四川芦山Mw 6.6级地震发震构造

2013年4月20日四川芦山Mw 6.6级地震发生在龙门山构造带南段,未见典型的同震地表破裂。作者在对震后400余个地震破坏宏观调查点重新厘定的基础上,参考四川数字强震台网的近场峰值加速度(PGA)记录,绘制的本次地震等震线图的极震区地震烈度为Ⅸ度,略呈长轴为NE向的扁椭圆状,不具明显的方向性。进一步综合3 323个早期余震重新定位结果、石油地震勘探剖面和震源机制解等,判定本次地震的主要发震构造为控制蒙山东麓的大邑断裂,系龙门山构造带南段NW-SE向缩短所导致的大邑断裂上冲作用的结果;新开店断裂亦在深部产生了同震破裂,造成了断裂上盘震害明显高于下盘的断层上盘效应现象。     

Far-field coseismic displacements associated with the 2011 Tohoku-oki earthquake in Japan observed by Global Positioning System

Analysis of GEONET observations covering the entire territory of Japan shows that the great Tohoku-oki earthquake that occurred on March 11, 2011 off the east coast of Honshu in Japan caused an eastward movement of the northern part of the island by as much as 5.3 m. The GPS data from TEONET in China were used to derive far-field coseismic displacements and to assess the impact of the Tohoku-oki earthquake on crustal deformation in eastern China. The results reveal that the coseismic horizontal displacement...     

“4·20”芦山地震与“5·12”汶川地震发震断裂初析

2013年4月20日8时2分在四川省雅安市芦山县发生的7.0级地震,是继"5.12"汶川地震之后相隔约5年发生的又一次强震。作者在收集了遥感、DEM、地面地质及芦山震区人工地震剖面基础上,对网上公布的芦山地震震中数据、地震机制解、余震分布数据和地震的地表破裂情况进行了分析,初步推断引发芦山地震的断裂是盆地内西南侧地腹隐伏断裂或新生断裂。将芦山地震与汶川地震进行了综合对比,认为2次地震均属构造地震,从构造动力学角度分析均与印度板块向北挤压碰撞有关;但2次地震发震断裂和发震构造单元特征是不同的,应属2次独立地震。     

The maximum coseismic vertical surface displacement and surface deformation pattern accompanying the Ms 8.0 Wenchuan earthquake

The amount of coseismic deformation and its distribution of the Wenchuan earthquake provide important scientific bases for revealing the mechanisms of earthquake preparation and characterizing the rupture propagation of the Wenchuan earthquake. The previous studies have indicated that the earthquake ruptured the middle-to-north segment of the Longmenshan central fault and the middle segment of the Longmenshan range-front fault, which are characterized by two surface rupture zones of 240 km and 90 km in length, respectively. Based on the pre-earthquake information and photos of landforms and buildings obtained through ge-ologic and geomorphic survey of the area around Shaba Village of Beichuan County, Sichuan Province and the extensive interview with local villagers, we measured the displacements of the major terrain features and the dislocated buildings by total station instruments and differential GPS and obtained the maximum vertical displacement of 9±0.5 m and right-lateral displacement of 2±0.5 m around the Zou’s house in Shaba Village. Though the near-surface deformation exhibits a normal faulting around Shaba Village, the dynamic environment has not changed on the whole. The NW wall of the fault uplifted but without gravity gliding as normally occurring on the hanging wall of a normal fault, which proves that the 9±0.5 m displacement should be the maximum coseismic vertical displacement of the May 12, 2008 Ms 8.0 Wenchuan earthquake.     

“4·20”芦山地震的构造破裂与发震断层

通过对"4.20"芦山地震构造破裂及变形特征的分析研究,阐明触发M=7.0级强烈地震的构造因素是NE向大川-双石断裂的逆断兼右旋走滑错动,断层面最大逆断-右旋滑动量达到1.51m。震中位置应在地震断裂通过的双石-太平区段而非震害严重的龙门乡。造成龙门乡震害异常的主要因素是该盆地较厚的第四系强烈的场地效应及建筑物结构强度不足。此次地震是龙门山断裂带地壳构造应力调整、地壳岩体应力-形变过程进入累进性发展阶段的必然结果。地壳破裂扩展方向具有向龙门山中央断裂发展的趋势。     

“4·20”芦山地震后的四川地质灾害形势预测与防治对策

"4·20"芦山地震诱发了大量次生地质灾害。针对此次地震引发的次生地质灾害,通过分析地形地貌、地质条件、地震活动和极端干湿气候对泥石流发育的影响,建立地质灾害易发性评价指标,利用GIS空间分析技术对四川震后地质灾害易发性进行了快速定量评价。结果显示,2013年四川省地质灾害高、中、低易发区面积分别为9.97×104 km2、6.67×104 km2、1.41×104 km2。其中高易发区主要集中于芦山地震影响区、汶川地震影响区、川东南和川南干旱区。在此基础上提出了防控建议。     

四川芦山Ms 7.0级地震空基联合观测与灾情增强识别

 以四川芦山M_s 7.0级地震后中国科学院遥感与数字地球研究所的有人机航拍为基础,辅以低空无人机平台进行联合观测,建立了空基多平台联合灾情观测模式下的灾情增强识别系统。介绍了空基多平台航测系统的组成及联合灾情观测的技术流程,使用有人机遥感平台与固定翼无人机遥感平台对重灾区芦山县进行航空联合观测。对震后有人机与无人机遥感影像进行综合对比,分析了地震中房屋典型受损的细节、滑坡体空间变化及重要电力线的破坏情况。结果表明,采用空基多平台的灾情监测模式,可显著增强对灾情的识别能力。     

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.     

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.     

