Dominant Fault Research Articles

Fault tracing in multistage gearbox systems based on an improved transfer path analysis method

This study, has developed a novel structural dynamics decoupling method based on TPA. This approach effectively facilitates fault diagnosis and tracing in multistage gearbox systems. Initially, the research explores the relationship between the transfer function of systems with rigid link decoupling and the coupled system’s frequency response function. Compared with Huangfu et al. (2023) , the signal measurement points are reduced. The MWI (Yu et al., 2023) is employed to solve the inverse problem of bearing force identification. Subsequently, the decoupled frequency response and bearing forces are multiplied to calculate the path contribution, determining the dominant fault transfer path and thereby facilitating fault tracing in gearboxes. The effectiveness of this method is validated through numerical simulations and experimental studies, with fault characteristic enhancement exceeding 200%. To evaluate the method’s universality and robustness, experiments on diverse gearbox systems under varying conditions show enhanced fault characteristics across three fault types, confirming its generalizability.

Multiscale discrete fracture network modelling of shallow-water carbonates: East Agri Valley Basin, Southern Italy

We investigate the multiscale geometrical and dimensional properties of fracture and fault networks crosscutting Lower Jurassic to Cretaceous shallow-water carbonate rocks. The carbonates are exposed along the flanks of the Viggiano Mt., on the eastern side of the High Agri Valley Basin of southern Italy. Furthermore, we employ the results of field and digital structural analyses to derive the input parameters for subsequent Discrete Fracture Network modelling (DFN) of geocellular volumes whose dimension and architecture resemble those of the investigated sites. DFN modelling is carried out for geocellular volumes representing the studied bed packages (5m-side volumes), outcrops (50m-side volumes), and reservoir-scale carbonate cliffs (500m-side volumes). Notably, modelling is obtained considering the minimum mechanical aperture value obtained in the field for porosity computations and theoretical values of fracture hydraulic aperture for permeability computations. This is because the mechanical aperture values and roughness profiles collected in the field along single fractures are unreliable due to weathering and localized karst-related dissolution. Our findings reveal that a scale-dependent geometry characterizes the Cretaceous carbonates over three orders of magnitude. These results support previously published data, and contrast with those obtained for the Lower Jurassic carbonates, which suffer of some bias due to the quality of the exposures. After DFN modelling, we show that the amount of computed fracture porosity is mainly due to the SB and NSB fractures, and that equivalent permeability is greater within faulted rock volumes. In terms of horizontal permeability, which is the most reliable result after DFN modelling, we document near isotropic horizontal permeability ellipses at all scales of observations. At individual outcrops, we note that the permeability ellipses are elongated parallel to the dominant fault sets that denotes how localized strain affects the directionality of fluid flow. Finally, we summarize the original data in a conceptual model illustrating the modalities of meteoric fluid infiltration through the vadose zone, and then subsequent horizontal flow in the phreatic zone present within the fracture carbonates at shallow depths.

Integrative mapping of radioactive and alteration zones in Um Had plutons, Egypt: Using Landsat 9, ASTER imagery, and airborne geophysical data

The study aims to assess the effectiveness of using ASTER, Landsat 9, and airborne geophysical data to generate maps depicting hydrothermally altered regions and their correlation with radioactive-mineralized zones in Egypt's Um Had area. Various image processing methods were applied, including color composite images, band ratios, selective principal component analyses, and lineament extraction with enhancement procedures. The ASTER ratios identified the three types of hydrothermal alterations; phyllic, argillic, and propylitic, with other significant alteration zones related to mineralization. Airborne gamma-ray spectrometry contour maps displayed marked varied levels of total count (T.C), eU, eTh, and K, ranging from 1.2 to 21.2 Ur, 0.5–12.34 ppm, 1.45–28 ppm, and 0.13–3.65 %, respectively. The highest anomalies of these radioelements concentration have coincided with the alkali feldspar granite and along their intrusive contact zone with the Hammamat Group sedimentary rocks. Higher anomalies are well recorded in the center and eastern regions of Um Had's, according to the radioelements composite image. The lowest concentrations of these radioelements are associated with gneiss, ophiolitic mélange, metavolcanic, Hammamat Group sedimentary rocks, Taref Formation, and Wadi sediments. To mitigate local magnetic effects, the total aeromagnetic data was reduced to the north magnetic pole (RTP). Power spectrum analysis of the RTP data identified distinct magnetic wavelengths for regional-residual components. In order to identify near-surface magnetic lineaments, such as contacts, shear zones, faults, and dykes, advanced algorithms were applied to the RTP data. The lineaments derived from ASTER and airborne magnetic data revealed dominant fault systems characterized by E–W, NE, NNW, NW and N–S trends, governing the structural framework of the study area. Depth levels of geological contacts and faults that represented pathways for altered and mineralized zones reached more than 1200 m (Euler deconvolution). These findings highlight the consistent results obtained when combining ASTER data with airborne survey data, allowing for the identification of hydrothermally altered zones and primary conductive zones.

