Determination of the radiated seismic energy for M≥6.0 earthquakes in the Qinghai-Xizang Plateau
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摘要:
地震辐射能量主要由高频体波携带，与震源动态特征直接相关，能够有效地弥补地震矩和矩震级对震源动态过程和高频成分描述的不足，为地震应急和灾害评估提供更为全面的参考。本文使用自主研发的地震辐射能量测定软件测定了中国青藏高原自1990年以来M≥6.0浅源地震的地震辐射能量，并初步分析了中国青藏高原地区浅源地震的能量释放规律。研究结果表明：① 利用该软件测定的中国青藏高原地区的34例浅源地震所得的测定结果稳定可靠。在一般情况下，地震的矩震级MW 与能量震级Me并不相等，为了更全面地评估地震动效应，不仅需要考虑地震断层错动的静态特征，还需要考虑震源的动态特性。因此，在表示震源特性时，矩震级MW 和能量震级Me 各有特点，优势互补。② 改则地震和尼玛地震的能量震级分别为6.47和6.00，地震辐射能量分别为1.26×1014 J和0.25×1014 J。两次震源位置相近、矩震级相同的地震，所释放的能量相差5倍之多。为了探究改则地震与尼玛地震能量释放差异的原因，我们通过S变换对两次地震的波形进行了时频分析。结果表明，震源动态过程的不同导致了地震辐射能量释放过程的差异。因此能量震级和地震辐射能量等动态震源参数比矩震级更适合描述震源的动态过程和地震的潜在破坏性。③ 结合地震矩资料得到中国青藏高原地区浅源地震的平均能矩比为1.9×10−5，是全球浅源地震平均能矩比的1.6倍。能矩比的大小与震源机制有关，走滑型地震的平均能矩比高于倾滑型地震。④ 中国青藏高原浅源地震的能矩比分布存在区域特征，东部和西部平均能矩比分别为2.25×10−5和1.62×10−5，东部明显高于西部。能矩比的区域性差异与地质构造背景有关，地震辐射能量能够反映该地区的地质构造状态。同一区域内地震的能矩比也存在差别，中国青藏高原地区浅源地震的能矩比范围为5.03×10−6—4.80×10−5，反映了不同断层上发生的地震能量释放过程存在差异。因此，为全面反映地震的震源特性有必要进行能量震级和矩震级的联合测定。
Abstract:This study focuses on the radiated seismic energy of earthquakes with a magnitude of 6.0 or greater in Qinghai-Xizang Plateau of China, a region known for its seismic activity due to its unique tectonic setting. Radiated seismic energy, predominantly carried by highfrequency body waves, is a critical parameter that reflects the dynamic rupture process of an earthquake and complements the static characteristics described by seismic moment and moment magnitude. The accurate measurement of the radiated seismic energy is essential for a comprehensive understanding of earthquake dynamics, emergency response, and disaster assessment. The research utilized self-developed software to measure the radiated seismic energy of shallow earthquakes with a moment magnitude （MW） above 6.0 that occurred in QinghaiXizang Plateau since 1990. The study involved 34 earthquakes and aimed to analyze the energy release patterns in the region. It will help us to enhance our understanding of energy release patterns and their implications for seismic hazard assessment.
Introduction
The Qinghai-Xizang Plateau, often referred to as the “Roof of the World”, is not only a significant geographical feature but also a critical area for the study of seismic activity due to its location at the convergence of multiple tectonic plates. The region’s seismicity is influenced by the ongoing collision and compression of the Indian Plate with the Eurasian Plate, leading to a high potentiality for earthquake occurrences. The accurate measurement and analysis of radiated seismic energy are crucial for the potential hazards assessment posed by earthquakes, emergency response strategies forewarning, and guidance on the development of resilient infrastructure.
Methodology
The study employed a self-developed software to measure the radiated seismic energy of shallow earthquakes with a moment magnitude （MW） above 6.0. The software operates on the principles of point-source modeling and integrates the seismic moment rate spectrum over a specific frequency range to calculate the radiated energy. The methodology incorporates corrections for geometric spreading and frequency-dependent attenuation, ensuring the reliability and accuracy of the measurements. Data from the Incorporated Research Institutions for Seismology （IRIS） and the Global Seismic Network （GSN） were utilized to provide a robust dataset for the analysis.
