川滇菱形块体东边界库仑应力演化及强震发生概率估算

本研究基于分层黏弹介质模型,考虑强震或大地震同震位错、震后黏滞松弛及主断层段震间构造应力加载三方面效应,给出1480年以来,川滇菱形块体东边界鲜水河断裂带、安宁河断裂带、则木河断裂带和小江断裂带共20个断层段由三方面效应引起的累积库仑应力变化随时间的演化,分析强震间相互作用和强震发生的应力累积背景,定性分析各断层段的地震危险性.同时,分别采用现今台网地震目录和川滇菱形块体东边界各断层段强震复发间隔两种资料,定量计算2030年各断层段的强震发生概率;并基于摩擦本构理论,将周边强震引起的库仑应力变化量作为应力扰动,修正强震发生概率的计算结果.各断层段累积库仑应力演化的结果表明,鲜水河断裂带中部八美段、色拉哈段及南部磨西段、安宁河断裂带冕宁-西昌段、小江断裂带北部巧家-东川段和南部建水段的累积库仑应力显著增加.修正的强震发生概率计算结果显示,鲜水河断裂带中部八美-色拉哈-康定一带、安宁河断裂带冕宁-西昌段、小江断裂带南部华宁-建水一带强震发生概率较高,地震危险性值得关注.本研究基于库仑应力演化计算定性分析强震危险性的同时,基于摩擦本构律理论,结合地震引起的应力扰动和强震发生背景,定量计算修正的强震发生概率,为川滇菱形块体东边界强震危险地点及中长期发震紧迫程度判定提供方法和依据.     

川滇菱形块体东边界断层闭锁程度与滑动亏损动态特征研究

利用1999—2007期和2009—2013期中国大陆GPS速度场数据,采用DEFNODE负位错反演程序估算了川滇菱形块体东边界——鲜水河—安宁河—则木河—小江断裂带在汶川地震前后的断层闭锁程度和滑动亏损空间分布动态变化特征,讨论了汶川地震对该断裂系统的影响范围和程度,并结合b值空间分布和地震破裂时-空结果分析了断裂系统的强震危险段.结果表明,汶川地震前鲜水河断裂最南端为完全闭锁(闭锁深度25km),中南段地表以下10~15km深度为强闭锁状态,中北段基本处于蠕滑状态;安宁河断裂最南端闭锁很弱,其余位置闭锁深度为10~15km;则木河断裂除最南端闭锁较弱以外,其余位置基本为完全闭锁;小江断裂在巧家以南、东川以南、宜良附近、华宁以北等四处位置闭锁较弱,其余位置为强闭锁.10年尺度的GPS速度场反演所得断层闭锁程度所指示的强震危险段,主要为鲜水河断裂道孚—八美段、安宁河断裂中段、则木河断裂中北段、小江断裂北段东川附近、小江断裂南段华宁—建水段,该结果与地质尺度的断层地震空区和30年尺度的b值空间分布所指示的危险段落具有一致性.汶川地震后断裂带远、近场速度分布和块体运动状态发生变化,这种区域地壳运动调整使得负位错模型反演得到的断裂带闭锁情况发生一定变化.汶川地震前后川滇菱形块体东边界平行断层滑动亏损速率均为左旋走滑亏损,且在安宁河断裂北端、则木河断裂中北段滑动亏损速率最大;除鲜水河断裂中南段与最南端和小江断裂东川附近以外,其余断裂震后滑动亏损速率均有所增加.垂直断层滑动亏损速率既有拉张亏损也有挤压亏损,且鲜水河断裂最南端由震前挤压转变为震后拉张,其余断裂除了安宁河断裂和小江断裂中段与最北端存在挤压滑动亏损速率外均为拉张速率.     