Investigation of the Dominant Direction of the Fault Structure Using the Radon Method at Mt. Pancar Geothermal Field

The Mt. Pancar geothermal field in Bogor, Indonesia, has been surveyed for radon in soil gas. There were 33 measurement points across the survey area that were separated by 100-200 meters. Through the radon method, this study aims to show the direction of the dominant fault structure based on the distribution of radon values in around observation area. The Radon concentration was measured by RAD 7 Electronic Radon Detector Durridge Company. The study showed the dominant structure was directed southwest-northeast, passing through the manifestation of the red crater. The result of radon soil gas survey performed highest radon concentration near the manifestations which was included survey area was about 10047 Bq⁄m^3. The manifestation was predicted to be controlled by the three faults in the Mt. Pancar geothermal field.

Machine Learning Based Open Switch Fault Detection and Localization of Inverters

The location and detection of switch faults is a crucial step in improving the dependability of inverters, which is a requirement for critical applications. This paper focuses on a machine learning-based approach for the open-switch fault detection system for cascaded H-bridge (CHB) multilevel inverters (MLI) used in high- and medium-power applications. Each switch failure is taken into account in this analysis, and the problem is used to model logically different machine learning algorithms, namely Gaussian Naive Bayes (GNB), support vector machines (SVM) and multinomial logistic regression (MLR) models for fault identification and localization based on multi-class classification (MCC) methods. This work includes the simulation and hardware-based data collection from five-level CHB-MLI and correlation-based selection of prominent features in the final dataset. The results of three MCC models for all possible combinations of predictors (features) prove that the mean voltage of bridges is the dominant feature for fault detection in the CHB inverter. Other major findings are machine learning-assisted fault identification and diagnosis is undoubtedly accurate and significantly more promising in condition monitoring and fault diagnosis in CHB-MLIs. The results reveal 100% accuracy in fault diagnosis. Therefore, the presented work confirms switch fault detection in CHB-MLI with mean value as dominant fault feature along with machine learning techniques simple, robust and accurate fault detection.

Petrogenesis of high heat producing granites and their contribution to geothermal resource in the Huangshadong geothermal field, South China

The Huangshadong geothermal field (HGF), situated in the contact zone between Mesozoic granites and NE-striking dominant faults in South China, has great geothermal potential. Petrogenesis of reservoir rock plays an important role in understandings its genetic mechanism and assessing geothermal potential. However, due to the lack of rock sample at depth collected from the geothermal reservoir, the petrogenesis of granites in the geothermal reservoirs of the HGF, remains an enigma. This study elucidated the petrogenetic characteristics of these granites sampled directly from geothermal reservoir at the depth of ∼3,000 km and their geothermal implications through zircon U-Pb dating, geochemical analysis, and Hf isotopic analysis. The zircon U-Pb ages indicate that the magmatism evolution of HGF contains three eras, namely, Cretaceous (135 ± 4 to 143.6 ± 2.8 Ma), Jurassic (152.7 ± 2.7 to 176.7 ± 1.8 Ma), and Permian granites (251 ± 9.1 to 251 ± 5 Ma) from the youngest to oldest. The reservoir granites were emplaced during the latest stage of Cretaceous intrusion, as indicated by the zircon U-Pb ages (135 ± 4 Ma and 135.3 ± 2.4 Ma) of rock samples from the deep part of well HR-1. These Cretaceous rocks are highly fractionated I-type granites, featuring high SiO2, K2O, and Na2O contents, high Rb/Sr ratios, low Zr/Hf, Nb/Ta, and Th/U ratios, and A/CNK values of 1.05–1.13. Compared to other Cretaceous granites outcropping on the margin of the HGF, these granites have undergone the strongest fractional differentiation. The Cretaceous granites in the HGF are high-heat-producing rocks (>5 μW/m3), with an average heat production rate of 6.63 μW/m3. Notably, the Cretaceous reservoir granites (as reservoir rocks) serve as an important heat source for the formation of geothermal resources in the HGF. In addition, the zircon Hf isotopic composition indicates that the reservoir Cretaceous granites originated from Meso-to Paleo-Proterozoic lower crustal materials (TDM2: 1,385 to 1907 Ma).

