Study on Seismic Activity of Reservoir in Complex Tectonic Environment −Take Nuozhadu Hydropower Station as An Example
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摘要: 糯扎渡水电站位于澜沧江中下游,该地区构造环境复杂,活动断层发育,地震频发。本文利用区域构造、糯扎渡库区水荷载变化、云南省区域地震台网2000—2021年地震监测资料,对糯扎渡水库区域断层性质、库水位荷载变化、地震震源参数和水库蓄水前后的地震活动空间等进行综合分析。研究结果表明,糯扎渡水库影响区及附近区域活断层密集,构造环境复杂且存在应力水平较高区域,蓄水前库区地震活动强度较高。伴随蓄水量的增加,微小地震活动频度和强度逐渐增强,显示出蓄水对库区内断层上的应力分布具有明显的扰动作用。蓄水后水库坝区附近和澜沧江库区中段窝拖寨断层区的地震活动频度和强度有所增强,普洱大河库段地震活动强度则低于区域背景地震,但微小地震活动的频度有所上升,且与库水位的周期性变化有一定的相关性。地震活动的空间位置与库区内复杂的构造断层密切相关。在区域构造应力和库区水加、卸载的共同作用下,构成了糯扎渡水库影响区微小地震时间、空间、强度的活动图像。未来区内地震活动仍将受到区域构造应力影响和水位变化及水的渗透作用影响,其地震活动强度可能达到5.0级左右。Abstract: Nuozhadu Hydropower Station (NHS) is located at the middle and lower reaches of the Lancang River, where the tectonic environment is complex with massive active faults and frequent earthquakes. In this paper we comprehensively analyzed the characteristics of regional faults, the variation of water level load in NHS, focal parameters, and the spatial distribution, frequency and intensity of seismicity before and after impoundment, based on the regional tectonics, the variation of water load, and the seismic monitoring data of Yunnan regional seismic network from 2000 to 2021. The results show that the affected areas in and around the reservoir have densely distributed active faults and tectonic environment with high stress level, and higher intensity of seismic activities before impoundment. The frequency and intensity of micro-seismic activities gradually increase on the rise of water level, indicating that water storage has a significant disturbance on the stress distribution along the faults. After impoundment, however, the intensity of seismic activities is lower than that of regional background earthquakes, but the frequency of micro-earthquakes increases and intensifies, which is correlated with the periodic change of reservoir water level. The spatial distribution of seismic activities is closely related to the complex faults in the area. The activity pattern of time, space and intensity of micro-earthquakes in the affected area of NHS are constructed by the joint action of regional tectonic stress and water loading and unloading. Seismicity in the region will still respond to the regional tectonic stress, the change of water level and the infiltration of water in the future and the magnitude may reach about M5.0.1)
1 2 叶建庆、李勇、徐誉宸等,2018.糯扎渡库区及邻区水库地震监测总结与地震活动特征研究报告(2008年—2017年). -
