大井坡航空地球物理试验场典型剖面综合地球物理解释

全面采集并分析我国首个航空地球物理综合实验场(大井坡实验场)的地质和地球物理特征,综合地质、地形、遥感、磁、重力和电磁等资料,在试验场内选取3条典型剖面,以电阻率测深剖面为约束,采用多边形2.5D棱柱体模型组合法建立典型剖面地质-地球物理模型;对剖面进行重、磁联合正反演,并通过剖面与平面相互验证的方式,开展重、磁、电综合解释研究。通过研究,全面掌握了试验场内断裂及岩性构造的分布规律,试验场被中部近EW向和北部呈NEE向展布的两条断裂分割成南部褶皱区、中部断隆区和北部坳陷区3个区域,为试验场综合解释填图提供了依据和约束条件。     

Shallow seismic reflection profiles and geological structure in the Benton Hills, southeast Missouri

During late May and early June of 1993, we conducted two shallow, high-resolution seismic reflection surveys (Mini-Sosie method) across the southern escarpment of the Benton Hills segment of Crowleys Ridge. The reflection profiles imaged numerous post-late Cretaceous faults and folds. We believe these faults may represent a significant earthquake source zone.

The stratigraphy of the Benton Hills consists of a thin, less than about 130 m, sequence of mostly unconsolidated Cretaceous, Tertiary and Quaternary sediments which uncomfortably overlie a much thicker section of Paleozoic carbonate rocks. The survey did not resolve reflectors within the upper 75–100 ms of two-way travel time (about 60–100 m), which would include all of the Tertiary and Quaternary and most of the Cretaceous. However, the Paleozoic-Cretaceous unconformity (Pz) produced an excellent reflection, and locally a shallower reflector within the Cretaceous (K) was resolved. No coherent reflections below about 200 ms of two-way travel time were identified.

Numerous faults and folds, which clearly offset the Paleozoic-Cretaceous unconformity reflector, were imaged on both seismic reflection profiles. Many structures imaged by the reflection data are coincident with the surface mapped locations of faults within the Cretaceous and Tertiary succession. Two locations show important structures that are clearly complex fault zones. The English Hill fault zone, striking N30°–35°E, is present along Line 1 and is important because earlier workers indicated it has Pleistocene Loess faulted against Eocene sands. The Commerce fault zone striking N50°E, overlies a major regional basement geophysical lineament, and is present on both seismic lines at the southern margin of the escarpment.

The fault zones imaged by these surveys are 30 km from the area of intense microseismicity in the New Madrid seismic zone (NMSZ). If these are northeast and north-northeast oriented fault zones like those at Thebes Gap they are favorably oriented in the modern stress field to be reactivated as right-lateral strike slip faults. Currently, earthquake hazards assessments are most dependent upon historical seismicity, and there are little geological data available to evaluate the earthquake potential of fault zones outside of the NMSZ. We anticipate that future studies will provide evidence that seismicity has migrated between fault zones well beyond the middle Mississippi Valley. The potential earthquake hazards represented by faults outside the NMSZ may be significant.     

Depth of the base of the Jackson aquifer, based on geophysical exploration, southern Jackson Hole, Wyoming, USA

 A geophysical survey was conducted to determine the depth of the base of the water-table aquifer in the southern part of Jackson Hole, Wyoming, USA. Audio-magnetotellurics (AMT) measurements at 77 sites in the study area yielded electrical-resistivity logs of the subsurface, and these were used to infer lithologic changes with depth. A 100–600 ohm-m geoelectric layer, designated the Jackson aquifer, was used to represent surficial saturated, unconsolidated deposits of Quaternary age. The median depth of the base of the Jackson aquifer is estimated to be 200 ft (61 m), based on 62 sites that had sufficient resistivity data. AMT-measured values were kriged to predict the depth to the base of the aquifer throughout the southern part of Jackson Hole. Contour maps of the kriging predictions indicate that the depth of the base of the Jackson aquifer is shallow in the central part of the study area near the East and West Gros Ventre Buttes, deeper in the west near the Teton fault system, and shallow at the southern edge of Jackson Hole. Predicted, contoured depths range from 100 ft (30 m) in the south, near the confluences of Spring Creek and Flat Creek with the Snake River, to 700 ft (210 m) in the west, near the town of Wilson, Wyoming. Received, May 1997 · Revised, February 1998 · Accepted, April 1998     

