芦山4.20地震破裂过程及其致灾特征初步分析

采用全球地震台网的远震地震波数据快速反演了2013年4月20日雅安芦山地震(芦山4.20地震)的破裂过程,在震后3小时得到并发布了相关测定结果.结果显示这次地震的震级约M_W6.8,包括两次破裂子事件,但都发生在断层面上震源(破裂起始点)附近,整个地震没有表现出明显的破裂方向性.雅安芦山地震的破裂没有大规模出露地表,主要地震灾害集中在断层上盘,位于芦山县和宝兴县一带.     

2013年四川芦山Ms7.0地震前的重力变化

利用川西地区2010-2012年期间的流动重力观测资料,系统分析了区域重力场变化及其与2013年4月20日四川芦山7.0级地震发生的关系.结果主要表明:①区域重力场异常变化与北东向龙门山断裂带南段和北北西向马尔康断裂带在空间上关系密切,反映沿该两断裂带(段)在2010-2012年期间发生了引起地表重力变化效应的构造活动或变形.②芦山7.0级地震前,测区内出现了较大空间范围的区域性重力异常,而震源区附近产生了局部重力异常,沿龙门山断裂带南段形成了重力变化高梯度带,其中,宝兴、天全、康定、泸定、石棉一带重力差异变化达100×10^-8m·s^-2以上;这些可能反映芦山地震前,区域及震源区附近均产生与该地震孕育、发生有关的构造运动或应力增强作用.③重力场差分动态演化图像和重力场累积变化动态图像均反映芦山7.0级地震孕育过程的最后2~3年出现较显著的流动重力异常变化,可视为该地震的中期前兆信息;本文第一作者等也曾基于该流动重力异常变化在芦山7.0级地震前做过一定程度的中期预测,尤其是地点预测.本文的例子再次证明流动重力观测能较好地捕捉到强震孕育发生过程中,特别是该过程最后阶段的重力异常变化信息.因此,区域流动重力场观测对未来强震的中-长期预测,尤其是在发震地点的判定上具有优势.     

云南地区地壳速度结构的层析成像研究

利用地震波到时和体波层析成像方法反演了云南地区的P波速度结构,根据不同深度的速度异常分析了主要断裂和区域动力作用的深部效应,揭示出壳内低速层的分布范围以及与下地壳流动的联系.研究结果表明,哀牢山-红河断裂两侧的地壳速度结构存在明显的差异,滇中地区的速度异常分布与小江断裂、元谋断裂、程海断裂等南北走向的断裂一致,反映了青藏东部地壳块体顺时针旋转产生的构造效应;滇西南的速度异常分布与哀牢山-红河断裂、无量山断裂、澜沧江等断裂的走向平行,显示了印支块体朝东南方向挤出产生的影响;沿着南汀河断裂分布的低速异常则与印缅块体侧向挤压引起的构造活动有关.壳内低速异常具有分层和分区特征:在哀牢山-红河断裂西侧和澜沧江之间主要分布在地壳中上部,在小江断裂和元谋断裂附近分布在地壳中下部,在滇中地区则广泛分布于地壳底部至莫霍面附近,东、西两侧分别受到小江断裂和哀牢山-红河断裂的限制.其中攀西地区的低速异常与小江断裂和元谋断裂在此附近交汇形成的热流传输通道以及张裂时期强烈的壳幔热交换有关;在哀牢山-红河和澜沧江地区,除了印支块体向东南方向的挤出之外,印缅块体的侧向挤压和向东俯冲也对地壳深部的构造变形产生了一定的影响,由此引发的地幔上涌将导致热流物质沿着断裂通道进入地壳形成低速层.因此,哀牢山-红河断裂不仅在地壳浅部是分隔印支块体和华南块体的地质界限,也是控制两侧区域深部构造变形和壳内韧性流动的分界.     

