Thrust Faults Research Articles

Depositional Responses to the Mongol-Okhotsk Ocean Closure in the Central Area of the Great Xing’an Range: Insights into Thrust Faults and Foreland Basins

Depositional Responses to the Mongol-Okhotsk Ocean Closure in the Central Area of the Great Xing’an Range: Insights into Thrust Faults and Foreland Basins

New details on the volcanic and tectonic evolution of the Mesoarchaean Dominion Group with special reference to the Syferfontein Formation in the Ottosdal area (South Africa)

Abstract The ca. 2.96 Ga Dominion Group (DG) preserves the first subaerial volcano-sedimentary succession on the Kaapvaal Craton. Based on field and core observations, this study provides revised stratigraphic logs and geological maps from the area around Ottosdal that refine the understanding of the stratigraphic and tectonic evolution of these ancient rocks. Fluvial sandstone and conglomerate of the Rhenosterspruit Formation (RsF) were deposited on granite basement, followed by andesitic to basaltic volcanic rocks of the Rhenosterhoek Formation (RhF). These amygdaloidal andesitic to basaltic lava units show fragmentation around lava flows that may represent an indication of prevalent subaerial environment. However, local hyaloclastite and pillow lava units indicate periodic aqueous conditions. The Syferfontein Formation (SF) has the most extensive exposures in the Ottosdal area and represents the youngest volcanic unit of the DG. The porphyritic and spherulitic volcanic rocks tell a story of subaerial volcanism interspersed with periods of lacustrine deposition of sandstone and shale. The Witwatersrand Supergroup (WSG) overlies the DG along an angular unconformity. Folding affected the succession of the DG, WSG and the Ventersdorp Supergroup (Rietgat Formation). This event is reflected in small-scale folds and mullion structures in the central part of the study area and by larger scale north-northwest–south-southeast-striking anticlines and synclines. Folding was accompanied by northwest-southeast-striking thrust faulting, either during or shortly after the formation of the Ventersdorp Supergroup. In the study area, post-Ventersdorp deformation is restricted to east-northeast–west-southwest-striking faults.

Complex Multi‐Fault Dynamics in Sikkim Himalaya: New Insights From Local Earthquake Analysis

AbstractAnomalously overturned thrust faults, lineaments and segmentation causing cross‐cutting basement structures characterize the tectonic setting of Sikkim Himalaya. However, its seismotectonics is poorly constrained along with the speculated northward extension of the Dhubri‐Chungthang Fault Zone (DCFZ) causing segmentation. Here, we utilize the precise location of newly acquired local earthquake data and fault plane solutions using full‐waveform moment tensor inversion to better constrain seismically active zones. Transtensional shearing along the Main Himalayan Thrust in central Sikkim is possibly incited by fluid‐rich upper‐crust. Cessation of the mapped 20 km wide mid‐crustal seismogenic zone of DCFZ at Chungthang and its northward discontinuation into the Higher Himalayas is confirmed by the striking variation in focal mechanisms. Earthquakes along imbricated segments in the lower‐crust originate possibly in response to crustal shortening. Extensional shearing along the Moho triggers seismicity to the northwest of Sikkim. Such complex tectonic dynamics instigating persistent seismicity indicates high potential for future great earthquakes in Sikkim Himalaya.

Late Mesoproterozoic iron and manganese deposition on a deep-water carbonate platform (Penganga Group), Adilabad, India: Constraints from C, O and Sr isotopes