Results
The research findings reveal several key insights into the radiated seismic energy and energy release patterns in the Qinghai-Xizang Plateau:
1） Stability and reliability of measurements: The radiated energy measurements for the 34 selected earthquakes were found to be stable and reliable, showing a high degree of consistency with that of the IRIS database. This validation confirms the effectiveness of the self-developed software in accurately determining radiated seismic energy.
2） Diversity in energy release: A significant variation in the energy release was observed between earthquakes, even those with similar MW and epicentral locations. For instance, the Garze and Nyima earthquakes, both with a moment magnitude of 6.4, exhibited substantial differences in their radiated energy and energy magnitude （Me）, underscoring the importance of considering both static and dynamic characteristics of seismic sources.
3） Regional characteristics of energy-to-moment ratio: The study identified distinct regional characteristics in the energy-to-moment ratio, with an average ratio （1.90×10−5） for Qinghai-Xizang Plateau which is 1.6 times higher than the global average. This suggests that earthquakes in this region are more energetically efficient, potentially leading to greater seismic hazards. A regional characteristic in the distribution of the energy-to-moment ratio was identified, with the eastern part of Qinghai-Xizang Plateau exhibiting a higher average ratio （2.25×10−5） than the western part （1.62×10−5）. This regional variation is believed to be linked to the geological structure background, indicating that radiated seismic energy can reflect the regioral geological state.
4） Mechanism-dependent energy release: The energy-to-moment ratio was found to be dependent on the focal mechanism of the earthquake, with strike-slip earthquakes exhibiting higher ratios compared to dip-slip earthquakes. This relationship provides valuable insights into the tectonic processes underlying seismic activity in the region. The study also found that within the same region, there is a significant range in the energy-to-moment ratio （from 5.03×10−6 to 4.80×10−5）, reflecting differences in energy release processes on various faults. The research concludes that the measurement of both energy magnitude and moment magnitude is necessary for fully understanding the source characteristics of an earthquake. The findings contribute to a better understanding of the potential destructiveness of earthquakes in Qinghai-Xizang Plateau and provide valuable insights for earthquake emergency response and disaster mitigation efforts in the region.
5） Geological significance: The regional variation in the energy-to-moment ratio appears to correlate with the underlying geological structure, indicating that the radiated seismic energy can serve as an indicator of the geological state and stress accumulation levels in the region.
Discussion
The research findings underscore the complexity of seismic energy release in Qinghai-Xizang Plateau and the need for a comprehensive assessment of earthquake hazards. The identification of regional characteristics in the energy-to-moment ratio provides valuable insights into the potentiality for seismic risk and the underlying tectonic processes. The research also highlights the importance of considering both the static （seismic moment and moment magnitude） and dynamic （radiated energy and energy magnitude） aspects of earthquakes for a more thorough understanding of their hazards.
The energy release patterns observed in this study have significant implications for the development of seismic hazard maps and the implementation of risk mitigation strategies. The higher energy release efficiency observed in Qinghai-Xizang Plateau suggests that earthquakes in this region may pose a greater threat to human settlements and infrastructure, necessitating enhanced preparedness and response capabilities.
Conclusion
The comprehensive analysis of radiated seismic energy in Qinghai-Xizang Plateau presented in this study contributes to a more nuanced understanding of earthquake dynamics in this seismically active region. The findings have significant implications for seismic hazard assessment and disaster mitigation strategies. By revealing the regional variations in energy release and their relationship with geological structures, this research aids in the development of targeted approaches to earthquake risk management in Qinghai-Xizang Plateau.
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引言
据江苏省测震台网测定，2016年10月9日9时5分，江苏省盐城市射阳县附近发生ML2.6地震，震中位于(120.14°E，33.86°N)，之后震中附近小震活跃，短时间内形成了小震序列. 2016年10月9日至2017年2月8日，江苏省测震台网共记录到射阳地区ML≥1.5地震44次，其中ML1.5—1.9地震23次，ML2.0—2.9地震17次，ML3.0—3.9地震3次，ML4.0—4.9地震1次，最大地震为2016年10月20日4时51分发生的射阳MS4.4(ML4.9)地震.此次射阳地震序列为前震-主震-余震型.