Control of décollement strength and dip on fault vergence in fold-thrust belts and accretionary prisms

Fault vergence in fold-and-thrust belts and accretionary prisms is characterized by mainly forward verging thrusts and pop-up structures, and only few examples exist where backthrusting dominates. However, backthrusting and triangle zones are known from most if not all fold-thrust belts in the world. The circumstances under which backthrusts instead of forethrusts form are still incompletely understood. Previous studies suggest that the strength and dip of the basal décollement of Coulomb wedges plays a key role. However, a systematic study of these parameters is still missing. In this study we model numerically the formation of brittle-ductile wedges, systematically, varying dip and strength of the basal décollement. To characterize wedges, we use cumulative vorticity as a measure of dominant fault vergence within the entire wedge. We find that backthrust-dominated wedges form in setups of very low basal dip (≤ 0.5°) and a weak décollement. Increasing décollement strength or basal dip results in the formation of pop-up-dominated wedges, before forethrust dominated wedges form. While our models corroborate the idea that thrust vergence and basal dip may control thrust vergence, comparison with natural examples indicates this cannot be the only explanation for the formation of backthrusts. Consequently, additional factors such as syntectonic sedimentation or changes of décollement rheology across strike may be required to explain backthrusting in fold-thrust belts.

Geometry and evolution of polygonal fault systems under a regionally anisotropic stress field: Insights from 3D seismic analysis of the Qiongdongnan Basin, NW South China Sea

AbstractPolygonal fault systems (PFS) are developed in many sedimentary basins, and their formation, growth, and ultimate geometry have been widely studied. The geometry and growth of PFS forming under the influence of regionally anisotropic stresses, however, are poorly understood, despite the fact these structures may serve as key paleo‐stress indicators that can help reconstruct the tectonic and stress history of their host basins. We here use high‐quality 3D seismic reflection data and quantitative fault analysis to determine the geometry and evolution of a PFS in the Qiongdongnan Basin (NW South China Sea), and its possible relationship with the geological and stress history of the basin. The PFS is dominated by two intersecting NNW‐to‐N‐ and E‐striking fault sets, which initiated in the Early Miocene. The dominant fault strike at the structural level at which the faults nucleated and where strain is greatest (i.e., Lower Miocene) is close to NW–SE. However, at the top and bottom of the PFS tier faults strike NNW–SSE, thereby defining a very slight vertical, clockwise rotation of strike. Based on the observation that the host rock is flat‐lying, it is unlikely that basin‐tilting perturbed (i.e., δ2 ≠ δ3) the otherwise radially isotropic stress field that typically characterize PFS. Likewise, diapirs that punctuate the host rock and that are spatially related to the PFS appear not to control fault geometry. We instead infer that the PFS geometry reflects a combination of local isotropic and regional, extension‐related tectonics stress affecting the Qiongdongnan Basin during the Early Oligocene to Middle Miocene. Regional studies suggest that during this time, extensional stresses in eastern Qiongdongnan Basin rotated clockwise from roughly NNW to N; we noticed the rotation of strike of the PFS, within which the vertical change in fault strike being relatively minor. Our study determines the timing of polygonal fault growth within the Qiongdongnan Basin and the associated geometry, highlighting the key role played by regional and local stresses.

Platform-to-Basin Evolution of a Tectonically Indistinct Part of a Multiple Foreland—Analysis of a 3D Seismic Block in the Northern Adriatic Sea (Croatian Offshore)

