Spatio-temporal variation and focal mechanism of the Wenchuan M_S8.0 earthquake sequence

Based on abundant aftershock sequence data of the Wenchuan MS8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic.Dense aftershocks distribute along Longmenshan central fault zone of NE direction and form a narrow strip with the length of 325 km and the depth between several and 40 km.The depth profile(section of NW direction) vertical to the strike of aftershock zone(NE direction) shows anisomer-ous wedgy distribution characteristic of aft...     

Spatio-temporal rupture process of the 2008 great Wenchuan earthquake

Focal mechanism and dynamic rupture process of the Wenchaun M _s8.0 earthquake in Sichuan province on 12 May 2008 were obtained by inverting long period seismic data from the Global Seismic Network (GSN), and characteristics of the co-seismic displacement field near the fault were quantitatively analyzed based on the inverted results to investigate the mechanism causing disaster. A finite fault model with given focal mechanism and vertical components of the long period P-waves from 21 stations with evenly azimuthal coverage were adopted in the inversion. From the inverted results as well as aftershock distribution, the causative fault of the great Wenchuan earthquake was confirmed to be a fault of strike 225°/dip 39°/rake 120°, indicating that the earthquake was mainly a thrust event with right-lateral strike-slip component. The released scalar seismic moment was estimated to be about 9.4×10²⁰-2.0×10²¹ Nm, yielding moment magnitude of M _w7.9–8.1. The great Wenchuan earthquake occurred on a fault more than 300 km long, and had a complicated rupture process of about 90 s duration time. The slip distribution was highly inhomogeneous with the average slip of about 2.4 m. Four slip-patches broke the ground surface. Two of them were underneath the regions of Wenchuan-Yingxiu and Beichuan, respectively, with the first being around the hypocenter (rupture initiation point), where the largest slip was about 7.3 m, and the second being underneath Beichuan and extending to Pingwu, where the largest slip was about 5.6 m. The other two slip-patches had smaller sizes, one having the maximum slip of 1.8 m and lying underneath the north of Kangding, and the other having the maximum slip of 0.7 m and lying underneath the northeast of Qingchuan. Average and maximum stress drops over the whole fault plane were estimated to be 18 MPa and 53 MPa, respectively. In addition, the co-seismic displacement field near the fault was analyzed. The results indicate that the features of the co-seismic displacement field were coincident with those of the intensity distribution in the meizoseismal area, implying that the large-scale, large-amplitude and surface-broken thrust dislocation should be responsible for the serious disaster in the near fault area. Supported by the National Basic Research Program of China (Grant No. 2004CB418404-4) and the National Natural Science Foundation of China (Grant Nos. 40574025 and 40874026)     

Spatio-temporal variation and focal mechanism of the Wenchuan MS8.0 earthquake sequence

Based on abundant aftershock sequence data of the Wenchuan M_S8.0 earthquake on May 12, 2008, we studied the spatio-temporal variation process and segmentation rupture characteristic. Dense aftershocks distribute along Longmenshan central fault zone of NE direction and form a narrow strip with the length of 325 km and the depth between several and 40 km. The depth profile (section of NW direction) vertical to the strike of aftershock zone (NE direction) shows anisomerous wedgy distribution characteristic of aftershock concentrated regions; it is related to the force form of the Longmenshan nappe tectonic belt. The stronger aftershocks could be divided into northern segment and southern segment apparently and the focal depths of strong aftershocks in the 50 km area between northern segment and southern segment are shallower. It seems like 'to be going to rupture' segment. We also study focal mechanisms and segmentation of strong aftershocks. The principal compressive stress azimuth of aftershock area is WNW direction and the faulting types of aftershocks at southern and northern segment have the same proportion. Because aftershocks distribute on different secondary faults, their focal mechanisms present complex local tectonic stress field. The faulting of seven strong earthquakes on the Longmenshan central fault is mainly characterized by thrust with the component of right-lateral strike-slip. Meantime six strong aftershocks on the Longmenshan back-range fault and Qingchuan fault present strike-slip faulting. At last we discuss the complex segmentation rupture mechanism of the Wenchuan earthquake.     