Abstract The Penganga Group in the Pranhita-Godavari Rift Valley of central India includes a rather unique example of Late Mesoproterozoic iron and manganese formations deposited in a deep-water below storm wave base distal carbonate platform environment. The carbonate rocks of the Penganga Group are mostly lime-mudstones that have been classified into a number of sedimentary cycles with intervals mostly distinguished by color, ranging from brown/pink and siliceous gray to steel-gray and black. At least two about one-meter-thick Mn-Fe formations occur in siliceous gray limestone of the distally steepened part of the Penganga carbonate platform. A number of northwest-southeast striking thrust faults repeat the succession in down dip sections bringing up distal profiles of the Penganga Group against proximal counterparts at the present exposure level. This contribution provides the first comprehensive record of stable C and O and radiogenic Sr isotopes for proximal and distal profiles, allowing for direct comparison and thus, providing context for the environmental conditions of Fe and Mn deposition in a Mesoproterozoic platform environment. Carbon and oxygen isotope compositions determined from the proximal and distal profiles of the platform yield trends that are attributed to variations in circulation pattern and cycles of warm and cold climatic stages across the platform. Secular trends of Sr-isotope compositions suggest a variation in continental input between cold (0.7065) and warm climatic stages (0.7149), similar to that observed for modern marine sediments. The sedimentation of siliceous deposits and ferromanganese deposits in the distal platform environment was likely favored by the onset of upwelling circulation during cold climatic stages. The moderately negative δ13CPDB values (-5.34‰ to -6.34‰) of the Mn-carbonates and variation in δ13Corg values 31.7‰ to -21.7‰ obtained for early diagenetic Mn-carbonate ovoids indicate oxidation of organic matter in the ferromanganese deposits by Mn-oxides during early diagenesis. We conclude that upwelling and platform-wide deposition of ferromanganese deposits on the Penganga carbonate platform may mark the transition from the stagnant Mid-Proterozoic ‘sulphidic’ ocean to a ‘respiring’ open ocean during the Late Mesoproterozoic Era.

Tectonic Evolution of the Proto‒Tethys in the Early Devonian: Insights From the Turbidite in the North Qilian Belt, NW China

AbstractThe Devonian tectonic setting is still controversial in the Proto‒Tethyan North Qilian belt. The Hexi Corridor of the North Qilian belt occupies a key position in constraining the tectonic evolution of the Proto‒Tethyan Ocean and the growth of the Asian continent. Turbidites, as an important component of the Jiayuguan mélange in the Hexi Corridor, consist of conglomerate, pebbly sandstone, sandstone, siltstone, calcareous mudstone, and chert that feature typical Bouma sequences of Ba, Bc, Bcd, Babc and/or Bab. They are strongly deformed into NW‒trending folds with NE‒ and SW‒inclined thrust faults. Detrital zircon U‒Pb dating results demonstrate that these sediments successively young to the southwest with maximum depositional ages (MDA) ranging from 560 Ma to 411 Ma, indicating that the youngest block was deposited after 411 Ma. Petrological, geochemical and detrital zircon U‒Pb age data indicate the sedimentary rocks provenanced from weak weathering, recycling, and multiple mixing sources, and that the dominant source was the Andean‒type Alxa arc. Together with the published data, we suggest that double‒sided subduction of the North Qilian Ocean (Proto‒Tethyan Ocean) occurred between the North Qilian arc and the Andean‒type Alxa arc during the early Devonian.

Growth of the northeastern Tibetan plateau since the Middle Miocene as revealed by syn-tectonic growth strata

Syn-tectonic deposition of sediments (growth strata) preserves a direct record of mountain building-erosion and basin deformation. When and how these sediments incorporated into forward propagating fold-and-thrust (FTB) belts can shed light on the above processes. Despite many years of research, there is still ongoing debate about the timing and mechanisms of the southern Qaidam fold-and-thrust belt in the northeastern Tibetan Plateau. Here, we provide insight into the deformation of the Qaidam Basin and the broader tectonic processes of the northeastern Tibetan Plateau through detailed analysis of the Dafengshan (DFS), Jiandingshan (JDS) and Heiliangzi (HLZ) anticlines along the southern Qaidam FTB. Identification of the growth strata by Area-Depth analysis and age determination indicate that deformation of the DFS anticline initiated in the mid-Miocene (∼15 Ma), and has successively experienced lateral growth (∼15–8.0 Ma) and uplift (∼8.0 Ma-present). This timeline of deformation coincides with periods of mountain building in the northeastern Tibetan Plateau and might be related to the removal of mantle beneath northern Tibet. The synchronization of growth strata with an increase in sedimentation and exhumation rates reveals the reactivation of the tectonic belt around the basin in the mid-Miocene, creating the current basin-range landform; since ∼8 Ma, compression has expanded rapidly into the interior of the Qaidam Basin, leading to incorporation of basin deposits into the FTB. Geomorphological analyses coupled with 3-D fold modeling demonstrate that the JDS and HLZ-fold train with S-shaped configuration is a coherent fold system developed by lateral growth and linkage of two different fold segments in the context of the N–S directional compression of the plateau. Considering the prevalent S-shaped constructions within the basin and the current seismicity, we propose that the dominant structures in the southwestern Qaidam Basin are a series of thrust faults and folds controlled by the compression component of the East Kunlun Fault, with a limited influence from the Altyn Tagh Fault.