The Aiza research area covers over 650 km2 of the northern Adriatic offshore, a common Adriatic foreland of the older Dinarides on the NE, and the younger Apennines on the SW. High-quality 3D reflection seismic data were used to investigate the area’s Mesozoic to Cenozoic tectono-stratigraphic evolution. Four main seismo-stratigraphical horizons were recognized: Base of Carbonate Platform (BCP), Top of Carbonate Platform (TCP), Messinian Erosional Surface (MES), and a Plio-Quaternary horizon (PlQh), as well as the dominant faults. The results depict the geological setting and tectonic evolution of the area. A long-lasting (Jurassic to Cretaceous) stable NW-SE striking platform margin evolved probably along the inherited Triassic normal fault. The marginal belt of the platform was affected during the Late Cretaceous to Palaeogene by extension and opening of the intra-platform basin, probably on the southern limb of the then developing Dinaric forebulge. The transverse fault system (Kvarner fault) was probably reactivated as a strike-slip zone during the late Miocene tectonic reorganization. The area was tilted to the SW during the Pliocene, in the distal foreland of the progressively northward propagating Northern Apennines. Sub-horizontal late Quaternary cover of Dinaric and Apenninic structures could imply active subsidence of the foreland in between nowadays sub-vertically exhuming neighboring orogenic belts.

Evaluation of Natural Gas Hydrate Fault System: A Case from a Sag in Deep-Water Slope Area of the Northern South China Sea

AbstractThe fault system is one of the structural carrier systems of gas hydrate accumulation, which plays a vital role in controlling the distribution of natural gas hydrate (NGH) accumulation. The previous studies mainly focus on summarizing the vertical migration mode of high flux fluid along the fault with obvious geophysical response characteristics on the seismic profile, such as “fault with gas chimney,” “fault with mud diapir,” and “fault with submarine collapse”, but lack of evaluation methods for the fault carrier system. We use the X sag in the deep-water continental margin slope area of the northern South China Sea as an example to study the fault systems closely related to NGH. This paper puts to use attribute technologies, such as coherence, curvature, and fusion, to analyze the characteristics and combination of the fault systems. We discussed migration patterns and evaluation methods of dominant fault carrier systems. This research proves that the strike-slip fault system in the platform area can directly connect the gas source bed with high-quality hydrocarbon generation to the gas hydrate stability zone (GHSZ). The activity of this fault system is more conducive to the accumulation of hydrocarbon in the GHSZ. This area has a good site for pore-filling gas hydrate prospecting and a preferential favorable fault carrier system. The composite fault system, consisting of a normal dip-slip fault system and a polygonal fault system, in the slope area can jointly communicate the biogenic gas-rich reservoir. Its activity and well-migration performance are the main reasons for the submarine gas leakage and collapse. It is a secondary favorable fault carrier system in the study area. There may be massive and vein natural gas hydrate formation in fractures in the leakage passage, and pore-filled gas hydrate may exist in the submarine nonleakage area. In this work, a three-factor evaluation method of the fault carrier system is proposed for the first time. This method is of great significance for the evaluation and exploration of NGH reservoirs in the continental margin slope area of the northern South China Sea.

GPS and InSAR derived evidences of intra‐basin stress and strike‐slip tectonics in the vicinity of 2001 (M7.7) earthquake, Kachchh, western India

The current geodetic investigation is based on nearly a decade of continuous Global Positioning System (GPS) data towards the western part of the Indian Plate (2009–2019). This research focused on the Kachchh Rift Basin (KRB), the seismically most active intra‐plate region of the Indian Plate, which has seen three ≥ M 7.0 earthquakes in the last two centuries. The GPS stations on the northern and southern margins show SSW and NNE directed motion, indicating that the KRB is currently under the influence of regional compressive stress on both flanks and the same is reflected in the form of earthquake activity in the center portion. Furthermore, the existence of intra‐basin stress, in addition to regional stress, increases strain accumulation and results in the creation of a Principal Deformation Zone (PDZ) in the central part of the KRB. The average annual deformation in the middle of KRB remains 1.0 ± 0.5 mm/year, while sites near the South Wagad Fault (SWF) experience 1.2 mm/year of fault parallel motion. The dominant fault normal motion along the flanks with a maximum fault parallel motion in the middle intimates the existence of strike‐slip tectonics in the central Kachchh. The geometric relationship of strike‐slip faults in a compressive margin and strain accumulation in pre‐existing faults (PDZ) is responsible for current strike‐slip and thrust motion in the Kachchh, including the 2001 Bhuj earthquake (M 7.7). Our geodetic model is well‐corroborated with the geological observations of the wrench fault model of strike‐slip faults. PS‐InSAR results in the northern part of the region between Khadir and Bela Islands show ≤6.0 mm of annual LOS displacement. GPS results indicate ≈ 1.3 to 1.4 ± 0.5 mm/year of fault parallel motion along the transverse Ekal Amrapar Fault (EAF). The non‐significant variation in GRACE‐derived TWS values (from 2009 to 2018) rules out non‐tectonic deformation in the vicinity of EAF and thus points to tectonic activity as the cause of the derived deformation in the region.