1833年嵩明8.0级地震对周围断层的影响

应用粘弹性计算程序,计算1833年嵩明8.0级大地震产生的同震和震后应力场变化,并计算对附近的小江断裂带、安宁河断裂带、则木河断裂带及云南境内红河断裂带造成的同震和震后库仑应力变化。结果表明,嵩明8.0级大地震对滇中南地区应力分布产生较大影响,对周围断层的影响甚至持续数百年的时间。嵩明8.0级地震使震中附近的小江断裂中段、安宁河断裂南段和红河断裂带中段库仑应力减小,降低发震危险;而小江断裂带南北段、安宁河断裂北段、则木河断裂带和红河断裂带南北两段库仑应力增加,地震危险性增强。红河断裂带中段在数百年时间尺度内始终处于嵩明8.0级地震库仑应力的减小区域,该研究结果有助于解释此断裂段的地震平静现象。     

COULOMB STRESS CHANGE ON ACTIVE FAULTS IN SICHUAN-YUNNAN REGION AND ITS IMPLICATIONS FOR SEISMIC HAZARD

Coulomb stress change on active faults is critical for seismic hazard analysis and has been widely used at home and abroad. The Sichuan-Yunnan region is one of the most tectonically and seismically active regions in Mainland China, considering some highly-populated cities and the historical earthquake records in this region, stress evolution and seismic hazard on these active faults capture much attention. From the physical principal, the occurrence of earthquakes will not only cause stress drop and strain energy release on the seismogenic faults, but also transfer stress to the surrounding faults, hence alter the shear and normal stress on the surrounding faults that may delay, hasten or even trigger subsequent earthquakes. Previously, most studies focus on the coseismic Coulomb stress change according to the elastic dislocation model. However, the gradually plentiful observation data attest to the importance of postseismic viscoelastic relaxation effect during the analysis of seismic interactions, stress evolution along faults and the cumulative effect on the longer time scale of the surrounding fault zone. In this paper, in order to assess the seismic hazard in Sichuan-Yunnan region, based on the elastic dislocation theory and the stratified viscoelastic model, we employ the PSGRN/PSCMP program to calculate the cumulative Coulomb stress change on the main boundary faults and in inner blocks in this region, by combining the influence of coseismic dislocations of the M≥7.0 historical strong earthquakes since the Yongsheng M7.8 earthquake in 1515 in Sichuan-Yunnan region and M≥8.0 events in the neighboring area, and the postseismic viscoelastic relaxation effect of the lower crust and upper mantle. The results show that the Coulomb stress change increases significantly in the south section of the Xianshuihe Fault, the Anninghe Fault, the northern section of the Xiaojiang Fault, the southern section of the Longmen Shan Fault, the intersection of the Chuxiong-Jianshui Fault and the Xiaojiang Fault, and the Shawan section of the Litang Fault, in which the cumulative Coulomb stress change exceeds 0.1MPa. The assuming different friction coefficient has little effect on the stress change, as for the strike-slip dominated faults, the shear stress change is much larger than the normal stress change, and the shear stress change is the main factor controlling the Coulomb stress change on the fault plane. Meanwhile, we compare the Coulomb stress change in the 10km and 15km depths, and find that for most faults, the results are slightly different. Additionally, based on the existing focal mechanism solutions, we add the focal mechanism solutions of the 5 675 small-medium earthquakes(2.5≤M≤4.9)in Sichuan-Yunnan region from January 2009 to July 2019, and invert the directions of the three principal stresses and the stress shape factor in 0.1°×0.1° grid points; by combining the grid search method, we compare the inverted stress tensors with that from the actual seismic data, and further obtain the optimal stress tensors. Then, we project the stress tensors on the two inverted nodal planes separately, and select the maximum Coulomb stress change to represent the stress change at the node. The results show that the cumulative Coulomb stress change increase in the triple-junction of Sichuan-Yunnan-Tibet region is also significant, and the stress change exceeds 0.1MPa. Comprehensive analysis of the Coulomb stress change, seismic gaps and seismicity parameters suggest that more attention should be paid to the Anninghe Fault, the northern section of the Xiaojiang Fault, the south section of the Xianshuihe Fault, the southern section of the Longmen Shan Fault and the triple-junction of the Sichuan-Yunnan-Tibet region. These results provide a basis for future seismic hazard analysis in the Sichuan-Yunnan region.     

