Explore the vast range of titles available.

Fault location and geometry are the most fundamental input data in seismic hazard analysis, the ultimate aim of which is to mitigate damage from future large earthquakes. In regions prone to large earthquakes or where cumulative deformation by multiple earthquake events are well expressed in the landscape, fault models are constructed primarily by (1) identifying active fault traces, mapped mostly by the surface ruptures associated with large earthquakes; (2) simplifying fault traces while capturing their geometrical characteristics; and (3) segmenting the simplified geometry, given that a single earthquake does not always rupture the entire length of a fault system. In slowly deforming regions, however, the construction of fault models is challenging, even though geologic records of large earthquakes exist, because of the lack of clear active fault traces. Indeed, surface-rupturing earthquakes may not be part of the historical periods owing to their long recurrence time of thousands of years or more. Nevertheless, seismic hazard analysis is required for densely populated and industrial areas in slowly deforming regions, such as South Korea. On the basis of criteria established previously for determining segmentation geometry in fault models, here we propose a methodology for identifying the segmentation geometry of strike-slip fault systems in slowly deforming regions. In terms of the criteria used to identify segment boundaries, we examine along-fault variations not only in fault geometry but also in fault-surrounding lithology and fault-related geomorphic features. We test the methodology for assessing the fault segmentation geometry in a case study of the Yangsan Fault, which is one of the most active seismogenic strike-slip faults on the Korean Peninsula. Results show that the ∼200 km length of the Yangsan Fault on land consists of 12 to 15 distinct fault segments. We discuss how models of fault segmentation geometry are able to improve seismic hazard analysis in regions that have not experienced surface-faulting earthquakes in historical period.

Siliceous minerals with the property of resistance to diagenetic alteration precipitate during the migration of hydrothermal fluids through strike-slip faults and the interaction of these fluids with host rocks during fault activity. Based on petrological analyses and U-Pb dating of siliceous minerals, the stages of strike-slip faulting of the ultra-deep-burial Ordovician in the Fuman oilfield were subdivided and their evolutionary process was discussed in combination with seismic interpretation. The results reveal the following: (1) the strike-slip faults contain hydrothermal siliceous minerals, including cryptocrystalline silica, crystalline silica, and radial silica. (2) Based on the twelve U-Pb ages of siliceous minerals (ranging from 458 ± 78 Ma to 174 ± 35 Ma) and five U-Pb ages of calcite, the activity of the strike-slip faults was divided into six stages: the Middle Caledonian, Late Caledonian, Early Hercynian, Middle Hercynian, Late Hercynian, and Yanshanian, corresponding to twelve siliceous U-Pb ages ranging from 458 ± 78 Ma to 174 ± 35 Ma, and five calcitic U-Pb ages. The Late Caledonian and Early Hercynian were the main periods of strike-slip fault activity, while the Late Hercynian period marked the final period of the fault system. (3) Later-stage faults inherited and developed from pre-existing faults. Steep linear strike-slip faults formed during the Middle and Late Caledonian movements. During the Late Hercynian and Yanshanian movements, mid-shallow faults, branch faults, and shallow echelon faults developed on the foundation of these linear faults. The methods and results of this study can guide future hydrocarbon exploration in the Fuman oilfield and can be applied to areas with similar tectonic backgrounds.

Strike-slip faults and their associated fractures in the ultra-deep marine carbonate reservoirs of the Fuman Oilfield, Tarim Basin, hold significant petroleum geological importance, with the developmental characteristics of fractures being a key factor controlling reservoir productivity. This study targets the FI17 strike-slip fault zone within the oilfield, where a comprehensive evaluation of fracture effectiveness was performed by integrating geological methods, including core and thin section observation, fluid inclusion thermometry, geophysical fracture identification approaches using imaging logging and seismic data, and geomechanical simulations. The results showed that: (1) structural fractures were developed in at least three stages, predominantly high-angle fractures with their strikes obliquely intersecting the main fault at a small angle, and were affected by multiple episodes of fluid activity, while early-phase fractures exhibited severe filling whereas late-phase fractures had good effectiveness; (2) ultra-deep carbonate rocks contained well-developed stylolites, with extensive horizontal stylolites reducing fracture effectiveness; (3) mechanical effectiveness evaluation parameters were proposed by integrating normal stress, shear stress, and formation pressure, with slip tendency as the dominant indicator, and referenced to the leakage factor and dilation tendency to characterize fracture effectiveness; (4) dynamic effectiveness was assessed using closure/opening pressures, defining a reasonable formation pressure range for hydrocarbon exploitation. The findings of this study can provide theoretical guidance for the further exploration and development of ultra-deep reservoirs in the Fuman Oilfield.

