小浪底库区近场地震活动特征分析

统计整理小浪底库区近场地震,对地震位置进行精确定位,并计算较大地震的震源机制解,结合水库地震的活动特点,对地震活动和震源机制特征进行分析,认为小浪底库区地震活动具有水库地震特征,且同时受区域地质构造影响。     

小浪底水库诱发地震的危险性分析

分析了小浪底库区的地质构造背景,论证了小浪底水库具有诱发地震的可能性(P= 0．499),得出最大诱发震级Ms为5．5级,洛阳潜在震源区震级上限为6．5级。分析了库区周围的历史地震、1970年以来的微震活动和能量释放规律,认为未来2年内,小浪底库区诱发中强地震的可能性较小。     

福建街面水库地震活动背景

福建街面水库2006年10月下闸蓄水,分析了街面水库库区历史地震和现今地震震中分布、震源深度、震源机制解等地震活动特点,并结合水库诱发地震的特点认为街面水库存在诱发地震的可能。     

双差定位法在小湾水库库区地震精确定位中的应用

利用双差定位法对小湾水库库区的16个地震台2011年至2012年的地震目录资料进行重新定位,得到了更精确的震源参数。定位结果显示了小湾水库库区地震震源分布的更加精细的图像;揭示出该地区地震活动与活动构造的密切关系;并对原始目录和重定位后的结果进行比较。应用结果表明,震源相对位置精度有了明显提高,更加清晰地反映出活动构造图像。     

小浪底水库诱发地震监测及研究

利用2009年小浪底地震台网数字化改造后记录到的2009-2011年水库周围20 km范围内发生的地震,分析其时空分布特征以及其中61次地震的震源机制解。结果表明,小浪底水库存在诱发地震活动,以弱震和微震为主,最大M_L2.8。地震集中分布在2个丛集区,分别与库区的石井河断层、塔底断层有关。库区地震的张应力轴与构造背景最大主压应力轴方向基本一致,倾角30°左右,表明这些地震是在受到一定的相对直立压应力作用下发生的,可能与水库蓄水后库水载荷的长期作用有关。     

福建水口库区地震活动及其动力成因分析

根据水库蓄水后地震活动的时间分布特征,将水库诱发地震分为三个阶段,通过对三个阶段地震活动的震中分布、震源深度、震源机制解等活动特征进行分析,同时考证震中区历史上曾发生过的强烈有感地震,得出以下认识:①库区三个阶段地震动力成因各不相同,第一阶段主要是水库蓄水引发的初始应力释放,第二阶段地震动力来自东南方向,第三阶段地震动力来自西北方向。②水库诱发地震震中区历史上曾发生过强烈有感地震,震中区将成为区域构造应力场调整释放的"窗口",因此应加强水口库区的地震监测与防御。③在讨论福建地区地震动力成因时,不能只强调来自台湾岛弧碰撞对福建地区地震的控制作用,而忽略来自喜马拉雅碰撞带对福建地区的作用力。     

云南省糯扎渡水库蓄水前后地震活动性研究

采用2008年6月至2013年10月糯扎渡水库地震台网记录的6 300个地震,对水库蓄水前后的地震活动进行分析,发现库区蓄水后,地震频度与水位同步增长,地震活动显著增强,表明库区有水库诱发地震发生。蓄水前后的地震活动图像显示,澜沧江上景谷、双江交界处的小震活动增加最为显著,采用Hypodd双差相对定位方法对该震群进行了重新定位,定位后地震在空间上更为丛集,地震震源深度从0~20 km都有分布。该震群发生在窝拖寨断裂上,该断裂历史上曾发生过5.3级地震,因此分析认为,该震群的发生时间虽与水位相关,但可能是触发了构造地震,所以震源深度显现的是构造活动的特征。     

利用谱聚类方法研究新丰江库区的震源机制解

为检验震源机制解谱聚类方法的实用性,选择新丰江库区为研究区域,利用FOCMEC方法反演了该区域2012年1月1日—2018年12月31日M_L2.0以上地震的震源机制解,并对其进行了谱聚类分析,最终获得该区域7种震源机制解类型;通过分析每种类型的震源机制解特征及其时空分布特征,探讨了震源机制解类型分布与区域构造的关系。结果表明:(1)新丰江库区地震破裂类型以正断型为主,兼有部分倾滑分量,其次为走滑型;(2)不同类型的震源机制解具有区域性的空间分布特征,主要受不同的构造背景影响,反映了新丰江库区地震活动和构造特征之间的关系;(3)不同类型震源机制解所描述的断裂分布反映了峡谷及大坝区库水渗透的构造条件,解释了区域地震频发的可能原因;(4)每种类型的震源机制解在研究时间范围内数量变化较为稳定。     