Polyphased gold enrichment as a key process for high-grade gold formation: Insights from the 10 Moz Jundee-Bogada camp (Yilgarn Craton, Western Australia)

High-grade (> 10 g/t) gold mineralization in orogenic gold deposits is of significant economic importance. Understanding the formation of such enriched ore zones is critical for gold exploration success. The world-class Jundee-Bogada gold camp in the Yilgarn Craton of Western Australia comprises both high-grade (avg. > 10 g/t, Jundee deposit) and low-grade (avg. < 3 g/t, Bogada prospect) lodes, despite shared host stratigraphy. The paragenetic framework established for the Jundee gold deposit suggests that the overall gold endowment developed over three deformation events. An early episode of low-grade gold mineralization is associated with colloform-crustiform veins that formed during extensional deformation (DJB2A). A switch to transtensional deformation (DJB2B) resulted in brecciation of the colloform-crustiform veins and coeval deposition of native gold. Late reverse faults record evidence for a third mineralization stage resulting from a NE-SW-directed shortening (DJB3). Mineralization during this late stage was dominantly low-grade, with local occurrences of ultra-high-grade ore zones (> 100 g/t). Each event records transient changes in fluid chemistry during continued hydrothermal activity that spanned local deformation histories. We argue that at the Jundee gold deposit, protracted gold enrichment during three polyphased mineralization episodes resulted in the formation of high-grade gold ores. Whereas the complete metallogenic history is recorded at the Jundee deposit, gold within the Bogada prospect was introduced solely during the late contractional stage (DJB3), resulting in a bulk low-grade endowment. We hypothesize that gold enrichment in high-grade orogenic gold deposits is a direct consequence of the spatial superimposition of protracted ore-forming events.

Hydrocarbon fluid evolution and accumulation process in ultradeep reservoirs of the northern Fuman Oilfield, Tarim Basin

Marine deep Ordovician reservoirs are significantly controlled by strike-slip fault zones, which govern reservoir fluid evolution during various activity periods. Such fluid evolution elucidates the process underpinning ultra-deep oil and gas accumulation and delineates the pivotal role of strike-slip fault zones in hydrocarbon aggregation. This method can improve the understanding of the mechanism of hydrocarbon accumulation in deep to ultradeep carbonate rocks. The findings indicate that the Ordovician reservoirs in the northern thrust fault zone of the Fuman Oilfield predominantly exhibit two stages of calcite vein formation. The distribution patterns of rare earth elements and Sr isotope characteristics suggest that both stages of vein formation were sourced from Middle to Lower Ordovician marine strata, with no evidence of oxidizing fluid infiltration. This indicates that late-stage oil and gas charging in deep-ultradeep formations has good sealing properties. In these calcite veins, early-, middle-, and late-stage fluid inclusions were primarily entrapped. By examining the development of primary oil inclusions and combining the U‒Pb isotope data of host minerals, this study confirms the occurrence of three stages of oil and gas charging in the deep Ordovician strata of the northern thrust fault zone in the Fuman Oilfield. These stages correspond to approximately 459 ± 7.2 Ma (mid-Caledonian), 348 ± 18 Ma (early Permian), and 268 Ma (late Permian). The key accumulation period of oil and gas reservoirs in the study area is the middle and late Caledonian, and there is a good correspondence between oil and gas charging and fault activity.

