汶川M_S8.0级地震发震构造大震复发间隔估算

汶川Ms8．0级地震发生在青藏高原东缘著名的龙门山断裂带上,造成了中央断裂和前山断裂共约330kin的地震地表破裂带。初步研究表明,龙门山断裂带上大震复发可能属特征地震模式。结合龙门山断裂带的地震地质情况和汶川地震地表破裂带的基本参数综合分析,本文从地质学、地震学和GPS数据分析三个方面评估了龙门山断裂带的大震复发周期。结果表明,上述三种方法获得的龙门山断裂带Ms8．0级地震的复发间隔分别为：3185a、170（02264a和4310a,平均为3000a左右：Ms7．5级地震的平均复发间隔为1000a左右;Ms7．0级地震的平均复发间隔为500a左右。这些结果与其他学者的研究结果相比,相差不多,基本反映了龙门山断裂带的地震能量水平和累积速度。     

汶川8.0级地震前龙门山地区小震活动与固体潮的关系

通过对汶川8.0级地震前,龙门山地区小震活动与月球上中天、下中天时刻对应关系的讨论,得到龙门山小震活动与月球引潮力的低潮对应关系不明显.另外,对龙门山小震与固体潮理论曲线对应的讨论,得到每组小震的头震在接近固体潮曲线的谷底发生,即地震的发生与固体潮的低潮有关.在临近大震前,地震多发生在固体潮曲线的上升部位,即引潮力增长...     

汶川Ms8.0地震及余震序列重新定位

从2008年5月12日汶川8.0级地震发震时刻起到2008年12月31日,四川省及其周边省区布设的区域台网、水库台网以及流动台共记录到10000余次余震序列(M≥2.0).我们采用双差定位法对主震及余震序列进行重新定位,得到7000多个地震的重新定位结果.结果表明,余震分布带长约350 km.在西南部,余震沿龙门山后山...     

龙门山断裂带中北段大震复发特征与复发间隔估计

汶川MS8.0地震发生在青藏高原东缘著名的龙门山断裂带上,造成了从映秀、北川至南坝长约240km的同震地表破裂带．然而目前关于龙门山断裂带的大震复发特征研究较少．通过地震地质科学考察和断层断错地貌的差分GPS测量,发现第一级河流阶地、河床和河漫滩上的垂直断距大致相当,均代表汶川地震的位错,而第二级河流阶地上的累计位移大致是最新地震垂直位移的2倍．利用断错地貌、地震矩率和滑动速率3种方法,分别估算了龙门山断裂带大地震的复发间隔．结果表明:龙门山断裂带中北段可能发生与汶川大地震相当的地震,大震复发符合特征地震模型;大震复发间隔为3000——6000a．该结果可为龙门山断裂带的大震预测和地震危险性评价等研究提供重要的定量数据．      

龙门山断裂带重力变化与汶川8.0级地震关系研究

利用成都地区1996~2008年绝对重力和相对重力观测资料获得区域重力场时空动态变化结果,系统分析了龙门山断裂带重力场变化特征及其与汶川8.0级地震的关系.①重力变化与龙门山断裂构造活动存在密切空间联系,重力测量较好地反映了伴随活动断层的物质迁移和构造变形引起的地表重力变化效应.②成都地区重力场动态图像较完整地反映了2008年5月12日汶川8.0级地震孕育、发生过程中出现的流动重力前兆信息.③映秀及北川重力点值时序变化累积量达120×10^-8m·s^-2,较好地反映了汶川地震前映秀和北川两个极震区附近的重力测点随时间的剧烈波动性上升变化.④汶川地震前,龙门山断裂带东侧的四川盆地相对稳定,而较显著的重力变化发生在龙门山断裂带西侧的川西高原上.     

汶川8.0级地震前龙门山断裂带孕震构造运动特征分析

根据弹性回跳理论,利用1999至2007年相对中国大陆的三期GPS水平运动速度场资料,着重对每一期跨龙门山断裂带的GPS站点运动速度,在平行龙门山断裂带上的投影速度进行计算,在此基础上,以图示和幂函数拟合方式,分析了龙门山断裂带两侧地面相对运动变形情况。结果显示:汶川8.0级地震前龙门山断裂带两侧地面相对运动出现了右旋剪切运动,且这种右旋剪切运动受阻于龙门山断裂带。这对于识别判定孕震弹性应变能积累变形异常,进而开展地震预测与研究具有积极意义。     

