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1.
在城市活断层调查中,利用电阻率二维层析成像测量方法,对郯庐断裂带山东潍坊段的地震活断层进行了探测试验,取得了较理想的勘探效果。沂水-汤头断裂、刘家庄断裂的二维电阻率反演结果表明,断裂带两侧的电性结构呈现出整体性的差异,正断层的上盘为低阻区和局部高、低阻扰动区;而断层下盘多为均匀的高阻区;断层为高角度断层。试验探测表明:在城市活断层调查中,选用合适的电极装置类型,电阻率层析成像是一种有效的勘探方法 相似文献
2.
L. M. Balakina 《Izvestiya Physics of the Solid Earth》2011,47(9):835-846
The paper addresses the interpretation of the location, type, and size of the source for the earth-quake of March 11, 2011.
The source—a subvertical reverse fault trending in the azimuth of ∼25° along the island arc—is located in the middle part
of the Pacific slope of Honshu Island, between 38°–38.5°N and 35.5°N. The length of the source, about 350 km, approximately
corresponds to a magnitude ∼8.7 earthquake. In the north, the source is bounded by a sublatitudinal reverse fault, which generated
an earthquake with magnitude 7.2–7.5 in 1978. On this segment of the Pacific slope of Honshu Island, there are probably another
one or a few other large seismic sources, which are still latent. They are longitudinal reverse faults, which are comparable
in scale with the source of the March, 2011 earthquake. The recurrence period of the maximal earthquakes in such sources is
more than 1000 years. 相似文献
3.
高黎贡山地处印度板块与欧亚板块碰撞缝合带附近的横断山脉南段,是大理一瑞丽铁路(大瑞线)的必经之地,地形起伏大、构造复杂、活动性强,高黎贡山隧道作为全线控制性工程之一,其地质选线的最大困难就是对隧道深部构造环境的了解,特别是缺少对与地热、地震等联系紧密的深部地质构造的认识.为此,本文以大地电磁方法为手段,以高黎贡山隧道为主要研究对象,通过对滇西龙陵地区高黎贡山隧道越岭段两条大地电磁剖面数据的处理解释对研究区的地壳电性结构特征进行了勘探研究.结合区域地质构造特征与主要工程地质问题之间关系的分析,根据隧道主要断层地质条件设计了三维垂直断层模型,利用三维有限元开展正演模拟研究发现,测点点距、位置与横向分辨率密切相关,点距越密,分辨率越高,测点位于断层在地表投影位置能有效提高分辨率.采用大地电磁阻抗张量分解技术对两条剖面上各测点的二维偏离度和电性走向进行了计算和分析,对剖面视电阻率和阻抗相位数据进行了二维NLCG联合反演研究,揭示了沿剖面的腾冲地块、龙陵一瑞丽断裂带及保山地块10 km深度的电性结构特征及相互关系.结果表明:剖面CD电性结构呈现区域构造的三分性,腾冲地块电性结构成层性较好,保山地块成层性较差,两者均以中高阻电性特征为主,中间夹龙陵一瑞丽断裂带,电性结构反映从3 km深度以下存在几乎近于直立延伸的低阻带,推测为班公湖一怒江缝合带滇西段丁青一怒江缝合带的反映;剖面AB共划分了6条与工程密切相关的深部隐伏断裂,结合地震地质、地表地质及龙陵地震深部背景研究,推测F7-3断裂为1975龙陵7.3级地震断裂;从地表黄草坝断裂开始向下延伸,有一条发育最大深度约为4 km的低阻通道,推测为地热断裂深循环通道,其与黄草坝断裂共同控制研究区地下热水的补给、径流和排泄条件,在高黎贡山隧道线位位置形成了一个相对低温通道,为隧道方案成立的关键工程地质条件.勘探结果表明:滇西龙陵地区地壳电性结构有效的反映了高黎贡山隧道深部隐伏断裂和地热断裂深循环通道等深部构造特征,为大瑞线隧道工程地质选线提供了深部地质背景依据. 相似文献
4.