汶川MS8.0地震前四川地区前兆异常及其统计分析

研究了2008年5月12日汶川MS8.0地震前四川地区观测到的各种异常．异常项与所有测项(或测站、台、场地、井点、泉点)之比称为异常测项（测点）比,以下类同. 地震前四川地区流动短水准观测存在中长期趋势异常的场地比为0.28,异常测项比为0.20;流动短基线存在中期趋势异常的场地比为0.13,异常测项比为0.13;地倾斜类观测存在中期趋势异常的台站比0.17,异常测项比为0.13;地下水位观测存在中期趋势异常的水位井点比为0.20;温泉观测存在水温短期异常的泉点比为0.15;温泉水氡、气氡观测存在短期异常的台点比为0.08,异常测项比为0.04;井泉水质组分观测存在短期异常的台点比为0.20,异常测项比为0.04;视电阻率观测存在中期异常的台站比为0.17, 异常测项比为0.06．对同一观测台或场地有不同观测手段,分别计算了台或场地数:四川地区在汶川8.0级地震前各类观测台或场地共有172个,存在观测异常台或场地比为0.14,其中出现中期与短期异常场地比分别是0.08和0.03;各类观测项共有335项,异常测项比为0.09,其中出现中期与短期异常测项的占比分别是0.06和0.01．可见,震前仪器微观监测台或测项多数没有观测到突出异常现象．本文中其它没有提及的观测手段或观测项的资料,经过研究没有分析检测出异常项．      

利用P波初动资料求解汶川地震及其强余震震源机制解

通过查阅国家地震台网、各省区域地震台网和流动地震台网,以及IRIS数据中心给出的一些国际台站的数字波形记录,读取P波初动方向,利用格点尝试法计算了2008年5月12日汶川8.0级（MS）特大地震以及其后发生的部分强余震（44次）的震源机制解.这组震源机制解是对哈佛大学已公布的9个地震的最佳双力偶解的很好补充.     

汶川地震强余震与引潮力关系的初步研究

以汶川地震为例,统计分析2008年5月12日—2009年9月30日5级以上强余震与引潮力的关系,发现平行断层方向的线应变引潮力峰(谷)值时间与汶川地震及强余震发震时间的对应关系较好,且其对应程度与断层性质有关。综合分析认为,引潮力可能是地震的诱发因素之一。     

汶川大地震震害特点与成因分析

2008年5月12日汶川地震造成巨大人员伤亡和财产损失.本文从工程抗震角度分析了震区房屋倒塌的原因,指出地震时房屋倒塌与否与诸多因素有关.在此基础上,分析了汶川地震震害严重的四个主要因素:震级大,烈度高,断层破裂长;震区人口稠密,房屋、路桥等人工工程多;抗震设防水平低;地震诱发地质灾害严重.最后,将汶川地震震害与1976年唐山地震震害作了对比.所得结论可供理解汶川地震震害、改进结构抗震设计参考.     

Preliminary site classification of free-field strong motion stations based on Wenchuan earthquake records

During the great Wenchuan earthquake, about 460 permanent free-field stations in National Strong Motion Observation Network System (NSMONS) of China captured the main shock acceleration records. These records can be applied to site effect analyses, and then the site classification of those permanent stations can be carried out firstly, which will served as the fundamental information for further research. In this paper, the site of near-fault stations is classified by horizontal-to-vertical spectral ratio (...     

汶川大地震中德阳地区液化特点分析

汶川大地震中八个主要地区均有液化现象出现,其中德阳地区液化现象及其震害最为显著.通过现场调查和工程地质资料分析,德阳地区的液化特点为:液化带主要集中在绵竹市、什邡市和德阳市,绵竹市最为严重;液化在烈度Ⅶ、Ⅷ、Ⅸ度区均有出现,但Ⅷ度区最为集中;液化喷水高度多在几公分到2m之间,最高一处超过10 m;液化场地喷出物基本涵盖...     

Relation between the characteristics of strong earthquake activities in Chinese mainland and the Wenchuan earthquake

This paper studies the relations between the great Wenchuan earthquake and the active-quiet periodic characteristics of strong earthquakes, the rhythmic feature of great earthquakes, and the grouped spatial distribution of M_S8.0 earthquakes in Chinese mainland. We also studied the relation between the Wenchuan earthquake and the stepwise migration characteristics of M_S?≥7.0 earthquakes on the North-South seismic belt, the features of the energy releasing acceleration in the active crustal blocks related to the Wenchuan earthquake and the relation between the Wenchuan earthquake and the so called second-arc fault zone. The results can be summarized as follows: ① the occurrence of the Wenchuan earthquake was consistent with the activequiet periodic characteristics of strong earthquakes; ② its occurrence is consistent with the features of grouped occurrence of M_S8.0 earthquakes and follows the 25 years rhythm (each circulation experiences the same time) of great earthquakes; ③ the Wenchuan M_S8.0 earthquake follows the well known stepwise migration feature of strong earthquakes on the North-South seismic belt; ④ the location where the Wenchuan M_S8.0 earthquake took place has an obvious consistency with the temporal and spatial characteristic of grouped activity of M_S≥?7.0 strong earthquakes on the second-arc fault zone; ⑤ the second-arc fault zone is not only the lower boundary for earthquakes with more than 30 km focal depth, but also looks like a lower boundary for deep substance movement; and ⑥ there are obvious seismic accelerations nearby the Qaidam and Qiangtang active crustal blocks (the northern and southern neighbors of the Bayan Har active block, respectively), which agrees with the GPS observation data.     