三维地震勘探技术在新疆沙吉海井田中的应用

针对沙吉海井田以往未开展过地震勘探,煤层多、局部间距小特点,介绍了研究区主要地震反射波与煤层对应关系.通过对T13、T12、T10、T6反射波研究,采用地震波阻抗反演技术对该区煤层厚度及煤层结构进行解释,查明井田构造形态和主要煤层赋存变化特征,取得了较好地震勘探效果.     

地震地貌学研究的现状及展望

地震地貌学是通过三维地震资料平面及空间特征,结合地震地层学理论,来解读和还原古地貌、古沉积和其他地质信息的一门综合性学科,其核心技术是通过快速浏览三维地震资料主测线、联络测线及时间切片等来识别"特殊地质体"。该学科的建立,在真正意义上实现了地震解释从二维到三维的跨越,已在指导勘探和储层预测上发挥了巨大作用。从层位解释、平行解释层位切片或地层切片、振幅属性提取和分析、地震信号体素追踪、特殊属性数据体分析以及多数据体属性叠加显示等六大方面介绍了地震地貌学分析技术的应用实例。地震地貌学还处在起步阶段,未来的发展趋势将会主要集中于:(1)海相和陆相背景下碎屑岩和碳酸盐岩沉积演化研究;(2)基于地震资料的生储盖层及源岩岩性的精确预测,如深水沉积环境下河道砂体精细追踪及河道内部沉积结构划分等;(3)层序地层学理论与模式的改进与发展;(4)储层物性定量化研究、储层非均质性研究以及更加先进的分析技术手段等。     

Spatial sensitivity of seismic hazard results to different background seismic activity and temporal earthquake occurrence models

Spatial sensitivity of seismic hazard results to different models with respect to background seismic activity and earthquake occurrence in time is investigated. For the contribution of background seismic activity to seismic hazard, background area source with uniform seismicity and spatially smoothed seismicity models are taken into consideration. For the contribution of faults, through characteristic earthquakes, both the memoryless Poisson and the time dependent renewal models are utilized. A case study, involving the assessment of seismic hazard for the Bursa province in Turkey, is conducted in order to examine quantitatively the influence of these models on seismic hazard results. The spatial variation of the difference in Peak Ground Acceleration (PGA) values obtained from these different models is presented in the form of difference maps for return periods of 475 and 2475 years. Best estimate seismic hazard maps for PGA and Spectral Accelerations (SA) at 0.2 and 1.0 s are obtained by using the logic tree method.     

Study on the S-wave Splitting Characteristics in the Longtan Reservoir Area,Guangxi,China

In this paper,the shear wave splitting features of the Longtan reservoir area are studied by adopting the traditional cross-correlation coefficient method and polarization analysis,using the data recorded by the seismic network founded by a project under the National Science and Technology Pillar Program from April 2009 to April 2010.We found that most of polarization directions at seismic stations are consistent with the direction of the overall regional stress field,but local structures and faults may con...     

Discovery of the Natural Deformation Vestige of Gaixia Remains,Guzhen County,Anhui Province,China and Its Implications

Recognition of natural deformation during the excavation of ancient remains and tombs is important for tracing or enriching historic and prehistoric deformation records. Recently, the earthquake agencies,in cooperation with the cultural relics and archaeological institutions, conducted a special excavation investigation to the Gaixia remains archaeological scene in Guzhen,Anhui Province. Faults and fissures were discovered there, which,as demonstrated by the preliminary study,are the traces of two stratum d...     

The Influence of Surface Building's Relative Position on the Seismic Response of Subway Structures

By using the finite element method and viscoelastic artificial boundary,a soil-structure interaction system is established to simulate the influence of surface buildings on the seismic response of subway structures.The conditions of different relative positions between ground building and subway structure are analyzed.The results indicate that when considering the existence of surface buildings,the relative story displacements and internal forces of subway structures are changed greatly.Further the influence of surface buildings on subway structure changes as the distance increases.