西吉县西南山区典型黄土地震滑坡高密度电法物探解译分析

本文运用高密度电法对宁夏西吉县西南山区典型的黄土地震滑坡进行了探测,并结合钻探资料进行验证分析,目的是查明滑坡区域的地层结构、黄土厚度、基岩埋深、富水地段以及空间展布等特征.结果表明:电阻率参数能够很好的反应研究区的地层分布特征,表层疏松干燥的黄土为高阻反映,随着埋深增加,含水量较大的黄土呈现出低阻反映,在黄土与泥岩接触带饱水区呈现低阻反映;滥泥河流域典型的黄土梁斜坡具有阳坡黄土沉积薄、富水层薄、基岩埋深浅的特征,而在阴坡则表现出黄土沉积厚、富水层厚、基岩埋深大的特征.探测结果可有效的应用于黄土地震滑坡的勘察,为进一步开展黄土地震滑坡的成因机理和防治研究提供参考数据.     

北京平原西北部地壳浅部结构和隐伏活动断裂——由地震反射剖面揭示

已有地质和地球物理研究结果表明,北京平原区存在有多条第四纪隐伏活动断裂和隐伏盆地.为了研究该区的地壳浅部结构、断裂的空间展布、断裂活动性以及深浅构造关系,2006年,在北京平原的西北部地区完成了1条60次覆盖的中深层地震反射剖面和跨断裂的浅层地震反射剖面.结果表明,沿剖面结晶基底埋深约为3～6 km在结晶基底以上,地震反射剖面揭示了一套连续性较好的强反射震相,应是新生代、中生代和古生代的沉积岩系;在结晶基底之下,为一系列横向连续性较差、能量较弱的短小反射事件,可能代表了变质程度较高的结晶变质岩系或不成层的其他岩体.中深层和浅层地震剖面揭示的断裂具有上下一致的对应关系和明显的第四纪活动,对本区地堑-地垒状盆岭构造和新生代地层厚度具有重要的控制作用.本项研究不仅可进一步提高对北京地区新构造活动的认识,而且研究中所采用的方法技术对其他地区的深浅构造探测研究也有借鉴意义     

关于黄海深部构造的地球物理认识

利用黄海海区重磁观测数据,以最新的地震层析成像和浅层反射地震探测结果作为约束,并利用小波分解、纹理特征图像处理等手段,对研究区进行了地球物理场特征分析、岩石物性总结、断裂信息提取和磁性基底埋深反演计算,同时对南黄海海域三条剖面进行了广义逆重磁数据拟合反演和地震P波速度成像.根据地球物理数据的各种处理结果,提出在南黄海西部存在一条串珠状地球物理线性构造带,并将这条NNW向断续延伸的构造带称之为南黄海西缘断裂带.该断裂带延伸长,断裂两侧前新生代地层差异较大,有可能是造成陆区和南黄海南部盆地区前新生代油气远景差异的原因之一.文中得到南黄海磁性基底埋藏分布具有“中间浅四周深”的分布特征,与地震层析成像结果相吻合.磁性基底的局部起伏和局部构造的边界断层共同控制了前新生代残留盆地的格架和残余厚度分布,反映出“区域控制局部,深层约束浅层”的规律.     

Test Of High-Resolution Seismic Reflection And Other Geophysical Techniques On The Boup Landslide In The Swiss Alps

Complementary geophysical surveys on large landslides help revealgeologic structures and processes, and thus can help devise mitigation strategies. The combined interpretation of these methods enhance the result of each data set interpretation and makes it possible to derive a geological model of the landslide.We chose a test site on the Boup landslide (Wallis, western SwissAlps) to test high-resolution seismic reflection surveyscombined with ground penetratingradar (GPR), electromagnetic (EM) and electrokinetic spontaneous potential (SP) measurements.The results of the high-resolution seismic surveys suggest thatthe sliding is within a gypsum layer at 50 m depth and not as previously believed along a deeper (70 m) gypsum-shale boundary, also mapped seismically. Inversion of electromagnetic profiles (EM-34) with constraints from seismic data provided a model cross-section of conductivity values of the landslide (20–25 mS/m) and of the surrounding stable ground (10–15 mS/m), and it helped outline their boundary at depth.The accurate surface location of the landslide limit could be detected withelectromagnetic measurements of shallower depths of investigation (EM-31). Positive PS anomalies revealed an upward flow of mineralised water interpreted to follow the lateral boundary of the Boup landslide on its east side. Limited success was obtained withGPR profiling. This method can be hampered by conductive shallow layers, and itssuccessful application on landslides is expected to be strongly site dependant.     

