Stress triggering of normal aftershocks due to strike slip earthquakes in compressive regime

A few cases of occurrence of normal aftershocks after strike slip earthquakes in compressive regime have been reported in the literature. Occurrence of such aftershocks is intriguing as they occurred despite the apparent stabilizing influence of compressive plate tectonic stresses on the normal faults. To investigate the occurrence processes of such earthquakes, we calculate change in static stress on optimally oriented normal and reverse faults in the dilational and compressional step over zones, respectively, due to slip on a vertical strike slip fault under compressive regime. We find that change in static stress is much more pronounced on normal faults as compared to that on reverse faults, for all values of fault friction. Change in static stress on reverse fault is marginally positive only when the fault friction is low, whereas for normal faults it is positive for all values of fault friction, and is maximum for high fault friction. We suggest that strike slip faulting in compressive regime creates a localized tensile environment in the dilational step over zone, which causes normal faulting in that region. The aftershocks on such normal faults are considered to have occurred as an almost instantaneous response of stress transfer due to strike slip motion.     

Stress history controls the spatial pattern of aftershocks: case studies from strike-slip earthquakes

International Journal of Earth Sciences - Earthquake ruptures perturb stress within the surrounding crustal volume and as it is widely accepted now these stress perturbations strongly correlates...     

Tidal triggering of reservoir-associated earthquakes

If the effect of a reservoir is to bring a fault zone gradually to failure and trigger an earthquake, then it is reasonable that rapidly fluctuating tidal stresses may influence the time of the induced earthquakes. An examination of earthquakes from eight reservoirs shows that earthquakes at six sites occur at preferred times in the semidiurnal tidal cycle. Tidal-stress orientations and the phase within the semidiurnal tidal cycle were calculated for only the largest earthquakes occurring at each site. This insures the elimination of aftershocks and selects earthquakes which are independent of each other. Sites of a significant earthquake/tide correlation with less than a 3% chance of occurring randomly include Hebgen Lake, Mont., U.S.A.; Kariba, Rhodesia; Kerr Dam, Mont., U.S.A.; Kremasta, Greece; Lake Mead, Nev., U.S.A.; and Monteynard, France. Each data set includes from about ten to twenty earthquakes. In most of the above cases earthquake triggering seems to occur when tidal stress enhances slip, i.e., when tidal stresses are oriented to enhance the tectonic stress.     

Static elastic deformation in an orthotropic half-space with rigid boundary model due to non-uniform long strike slip fault

The solution of static elastic deformation of a homogeneous, orthotropic elastic uniform half-space with rigid boundary due to a non-uniform slip along a vertical strike-slip fault of infinite length and finite width has been studied. The results obtained here are the generalisation of the results for an isotropic medium having rigid boundary in the sense that medium of the present work is orthotropic with rigid boundary which is more realistic than isotropic and the results for an isotropic case can be derived from our results. The variations of displacement with distance from the fault due to various slip profiles have been studied to examine the effect of anisotropy on the deformation. Numerically it has been found that for parabolic slip profile, the displacement in magnitude for isotropic elastic medium is greater than that for an orthotropic elastic half-space, but, in case of linear slip, the displacements in magnitude for an orthotropic medium is greater than that for the isotropic medium.     

Elastic and visco-elastic stress triggering in the South Iceland Seismic Zone due to large earthquakes since 1706

Damaging earthquakes in the South Iceland Seismic Zone (SISZ) occur fairly regularly and often as a series of events with a few days only between individual events. Tolerably reliable information on epicentre locations and mechanisms are available for 13 M ≥ 6 events between 1706 and 2000. For these events, we computed the co- and post-seismic stress fields, hereby approximating the SISZ by a mixed elastic/visco-elastic layered half-space. The horizontal shear stress and the Coulomb stress changes were analysed to detect possible trigger mechanisms, which may aid future earthquake mitigation efforts. We tested several criteria but must conclude that the start of an earthquake series in the SISZ cannot be explained by triggering through previous events. Inside an individual series, however, one may infer triggering. Our results are in contradiction with the findings in other regions of the world. The reason might be related to the fact that the SISZ is not a mature fault zone, in which old faults are re-activated if a certain stress level threshold is passed. In addition, uncertainties in the model parameters as well as the neglect of horizontal variations in the model and of possible stress transfer due to volcanic activity further complicate the evaluation of our results and need to be taken into account in future studies.     