基于库仑应力变化分析巴颜喀拉地块东端的强震相互关系

本研究基于分层黏弹介质模型,考虑同震位错效应和震后黏滞松弛效应,分析巴颜喀拉地块东端1976年松潘地震序列、2008年汶川8.0级地震、2013年芦山7.0级地震和2017年九寨沟7.0级地震等多次大地震的可能存在的触发关系,计算大地震引起的周边各主要断裂的库仑应力变化.结果显示,1976年松潘地震序列各次地震间关系密切,存在明显的相继触发作用;综合考虑同震和震后效应,汶川8.0级地震对同属于龙门山断裂带的芦山7.0级地震有触发作用,且震后效应影响不可忽略;1976年地震序列,特别是1976年8月16日7.2级地震促进了2017年8月8日九寨沟7.0级地震的发生;汶川地震对九寨沟地震的影响研究中,采用不同的汶川地震同震位错模型,计算结果有差异.综合考虑多次大地震对周边断裂带的影响,龙门山断裂带南段、鲜水河断裂带中南段、平武—青川断裂北段、灌县—安县断裂北段、文县断裂的累积库仑应力增加显著,巴颜喀拉地块东端的东昆仑断裂带东段、迭部—白龙江断裂带西段以及金沙江断裂带库仑应力亦有所增加.综合考虑各重要断裂带已有的大地震危险性分析结果和库仑应力变化计算结果,龙门山断裂带南段、鲜水河断裂带中南段、东昆仑断裂带玛沁—玛曲段和金沙江断裂带的发震紧迫性有所增强,需引起关注.     

Influence of 2008 Wenchuan earthquake on earthquake occurrence trend of active faults in Sichuan-Yunnan region

The Wenchuan earthquake coseismic deformation field is inferred from the coseismic dislocation data based on a 3-D geometric model of the active faults in Sichuan-Yunnan region. Then the potential dislocation displacement is inverted from the deformation field in the 3-D geometric model. While the faults' slip velocities are inverted from GPS and leveling data, which can be used as the long-term slip vector. After the potential dislocation displacements are projected to long-term slip direction, we have got the influence of Wenchuan earthquake on active faults in Sichuan-Yunnan region. The results show that the northwestern segment of Longmenshan fault, the southern segments of Xianshuihe fault, Anninghe fault, Zemuhe fault, northern and southern segments of Daliangshan fault, Mabian fault got earthquake risks advanced of 305, 19, 12, 9.1 and 18, 51 years respectively in the eastern part of Sichuan and Yunnan. The Lijiang-Xiaojinhe fault, Nujiang fault, Longling-Lancang fault, Nantinghe fault and Zhongdian fault also got earthquake risks advanced in the western part of Sichuan-Yunnan region. Whereas the northwestern segment of Xianshuihe fault and Xiaojiang fault got earthquake risks reduced after the Wenchuan earthquake.     

鲜水河断裂带库仑应力演化与强震间关系

以鲜水河断裂带为研究区,首先验证了该断裂带上1893年以来M6.7以上地震的相互触发作用,然后采用更符合实际的分层黏弹介质模型研究强震震后黏滞松弛引起的库仑应力变化对后续地震的影响,并基于负位错理论计算鲜水河断裂带10个断层段的震间长期构造加载作用引起的断层上的应力积累.在此基础上,讨论同震、震后、震间效应引起的累积库仑应力变化与区域强震活动的关系,给出断层上库仑应力随时间的演化.结果表明,鲜水河断裂带上1893年以来发生的7次强震均在其前面一系列强震及构造应力加载的驱使下发生,同震、震后、震间三方面效应均引起了鲜水河断裂带不可忽略的库仑应力变化.对断层上的库仑应力状态的研究,可进一步为揭示地震的发生规律、找寻危险断层段提供线索.     

