The Lushan M S7.0 earthquake and activity of the southern segment of the Longmenshan fault zone

Following the Lushan M _S7.0 earthquake on 20 April 2013, a topic of much concern is whether events of M _S7 or greater could occur again on the southern segment of the Longmenshan fault zone. In providing evidence to answer this question, this work analyzes the tectonic relationship between the Lushan event and the 2008 Wenchuan earthquake and the rupture history of the southern segment of the Longmenshan fault zone, through field investigations of active tectonics and paleoearthquake research, and our preliminary conclusions are as follows. The activity of the southern segment of the Longmenshan fault zone is much different to that of its central section, and the late Quaternary activity has propagated forward to the basin in the east. The seismogenic structure of the 2008 Wenchuan earthquake is the central-fore-range fault system, whereas that of the 2013 Lushan event is attributed to the fore-range-range-front fault system, rather than the central fault. The southern segment of the Longmenshan fault zone becomes wider towards the south with an increasing number of secondary faults, of which the individual faults exhibit much weaker surface activity. Therefore, this section is not as capable of generating a major earthquake as is the central segment. It is most likely that the 2013 earthquake fills the seismic gap around Lushan on the southern segment of the Longmenshan fault zone.     

Preliminary results pertaining to coseismic displacement and preseismic strain accumulation of the Lushan M S7.0 earthquake, as reflected by GPS surveying

This paper presents the coseismic displacement and preseismic deformation fields of the Lushan M _S7.0 earthquake that occurred on April 20, 2013. The results are based on GPS observations along the Longmenshan fault and within its vicinity. The coseismic displacement and preseismic GPS results indicate that in the strain release of this earthquake, the thrust rupture is dominant and the laevorotation movement is secondary. Furthermore, we infer that any possible the rupture does not reach the earth’s surface, and the seismogenic fault is most likely one fault to the east of the Guanxian-Anxian fault. Some detailed results are obtainable. (1) The southern segment of the Longmenshan fault is locked preceding the Lushan earthquake. After the Wenchuan earthquake, the strain accumulation rate in the southeast direction accelerates in the epicenter of the Lushan earthquake, and the angle between the principal compressional strain and the seismogenic fault indicates that a sinistral deformation background in the direction of the seismogenic fault precedes the Lushan earthquake. Therefore, it is evident that the Wenchuan M _S8.0 earthquake accelerated the pregnancy of the Lushan earthquake. (2) The coseismic displacements reflected by GPS data are mainly located in a region that is 230 km (NW direction) × 100 km (SW direction), and coseismic displacements larger than 10 mm lie predominantly in a 100-km region (NW direction). (3) On a large scale, the coseismic displacement shows thrust characteristics, but the associated values are remarkably small in the near field (within 70 km) of the earthquake fault. Meanwhile, the thrust movement in this 70-km region does not correspond with the attenuation characteristics of the strain release, indicating that the rupture of this earthquake does not reach the earth’s surface. (4) The laevorotation movements are remarkable in the 50-km region, which is located in the hanging wall that is close to the earthquake fault, and the corresponding values in this case correlate with the attenuation characteristics of the strain release.     

九寨沟Ms 7.0级地震的左旋走滑作用与动力机制

2017年8月8日四川九寨沟发生的Ms 7.0级地震是继2008年汶川Ms 8.0地震、2013年芦山Ms 7.0级地震后在青藏高原东缘发生的又一次强震。本文通过综合分析九寨沟Ms 7.0级地震及历史地震的震源机制解、余震和历史地震分布、区域应力场、活动断层等资料,来揭示九寨沟地震的发震构造与动力机制。初步研究结果表明:(1)此次地震的震中位于塔藏断裂、岷江断裂和虎牙断裂之间的交汇区,显示活动断裂的交汇区对此次地震的发生具有控制作用;(2)发震断裂为虎牙断裂,断裂走向为北西西向,倾向南西,倾角较陡,属于高倾角左旋走滑型地震;(3)震中位于虎牙断裂北段的北部地震空区,充填了1973年和1976年4次大于Mw6.0级地震空区;(4)此次地震位于2008年汶川Ms 8.0级地震的库仑应力增加区,应是汶川地震的应力传递和触发的结果;(5)此次地震位于巴颜喀拉块体的东北部顶角区,青藏高原东缘下地壳流向北东方向的挤出是驱动此次地震的动力机制。     