Depositional and diagenetic processes in travertines: A comprehensive examination of Tocomar basin lithotypes, Northwest Argentina

The use of travertines in active fault studies is known as travitonics. Their geobody shape, veins, faults and fractures, are commonly used as neotectonic proxies. The surficial travertines in the pull apart Tocomar Basin (Puna Plateau, Argentina) occur in the center of the Calama – Olacapato – El Toro (COT) transcurrent fault zone and have never been substantially buried. The Tocomar area exhibits complex tectonic with N–S thrust faults and NW-SE transfer faults, crucial in shaping its travertine deposits and geothermal activity. The travertine bodies are characterized in terms of geometry as a fissure ridge type, coexisting with ash tuff, siliciclastic sandstone, and conglomerate deposits. The travertines mainly consist of crystalline crusts, with occasional occurrences of granular, arborescent, and porous textures. Mineralogical analyses by X-ray diffraction (XRD) reveal the predominance of magnesian calcite, along with trace minerals identified as dolomite, anhydrite, gypsum, halite, fluorite, bassanite, and barite. Petrographic analyses, including cathodoluminerscence (CL), indicate intense diagenesis in the travertine samples. Isotopic signatures of C and O in these samples exhibit normally a negative trend, ranging from −6.38 to +2.45 ‰ VPDB for δ13C and from −20.48 to −11.21 ‰ VPDB for δ18O. Laboratory analysis and field observations allow to classify three distinct lithotypes in the Tocomar travertine: (1) crystalline crust, further divided into three sub-lithotypes: (1.1) laminated crystalline crust (LCC), (1.2) filamentous-like crystalline crust (FlCC) and (1.3) fiber-like crystalline crust (FbCC); (2) granular travertine (GT) and (3) porous travertine (PT). These different lithotypes likely reflect variations in fluid velocity during deposition, although some of them may result from diagenetic processes. The three lithotypes give rise to four facies association (steep slope, marshy/pools, drainage, and fracture-associated facies), forming two distinct depositional systems (slope and channel), which comprises the Tocomar travertine system.

The role of pre-existing faults in the early–middle eocene palaeogeographic evolution of the PY4 sag, Pearl River Mouth basin, South China Sea

The early–middle Eocene represents a pivotal geological phase in the Pearl River Mouth Basin, as it witnessed the emergence and transformation of numerous Cenozoic rifted basins. Nonetheless, the research on the palaeogeography of this period and its interplay with pre-existing faults within the pre-Cenozoic basement remains scant. This article delves into this topic through the lens of the PY4 Sag, a prominent ENE-striking rifted basin situated in the central region of the basin. Initially, we reconstruct the palaeogeography of five third-order sequences within the study interval, using 3D seismic data and drilling data. Then, by amalgamating characteristics of pre-existing faults in the pre-Cenozoic basement, garnered from the published literature, and analyzing their Cenozoic evolution and influence on lake basin structure, sedimentary environment, and sediment distribution, we delve into the correlation between these pre-existing faults and the stratigraphic palaeogeographic evolution in the study area. Our findings reveal that the PY4 Sag experienced five distinct stages of palaeogeographic evolution from the early to middle Eocene, including the initial formation of an ultradeep lake (SQ1), filling of an ultradeep lake (SQ2), early expansion of a shallow lake (SQ3), late expansion of a shallow lake (SQ4), and expansion of a semideep lake (SQ5). This process was accompanied by a gradual migration of the subsidence and sedimentation center of the lake basin from northeast to southwest. Since the Cenozoic, influenced by northwest extension and its clockwise rotation, two pre-existing thrust fault systems striking ENE and EW–WNW within the basement of the Pearl River Mouth Basin have been successively activated. This led to the emergence of numerous ENE-striking normal faults (exhibiting relatively stronger activity) during the early Eocene (SQ1) and EW–WNW-striking normal faults (mainly distributed in the west of the study area) during the middle–late Eocene. Consequently, the PY4 Sag developed a deep and expansive ENE-striking lake basin in the early Eocene, followed by the formation of several smaller EW–WNW-striking lake basins in the middle–late Eocene. The early ENE-striking deep lake progressively evolved into a shallow one due to continuous filling, while the later E–W-striking lake basins broadened and deepened, culminating in the amalgamation of these two distinctively oriented lake basins. In essence, the different spatio-temporal evolution of these two basement pre-existing fault systems during the Eocene, together with episodic magma intrusions in the middle Eocene, are the primary factors controlling the palaeogeographic evolution in the PY4 Sag. Analogously, other ENE-striking sags within the Zhu I Subbasin of the Pearl River Mouth Basin underwent a comparable palaeogeographic transformation during the early–middle Eocene.