射阳MS4.4地震的震中为(120.35°E，33.66°N)，位于郯庐断裂带以东、苏鲁造山带以南的苏北盆地.该盆地为苏北—南黄海盆地西部的陆上部分，总体为NE走向，延伸长度大于260 km，主要由盐城—阜宁凹陷、建湖隆起和东台凹陷等3大构造单元组成，坳中有凸，隆中有凹，一系列凹凸构造组成盆地的二级单元(舒良树等，2005；邱海峻等，2006；刘建达等，2012).盆地内部各断陷盆地的边界断裂多数为正断层，其中：盐城—南洋岸断裂为盐城凹陷南侧边界，断面倾向北，倾角为55°，控制了盐城凹陷的发育；洪泽—沟墩断裂为弧形北界断裂，走向由NE转为近EW，倾向为NW，倾角为30°—40°，控制了中、新生带盆地沉积.射阳MS4.4地震即发生在洪泽—沟墩断裂以南、盐城—南洋岸断裂以北的盐城凹陷内部.
射阳地区地震活动水平较低，大震相对较少. 1970年以来，该区域及附近曾发生过3次中强地震，分别为1987年2月17日射阳MS5.1地震，1991年11月5日射阳MS4.7地震，1992年10月22日射阳MS4.6地震.关于该地区地震的研究较少，仅贺楚儒(1999)对1987年射阳MS5.1地震的震源机制进行了简单分析，而震源机制参数是深入了解区域应力状态的重要基本资料.为了给本区域的地球动力学研究提供基础信息，本文拟利用江苏测震台网记录的波形资料，采用CAP(cut and paste)方法(Zhao，Helmberger，1994)反演射阳MS4.4地震的震源机制解和震源深度，并基于江苏省测震台网提供的射阳地震序列的震相报告，采用双差定位方法HypoDD(Waldhauser，Ellsworth，2000)对射阳地震序列进行重新定位，以期得到该序列较为准确的震中位置，并在此基础上进一步探讨射阳MS4.4地震的破裂方向以及地震序列的时空分布特征.
1. 震源深度和震源机制解
波形反演方法可以较充分地利用地震仪器记录到的震相、振幅等信息，对震源机制的约束较为全面(Kanamori，Given，1981；Zhao，Helmberger，1994；Thio，Kanamori，1995；马淑田等，1997；许力生，陈运泰，2004)，其中Zhao和Helmberger (1994)提出的CAP方法将地震仪器记录到的波形分为体波部分和面波部分，允许其在时间窗内相对滑动，较好地改善了波形拟合中由于介质的速度模型差异所造成的震相到时误差，因而应用广泛(吕坚等，2008；郑勇等，2009；韩立波，蒋长胜，2012；谢祖军等，2012；张致伟等，2015；郑建常等，2015；李金等，2016).由于射阳MS4.4地震发生于苏北盆地东侧的盐城凹陷内部，震中东侧为南黄海海域，无测震台站分布(图 1)，可利用的P波初动资料有限, 因此本文采用CAP方法来反演此次地震的震源机制参数和震源深度.
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图 1 射阳地区地震震中及周围台站分布F1：淮阴—响水断裂；F2：洪泽—沟墩断裂；F3：盐城—南洋岸断裂；F4：陈家堡—小海断裂；F5：泾口—沙沟断裂；阴影区域为苏北盆地Figure 1. Distributions of earthquake epicenters and seismic stations in Sheyang areaF1: Huaiyin-Xiangshui fault; F2: Hongze-Goudun fault; F3: Yancheng-Nanyang'an fault; F4: Chenjiabao-Xiaohai fault; F5: Jingkou-Shagou fault. The shadow region denotes Subei basin1.1 数据
根据波形信噪比高、P波初动明显及台站方位分布较全面的选择标准，从江苏省测震台网波形记录资料中挑选了震中距在385 km以内的17个波形质量较高的近震台站(图 1)的数据参与震源机制的反演.首先去除观测波形数据的仪器响应，将坐标系旋转至大圆坐标系内; 然后采用4阶巴特沃斯(Butterworth)带通滤波器对所选取台站的波形进行滤波.波形中体波部分的滤波范围为0.15—0.2 Hz，面波部分的滤波范围为0.05—0.1 Hz.滤波后的波形即为与计算波形比较的数据.