利用强震数据获取汶川地震近断层地面永久位移

利用汶川地震中得到的靠近映秀—北川主断裂的64个强震台站的三分量记录数据, 对加速度记录进行基线校正的基础上获取近断层地面运动的永久形变位移, 并将由强震记录获取到的地面位移结果与GPS观测到的同震位移进行对比分析, 研究汶川M_S8.0地震的近断层地面运动的位移特征. 结果表明： ① 在靠近映秀—北川主断层的上盘和下盘, 东西相向的地面运动非常剧烈. 下盘的51SFB, 51MZQ和51JYH台东西向位移均为负(即地面运动向西), 其中51SFB台位移量最大, 达到1.49 m; 上盘的51WCW台位移向东, 位移量为1.26 m. ② 地面运动的位移分布主要表现为以龙门山断裂带的映秀—北川断裂为核心的相向运动, 东西方向上的永久位移要大于南北方向. 从断层机制上来讲, 断层的错动以逆冲运动为主(即逆冲位移要大于走滑分量的位移), 这与震源机制反演及地质考察的结果一致. ③ 大的地面永久位移集中分布在以龙门山断裂带为中心的狭长范围内, 离开发震断裂地面位移的衰减很快. 相比而言, 在发震断层的下盘一侧(即四川盆地)的地面位移的衰减比上盘一侧明显要快.     

利用强震数据获取汶川地震近断层地面永久位移

利用汶川地震中得到的靠近映秀-北川主断裂的64个强震台站的三分量记录数据,对加速度记录进行基线校正的基础上获取近断层地面运动的永久形变位移,并将由强震记录获取到的地面位移结果与GPS观测到的同震位移进行对比分析,研究汶川Ms8.0地震的近断层地面运动的位移特征.结果表明:①在靠近映秀-北川主断层的上盘和下盘,东西相向的地面运动非常剧烈.下盘的51SFB,51MZQ和51JYH台东西向位移均为负(即地面运动向西),其中51SFB台位移量最大,达到1.49m;上盘的51WCW台位移向东,位移量为1.26 m.②地面运动的位移分布主要表现为以龙门山断裂带的映秀-北川断裂为核心的相向运动,东西方向上的永久位移要大于南北方向.从断层机制上来讲,断层的错动以逆冲运动为主(即逆冲位移要大于走滑分量的位移),这与震源机制反演及地质考察的结果一致.③大的地面永久位移集中分布在以龙门山断裂带为中心的狭长范围内,离开发震断裂地面位移的衰减很快.相比而言,在发震断层的下盘一侧(即四川盆地)的地面位移的衰减比上盘一侧明显要快.     

汶川地震中强震动相对持时的空间变化特性研究

使用70％和90％能量持时定义,计算了汶川Ms8.0大地震中获取的来自109个台站强震动加速度记录的相对持时,并以此在竖向及两个水平向上分别进行了回归统计分析,得到了地震动持时的空间变化关系,给出了适合汶川地震地震动的持时定义.对比分析了上盘和下盘2个区域持时空间变化特征,进一步计算了地震动竖向持时与两个水平向持时的比...     

Evaluation model of landslide hazards induced by the 2008 Wenchuan earthquake using strong motion data

Landslides induced by the 2008 Wenchuan earthquake in the Longmenshan area were relatively well instrumented,which makes it possible to investigate the landslides using ground motion records.Firstly,this paper analyzes the data from Wenchuan earthquake on both regional and local site scale.The analyses show that the Newmark accumulative displacement calculated from the ground motion recorded in a particular geological hazard zone corresponds to the hazard intensity in that zone;the larger the displacemen...     

Wenchuan earthquake fault and seismic disaster

Major cases of the MS8.0 Wenchuan earthquake are obtained through field investigations of the epicenter and high-intensity areas, and the relationships among earthquake faults, ground motion and earthquake disasters near fault zones are analyzed.Both strong deformation and ground rupture lead to significant damages of the buildings, indicating that it is necessary to keep safe distance away from active faults and to take other necessary measures.There are two reasons for that the buildings near the surface ...     

