Seismic reflection imaging of active faults and their tectonic behavior in the Northern Moroccan margin. Is the Nekor fault a pure strike-slip fault?

The study of 1000-km seismic reflection profiles, along the Northern Moroccan margin, allowed browsing new imaging in detail about the regional geological structures and their functioning. To achieve this goal, we elaborated a high-resolution depth model and a global tectonic sketch. The influence of recent tectonic activity is manifested by normal and strike-slip faults, trending mainly 70° N and 125° N. In this segment, the Nekor strike-slip fault seems to be connected to a secondary major fault system that changes direction from 30° N to 70° N, and changing behavior to left-lateral strike-slip fault with normal component. Analysis of local seismic activity recorded from 1990 to 2014 with moderate magnitudes activity shows alignments in clear superposition with the detected active faults in seismic reflection lines.     

Global-scale analysis of seismic activity prior to 2004 Sumatra-Andaman mega-earthquake

Following our experience in intermediate-term monitoring of seismicity before large earthquakes worldwide and in some regions we apply a similar approach to the analysis of seismicity on global scale several decades before the December 26, 2004 Sumatra–Andaman mega-earthquake. The Earth lithosphere is being considered as a single whole, representing the ultimate level of the complex Earth's hierarchy. The study brings up the following questions: Are there any anomalies of the global seismicity behaviour observed in advance of the mega-earthquake? Do these anomalies correspond to the global scale seismic patterns similar to those detected on the regional scale before great, major, and strong events? In other words, does the Earth lithosphere considered as a single whole show up an approach of the mega-earthquake in the way typical for events on the smaller levels of hierarchy? The results of our investigation favour the positive answer to the questions. Specifically we found that during the decade before the Sumatra–Andaman mega-earthquake the Earth lithosphere reveals, at least in intermediate-term scale, classical symptoms of instability, which can be depicted by known precursory seismic patterns. These are: (i) transformation of frequency–magnitude distribution, (ii) change in the rate of seismic activity, and (iii) depth redistribution of activity. Moreover changes of dependencies between magnitudes of different types are detected at the same time. The observed global scale patterns of collective behaviour of seismicity may indicate the state of criticality of the Earth lithosphere before the Sumatra–Andaman mega-earthquake.     

对后续震相的认识促进了地震层析成像的发展

与地震初动震相相比,后续震相包含有更为丰富的地球内部信息,因此逐渐地在地震层析成像研究中得到重视。文中以赵大鹏等最近的层析成像研究为例,介绍了通过增加后续震相到时信息得到的新的层析成像研究成果,包括通过使用反射波,仅用两个地震台站就可以进行地壳成像研究;深度震相到时的增加,拓宽了区域成像范围,成功实现了台网外部层析成像;随着国际地震中心(ISC)提供的更丰富的各种后续震相到时,对后续震相的认识和使用促进了全球体波走时成像的发展和对地球深部结构及动力学过程的认识。另一方面,地震学相关领域的进步,使得更多的后续震相能够被拾取并被应用到成像研究中,这将大大提高对地震波形信息的挖掘,提高对研究地区下三维结构的认识,极大地促进地震层析成像学的发展。     

断块构造|活动断块构造与地震活动

张文佑院士是我国最杰出的构造地质学家和大地构造学家,他提出和倡导的地质构造力学分析和历史分析相结合及断块构造理论符合当代构造地质和构造运动研究的新方向。断块构造是地球构造运动最基本的型式,板块构造是全球范围内的岩石圈构造,是最高一级的岩石圈断块构造。活动断块是现今构造运动最基本的型式,它既控制主要活动构造带和地震活动带的分布,也控制不同地区地震活动特征的差异。断块边界构造带是在构造变形和运动场中的不连续变形带,应力在此释放,应变在此局部化,位移在此发生,其差异活动最为强烈,因此,断块边界构造带是强震发生带,其活动性质会控制震源断层的特性。大地震孕育和发生在边界活动构造带的某些特殊部位,对其成核的构造和物理过程尚需深入进行研究。要特别注意断块整体性活动对地震活动的控制作用,断块的这种整体性活动与一定时期内地震活动主体地区分布有密切关系,所以,在活动构造研究中,要把断块的整体性活动与活动构造带的个体活动结合起来。     

奇村地震水汞动态图象分析

本文通过对山西省奇村地热异常地区地震水汞动态图象的特征分析，认为该水汞测量值受干扰小，其水汞值变化可反映地下深部信息。监测井中水汞值变化受区域地震活动地应力和应变状况及地质构造条件影响。监测井的汞动态可反应地区水汞值变化趋势。     

New Data on Seismotectonics of the Laptev Sea from Observations by Ocean Bottom Seismographs

Doklady Earth Sciences - The results of new local seismic observations in the Laptev Sea obtained using ocean bottom seismographs were compared with actual data from global and regional earthquake...     