Interseismic and coseismic displacements of the Lushan Ms 7.0 earthquake inferred from leveling measurements

By using precise leveling data observed between 1985 and 2010 across the south section of the Longmenshan fault zone, and eliminating the coseismic displacements caused by the Wenchuan Ms 8.0 earthquake, the interseismic vertical deformation field was obtained. The result shows that the Lushan region, located between the Shuangshi-Dachuan fault （front range of the Long- menshan fault） and the Xinkaidian fault （south section of the Dayi fault）, is situated in the intersection zone of positive and negative vertical deformation gradient zones, indicating that this zone was locked within 25 years before the Lushan earthquake. Based on leveling data across the rupture zone surveyed between 2010 and 2013, and by eliminating the vertical deformation within 3 years before the earthquake, the coseismic vertical displacement was derived. The coseismic vertical displacement for the benchmark DD35, which is closest to the epicenter, is up to 198.4 mm （with respect to MY165A）. The coseismic dis- placement field revealed that the northwest region （hanging wall） moved upwards in comparison with the southeastern region （foot wall）, suggesting that the seismogenic fault mainly underwent thrust faulting. By comparing the coseismic and interseismic vertical deformation fields, it was found that the mechanisms of this earthquake are consistent with the elastic rebound theory; the elastic strain energy （displacement deficit） accumulated before the Lu- shan earthquake was released during this quake.     

Source rupture process of Lushan M S7.0 earthquake, Sichuan, China and its tectonic implications

The source rupture process of the M _S7.0 Lushan earthquake was here evaluated using 40 long-period P waveforms with even azimuth coverage of stations. Results reveal that the rupture process of the Lushan M _S7.0 event to be simpler than that of the Wenchuan earthquake and also showed significant differences between the two rupture processes. The whole rupture process lasted 36 s and most of the moment was released within the first 13 s. The total released moment is 1.9×10¹⁹N m with M _W=6.8. Rupture propagated upwards and bilaterally to both sides from the initial point, resulting in a large slip region of 40 km×30 km, with the maximum slip of 1.8 m, located above the initial point. No surface displacement was estimated around the epicenter, but displacement was observed about 20 km NE and SW directions of the epicenter. Both showed slips of less than 40 cm. The rupture suddenly stopped at 20 km NE of the initial point. This was consistent with the aftershock activity. This phenomenon indicates the existence of significant variation of the medium or tectonic structure, which may prevent the propagation of the rupture and aftershock activity. The earthquake risk of the left segment of Qianshan fault is worthy of attention.     

The spatial distribution pattern of landslides triggered by the 20 April 2013 Lushan earthquake of China and its implication to identification of the seismogenic fault

After the 20 April 2013 Lushan MS6.6 earthquake occurred,investigation and identification of the seismogenic fault for this event have become a focused and debatable issue.This work prepared an initial landslide inventory map related to the Lushan earthquake based on field investigations and visual interpretation of high-resolution aerial photographs and provided evidence for solving the issue aforementioned.The analysis of three landslide-density profiles perpendicular to strike direction of the probable seismogenic fault shows that many landslides occurred on the footwall of the Shuangshi–Dachuan fault(SDF),without sudden change of landslide density near the fault.Very few landslides were detected near the Dayi fault(DF)and also no change of landslide density there.While obvious sudden change of landslide density appeared about 1–2 km from the northwest to the western Shangli fault(WSF),and the landslide density on the hanging wall of the fault is obviously higher than that of on the footwall.Therefore,we infer that the seismogenic fault for the Lushan earthquake is neither the SDF nor the DF,rather probably the WSF located between these two faults,which is an evident linear trace on the earth surface.Meanwhile,the coseismic slip did not propagate upward to the ground,implying the Lushan earthquake was spawned by a blind-thrust-fault beneath the WSF.     