The Portland Hills Fault: uncovering a hidden fault in Portland, Oregon using high-resolution geophysical methods

The Portland metropolitan area historically is the most seismically active region in Oregon. At least three potentially active faults are located in the immediate vicinity of downtown Portland, with the Portland Hills Fault (PHF) extending directly beneath downtown Portland. The faults are poorly understood, and the surface geologic record does not provide the information required to assess the seismic hazards associated with them. The limited geologic information stems from a surface topography that has not maintained a cumulative geologic record of faulting, in part, due to rapid erosion and deposition from late Pleistocene catastrophic flood events and a possible strike-slip component of the faults. We integrated multiple high-resolution geophysical techniques, including seismic reflection, ground penetrating radar (GPR), and magnetic methods, with regional geological and geophysical surveys to determine that the Portland Hills Fault is presently active with a zone of deformation that extends at least 400 m. The style of deformation is consistent with at least two major earthquakes in the last 12–15 ka, as confirmed by a sidehill excavation trench. High-resolution geophysical methods provide detailed images of the upper 100 m across the active fault zone. The geophysical images are critical to characterizing the structural style within the zone of deformation, and when integrated with a paleoseismic trench, can accurately record the seismic history of a region with little surface geologic exposure.     

Effects of structural faults on ground control in selected coal mines in southwest Virginia

Summary Two faults related to the Pine Mountain overthrust sheet near Buchanan County, Virginia, were investigated to determine their effect on ground control and to develop recognition criteria for prediction. Both faults are right lateral, strike-slip faults overprinted simultaneously with thrust faulting. Offsets of the coal seam due to thrust faulting average 6 ft with severe roof conditions (20 ft high roof falls) occurring through an average 30 ft wide zone of disturbance. Recognition criteria include characteristic overthrusting, coalbed swag, bedding plane slippage, and fault gouge. Ground control strategies include mine designs that minimize fault exposure.     

Coal mining along the Warfield Fault, Mingo County, West Virginia: a tale of ups and downs

Mine development along a 15-mile (24 km) section of the Warfield Fault in Mingo County, West Virginia has broadened the geological understanding of the fault and its related structures. The fault has been exposed in two new road cuts, one in the northeast-trending segment at Neely Branch and one in the eastern east-trending segment at the head of Marrowbone Creek. Both exposures show a well-defined normal fault with a 45° to 55° N dip, juxtaposing sandstone/shale packages from the roof and the floor of the Coalburg seam. The fault is associated with a thin gouge zone, some drag folding, and parallel jointing. Its trace tends to run parallel to the crest of the adjacent Warfield Anticline. Based on underground mine development and detailed core drilling, the vertical offset along the fault plane ranges from a maximum of 240 ft (73 m) in the central part of the area near the structural bend to less than 100 ft (30 m) in western and eastern directions. The fault is located along the relatively steeply dipping (locally in excess of 25%) southern limb of the Warfield Anticline, and appears related to a late phase of extension involving folded Pennsylvanian strata. On a regional scale, the lithological variations across the fault do not suggest any appreciable strike-slip component.Underground room and pillar mines in the Coalburg seam north and south of the fault have been greatly impacted by the Warfield structures. Due to the combined (and opposite) effects of the folding and faulting, the northern mines are located up to 400 ft (125 m) higher in elevation than the southern ones. Overland conveyor belts connect mining blocks separated by the fault. The practical mining limit along the steep slopes toward the fault is around 15%. Subsidiary normal faults with offsets in the 5- to 15-ft (1.5–4.5 m) range are fairly common and form major roof control and production hurdles. Overall, the Warfield structures pose an extra challenge to mine development in this part of the Appalachian Coalfields.     