Data-Driven Optimization of Transmission Section Limits and Their Adaptability for New Power Systems With High Penetration of Renewable Energy

In traditional power systems, the transmission section limits are often set to predetermined values according to the typical peak-to-valley demand modes, which may be difficult to adapt to the complex and diverse operation modes of the new power systems with high penetration of renewable energy, and it cannot consider the coupling characteristics of AC and DC transmission sections also. In order to make better use of the efficiency of the transmission sections, a mathematical model for optimizing the adaptability of the transmission section limit is firstly proposed, in which a data-driven typical demand mode extraction method based on K-means clustering is proposed according to the load forecast, renewable energy forecast and market transaction data. Then, the adaptability assessment of the section limit and the transmission requirements are carried out. Finally, the power perturbation method is used to calculate the influence factor matrix of associated transmission section limit and stability margin of its dominant fault. And the influence factors are optimized according to section limit adaptability and stability margin influence, and the best adaptable limit of the associated transmission sections are obtained. The calculation and optimization results of the actual case of the interconnection corridor between Xinjiang and the northwest main power system of China verify the effectiveness and practicability of the proposed limit optimization model, which is able to improve the flexibility and adaptability of the actual power system operation.

Influence of a Dominant Fault on the Deformation and Failure Mode of Anti-dip Layered Rock Slopes

Toppling is a kind of failure mode that commonly exists in anti-dip rock slopes. Toppling deformation has a great influence on the stability of rock slopes, which often leads to geological disasters such as sliding and collapse of anti-dip slopes. However, a large number of faults and other structural planes will be produced in many rock slopes due to the action of geological structure movement. In the investigation, it is found that there are not only toppling deformation, but also faults and other geological structures in the toppling deformation rock slope. Previous studies have calculated the depth of toppling deformation, which is considered from the development characteristics of toppling deformation itself. In this paper, based on the field investigation of the anti-dip rock slope with bedding faults, the relationship between the depth of toppling deformation and the location of faults is analyzed by three-dimensional discrete element method. When the dominant structural plane and toppling fracture surface exist at the same time, the main factors affecting the failure of the reverse dip rock slope can be obtained by determining the different depths of the two planes. The final failure depth and failure mode of the toppling deformation in an anti-dip rock slope with a dominant structural plane can be preliminarily determined.

Controlling effect of tectonic-paleogeomorphology on deposition in the south of Lufeng sag, Pearl River Mouth Basin

Paleogene depositional systems in the south of Lufeng sag have complex spatial distribution, which are influenced by pre-depositional paleogeomorphology and multi-period tectonic activities. In this paper, to clarify the controlling effect of tectonic-paleogeomorphology on sedimentary facies distribution and effectively guide oil and gas exploration, the Paleogene paleogeomorphic pattern in the south of Lufeng sag is reconstructed by the impression method, and the temporal and spatial evolution laws of the main faults are clarified. The results show that braided river deltas developed stably in the long-axis gentle slope belt of the lake basin, while the short-axis sedimentary system changed from fan deltas to braided river deltas in response to the change of active strength of dominant faults from strong to weak. It is found that the scale of the sedimentary fan is closely related to the activity of the main fault, the area of the catchment, and the vertical elevation difference. The steep cliff is controlled by the boundary fault with large fault throw and steep section, and there are wedge-shaped sand bodies near the steep cliff. The multi-level fault-step zone provides the driving force for the advancement of the sedimentary system, and the sand body extends for a long distance. It is established that the supply capacity of the source area and the accommodated space of the lake basin are coupled to control the deposition scale. Moreover, the slope controlled by the combination of paleogeomorphic assemblage and the activity of the main fault determines the sedimentary type, and the structural slope-break zone defines the spreading pattern of the sands. Cited as : Jiang, M., Chen, D., Chang, X., Shu, L., Wang, F. Controlling effect of tectonic-paleogeomorphology on deposition in the south of Lufeng sag, Pearl River Mouth Basin. Advances in Geo-Energy Research, 2022, 6(5): 363-374. https://doi.org/10.46690/ager.2022.05.02

Multi-Method Geophysical Mapping of a Geothermal Reservoir and Buried Channel in Langfang, Northern Part of China