Seismic Activity and Fuzzy Comprehensive Evaluation of Crustal Stability in the Beijing Region

This paper discusses the seismic activity in Beijing M unicipality and its adjacent areas (which are referred to as the Beijing region in the paper). By using fuzzy mathematics, the factors controlling regional crustal stability are transformed into fuzzy information and then a model of fuzzy diagnosis is established. A fuzzy comprehensive evaluation of regional crustal stability in the Beijing region is made according to the seismic and geological conditions of the region.     

鄂西清江两水利枢纽坝址区地震危险性对比分析

本文在研究清江流域及外围区域地震地质条件和地震分布规律的基础上，划分了１、２个潜在震源区，并确定其相应的地震活动性参数，同时探讨区域地震烈度衰减规律及各潜在震源区对隔河岩和水布垭两坝址的影响烈度、进而复泊松模型，评价两坝址的地震危险性，获得了丙坝址不同期限内的地面峰值加速度及其相应的超越概率。根据对比分析，水布垭坝址的地震危险性比隔洒岩坝址小。     

2019年四川长宁MS6.0地震的地质构造成因——区域性构造节理贯通、破裂结果

根据野外地质调查结果并结合区域地质资料, 对2019年长宁MS6.0地震震区的地质背景和新构造运动特征进行分析后, 讨论了此次地震的发震构造并给出该地区孕震模型。基于区域地质与地震资料, 结合地表调查结果发现, 该区的新构造运动具有间歇性整体弱隆升、断裂晚第四纪活动不明显以及地震活动相对微弱等特征。此次强震的仪器震中位于长宁双河大背斜的西段, 该背斜经历了古老的NE向挤压应力场和顺时针旋转应力场的双重叠加构造作用。在大背斜的核部和翼部普遍发育了两组NW向节理和一组NE向节理, 并显示出区域性分布特征, 构成了具一定规模的构造破碎带(软弱带)。地震记录显示, 此次强震的地震序列呈现出明显的NW向线性条带, 震源机制解主要指示了NEE—NE向水平挤压应力作用的结果。结合地表构造特征可进一步推断, 长宁地震的震源破裂型式是以沿NW向破裂面发生以逆冲为主兼具左旋走滑分量的破裂过程为特征。综合分析认为, 2019年长宁MS6.0地震可能是双河背斜中的赋存超压环境叠加NE向古构造应力场和旋转应力场作用, 导致区域性NW向纵向节理发生构造强化、贯通, 并进一步破裂的结果。     

A Study of Spatial Distribution of Induced Seismicity in the Upper Silesian Coal Basin

The Upper Silesian Coal Basin (USCB) is a region where high seismic activity is observed. Most of these seismic events have a local magnitude not exceeding 2.3. Their location and type of focal mechanism suggest that they are connected with new discontinuities in the rock mass caused by mining activity. Shocks with higher magnitude are also observed but their frequency is much lower. The strong events have a different focal mechanism than the low energetic events. The spatial distribution of shock epicentres is not uniform in the USCB area and shows the fractal character of seismic phenomena. Despite extensive mining activity throughout the area, the epicentres of strong events are concentrated in four regions belonging to different geological units. The temporal variability of epicentre co-ordinates and the general decrease of seismic activity points to the migration of seismicity across the investigated area. Analysing the spatial and temporal distributions of the strongest shocks, one can suppose this area to be critically self-organised. These facts suggest that induced seismicity in the USCB is triggered by a nonlinear dynamic process, having regional character and connected with recent tectonic activity.     

青藏高原巴塘断裂带地震滑坡危险性预测研究

全新世以来青藏高原东部巴塘断裂带活动强烈,地形地貌和地质构造复杂,历史地震频发,并诱发大量滑坡灾害。基于巴塘断裂带地震滑坡长期防控的需要,在分析区域地质灾害成灾背景和发育分布特征的基础上,采用Newmark模型完成了巴塘断裂带50年超越概率10%的潜在地震滑坡危险性预测评价,并完成地震滑坡危险性区划。结果表明:巴塘断裂带及其临近的金沙江断裂带区域、金沙江及其支流沿岸具有较高的潜在地震滑坡危险性,地震滑坡危险区具有沿断裂带和大江大河等峡谷区分布的总体趋势,受活动断裂和地形地貌影响显著;距离断层越近、坡度越大的斜坡,地震滑坡危险性越高;规划建设中的川藏铁路经巴塘县德达乡、白玉县沙马乡,向西北延伸,跨越金沙江,可以穿越较少的地震滑坡危险区,金沙江水电工程规划建设需加强潜在地震滑坡危害研判及防控。巴塘断裂带潜在地震滑坡危险性评价结果可为区域城镇开发和重大工程规划建设的地震滑坡长期防控提供科学参考。     