综合物探方法在广西柳州隐伏断裂探测中的应用

据野外地震地质调查研究,柳州市柳北区存在多条隐伏断裂带,这些断裂带的具体位置尚未确定,这对柳北区的建设发展存在极大隐患。为此,在地质调查的基础上,本文采用高密度电法和地震映像综合方法来探测柳北区隐伏断裂带的具体位置,通过钻探验证和地质调查研究,确定了隐伏断裂带的具体位置,为柳州市柳北区的建设发展提供安全保障。     

脉状金矿定位预测的关键——主控矿因素分析

华北地台3个脉状金矿矿床(体)定位预测的实例说明,主控矿因素在矿床(体)定位预测过程中起到关键作用——"战略"指向作用。内蒙古赤峰热水金矿的主控矿因素为宽缓闪长玢岩脉,其上方约100~300 m范围内为工业矿脉集中产出的部位,控制了主要矿脉群和工业矿体的空间分布。山东招远界河金矿的主控矿因素为位于郭家岭花岗闪长岩岩体与玲珑花岗岩体外接触带附近的断裂交汇部位(构造结环)。山东平度旧店金矿的主控矿因素则为北西向硅化带,主要的含矿石英脉均分布于其两侧约2 km范围以内。确定主控矿因素是矿床定位预测最重要的任务之一,矿山资料二次开发、详尽的矿床地质研究以及物化探资料的综合利用是确定主控矿因素的主要手段。     

2-D seismic trenching of colluvial wedges and faults

Images of the depth and shape of colluvial wedges by 3-D travel time tomography can be valuable in estimating the past history of ancient earthquakes and assessing the earthquake hazard of a fault. Unfortunately, 3-D seismic surveys can be both costly and time consuming. In this paper, we report our first successful results of detecting the shapes and depths of colluvial wedges with 2-D travel time tomography. The locations of the colluvial wedges are along the Oquirrh fault and the Salt Lake City segment of the Wasatch fault. We also report that the tomogram from one of our 2-D surveys suggests the possibility of detecting multiple colluvial wedges at depth. Using both reflection and tomographic images at another site clearly reveals the presence of a known shallow fault and the contact between native soil and recent fill. Our results suggest the synergistic use of both seismic tomography and reflection imaging, we denote as seismic trenching, as a means of detecting shallow colluvial wedges and faults. Seismic trenching has the potential to significantly expand the lateral extent and depth of investigation of paleoseismology.     

The 1988 Tennant Creek,northern territory,earthquakes: A synthesis

Three large earthquakes with surface‐wave magnitudes 6.3–6.7 on 22 January 1988 were associated with 32 km of surface faulting on two main scarps 30 km southwest of Tennant Creek in the Northern Territory. These events provide an excellent opportunity to study the mechanics of midplate earthquakes because of the abundance of geological and geophysical data in the area, the proximity of the Warramunga seismic array and the ease of access to the fault zone. The 1988 earthquakes were located in the North Australian Craton in an area that had no history of moderate or large earthquakes before 1986. Additionally, no smaller earthquakes from the fault zone were identified at the Warramunga array, which is situated only 30 km from the nearest scarp, between the 1965 installation of the array and 1986. The main shocks were preceded by a swarm of moderatesized (magnitude 4–5) earthquakes in January 1987 and many smaller aftershocks throughout 1987. Careful relocation of all teleseismically recorded earthquakes from the fault zone shows that the 1987 activity was concentrated in an area only 6 km across in the gap between the two main fault scarps. The main shocks also nucleated in the centre of the fault zone near the 1987 activity. Field observations of scarp morphology indicate that the scarp is divided into three segments, each showing primarily reverse faulting. However, whereas the western and eastern segments show movement of the southern block over the northern, the central scarp segment shows the opposite, with the northern block thrust over the southern block.

