CHARACTERISTICS OF FOCAL MECHANISMS IN THE DOWNSTREAM RESERVOIR AREAS OF JINSHA RIVER

doi:10.3969/j.issn.0253-4967.2019.05.006

Abstract

Abstract: We select the Xiluodu-Wudongde reservoir area in the downstream of Jinsha River as the research area, and use the CAP and GPAT method to obtain focal mechanisms of M_L ≥ 2.0 earthquakes from 2016 to 2017 in this region. Then, we analyze the spatial distribution characteristics of focal mechanism solutions in each local region and investigate the relationship between seismicity and regional structures. According to 414 focal mechanism solutions we get following conclusions:1)The Xiluodu dam began to impound water on May 4, 2013, and seismicity increased significantly after impoundment. We get 49 focal mechanisms in the Xiluodu dam and its adjacent area which are dominated by thrust faulting and next by strike-slip faulting, which are mainly distributed near the middle section of the Ebian-Jinyang fault zone. The distribution of nodal planes striking in NNW to NE direction is consistent with that of regional faults, and some large earthquakes are controlled by regional structures. 2)There are 39 and 24 focal mechanisms obtained in the unimpounded Baihetan and Wudongde dams and adjacent areas, and the spatial distribution of focal mechanism solutions are relatively consistent, dominated by strike-slip faulting with a small amount of thrust and normal faulting. The sinistral strike-slip earthquakes are consistent with the activity of Xiaojiang fault zone and Puduhe-Xishan Fault. The strikes of the nodal planes are distributed discretely, and many groups of faults intersect with each other in the area, suggesting that the seismogenic environment is relatively complex. 3)The seismicity in Ludian continues to be active after the Ludian M6.5 earthquake. By the end of 2017, we got 260 focal mechanism solutions in the aftershock area of the Ludian M_S6.5 earthquake of Aug 3rd, 2014, which show an "L-shape" in distribution and are dominated by thrust and strike-slip faulting. The long axis is distributed in EW direction, and the short axis is distributed in near NNW direction. The strikes of nodal planes are mainly near EW and near NE, and the nodal planes in the NW direction are less. According to characteristics of a large number of focal mechanism solutions, we deduce that there may exist a buried structure in the EW direction, the seismicity is controlled by different types of faults and the seismogenic structure is very complex. 4)The centroid depth in each region is concentrated in the range of 5~15km, indicating that the seismogenic layer in the study area is 5~15km deep in the middle and upper crust.

Key words: the downstream reservoir area of Jinsha River, the focal mechanism solution, the aftershock area of Ludian earthquake, centroid depth

摘要： 文中选取金沙江下游水库区溪洛渡-乌东德段为研究区，采用CAP和GPAT方法获得区域内2016-2017年2.0级以上地震的震源机制解，分析各分区震源机制解的空间分布特征，探究地震活动与区域构造的关系。研究结果表明：1）溪洛渡大坝及邻区的地震震源机制解以逆冲型为主，其次为走滑型，主要分布在峨边-金阳断裂带中段附近。节面走向在NNW-NE范围内的地震与区域断裂带的分布特征相符，且一些较大地震的发生受区域构造控制。2）尚未蓄水的白鹤滩、乌东德大坝及邻区的地震震源机制解的空间分布较为一致，其中左旋走滑型地震与小江断裂带和普渡河-西山断裂的活动性质相符。区域内存在多组断裂的交会部位，震源机制解的节面走向离散分布，孕震环境较为复杂。3）鲁甸地震余震区的震源机制解以逆冲型和走滑型为主，呈"L"形分布，其中长轴近EW向，短轴近NNW向。大量余震震源机制解结果显示，可能存在近EW向的隐伏构造，不同类型的断层共同控制该地区的地震活动，发震构造十分复杂。4）各分区的地震矩心深度集中在5~15km范围内，推断研究区孕震层在深度为5~15km的中上地壳内。

关键词: 金沙江下游水库区, 震源机制解, 鲁甸地震余震区, 矩心深度

CLC Number:

P315.2

DUAN Meng-qiao, ZHAO Cui-ping. CHARACTERISTICS OF FOCAL MECHANISMS IN THE DOWNSTREAM RESERVOIR AREAS OF JINSHA RIVER[J]. SEISMOLOGY AND GEOLOGY, 2019, 41(5): 1155-1171.

段梦乔, 赵翠萍. 金沙江下游水库区地震震源机制特征[J]. 地震地质, 2019, 41(5): 1155-1171.

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