Inversions of interseismic geodetic surface velocities often cannot uniquely resolve the three‐dimensional slip‐rate distribution along closely spaced faults. Microseismic focal mechanisms reveal stress information at depth and may provide additional constraints for inversions that estimate slip rates. Here, we present a new inverse approach that utilizes both surface velocities and subsurface stressing‐rate tensors to constrain interseismic slip rates and activity of closely spaced faults. We assess the ability of the inverse approach to recover slip rate distributions from stressing‐rate tensors and surface velocities generated by two forward models: (a) a single strike‐slip fault model and (b) a complex southern San Andreas fault system (SAFS) model. The single fault model inversions reveal that a sparse array of regularly spaced stressing‐rate tensors can recover the forward model slip distribution better than surface velocity inversions alone. Because focal mechanism inversions currently provide normalized deviatoric stress tensors, we perform inversions for slip rate using full, deviatoric or normalized deviatoric forward‐model‐generated stressing‐rate tensors to assess the impact of removing stress magnitude from the constraining data. All the inversions, except for those that use normalized deviatoric stressing‐rate tensors, recover the forward model slip‐rate distribution well, even for the SAFS model. Jointly inverting stressing rate and velocity data best recovers the forward model slip‐rate distribution and may improve estimates of interseismic deep slip rates in regions of complex faulting, such as the southern SAFS; however, successful inversions of crustal data will require methods to estimate stressing‐rate magnitudes. Key Points Joint inversions of velocity and stressing‐rate data can better estimate slip rates along complex faults than individual inversions Inverting data at multiple depths can better estimate fault locking depth than inverting data at a single depth Application of the new method requires estimates of crustal deviatoric stressing‐rate tensors with magnitude

Trenched pipelines may experience significant lateral displacement due to natural geohazards such as strike slip-fault movements, landslides, etc. Using pre-excavated soil to backfill trenches is a cost-effective option to protect pipelines against large deformations. These backfilling materials are heavily remolded and therefore softer than the native ground. Therefore, the shear strength difference between the backfill and native ground may affect the pipeline–backfill–trench interaction and the failure mechanism of the surrounding soil. By assuming a simplified uniform soil domain, the influence of softer pre-excavated backfilling material on the pipeline–backfill–trench interaction is neglected in the analytical methods that are usually used in the structural health monitoring of buried pipelines. In this study, the effects of trenching and backfilling were incorporated into an analytical solution for a fast assessment of the pipeline response at the early stages of engineering design projects and structural health monitoring. In comparison with other methods, this methodology provides a convenient and efficient method for computing pipeline strain and deflection curves in geohazardous regions.

The southeastern Tibetan Plateau has undergone complex deformation due to the India‐Eurasia collision. Although late‐stage internal rotations are documented in the Lanping‐Simao Terrane to the south, it remains unclear whether similar processes have affected the north. This study presents new paleomagnetic data from Eocene red beds in Baizha of the northern region. Fourteen sites yield primary ChRMs, with mean of Ds = 51.6°, Is = +33.3° (k = 28.2, α95 = 7.6°), suggesting a ∼40° clockwise rotation occurred after the late Eocene. This rotation includes both a regional oroclinal bending component and an additional local rotation. We interpret the local rotation as resulting from early Miocene left‐lateral motion on the Lancang and Ganzi‐Yushu faults. Combined with existing evidence, our findings support a three‐stage Cenozoic tectonic evolution for the southeastern Tibetan Plateau and further suggest that the distributed strike‐slip faulting and widespread local rotations since the early Miocene were facilitated by pincer‐like convergence between the Chuandian and Burma terranes.