Tsuyoshi Nohara Hidemi Tanaka Kunio Watanabe Noboru Furukawa Akira Takami 《Island Arc》2006,15(4):537-545
Abstract The spatial hydrogeological and structural character of the active Mozumi-Sukenobu Fault (MSF) was investigated along a survey tunnel excavated through the MSF in the Kamioka Mine, central Japan. Major groundwater conduits on both sides of the MSF are recognized. One is considered to be a subvertical conduit between the tunnel and the surface, and the other is estimated to be a major reservoir of old meteoric water alongside the MSF. Our studies indicate that part of the MSF is a sub-vertical continuous barrier that obstructs younger meteoric water observed in the south-eastern part of the Active Fault Survey Tunnel (AFST) and water recharge to the rock mass intersected by the north-western part of the AFST. The MSF might be a continuous barrier resulting in the storage of a large quantity of older groundwater to the northwest. The observations and results of in situ hydraulic tests indicate that the major reservoir is not the fault breccia associated with the northeast–southwest trending faults of the MSF, but the zone in which blocks of fractured rocks occur beside high angle faults corresponding to X shears whose tectonic stress field coincides with the present regional stress field and antithetic Riedel shears of the MSF. The results from borehole investigations in the AFST indicate that secondary porosity is developed in the major reservoir due to the destruction of filling minerals and fracture development beside these shears. The increase in hydraulic conductivity is not directly related to increased density of fractures around the MSF. Development of secondary porosity could cause the increase in hydraulic conductivity around the MSF. Our results suggest that minor conduits of the fracture network are sporadically distributed in the sedimentary rocks around the MSF in the AFST. 相似文献
5.
The results of geophysical surveys carried out in the Kopili Hydel Project site in the United North Cachar and Mikir Hills district, Assam, to locate and trace underground caverns in limestone are presented. Electrical resistivity observations over known limestone caverns showed significant anomalies (high resistivity). In the course of the systematic electrical resistivity survey conducted at the eastern fringe of the Umrong basin to study the competency of the proposed reservoir, a number of indications of possible caverns in limestone were obtained and a few of them have been verified by drilling. An analysis of the electrical resistivity data also suggests that the deep seated caverns are aligned along an axis trending NNW-SSE, which may represent a zone of weakness– presumably a fault–that has influenced the formation of the caverns in preferred direction. Drilling over a few of the geophysical indications have corroborated the presence of a fault along the eastern fringe of the Umrong basin. 相似文献
6.
In order to estimate the influence of seismic effects from quarry blasts on the state of rock massif by means of electrotomography, magnetometry, and seismological observations, the variations in the physical properties of rocks before and after massive blasts have been studied. Experimental monitoring along the geophysical profile directed across one of the regional faults crossing the quarry field of the Neryungri open-pit coal mine has revealed no significant changes in the magnetic field after blasts. The revealed features include an increase in the electrical resistivity of rocks in the blast-directed wall of the tectonic fault and a decrease in the fault zone; the change in electrical resistivity in the hanging wall is insignificant. It has been found that the change in physical properties of the rock massif is determined mostly by the state (frozen or thawed) of the rocks, rather than by the power of the blast. 相似文献
7.
S. Marzorati C. Ladina E. Falcucci S. Gori M. Saroli G. Ameri F. Galadini 《Bulletin of Earthquake Engineering》2011,9(3):841-868
The April 6, 2009 L’Aquila earthquake was responsible for an “anomalous”, relatively high degree of damage (i.e. Is 7 MCS
scale) at Castelvecchio Subequo (CS). Indeed, the village is located at source-to-site distance of about 40 km, and it is
surrounded by other inhabited centres to which considerably lower intensities, i.e. Is 5–6, have been attributed. Moreover,
the damage was irregularly distributed within CS, being mainly concentrated in the uppermost portion of the old village. Geophysical
investigations (ambient seismic noise and weak ground motions analyses) revealed that site effects occurred at CS. Amplifications
of the ground motion, mainly striking NE–SW, have been detected at the uppermost portion of the carbonate ridge on which the
village is built. Geological/structural and geomechanical field surveys defined that the CS ridge is affected by sets of fractures,
joints and shear planes—mainly roughly NW–SE and N–S trending—that are related to the deformation zone of the Subequana valley
fault system and to transfer faults linking northward the mentioned tectonic feature with the Middle Aterno Valley fault system.
