【作者】 薛艳；

【导师】 朱元清；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理学， 2012， 博士

【摘要】 在天然地震研究中,巨大地震(本文指8级以上地震)占有特别重要的位置,这首先是因为巨大地震具有极大的破坏性,是地震预测的首要对象。2004年以来全球特大地震活动频繁,地震及其次生灾害造成了巨大的人员伤亡和财产损失,因此开展全球地震活动,特别是巨大地震的预测研究已成为全球地球科学领域关注的焦点。从科学意义上看,巨大地震的孕育、发生需要特殊的构造环境和条件,包括地质构造环境与构造条件和地球内部物理条件。因此,本文首先地震活动性方面研究全球巨大地震,再对巨大地震的深部、浅部孕震环境中的一些重要问题进行数值模拟研究。在地震活动性方面,本文定量计算了全球及主要构造带地震活动的显著周期,分析了全球巨大地震活动的空间特征,总结归纳了板内和板缘巨大地震前中强地震活动的共性及差异性特点,研究了1976年以来全球8级以上巨大地震序列演化的统计特征。数值模拟方面,首先从区域应力应变场特征、动力学发震机制、大震间的黏弹性应力触发、库水载荷触发等方面研究了2008年汶川Ms8.0地震；其次,研究了板块俯冲带附近区域应力场特征,解释了逆冲型浅源巨大地震震源区附近俯冲角度比较小的原因,探讨了中深源地震的发生对浅源地震的影响。地震活动性方面的研究结果为：①全球地震活动的显著周期为45.5年,其次为32年；环太平洋地震带的显著周期为45.5年；低纬度环球剪切带为30.9年,其次为47.5年。②全球8级以上浅源地震中绝大多数为逆冲型,主要发生在俯冲型板块边界带上,其震源附近Benioff带倾角较小,俯冲板块的运动方向与海沟夹角较大；逆冲型巨大地震发生在两个板块接触部位,正断层型巨大地震发生在洋壳的侧坡上。③绝大多数板内和板缘巨大地震前出现两类地震空区(空段)；板内巨大地震前长期阶段中强以上地震形成增强活动环分布区(也称增强区),主震位于活动环包围的空区内,增强区内地震分布不均匀,震群活动显著；板缘巨大地震前长期阶段表现为强震的集中活跃或异常平静；板内巨大地震前中短期阶段震群频度增多,并形成小震活动图像；中深源地震活动增强、震源深度增大是板缘特大浅源地震前中短期阶段的特有现象。④1976年以来全球8级以上地震以逆冲型破裂为主,序列类型以主-余型为主；前-主-余型地震和多震型地震均为逆冲型破裂；全球8.5级以上特大地震中29.4%具有7级前震,明显高于中强地震中有前震的比例。数值模拟方面的研究结果为：①在印度板块的强烈推挤作用和下地壳软流层的水平拖拽下,巴颜喀拉地块向东南的水平运动受到坚硬的四川盆地的阻挡,造成川西高原相对于四川盆地的差异性抬升,这是汶川高角度逆冲型地震发生的重要动力学成因；汶川地震受到的来自巴颜喀拉地块边界带7级以上大震的应力触发作用很小。地震孕育主要依赖于在背景应力场作用下,孕震断层自身的能量积累,地震间的触发作用仅仅是外因。地震强度和空间距离是影响触发作用的主要因素。本文从应力触发角度解释了龙门山南段未破裂的原因；汶川地震的初始破裂点位于紫坪铺水库蓄水时库伦应力的减少区和放水时的库仑应力的增加区,但引起的库仑应力变化量非常有限,库水载荷对汶川地震的发生没有明显的触发作用。②通过库仑应力计算,得到当俯冲带倾角为30。时,最容易产生逆冲型破裂；当倾角大于60。和小于10。时,发生逆冲型地震的可能性不大。③岩石圈分层结构的水平差异运动(或地幔和岩石圈的水平差异运动)对地形具有非常大的影响。更多还原