1.2 速度模型
苏北盆地的新生代沉降层较厚，厚约5—6 km，地壳厚为31—32 km(张锁喜等，1990；黄耘等，2011；段永红等，2015; 熊振等，2016).张锁喜等(1990)基于该区域的人工地质探测剖面资料得到的速度结构结果显示：上地壳平均速度为5.5—5.9 km/s，埋深为7—9 km；中地壳平均速度为6.25—6.29 km/s, 埋深为18—24 km；下地壳平均速度为6.6—7.0 km/s，埋深为29—34 km；上地幔顶部速度为7.9—8.1 km/s.黄耘等(2011)认为在20—25 km深度范围内，P波速度相对偏低.基于上述研究结果，本文采用的速度模型如表 1所示.采用表 1给出的射阳地区的速度模型，我们采用频率-波数法(Zhu，Rivera, 2002)计算各频率下的地震波波形.
表 1 射阳地区地壳速度模型参数Table 1. The parameters of crustal velocity model for Sheyang area地层 模型分层厚度/km ρ/(kg·m-3) vP/(km·s-1) vS/(km·s-1) 软沉积层 0.5 2.10 2.50 1.44 硬沉积层 1.5 2.50 4.40 2.54 3.0 2.75 5.22 3.01 上地壳 5.0 2.80 5.59 3.23 5.0 2.80 6.17 3.56 中地壳 5.0 2.90 6.49 3.75 下地壳 5.0 2.90 6.43 3.71 7.0 3.30 7.03 4.08 上地幔 300 3.30 8.00 4.62 1.3 震源深度和震源机制反演
基于图 1中的地震台站波形记录和区域介质速度模型，在参数全空间范围内搜索地震观测波形与理论波形的拟合误差，该误差随深度的变化如图 2所示.可见，误差函数在约14 km深度处呈极小值，14 km即为反演所得的最佳深度.由图 2还可以看出，在14—17 km深度范围内，震源机制解的变化并不大.图 3给出了计算波形与观测波形的对比，可以看出，在参与计算的85个震相中，相关系数大于0.7的有54个，占64%，表明计算波形与观测波形的相关性较好.图 2所示的最小拟合误差为5.472×10-4，说明反演结果相对可靠.反演得到的最佳震源机制解参数为节面Ⅰ:走向304°，倾角53°，滑动角0°，为左旋走滑；节面Ⅱ:走向214°，倾角90°，滑动角143°，为右旋走滑，有一定的垂直运动分量；P轴的方位角为265°，倾角为25°；T轴的方位角为163°，倾角为25°；P轴方位近东西向，T轴近南北向，P轴和T轴的倾角均近水平.
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图 2 射阳MS4.4地震的矩张量反演中波形拟合误差随震源深度的变化Figure 2. Misfit variation with focal depth of the Sheyang MS4.4 earthquake![]()
图 3 射阳MS4.4地震计算地震波形(红色)与实际观测地震波形(黑色)的比较波形左侧为地震观测台站和震中距(单位：km)，波形下面依次为计算波形相对观测波形的到时差(单位：s)和计算波形与观测波形的相关系数Figure 3. Comparison between calculated seismograms (red) and observed ones (black) of the Sheyang MS4.4 earthquakeThe focal mechanism solution of the Sheyang earthquake is also given, the texts on the left of waveform denote the station and epicentral distance (unit in km), the numbers below the seismic wave show the time difference (unit in s) between the calculated and observed seismograms and their correlation coefficient, respectively为了测试速度结构的差异对计算结果的影响，本文基于震中附近区域的Crust2.0速度模型，使用相同的台站资料对此次射阳MS4.4地震的震源参数进行了反演.结果表明，采用不同的速度模型计算所得结果的误差均在网格搜索步长(5°)以内，因此介质速度模型的差异对震源机制解的影响不大.