Modelling a foreland fold-and-thrust petroleum system: a Permian example in the NW Sichuan Basin, Southwest China

ABSTRACT Foreland thrust belts are globally significant areas for oil and gas exploration. These belts undergo unique tectonic activity, resulting in distinct variations in the accumulation of oil and gas. Studying the genetic evolution of deep oil and gas in these thrust belts is a crucial means of revealing the patterns of deep oil and gas accumulation. This study utilized a novel approach that combines reservoir geochemistry and basin simulation to determine the migration process of oil and gas in the foreland thrust fault belt of northwestern Sichuan Province. To achieve this goal, we established a thermal evolution model of lower Palaeozoic source rocks through organic chemical analysis. The balanced profile technique was used to determine the paleotectonic evolution pattern of the critical period in this area. Additionally, the mixed flow migration algorithm was employed to simulate the evolution of the Palaeozoic petroleum system. Through basin petroleum system modelling (BPSM), it was discovered that the bitumen found in the thrust nappe belt originated from the lower Cambrian strata. Furthermore, the gas reservoir in the hidden fault belt primarily migrated from the lower Cambrian strata and was also partially mixed with thermogenic gas from Permian source rocks. After establishing the genetic models of various tectonic belts in the study area, it became clear that there are notable differences in hydrocarbon accumulation within these belts. The BPSM results revealed that the oil present in the thrust nappe belt was generated in Lower Cambrian source rocks through early Indosinian hydrocarbon expulsion and continuous charging. The gas found in the thrust nappe belt was produced through the process of oil cracking in the deep reservoir located in the hidden front belt during the late Indosinian. The depth of the thrust nappe belt has helped to preserve hydrocarbon reservoirs. The natural gas present in the hidden fault belt primarily originates from lower Cambrian source rocks, which are combined with gas generated by oil cracking in lower Permian source rocks after the Yanshanian. Therefore, hydrocarbons accumulate deeply in the footwall of the thrust fault belt. The BPSM offers a fresh approach to hydrocarbon genetic models of thrust fault zones in the western Sichuan Basin, and it is beneficial for accurately evaluating the potential for deep hydrocarbon resources in comparable geological settings.

Upper Bound Finite Element Limit Analysis of the Response of Shallow Foundations Subjected to Dip-Slip Reverse Fault Rupture Outcrop

Upper Bound Finite Element Limit Analysis of the Response of Shallow Foundations Subjected to Dip-Slip Reverse Fault Rupture Outcrop

Mesozoic to Cenozoic tectonic evolution in the central Bohai Bay Basin, East China

The Mesozoic and Cenozoic tectonic evolutionary history of the East Asian continental margin has been the focus of many researchers because of the overprinting of multiple tectonic domains. Previous studies have suggested that the westward subduction of the Paleo-Pacific Plate and the Pacific Plate resulted in the deconstruction of the North China Craton and controlled the formation of the related basins on the continental margin of East Asia. However, controversy remains regarding the tectonic transition processes and mechanisms that occurred from the Mesozoic to the Cenozoic. Since the Mesozoic, the Bohai Bay Basin on the eastern margin of the North China Craton of East China has been influenced by multiple tectonic domains of the Paleo-Tethys, Paleo-Pacific, and Pacific oceans, and there are complete records of these tectonic transition processes. The Bozhong Depression is a subbasin in the Bohai Bay Basin, which is a crucial area for researching the tectonic evolution of the Bohai Bay Basin throughout the Mesozoic−Cenozoic and the regional tectonic evolution of the eastern continental margin of China. Based on 3-D seismic data, logging core data, and a balanced cross section in the Bozhong area, combined with data from the apatite fission-track inversion model, we reconstructed the tectonic evolutionary history of central Bohai Bay Basin and established a three-cycle and eight-stage tectonic model of the central Bohai Bay Basin during the Mesozoic−Cenozoic. The three cycles are the Indosinian, the Yanshinian, and the Himalayan. (1) The Indosinian was marked by two stages. During the early Indosinian, NW-trending thrust faults were formed due to the collision and northward subduction of the South China Block underneath the North China Block. In the late Indosinian, the tectonic stress in the central Bohai Bay Basin shifted from compression to extension. Consequently, the thrust faults reversed, leading to the deposition of Early−Middle Jurassic strata. (2) The Yanshanian cycle comprises three main phases. Early Yanshanian transpressional shearing led to the formation of a NE/NNE-trending, left-lateral strike-slip fault due to NWW-directed subduction of the Paleo-Pacific Plate. Middle Yanshanian transtensional shearing was driven by Paleo-Pacific Plate rollback and resulted in regional extension and the negative inversion of previous compressive faults. Late Yanshanian compression gave rise to the basin reversion, which resulted from an increased subduction speed of the Paleo-Pacific Plate and a transition from a high angle to a low angle. (3) The Himalayan cycle was marked by three phases. During the early Paleogene, the region was characterized mainly by extension, and NE-trending, right-lateral strike-slip normal faults began to form. This coincided with a decrease in the Pacific Plate’s subduction speed. In the late Paleogene, the subduction rate of the Pacific Plate increased, resulting in the change of the central Bohai Bay Basin from an extensional environment to one marked by regional differential compression. In the Neogene, regional thermal subsidence and depression sedimentation occurred, which were probably induced by the increasing subduction speed and rollback of the Pacific Plate. The Bozhong Depression has experienced multiple stages of tectonic evolution, which indicates the concurrent and superimposed effects and transition of multiple tectonic domains.

