STUDY ON RELOCATION AND ACTIVITY CHARACTERISTIC OF SMALL EARTHQUAKES IN PUBUGOU RESERVOIR AREA

doi:10.3969/j.issn.0253-4967.2013.01.010

Abstract

Abstract:

The small earthquakes in and around Pubugou reservoir area are relocated by the double-difference method,and the earthquake properties of two cluster regions near water area are also analyzed.The 1834 earthquakes in the study area from 14 October 2006 to 31 December 2011 are relocated, and we have gotten 1708 earthquake relocation results eventually,amounting to 93.1% of the total. After the relocation,the RMS average value of arrival time residual decreases from 0.93s to 0.21s,the average error is 0.5km in EW direction,0.6km in NS direction,and 2.9km in vertical direction.The epicenter distribution is more concentrated,and the dominant distribution is also more obvious,the cluster region of small earthquakes distributes in the middle part of reservoir area,near to and downstream of the dam.The average focal depth is 9.2km. Earthquakes with focal depths less than 10km amount to 59% of relocation results,and those within 15km amount to 72%,the deepest focal depth is 33.1km.According to spatial distribution of relocation results,we divide the study area into four main regions (A,B,C and D) to discuss respectively.The evolutions of earthquake activities with time show that the variation of earthquake activities in region C and D is relativity larger than that in region A and B; the earthquakes of region C and D are highly centralized,and the focal depth is obviously shallow. With respect to the origin time of earthquakes,the earthquakes in region A and B occurred randomly in 24 hours of a day,which is accord with the time characteristic of natural earthquakes,while the occurrence time of earthquakes in region C and D had obvious regularity,most of them occurred in daytime,and focused on pre- and post 12'clock at noon and 18'clock in the afternoon.The results of field survey show that the seismic cluster area in region C is in accord with the construction sites of Ya'an-Xichang expressway and new Hanyuan county,and the cluster in region D is in accord with the quarry of Kaergou and Jialiega which are all near the reservoir dam. By synthesis analysis,we think that small earthquakes of region C and D may not be tectonic earthquakes; moreover,most of them occurred before November 2009,a time before the impoundment of Pubugou reservoir. So the earthquakes are not related with the impoundment either,but possibly the explosion ones caused by all kinds of construction.

Key words: double-difference location, earthquake clustering, explosion earthquake, Pubugou Reservoir

摘要：

利用双差定位法对瀑布沟水库及邻区1 834次小震进行了重新定位,并对距水库水域最近的2个小震集中区的地震性质进行了分析。重新定位后得到1 708次小震结果,定位残差由原来的0.93s降为0.21s,水平向估算误差平均为0.6km,垂直向估算误差平均为2.9km; 平面空间分布显示,重新定位地震主要分布在研究区的西南(A区)、库中区(C区)和水库大坝附近(D区); A区小震密集与其处于鲜水河断裂中南段、安宁河北段和大凉山断裂北段交会区的特殊地理位置有关。C,D区高度集中分布的小震与水库蓄水无关,属于各种建设施工造成的爆破地震。

关键词: 双差定位, 地震从集, 爆破地震, 瀑布沟水库

CLC Number:

P315.6

ZHANG Yong-jiu, XIE Rong-hua, ZHANG Zhi-wei, HU Xian-ming. STUDY ON RELOCATION AND ACTIVITY CHARACTERISTIC OF SMALL EARTHQUAKES IN PUBUGOU RESERVOIR AREA[J]. SEISMOLOGY AND GEOLOGY, 2013, 35(1): 113-124.

张永久, 谢蓉华, 张致伟, 胡先明. 瀑布沟水库区域小震重新定位与地震性质研究[J]. 地震地质, 2013, 35(1): 113-124.

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