Analysis of the first arrival times at Warramunga suggests that the three main shocks were associated with the western, central and eastern scarp segments, respectively. The locations of aftershocks determined using data from temporary seismograph arrays in the epicentral area define three inclined zones of activity that are interpreted as fault planes. In the western and eastern portions of the aftershock zone, these concentrations of activity dip to the south at 45° and 35°, respectively, but in the central section the aftershock zone dips to the north at 55°. Focal mechanisms derived from modelling broadband teleseismic data show thrust and oblique thrust faulting for the three main shocks. The first event ruptured unilaterally up and to the northwest on the westernmost fault segment, while the third main shock ruptured horizontally to the southeast. Modelling of repeat levelling data from the epicentral area requires at least three distinct fault planes, with the eastern and western planes dipping to the south and the central plane dipping to the north. The combination of scarp morphology, aftershock distribution and elevation data makes a strong case for rupture of fault planes in conjugate orientation during the 22 January 1988 Tennant Creek earthquakes. More than 20000 aftershocks have been recorded at Warramunga and activity continues to the present‐day with occasional shocks felt in the town of Tennant Creek and some recent off‐fault aftershocks located directly under the Warramunga seismic array. Stratigraphic relationships exposed in trenches excavated across the scarps suggest that during the Quaternary, a large earthquake ruptured the surface along one segment of the 1988 scarps.     

低飞航磁技术在江西朱溪矿区中的应用

为验证低飞航磁技术在推断断裂带和预测成矿远景区中的应用效果,以江西朱溪矿区以往的地质构造、物化探工作为背景,对朱溪测区的低飞航磁数据进行向上延拓和梯度处理,即总梯度模、斜导数和垂向一阶导数计算。将计算后的多幅异常等值线图与测区的区域地质构造及江西矿区成矿特点相结合,在该地区共推断出地质断裂8条,构造走向为NE向、近EW向及NW向。其中,NE向断裂为该区域主要的深大断裂,形成于下扬子板块和上华夏板块之间由于推覆构造所产生的压挤作用,主要位于塔前—赋春断裂带和双田—石劈山断裂带附近;近EW向和NW向断裂为次生断裂,近EW向断裂可能由九江—德兴断裂带产生。同时,通过分析朱溪矿区矽卡岩矿床所具有的特殊磁梯度异常现象,共推断成矿远景区4个,主要位于断裂带附近。     

Identification of cross-valley faults in the Maynardville Limestone,Oak Ridge Reservation,Tennessee, using seismic refraction tomography

First arrival times from P-wave refraction and reflection seismic surveys along Bear Creek Valley on the Oak Ridge Reservation, Tennessee, were inverted to produce refraction tomographic velocity images showing seismic velocity variations within thinly mantled karstic bedrock to a depth of approximately 20 m. Inverted velocities are consistent with two distinct bedrock groups: the Nolichucky Shale (2,730–5,150 m/s) and Maynardville Limestone (3,940–7,575 m/s). Low-velocity zones (2,700–4,000 m/s) in the tomographic images correspond to previously inferred cross-valley strike-slip faults; in places, these faults create permeability barriers that offset or block groundwater flowing along Bear Creek Valley. These faults may also force groundwater contaminants, such as dense non-aqueous phase liquids, to migrate laterally or downward, spreading contamination throughout the groundwater system. Other, previously unmapped cross-valley faults may also be visible in the tomographic images. Borehole logs suggest the low-velocity values are caused by low rigidity fractured and vuggy rock, water zones, cavities and collapse features. Surface streams, including Bear Creek, tend to lie directly above these low-velocity zones, suggesting fault and fracture control of surface drainage, in addition to the subsurface flow system. In some cases, fault zones are also associated with bedrock depressions and thicker accumulations of unconsolidated sediment.     