【Abstract】 The great earthquakes(M≥8.0) play significant roles on behalf of the devastating destructive in disasters so its prediction is the primary object in the study of tectonic earthquakes. Frequently great shocks have caused severe seismic hazard since2004. Study on seismic activity, especially on the great earthquake prediction, has become a focus in the research field of seismology.While the preparation and occurrence of great earthquakes requires specific geological and tectonic environment, including geological settings, tectonic environment, as well as geophysical conditions inside the Earth. Therefore, in this paper we try to numerically simulate some issues of the deep and shallow seismogenic environments based on the statistical studies of the characteristics of great earthquake activities.In this paper, the great earthquakes were studied in two aspects of seismcity and numerical simulation.①In the aspect of seismic activity, firstly, we quantitatively calculated the seismicity periods of the globe and the main tectonic zones. Next, the spatial characteristics of the worldwide great earthquakes were studied. Then, the similarities and differences of seismic activity prior to the great intraplate and interplate shocks were researched. Finally, we analysis the statistical features of the great earthquake sequences.②In the aspect of numerical simulation, we firstly studied on the2008Wenchuan M8.0earthquake from the aspects of regional stress and strain field, the geodynamic mechanics of high-angle reverse fault slip, the influence from the Zipingpu reservoir, and the Coulomb stress triggering from the strong earthquakes in the boundary zones of the Bayan Har block since1900. Next, we made analysis of the regional stress field characteristics and explored the impact of deep focus earthquake on great shallow earthquakes. Finally, we explain why the great shallow shocks with thrusting-slip rupture occurred in the area where the dip-angle of the Benioff zone is rather small.The results of the study on seismic activity show that①There are two principal periodic components,45.5-year and32.0-year, in the global seismicity. For the Circum-Pacific seismic belt, the principal period is45.5-year. The principal periodic components are30.9-year and47.5-year in the seismicity of the low-latitude circum-earth zone.②Most of the great shallow shocks are the type of thrusting-slip rupture, which mainly occurred in the subduction plate boundary zones. In the source region the dip-angle of the subdution plate is small and the movement direction of the subduction plate is approximately vertical with the trench. The great shocks with thrusting-slip rupture occurred in the contact area of the two plates, while the great normal-fault events occurred in the oceanic crust.③Two types of gap usually appear before the most of the great intraplate and interplate shocks. The doughnut-shape pattern with large scale often appear around the source region prior to great intraplate shocks, which is the long-term background anomaly. The spatial distribution of seismic activity shows the heterogeneous features and the seismicity of earthquake swarms is significant. While in the long term prior to the great interplate earthquakes, the notable anomaly is the seismic strengthening or the obvious quiescence of strong shocks. In the short term the frequency of earthquake swarms increase and some seismic patterns are formed. While in the middle-short term prior to the great shallow interpolates events, the strengthening of deep and intermediate-depth earthquake activity in the subduction zone, showing an increased frequency, magnitude and depth, is the special anomaly.④Most of the global great shallow shocks since1976are the type of thrusting-slip rupture and most of the sequences are the type of main shock-aftershock. The types of foreshock-mainshock-aftershock and multiple mainshock sequences show the feature of thrusting-slip rupture. Statistical records show that17earthquakes with Mw≥8.5have occurred since1900globally. Five of these were preceded by a foreshock of M≥7.0, accounting for29.4%. This is significantly higher than the proportion of foreshocks identified before moderate or strong earthquakes.The results of numerical simulation research show that①Under strong subduction of Indian Plate and the horizontal drag of the lower crust, the horizontal southeast-ward movement of the Bayan Har block was counterworked from the Sich basin and caused the differential uplift of the western Sichuan plateau relative to Sichuan basin. It provides an essential geodynamic condition for the M8.0Wenchuan earthquake on high dip-angle reverse fault. The influence of stress triggering on the Wenchuan shock from the earthquakes with Ms≥7.0occurred in the boundary zones of the Bayan Har block from1900is very weak. Earthquake preparation depends on the seismogenic fault’s own energy accumulation in the background stress field, and stress triggering between earthquakes is only external cause. Earthquake intensity and distance between shocks are the main factors affecting the Coulomb stress triggering. In addition, we explain why the southern section of the Longmenshan fault did not rupture based on the research of stress triggering. The seismic source of the Wenchuan earthquake is in the field where the static Coulomb changes are positive when the Zipingpu reservoir storage, as well as are negative when the reservoir sluice. But because of the remoteness from the reservoir, the magnitude of about0.0021MPa is too small. So the reservoir has no significant influence on the Wenchuan earthquake.②Results based on the Coulomb stress calculation show that the fault easily generates thrusting-slip rupture when the dip-angle is about30°, yet the possibility that the thrusting rupture of the fault is small when the dip-angle is larger then60°or less than10°.③The lithosphere horizontal movement differences in the hierarchy(or the differential horizontal movement of the Mantle and the lithosphere) has great influence on topography.更多还原