年获取的5期流动重力资料为基础， 分别采用小波多尺度分解和三维视密度反演等位场分离方法， 对测区内重力场的动态变化进行多层次分解及异常特征提取， 以探求四川测区范围内重力异常动态变化特征以及地震前后不同深度范围内密度变化情况与重力场响应之间的关系. 结果表明， 对同一期资料进行小波分解得到不同阶次的细节图像， 揭示了不同深度处重力异常动态变化特征； 分解结果同时也表明了四川测区范围内重力场的变化形态与川内特有的断裂构造格架和深部结构环境及过渡带特征密切相关. 通过对不同时期的差分重力异常资料进行三维视密度反演对比研究发现， 在地震前后四川测区范围内由浅到深密度变化呈现出不同程度的差异， 震区附近出现较为明显的横向密度变化特征且浅层物质密度局部性的异常变化差异较为突出， 测区范围内中上地壳深度层密度反演切片显示出的趋势性差异基本上反映了地震前后测区内地下物质的动态变化趋势， 因此， 深刻认识不同深度范围内重力场的动态演化特征， 对研究壳内物质密度变化以及与地震的孕育和发展有关的深部介质环境具有积极的意义.
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| 关 键 词： | 四川地区 流动重力 小波多尺度分解 三维视密度反演 密度变化 |
| 收稿时间： | 2013-01-19 |
Field separation and anomaly feature extraction of mobile gravity data in Sichuan area |
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| Affiliation: | 1.Institute of Geophysics, China Earthquake Administration, Beijing 100081, China2.Earthquake Administration of Sichuan Province, Chengdu 610041, China3.Geophysical Institute of Chengdu University of Technology， Chengdu 610059, China |
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| Abstract: | The mobile gravity measuring network for monitoring the Sichuan area gravitational field varying along with the time has made an overall transformation after the Wenchuan MS8.0 earthquakes on 12 May 2008, forming a new closed loop with gravity observation to all of the point locations twice every year. Taking five-issue mobile gravity data in the period of 2010—2012 as the foundation, this paper detects dynamic change of gravitational field in multi-scale decomposition and extracts anomaly features by using wavelet multi-scale decomposition and the 3-D apparent density inversion, so as to search for dynamic change characteristics of gravity anomaly and the relationship between the range of density variation and the gravity field response within different depths before and after the earthquake in Sichuan measuring area. The results show that different order details chart got from wavelet decomposition on the same stage gravity data reveals dynamic change characteristics of gravity anomaly in the different depth. Decomposition results also show that changes of gravitational field are closely related with fracture structure framework, deep structure and characteristics of transitional zone in Sichuan measuring area. Comparison of 3-D apparent density inversions based on the differential gravity anomaly data of different periods suggests density change is different from shallow to deep depth before and after an earthquake. Variation of transverse density characteristics is obviously presented nearby the seismic region, and anomalous change difference in the density of shallow matter is especially prominent. The apparent density slice maps within the depth of the middle-upper crust of the testing area shows trend differences, which basically reflects the dynamic change process of underground substances before and after the earthquake. Therefore deep understanding of gravity dynamic evolution characteristics in the different depth bounds is of positive significance to study the matter density change in the crust and deep medium environment related to the pregnancy and development of the earthquake. |
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