浅层结构不确定性对广角地震走时正演模拟结果的影响——以西沙地块OBS2011-1测线为例

海洋地球物理勘探中常使用多道地震数据建立浅部地层模型,结合海底地震仪广角地震数据进行射线追踪和走时反演求取地层速度特征.受采集环境和成本限制,部分海底地震仪测线缺少同步采集的多道地震数据,建立的初始模型其浅层结构有较大不确定性,可能会对正演模拟结果造成严重影响.本研究针对海底地震仪广角地震走时模拟中浅部结构的不确定性因素,使用RayInvr软件构建了理论模型和走时数据体,分析讨论了初始模型沉积层厚度与速度变化对正演模拟结果的影响.之后进行实测数据处理,在MCS2019-3测线数据的约束下建立初始模型,对OBS2011-1测线震相重新进行了走时拟合,将得到的模型结果与先前结果进行对比,得到以下结论：沉积层厚度及速度不确定性对走时模拟结果的浅部结构影响较大,深部结构影响较小;使用错误的速度与基底深度组合来拟合沉积层反射震相PsP,会使台站下方的地壳和地幔折射震相Pg和Pn,以及莫霍面反射震相PmP都出现走时小起伏,走时提前对应沉积层速度与厚度偏大,走时延后对应沉积层速度与厚度偏小;PsP震相缺失时,不同的速度-深度组合都可以很好地拟合震相,但会增加结果的不确定性.

     

Investigation of a landslide in the new site of Badong County by integrated geophysical survey

An integrated geophysical survey which combines vertical seismic profile method, shallow reflection seismic method, electric sounding, soil temperature measurement and radioactive gas measurement was used to investigate Zhaoshuling landslide in the new site of Badong County and to assess the stability of the landslide. By rational use of these methods together with borehole geological profile and other geological information, the spatial distribution of the landslide body, the formations and structures within and without the landslide body were determined and the stability of the landslide was also assessed, thus making great contribution to the successful and rational investigation and assessment of the landslide.     

Application of 2D magnetotelluric methods in a geological complex area, Xinjiang, China

Magnetotelluric (MT) data along two profiles were collected in Tulargen Cu-Ni mining area, Xinjiang, China. The MT profiles, crossing the known ore-bearing magmatic body, are interpreted to have further understanding of the ore-bearing magmatic bodies' stretch and shape in depth, and to evaluate the prospect in the mining area. The values of phase sensitivity skewness indicate a contaminated two-dimensional (2D) structure (there exist local three-dimensional (3D) structures at shallow level) over 3D structures. G-B decomposition of the impedance tensors indicates the dominant geoelectrical strike in survey area is in East-West direction. To obtain reliable electrical structures, four different 2D inversion codes as REBOCC, NLCG, OCCAM, and ABIC are adopted, inversions of a synthetic 3D model using these codes indicate TM data are more suitable to invert the electrical structures along the profiles in Tulargen Cu-Ni mining area, while TE and TE + TM inversions can be used to verify the transverse variation of electrical structures at shallow level. The 2D electrical structures show high-resistivity basement covered by relatively low-resistivity strata in the mining area, the conductive anomalies are imbedded in the upper covers. The known ore-bearing magmatic body is coincided with the positions of two conductive anomalies in both profiles at shallow level; its extension at depth is deduced according to the shapes of the anomalies. Other conductive anomalies, isolated and existing only at limited depth as the known ore-bearing magmatic body, are presumed of good prospect.     

技术应用综合物探方法在张家口某工程场地地震安全性评价中的应用研究

结合地质和遥感图像解译资料,以物探方法查找活断层是行之有效的方法。针对单一的物探方法在反演解释中具有多解性的弊端,本文提出以高密度电阻率法为主,浅层地震反射波法为辅的综合物探勘察组合模式。经实际钻探证明,这种综合物探模式对隐伏活断层的勘察是完全可行的,并具有较强的实用推广性。     

综合地球物理方法在山前隐伏断裂探测中的应用——以巍山—长山南坡断裂为例

针对探测山前隐伏断裂复杂困难的特点,以巍山—长山南坡断裂为例,采用浅层地震勘探和高密度电法勘探等地球物理方法并结合钻孔联合地质剖面资料,对巍山—长山南坡断裂的隐伏段的准确位置和活动性进行研究,确定断层的准确位置和产状等。研究结果表明,巍山—长山南坡断裂在唐山市区的隐伏段为S倾的正断层,倾角约78°,断距约3 m,上断点埋深约19 m;该断裂在市区的隐伏段为中更新世断裂,晚更新世以来不活动。     