汶川地震断裂带滑移行为、物理性质及其大地震活动性——来自汶川地震断裂带科学钻探的证据

断裂带物质组成、结构及其物理性质是理解断裂变形机制和地震破裂过程的基础和关键,断裂带地震（黏滑）和非地震（蠕滑）滑移行为不仅对了解地震活动性和山脉隆升过程具有重要意义,而且直接为防震减灾提供科学依据.我们以穿过龙门山映秀—北川和灌县—安县断裂带的汶川地震断裂带科学钻探（WFSD）岩心和地表出露的断裂带为研究对象,通过对断裂岩组成、结构、显微构造和钻孔物性测井数据进行分析研究,确定了龙门山逆冲断裂带滑移行为和物性特征,初步探讨了大地震活动性和有关断裂带的隆升作用：（1）映秀—北川断裂带倾向NW,浅部倾角~65°,发育的断裂岩厚约180~280 m,由碎裂岩、假玄武玻璃（地震化石）、断层泥和断层角砾岩组成.断裂带具有高自然伽马、高磁化率值、低电阻率、低波速等物理性质以及对称型破碎结构.断层泥普遍具有摩擦热效应的高磁化率值和石墨化作用特征,是古地震滑动的岩石记录.表明映秀—北川断裂带为经常发生大地震的断裂带,晚新生代以来类似汶川地震的大地震复发周期小于6000—10000年,具有千年复发周期特征.（2）灌县—安县断裂带倾向NW,浅部倾角~38°,发育的断裂岩厚约40~50 m,仅由断层泥和断层角砾岩组成,具有典型的"压溶"结构,表现出蠕滑性质.除压溶作用外,定向富集的层状黏土矿物和微孔隙的发育使断层强度变弱.断裂带具上盘破碎的非对称型破碎结构,除具低磁化率值特征外,其他物性与映秀—北川断裂带一致.（3）根据断裂岩厚度与断层滑移量相关经验公式关系,以及断层产状,粗略估算映秀—北川断裂带自中生代以来累积垂直位移量大于9 km,灌县—安县断裂带累积垂直位移量小于3 km.映秀—北川断裂带长期大地震产生的累积垂直位移量是龙门山隆升的主要贡献.     

地震的复发周期

本文提出了一个计算某一地震带(区)上地震复发周期的简单公式: T_M=m·10~(bM-a)式中T_M为震级是M的地震周期,m表示在求震级—频度关系式logN=a-bM中的系数a及b时,使用了m年的资料(时间单位也可以采用年、季度、月、旬等等)。 采用上述公式,作者研究了地震预报中的长期、中期及短临预报的问题。一些震例的研究表明:复发周期在地震预报的许多方面具有广泛的实用意义。不失为地震预报中的一个重要指标。     

利用地震复发周期考察汶川8．0级地震前兆异常

通过对汶川Ms8．0地震复发周期的时间和空间进行扫描,发现地震发生前,在时间上和空间上,地震复发周期均出现低值异常。因此,对地震发生的时间和地区进行异常判断,地震复发周期是一个可以参考利用的指标。     

2008年5月12日汶川MS8.0地震动力学背景的数值模拟实验

2008年5月12日汶川M_S8.0地震发生在龙门山断裂带.本文基于龙门山断裂带的地质与地球物理研究结果,以及高精度的地形数据、大地热流测量数据,建立了以龙门山断裂带为主要研究对象的有限元模型;以GPS观测数据、构造应力场和震源破裂过程研究结果为约束,研究了此次强烈地震的动力学背景.模拟实验结果显示:在考虑青藏高原物质向东挤压流动的同时,青藏高原与四川盆地的地形差异和流变强度差异、断层摩擦强度差异和断层产状形式均对地震起始破裂的发生位置和断层错动形式有着重要影响.本文利用地球动力学的有限元软件模拟了汶川地震地表破裂在龙门山断裂带上传播的过程.     

Numerical simulation on the influences of Wenchuan earthquake on the surrounding faults

