云南和四川中小地震应力降时空特征研究

通过消除S波观测谱中的传播路径、场地响应、仪器响应、噪声等的影响,得到中小地震的震源谱。根据Brune震源模型,运用遗传算法计算了云南地区2121次ML2.0～5.3地震和四川地区323次ML3.0～5.1地震的应力降参数Δσ,分析了云南地区和四川地区中小地震应力降时空变化特征。结果表明:云南地区的地震应力降范围为0.03～47.55MPa,其中Δσ≥10.0MPa(高应力降)的地震占4.8%,Δσ的年均值在2.30～5.05MPa之间;四川地区应力降范围为0.19～47.47MPa,其中Δσ≥10.0MPa(高应力降)的地震占21.7%,Δσ的年均值在5.11～8.72MPa之间。Δσ≥10.0MPa(高应力降)的地震主要分布在滇西北至滇东北及川滇交界一带,尤其是在龙门山断裂带有较明显分布。龙门山断裂带Δσ≥10.0MPa的地震占35.8%,Δσ的年均值在5.20～12.09MPa之间,2004～2007年高应力降地震事件明显增多,反映了汶川8.0级大震前的高应力变化过程。     

Review and new interpretation for the propagation characteristics associated with the 1999 Chi‐Chi earthquake faulting event

The Chi‐Chi earthquake (M_W = 7.6) took place in central western Taiwan in 1999. The earthquake caused reactivation of the Chelungpu Fault and resulted in 100‐km‐long surface ruptures. The fault strikes mostly north–south to NNE–SSW; however, the northern tip of the southern segment of the surface ruptures rotates clockwise to define an east–west trend, then jumps to a shorter NNW‐trending rupture. The largest vertical displacement is recorded in the Shihkang area of the Shihkang–Shangchi Fault Zone, where vertical slips are up to 8–10 m. The Shihkang–Shangchi Fault Zone displays a complex fault pattern as a linkage damage zone between two fault segments with the greatest concentration of faults and fractures. Our new interpretation, based on recent published geometric, kinematic, and geophysical studies on the Chi‐Chi earthquake fault, suggests that the Shihkang–Shangchi Fault Zone is not a simple termination zone, but may be an ‘overstep zone’ or a ‘transfer zone’. Slip analysis along the surface ruptures indicates that they are composed of three fault segments and the amount of slip partly depends on the intersection angle between slip direction and fault strike. Our numerical modeling for the area indicates that Coulomb stress changes are mainly concentrated on tips and bends of the surface ruptures. Slip patterns indicate that the fault propagates toward the northeast. Therefore, this study suggests high potential for future earthquake activity along the unruptured Shangchi segment. Hence, future geohazard studies should focus on the Shangchi segment to evaluate potential earthquakes, determine recurrence intervals, and reduce future earthquake hazards.     

青海玉树M_S7.1地震两个典型地点的地表破裂特征

2010年4月14日在青海省玉树县发生了MS7.1地震,形成了长达65km的地表破裂带,甘达村西D1、果庆益荣松多D2是地表破裂带上破裂特征具代表性的2个地点。这2个地点的同震地表破裂特征调查结果显示:1)破裂沿先存的断裂晚第四纪活动遗迹展布,在甘达村西主要表现为张剪切破裂呈雁列状展布,在不连续的岩桥区分布了挤压鼓包,地表破裂带主要集中在古地震坳槽中,通过测量一个错断的围墙得到该点的位错量为1.4m;2)在果庆益荣松多,山前坡积物中展布的破裂带由斜列距约30m的次级破裂右阶斜列组成,而次级破裂则由一系列斜列距3～5m的单条破裂右阶斜列组成,单条破裂主要表现为挤压鼓包-张裂缝相间排列与裂缝带等2种破裂样式,在河谷中则表现为挤压垄脊和陷落塘,实测栅栏位错量为1.3m;3)破裂整体为左旋走滑性质,未见明显垂直错动分量,破裂样式为典型的走滑破裂特征,地表破裂带沿先存断错地貌分布,反映晚第四纪活动的甘孜-玉树断裂是此次地震的发震断裂,该断裂大震活动具有原地重复发生的特点     

The Quaternary Tectonic Stress Field of the Kunming Basin and Its Surrounding Areas

The Kunming basin is a Cenozoic faulted basin controlled by N-S trending active faults. there are totally 8 main active faults in and around the Kunming basin area. Inversion of fault slip data suggests that the stress field of the Kunming basin has experienced two major stages. In the first stage (from the late-Pliocene to mid-Pleistocene), the regional tectonic stress field was characterized by near E-W compression and near N-S extension. In the second stage (from the late-Pleistocene to the present), the tectonic stress field has been mainly characterized by NNW-SSE compression and NEE-SWW extension. Under such a stress field, the near N-S trending faults in the region mainly show a lateral slip.     