Landslide activation behaviour illuminated by electrical resistance monitoring

A common factor in landslide activation (or reactivation) is subsurface moisture and associated pore pressure variations linked to rainfall. Monitoring of these subsurface hydrogeological processes is necessary to improve our understanding of water‐induced landslide activation. Geophysical approaches, electrical methods in particular, are increasingly being applied to landslide monitoring because they provide non‐invasive spatial information in heterogeneous subsurface environments that can be difficult to characterise using surface observations or intrusive sampling alone. Electrical techniques are sensitive to changing subsurface moisture conditions, and have proven to be a useful tool for investigating the hydrogeology of natural and engineered slopes. The objectives of this investigation were to further develop electrical resistance monitoring for slope stability assessment, and to validate the approach at an intermittently‐active UK landslide system to advance the understanding of complex landslide activation mechanisms. A long‐term transfer resistance dataset was collected from a grid of electrodes to allow spatial monitoring of the landslide. These data were interpreted using a synthesis of rainfall, temperature, GPS and piezometric records. The resistance data were corrected for seasonal temperature variations and electrode movements were monitored, as these processes were shown to mask moisture related changes. Results reveal that resistance monitoring is sensitive to soil moisture accumulation, including changes in piezometric levels, and can be used to study the principal activation mechanism of slow‐moving shallow earthflows. Spatial monitoring using resistance maps was shown to be particularly valuable as it revealed the evolution of subsurface moisture distribution, in the lead up to landslide activation. Key benefits of this approach are that it provides a simple, rapid and non‐invasive means of spatially monitoring subsurface moisture dynamics linked to landslide activation at high‐temporal resolution. Crucially, it provides a means of monitoring subsurface hydraulic changes in the build‐up to slope failure, thereby contributing to early warning of landslide events. Copyright © 2018 John Wiley & Sons, Ltd.     

Subsurface electrical imaging of anisotropic formations affected by a slow active reverse fault, Provence, France

In seismic hazard assessment studies, near-surface geophysical prospecting is increasingly used to help in identifying active faults and to constrain seismic deformation parameters (fault offset, recurrence…). In the current study, electrical tomography was used (1) to locate the Trévaresse slow reverse fault (Provence, SE France), the source of the most important seismic event recorded in the 20th century in France and (2) to test electrical tomography's ability to detect faults and tectonic deformation in a complex geological environment. Our study is supported by a detailed geologic and geomorphic field study. In the investigated area, where the geology is made of a succession of folded marl and limestone layers, electrical images are strongly influenced by electrical macro-anisotropy which plays a critical role in this survey, depending on the investigation scale. When resolution (i.e. the smallest target that can be resolved) is larger than the layer thickness (at depth and/or for large electrode spacing), inversion is unable to retrieve the real structure. To successfully interpret these electrical images, in terms of tectonically induced dip variations, we constrain field data interpretation by comparing measured and inverted electrical data with synthetic modelling results and geological data. The synthetic models were hypothetical coarse geological structures determined on the basis of geological/geomorphologic information (e.g. outcropping layers). For shallow depths, when the resolution is smaller or equal to the anisotropy scale, an electrical tomogram yields straightforward interpretation of the subsurface structure. Coupled with numerical modelling, electrical results successfully helped in positioning a trench for fault characterization.     

Structural deformation and sedimentation in an active Caldera, Rabaul, Papua New Guinea