Preliminary Derived DInSAR Coseismic Displacements of the 2022 Mw 5.7 Stolac Earthquake

On 22 April 2022, a Mw 5.7 earthquake was generated near Stolac (Bosnia and Herzegovina). The mainshock was succeeded by several aftershocks, three of which were significant. Two Mb 4.3 earthquakes occurred on 23 April 2022, and a Mw 4.8 earthquake was generated on 24 April 2022. Available data from fault mechanism solutions revealed that the mainshock activated a reverse fault, while the aftershock generated a normal fault with a right-lateral component. The Balkan Peninsula stands as one of the most active geodynamic areas in Central and Eastern Europe due to its location within the collision zone between Eurasian and African tectonic plates and the Anatolian microplate. Recorded earthquakes in Bosnia and Herzegovina are related to the energy generated by the subduction of the African tectonic plate under Eurasia. Furthermore, the seismicity of Bosnia and Herzegovina, particularly its southern part, is profoundly influenced by the subduction of the Adriatic microplate under the Dinarides. The Dinarides are a mainly fold and thrust belt that extends from the Southern Alps in the northwest to the Hellenides in the southeast and make dominant the tectonic system of Bosnia and Herzegovina. In this study, two pairs of SAR images obtained from the Sentinel-1 satellite mission were utilized to generate satellite LOS surface displacements using the DInSAR method. Moreover, LOS displacements were decomposed into vertical and east–west horizontal components by combining ascending and descending satellite orbits. Ultimately, the InSAR results were analyzed and compared with the data obtained from the CROPOS CORS GNSS station in Metković (MET3).

Exploration Vectors and Indicators Extracted by Factor Analysis and Association Rule Algorithms at the Lintan Carlin-Type Gold Deposit, Youjiang Basin, China