Relocation of the mainshock and aftershock sequences of M S7.0 Sichuan Lushan earthquake

The mainshock of April 20, 2013 Sichuan Lushan M _S7.0 earthquake was relocated using a 3-D velocity model. Double difference algorithm was applied to relocate aftershock sequences of Lushan earthquake. The locations of 2405 aftershocks were determined. The location errors in E-W, N-S and U-D direction were 0.30, 0.29 and 0.59 km on average, respectively. The location of the mainshock is 102.983°E, 30.291°N and the focal depth is 17.6 km. The relocation results show that the aftershocks spread approximately 35 km in length and 16 km in width. The dominant distribution of the focal depth ranges from 10 to 20 km. A few earthquakes occurred in the shallow crust. Focal depth profiles show fault planes dip to the northwest, manifested itself as a listric thrust fault. The dip angle is steep in the shallow crust and gentle in the deep crust. Although the epicenters of aftershocks distributed mainly along both sides of the Shuangshi-Dachuan fault, the seismogenic fault may be a blind thrust fault on the eastern side of the Shuangshi-Dachuan fault. Earthquake relocation results reveal that there is a southeastward tilt aftershock belt intersecting with the seismogenic fault with y-shape. We speculate it is a back thrust fault that often appears in a thrust fault system. Lushan earthquake triggered the seismic activity of the back thrust fault.     

Lushan M S7.0 earthquake: A blind reserve-fault event

In the epicenter of the Lushan M _S7.0 earthquake there are several imbricate active reverse faults lying from northwest to southeast, namely the Gengda-Longdong, Yanjing-Wulong, Shuangshi-Dachuan and Dayi faults. Emergency field investigations have indicated that no apparent earthquake surface rupture zones were located along these active faults or their adjacent areas. Only brittle compressive ruptures in the cement-covered pavements can be seen in Shuangshi, Taiping, Longxing and Longmen Townships, and these ruptures show that a local crustal shortening occurred in the region during the earthquake. Combining spatial distribution of the relocated aftershocks and focal mechanism solutions, it is inferred that the Lushan earthquake is classified as a typical blind reverse-fault earthquake, and it is advised that the relevant departments should pay great attention to other historically un-ruptured segments along the Longmenshan thrust belt and throughout its adjacent areas.     

四川芦山Ms 7.0级地震前卫星线性云异常现象

 对四川芦山地震前1个月内的FY-2卫星云图与红外亮温数据分析发现,震前3d即4月17日的06:30—09:30,在青藏高原东部出现延展达数百千米的两条线性云,两者延伸交叉处正是芦山地震的震中位置。通过与汶川Ms 8.0级地震前数小时出现的线性云异常进行比较,认为龙门山断裂带强震前屡次出现的“无中生有”线性云异常现象,可能与青藏高原东部地下未知的隐伏构造及油气赋存有关,具有一定的临震指示性,应该作为该地区地震遥感监测的重点。今后,在全球综合地球观测系统(GEOSS)大数据的支持下,考虑孕震过程中的地球系统多圈层作用与耦合效应,将开展遥感多参数异常时空特征及其关联性分析,为解开该地区的线性云异常之谜提供科学依据。     

探讨与汶川地震有关的焦点科学问题

基于孕震断层多锁固段脆性破裂理论和新划定的3.6版汶川地震区,再次探讨了与2008年汶川地震有关的若干科学问题,包括该震是否为主震?该震、2013年芦山MS7.0地震、2017年九寨沟M_S7.0地震之间关系?该震是否存在复发周期?该震发生前是否存在显著物理前兆?该震与紫坪铺水库之间关系?研究结果表明:汶川地震并非汶川地震区当前地震周期主震,未来将发生MS8.0~8.3标志性地震;2013年芦山地震和2017年九寨沟地震有直接联系且均与汶川地震密切相关,两者同为下一次标志性地震前的两次显著预震;汶川地震区标志性地震及其未来主震是否存在复发周期目前尚不能作出明确判断;在汶川地震前,由于自1995年12月18日后其震源体的物理状态长期保持近似不变,故不可能观测到显著的中长期与短临物理前兆;紫坪铺水库对汶川地震孕育过程的影响很小,可以忽略。     