Recent seismic and tectonic activity in Rabaul Caldera, Papua New Guinea, suggests that magma is accumulating at a shallow depth beneath this partially submerged structure and that a new volcano may be developing. Changes in onshore elevation since 1971 (as much as 2 m on south Matupit Island) indicate that rapid and large-scale uplifts have occurred on the seafloor near the center of the caldera. The frequency of seismic events within the caldera has also increased during this period. Earthquake locations define an elliptical ring surrounding the center of this uplift within the caldera.A marine geophysical survey in 1982 by the U.S. Geological Survey's R/V “S.P. Lee” in Rabaul Caldera shows the development of a bulge in the seafloor near the center of the caldera. High-resolution seismic reflection profiles show that this bulge consists of two domal uplifts bounded and separated by two major north-south-trending fault zones. Deformed sediments overlie these zones; a prominent slump flanks the area of the bulge.Five major acoustic units were identified in the seismic reflection profiles: an acoustic basement and four sedimentary units consisting of irregularly layered, cross-layered, contorted, and well-layered sequences. The acoustic basement is probably composed of crystalline volcanic rocks, and the layered acoustic units are probably sediments, primarily ash deposited in different environments. The cross-layered, irregularly layered, and contorted units appear to have been deposited in a dynamic environment subjected to strong currents, seismicity, and/or mass wasting, while the well-layered units were deposited in a low-energy environment. Locally, well-layered sequences interfinger with the other sedimentary units, indicating a transitional environment that alternated between high-energy and low-energy depositional processes.A submarine channel cuts most of the acoustic units and appears to be the conduit for sediment transport out of the caldera; it occupies an older buried channel north of the caldera that is presently being exhumed. In the south, active erosion of well-layered sediments is taking place. What are believed to be several young volcanic cones also disrupt the depositional layers.We conclude that the bulge in the seafloor and the associated fault zones are a result of emplacement of magma at a shallow depth. Contorted sediment and slumps adjacent to the bulge are probably the result of uplift and seismic activity. The pattern of seismicity appears to reflect increased magma pressure at depth beneath the caldera floor. This activity may eventually lead to an eruption.     

Temporal and spatial variation of infilling processes in a landslide scar in a steep mountainous region,Japan

The duration of the soil‐depth recovery needed for reoccurrence of shallow colluvial landslides at a given site in humid regions is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the rate of change in soil depth in landslide scars is therefore necessary to evaluate return intervals of landslides. Spatial variation in sediment transport at the Kumanodaira landslide scar in central Japan was investigated by field observations. Spatial distribution of the rate of change in soil depth was estimated using sediment transport data and geographic information system (GIS) analysis. Observations revealed that the timing of sediment transport differed for shallow and deep soil layers. Near‐surface sediment transport (mostly dry ravel and some shallow soil creep at depths ≤0·05 m) measured in sediment traps was active in winter and early spring and was affected by freezing–thawing; soil creep of subsoil (i.e. >0·05 m), monitored by strain probes, was active in summer and autumn when precipitation was abundant. Near‐surface sediment flux was estimated by a power law function of slope gradient. Deeper soil creep was more affected by relative location to the landslide scar, which influences soil depth, than by slope gradient. Our study indicated that the rate of soil‐depth recovery is high just below the head scarp of the landslide. Abrupt changes in the longitudinal slope topography immediately above, within and just below the head scarp became smoother with time due to degradation proximate to the landslide head scarp and flanks, as well as aggradation just below the head scarp. Copyright © 2014 John Wiley & Sons, Ltd.     

北京西北地区壳幔结构的非均匀性特征与地震活动

利用在北京西北部地区穿过张家口——渤海地震带北西段地震测深剖面进行了综合解释和研究, 揭示了延庆——怀来、 张北——尚义地震活动区异常的深浅地壳结构特征. 结果表明： 研究区基底结构具有明显的起伏变化, 不同的地质构造单元基底埋深存在着较大差异. 基底埋深在局部地段呈现出的急剧变化可视其为基底断裂存在的一种标志, 基底断裂与地壳深断裂的存在为岩浆的上溢提供了条件, 从而导致了地壳结构强烈的非均匀性. 延怀地区壳内复杂反射波组序列和局部强弱不连续反射带现象的出现, 表明该地区地壳结构发生了强烈的挤压变形, 从而构成了该地区复杂的地壳结构, 为该地区地震的发生提供了动力来源; 张北——尚义地区壳内不同深度范围低速异常体和局部的C1界面的存在, 可以认为是岩浆多期活动的产物, 在区域构造活动的作用下脆性的上地壳内, 当局部应力积聚到一定的程度从而引发了地震的发生.     