Far-field coseismic displacements associated with the great Sumatra earthquakes of December 26, 2004 and March 29, 2005 constrained by Global Positioning System

On December 26, 2004, a great earthquake along the northern Sumatra coast, with its consequent tsunami, caused about 300000 deaths (refer to the 2004 earth-quake hereafter). This great thrust faulting event oc-curred on the subduction zone between Indian …     

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。     

Near-field postseismic deformation along the rupture of 2008 Wenchuan earthquake and its implications

At first time, we observed the postseismic deformation, which actually is a kind of creep after slip, along the intra-plate active fault associated with the Wenchuan earthquake. To understand the near-field postseismic deformation following 2008 Wenchuan earthquake in Sichuan Province of China, we compared the fault scarp or flexure scarp profiles measured in different campaigns. Our result shows that among total 19 observation sites, on 13 sites (68% of 19) fault scarps fall back with an average about 9.7% decrease; on 5 sites (26% of 19) fault scarps present no change; and on one site (6% of 19) fault scarp continues to uplift with 12.8% increase. The variety of fault scarp we observed results mainly from near-field postseismic deformation, after slip occurred in shallow. Based on our observations, the following are demonstrated: except for the southwestern end near Yingxiu Town where coseismic slip deficit and some elastic energy residue exist there, fall back (68%) or non-changing (26%) of fault scarp shows energy balance or energy deficit due to overthrust, implying that the likelihood of occurrence of strong aftershocks of ≥ M7 becomes very small in these energy-released areas. Moreover, we suggest that a minimum of 10% error due to near-field postseismic deformation should be considered when evaluating the magnitude of historic and paleoearthquake or slip rate based on the fault scarp dis-placement, even though the error caused by erosion has been accounted already.     

Characteristics of the crustal structure and hypocentral tectonics in the epicentral area of Nan’ao earthquake (M7.5), the northeastern South China Sea

1918 Nan’ao earthquake (M7.5) occurred in the northeast coastal areas of Guangdong Province. With the seismogeological survey of the epicentral area and history materials analyses, the earthquake epicenter was estimated to locate in the intersection part of the Binhai fault zone (Littoral) and Huanggangshui fault, which strikes NEE and NW, respectively. The activities of the NEE-striking thrust fault and NW-striking extensional fault that were attributed to 1918 Nan’ao earthquake occurred in the Dongshan Island of the epicentral area; they reflected the focal stress field with compression in NW-SE direction and extension in NE-SW direction. The isoseismal contour of seismic intensity X shows a shape of ‘X’ composed of two mutually overlapping ellipses with two axes striking NEE and NW, respectively, and such shape implies that the occurrence of this earthquake is controlled by a pair of conjugate seismotectonic faults constituted by the NEE-striking Binhai fault zone and the NW-striking Huanggangshui fault. The Binhai fault zone is a dominant seismogenic structure, and the NW-striking Huanggangshui fault is the subdominant one. The onshoreoffshore deep seismic profile that crossed the epicentral area and was perpendicular to the strike of the Binhai fault zone was obtained. According to the analyses of the seismic data, the Binhai fault zone is defined as a low velocity zone with SE dip-slip in thecrustal structure section. The Binhai fault zone is a boundary fault between the South China subplate and South China Sea subplate. The crust structure on the northwest side of Binhai fault zone is a normal continental crust with a thickness of 30 km, and the one on the southeast side of the fault zone is a thinning continental crust with a thickness of 25―28 km. The Binhai fault zone is an important seismogenic fault and also is an earthquake-controlling fault. The intersection part between the Binhai fault zone and the low velocity zone of upper crust is advantageous to stress concentration and strain energy accumulation, and presents the deep dynamic conditions for the earthquake’s pregnancy and occurrence.     

Structural deformation and fault activity of the Tan-Lu Fault zone in the Bohai Sea since the late Pleistocene

The Tan-Lu Fault zone (TLFZ) is a significant fractural zone in eastern China and also a seismicity belt in North China. Based on total 4000-km-long shallow penetrated single seismic data with high-resolution, structural deformation and fault activity of the TLFZ in the Bohai Sea since the late Pleistocene are discussed in detail. The results show that the TLFZ with a discontinuous distribution and a general NNE-trending consists of 14 active subfaults with an NNE or NE strike in the Bohai Sea. Seismic data reveal that de-formation zones along the subfaults in the central Bohai Sea and the Laizhou Bay are wider and more complex than those in the Liaodong Gulf. Related folds and lots of secondary normal faults which are characterized by nearly vertical fault planes and a same or reverse dip construct the fractural zone in the Laizhou Bay and the central Bohai Sea. Usually, micro symmetrical grabens develop on the top of anticlines. In the Liaodong Gulf, subfault fractural zones usually consist of secondary normal faults with the same inclination or opposite inclination. Ages of seismic sequences and cutting relation between subfaults and seismic sequences suggest that the latest faulting age of the TLFZ is the end of the late Pleistocene in the Liaodong Gulf and the early Holocene in the Laizhou Bay and the central Bohai Sea. There is a good match between distribution of earthquakes and that of the subfaults in the Laizhou Bay and the central Bohai. Statistical result shows that total vertical offset of the TLFZ since the late Pleistocene ranges from 6 to 11 m. On the basis of offsets of the subfaults, the vertical slip rate is calculated and results show that average vertical slip rates in the central Bohai Sea are larger than those in the Liaodong Gulf and the Laizhou Bay. Slip rates more than 0.06 mm/a during 23–10 ka B.P. and 85–65 ka B.P. are larger than those in other stages. The TLFZ was mainly dominated by tensional normal component since the late Pleistocene. Synthesizing shallow deformation, activity and distribution of earthquakes, the TLFZ in the Bohai Sea can be divided into three segments: the Laizhou-Bay segment, the Bozhong segment, and the Liaodong-Gulf segment.