2017年MW6.5九寨沟地震激发的同震库仑应力变化及其对周边断层的影响

2017年8月8日21时19分在我国四川省北部阿坝州九寨沟县发生了M_W6.5左旋走滑型地震.该地震发生在青藏高原巴颜喀拉块体东北缘,东昆仑断裂南东段的塔藏断裂、岷江断裂和虎牙断裂的交汇地带.包括此次地震,近年来在巴颜喀拉块体周缘已发生了九次6级以上强震,表明巴颜喀拉块体周缘主要活动断裂上的应力水平仍处于不断调整之中.本文采用库仑应力模型研究2017年M_W6.5九寨沟地震激发的库仑应力变化、该地震与周边地震的应力触发关系以及强震对周边主要活动断裂的应力扰动.强震序列包括周边区域1536-1975年M≥6历史强震和1976-2017年的M_W≥ 6 gCMT地震目录中的强震,共计32个.研究结果表明：（1）2017年M_W6.5九寨沟地震激发的同震库仑应力变化仅在局部范围内超过0.1×10⁵Pa,且75%的余震（~12.7天）受到该地震明显的同震应力触发作用,而其余25%的余震落在应力影区,采用最优破裂面可以进一步提高同震库仑应力变化与余震分布的空间相关性;（2）2008年M_W7.9汶川地震对2017年M_W6.5九寨沟地震的发生有一定的促进作用,在后者震源处激发的同震库仑应力变化为（0.026~0.263）×10⁵Pa,震后黏弹性库仑应力变化为（0.010~0.032）×10⁵Pa.该库仑应力的变化范围取决于汶川地震源断层参数和九寨沟地震接收断层参数.2013年M_W6.6芦山地震对九寨沟地震的发生几乎没有影响（< 0.001×10⁵Pa）;（3）1654年M8.0甘肃天水南地震对九寨沟地震的发生有明显的促进作用,在九寨沟地震震源处激发的同震库仑应力变化为（0.410~1.266）×10⁵Pa,震后库仑应力变化为（0.147~0.490）×10⁵Pa.1879年M8.0甘肃武都地震可能有比1654年M8.0甘肃天水南地震更强的应力触发作用,但也有可能对九寨沟地震的发生起到抑制作用.在选取的8个九寨沟地震接收断层面上,其中6个接收断层面上该地震所激发的同震库仑应力变化为（0.913~2.364）×10⁵Pa,2个接收断层面上该地震所激发的同震库仑应力变化为（－1.326~－0.454 ）×10⁵Pa;在4个接收断层面上震后库仑应力变化为（0.094~1.072）×10⁵Pa,在另外4个接收断层面上震后库仑应力变化为（－1.593~－0.106）×10⁵Pa.1933年四川叠溪地震对九寨沟地震的发生影响较弱,其所激发的同震库仑应力变化为（0.015~0.080）×10⁵Pa,震后库仑应力变化为（－0.029~0.025）×10⁵Pa;（4）九寨沟地震仅在其附近的岷江断裂北段、塔藏断裂和虎牙断裂南段造成较明显的同震库仑应力变化,其分别为0.09×10⁵Pa、（0.14~2.03）×10⁵Pa和0.25×10⁵Pa.而进一步顾及其余31个强震的库仑应力作用则发现,同震库仑应力增加非常显著的主要活动断裂分段为：岷江断裂北段南侧和岷江断裂南段的库仑应力变化分别升高5.6×10⁵Pa和9.8×10⁵Pa.鲜水河断裂北段南侧库仑应力升高23.0×10⁵Pa,鲜水河断裂南段道孚-康定段的北侧库仑应力升高9.0×10⁵Pa,而最南端库仑应力升高3.0×10⁵Pa;龙门山断裂带中段的北侧库仑应力变化为（6.1~7.4）×10⁵Pa,中段库仑应力增加（2.1~11.5）×10⁵Pa;西秦岭北缘断裂东段库仑应力变化为4.4×10⁵Pa;龙日坝断裂北段最北侧的库仑应力变化为2.0×10⁵Pa;小金河断裂北段库仑应力变化为1.7×10⁵Pa;安宁河断裂北段库仑应力变化为1.6×10⁵Pa;（5）由于下地壳和上地幔的黏弹性松弛作用,所有强震在九寨沟地震震后20年造成的黏弹性库仑应力变化在鲜水河断裂、龙门山断裂中段、塔藏断裂以及秦岭南缘断裂西段比较显著,其分别为：（1.0~3.0）×10⁵Pa、2.8×10⁵Pa、（2.3~2.7）×10⁵Pa和0.9×10⁵Pa.但总体上黏弹性库仑应力变化没有改变各断裂上的同震库仑应力变化空间分布.总的库仑应力变化在鲜水河断裂北段南侧和南段的道孚至康定段北侧、龙门山断裂中段北侧、岷江断裂南段和北段南侧、虎牙断裂、塔藏断裂以及西秦岭北缘东段很显著（均超过4×10⁵Pa）.由于库仑应力明显升高可能预示着地震潜在危险性增强,因此这些断裂分段可能将来需要重点加以关注.     