Jurassic strike slip versus subduction in the Eastern Alps

Late Jurassic formations of the Northern Calcareous Alps (NCA) contain ample evidence of synsedimentary tectonics in the form of elongate basins filled with turbidites, debris flows and slumps. Clasts are derived from the Mesozoic of the NCA; they commonly measure tens of metres in diameter and occasionally form kilometre-size bodies. These sedimentologic observations and the presumed evidence of Late Jurassic high-pressure metamorphism recently led to the hypothesis of a south-dipping Jurassic subduction zone with accretionary wedge in the southern parts of the NCA. We present new ⁴⁰Ar/³⁹Ar dates from the location of the postulated high-pressure metamorphism that bracket the age of this crystallization not earlier than 114–120 Ma. The event is therefore part of the well-documented mid-Cretaceous metamorphism of the Austro-alpine domain. Thus, there is currently no evidence of Late Jurassic high-pressure metamorphism to support the subduction hypothesis. The sediment record of the Late Jurassic deformation in the NCA, including the formation of local thrust sheets, is no conclusive evidence for subduction. All these phenomena are perfectly compatible with synsedimentary strike-slip tectonics. Large strike-slip fault zones with restraining and releasing bends and associated flower structures and pull-apart basins are a perfectly viable alternative to the subduction model for the Late Jurassic history of the NCA. However, in contrast to the Eastern Alps transect, where arguments for a Jurassic subduction are missing, a glaucophane bearing Jurassic high-pressure metamorphism in the Meliatic realm of the West Carpathians is well documented. There, the high-pressure/low-temperature slices occur between the Gemeric unit and the Silica nappe system (including the Aggtelek-Rudabanya units), which corresponds in facies with the Juvavic units in the southern part of the NCA. To solve the contrasting palaeogeographic reconstructions we propose that the upper Jurassic left lateral strike-slip system proposed here for the Eastern Alps continued eastwards and caused the eastward displacement of the Silica units into the Meliatic accretionary wedge.     

Classification of road damage due to earthquakes

Earthquakes cause massive road damage which in turn causes adverse effects on the society. Previous studies have quantified the damage caused to residential and commercial buildings; however, not many studies have been conducted to quantify road damage caused by earthquakes. In this study, an attempt has been made to propose a new scale to classify and quantify the road damage due to earthquakes based on the data collected from major earthquakes in the past. The proposed classification for road damage due to earthquake is called as road damage scale (RDS). Earthquake details such as magnitude, distance of road damage from the epicenter, focal depth, and photographs of damaged roads have been collected from various sources with reported modified Mercalli intensity (MMI). The widely used MMI scale is found to be inadequate to clearly define the road damage. The proposed RDS is applied to various reported road damage and reclassified as per RDS. The correlation between RDS and earthquake parameters of magnitude, epicenter distance, hypocenter distance, and combination of magnitude with epicenter and hypocenter distance has been studied using available data. It is observed that the proposed RDS correlates well with the available earthquake data when compared with the MMI scale. Among several correlations, correlation between RDS and combination of magnitude and epicenter distance is appropriate. Summary of these correlations, their limitations, and the applicability of the proposed scale to forecast road damages and to carry out vulnerability analysis in urban areas is presented in the paper.     