2. 地震序列重新定位
双差定位反演方法(Waldhauser，Ellsworth，2000)能够获得丛集地震中每次地震相对于其矩心的相对位置，有效地减少地壳速度结构对定位精度的影响(杨智娴等，2003；Zhang，Thurber，2003; 曹凤娟等，2013；房立华等，2013；王未来等，2014；王亮等，2015；王光明等，2015；刘建明等，2016)，因此本文采用双差定位方法HypoDD, 使用江苏省测震台网报告中的Pg和Sg到时信息和射阳MS4.4地震震中附近的6个地震台站(SY，LYG，GUY，SQ，HUA，XY), 参考表 1给出的P波速度模型(波速比设为1.73)，对射阳地震序列中44次ML≥1.5地震事件进行重新定位.设最小连接数和最小观测数均为8，震源间距小于10 km，地震对到台站的距离小于200 km，P波到时的权重为1.0，S波到时的权重为0.7.最终，采用共轭梯度法得到了南北、东西、垂直方向的平均定位误差分别为0.32，0.38，和0.25 km.
图 4给出了射阳地震序列重新定位后的地震震中分布图，可以清楚地看到，精定位后的震中位于洪泽—沟墩断裂与盐城—南洋岸断裂之间.地震序列震中水平空间分布的长轴AA′长约16 km，短轴BB′长约8 km.在水平空间内，地震序列分布的优势方向为NW60°，这与采用CAP方法反演获得的射阳MS4.4地震震源机制节面Ⅰ的走向(NW56°)一致，说明射阳MS4.4地震的断层面可能是震源机制解中的节面Ⅰ.
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图 4 射阳地震序列重新定位后的地震震中分布图AA′ and BB′分别为地震序列分布的长轴和短轴Figure 4. Relocation of event epicenters for the Sheyang earthquake sequenceAA′ and BB′ are the major axis and minor axis of the earthquake sequence, respectively图 5a, b给出了射阳地震序列沿AA′和BB′剖面的地震深度分布，可以看出：地震序列的深度主要集中在6—23 km范围内，其中ML≥3.0地震的深度相对较深，集中在18—23 km范围内. 2016年10月20日射阳MS4.4地震的震源深度约为21 km，处于射阳地震序列的东南端.垂直于震中优势长轴走向的剖面BB′反映了沿地震破裂方向的震源几何特征，由图 5b可见，在6—23 km的深度范围内，地震优势分布的倾向为NE，倾角较陡.
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重定位后的射阳地震序列深度随时间的变化如图 5c所示，可以看出，地震序列活动存在有序破裂的现象. 2016年10月15日射阳ML3.5地震发生后，地震序列的震中分布由SE至NW，向浅部扩展；2016年10月20日至2016年10月27日期间，地震序列由SE至NW向深部扩展；2016年11月7日之后，地震序列的震源深度集中在17—23 km，向SW方向迁移(图 4，5c).
3. 讨论与结论
本文采用CAP方法反演了2016年10月20日射阳MS4.4地震的震源机制解参数和震源深度，采用双差定位方法对射阳地震序列中44次ML≥1.5地震事件进行了重新定位.反演得到射阳MS4.4地震的P轴方向近东西向(265°)，T轴方向近南北向(163°)，P轴和T轴的倾角均近水平(25°)，震源机制的应力轴方向与该区域背景应力场已有的相关研究结果一致(汪素云, 许忠淮，1985；张邵治等, 1989；徐鸣洁等, 1996).说明此次射阳MS4.4地震是在背景应力场的作用下发生的.此外，该地震震源机制解的节面Ⅰ走向为304°(N56°W)，与双差定位后的射阳地震序列在水平空间内分布的优势方向(N60°W)一致，据此推测，此次射阳MS4.4地震的运动方向为NW，运动类型为左旋走滑.