表 1 糯扎渡库区及邻近地区主要断裂活动特征
Table 1. Major faults activity characteristics of Nuozhadu hydropower station and affected area
断裂名称 断裂长度/km 产状 断裂性质 最新活动年代 地震活动 走向 倾向 倾角/(°) 澜沧江断裂 800 NNW SE 近直立,
微向西倾右旋走滑 10万年以内 永平、鲁史附近发生过5.5级地震 南汀河断裂 210 NE — 40~50 左旋走滑压扭 第四纪 1941年耿马大寨7级地震、1988年11月7.2级地震 营盘山断裂 140 NS SE 60 — 更新世 第四纪以来活动减弱 邦东断裂 50 NW NE 40~70 左旋,北为正断,
南为逆断10万年以内 历史上发生过多次中震 窝拖寨断裂 26.5 NE NW — 左旋 全新世 现代有多次中震记载 漫罗断裂 38 NE — — 平移断层 — — 孟连-澜沧断裂 150 NE NW 70~80 左旋 全新世 1952年孟连-澜沧交界6.5级地震、1984年4月
孟连6.4级地震、1995年7月中缅边境7.3级地震木戛-谦迈断裂 120 NW SW/NE 60~80 右旋走滑 全新世 1988年澜沧7.6级地震 澜沧-勐遮断裂 160 NW SW 60~80 右旋走滑 全新世 1988年11月6日澜沧-耿马7.6级地震的6.7级强余震
发生在断裂北段,现代小震活动频繁谦六断裂 92 SN W — 逆断 中更新世中晚期 — 平掌寨断裂 90 NS W/E — 正断层、逆断 前第四纪 近现代无地震记载 白马山断裂 35 NW SW — 正倾滑断裂 中更新世中期 断裂东侧现代有地震活动记载 酒房断裂 50 NNW NE 80 逆断 中更新世 断裂中段有中震记载 普文断裂 220 NNW — — — — 2014年12月7日普文断裂北西(隐伏)延长段上发生的
景谷6.6级地震是距今最近的一次强震肖塘断裂 100 SE W 45 逆断 前第四纪 现代有中强震记载 肖塘箐断裂 — NS W — 压扭左旋 第四纪 断裂中段东侧及南段现代有强震记载 麻栗坪断裂 40 NNW SW — 逆断 第四纪 断裂中段东侧现代有中强震记载,断裂南段有小震记载 李子箐断裂 40 NW SW — 逆断 第四纪 断裂南段近代有中强震记载 表 2 糯扎渡水库蓄水后水位年变幅度
Table 2. Annual variation of water level after Nuozhadu hydropower station impoundment
年份/年 极低位时间/(年-月-日) 极低位值/m 极高位时间/(年-月-日) 极高位值/m 变化幅度/m 2011 2011-11-29 610.33 2011-12-17 666.23 55.90 2012 2012-01-02 663.04 2012-12-31 774.69 111.65 2013 2013-03-16 771.27 2013-10-18 812.09 40.82 2014 2014-06-16 769.35 2014-10-24 812.34 42.99 2015 2015-07-01 770.05 2015-12-31 795.26 35.41 2016 2016-06-05 770.38 2016-11-01 812.31 41.93 2017 2017-07-04 770.03 2017-10-26 811.73 41.70 2018 2018-06-06 765.12 2018-10-30 811.93 46.81 2019 2019-06-19 765.40 2019-01-29 811.12 45.72 2020 2020-06-26 766.70 2020-12-03 811.61 44.91 2021 2021-07-05 774.97 2021-10-21 807.54 32.57 表 3 蓄水后糯扎渡水库影响区内地震活动情况
Table 3. Seismic activity after impoundment in Nuozhadu hydropower station adjacent region
年份/年 频次/次 最小震级/级 3.0级以上地震
次数/次最大地震发震时间/
(年-月-日)震级/级 震源深度/km 距坝区距离/km 距库岸距离/km 震中参考位置 2012 189 1.0 12 2012-09-18 4.2 10 82.0 0.5 窝拖寨断裂 2013 176 1.1 12 2013-07-21 4.2 12 53.0 4.8 普洱大河支库附近 2014 183 1.0 6 2014-08-27 4.1 5 71.0 8.0 普洱大河支库尾段 2015 327 1.0 4 2015-12-08 4.0 7 6.2 2.0 黑河支库附近 2016 101 1.0 2 2016-11-06 3.8 5 75.0 5.0 普洱大河支库尾段 2017 97 1.0 4 2017-07-29 4.0 13 14.0 0.0 澜沧江主库段 2018 91 0.4 5 2018-08-28 3.8 5 76.0 5.0 普洱大河支库尾段 2019 77 0.4 7 2019-01-06 4.1 7 74.0 3.0 普洱大河支库尾段 2019-05-11 4.1 8 61.0 1.0 普洱大河支库附近 2020 64 0.7 2 2020-03-27 3.6 13 54.0 7.0 普洱大河支库附近 2021 81 0.4 8 2021-06-20 4.3 10 5.4 5.4 澜沧江主库附近 -
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