西南三江地区新生代走滑造山

本文系统论述了西南三江地区那邦、高黎贡山、崇山-澜沧江、点苍山-哀牢山-红河剪切走滑带、区域性伸展与变质核杂岩、新生代盆地及走滑过程中的碱性岩浆活动等特征,认为西南三江地区经历了挤压收缩变形（60~40Ma）、走滑伸展热隆（40~38Ma）、走滑剪切深熔（38~23Ma）、走滑剪切伸展（23~11Ma）、走滑剥蚀隆升（11~5Ma）5个时空演化阶段,并对应5种运动机制及动力学机制：碰撞挤压、走滑拉张热隆（岩浆）、走滑剪切深熔、剪切伸展、走滑垮塌,主要表现为走滑造山。西南三江造山带是印度板块向欧亚板块斜向俯冲形成的多条巨型顺时针走滑剪切带,其间的块体向南逸出并顺时针旋转。走滑断层系起了位移量调节和构造变换的作用,西南三江造山带为典型的走滑造山带。     

Analogue and numerical modeling of normal fault patterns produced due to slip along a detachment zone

In this paper, we investigate normal fault patterns produced by the sliding motion along a gently dipping normal fault by using analogue model tests and numerical modeling. The motivation for this study was offered by microseismic test data that indicate the existence of an active low-angle shear zone at a depth of 9–11 km in the extensional region of high seismic activity of the Gulf of Corinth (Greece). Both modeling techniques seem to support the hypothesis that the system of high-angle normal faults that are responsible for the final asymmetrical graben formation initiate at the tip of the active basal detachment nearest to the free surface. The normal faults propagate upwards with progressive sliding of the inclined basal plane, resulting in a first phase of symmetrical graben configuration that is delimited by a main synthetic fault and an antithetic fault forming a Rankine zone. Subsequent sliding on the inclined base induces a family of secondary antithetic normal faults, which are responsible for the asymmetry of the failure pattern and the diffusive character of deformation in that area. Shear deformation is more intense and localized along the synthetic normal fault than along the antithetic faults. Elaboration on the analogue test results has led to the phenomenological relations among four main parameters that describe the geometry of grabens, namely, (i) the width and (ii) the maximum subsidence of the graben, (iii) the dip angles of the conjugate normal faults, and (iv) the amount of sliding along the low-angle normal fault. However, analogue models do not produce the system of synthetic faults that is observed in the Gulf of Corinth. The effects of both friction angle variation along the detachment base and of the constitutive behavior of the model material on the configuration of the final structural pattern were also studied with a series of numerical continuum models. It was found that (a) the fault pattern of the Gulf of Corinth may be reproduced with either a strain-softening material with low elastic modulus or a constant strength material, and (b) two consecutive grabens, such as those of Gulfs of Corinth and Evia, may also be reproduced by an appropriate combination of variation of dip and frictional properties along the hypothesized detachment zone.     

Focal mechanism dependence of static stress triggering of earthquakes

We perform a global statistical investigation into the problem of Coulomb stress triggering of earthquakes by using the Harvard CMT catalogue of shallow earthquakes from 1976 to 2001. We consider ‘earthquake pairs’, i.e., pairs of successive earthquakes occurring near each other with similar focal mechanisms, and address the problem of whether or not the change of the Coulomb failure stress (CFS) produced by the first earthquake of the pair ‘encourages’ the occurrence of the second one. An interesting feature is that such a Coulomb stress-triggering phenomenon has an apparent focal mechanism dependence: for thrust earthquakes, a more evident triggering effect can be observed.     