In particular, our investigations highlight that seismic amplifications occur where joints set NW–SE trending are open. On
the other hand, no amplification is seen in portions of the ridge where the bedrock is densely fractured but no open joints
occur. The fracture opening seems related to the toppling tendency of the bedrock slabs, owing to the local geomorphic setting.
These investigations suggest that the detected amplification of the ground motion is probably related to the polarization
of the seismic waves along the Castelvecchio Subequo ridge, with the consequent oscillation of the rock slabs perpendicularly
to the fractures azimuth. 相似文献
8.
9.
Behrooz Oskooi Mahmoud Mirzaei Behnam Mohammadi Mohammad Mohammadzadeh-Moghaddam Feridon Ghadimi 《Studia Geophysica et Geodaetica》2016,60(1):141-161
Magnetotelluric (MT) and ground magnetic surveys were conducted on the Mahallat geothermal field situated in Markazi province, central Iran, as a primary part of the explorations and developments of a geothermal energy investigation program in the region. Mahallat region has the greatest geothermal fields in Iran. MT survey was performed in November 2011 on an 8 km profile crossing the hot springs with a total of 17 stations. The 2D inversion of the determinant MT data was performed using a 2D inversion routine based on the Occam approach. The 2D resistivity model obtained from the determinant data shows a low resistivity zone at 800-2000 m depth and a higher resistivity zone above the low resistivity zone, interpreted as geothermal reservoir and cap rock, respectively. It also revealed two major concealed faults which are acting as preferential paths for the circulation of hydrothermal fluids. To obtain more geophysical evidence, a ground magnetic survey with 5000 stations was also performed over an area of 200 km2 around the MT profile. Magnetic measurements show a main positive anomaly of about +1000 nT over the study area, which could be interpreted as an intrusive body with the high magnetic susceptibility (i.e. mafic and ultramafic rocks) into the sedimentary host rocks. We interpret the body as the heat source of the geothermal system. Structural index and depth estimation of the anomaly indicate that the intrusive body is similar to a cylinder extending from about one kilometer depth down to greater depths. The results of MT and magnetic investigations indicate a geothermal reservoir which proves the preliminary geological observations to a great extent. 相似文献
10.
Takeshi Hashimoto 《Island Arc》2001,10(3-4):306-317
Abstract A resistivity survey method using artificial telluric noise was examined and applied to a field of a fault zone. The electric earth current was measured at 50 sites in the Nojima Fault zone, which is in the northwestern part of Awaji Island, southwestern Japan. The dominant component of the observed electric field is supposed to be leakage currents from DC electric railways running outside the island. Amplitude and polarization of the stray current were systematically investigated and were revealed to represent the subsurface electrical structure of the study area. Some features on the fault zone's electrical structure have been pointed out, including: (i) an electrical boundary that corresponds to a geological one between granite (resistive) and sediments (conductive); and (ii) a low resistivity spot on the surface rupture of the earthquake fault. The structure estimated in the present study is both qualitatively and quantitatively consistent with previous resistivity surveys done using other methods pursued in the same area. It shows the validity of the 'stray current method' as one that is easy and uses low-cost resistivity exploration tools in a region where the effect of artificial noise caused mainly by leakage currents from electrical railways cannot be ignored. 相似文献
11.
Jérome Salichon Carine Kohrs-Sansorny Etienne Bertrand Françoise Courboulex 《Journal of Seismology》2010,14(3):523-541
The southern Alps–Ligurian basin junction is one of the most seismically active zone of the western Europe. A constant microseismicity
and moderate size events (3.5 < M < 5) are regularly recorded. The last reported historical event took place in February 1887
and reached an estimated magnitude between 6 and 6.5, causing human losses and extensive damages (intensity X, Medvedev–Sponheuer–Karnik).