断裂附近源断砂空间配置油气运聚有利部位预测方法及其应用

为研究含油气盆地下生上储式断裂附近断砂空间配置圈闭中油气分布规律,在断裂附近源断砂空间配置油气运聚机理及有利部位研究的基础上,利用源岩排烃分布区和断裂输导油气有利部位,确定断裂附近源断空间配置油气运移有利部位;通过断裂侧向封闭分布部位和油气储集砂体发育部位,厘定断裂附近断砂空间配置油气圈闭部位,两者叠合建立了一套断裂附近源断砂空间配置油气运聚有利部位的预测方法,并将其应用于渤海湾盆地冀中坳陷廊固凹陷大柳泉地区旧州4条分支断裂附近沙三中下亚段源断砂空间配置油气运聚有利部位的预测中。结果表明:旧州4条分支断裂附近沙三中下亚段源断砂空间配置油气运聚有利部位主要分布在F9断裂、F8断裂中部西南及东北部局部和F7断裂西南部,有利于下伏沙四段源岩生成油气沿断裂附近源断空间配置油气运移有利部位向上覆沙三中下亚段断砂空间配置圈闭中运聚成藏,与目前旧州4条分支断裂附近沙三中下亚段已发现油气主要分布相吻合,表明该方法用于预测断裂附近源断砂空间配置油气运聚有利部位是可行的。     

Late Quaternary deformation and slip rates in the northern San Andreas fault zone at Olema Valley, Marin County, California

Quaternary sedimentary deposits along the structural depression of the San Andreas fault (SAF) zone north of San Francisco in Marin County provide an excellent record of rates and styles of neotectonic deformation in a location near where the greatest amount of horizontal offset was measured after the great 1906 San Francisco earthquake. A high-resolution gravity survey in the Olema Valley was used to determine the depth to bedrock and the thickness of sediment fill along and across the SAF valley. In the gravity profile across the SAF zone, Quaternary deposits are offset across the 1906 fault trace and truncated by the Western and Eastern Boundary faults, whose youthful activity was previously unknown. The gravity profile parallel to the fault valley shows a basement surface that slopes northward toward an area of present-day subsidence near the head of Tomales Bay. Surface and subsurface investigations of the late Pleistocene Olema Creek Formation (Qoc) indicate that this area of subsidence was located further south during deposition of the Qoc and that it has migrated northward since then. Localized subsidence has been replaced by localized contraction that has produced folding and uplift of the Qoc. This apparent alternation between transtension and transpression may be the result of a northward-diverging fault geometry of fault strands that includes the valley-bounding faults as well as the 1906 SAF trace. The Vedanta marsh is a smaller example of localized subsidence in the fault zone, between the 1906 SAF trace and the Western Boundary fault. Analyses of Holocene marsh sediments in cores and a paleoseismic trench indicate thickening, and probably tilting, toward the 1906 trace, consistent with coseismic deformation observed at the site following the 1906 earthquake.New age data and offset sedimentary and geomorphic features were used to calculate four late Quaternary slip rate estimates for the SAF at this latitude. Luminescence dates of 112–186 ka for the middle part of the Olema Creek Formation (Qoc), the oldest Quaternary deposit in this part of the valley, suggest a late Pleistocene slip rate of 17–35 mm/year, which replaces the unit to a position adjacent to its sediment source area. A younger alluvial fan deposit (Qqf; basal age 30 ka) is exposed in a quarry along the medial ridge of the fault valley. This fan deposit has been truncated on its western side by dextral SAF movement, and west-side-down vertical movement that has created the Vedanta marsh. Paleocurrent measurements, clast compositions, sediment facies distributions, and soil characteristics show that the Bear Valley Creek drainage, now located northwest of the site, supplied sediment to the fan, which is now being eroded. Restoration of the drainage to its previous location provides an estimated slip rate of 25 mm/year. Furthermore, the Bear Valley Creek drainage probably created a water gap located north of the Qqf deposit during the last glacial maximum 18 ka. The amount of offset between the drainage and the water gap yields an average slip rate of 21–30 mm/year. Finally, displacement of a 1000-year-old debris lobe approximately 20 m from its hillside hollow along the medial ridge indicates a minimum late Holocene slip rate of 21–25 mm/year. Similarity of the late Pleistocene rates to the Holocene slip rate, and to previous rates obtained in paleoseismic trenches in the area, indicates that the rates may not have changed over the past 30 ka, and perhaps the past 200–400 ka. Stratigraphic and structural observations also indicate that valley-bounding faults were active in the late Pleistocene and suggest the need for further study to evaluate their continued seismic potential.     