The heterogeneous characteristics of crust-mantle structures and the seismic activities in the northwest Beijing region

Introduction Zhangjiakou-Bohai seismic zone is a major active seismic zone that passes through the north-ern part of North China. Zhangjiakou-Beijing area, the northwest part of North China, is located at the intersection position of Yanshan, Taihangshan uplift, and Shanxi down-faulted zone, and the geological structures in this area are extremely complicated. Many researchers in the geoscience circle always pay close attention to this region because Yanqing-Huailai region is located in th…     

Joint Audio-Magnetotelluric and Passive Seismic Imaging of the Cerdanya Basin

The structure of Cerdanya Basin (north-east of Iberian Peninsula) is partly known from geological cross sections, geological maps and vintage geophysical data. However, these data do not have the necessary resolution to characterize some parts of Cerdanya Basin such as the thickness of soft soil, geometry of bedrock or geometry of geological units and associated faults. For all these reasons, the main objective of this work is to improve this deficiency carrying out a detailed study in this Neogene basin applying jointly the combination of passive seismic methods (H/V spectral ratio and seismic array) and electromagnetic methods (audio-magnetotelluric and magnetotelluric method). The passive seismic techniques provide valuable information of geometry of basement along the profile. The maximum depth is located near Alp village with a bedrock depth of 500 m. The bedrock is located in surface at both sites of profile. The Neogene sediments present a shear-wave velocity between 400 and 1000 m/s, and the bedrock basement presents a shear-wave velocity values between 1700 and 2200 m/s. These results are used as a priori information to create a 2D resistivity initial model which constraints the inversion process of electromagnetic data. We have obtained a 2D resistivity model which is characterized by (1) a heterogeneous conductivity zone (<40 Ohm m) that corresponds to shallow part of the model up to 500 m depth in the centre of the profile. These values have been associated with Quaternary and Neogene sediments formed by silts, clays, conglomerates, sandstones and gravels, and (2) a deeper resistive zone (1000–3000 Ohm m) interpreted as Palaeozoic basement (sandstones, limestones and slates at NW and conglomerates and microconglomerates at SE). The resistive zone is truncated by a discontinuity at the south-east of the profile which is interpreted as the Alp-La Tet Fault. This discontinuity is represented by a more conductive zone (600 Ohm m approx.) and is explained as a combination of fractured rock and a fluid network. The result highlights that the support between different geophysical methods is essential in producing geophysical meaningful models.     

The Best Combination Methods and Applied Research of Seismic Prospecting for Active Faults in Urban Areas

This paper introduces briefly the basic principles of various seismic prospecting techniques and working methods according to nationwide practices of seismic prospecting of active faults beneath big cities in recent years.Furthermore,it analyzes the application range of different seismic prospecting methods,main achievements and solved problems,and discusses the best combination of seismic exploration methods for detecting crustal structures and locating the faults used in the present stage,that is,to trace faults which are at depths of hundred of meters underground using shallow seismic investigation,to detect the faults which are above basement(at a depth of kilometers) using high resolution refraction sounding,and the deep crustal faults using combined seismic prospecting methods of reflection seismic sounding and wide-angle reflection/refraction sounding,and furthermore,to use the 3-D deep seismic sounding method to obtain 3-D velocity structures beneath urban areas.Thus,we can get information about fault attitude and distribution at different depths and a complete image of faults from their shallow part to deep part using the combined seismic exploration method.Some application examples are presented in the article.     

四川省理县西山村滑坡运动变形过程中的微震研究

全球地震台站的增加及数据处理、建模和解释方面的进步为利用地震学研究滑坡区地下介质的动态变化提供了有利条件,使得利用滑坡地震信号研究滑坡特征逐渐成为滑坡监测中的重要手段之一。本文主要介绍了利用被动源地震学方法对滑坡信号进行识别分析和过程监测的技术和实际应用。通过案例研究表明,在合适的条件下,利用滑坡产生的地震信号可以经济又有效地监测滑坡过程,甚至能识别出滑坡灾害的前兆信号,为滑坡灾害预警提供技术支撑。未来若结合其它地球物理或遥感方法,建立多参数地球物理监测系统,将能大幅降低因滑坡灾害所导致的人员伤亡和经济损失。

     

The Argo Abyssal Plain

Eighteen geophysical transects were made in the Argo Abyssal Plain to study the magnetic anomalies, bathymetry and seismic structure. Magnetic anomalies were identified as being the Mesozoic anomalies M-10 to M-25, increasing in age from the Java Trench to the northwest continental shelf of Australia. A new bathymetric map shows that the Argo Abyssal Plain is bounded by the 5600-m contour and reaches a maximum depth of 5730 m against the inshore side of the Exmouth Plateau. Joey Rise was found to limit the Argo Abyssal Plain on the southwest. Continuous seismic profiles, sonobuoy data and seismic data from other cruises permit one to contour the depths to oceanic basement. Numerous diapir-like structures were observed, but their nature and origin is obscure.