Repeating aftershocks of the great 2004 Sumatra and 2005 Nias earthquakes

We investigate repeating aftershocks associated with the great 2004 Sumatra–Andaman (Mw 9.2) and 2005 Nias–Simeulue (Mw 8.6) earthquakes by cross-correlating waveforms recorded by the regional seismographic station PSI and teleseismic stations. We identify 10 and 18 correlated aftershock sequences associated with the great 2004 Sumatra and 2005 Nias earthquakes, respectively. The majority of the correlated aftershock sequences are located near the down-dip end of a large afterslip patch. We determine the precise relative locations of event pairs among these sequences and estimate the source rupture areas. The correlated event pairs identified are appropriately referred to as repeating aftershocks, in that the source rupture areas are comparable and significantly overlap within a sequence. We use the repeating aftershocks to estimate afterslip based on the slip-seismic moment scaling relationship and to infer the temporal decay rate of the recurrence interval. The estimated afterslip resembles that measured from the near-field geodetic data to the first order. The decay rate of repeating aftershocks as a function of lapse time t follows a power-law decay 1/t^p with the exponent p in the range 0.8–1.1. Both types of observations indicate that repeating aftershocks are governed by post-seismic afterslip.     

Evidences of landslide earthquake triggering due to self-excitation process

The basin-like setting of stiff bedrock combined with pre-existing landslide masses can contribute to seismic amplifications in a wide frequency range (0–10 Hz) and induce a self-excitation process responsible for earthquake-triggered landsliding. Here, the self-excitation process is proposed to justify the far-field seismic trigger of the Cerda landslide (Sicily, Italy) which was reactivated by the 6th September 2002 Palermo earthquake (M _s = 5.4), about 50 km far from the epicentre. The landslide caused damage to farm houses, roads and aqueducts, close to the village of Cerda, and involved about 40 × 10⁶ m³ of clay shales; the first ground cracks due to the landslide movement formed about 30 min after the main shock. A stress–strain dynamic numerical modelling, performed by FDM code FLAC 5.0, supports the notion that the combination of local geological setting and earthquake frequency content played a fundamental role in the landslide reactivation. Since accelerometric records of the triggering event are not available, dynamic equivalent inputs have been used for the numerical modelling. These inputs can be regarded as representative for the local ground shaking, having a PGA value up to 0.2 m/s², which is the maximum expected in 475 years, according to the Italian seismic hazard maps. A 2D numerical modelling of the seismic wave propagation in the Cerda landslide area was also performed; it pointed out amplification effects due to both the structural setting of the stiff bedrock (at about 1 Hz) and the pre-existing landslide mass (in the range 3–6 Hz). The frequency peaks of the resulting amplification functions (A(f)) fit well the H/V spectral ratios from ambient noise and the H/H spectral ratios to a reference station from earthquake records, obtained by in situ velocimetric measurements. Moreover, the Fourier spectra of earthquake accelerometric records, whose source and magnitude are consistent with the triggering event, show a main peak at about 1 Hz. This frequency value well fits the one amplified by the geological setting of the bedrock in correspondence with the landslide area, which is constituted of marly limestones and characterised by a basin-like geometry.     

Structural evidence of orogen-parallel strike slip displacements in the Precordillera of northern Chile

The Chilean Precordillera, situated between the Longitudinal Valley and the Western Cordillera of northern Chile, is made up of several elongate basement ridges following the trend of the Andes. These ridges, which morphologically rise above the Mesozoic-Tertiary cover rocks, are developed as anticlinal cores or as pressure ridges bounded by reverse faults and, thus, show considerable orogennormal shortening. Several nearly vertical faults cut through the Precordillera, parallel or at a very low angle to the mountain ranges. From the following structures it can be inferred that orogen-parallel transcurrent movements took place along the faults: (a) asymmetric en echelon fault arrays, (b) stratigraphic and structural discontinuities across major faults, (c) fabrics in fault rocks, and (d) vertical folds. A dextral displacement of the order of tens of km is probable. The orogen-parallel strikeslip movements as well as the orogen-normal shortening are considered as phenomena of magmatic arc tectonics due to the focussing of central Andean igneous activity on the Precordillera from the Late Cretaceous until the paroxysm of deformation (45-30 Ma). Deformation along the Precordilleran Fault System is related with the development of the large porphyry copper ore deposits of that area. The structural evolution of the Precordillera can be explained by oblique subduction resulting in dextral transpression.