Ground-penetrating radar investigation of active faults along the Dead Sea Transform and implications for seismic hazards within the city of Aqaba, Jordan

Ground-penetrating radar (GPR) was used in an effort to locate a major active fault that traverses Aqaba City, Jordan. Measurements over an exposed (trenched) cross fault outside of the city identify a radar signature consisting of linear events and horizontal offset/flexured reflectors both showing a geometric correlation with two known faults at a control site. The asymmetric linear events are consistent with dipping planar reflectors matching the known direction of dip of the faults. However, other observations regarding this radar signature render the mechanism generating these events more complex and uncertain.GPR measurements in Aqaba City were limited to vacant lots. Seven GPR profiles were conducted approximately perpendicular to the assumed strike of the fault zone, based on regional geological evidence. A radar response very similar to that obtained over the cross fault was observed on five of the profiles in Aqaba City, although the response is weaker than that obtained at the control site. The positions of the identified responses form a near straight line with a strike of 45°. Although subsurface verification of the fault by trenching within the city is needed, the geophysical evidence for fault zone location is strong. The location of the interpreted fault zone relative to emergency services, military bases, commercial properties, and residential areas is defined to within a few meters. This study has significant implications for seismic hazard analysis in this tectonically active and heavily populated region.     

Holocene displacement along branch and secondary faults in the San Andreas fault zone, southern California

Detailed geologic mapping of the San Andreas fault zone in Los Angeles County since 1972 has revealed evidence for diverse histories of displacement on branch and secondary faults near Palmdale. The main trace of the San Andreas fault is well defined by a variety of physiographic features. The geologic record supports the concept of many kilometers of lateral displacement on the main trace and on some secondary faults, especially when dealing with pre-Quaternary rocks. However, the distribution of upper Pleistocene rocks along branch and secondary faults suggests a strong vertical component of displacement and, in many locations, Holocene displacement appears to be primarily vertical. The most recent movement on many secondary and some branch faults has been either high-angle (reverse and normal) or thrust. This is in contrast to the abundant evidence for lateral movement seen along the main San Andreas fault. We suggest that this change in the sense of displacement is more common than has been previously recognized.The branch and secondary faults described here have geomorphic features along them that are as fresh as similar features visible along the most recent trace of the San Andreas fault. From this we infer that surface rupture occurred on these faults in 1857, as it did on the main San Andreas fault. Branch faults commonly form “Riedel” and “thrust” shear configurations adjacent to the main San Andreas fault and affect a zone less than a few hundred meters wide. Holocene and upper Pleistocene deposits have been repeatedly offset along faults that also separate contrasting older rocks. Secondary faults are located up to 1500 m on either side of the San Andreas fault and trend subparallel to it. Moreover, our mapping indicates that some portions of these secondary faults appear to have been “inactive” throughout much of Quaternary time, even though Holocene and upper Pleistocene deposits have been repeatedly offset along other parts of these same faults. For example, near 37th Street E. and Barrel Springs Road, a limited stretch of the Nadeau fault has a very fresh normal scarp, in one place as much as 3 m high, which breaks upper Pleistocene or Holocene deposits. This scarp has two bevelled surfaces, the upper surface sloping significantly less than the lower, suggesting at least two periods of recent movement. Other exposures along this fault show undisturbed Quaternary deposits overlying the fault. The Cemetery and Little Rock faults also exhibit selected reactivation of isolated segments separated by “inactive” stretches.Activity on branch and secondary faults, as outlined above, is presumed to be the result of sympathetic movement on limited segments of older faults in response to major movement on the San Andreas fault. The recognition that Holocene activity is possible on faults where much of the evidence suggests prolonged inactivity emphasizes the need for regional, as well as detailed site studies to evaluate adequately the hazard of any fault trace in a major fault zone. Similar problems may be encountered when geodetic or other studies, Which depend on stable sites, are conducted in the vicinity of major faults.     