Geothermal resources are a clean and renewable energy source that can play a critical role in drastically reducing air pollution. The utilization of geothermal resources requires technical support to decrease the developing risk by applying an integrated interpretation of geophysical methods. In this study, we used geophysical methods in the Langfang region of China to design a workflow for the safe yield of geothermal resources. To do so, we conducted controlled-source audio-frequency magnetotelluric (CSAMT) soundings, shallow soil temperature surveys, radon gas measurements, and the microtremor survey method (MSM) at the geothermal exploration and development site. These geophysical analyses identified a geothermal reservoir and a buried channel in the region. The dominant fault developing in the area was identified as the best channel for heat and water based on the developed geothermal wells. In areas with relatively little geothermal exploration, this study provides a reference and demonstration for geothermal development.

Integrated Fracture Characterization of Thamama Reservoirs in Abu Dhabi Oil Field, United Arab Emirates

Summary Volumetric maximum curvature attribute computed from 3D ocean bottom cable (OBC) seismic data, production logging tool (PLT), inorganic chemical tracer data, and fractures observed from core and full-bore formation microimager (FMI) logs were integrated to characterize fractured carbonate reservoirs of an offshore oil field in Abu Dhabi, United Arab Emirates (UAE). The extracted maximum curvature anomalies are predominantly orientated in NNE-SSW and NE-SW, a trend perpendicular to the dominant fault direction in the oil field and similar to the dominant strike directions of fractures measured from core data and FMI logs. Because the fracture strike directions of well data mimic the strike directions of curvature anomalies at corresponding reservoir levels, we interpreted the maximum curvature anomalies to represent dilatational fractured zones or fracture corridors. Integration of dynamic data, such as PLT and chemical tracers, and maximum curvature anomalies demonstrate that the inferred fracture zones can determine water breakthroughs as well as inter- and intrareservoir communications. As a result, this study highlights possible fracture zones and their internal architecture, as well as their potential flow capabilities. These results play a key role in reservoir management and monitoring of water movement through structural pathways.

Effects of Salt Thickness on the Structural Deformation of Foreland Fold-and-Thrust Belt in the Kuqa Depression, Tarim Basin: Insights From Discrete Element Models

The salt layer is critical for the structural deformation in the salt-bearing fold-and-thrust system, which not only acts as the efficient décollement layer but also flows to form salt tectonics. Kuqa Depression has a well-preserved thin-skinned fold-and-thrust system with the salt layer as the décollement. To investigate the effects of salt thickness on the structural deformation in the Kuqa Depression, three discrete element models with different salt thicknesses were constructed. The experiment without salt was controlled by several basal décollement dominant faults, forming several imbricate sheets. The experiments with salt developed the decoupled deformation with the salt layer as the upper décollement (subsalt, intrasalt, and suprasalt), significantly similar to the Kuqa Depression along the northern margin of Tarim Basin. Basal décollement dominant imbricated thrusts formed at the subsalt units, while the monoclinal structure formed at the suprasalt units. The decoupled deformation was also observed in the tectonic deformation graphics, distortional strain fields, and max shear stress fields. However, the salt layer was thickened in the thick salt model, and the salt thickness of the thin salt model varied slightly because the thin salt weakened the flowability of the salt. The lower max shear stress zone was easily formed in the distribution region of salt under the action of compression stress, which is conducive to the flow convergence of salt and the crumpled deformation of interlayer in salt. The results are well consistent with the natural characteristics of structural deformation in the Kuqa Depression. Our modeling result concerns the structural characteristics and evolution of salt-related structures and the effects of salt thickness on the structural deformation in the compressional stress field, which might be helpful for the investigations of salt-related structures in other salt-bearing fold-and-thrust belts.

An integrated critical approach to off-fault strike-slip motion triggered by the 2011 Van mainshock (Mw 7.1), Eastern Anatolia (Turkey): New stress field constraints on subcrustal deformation