红河断裂带库仑应力演化及未来地震危险性估计

现今地震活动性显示红河断裂带强震主要发生在断裂带的北段,中段长期存在地震空区.为了更好地理解红河断裂带不同段落地震活动性差异和评估未来潜在地震危险性,本研究基于分层半无限空间黏弹性地球模型计算了自1833年嵩明M8.0地震以来,红河断裂带上及其周边共25次强震由于同震应力阶变、震后黏滞松弛和震间构造应力加载的综合作用,红河断裂带上库仑应力变化的演化过程.结果表明,在近180年红河断裂带南北两段得到加载,中段始终位于应力影区,这可能部分解释红河断裂带南北段地震相对活跃、中段长期存在的地震平静现象.假设未来三十余年该地区不再发生大震,考虑震后和震间作用,红河断裂带中段应力影区仍然存在,但范围在缩小;洱源附近、大理至大斗门以北地区、元江以南地区应力增加超过0.1 MPa,可能仍是地震潜在危险区段.     

川滇活动地块东边界强震危险性研究

以川滇活动地块东边界为例,利用最近31年的地震资料,根据精细b值计算结果,研究该边界断裂带的应力空间分布及其强震危险性. 研究结果显示：（1）沿川滇活动地块东边界,b值空间分布显示在不同断裂以及同一断裂不同断裂段存在较大差异,从而反映出应力积累水平的空间差异.（2）小江断裂带主干断裂上的嵩明凹凸体及存在于主干断裂附近巧家与东川间以及嵩明北西的2个凹凸体、存在于安宁河断裂冕宁附近和则木河断裂西昌附近的凹凸体以及位于鲜水河断裂中南段道孚—乾宁间大尺度的凹凸体将是川滇活动地块东边界未来大震或强震的震源区.     

川滇地区强震序列库仑破裂应力加卸载效应的数值模拟

通过建立较精细的川滇地区三维有限元模型,数值模拟了川滇地区主要活动断裂的强震活动对于其他活动断裂潜在强震孕育进程的库仑破裂应力加卸载效应.模拟结果显示在川滇地区主要活动断裂带的几何学展布形态和运动学性质的构造背景之上,川滇地区强震活动相互影响的主要特征是活动断裂面库仑破裂应力变化大多处于增大状态.其中,金沙江断裂带、小江断裂带、楚雄—建水断裂带、鲜水河断裂带和安宁河断裂带上的强震所产生的加载作用比较强,而丽江—小金河断裂带和腾冲—澜沧断裂带则较弱.1981~2000年川滇地区M≥6.5地震序列的模拟结果显示,后续地震全部位于已发生地震所引起的库仑破裂应力增大区之内.数值模拟结果显示,在川滇地区,一个强震发生之后,发震断层本身强烈卸载的同时,库仑破裂应力的加载效应在其他主要活动断裂带潜在强震孕育进程中占据了主导地位,强震活动之间相互作用的主要效应是应力加载,已发生的强震加速了下一个强震的孕育进程,进而导致一系列地震的发生,直至整个区域所积累的应变能处于较低水平之后,区域地震活动进入一个新的平静期.     

东昆仑活动断裂带大地震之间的黏弹性应力触发研究

对青藏高原北部东昆仑破裂带大地震之间的应力转移和断层相互作用进行研究. 考虑1937年以来沿此破裂带发生的5个M≥7的地震：1937年M7.5花石峡地震，1963年MS7.1都兰地震，1973年MS7.3玛尼地震，1997年MW7.5玛尼地震和2001年MW7.8可可西里地震，模拟了黏弹性成层介质中地震断层错动产生的应力演化过程，并计算了在后续地震破裂面上产生的库仑破裂应力变化. 结果表明，前面4个地震均造成2001年可可西里地震断层面上库仑破裂应力的增加，并且中地壳和下地壳的黏弹性松弛效应使得库仑破裂应力场随着时间的推移而逐渐加强. 在计算过程中定量估计了可可西里地震发生时前面4个地震同震形变和黏弹性松弛导致可可西里地震破裂面上库仑破裂应力变化之间的比值，发现前3个地震由黏弹性松弛造成的变化远远大于同震形变所造成的变化. 可可西里地震之后应力场的模拟表明东昆仑断层中段的东大滩－西大滩断层段（位于可可西里地震破裂以东及都兰地震以西）的库仑破裂应力显著增加，变化值达0.05～0.1 MPa，预示这一地区地震危险性的增加.     