Such an event, occurring nowadays, could have critical consequences given the high density of population living on the French
and Italian Riviera. We study the case of an offshore Mw 6.3 earthquake located at the place where two moderate size events
(Mw 4.5) occurred recently and where a morphotectonic feature has been detected by a bathymetric survey. We used a stochastic
empirical Green’s functions (EGFs) summation method to produce a population of realistic accelerograms on rock and soil sites
in the city of Nice. The ground motion simulations are calibrated on a rock site with a set of ground motion prediction equations
(GMPEs) in order to estimate a reasonable stress-drop ratio between the February 25th, 2001, Mw 4.5, event taken as an EGF
and the target earthquake. Our results show that the combination of the GMPEs and EGF techniques is an interesting tool for
site-specific strong ground motion estimation. 相似文献
12.
In many coastal areas of North America and Scandinavia, post-glacial clay sediments have emerged above sea level due to iso-static uplift. These clays are often destabilised by fresh water leaching and transformed to so-called quick clays as at the investigated area at Smørgrav, Norway. Slight mechanical disturbances of these materials may trigger landslides. Since the leaching increases the electrical resistivity of quick clay as compared to normal marine clay, the application of electromagnetic (EM) methods is of particular interest in the study of quick clay structures.For the first time, single and joint inversions of direct-current resistivity (DCR), radiomagnetotelluric (RMT) and controlled-source audiomagnetotelluric (CSAMT) data were applied to delineate a zone of quick clay. The resulting 2-D models of electrical resistivity correlate excellently with previously published data from a ground conductivity metre and resistivity logs from two resistivity cone penetration tests (RCPT) into marine clay and quick clay. The RCPT log into the central part of the quick clay identifies the electrical resistivity of the quick clay structure to lie between 10 and 80 Ω m. In combination with the 2-D inversion models, it becomes possible to delineate the vertical and horizontal extent of the quick clay zone. As compared to the inversions of single data sets, the joint inversion model exhibits sharper resistivity contrasts and its resistivity values are more characteristic of the expected geology. In our preferred joint inversion model, there is a clear demarcation between dry soil, marine clay, quick clay and bedrock, which consists of alum shale and limestone. 相似文献
13.
14.
Evidence of fluid interaction with normal faults comes from their varied role as flow barriers or conduits in hydrocarbon basins and as hosting structures for hydrothermal mineralisation, and from fault-rock assemblages in exhumed footwalls of steep active normal faults and metamorphic core complexes. These last suggest involvement of predominantly aqueous fluids over a broad depth range, with implications for fault shear resistance and the mechanics of normal fault reactivation. A general downwards progression in fault rock assemblages (high-level breccia-gouge (often clay-rich) → cataclasites → phyllonites → mylonite → mylonitic gneiss with the onset of greenschist phyllonites occurring near the base of the seismogenic crust) is inferred for normal fault zones developed in quartzo-feldspathic continental crust. Fluid inclusion studies in hydrothermal veining from some footwall assemblages suggest a transition from hydrostatic to suprahydrostatic fluid pressures over the depth range 3–5 km, with some evidence for near-lithostatic to hydrostatic pressure cycling towards the base of the seismogenic zone in the phyllonitic assemblages. Development of fault-fracture meshes through mixed-mode brittle failure in rock-masses with strong competence layering is promoted by low effective stress in the absence of thoroughgoing cohesionless faults that are favourably oriented for reactivation. Meshes may develop around normal faults in the near-surface under hydrostatic fluid pressures to depths determined by rock tensile strength, and at greater depths in overpressured portions of normal fault zones and at stress heterogeneities, especially dilational jogs. Overpressures localised within developing normal fault zones also determine the extent to which they may reutilise existing discontinuities (for example, low-angle thrust faults). Brittle failure mode plots demonstrate that reactivation of existing low-angle faults under vertical σ1 trajectories is only likely if fluid overpressures are localised within the fault zone and the surrounding rock retains significant tensile strength. Migrating pore fluids interact both statically and dynamically with normal faults. Static effects include consideration of the relative permeability of the faults with respect to the country rock, and juxtaposition effects which determine whether a fault is transmissive to flow or acts as an impermeable barrier. Strong directional permeability is expected in the subhorizontal σ2 direction parallel to intersections between minor faults, extension fractures, and stylolites. Three dynamic mechanisms tied to the seismic stress cycle may contribute to fluid redistribution: (i) cycling of mean stress coupled to shear stress, sometimes leading to postfailure expulsion of fluid from vertical fractures; (ii) suction pump action at dilational fault jogs; and, (iii) fault-valve action when a normal fault transects a seal capping either uniformly overpressured crust or overpressures localised to the immediate vicinity of the fault zone at depth. The combination of σ2 directional permeability with fluid redistribution from mean stress cycling may lead to hydraulic communication along strike, contributing to the protracted earthquake sequences that characterise normal fault systems. 相似文献
15.