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Zusammenfassung Die nordchilenische Präkordillere, zwischen Längstal und Westkordillere gelegen, ist aus mehreren langgestreckten prämesozoischen Grundgebirgsrücken aufgebaut, die sich als Antiklinalkerne oder als aus diesen hervorgegangene, durch Aufschiebungen begrenzte Rücken über das mesozoisch-tertiäre Deckgebirge erheben. Das Gebiet ist durchzogen von einem System steiler, parallel oder in spitzem Winkel zu diesen Einengungsstrukturen verlaufenden Störungen. Folgende Strukturen zeigen, daß es an diesen Störungen Seitenverschiebungen gegeben hat: (a) asymmetrische en-echelon-Störungsanordnungen, (b) stratigraphische und strukturelle Diskontinuitäten an Störungen, (c) Gefüge der Störungsgesteine und (d) Schlingen. Ein dextraler Versatz von mehreren Zehnern von km ist wahrscheinlich. Orogenparallele Seitenverschiebungen und Orogen-normale Einengung können als Phänomene der Magmatic-Arc-Tektonik gesehen werden, da von der höchsten Oberkreide bis zum Höhepunkt der Deformation (45-30 Ma) die magmatische Aktivität der Anden in der Präkordillere lag. In diesem Zusammenhang stehen auch die Vererzungen der großen porphyry-copper-Lagerstätten des Gebietes. Schiefe, zu dextraler Transpression führende Subduktion wird für die Strukturbildung der Präkordillere verantwortlich gemacht.

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Resumen La Precordillera del norte chileno, situada entre el Valle Longitudinal y la Cordillera Occidental, esta constituida de uno o más dorsales de basamento, los que forman núcleos de grandes anticlinales o pilares en compresión que se elevan morfologicamente sobre las rocas mesozóicas y terciarias de su cobertura. Varias fallas más o menos verticales cortan a la Precordillera paralelamente o con angulo agudo a su rumbo. Las siguientes estructuras permiten deducir que se produjeron movimientos transcurrientes paralelos al orogeno en las fallas: (a) juegos asimétricos escalonados de fallas, (b) discontinuidades estratigráficas y estructurales ligados a la falla, (c) fábricas de las rocas de falla y (d) pliegues con ejes verticales. Un desplazamiento dextral de decinas de kilométras es probable. Las fallas de desplazamiento en el rumbo paralelas al orógeno asi como el acortamiento normal al orógeno se consideran como fenomenos de la tectónica de arco magmático, puesto que desde el Cretácico superior hasta el tiempo de la deformatión (45-30 Ma), la actividad magmática de los Andes Centrales estuvo ubicada en la Precordillera. La deformación en el sistema de fallas de la Precordillera está tambien relacionada con la mineralizatión de los grandes yacimientos de pórfidos cupriferos de la zona. La evolutión tectónica de la Precordillera puede haber sido originada por subductión oblicua produciendo transpresión dextral.

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Elastic and inelastic triggering of earthquakes in the North Anatolian Fault zone