川滇地块东边界中南段构造应力分布特征与历史强震活动关系的数值模拟

本文以构造应力场观测结果、 岩石圈流变特性为约束, 采用摩擦接触单元反映断裂带空间分段特征, 以最接近真实地下环境的非线性黏弹性材料为模型的本构关系, 建立包括安宁河—则木河—小江断裂带的三维有限元模型, 模拟在速度边界条件和重力势能等动力因素共同作用下的断裂带应力分布特性. 研究结果表明, 模拟得到的断裂带现今构造应力场与地震活动有明显的对应关系, 应力比较集中的区域, 如石棉、 西昌、 巧家、 东川附近, 极有可能是未来的地震危险区域.      

祁连—海原断裂带库仑应力演化及地震危险性

祁连—海原断裂带是青藏高原东北缘重要的活动断裂带,调节着青藏高原北东向推挤作用和阿拉善地块的东西向运动.已有地震地质和数值模型结果显示,祁连—海原断裂带目前存在几个强震破裂空段且其上应力积累显著、断层闭锁程度高,2022年1月8日门源MS6.9地震即发生在祁连—海原断裂带西段的断层高闭锁、应力积累显著的破裂空段.为进一...     

DISCUSSING THE INFLUENCE OF MAJOR EARTHQUAKE SEQUENCE IN THE LONGMENSHAN AREA ON THE LUSHAN EARTHQUAKE FROM STRESS EVOLUTION

Calculating the coseismic static Coulomb stress change induced by an earthquake and interseismic stress change permits to explain the distribution of aftershocks, the earthquake sequence and other seismic observations. Four earthquakes greater than M7 have occurred in the Longmenshan area before the 2013 Lushan earthquake since 1900. This paper analyzes the influence of these four events on the Lushan earthquake, the stress evolution after the Lushan earthquake accompany with strong earthquake sequence on Longmenshan Fault, and the stress state of the gap between the Lushan and Wenchuan earthquakes. To address these issues would help future seismic risk assessment in the region. We construct a three dimensional finite element model based on the geological structure, the deep inversion results of density and velocity, and the GPS and the stress observation data. The simulation results show that the annual variation rate of Coulomb stress is higher on the Xianshuihe fault and southern segment of the Longmenshan fault, which is consistant with the regional seismicity. The coseismic Coulomb stresses induced by Kangding, Songpan, and Wenchuan earthquakes at the Lushan earthquake epicenter is greater than 0, implying that the three earthquakes may promote the occurrence of the Lushan earthquake, especially the Wenchuan earthquake. The viscous relaxation is remarkable which cannot be ignored in the analysis of stress evolution. From the stress evolution of this area, we can find that the gap between the Wenchuan and Lushan earthquakes is still at a relatively high stress level after the Lushan earthquake.     

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.     

Precise Location of Earthquakes at the Eastern Boundaries of the Sichuan-Yunnan Rhombic Block

Based on the seismic station data sets from Sichuan and Yunnan provinces, we employed a multi-step seismic location method (Hypo2000 + Velest + HypoDD) to precisely locate the 7,787 earthquakes that occurred during 2010-2015 along the eastern boundaries of the Sichuan-Yunnan rhombic block, namely from southern Dawu to the Qiaojia segment. The final results show that location precision is greatly advanced and epicenter distribution exhibits good consistency with the linear distribution of the seismic faults. Earthquake distribution is quite intensive at the intersection region in the southern segment of the Xianshuihe fault, the Anninghe fault zone, the Xiaojinhe fault zone and the Daliangshan fault zone to the east. The depth profile of seismicity shows a clear stepwise activity along the active seismic fault zones. The profile crossing the faults of the Xianshuihe, Anninghe, and Daliangshan presents a complex interaction among faults near the multiple faults intersection region, Shimian, where the earthquakes are obviously divided into two groups in depth. Earthquakes are very rare at the depth of 15km-20km, which is consistent with the region of the plastic rheology between 14km-19km calculated by Zhu Ailan et al.,(2005).     