Rupture process of the Wenchuan <Emphasis Type="Italic">M</Emphasis>8.0 earthquake of Sichuan China: the segmentation feature

Moment tensor solution, rupture process and rupture characteristics of the great Wenchuan M8.0 earthquake are studied by using 39 long-period P and SH waveforms with evenly azimuth coverage of stations. Our results reveal that the Wenchuan M8.0 event consisted of 5 sub-events of Mw≥7.3 occurring succesively in time and space. Rupture started with a Mw7.3 introductory strike-slip faulting in the first 12 s, then within 12?40 s, two sub-events with Mw7.6 and Mw7.4 occurred within 80 km northeast from the init...     

民间组织在地震应急救援与灾后重建中的作用、角色与分类研究

地震灾害频繁发生,快速救援的民间组织发挥了重要作用。根据现实状况和地震中应急管理的需求,对地震中出现的任务导向型民间组织的研究必不可少。将民间组织按照在救援和重建过程中的运作模式和服务时间进行划分,包括临时型、短期型以及永久型三大类,从组建、运作方式、人数、组织架构以及解体这几个方面来分析其差异性,从而对民间组织在救援和灾后重建中的角色以及作用进行分析界定。以民间组织参与汶川地震和雅安地震为背景,运用SWOT分析总结其与官方和半官方不同之处,并提出相应的管理对策。这对提高在应急救援和灾后重建中民间组织的理性认识、满足新历史条件下的社会需求具有重要的现实意义。     

Lushan M S7.0 earthquake: A special earthquake occurs on curved fault

Relocation result shows that the aftershocks of the Lushan M _S7.0 earthquake spatially distribute in a shape like “half bowl”, indicating that the rupture structure of the mainshock is a highly curved surface. Kinematic analysis reveals that a laterally varied dislocation pattern occurs on this curved fault even though a single relative horizontal movement controls slip on this fault. Reverse slip prevails on curved fault. However, significant normal slip is predicted near the edge of north flank. Moreover, the north flank features left-lateral slip while the south flank contrarily features right-lateral slip. The relative scope of aftershock distribution implies inadequate breaking of the curved fault during the mainshock, calling for the attention to potential earthquake risk on the neighboring portions of the coseismic rupture due to significant increase of the coseismic Coulomb stress. Coseismic stress modeling also reveals that it is unnecessary for the stress on ruptured part to be unloaded following the earthquakes on the curved fault. The coseismic stress loading on ruptured elements unveils the specialty of faulting for the Lushan earthquake and we conclude that this specialty is due to the highly curved fault geometry.     

中国汶川Ms 8.0级地震前NDVI变化特征及其佐证

 利用归一化植被指数（NDVI）数据,探测了汶川Ms 8.0级地震前植被变化情况。对震前9年的NDVI数据先做整体变化分析,没有发现明显的植被退化现象;再对时间序列数据进行逐年比对,发现两个比较明显的植被退化现象。其一,2006年与2005年相比,龙门山断裂东部的四川盆地大部分地区6—9月NDVI均值明显减小,幅度为0～20％。推测原因为震前四川盆地受挤压变形,产生热弹效应放热致使地表升温,进一步与大气耦合导致长期干旱少雨,破坏植被正常生长条件,使植被退化。因此,2006年四川盆地大范围植被退化现象可视为震前异常。其二,2008年5月上旬与2007年相比,龙门山断裂带上发现明显的植被退化现象,成条带状分布,NDVI下降幅度超过20%。这可能与临震前龙门山断裂带上发生某些物理化学变化有关,即临震前龙门山断裂带地壳岩石的破裂发育、断裂之间以及岩石之间的摩擦滑移,导致地下热物质上涌和摩擦生热释放,造成短期（近）地表高温,破坏了植被的正常生长条件,使其退化。因此,可以看作震前短期异常。此外,沿着时间尺度和空间尺度,找到一些震前中期和短期异常佐证,以增加植被异常判断的可信度。     