On 12 May 2008, the devastating Wenchuan earthquake struck the Longmenshan fault zone, which comprised the eastern margin of the Tibetan Plateau, and this fault zone was predominantly a convergent boundary with a right-lateral strike-slip component. After such a large-magnitude earthquake, it was crucial to analyze the influences of the earthquake on the surrounding faults and the potential seismic activity. In this paper, a complex viscoelastic model of western Sichuan and eastern Tibet regions was constructed including the topography. Based on the findings of co-seismic static slip distribution, we calculated the stress change caused by the Wenchuan earthquake with the post-seismic relaxation into consideration. Our preliminary results indicated that: (1) The tectonic stressing rate was relatively high in Kunlun mountain pass-Jiangcuo, Ganzi-Yushu, Xianshuihe and Zemuhe faults; while in the east Kunlun and Longriba was medium; also the value was less in the Minjiang, Longmenshan, Anninghe and Huya faults. As to the Longmenshan fault, the value was 0.28×10^-3 MPa/a to 0.35×10^-3 MPa/a, which is coincident with the previous long recurrence interval of Wenchuan earthquake; (2) The Wenchuan earthquake not only caused the Coulomb stress decrease in the source region, but also the stress increase in the two terminals, especially the northeastern segment, which is comparatively consistent with the aftershock distribution. Meanwhile, the high concentration areas of the static slip distribution were corresponding to the Coulomb stress reductions; (3) The Coulomb stress change caused by Wenchuan earthquake showed significant increase on five major faults, which were northwestern segment of Xianshuihe fault, eastern Kunlun fault, Longriba fault, Minjiang fault and Huya fault respectively; also the Coulomb stress on the fault plane of the Yushu earthquake was faintly increased; (4) We defined the recurrence interval as the time needed to accumulate the magnitude of the stress drop, and the recurrence interval of Wenchuan earthquake was estimated about 1 714 a to 2 143 a correspondingly.     

Time interval of earthquake recurrence for strike - slip fault

On the basis of fault’s dynamic model of Knopoffet al. (1973), this paper has finally obtained a simple approximate formula to be able to estimate the recurrence time intervalT _R of earthquake on strike-slip fault. Preliminary result holds thatμ andδ _s — δ _f have not much effect onT _R . Leta is the ratio of the coseismic displacementD _s to the total displacementD _t in whole event course, i.e.,a =D _s /D _t , thena = 1/3 may represent the standard theoretical state in whichT _R is independent onμ andδ _s — δ _f . At this time,T _R is the arithmetic average ofs ₀/v andkd/β, wheres ₀ is the long-term preseismic accumulated slippage,v is fault’s average displacement rate,d is the fracture length on the fault of seismic focal region andβ is shear wave velocity. In addition,k =υ ₀/aυ, whereυ ₀ is the initial fracture velocity of actual structure at the coseismic instant. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 187–194, 1992. This paper is a part of contracted item of State Seismological Bureau — Tectonic Physical Study of Earthquake Recurrence Period and Characteristic Magnitude.     

龙门山断裂带地壳精细结构与汶川地震发震机理

利用2001年1月至2008年6月四川固定地震台网和临时地震台站记录到的大量P波到时资料,反演了龙门山断裂带及周边地区的地壳精细三维P波速度模型. 结果表明,汶川主震以北和以南地区的结构存在较大差异,以北地区的龙门山断裂带具有很强地壳不均匀性,这与该区发生了大量汶川地震的余震相一致. 这些结果有意义地改进了前人对龙门山断裂带仅为不同块体过渡带的认识. 汶川主震震源区下方存在有明显低波速异常体,表明流体可能存在于龙门山断裂带内. 这些流体可能直接影响汶川大震的形成. 本文的成像结果为下地壳流沿龙门山断裂带上浸提供了可靠的地震学证据.     

Relocation of the M8.0 Wenchuan earthquake and its aftershock sequence

We relocated M8.0 Wenchuan earthquake and 2706 aftershocks with M≥2.0 using double-difference algorithm and obtained relocations of 2553 events. To reduce the influence of lateral variation in crustal and upper mantle velocity structure, we used different velocity models for the east and west side of Longmenshan fault zone. In the relocation process, we added seismic data from portable seismic sta-tions close to the shocks to constrain focal depths. The precisions in E-W, N-S, and U-D directions after relocation are 0.6, 0.7, and 2.5 km respectively. The relocation results show that the aftershock epi-centers of Wenchuan earthquake were distributed in NE-SW direction, with a total length of about 330 km. The aftershocks were concentrated on the west side of the central fault of Longmenshan fault zone, excluding those on the north of Qingchuan, which obviously deviated from the surface fault and passed through Pingwu-Qingchuan fault in the north. The dominant focal depths of the aftershocks are between 5 and 20 km, the average depth is 13.3 km, and the depth of the relocated main shock is 16.0 km. The depth profile reveals that focal depth distribution in some of the areas is characterized by high-angle westward dipping. The rupture mode of the main shock features reverse faulting in the south, with a large strike-slip component in the north.     