The Seismic Project of the National Tsunami Hazard Mitigation Program

In 1997, the Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and the five western States of Alaska, California, Hawaii, Oregon, and Washington joined in a partnership called the National Tsunami Hazard Mitigation Program (NTHMP) to enhance the quality and quantity of seismic data provided to the NOAA tsunami warning centers in Alaska and Hawaii. The NTHMP funded a seismic project that now provides the warning centers with real-time seismic data over dedicated communication links and the Internet from regional seismic networks monitoring earthquakes in the five western states, the U.S. National Seismic Network in Colorado, and from domestic and global seismic stations operated by other agencies. The goal of the project is to reduce the time needed to issue a tsunami warning by providing the warning centers with high-dynamic range, broadband waveforms in near real time. An additional goal is to reduce the likelihood of issuing false tsunami warnings by rapidly providing to the warning centers parametric information on earthquakes that could indicate their tsunamigenic potential, such as hypocenters, magnitudes, moment tensors, and shake distribution maps. New or upgraded field instrumentation was installed over a 5-year period at 53 seismic stations in the five western states. Data from these instruments has been integrated into the seismic network utilizing Earthworm software. This network has significantly reduced the time needed to respond to teleseismic and regional earthquakes. Notably, the West Coast/Alaska Tsunami Warning Center responded to the 28 February 2001 Mw 6.8 Nisqually earthquake beneath Olympia, Washington within 2 minutes compared to an average response time of over 10 minutes for the previous 18 years.     

Finite element models to represent seismic activity of the Indian plate

Quantification of seismic activity is one of the most challenging problems faced by earthquake engineers in probabilistic seismic hazard analysis. Currently, this problem has been attempted using empirical approaches which are based on the regional earthquake recurrence relations from the available earthquake catalogue. However, at a specified site of engineering interest, these empirical models are associated with large number of uncertainties due to lack of sufficient data. Due to these uncertainties, engineers need to develop mechanistic models to quantify seismic activity. A wide range of techniques for modeling continental plates provides useful insights on the mechanics of plates and their seismic activity. Among the different continental plates, the Indian plate experiences diffused seismicity. In India, although Himalaya is regarded as a plate boundary and active region, the seismicity database indicates that there are other regions in the Indian shield reporting sporadic seismic activity. It is expected that mechanistic models of Indian plate, based on finite element method, simulate stress fields that quantify the seismic potential of active regions in India. This article explores the development of a finite element model for Indian plate by observing the simulated stress field for various boundary conditions, geological and rheological conditions. The study observes that the magnitude and direction of stresses in the plate is sensitive to these conditions. The numerical analysis of the models shows that the simulated stress field represents the active seismic zones in India.     

Critical parameter investigation for earthquake hazard assessment in the Sannio-Matese area of Southern Italy

Probabilistic methods have been applied for the assessment of seismic hazard in a selected region of Southern Italy (Sannio-Matese). This method is mainly suitable for engineering and planning purposes and was first introduced in 1968 by Cornell and efficiently codified into a FORTRAN computer program by McGuire. Special attention is paid in this paper to the specific input parameters, i.e. completeness of data catalogues, time variability of seismic activity, different forms of frequency distributions, and regional attenuation characteristics.     

A Preliminary Study on the Soft–Sediment Deformation Structures in the Late Quaternary Lacustrine Sediments at Tashkorgan, Northeastern Pamir, China

This study identified soft–sediment deformation structures(SSDS) of seismic origin from lacustrine sediments in the late Quaternary paleo–dammed lake at Tashkorgan, northeastern Pamir. The observed deformation structures include sand dykes, liquefied diapir and convolute structures, gravity induced SSDS, and thixotropic pillar and tabular structures. We conducted a preliminary study on the morphology, formation and trigger mechanisms of pillar and tabular structures formed by liquefaction of underlying coarse sand and thixotropy of the upper silty clay. The regional tectonic setting and distribution of lacustrine strata indicate that the most probable trigger for the SSDS in lacustrine sediments was seismic activity, with an approximate earthquake magnitude of M6.0; the potential seismogenic fault is the southern part of the Kongur normal fault extensional system. AMS 14 C dating results indicate that the SSDS were formed by seismic events occurring between 26050±100 yr BP and 22710±80 yr BP, implying intense fault activity in this region during the late Pleistocene. This study provides new evidence for understanding tectonic activity and regional geodynamics in western China.     

