Abstract: Lying on the eastern margin of the Tibetan Plateau,the northwestern Yunnan Province has attracted many tourists all over the world for its beautiful scenery and maltinational cultures. At the same time,however,it is also famous for frequent destructive earthquakes that have caused serious loss of life and properties. With rapid economic development,deficiency of electric power in China has become very serious. Therefore,it is inevitable to build a lot of hydropower stations in southwestern China,where hydropower resources are very abundant. A series of dams are planed to construct along the Jinshajiang River. The seismic safety evaluation should be done before the construction of hydropower station,while the appropriate delineation of potential seismic source (PSS) is a key point of the evaluation. In the probabilistic seismic hazard analysis,the distribution and upper bound magnitude of the PSS affect the determination of the design parameters in different engineering sites. For this reason,we have collected the former research results and the data obtained from recent geologic investigation on engineering sites of a series of hydropower stations and on regional seismicity. In order to get an insight into the seismotectonic indicator for the northwestern Yunnan Province,we have analyzed the seismogenic structures of several typical strong earthquakes,including the 1515 Yongsheng M 7^3/4,1925 Dali M 7.0 and 1996 Lijiang M 7.0,and delineate again the PSS for the northwestern Yunnan Province. The following principles and methods have been applied to the delineation of PSS: In the region where strong earthquake has occurred,upper bound magnitude of PSS is determined in the light of “Earthquake Recurrence” principle; in the region where seismogenic structures are clear but no strong earthquake was recorded,PSS are delineated according to“Tectonic Analog”principle; in the region where the segmentation of active fault has been studied thoroughly,the PSS can be demarcated precisely; early-middle Pleistocene faults can be taken as tectonic indicator for moderate-strong earthquake; in the region of buried active fault,images of seismic activity and geophysical anomaly can be used to determine the extension direction of the PSS. In the studied region,21 PSS are delineated with different upper bound magnitude,among which 1 is of upper bound magnitude 8.0,3 are of magnitude 7.5,9 are of magnitude 7.0,and 8 are of magnitude 6.5.

Key words: potential seismic source, seismic safety evaluation, northwestern Yunnan Province

摘要： 在收集、分析前人研究成果的基础上,参考近年来多次工程场地地震安全性评价的野外调查与分析结果,确定了滇西北及其邻区的地震构造标志,进而在该地区重新划分潜在震源区。在有强震发生的地区依地震重复原则划分潜在震源区并确定其震级上限;对于发震构造明显但没有强震记录的地区,根据发震构造规模和活动性特征,依构造类比原则划分潜在震源区;对于活动断裂分段性研究较为清楚的地方,潜在震源区被划分得更细一些;而在断裂隐伏区,则依据地震活动图像及地球物理异常判断潜在源震区的长轴方向。

关键词: 潜在震源区, 地震安全性评价, 滇西北地区