摘要
广东河源新丰江水库位于华南典型断层上,自1959年水库蓄水以来,库区地震活动性明显增强,并发生了6.1级触发地震.然而我们对其地下结构的了解还远远不够,对库区地震的研究也因此存在很多不确定性.为了研究库区浅层地下结构,我们在2015年初在新丰江库区人字石断裂周边布设了42个短周期地震仪的密集地震台网.台间距大约为100~500m,时间跨度为1个月.我们对获得的每个台站的连续信号分段进行处理,并对任意台站对的信号进行互相关和叠加处理,恢复所有台站对间的经验格林函数(EGF).然后利用多次滤波分析方法测量瑞利波群速度频散曲线,并反演该区域的群速度分布和三维剪切波速度结构.我们的结果表明,对于这样比较密集的台站间距,高频(0.2~1.2s)频散信号基本可以得到很好的恢复,且该频段信号对浅层地下结构(<1km)较为敏感.剪切波速度分布表明该区域人字石断裂位置出现明显的低速分布,并且低速区在断裂南端向两侧延伸,有可能代表与人字石断裂交错的小断裂区域.同时,人字石断裂把该区域划分成了东西两部分,两侧整体上呈现高速异常,与地表山丘相吻合.我们的结果得到了新丰江人字石断裂附近的近地浅层的小尺度精细速度结构,为进一步理解该区域的构造以及地震发生提供了重要依据.
The Xinfengjiang （XFJ） water reservoir in Guangdong, China granites. After the impoundment of the reservoir in 1959, numerous locates in Yanshanian earthquakes occurred, including the M6.1 one in 1962. XFJ water reservoir is one of the most active seismic zones in Guangdong. However, the underground structure of this area is not yet well understood, and there are uncertainties about the mechanism of reservoir earthquakes. To investigate the shallow crustal structure near XFJ water reservoir area, we deployed 42 short period stations near Renzishi Fault （RZSF） ,with inter-station distance between 100-500 m in year 2015. We retrieved the empirical Greenls function （EGF） of all possible station pairs, and obtained their Rayleigh wave group velocity dispersion. Finally, we inverted Rayleigh group velocity and 3D shear wave velocity beneath RZSF area. Our results show that for such dense spacing stations, high frequency （0. 2-1.2 s） dispersion signals can be well retrieved, which are important to resolve shallow crustal structure （〈1 km）. Shear wave velocity maps show obvious low velocity anomalies beneath RZSF, and this slow anomaly extend to both sides of the fault in the south. The two sides of the RZSF show relatively high velocities, which may correlate with surfieial geology. Our results show fine structures of the distribution and geometry of fractures near the RZSF, and provide important constraints in understanding the geological tectonics and seismicity in XFJ water reservoir area.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第2期593-603,共11页
Chinese Journal of Geophysics
基金
广州市科技计划项目(201707020029),国家自然科学基金(41774053)和同位素地球化学国家重点实验室(中国科学院广州地球化学研究所)基金(SKLabIG16-03)共同资助.
关键词
新丰江水库
密集台网
环境噪声
层析成像
Xinfengjiang water reservoir
Dense array
Ambient noise
Tomography