In this study, we retrieved the finite source characteristics of the October 23, 2011 Van earthquake (Mw 7.1) using the teleseismic waveforms to focus on the source location. The outstanding off-fault aftershock sequence of the Van mainshock was readily explained by calculating the Coulomb stress changes imparted to the surrounding crust. This may be accomplished through finite source modelling to examine the stress interaction between the fault, ruptured by the Van mainshock, and the surrounding fault(s) triggered by the same mainshock. In addition, to provide further support for the Coulomb failure stress changes in the off-fault area, centroid moment tensor (CMT) inversion of the off-fault aftershocks was performed and stress tensors were derived from their focal solutions. This identified the dominant fault slip, the constraints of the crustal stress fields and illuminated the crustal nature of the stress interaction. The off-fault aftershocks showed a strike-slip stress regime in rotational (to NW) and non-rotational (to N) stress fields of the upper and lower crusts, respectively. However, this was inconsistent with a horizontal compressional stress direction striking to the north. This suggests that a local source and/or rotation of lateral variation in stress magnitudes in crustal and sub-crustal structures strongly perturbed the regional stress field. It was also evident that these strike-slip aftershocks increased the intensity of stress in an off-fault area, NE of the source rupture. This revealed a uniquely triggered strike-slip motion, activated and rooted in the weak lower crust. We conclude that the Van mainshock rupture source area, associated with the stress changes imparted to the surrounding crust, had undergone anomalous modifications to generate distinctive off-fault aftershock responses in the entire crust, and also triggered and loaded the weak lower crust. We hypothesize that the strike-slip motion, the so called “transfer fault”, as a distinctly triggered slip event, was generated or selectively activated by subcrustal ductile processes in the absence of mantle lid beneath the study area. However, local slab fragmentation, tearing and cold mantle beneath the study area lead to paradigm changes in interpreting the strike-slip motion and subcrustal deformation. The presence of a small piece of oceanic lithosphere, consistent with fragmented, torn slab and cold mantle, may be an alternative hypothesis that remains to be tested. The Van earthquake, combined with careful examination of associated off-fault aftershocks, revealed new information about stress field constraints on subcrustal deformation. This investigation also provided insights into an important role of stress interaction, with a newly discovered transfer fault within the off-fault area, which extends through the entire crust beneath Lakes Van and Erçek areas.

New insights into the contribution of gravity data for mapping the lithospheric architecture

Amongst all the potential field methods, gravity data constitutes the frequently measured geophysical information for deep seated lithospheric structures. The present work aims to outline the structural pattern, the main basins of Sinai and the depths to both Conrad and Moho discontinuities (CMD) by utilizing the gravity data. Several basins were depicted based on high-pass filtered gravity map and much of them are in a close agreement with the former studies. Additionally, the dominant fault trends are NE, NW, EW and ENE. An empirical equation was applied to low-pass-filtered gravity data to estimate the depth of the CMD. However, the thickness of the sedimentary basins increases northwards, reaching approximately 8 km, the minimum depths of Conrad and Moho discontinuities were attained in the northern compartments to be about 18 and 31 km respectively. Meanwhile, far a way to the south, the maximum detectable depth of Conrad and Moho discontinuities are 21 and 37 km. Eventually, 2D gravity modeling was constructed and constrained by 15 drilled wells and the calculated depth of CMD to figure out the comprehensive lithospheric geometry beneath Sinai Peninsula.

Fold segment linkage and lateral propagation along the Qiulitage anticline, South Tianshan, NW China

The east-west trending Qiulitage anticline is one of the most active elements of the Kuqa fold-and-thrust belt located along the southern margin of the Tianshan Mountains. Subsurface data and the well-preserved tectonic geomorphology provide a natural laboratory for exploring the detailed spatio-temporal evolutionary processes of a “mature fold”. We present a study of fluvial/alluvial terraces which passively record the progressive deformation of active folds across the rapidly uplifting Qiulitage anticline. The vertical incision and lateral erosion rates of the Kezile river derived from 10Be exposure dating are ~1.3–2.0 mm/a and >1.3 mm/a, respectively, while those of the Bositankelake River, located near the central part of the fold, are only ~0.8 ± 0.04 mm/a and <0.8 ± 0.04 mm/a, respectively. This difference indicates that the lateral propagation rate of active fold increases gradually away from its central peak to its tip. In the meanwhile, a comprehensive analysis of stratigraphy, landforms, dominant faults at depth, and inherited drainage patterns reveal that the eastern segment of the Qiulitage anticline initially develop from the linkage of two smaller fold, i.e. the Kuqadawu anticline and the East Qiulitage anticline, and subsequently this fold assemblage has propagated eastward. Although there is an apparent topographic-relief transfer relationship between the eastern segment of the Qiulitage anticline and the adjacent Yaken anticline, a long-term spatio-temporal variation in surficial erosion may have accentuated this relationship by significantly reducing the elevation of the Qiulitage anticline near its central peak.