应对全球变化的中国地质灾害综合减灾战略研究

为了探索极端气候事件引发重大地质灾害的综合减灾防灾战略,提高主动减灾防灾的科技能力与管理水平,积极应对全球变化条件下中国地质灾害防治面临的挑战,本文在"全球灾变事件与重大地质灾害减灾战略研究会"与会专家汇报和讨论的基础上,结合近年来国内重大地质灾害事件,从新构造与地震活动,气候变化,人口与城镇化进程三个方面开展分析,试图探讨我国2010年重大地质灾害多发,群发的原因,并对我国地质灾害今后面临的总体形势做出宏观研判。综合分析认为:①近年来全球构造运动和地震活动进入一个新的相对活跃期,我国处于欧亚地震带和环太平洋地震带的交汇区,是现今构造地震活动强烈响应区,尤其是印度板块的强烈活动,使青藏高原周缘地区的地震活动频繁,断裂活动增强,内外动力耦合作用下的地质灾害频发是总体趋势;②全球气候变化引起的极端气候异常条件使地质灾害的成灾模式趋于多样化和复杂化,由于中国大陆是全球最大大陆性气候和海洋性气候交汇地带,也是地貌高差气候变化最大的地区,特别是2010年长时间干旱,汛期集中的高强度、长持时的降雨、局部强暴雨导致大规模滑坡泥石流灾害,尤其是在青藏高原周缘等内动力作用强烈地区,导致地质灾害频发;③人口增长、城镇化进程及工程经济活动是地质灾害发生不可忽视的重要因素,城镇化建设和工程经济活动规模大,且逐步向生态地质环境相对脆弱的地区转移,城镇人口密度快速增加,特别是山区城镇自主防灾减灾意识薄弱,直接导致地质灾害伤亡和损失程度加重。为了应对全球变化条件下的中国地质灾害形势,提高我国地质灾害防灾科技能力与管理水平,从我国地质灾害防灾减灾的现状分析入手,充分借鉴国际自然灾害综合减灾与风险管理的成功经验与策略,从推进中国地质灾害风险管理的角度提出了7点综合减灾建议,以期起到抛砖引玉的作用,推动政府管理部门、专业技术人员参与地质灾害综合减灾的广泛交流与讨论,促进防灾减灾科技与策略在实践中应用,为应对全球变化的中国地质灾害综合减灾集思广益。     

惠民凹陷东部区域性走滑断裂构造系统的发现和意义

惠民凹陷东部地区油气勘探程度相对较低,岩浆活动剧烈,深部地质构造复杂。为此,通过岩石物性特征的研究和引起重、磁异常的地质因素分析,将重、磁、震综合地球物理解释技术应用于解决盆地深层地质构造问题,确定了重力和磁力异常在研究区的分布特征,结合地震资料解释发现了近SN向延伸的滨县-高青-博山区域性右旋走滑断裂构造系统和NNW向延伸的白桥-文祖区域性左旋走滑断裂构造系统。这两条区域性走滑断裂构造系统对本区中新生代构造格局具有重要控制作用,并控制了研究区内线性分布的火山活动和幔源CO2气的分布。     

从断裂构造形迹分析汶川地震构造应力场特征

通过对四川汶川地震野外断裂构造形迹的实地考察的部分资料,结合汶川地震震源机制解等,分析了该区域构造应力场特征,对研究该区域地震活动有一定的指导意义.     

上海罗店-周浦隐伏断裂第四纪活动性综合探测与研究

罗店-周浦断裂是纵贯上海市中心城区重要的北西向隐伏活动断裂,其第四纪活动性对城市地质安全至关重要.通过高精度重力勘探、浅层地震勘探及可控源大地音频电磁测深勘探等地球物理方法,结合钻探联井剖面及光释光年代学测定,对罗店-周浦断裂在区域内的展布特征及第四纪活动性进行了探测与研究.结果表明,该断裂在上海市南部区域仍具有较好的...     

强震区岩体动力破坏机制研究

黄河黑山峡大柳树坝址区存在大范围的岩体破坏现象。在详细调查区域地质背景条件及区域地震动力作用基础之上,提出了地震动力作用与岩体破坏现象的内在联系,并通过动力模拟试验分析、证明了岩体破坏现象与历史上该地区发生的强烈地震有着密切关系。因此,在目前的工程地质条件下,一旦发生强度较大的地震活动,坝址区所遭受的破坏程度会更大,对拟建的水利工程设施将产生严重威胁。