广西防城-灵山断裂带北东支灵山段活动性初探

防城-灵山断裂北东支灵山段为北部湾经济区内地震活动最为频繁的地区。为了查明防城-灵山断裂带北东支灵山段的断裂活动变形特征,尤其是在活动性特征的关键部位控制断裂构造的产状特征,断裂产状深部变化、断裂带规模及展布方向,本文通过遥感解译、地质地貌调查以及浅层地震和地质雷达勘探等物探方法对广西防城-灵山断裂带北东支灵山段的平面展布特征以及活动性进行了初步探讨。结果表明该断裂带呈北东向展布并被多条北西向断裂错断,东西边界分别为灵山断裂和石塘断裂。灵山断裂错断了晚更新世洪积扇阶地,河流流经灵山断裂后发生右旋偏转;石塘断裂表现为宽约250 m的破碎带,次级断裂密集发育。物探结果显示防城-灵山断裂北东支灵山段的东西两支在晚更新世以来均具有较强的活动性。     

Normal faulting and flexure in an elastic-perfectly plastic plate

An elastic-perfectly plastic plate model has been developed to analyze the flexure associated with normal faulting. The model consists of a thin layer, which is completely cut by a normal fault, overlying a fluid substratum. For a given applied bending moment at the fault, the relationship between the amount of displacement on the fault and the extent of the failure zone can be calculated. The model is applied to the Wasatch Front region in the eastern Basin and Range Province, USA to determine the correlation of its parameters with geological and geophysical data in the vicinity of a major normal fault, the Wasatch fault, along which there has been 3–4 km of Late Cenozoic uplift. In this region, most seismic activity occurs away from the Wasatch fault in a zone 30 km wide, roughly centered 30 km east of the fault. This activity occurs at depths of 15 km or less. In order to match the observations, the lithospheric layer must have a flexural rigidity of 0.5 to 1.1 · 10²² n-m and a yield stress of 1–2 kb and must have zero applied bending moment at the fault. The effective mechanical thickness of the lithosphere in this region is 20–25 km. These results indicate that the lithosphere in long-term mechanical studies in the eastern Basin and Range is thin and weak. Evaluating these results as compared to the seismic lithospheric thickness and temperature regime of the region produces some interesting correlations with studies in oceanic regions.     

高密度电法在和田隐伏断层探测中的应用

西昆仑山前一系列的新生代背斜的翼部往往伴生向南斜倾的逆断裂,这些断裂隐伏于早更新世或中更新世洪积砂砾石层,构成了和田隐伏断裂带。该断裂带由2条陡坎状断层组成,宽约10.6km,深度20~300m,落差110~270m。根据卫星影像和地质工作成果,和田隐伏断裂的一支从和田市南部穿过,但南郊飞机场附近没有露头,为探查断层在该区域的位置及深度,沿垂直于推测的断层走向布设2条测线,采用温纳（WN）测量系统对其进行探测。探测结果表明：2条测线皆发现了逆断层,均上切错断了上覆晚更新世地层,其中测线1存在2处断层,一处断层倾向南,倾角50°左右,另一处断层倾向北,倾角约55°;测线2存在一处断层,倾向北,倾角近80°。通过比对高密度电法资料和地质出露点剖面,推断和田断层在第四系以来有过两次明显的活动,导致晚更新世砂砾石土层被断错。     

黔西南泥堡金矿床构造特征及其控矿作用

位于扬子板块西南缘的右江盆地是我国卡林型金矿的集中分布区之一,素有滇-黔-桂"金三角"之称.泥堡金矿是右江盆地西北侧一个大型矿床,矿区构造主要有NEE向泥堡背斜、二龙抢宝背斜和同方向的F1、F3、F4、F5和F9断层,以及产于F1断层下盘的层间破碎带等.详细构造调查和新近勘查资料的综合研究表明:F1、F5和F9为逆冲断...