2015年尼泊尔M_W7.9地震对青藏高原活动断裂同震、震后应力影响

2015年尼泊尔MW7.9地震重烈度区从震中向东延伸,致灾范围包括尼泊尔、印度北部、巴基斯坦、孟加拉和中国藏南地区,其应力调整对邻区和周边活动断裂可能产生重要影响.本文基于地震应力触发理论,采用岩石圈地壳分层黏弹性位错模型,计算了尼泊尔MW7.9地震引起的周边断裂,特别是青藏高原活动断裂的同震和震后库仑应力变化.结果显示,尼泊尔地震同震效应引起大部分震区库仑应力升高,余震主要分布在最大同震滑动等值线外部库仑应力升高区域;少量余震靠近最大滑动量区域,可能该区域积累的地震能量在主震期间没有完全释放.尼泊尔地震同震库仑应力对青藏高原,特别是中尼边境区域活动断裂有一定影响.亚东—谷露地堑南段、北喜马拉雅断裂西段、当惹雍错—定日断裂和甲岗—定结断裂同震库仑应力升高,其中当惹雍错—定日断裂南端,北喜马拉雅断裂西段同震库仑应力变化峰值超过0.01 MPa;帕龙错断裂、班公错断裂、改则—洞措断裂库仑应力降低,其地震发生概率有所降低.震后应力影响方面,未来40年内黏弹性松弛作用导致北喜马拉雅断裂、改则—洞措断裂和喀喇昆仑断裂整体应力卸载;藏南一系列正断层震后应力持续上升,其中帕龙错断裂南段受到震后黏弹性库仑应力影响,由应力阴影区逐渐转化为应力增强区,当惹雍错—定日断裂南段应力进一步加强,震后40年其南端应力变化峰值达到0.1345 MPa,亚东—谷露断裂南段应力亦持续增强.藏南正断层的地震活动性值得进一步关注.     

鲜水河断裂带断层间相互作用的触震与缓震效应

探讨了断层间相互作用产生的同震库仑应力改变及对地震的触发与延缓效应，并以鲜水河断裂带不同断裂段时间上连续发生的4次MS6.0以上地震为例，计算和分析了每次地震发生后，在周围其它断裂上产生的同震库仑应力改变及其对后续地震的触发，以及1973年炉霍MS7.6地震和1981年道孚MS6.9地震发生后，在其周围最易破坏失稳的微破裂上产生的同震库仑应力改变及对余震活动的影响．在其它条件保持不变的情况下，将这4次地震的累积触震与缓震效应加以定量考虑，对鲜水河断裂带各断裂段的地震潜势进行了重新计算，并与已有预测结果进行对比分析，检验和评估了鲜水河断裂带断层间相互作用触震与缓震效应的重要性．结果表明:鲜水河断裂带每次地震都发生于受其先前发生的地震影响而产生同震库仑应力增加的断裂段上，不同断层间相互作用的触震和缓震效应导致地震复发概率的改变可高达30.5％以上， 主震后的余震大多发生于同震库仑应力增加较高的微破裂上．      

Earthquake triggering and delaying caused by fault interaction on Xianshuihe fault belt,southwestern China

The coseismic Coulomb stress change caused by fault interaction and its influences on the triggering and delaying of earthquake are briefly discussed.The Xianshuihe fault belt consists of Luhuo,Daofu,Kangding,Qianning and Ganzi fault.Luohuo(Ms=7.6,1973)-Kangding(Ms=6.2,1975)-Daofu(Ms=6.9,1981)-Ms=6.0,1982)earthquake is a seismic sequence continuous on the time axis with magnitude greater than6.0.They occurred on the Luhuo.Kangding,Daofu and Ganzi fault,respectively.The coseismic Coulomb stress changes caused by each earthquake on its surrounding major faults and microcracks are calculated,and their effects on the triggering and delaying of the next earthquake and aftershocks are analyzed.It is shown that each earthquake of the sequence occurred on the fault segment with coseismic Coulomb stress increases caused by its predecessors,and most after-shocks are distributed along the microcracks with relatively larger coseismic Coulomb stress increases resulted from the main shock.With the fault interaction considered,the seismic potential of each segment along Xianshuihe fault belt is reassessed,and contrasted with those predicted results ignoring coseismic Coulomb stress change,the significance of fault interaction and its effect on triggering and delaying of earthquake are emphasized.It is con-cluded that fault interaction plays a very important role on seismic potential of Xianshuihe fault belt,and the maximal change of future earthquake probability on fault segment is up to 30.5%.