射阳MS4.4地震序列位于洪泽—沟墩断裂与盐城—南洋岸断裂之间，两条断裂的走向均近NE.我们查阅了该区域相关的地质资料，没有发现震中附近NW断裂的相关报道，无法确定此次射阳MS4.4地震序列是否由震中附近既有断裂的运动所产生.库伦-摩尔破裂准则(Zang，Stephansson，2010)表明，当岩石发生剪切破裂时，破裂面与最大主应力方向的夹角为
(1) 式中φ=arctanμ为内摩擦角，μ为岩石的内摩擦系数(0.5 < μ < 1).根据所选的岩石摩擦系数，破裂角a的范围为22°—32°，一般为30°(Zang，Stephansson，2010).射阳地震断层面与区域最大主应力轴的夹角约为30°，处于库伦-摩尔破裂角的范围内，由此推测，射阳MS4.4地震是在区域应力场的作用下，沿NW向剪切破裂发生的地震事件.
双差定位结果显示，射阳地震序列存在有序破裂的现象，2016年11月7日后，余震向SW迁移，与前震序列扩展方向(NW)不一致，可能反映了震中区域剪应力释放已经较为充分、余震活动处于震后调整的过程.
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图 1 中国青藏高原MW≥6.0浅源地震分布
Figure 1. Earthquakes with MW≥6.0 occurred in Qinghai-Xizang Plateau in China
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图 2 本文测定的地震辐射能量（a）和能量震级（b）与IRIS结果的对比
Figure 2. Comparison of radiated seismic energy （a） and Me （b） between IRIS and this paper
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图 5 2008年1月9日改则MW6.4地震和2020年7月22日尼玛MW6.4地震
Figure 5. Gerze MW6.4 earthquake occurred on 9 January 2008 and Niyma MW6.4 earthquake occurred on 22 June 2020 in Xizang，China
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图 6 牡丹江台（IC.MDJ）记录到的改则地震（a）和尼玛地震（b）的波形（左）和时频分析（右）图
Figure 6. Waveforms （left） recorded by station IC.MDJ of Gerze earthquake （a） and Niyma earthquake （b） and their time-frequency analysis （right）
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图 7 中国青藏高原浅源地震的能矩比
Figure 7. The energy-moment ratio of shallow earthquakes in Qinghai-Xizang Plateau of China
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图 8 中国青藏高原东部（红色框）和西部（蓝色框）浅源地震慢度系数（能矩比的对数）的区域分布特征
Figure 8. Characteristics of regional distribution of the slowness coefficient （logarithm of energy-moment ratio） in east （red box） and west （blue box） part of Qinghai-Xizang Plateau in China
表 1 中国青藏高原浅源地震的震源参数
Table 1 Source parameters of shallow earthquakes in Qinghai-Xizang Plateau in China
发震日期
a-mo-d震中位置 震源
深度
/kmM0
/（1018 N·m）MW MS ES
/（1013J）Me I Me 震源机制
类型参考位置 东经/° 北纬/° 1 990-04-26 100.28 36.02 10.0 5.61 6.4 6.9 26.7 6.65 6.68 走滑型 青海共和 1 992-07-30 90.18 29.57 31.4 1.79 6.1 5.8 1.93 5.92 5.92 正断型 西藏尼木 1 993-10-02 88.66 38.17 14.1 1.64 6.1 6.3 7.76 6.28 6.33 走滑型 新疆若羌 1 996-02-03 100.29 27.29 10.0 9.94 6.6 6.5 23.2 6.62 6.64 正断型 云南丽江 1 997-04-11 96.95 39.56 20.0 2.06 6.1 6.1 2.96 6.09 6.05 走滑型 新疆伽师 1 997-11-08 87.37 35.12 38.1 223 