本文对位于青藏高原东缘川滇构造区的贡山一绥江大地电磁测深(MT)剖面数据进行反演,获得沿剖面的深部电性结构,为研究喜马拉雅东构造结、川滇菱形地块与华南地块的构造变形特征、壳幔耦合关系、地块间接触关系以及相互作用等问题,提供电性结构的依据.研究发现:(1)电性结构揭示澜沧江断裂带和小金河断裂带为深大断裂带,控制着研究区的深部结构特征和形变机制;(2)澜沧江断裂带和金沙江断裂带之间的高阻体,可能是扬子古地块的残留部分;小金河断裂带和安宁河断裂带之间的高阻体,则是峨眉山大火山省喷发形成的冕宁一越西杂岩带;(3)在滇西地块、川滇地块和大凉山地块均存在低阻层,它们的介质属性有所不同,滇西地块下的低阻层"疑似"高热状态的岩浆囊,主要由缅甸弧向东俯冲运动引起的,中上地壳的高热状态使地块的活动性增强;川滇地块内部的壳内低阻层的成因为:理塘断裂带和小金河断裂带之间的地表低阻层由破碎带充水所致,而金沙江断裂带和理塘断裂带之间的中地壳低阻层可能是由局部熔融物质或含盐流体导致的,其为壳内物质运移的通道.从而在地下物质发生大规模走滑运动的过程中起到引导作用;川滇地块东部和大凉山地块西部的壳内低阻层可能与地慢物质的上涌有关;马边断裂带附近的低阻体可能与破碎带变宽和破碎带内的流体有关. 相似文献
16.
A series of 112 earthquakes was recorded between October 2005 and August 2007 during the excavation of the MFS Faido, the
southernmost access point of the new Gotthard Base Tunnel. Earthquakes were recorded at a dense network of 11 stations, including
2 stations in the tunnel. Local magnitudes computed from Wood–Anderson-filtered horizontal component seismograms ranged from
−1.0 to 2.4; the largest earthquake was strongly felt at the surface and caused considerable damage in the tunnel. Hypocenter
locations obtained routinely using a regional 3-D P-wave velocity model and a constant Vp/Vs ratio 1.71 were about 2 km below
the tunnel. The use of seismic velocities calibrated from a shot in the tunnel revealed that routinely obtained hypocenter
locations were systematically biased to greater depth and are now relocated to be on the tunnel level. Relocation of the shot
using these calibrated velocities yields a location accuracy of 25 m in longitude, 70 m in latitude, and 250 m in focal depth.
Double-difference relative relocations of two clusters with highly similar waveforms showed a NW–SE striking trend that is
consistent with the strike of mapped faults in the MFS Faido. Source dimensions computed using the quasidynamic model of Madariaga
(Bull Seismo Soc Am 66(3):639–666, 1976) range from 50 to 170 m. Overlapping source dimensions for earthquakes within the two main clusters suggests that the same
fault patch was ruptured repeatedly. The observed seismicity was likely caused by stress redistribution due to the excavation
work in the MFS Faido. 相似文献
17.