汶川8.0级地震前紫坪铺库区震源机制及应力场特征

利用2004年8月16日到2008年5月12日汶川8.0级地震前紫坪铺水库数字地震台网和成都数字地震台网的地震波形资料,运用振幅比方法计算了紫坪铺库区486次1.6级以上地震的震源机制参数;根据得到的震源机制参数分析了紫坪铺库区震源机制和应力场的时空变化特征。结果显示:2006—2008年紫坪铺水库水域范围内逆冲型地震很少,走滑型地震增加;距水域较远的区域逆冲型地震的比例偏高,走滑型地震没有增加;各区域的平均主压应力场的方位在汶川8.0级地震前出现了不同程度的偏转和扰动。     

汶川8.0级地震后紫坪铺水库库区地震的分布特征

采用双差定位方法对紫坪铺水库库区12个地震台站2009年记录的857个地震进行了重新定位,获得了815个地震的震源位置。定位结果显示库区有3个地震相对集中区域,在各个集中区域地震震源深度的分布特征各不相同。与已有的汶川8.0级地震前库区地震精定位的研究结果相比较,汶川8.0级地震后库区地震相对集中区域的位置关系发生了明显变化。     

Distribution Characteristics of the Seismicity of Zipingpu Reservoir Region after the Wenchuan Earthquake

815 earthquakes recorded by 12 seismic stations of the Zipingpu reservoir seismic network in 2009 were relocated using the double difference algorithm to analyze the seismic activity of the Zipingpu reservoir.Relocation results show that the earthquakes are concentrated relatively in three zones.The distribution characteristics of focal depth are obviously different among different concentration zones.This means earthquakes in different concentration zones may have different causes.Compared to relocation of...     

Prediction and verification of earthquakes induced by the Xiluodu hydropower station reservoir

Research has been conducted on reservoir-induced earthquakes in China since the Xinfengjiang reservoir-induced earthquakes in the 1960s. Regulations now require the risk of reservoir-induced earthquakes to be evaluated in the pre-research stage of all hydropower projects. Although nearly 40 cases of reservoir-induced earthquakes have been reported in China, analyses comparing the changes in seismic activity following reservoir impoundment with predictions are rare. In this study, we compared seismic activities observed in the reservoir area before and after the impoundment of the Xiluodu hydropower station in terms of the spatial distribution, frequency, and focal depths of the earthquakes, and clarified the correlation between their frequency/timing and reservoir level after impoundment. We then concluded that the seismic events in the head region were karst-type earthquakes, while those in the second segment of the reservoir were tectonic earthquakes. The spatial distribution of the earthquake epicenters and the seismic intensities validated some of the results for the reservoir-induced seismic risk assessment for the Xiluodu hydropower station, indicating that the proposed earthquake triggers and predictive models are reasonable. This study can provide a valuable reference for investigating the mechanism (s) of reservoir-induced earthquakes, revising reservoir-induced earthquake hazard assessment codes, and predicting the hazard zones of reservoir-induced seismicity under similar conditions.     

水口水库地区地震震源机制解特征分析

求解了福建水口水库地区15个地震的震源机制解。 结果表明, 水库蓄水早期地震震源参数变化较大, 而蓄水晚期地震震源参数基本一致。 此外, 还对蓄水早期和蓄水晚期构造主应力方位、作用类型以及地震断层滑动性质特征进行了分析, 虽然这些地震都属于水库蓄水诱发地震, 但相对而言, 蓄水晚期的诱发地震具有明显的构造地震特征。 这些结论将对其他水库地震分析具有一定的参考价值。     

巴颜喀拉块体强震活动与2010年玉树7.1级地震的关系

系统地总结分析了巴颜喀拉地块北、东、南边界带的构造特征、各个边界带上的强震活动、部分强震的震源机制解和区域地震活动,从而探讨了2010年玉树7.1级地震发生前巴颜喀拉地块地震活动特征。从2008年玉树地区地震活动变化、巴颜喀拉块体北边界和南边界强震呼应及块体动力学过程进行了地震趋势预测的思考。     

大桥水库MS4.6级诱发地震的初步研究

2002年3月3日大桥水库诱发了Ms4．6级水库地震，其发震构造是安宁河东支断裂近傍具有正断层性质的一个分支断裂。据大桥台网7年多库区地震观测事件记录，地震空间分布上水体附近有一个明显的活跃过程，大坝上游发生小震群，大坝下游发生主震序列。地震的震源深度在蓄水前后有明显变化。4．6级地震的震源机制解的主压应力轴方位和倾角与大多数活动断裂上的地震有明显的差别，主压应力轴的倾角与其它的水库地震相比也存在较大差别。     

The Focal Mechanism and Characteristic of Stress Field in the Zipingpu Area before the M_S8.0 Wenchuan Earthquake

Based on seismic wave records of the Chengdu digital seismic network and Zipingpu reservoir digital seismic network from August 16,2004 to May 12,2008 when the Wenchuan MS8.0 earthquake occurred,the parameters of focal mechanisms of 486 earthquakes with magnitude larger than M1.6 in the Zipingpu reservoir area were calculated using amplitude ratio method,meanwhile the temporal-spatial variation characteristics of mechanisms and stress field were analyzed based on these parameters.Results show a low ratio of thrust earthquakes and an increased number of strike-slip earthquakes in the reservoir water area in the period from 2006 to 2008.While in the areas far from the reservoir waterfront,the thrust earthquakes took up a high proportion and the strike-slip ones did not increase.The direction of mean principal compressive stress field was deflected and disturbed differently in each area before the Wenchuan MS8.0 earthquake.     

