地震活动不均匀性及地震断层相互作用的力学机制研究

【作者】 刘桂萍；

【导师】 傅征祥；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理， 2000， 博士

【摘要】 一次地震的孕育过程由震源自身的演化过程和所受外界影响两种因素决定。地震活动的复杂性主要山地震断层活动相互作用以及在这种作用下地震孕育过程发生复杂变化引起。本文在摩擦状态—速率依从理论和断层相互作用理论的基础上，将地震看作是摩擦失稳现象，建立地震孕育及其活动特征的物理模型，研究地震触发现象和地震强度分布不均匀性的力学机制。 （1）大地震触发区域地震活动及其力学机制研究 美国Landers地震后诱发的距震中远达1250公里的14个区域出现的地震活动增强，被称为是大地震触发小地震的首次证据。本文对1995年1月17日日本兵库县南部7．2级大地震和 1976年7月 28日唐山7．8级大地震前后震中周围几百公里范围内的地震活动研究表明，多个区域中的地震活动速率明显增强。为确认这些地震活动变化确实与两次大地震之间存在相关关系，采用定量统计方法对这些地震活动变化的显著性进行检验，结果表明地震活动速率上升的变化是可信的，并与大地震之间确实存在着相关关系，被认为是触发地震。区域地震触发现象虽然不是普遍存在的，但为我们认识这些复杂现象的物理本质提供了难得的观测依据。本文应用库仑静应力变化模型和设计一个具有摩擦状态—速率依从机制的数学物理模型，试图认识触发地震的机制。该模型能够解释部分与区域地震触发有关的现象。同时，大地震发生会使某些区域的地震活动减弱。例如，1906年旧金山8级大地震和1679年河北三河8级大地震后，观测到其周围几百公里内几十年内地震活动明显降低，本文研究了粘弹介质中平行断层相互作用的“减震”力学机制。 （2）强地震之间相互作用及其力学机制研究 鲜水河断裂带以其高强度、高频度的地震活动倍受注目。综合分析鲜水和的地质构造、地震地表破裂、震源机制等多种资料，建立鲜水河断裂带上本活跃期以来的7（1/4）以上地震的弹性破裂位错模型，研究一个多世纪以来鲜水河断裂带及周围地区的区域应力场的演化过程并与1893年以来该地区强地震活动的特点进行对比分析。结果表明，7（1/4）级以上地震都发生在前次大地震引起的库仑破裂应力变化 。、，＿。。＿，，、．＿、，，，＿＿．＿3、。，、，＿，。＿＿＿＾＿。＿．．＿。＿（凸＊n）为正的区域：大多数强震（MZ5二）发生在大地震后库仑破裂应力增 4高的地区。此外，分析了该断裂带上大地震后区域应力变化对与鲜水河断裂相邻断裂带可能产生的影响，对未来强震可能发生的地点进行了分析。 1920年12月16 R海原地震与1927年5月23日古浪2次8级地震时空相距之近是十分罕见的。本文通过建立海原地震的震源破裂弹性位错模型，计算海原地震后区域应力变化，结果表明古浪地震的发震断层应力增高，古浪地震可能被提前约八年发生。 （3）地震活动频度一震级关系曲线拐折及其力学机制研究 地震活动不均匀性除反映在上述时间、空间分布上外，还表现为地震强度统计结果的不连续性。地震学最基本的统计规律，即地震累积频度一震级的对数关系中存在的拐点现象是一个典型的例子。中国和希腊等多个地区的地震目录都存在这种现象。本文设计了一个摩擦时间依从的地震活动性细胞自动机模型，通过改变参数选取方法和设计非线性的相互作用力学机制，模拟出与观测事实相似的存在拐点、分段成线性的GE关系。为进一步认识影响拐点存在的因素，本文从多种观测事实出发，提出拐点的存在是大地震以“级联破裂”方式发生的结果。该模型还对地震活动复发周期变化的特点及其原因进行分析研究。 通过本文的研究，深入了对地震孕育物理过程和地震活动不均匀特性的力学机制的认识。更多还原

【Abstract】 The generation of a earthquake is detendned by the evolution of seismic source and the influencefrom outside. The complexion of seismiclty is due to the earthquake interaction of seismic faultactivity and the change of seismic generation process caused by the interaction. In this paper, aphysical model of earthquake generation and seismicity is designed to study the mechanics oftriggered earthquake and heterogenelty of earthquake magnitude distributlon based on friction rate-state dependent and fault interaction theory.(1) The study on the triggered and inhibited regional seismicity and its mechanismIt is thought the first evidence of triggered small earthquakes by big earthquake that the LandersEarthquake in Amenca triggered seisndcity increasing in 14 regions with epicenter up to l250km. Inthis paper, the studies on the seismicity within several hundred kilometers around the epicenters of theHyogo-Ken Nanbu, Japan, M=7.2 earthquake and the Tangshan, China, M=7.8 earthquake show thatseisndcity increased remarkably in many regions. A quantitative statistic method is used to test theslgnificance of these change to the correlation between the seismicity increasing and the two bigearthquakes and the results show that the increasing of seismic rate is significance and is caused by thetwo big earthquake and called regional triggered seismicity. Though the regional triggered seisndcityis not common, it provides us valuable observational evidence to understand the physical intrinsic ofthese complex phenomena. In other hand, regional seismicity night be inhibited by big earthquake.For example, during several ten years, after the San Francisco M=8 earthquake in l906 and the SanheM=8 earthquake in l679, seismicity decreased remarkably within several hundred kilometerssurrounding the eplcenters. In this paper, we studied the mechanism of "regional seismicity inhibition"due to the interaction of parallel faults in viscoelastic medium. The Coulomb Static Stress Changemodel is applied and a mathematics-physics model with friction rate-state dependent constructive lawls designed to understand the mechanism of regional triggered seismicity. The results demonstrate thatthis model could explain some features of regional seismicity triggrring.(2) Interaction among strong earthquake and its mechanism.The Xianshuihe Fault Zone in southwestern China is noted for its hlgh intensity and frequencyselsmicity. Based on the comprehensive analysis on the geologic structure, selsmic surface fissure andfocal mechanism solution, the elastic dislocation models of earthquakes above M(1/4) since the lastseisrnic active episode of the Xianshuihe Fault Zone are set to study the regional static stressevolution and analyze the correlatlon between it and the strong earthquake occurrences since l893.The results show that the earthquakes above M7 and majority of earthquake above M5(1/4) occurred in Places with Positive Coulombmb Failure S阶“ change（ACFSCFS）·In addition，the effectofreglonal static ＼ stress change due to the big e tthquakes in Xianshuihe FanFault Zone on the neighbouring fault zone is analyzed and the possible place of future s血ng earthqu业e is predicted pre皿rily．一 Tha tampealspSCICI CICS比dllg Of山e HO勺UUll，＊milli，M＝8．6 lll ribthqUUkU UUd山e GCICCg，＊hCC， M＝8．000n…OO卜CISSXCCpd0001．Alldll悦IC山dOCCdollllloddof山OHOlyOOllllllnbqll＊1llSSCtIO calculate the ACFSCFS due to it and the resalt shows that the CFSCFS on seismogenic fault plane of the Gulang earthquake IncfCased and the Gulang e tthquake is pfo口D口tCd by Mout tCn years． （3）The breading ofmagnitude－地quency relation curve and its mechanism． The hetefogeneity of seismicity is also displayed by the discontinuity of statistic featufC of som seisndc para。ter in addition to the phenomena mentioned above．A t…l更多还原