Probabilistic seismic hazard assessment for Thailand 总被引：3，自引：1，他引：2
Teraphan Ornthammarath Pennung Warnitchai Kawin Worakanchana Saeed Zaman Ragnar Sigbj?rnsson Carlo Giovanni Lai 《Bulletin of Earthquake Engineering》2011,9(2):367-394
A set of probabilistic seismic hazard maps for Thailand has been derived using procedures developed for the latest US National
Seismic Hazard Maps. In contrast to earlier hazard maps for this region, which are mostly computed using seismic source zone
delineations, the presented maps are based on the combination of smoothed gridded seismicity, crustal-fault, and subduction
source models. Thailand’s composite earthquake catalogue is revisited and expanded, covering a study area limited by 0°–30°N
Latitude and 88°–110°E Longitude and the instrumental period from 1912 to 2007. The long-term slip rates and estimates of
earthquake size from paleoseismological studies are incorporated through a crustal fault source model. Furthermore, the subduction
source model is used to model the megathrust Sunda subduction zones, with variable characteristics along the strike of the
faults. Epistemic uncertainty is taken into consideration by the logic tree framework incorporating basic quantities, such
as different source modelling, maximum cut-off magnitudes and ground motion prediction equations. The ground motion hazard
map is presented over a 10 km grid in terms of peak ground acceleration and spectral acceleration at 0.2, 1.0, and 2.0 undamped
natural periods and a 5% critical damping ratio for 10 and 2% probabilities of exceedance in 50 years. The presented maps
give expected ground motions that are based on more extensive data sources than applied in the development of previous maps.
The main findings are that northern and western Thailand are subjected to the highest hazard. The largest contributors to
short- and long-period ground motion hazard in the Bangkok region are from the nearby active faults and Sunda subduction zones,
respectively. 相似文献
18.
Prantik Mandal 《Pure and Applied Geophysics》2008,165(7):1307-1324
Double difference relocations of the 1402 Kachchh events (2001–2006) clearly delineate two fault zones viz. south-dipping
North Wagad fault (NWF) and almost vertical Gedi fault (GF). The relocated focal depths delineate a marked variation of 4
and 7 km in the brittle-ductile transition depths beneath GF and NWF, respectively. The focal mechanism solutions of 464 aftershocks
(using 8–12 first motions) show that the focal mechanisms ranged between pure reverse and pure strike-slip except for a few
pure dip-slip solutions. The stress inversions performed for five rectangular zones across the Kachchh rift reveal both clockwise
and anticlockwise rotation (7–32°) in the σ1 orientation within the rupture zone, favoring a heterogeneous stress regime with an average N-S fault normal compression.
This rotation may be attributed to the presence of crustal mafic intrusives (5–35 km depth) in the rupture zone of the 2001
Bhuj main shock. Results suggest a relatively homogeneous stress regime in the GF zone favoring strike-slip motion, with a
fault normal N-S compression. 相似文献
19.
The three-dimensional (3D) geoelectric model of the Kuznetsk-Alatau folded area is reconstructed by magnetotelluric inversion using 3D fitting. It is established that the zones of ore mineralization within the Batenevsky massif are confined to the subvertical faults characterized by the electric resistivity of 100–300 Ω m. Blocks with ρ ≈ 10−100 Ω m are identified at a depth below 10 km in the western part of the model. The blocks are located close to the areas marked by the increased thermal flux, reduced seismic velocities, and elevated Moho boundary. This is probably associated with the presence of the rift zone in this area.
相似文献20.
This paper reports the results of magnetotelluric sounding (MTS) in the area where the Bol’she-Bannyi hydrothermal springs are discharged. The MTS curves were inverted on the assumption of a twodimensional inhomogeneous model using longitudinal and transverse curves of apparent resistivity. It was found that the geoelectric section contains a nearly vertical anomaly of high electrical conductivity at depths of 5.5–8 km, which is the signature of a deep-seated fault. The resulting geoelectric section for the upper crust and data from regional magnetotelluric soundings were used as a basis for developing a conceptual deep model of the Bol’she-Bannyi hydrothermal system. We quote an approximate estimate of rock porosity. According to the model, deep fluids come from a crustal layer into the subvertical deep-seated fault then penetrate via fissures into the sedimentary–volcanogenic cover, and finally arrive at the ground surface in zones of high rock permeability. We provide a recommendation for drilling a deep well in order to determine the potential of the Bol’she-Bannyi hydrothermal field. 相似文献