The MW(moment magnitude) 7.9 Denali fault earthquake on 3 November 2002 was associated with 340 kilometers of surface rupture and was the largest strike-slip earthquake in North America in almost 150 years. It illuminates earthquake mechanics and hazards of large strike-slip faults. It began with thrusting on the previously unrecognized Susitna Glacier fault, continued with right-slip on the Denali fault, then took a right step and continued with right-slip on the Totschunda fault. There is good correlation between geologically observed and geophysically inferred moment release. The earthquake produced unusually strong distal effects in the rupture propagation direction, including triggered seismicity.

Strike‐slip faults act as landscape change agents, offsetting rivers, driving river capture, and generating hillslope responses. In this study, inspired by the hyperarid Atacama Fault System in Chile, we use numerical models to investigate how landscapes that experience oscillatory dry and humid periods respond to strike‐slip faulting at variable slip rates. Our results show that riverbed aggradation from hillslope sediment flux during dry periods delays stream capture, increases deflection angles of fault‐crossing channels, and produces highly perturbed longitudinal river profiles. In some cases, these phenomena, as well as the thickness of aggraded sediment, are slip‐rate dependent. Lags in capture timing and/or fully missed captures that occur in landscapes with climatic oscillation have a profound impact on the long‐term evolution of strike‐slip landscapes. Our work also highlights the importance of hillslope contributions to landscape modification in arid and semi‐arid settings with ephemeral rivers.

Considering the influence of active faults on an in-situ stress field is of great significance in guiding the construction of tunnel engineering projects crossing active fault zones. Because the traditional multiple linear regression method violates the linear superposition principle concerning unified boundary conditions, a multiple linear regression method with improved boundary conditions for in-situ stress inversion was proposed. However, since the two multiple linear regression methods cannot restore the in-situ stress field, the nonlinear method was proposed to solve the nonlinear problem caused by the irregular ground surface. After obtaining the in-situ stress field of a tunnel in southwest China, the disturbance law of the strike-slip activity of the fault on the in-situ stress field was assessed. The results showed that the inversion accuracy from high to low was the nonlinear fitting method, the multiple linear regression method with improved boundary conditions, and the traditional multiple linear regression method. Their inversion errors were 14.7%, 18.4%, and 19.4%, respectively. The in-situ stress showed a slight upward trend near the fault area and a sudden drop while entering the fault, with an average decrease of 36.3%. Inside the fault, the orientation of the in-situ stress was deflected toward the fault tendency. For sudden strike-slip activity, the in-situ stress was manifested as the stress release outside the fault region with an average decrease of 8.4%. In comparison, the stress inside the fault region tended to increase with an average increase of 11.8%. For continuous strike-slip activity, the in-situ stress was basically unchanged. In addition, the strike-slip activity of the fault caused the in-situ stress to be deflected toward the strike-slip direction.HighlightsA multiple linear regression method with unified displacement boundary conditions is proposed to improve the in-situ stress inversion accuracy.The nonlinear problem caused by the irregular ground surface in in-situ stress inversion is assessed.The distribution characteristics of the in-situ stress field near the fault strata are analyzed.The disturbance law of the sudden strike-slip activity and continuous strike-slip activity on the in-situ stress field is investigated.

Over the past few years, there has been an increased focus on offshore pipeline safety due to the development of offshore oil and gas resources. Both onshore and offshore pipelines may face significant geological hazards resulting from active faults. Pre-excavated soil can be used as backfill for trenches to prevent major pipeline deformations. Since these backfill materials have been heavily remolded, they are softer than the native soil. Therefore, the difference in shear strength between the backfill and native ground may have an effect on the interaction between the pipeline and the backfill. In this paper, the pipeline–backfill–trench interaction is investigated using a hybrid beam–spring model. The P-Y curves obtained from CEL analysis are incorporated into a 3D beam–spring model to analyze the pipeline’s response to lateral strike-slip faults. Additionally, the nonlinearity of pipeline materials is considered to study pipeline failure modes under strike-slip fault movements. A series of parametric studies were conducted to explore the effects of fault intersection angle, pipe diameter, buried depth of the pipe, and soil conditions on the failure modes of buckling pipelines. The developed method can be used to analyze and assess pipeline–backfill–trench interaction when subjected to strike-slip fault displacements.