Deformation models used to explain the triggering mechanism often assume pure elastic behaviour for the crust and upper mantle. In reality however, the mantle and possibly the lower crust behave viscoelastically, particularly over longer time scales. Consequently, the stress field of an earthquake is in general time-dependent. In addition, if the elastic stress increase were enough to trigger a later earthquake, this triggered event should occur instantaneously and not many years after the triggering event. Hence, it is appropriate to include inelastic behaviour when analysing stress transfer and earthquake interaction.In this work, we analyse a sequence of 10 magnitude M_s > 6.5 events along the North Anatolian Fault between 1939 and 1999 to study the evolution of the regional Coulomb stress field. We investigate the triggering of these events by stress transfer, taking viscoelastic relaxation into account. We evaluate the contribution of elastic stress changes, of post-seismic viscoelastic relaxation in the lower crust and mantle, and of steady tectonic loading to the total Coulomb stress field. We analyse the evolution of stress in the region under study, as well as on the rupture surfaces of the considered events and their epicentres. We study the state of the Coulomb stress field before the 1999 İzmit and Düzce earthquakes, as well as in the Marmara Sea region.In general, the Coulomb stress failure criterion offers a plausible explanation for the location of these events. However, we show that using a purely elastic model disregards an important part of the actual stress increase/decrease. In several cases, post-seismic relaxation effects are important and greater in magnitude than the stress changes due to steady tectonic loading. Consequently, viscoelastic relaxation should be considered in any study dealing with Coulomb stress changes.According to our study, and assuming that an important part of the rupture surface must be stressed for an earthquake to occur, the most likely value for the viscosity of the lower crust or mantle in this region is 5 · 10¹⁷–10¹⁸ Pa · s. Our results cannot rule out the possibility of other time-dependent processes involved in the triggering of the 1999 Düzce event. However, the stress increase due to viscoelastic relaxation brought 22% of the 1999 Düzce rupture area over the threshold value of Δσ_c ≥ 0.01 MPa (0.1 bar), and took the whole surface closer to failure by an average of 0.2 MPa. Finally, we argue that the Marmara Sea region is currently being loaded with positive Coulomb stresses at a much faster rate than would arise exclusively from steady tectonic loading on the North Anatolian Fault.     

渤海湾盆地晚中生代-新生代伸展和走滑构造及深部背景

渤海湾盆地是一个在早白垩世被动裂陷盆地基础上发育起来的新生代主动裂陷盆地, 走滑作用贯穿始终, 特别是在兰聊-盐山断层以东, 使这个裂陷盆地具有鲜明的走滑特征。伸展和走滑作用此消彼长, 伸展构造和走滑构造相互叠加、转换, 垂向上相互叠置、交切, 并由此导致变换带的产生。晚中生代以来太平洋板块向欧亚板块俯冲的方向和速度变化、后撤以及板片窗效应、中始新世印欧板块碰撞导致的地幔上涌是控制盆地形成的深部背景, 郯庐断裂带早白垩世强烈的左行走滑、古新世-早始新世弱的左行走滑以及中始新世后的右行走滑活动也深刻地控制和影响着盆地的发育, 盆地内晚中生代-新生代的伸展和走滑构造的演化则是其浅部响应, 并由此控制着岩浆活动以及油气生成、运聚和分布的时空迁移。     

苏拉威西岛北部左旋走滑与俯冲后撤的动力学分析

苏拉威西岛北部属于马鲁古海板块,其主体是北苏拉威西海沟俯冲带与帕卢-科洛左旋走滑断裂所围限的岛北支和岛东支。大约5 Ma前,苏拉群岛沿Sorong断层与苏拉威西岛东支碰撞,导致北苏拉威西海沟俯冲后撤,引起了岛北支顺时针旋转约20°～25°,同时,西侧的帕卢-科洛断层发生了约4 cm/a的左旋走滑。本文利用综合地球物理方法,计算了该区三维温度、速度、黏性特征,认为：苏拉威西岛北部在左旋走滑、俯冲后撤过程中,地壳以脆性变形为主,但由于北苏拉威西海沟俯冲带在地壳内形成南向倾斜的软弱层,Moho面和地形“镜像”区域内形成脆、韧变形共存的组合。地幔变形为韧性变形,深度约100 km的上地幔低速流变层是地幔韧性变形的主控层位。在周边板块边界不断移动的动力学背景中,苏拉威西岛北部在地壳尺度以收缩-伸展变形为主,在岩石圈尺度以旋转变形为主。     

Water level fluctuations due to earthquakes in Koyna-Warna region,India

Earthquakes cause a variety of hydrological phenomena, including changes in the ground water levels in bore wells. The Koyna region in the peninsular shield of India, hitherto considered stable in terms of seismic activity, has been active since 1967. More recently, the earthquakes have been localized to the newly impounded Warna reservoir, which is located south of Koyna, where a burst of seismicity occurred in 1993. The region continues to remain seismically active even after four decades. Twenty-one bore wells were drilled around the seismic source volume in the region to observe water level changes resulting from earthquake phenomena. Our studies have shown coseismic anomalous water level changes to be associated with the moderate earthquakes of April 25, 1997 and February 11, 1998. Our results show that changes in the ground water level in bore wells are correlated with micro-earthquake activity, both preceding and following moderately sized earthquakes. The results have implications in enhancing our understanding of earthquake mechanisms.     