Relocation of the M 8.0 Wenchuan earthquake and its aftershock sequence

We relocated M8.0 Wenchuan earthquake and 2706 aftershocks with M⩾2.0 using double-difference algorithm and obtained relocations of 2553 events. To reduce the influence of lateral variation in crustal and upper mantle velocity structure, we used different velocity models for the east and west side of Longmenshan fault zone. In the relocation process, we added seismic data from portable seismic stations close to the shocks to constrain focal depths. The precisions in E-W, N-S, and U-D directions after relocation are 0.6, 0.7, and 2.5 km respectively. The relocation results show that the aftershock epi-centers of Wenchuan earthquake were distributed in NE-SW direction, with a total length of about 330 km. The aftershocks were concentrated on the west side of the central fault of Longmenshan fault zone, excluding those on the north of Qingchuan, which obviously deviated from the surface fault and passed through Pingwu-Qingchuan fault in the north. The dominant focal depths of the aftershocks are between 5 and 20 km, the average depth is 13.3 km, and the depth of the relocated main shock is 16.0 km. The depth profile reveals that focal depth distribution in some of the areas is characterized by high-angle westward dipping. The rupture mode of the main shock features reverse faulting in the south, with a large strike-slip component in the north. Supported by the Basic Research Project of Institute of Geophysics, China Earthquake Administration (Grant No. DQJB08Z03)     

Internal structures and high-velocity frictional properties of Longmenshan fault zone at Shenxigou activated during the 2008 Wenchuan earthquake

This paper reports internal structures of a wide fault zone at Shenxigou, Dujiangyan, Sichuan province, China, and high-velocity frictional properties of the fault gouge collected near the coseismic slip zone during the 2008 Wenchuan earthquake. Vertical offset and horizontal displacement at the trench site were 2.8 m (NW side up) and 4.8 m (right-lateral), respectively. The fault zone formed in Triassic sandstone, siltstone, and shale about 500 m away from the Yingxiu-Beichuan fault, a major fault in the Longmenshan fault system. A trench survey across the coseismic fault, and observations of outcrops and drill cores down to a depth of 57 m revealed that the fault zone consists of fault gouge and fault breccia of about 0.5 and 250–300 m in widths, respectively, and that the fault strikes N62°E and dips 68° to NW. Quaternary conglomerates were recovered beneath the fault in the drilling, so that the fault moved at least 55 m along the coseismic slip zone, experiencing about 18 events of similar sizes. The fault core is composed of grayish gouge (GG) and blackish gouge (BG) with very complex slip-zone structures. BG contains low-crystalline graphite of about 30 %. High-velocity friction experiments were conducted at normal stresses of 0.6–2.1 MPa and slip rates of 0.1–2.1 m/s. Both GG and BG exhibit dramatic slip weakening at constant high slip rates that can be described as an exponential decay from peak friction coefficient μ _p to steady-state friction coefficient μ _ss over a slip-weakening distance D _c. Deformation of GG and BG is characterized by overlapped slip-zone structures and development of sharp slickenside surfaces, respectively. Comparison of our data with those reported for other outcrops indicates that the high-velocity frictional properties of the Longmenshan fault zones are quite uniform and the high-velocity weakening must have promoted dynamic rupture propagation during the Wenchuan earthquake.     

四川芦山7.0级地震及其与汶川8.0级地震的关系

2013年4月20日在四川省雅安市芦山县发生M7.0级地震.根据四川省台网资料和收集的国内外相关资料,我们分析了芦山地震的基本参数、余震分布、序列衰减等特征.结果表明:芦山地震位于龙门山断裂南段,其震源力学机制显示为纯逆冲性质,与龙门山断裂构造特征相符合;芦山地震的余震较丰富,震后15天震区已发生7800多次余震,其中,5级以上余震4次,最大余震是4月21日17时5分芦山、邛崃交界M5.4级地震;余震分布形成的图形显示其长轴走向与龙门山断裂构造走向一致,余震分布显示密集区长轴约40 km,短轴约20 km.与汶川M8.0级地震在震源力学机制、破裂过程、余震空间展布以及地表破裂等对比分析后表明:芦山地震与汶川地震的震源错动类型、破裂过程、地表破裂以及余震活动等特征存在明显差异;芦山地震与汶川地震震中位置相距90 km,两次地震的余震密集区相距50 km;汶川8.0级地震造成龙门山断裂中北段较充分破裂,芦山7.0级地震则展布于龙门山断裂南段且破裂尺度有限;两者有发震构造上的联系,但两次地震是相对独立的地震事件.