汶川与昆仑山强烈地震激发的地球自由振荡频谱的对比分析

强烈地震激发的地震波信息非常丰富,高频信息能量部分会在小范围短时间内迅速衰减,而低频信息特别是较低频信息能量部分则衰减较慢,会绕地球很多圈后才会消耗殆尽,从而激发地球的自由振荡.虽然地球自由振荡的固有频率不变,但不同震源机制的地震激发的地球自由振荡频率成分会随着震级、震源机制、方位等的不同而有显著差别.本文利用2008年5月12日汶川(Mw7.9)地震与2001年11月14日昆仑山(Mw7.8)地震这两个能量震级相当但震源机制不同的地震,基于地震波传播理论,考虑横向各向同性PREM地球模型并融合Crust2.0地壳模型、S20RTS地幔模型及PREM径向衰减模型,利用谱元法结合高性能并行计算,对这两次强烈地震激发的全球地震波传播进行了数值模拟,计算它们激发的地球自由振荡频谱特征差异.计算结果显示了汶川地震的逆冲-走滑特性及昆仑山地震的水平左旋走滑特征.利用理论计算得到的地震波动记录进行功率谱密度估计对比分析,研究结果显示这两次强烈地震释放的低频信息能量大小相当,但总体上看昆仑山地震释放的能量略小于汶川地震的.对比分析表明,不同地震激发的地球自由振荡模式在同一台站处的发育程度不同;同一地震激发的地球自由振荡在不同台站处记录到的振型频率成分也有很大差异.对于不同地震激发的地球自由振荡,有一些频率成分共同出现,表现为地球自由振荡功率谱能量均较大;也有一些振型由于相长干涉,仅在某些地震中被激发而得以良好发育,表现为功率谱能量明显较大;而一些振型由于相消干涉,在一些地震激发方式下被压制,表现为功率谱能量明显很小,甚至接近于0.计算结果清楚地显示了不同地震激发方式下地球振荡模式丰富而复杂的特性,需要对不同地震激发的地球振荡信息进行综合深入的分析,才能对地球内部结构尤其横向不均匀特性给予全面的科学解释.     

Rupture directivity effect on strong ground motion during the 12 May 2008 MW7.9 Wenchuan earthquake

We focus here on the rupture directivity effect on the spatial distribution and attenuation characteristics of near-field ground motions during the 2008 MW7.9 Wenchuan earthquake. We examine the difference between the observed ground motions in and opposite the rupture directions and compare them with Next Generation Attenuation-West2 (NGA-West2) ground motion prediction models. The isochrone directivity predictor is used to quantify the band-limited nature of the rupture directivity effect on strong ground motion. Our results show that the observed peak ground velocity (PGV) and spectral accelerations of periods of 1.0 s and longer are significantly amplified in the rupture direction, but de-amplified in the opposite direction affected by rupture directivity effect of this event. In contrast, the effect of rupture directivity on the observed peak ground acceleration (PGA) and periods of shorter than 1.0 s are relatively weak. The rupture directivity of this event shows clear period dependent and band limited characteristics with the strongest effect occurring around the period of 7.5 s.     

2008年汶川地震近断层地震动的非平稳特征

利用中国强震动台网获得的汶川地震近断层强震动数据,研究汶川地震近断层地震动的强度和频率的非平稳特征,并对其非平稳特征的原因进行初步分析.研究表明近断层地震动强度和频率表现出很强的非平稳特性,这种非平稳特征主要受震源破裂机制、台站方位和局部场地条件的影响.破裂传播正向和反方向上地震动强度和频率的时间过程有显著的不同.在破裂正向上,地震动加速度记录表现为大幅值、短持时的强度过程,强度过程的持续时间为15 s左右,加速度时程的主要周期约为0.4 s,地震动速度时程有较明显的速度脉冲,脉冲周期可以达到8 s;在破裂的反方向上,地震动强度过程的时间跨度长达90 s,加速度记录的主要周期约为0.6 s,速度时程中没有明显的脉冲.小波功率谱的分析结果表明破裂正向上速度脉冲表现为在很小的时间尺度和频域内能量的集中,值得注意的是,观测到的速度脉冲的周期长达8 s,比Chi-Chi地震和Kobe地震中观测到的脉冲周期要长,这可能与汶川地震的震级相对较大有关.     

汶川地震特大型滑坡分布特征研究

2008年＂5.12＂汶川特大地震引发了数以万计的滑坡、崩塌、危岩等次生地质灾害,对灾区人民生命财产造成了惨痛损失。尤其是破坏面积大、危害范围广的特大型滑坡,给人们生命财产造成了巨大灾难,而且潜在危险性仍然存在。笔者通过实地调查、资料查阅等方式搜集统计了汶川地震区的特大型滑坡并对其分布特征作了较为全面的归纳总结和分析研究。