塔里木盆地深层走滑断层分段特征及对油气富集的控制:以塔北地区哈拉哈塘油田奥陶系走滑断层为例

塔里木盆地奥陶系走滑断层是发育在克拉通内部稳定区的小滑移距走滑断层,对于深部储层形成与油气富集具有重要的控制作用。基于哈拉哈塘油田4 140 km2三维地震资料,在高精度相干切片提取与地震精细解释基础上,对研究区奥陶系走滑断层进行了分段研究并讨论了分段性对于储层发育与油气富集的控制作用。结果表明：(1)哈拉哈塘油田奥陶系走滑断层整体格局为由北东、北西向断层组成的纯剪机制下形成的共轭走滑断层,单条走滑断层的构造特征符合Riedel剪切模型,主干断层周围主要发育R剪切分支断层。(2)根据走滑断层不同部位构造样式、应力状态的差异,建立了小滑移距走滑断层分段发育模式。走滑断层端部为应力发散区,多表现为马尾状构造,可分为伸展型和挤压型马尾状构造。走滑断层内部由线性段、斜列叠覆段、分支断层段、辫状构造段组合而成。线性段呈线性延伸,剖面上为孤立的高陡直立断层。斜列叠覆段分为拉张型叠覆段和挤压型叠覆段,其类型受控于次级断层旋向与阶步的关系。分支断层段多为斜交压扭样式,羽状断层发育较少。辫状构造段内部断垒与断堑交错发育,划分为张扭段、压扭段。(3)不同段具有不同的储层发育特征。马尾状构造段、斜列叠覆段、辫状构造段储层最为发育,分支断层段储层较为发育,线性段储层相对不发育。(4)综合储层发育位置、油源断裂与分支断层配置关系、局部构造高3方面因素,建立了6类与走滑断层相关的油气富集模式。R剪切分支断层与主干断层夹持部位、压扭段内部、马尾状分支断层高部位是北部潜山顺层岩溶区最为发育的3种油藏富集模式;压扭段内部、张扭段是南部断控岩溶区油气更富集的部位。论文成果认识对于完善克拉通盆地稳定区小滑移距走滑断层分段发育规律具有重要的理论意义,对于受控于走滑断层的岩溶缝洞型油气藏的勘探开发具有一定的生产指导意义。     

活动走滑断裂上断塞塘沉积特征及其构造含义

活动断裂与地震和地质灾害紧密相关,对与其相关的沉积记录进行研究可以认识其活动习性与规律。通过揭露并分析典型断裂地貌——断塞塘的沉积建造特征,能够帮助识别活动走滑断裂作用的信息。选取青藏高原东北缘的西秦岭北缘断裂带黄香沟段,利用组合探槽对沿其发育的断塞塘及其沉积进行研究,分析其沉积特征,并建立断塞沉积序列。研究发现:断塞塘沉积层序由几个沉积韵律组成,一个沉积韵律组合分为下部的粗粒层与上部的细粒层,粒度下粗上细;粗粒层一般为细砂、粗砂和砾石层,具快速堆积的特征;细粒层均为含炭的粘土、亚粘土和粉砂,具湖塘相沉积的特点。断塞沉积层序是分期的,一个沉积韵律组合是一期断塞作用沉积。分析认为,断塞沉积粗细组合的韵律性结构是断裂周期性活动的产物。这一研究是揭示走滑断裂的构造演化与活动习性,反演断裂走滑活动历史并预测其未来行为的基础。