The Youjiang Basin in China is the world’s second-largest concentrated area of Carlin-type Au deposits after Nevada, USA, boasting cumulative Au reserves nearing 1000 t. This study examined the recently unearthed Lintan Carlin-type Au deposit within the Youjiang Basin. Factor analysis and association rule algorithms were used to identify exploration vectors and indicators essential for navigating this promising geological territory. In the Lintan mining area, the geological strata encompass the Triassic Bianyang, Niluo, and Xuman formations comprised clastic rocks, followed by the deeper Permian Wujiaping Formation with massive carbonate rocks. The orebodies are restricted to the F14 inverse fault, cutting through the Xuman Formation, with an additional F7 fault between the Wujiaping and Xuman formations. A total of 125 rock samples from the F14 fault and a representative cross-section were analyzed for 15 elements (Au, Ag, As, Bi, Cd, Co, Cu, Hg, Mo, Ni, Pb, Sb, Tl, W, and Zn). The elements were divided into four groups based on cluster and factor analysis. Group 1 (Co, Cu, Zn, Ni, Tl, W, and Bi) was mainly enriched in the Xuman, Niluo, and Bianyang formations controlled by sedimentary diagenesis. Group 2 (Au, As, Hg, and Sb) was concentrated in the F14 and F7 faults, representing Au mineralization. Group 3 (Pb, Ag, and Mo) was mostly enriched near the F14 and F7 faults, displaying a peripheral halo of Au mineralization, and was probability controlled by ore-forming hydrothermal activities. Group 4 (Cd and Mo) exhibited extreme enrichment along the periphery of the F7 fault. This pattern indicates the presence of a substantial hydrothermal alteration zone surrounding the fault, likely influenced by ore-forming hydrothermal processes. Additionally, Pb, Ag, Cd, Mo, and W are considered essential indicators for ore formation besides Au, As, Sb, Hg, and Tl. Twelve effective association rules were derived using the association rule algorithm, which can aid in discriminating Au mineralization. The spatial distributions of the 15 elements indicated that the F14 fault is the main ore-bearing fracture zone, while the F7 fault serves as the ore-conducting structure, channeling ore-forming fluids into the F14 fault. Faults between the Wujiaping and Xuman formations, along with their associated reverse faults, present potential prospecting targets both within and outside the Lintan Au deposit in the Youjiang Basin. Exploration geochemical data can be fully utilized by combining factor analysis and association rule algorithms, offering key guidance for prospecting Carlin-type gold and similar deposits.

Numerical modelling of earthquake sequences involving valving and pumping of fluids

SUMMARY Faults in the upper crust are sometimes thought to act as self-sealing valves, episodically releasing highly overpressured fluids trapped at greater depth during earthquakes. They are also often considered to be capable of actively pumping fluids into or out of faults in response to coseismic volumetric strain, thermal pressurization or other mechanisms. In this study, we investigate how these different types of behaviour (i.e. valve versus pump) are manifested in earthquakes. We do this using a 2-D plane strain model where frictional sliding on a thrust fault that is fed by a fluid source at its base is coupled to porous flow, thermal pressurization and strong variations in permeability. Our results show that thermal pressurization leads to dramatic dynamic weakening that produces earthquakes that propagate as slip pulses producing large stress drop, large slip and high slip velocities. On the other hand, valve-type behaviour typically produces smaller, less energetic earthquakes that commonly arrest before rupturing the entire fault. In some valve models, we observe complex compound ruptures and swarm activity, which is linked to the ascent of a propagating fluid pressure pulse driven by a large increase in permeability during sliding. Both pump and valve mechanisms can produce anomalously weak faults, though they are each associated with distinctly different fluid pressure and strength evolution over the seismic cycle and during rupture. Our models highlight the complex way in which fluids may interact with earthquakes, especially if valve and pump models coexist.

Effects of Reverse Fault Dislocation Application Method for Tunnelling Through Active Faults

Active faults seriously threaten the structural integrity of mountain tunnels in seismic zones, and reverse faults are the most hazardous. A tunnel project in the western region was used as a reference to analyze the damage mechanism of tunnels under different modes of reverse fault displacement. The ABAQUS finite element analysis software was employed for the numerical simulation, and a quasi-static method was adopted to analyze the displacement and stress response patterns of the tunnel structure traversing the fault under three typical modes of reverse fault displacement. This led to deriving the tunnel structure’s longitudinal damage modes and impact zones based on reverse fault displacement. The study revealed that the damage modes of the tunnel under different fault displacement modes varied, which was reflected in the different degrees of shear and compression. Regardless of the fault displacement mode, the tunnel structure located within the fault fracture zone was severely damaged, with the most severe damage occurring at the interface between the fixed plate and the fault displacement section. Therefore, in the design, special attention should be paid to the displacement resistance performance of the dangerous sections of the tunnel. The research results provide significant reference and guidance for similar projects.