7.5 7.9 150 7.22 7.18 走滑型 西藏尼玛 1 998-08-27 77.34 39.58 33.0 3.89 6.3 6.4 9.61 6.43 6.39 走滑型 新疆伽师 2 000-09-12 99.37 35.37 12.0 1.76 6.1 6.3 1.92 5.95 5.92 走滑型 青海兴海 2 001-11-14 90.59 35.93 11.0 590 7.8 8.0 582 7.60 7.58 走滑型 昆仑山口 2 003-02-24 77.21 39.52 26.2 3.74 6.3 6.3 2.14 6.00 5.95 逆断型 巴楚—伽师 2 003-04-17 96.51 37.52 15.0 4.12 6.3 6.3 6.55 6.26 6.28 逆断型 青海德令哈 2 004-03-27 89.18 33.99 9.0 1.11 6.0 5.8 1.41 5.84 5.83 正断型 西藏班戈 2 004-07-11 83.67 30.72 8.1 2.36 6.2 6.2 2.14 6.00 5.95 正断型 西藏仲巴 2 005-04-07 83.66 30.52 14.7 3.35 6.3 6.1 3.23 6.07 6.07 正断型 西藏仲巴 2 007-05-05 82.03 34.27 14.2 1.54 6.1 6.0 3.27 6.03 6.08 走滑型 日土—改则 2 008-01-09 85.26 32.4 27.7 5.02 6.4 6.4 12.6 6.42 6.47 正断型 西藏改则 2 008-03-20 81.51 35.55 10.0 54.3 7.1 7.3 39.5 6.82 6.80 正断型 新疆于田 2 008-05-12 103.37 31.06 7.6 897 7.9 8.1 2910 8.06 8.04 逆冲型 四川汶川 2 008-05-12 103.63 31.24 11.5 1.65 6.1 6.1 3.55 6.15 6.10 走滑型 四川汶川 2 008-10-06 90.38 29.84 6.4 3.65 6.3 6.3 3.70 6.11 6.11 走滑型 西藏当雄 2 008-11-10 95.89 37.62 0.1 4.06 6.3 6.4 10.1 6.38 6.40 走滑型 青海海西 2 009-08-28 95.76 37.67 12.1 3.04 6.3 6.2 2.62 6.05 6.01 逆断型 青海海西 2 010-04-13 96.75 33.19 13.8 25.3 6.9 7.0 46.8 6.83 6.85 走滑型 青海玉树 2 012-08-12 82.54 35.65 14.0 2.55 6.2 6.3 2.18 6.00 5.96 走滑型 新疆于田 2 013-04-20 103.02 30.27 18.0 10.2 6.6 6.8 25.3 6.70 6.67 逆断型 四川雅安 2 014-02-12 82.58 35.88 4.1 28.7 6.9 6.9 113 7.07 7.10 走滑型 新疆于田 2 014-08-03 103.43 27.25 10.0 2.12 6.2 6.2 10.2 6.39 6.41 走滑型 云南鲁甸 2 015-07-03 78.12 37.47 19.0 5.33 6.4 6.4 3.10 6.11 6.06 逆断型 新疆皮山 2 016-10-17 94.87 32.91 32.1 1.20 6.0 5.9 1.81 5.88 5.90 走滑型 青海杂多 2 016-11-25 74.02 39.23 17.0 11.3 6.6 6.6 51.6 6.90 6.87 走滑型 新疆阿克陶 2 017-08-08 103.86 33.19 9.0 6.98 6.5 6.5 10.8 6.40 6.42 走滑型 四川九寨沟 2 020-06-25 82.42 35.59 10.0 3.23 6.3 6.3 1.81 5.91 5.91 正断型 新疆于田 2 020-07-22 86.87 33.15 10.0 5.04 6.4 6.3 2.54 6.04 6.00 正断型 西藏尼玛 2 021-05-21 98.24 34.59 10.0 166 7.4 7.3 137 7.20 7.16 走滑型 青海玛多 注：经纬度信息及MeI来自IRIS；M0，MW和MS来自GCMT；ES和Me为本文测定的地震辐射能量和能量震级。 
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表 2 西藏改则地震和尼玛地震的地震参数
Table 2 Earthquake parameters of the Gerze MW6.4 earthquake and Niyma MW6.4 earthquake
发震地点 发震日期 震源深度/km MW Me 辐射能量/（1014J） 能矩比/10−5 震源机制类型 改则 2 008-01-09 13.3 6.4 6.47 1.26 2.5 正断型 尼玛 2 020-07-22 16.8 6.4 6.00 0.25 0.5 正断型
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