面向雅安与汶川地震灾害的脆弱性与抗逆力评价

雅安地震与汶川地震是国内近年来发生的较为严重的突发自然灾害事件,本文分别构建地震灾害脆弱性与应急抗逆力评价模型,根据模糊评判法和层次分析法,对汶川和雅安地区脆弱性和抗逆性进行评估,认为两地区的脆弱性和抗逆性略有差异,并探究差异性产生的原因,有助于地区提高综合减灾能力。     

龙门山汶川地震特征及构造运动学初析

2008年5月12日发生的龙门山汶川地震具有震级巨大、波及面宽、震中成线性展布的特点.根据震后构造地质调查,引发本次地震的断层活动主要表现为幕式斜冲与逆冲,其运动学特征是:断裂具有先走滑后逆冲,总体表现以逆冲运动为主.根据断裂面多期擦痕特征确定,断层活动主要为三期幕式活动,第一期为逆冲走滑,第二期为逆冲冲断,第三期为走滑逆冲.由地震破裂构造确定的主压应力方向为北西一南东方向.     

四川芦山Ms 7.0级地震导致周边断层的应力变化

 2013年4月20日,四川雅安市芦山县发生M_s 7.0级强烈地震,造成重大的人员伤亡和经济损失。地震造成的区域库仑应力变化、对周围断层的影响及后续地震带发展趋势是应该关注的问题。利用USGS震源机制解,根据地震静态触发原理,基于弹性位错理论和分层地壳模型,计算得出芦山地震引起同震库仑应力变化从断层的1.0MPa量级减小到200km外的0.1kPa,研究认为在地震之后大部分区域的应力得到释放,鲜水河断裂道孚—康定段和玉龙希断裂南段危险性增加。     

川滇地区典型强震诱发滑坡分布对比研究

近年来,川滇地区相继发生了2008年汶川M_s 8.0级地震、2013年芦山M_s 7.0级地震、2014年鲁甸M_s 6.5级地震以及2017年九寨沟M_s7.0级地震,4次地震均引发了大量的地震滑坡灾害。通过统计分析,从地震、地形地貌和地质3个大类因素中,选取地面峰值加速度(ground peak acceleration, PGA)、地震烈度、距断层距离、地层岩性、高程、坡度、坡向7个因子,对比分析此4次强震诱发滑坡分布规律。研究发现它们存在共性特征：(1)4次地震均呈现出滑坡分布(数量和密度)与PGA和震级的正相关关系;(2)地质地貌越复杂地区(沟谷发育、坡降大)滑坡数量越多;(3)滑坡分布最大距离随地震震级增加而增加。此外,也发现了差异性特征：(1)在最大影响距离0.2倍的近断层区域,汶川地震滑坡占76%,而其他3次地震仅占27%;(2)滑坡在相对软弱地层(第四系地层、软层等)分布数量反而较硬岩区滑坡分布最少。针对差异性,从发震断裂性质、震级、地层岩性、地震烈度、断层错动方向讨论了成因。     

基于“情景—应对”的地震灾区多层次物资需求建模分析

在地震灾害抢险中,应急物资能否准确高效的配送至需求点,决定整个突发事件应对工作的成败。本研究通过分析2008年“5·12汶川地震”和2013年芦山地震对应急物资的需求状况,提出了地震抢险期间应急物资需求的四个层次,并从三个维度对应急资源的需求情景进行了分类,结合突发事件的“情景-应对”模式,讨论了不同层次物资需求在不同情景下的物资保障策略。     

分量钻孔应变仪记录的汶川、芦山强震前兆应变异常

 2007年全国布设了由40台4分量钻孔应变仪组成的分量应变监测网络。位于四川姑咱地震台的应变仪先后记录了汶川和芦山强震孕震过程中的潮汐畸变应变异常现象。这些异常变化基本满足地震前兆的3项判据,故被初步认证是这两次强震孕育过程中的应变前兆。本研究对相关记录资料进行了分析,以期为后续强震预测和预报研究提供参考。