Rapid determination of source parameters of the M6.2 Jishishan earthquake in Gansu Province and its application in emergency response

In this study, we swiftly determined the focal parameters (focal mechanism, seismic imaging process, magnitude) of the Jishishan earthquake, leveraging a solved fault model to assess the intensity field and casualties promptly. The investigation began by retrieving the source mechanism through the P-wave initial motion and W-phase method. This enabled us to chart the spatial and temporal distribution of energy release in the source area via the back-projection technique. Following this, we estimated the earthquake's intensity field by merging the source inversion findings with the ground motion prediction equation. This analysis facilitated the evaluation of earthquake casualties, utilizing the theoretical intensity field and a casualty assessment model. Our findings indicate that the fault type is a thrust fault, characterized by a unilateral rupture in the direction of NW, with a rupture length spanning approximately 10–15 ​km and a duration ranging between 8 and 10 ​s. The earthquake's magnitude varied from M 5.9 to M 6.2. The demarcated high-intensity areas, as per our intensity assessment, align closely with the actual survey results. Furthermore, the predicted total casualties and identified critical rescue zones closely match the real-world casualty figures. These insights offer crucial technical support for governmental emergency command and rescue operations.

Fairweather transform boundary Oligocene to present orogenesis: Fairweather Range vertical extrusion and rotation of the Yakutat microplate at ca. 3 Ma

Oblique-slip along transform fault boundaries is often partitioned between a strike-slip system and thrust faults that accommodate contraction. However, topography along the Yakutat-North American transform (Fairweather fault), is asymmetric with low-terrain above active thrusts on the western, Yakutat side of the transform and high topography on the continental side with peaks >4500 m (Mount Fairweather: 4671 m) to the west of the Border Ranges fault, limited recorded earthquakes >M4, and no apparent reverse faults to generate the highest terrain. In this study we compile, for the first time, published U-Pb zircon, 40Ar/39Ar and K-Ar (hornblende, muscovite, and biotite) and U-Th/He and fission-track (zircon and apatite) bedrock ages (109) from 75 samples to investigate the exhumation history of the Fairweather Range region, complemented by a published detrital sample (ZFT and AFT) and 13 new 40Ar/39Ar (hornblende, biotite, and K-feldspar) ages on 9 bedrock samples from both sides of the Fairweather fault. Additionally, we examined published seismicity and geodetic data of the Fairweather region and assessed if plate paleo-vectors correlate with the cooling history of the Fairweather Range. Cooling age, seismic, and block-motion patterns indicate the Fairweather Range has been vertically extruded between the Fairweather and the Border Ranges faults as a coherent block since ca. 25 Ma. The pre-6 Ma Pacific plate motion (N30°W) aligns with the N33°W strike of the Fairweather Fault whereas a hypothetical pre-6 Ma Yakutat microplate paleo-vector of (N39°W) does not: indicating a post-6 Ma timing for Yakutat microplate counter-clockwise rotation (9°). We infer that rotation and impingement of the Yakutat microplate along the Fairweather fault at ca. 3 Ma led to the development of the Fairweather restraining bend and increased cooling rates. The resultant thickened Fairweather welt and the ∼30 km thick southeast end of the Yakutat microplate compounded double-indenter tectonics into Alaska's southeast convergent corner

Middle to lower crustal earthquakes in the western East Sea (Sea of Japan) and their implications for neotectonic evolution

The western East Sea (Sea of Japan) is a seismically active region. A major earthquake in the western East Sea may cause damage in the eastern Korean Peninsula. The nature of seismicity in the western East Sea is important information for mitigation of seismic hazards. The seismicity in the western East Sea occur around the paleo-rifting structures where seismic and geophysical properties apparently change. Both reverse faulting and strike slip earthquakes occur in the region. Earthquake locations and focal depths are refined. The maximum focal depth generally increases from ∼10 km in the coast to ∼32 km in the continental slope of the western East Sea that is located in distance of ∼60 km from the coast. Mid to lower crust earthquakes continue around the paleo-rifting structures that may extend to the lower crust and Moho. Offshore earthquakes rarely occur in oceanic basins of bathymetry with >2 km. Clustered episodic earthquakes occur in four local offshore areas including the stress-induced areas by the 12 September 2016 ML5.8MW5.4 Gyeongju and 15 November 2017 ML5.4MW5.5 Pohang earthquakes. The spatiotemporal clustering of earthquakes suggests stress accumulation at localized paleo-rifting structures and episodic stress release. The mid to lower crustal earthquakes are confirmed from phase arrival time analyses with collocated vertically-separated sensors. The laterally progressive focal depth changes suggest neotectonic evolution of thrust across the crust in the paleo-rifting structure.