Simulations of Vertical and Horizontal Displacement Fields in the 2008 Wenchuan Earthquake

By using the Yoshimitsu Okada and Steketee fault dislocation model,we calculated the vertical and horizontal displacements along the Yingxiu-Beichuan inverse fault and Guanxian-Anxian inverse fault along which the Wenchuan MS8. 0 earthquake occurred in 2008. Compared to the achievements of field surveying along the surface rupture zone,we found that our computational results are comparable to the real displacement variation trend. Furthermore,the computational results indicated that the surface displacement...     

深圳市断裂新活动与地震研究进展

回顾了深圳地区断裂最新活动性和地震的研究历史,总结了前人所作的主要工作与认识,以此为基础进一步介绍了深圳市活断层探测与地震危险性评价项目的最新工程探测成果与研究进展。项目选择了横岗-罗湖断裂、莲塘断裂、温塘-观澜断裂为研究对象,采用了卫星遥感解译、微震精确定位、野外地震地质调查、钻孔和探槽探测、浅层地震勘探、深部结构大地电磁阵列探测、地下电磁波勘探等工程技术方法,对断裂的近地表及中深部结构特征、新活动性和地震危险性进行了探测与评价,获得了一系列新的认识。最后,结合深圳市断裂构造运动和地震研究现状与存在的问题,提出了今后开展工作的若干建议。     

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.     

late quaternary activity of the qujiang fault and analysis of the slip rate

The Qujiang Fault is one of the most seismically active faults in western Yunnan, China and is considered to be the seismogenic fault of the 1970 M_S7.7 Tonghai earthquake. The Qujiang Fault is located at the southeastern tip of the Sichuan-Yunnan block. In this study, we examine the geometry, kinematics, and geomorphology of this fault through field observations and satellite images. The fault is characterized by dextral strike-slip movements with dip-slip components and can be divided into northwest and southeast segments according to different kinematics. The northwest segment shows right-lateral strike-slip with normal components, whereas it is characterized by dextral movements with the northeast wall thrusting over the opposite in the southeast segment. The offset landforms are well developed along the strike of the fault with displacements ranging from 3.7m to 830m. The Late Quaternary right-lateral slip rate was determined to be 2.3～4.0mm/a through dating and measuring on the offset features. The variation of the slip and uplift rates along the fault strike corresponds well to the fault kinematics segmentation: the slip rate on the northwest segment is above 3mm/a with an uplift rate of 0.6～0.8mm/a; however, influenced by the Xiaojiang Fault, the southeast segment shows apparent thrust components. The slip rate decreases to below 3.0mm/a with an uplift rate of 1.1mm/a, indicating different uplift between the northwest and southeast segments.     

垂直和倾斜断层围陷波的谱元法数值模拟及其波场特征对比

Fault zone trapped waves( F ZTWs) m ainly travel along the fractured fault zone( F Z)which is of low velocity and high attenuation. FZTWs often carry significant information about a fault  s internal structure,so it is important to understand their wave field characteristics for FZ structure inversion. Most previous simulations are based on vertical faults,while in this paper we implement the FZTW simulations on vertical or inclined faults and compare their wave fields in both time and frequency domains. The results show that the existence of fault zone and inclined angle of fault can significantly influence the features of waves near faults. In amplitude,a fault zone can generate a larger amplitude of waves. The velocity contrast between two walls of fault may lead to amplification of amplitudes in the low velocity fault wall. In frequency,a fault zone tends to influence the waves in the low frequency range. In a pattern of particle polarization of FZTWs,it tends to be single direction for vertical faults but fork to multiple directions for inclined faults,which might provide a new way to study the fault zone with FZTWs. These conclusions may be valuable for FZ structure inversion,and will enhance the knowledge on near-fault strong ground motions.     

利用水准测量数据分析芦山M_S7.0地震前龙门山断裂带南段应变积累

利用2010年和2013年两期一等水准测量数据分析了龙门山断裂带南段芦山MS7.0地震前的应变积累。结果表明:(1)汶川地震的发生明显加速了该区域应变积累的过程,龙门山断裂带南段主要断层区域垂直形变速率为6~9 mm/a,表明汶川地震的发生加速了此次芦山地震的孕育过程;靠近鲜水河断裂带区域垂直形变速率为1~5 mm/a,低于汶川地震前的隆升速度。(2)芦山地震并未释放该区域长期积累的应变能,龙门山断裂带南段仍然具有发生破坏性地震的可能。