水口水库地震对南平地区的影响

水口水库建成蓄水后诱发了频繁的地震活动，延续时间已达8年之久，,学在继续活动。近年来，南平地区的邵武，政和等地也相继有中小地震活动，为了摸清南平地区地震活动与水口水库诱发地震是否关联，本文对该地区及水口水库诱发地震前后的地震活动性及时空特征，区域构造背景及水库诱发地震的活动趋势进行综合分析研究。     

CHARACTERISTICS OF TECTONIC STRESS FIELD OF THE XIAOWAN RESERVOIR BEFORE AND AFTER THE IMPOUNDMENT

Using the seismic waveform data of Xiaowan seismic network and Yunnan seismic network, we determined the focal mechanisms of 36 earthquakes(M_L ≥ 3.0)from Jun. 2005 to Dec. 2008 and 51 earthquakes(M_L ≥ 2.5)from Jan. 2009 to Dec. 2015 by generalized polarity and amplitude technique. We inverted tectonic stress field of the Xiaowan reservoir before impounding, using the focal mechanisms of 36 earthquakes(M_L ≥ 3.0)from Jun. 2005 to Dec. 2008 and CAP solutions of 58 earthquakes(M_L ≥ 4.0)collected and the solutions in the Global Centroid Moment Tensor(GCMT)catalog; We inverted local stress field of the reservoir-triggered earthquake clustering area, using 51 earthquakes(M_L ≥ 2.5)from Jan. 2009 to Dec. 2015. Focal mechanisms statistics show that, the Weixi-Qiaohou Fault is the seismic fault. Focal mechanisms were strike-slip type in initial stage, but normal fault type in later stage. Focal depths statistics of 51 earthquakes(M_L ≥ 2.5)show that, the average value of focal depths in period Ⅰ, period Ⅱ and period Ⅲ are 8.2km, 7.3km and 7.8km respectively and the standard deviations are 4.3km, 3.5km and 6.0km respectively. The average value of focal depths is basically stable in different period, only the standard deviation is slightly different. Therefore, there is not positive connection between focal depth and deviation of focal mechanisms. What's more, there are 2 earthquakes(number 46 and number 47 in Fig.5 and Table 3)with almost the same magnitude, epicenter and focal depth, but they have different faulting types as normal and strike-slip. The focal mechanism of event No.46 is strike:302°, dip:40° and rake:-97° for plane Ⅰ, however, the focal mechanism of event No.47 is strike:292°, dip:82° and rake:140° for plane Ⅰ. Likewise, earthquake of number 3 and number 18 have similar characteristic. Therefore, the obvious focal mechanism difference of similar earthquake pair indicates the complexity of Weixi-Qiaohou Fault. Considering the quiet-active character of reservoir-triggered earthquakes, we discussed the change of local stress field in different period. The σ₁ of tectonic stress field was in the near-south direction, with a dip angle of 14° before the impoundment, however, the direction of σ₁ of local stress field changed continuously, with the dip angle getting larger after the impoundment. The direction of σ₁ of local stress field of reservoir-triggered earthquake clustering area is close to the strike of Weixi-Qiaohou Fault, and reservoir impoundment increased the shear stress in the fault, so the weakening of fault was beneficial to trigger earthquakes. Comprehensive analysis suggests that fluid permeation and pore pressure diffusion caused by the water impounding, and the weakening of fault caused by local stress field are the key factors to trigger earthquake in the Xiaowan reservoir.     

构造"稳定"区强震长期预测的简便途径--以张北地震为例

作为强震长期预测基础的地震带、潜在震源区的划分,仍然依据地震构造类比和地震活动重复两原则。现有的强震长期预测方法在构造“稳定”区,即没有活动构造、没有历史地震(包括古地震)资料的条件下,无能为力。通过张北地震资料的分析,高精度地震定位并结合波形数据反演震源机制的结果表明：在稳定而统一的构造应力场的作用下,沿其最大剪切应力方向上的小地震集中成带,并且持续活动、震源机制的优势取向与应力场吻合,小震带便可以看作属于现今活动的震源断层,在地震长期预测工作中可以作为划分潜在震源区的依据。构造“稳定”区发生的强震属于新破裂。