| 位于构造活跃区的小湾水库地震活动特征——基于地震精定位的分析 |
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| 引用本文： | 姜金钟,付虹,陈棋福.位于构造活跃区的小湾水库地震活动特征——基于地震精定位的分析[J].地球物理学报,2016,59(7):2468-2485. |
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| 作者姓名： | 姜金钟 付虹 陈棋福 |
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| 作者单位： | 1. 中国科学院地质与地球物理研究所, 中国科学院地球与行星物理重点实验室, 北京 100029;2. 云南省地震局, 昆明 650224 |
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| 基金项目： | 国家自然科学基金项目(41174051,41130316,41490612)资助. |
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| 摘 要： | 针对我国在西南构造活跃区修建的水库蓄水与地震活动的关系,本文对蓄水已长达7年并在高水位运维多个周期的云南小湾水库,采用结合波形互相关技术的双差地震定位法对水库库区及周边地区2005年7月至2014年12月发生的M≥1.0级地震进行了精定位处理,结果显示出明显的地震成丛活动特征,库区内外的地震震源深度差别较大.对地震震源深度、地震活动与水库蓄水水位及b值分析结果表明:小湾水库蓄水后地震活动明显增多,有水库触发地震发生,触发地震主要分布在沿黑惠江(A)和澜沧江流域(B、C)的3组地震丛中,且3个区的触发地震类型均为快速响应型;在水库蓄水响应活动最明显的地震丛集区A,展现出明显的随水库蓄水水体渗透发生地震"迁移"活动的现象;但库区内也存在着与蓄水关系不大的可能属于正常构造地震的活动,而库区外的地震活动与水库蓄水没有什么相关性,很可能是属于正常的构造地震.综合断层展布、岩性分布及震源深度分析,认为水库蓄水引起的溶岩作用和渗透作用及断层活动可能是小湾水库触发地震的主控因素.
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| 关 键 词： | 小湾水库 水库触发地震 双差地震定位法 波形互相关 地震活动性 |
| 收稿时间： | 2015-12-24 |
Characteristics of seismicity of the Xiaowan reservoir in an area of active tectonics from double-difference relocation analysis |
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| JIANG Jin-Zhong,FU Hong,CHEN Qi-Fu.Characteristics of seismicity of the Xiaowan reservoir in an area of active tectonics from double-difference relocation analysis[J].Chinese Journal of Geophysics,2016,59(7):2468-2485. |
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| Authors: | JIANG Jin-Zhong FU Hong CHEN Qi-Fu |
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| Institution: | 1. Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Earthquake Administration of Yunnan Province, Kunming 650224, China |
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| Abstract: | The Xiaowan reservoir, located in the middle and lower reaches of the Lancang river in western Yunnan province, lies in an area of active tectonics. It has a maximum height of the dam about 292 m, normal elevation of storage water level 1242 m and the maximum storage capacity about 149 ×108 m3. The Lancang river and the Heihui river and several active faults (for instance, the Lancangjiang fault zone and the Qiaoxi-Weihou fault zone) run through the Xiaowan reservoir area. In order to monitor seismicity within and outside of the reservoir area, the Xiaowan Seismic Networks (XSN) has been established and operated since May 2005 and recorded 36836 M>0 earthquakes from July 2005 to December 2014.#br#We simultaneously relocate 12481 M≥1.0 earthquakes within and outside of the Xiaowan reservoir area using the waveform cross-correlation (CC) and double-difference method (DD). Of them, 8835 hypocenter locations are computed by the DD method with location errors approximately 1.0 km and 2.5 km in the horizontal and vertical direction, respectively. The relocated epicenters are distinctly clustered in 8 subareas which are labeled from subareas A to H. Earthquakes located in the reservoir area (subareas A to F) are generally shallower than those outside the reservoir area (subareas G and H). From subareas A to H, the percentages of earthquakes with focal depths less than 10 km are 79%, 98%, 59%, 79%, 97%, 81%, 30% and 43%, respectively. Their average focal depths are 7.2 km, 6.1 km, 8.7 km, 7.2 km, 5.2 km, 6.9 km, 12.7 km and 10.8km, respectively.#br#Moreover, statistics of relocated focal depths and frequency of earthquakes suggest that there are significantly increasing seismic events in subarea A, B and C after the first impounding of the reservoir. The annual number of M≥1.0 earthquakes with focal depth less than 10 km increased by 20, 45 and 35 times in subareas A, B and C, respectively. The seismicity has rapid response to the impounding water level in these subareas. However, we observed no any correspondence between seismicity and water level in subareas D to H after the impounding. Furthermore, the b-values of M≥1.0 earthquakes in subareas G and H, which are in the range of b-values of tectonic seismicity, are lower than those in subareas A, B and C. #br#The relocated focal depths, relation between the seismicity, water level and calculated b-values in different subareas indicate that the characteristics of seismicity within the Xiaowan reservoir area are quite complicated. The earthquakes outside the reservoir areas are likely tectonic earthquakes irrelevant to the impounding of the Xiaowan reservoir, and there are both reservoir-triggered earthquakes and tectonic earthquakes in the Xiaowan reservoir area. The reservoir-triggered earthquakes are mainly located along the Heihui river (subarea A) and Lancang river (subareas B and C), and could be classified into rapid response seismicity. In subarea A, a significant "migration" of hypocenters is observed in the first impounding circle along the Heihuijiang valley and Qiaoxi-Weihou fault zone, which probably links to the process of water permeation in this area. According the distribution of active faults, rock properties and relocated focal depths in the reservoir area, we suggest that the karst action and fluid permeation caused by the water impounding, and fault movements are the key factors to trigger seismicity in the Xiaowan reservoir. However, it needs further study to better understand the physical process of reservoir-induced earthquakes and tectonic seismicity in some subareas of the reservoir. |
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| Keywords: | Xiaowan reservoir Reservoir-triggered seismicity Double-difference method Cross-correlation method Seismic activity |
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