Tectonic Stress Regime Research Articles

Neoproterozoic High-K calc-alkaline granites forming the large Agudos Grandes and Socorro batholiths, SE Brazil: Crystallization conditions and tectonic implications

I-type, high-K calc-alkaline (HKCA) granites are the main components of two large Neoproterozoic batholiths that occur in different tectonic domains in SE Brazil (Agudos Grandes (emplaced in the central Ribeira Fold Belt) and Socorro (emplaced in the Socorro-Guaxupé Nappe). We investigated representative samples from both batholiths using detailed petrography by optical and electronic microscopy and chemical analysis of main minerals (amphibole, biotite and plagioclase) by EPMA aiming to obtain reliable estimates of magmatic temperatures and pressures. Granites from both batholiths show broadly similar whole-rock compositions and crystallized from oxidized magmas at ∼ NNO+1 to +2. However, they were emplaced at different depths (Agudos Grandes: 3–5 kbar; Socorro: 5–6 kbar; Al-in-hornblende geobarometry) and crystallized at slightly, but consistently different temperatures (respectively, lower and greater than 800 °C). The lower temperatures of the Agudos Grandes granites may account for the presence of titanite as a main accessory mineral, in contrast with its absence, or occurrence as thin rims in ilmenite in the Socorro granites. The pressure estimates are consistent with the metamorphic conditions of the country rocks and suggest that magma emplacement was influenced by a combination of density control and evolving tectonic stress regimes, with the dominantly more mafic rocks of Socorro emplaced at greater depths. On the other hand, higher Sr/Y ratios and REE fractionation shown by the Agudos Grandes whole-rocks may result from magma equilibration in a thicker crust (>60 km, as contrasted with ∼50 km for Socorro) at the time of magma generation. However, the possible presence of cumulate components (as suggested, for instance, by high apatite and hornblende saturation temperatures) requires that these contrasts are tested in the future by proxies that are independent of whole-rock composition (e.g., trace-element chemistry of minerals).

Tectonic Stress Analysis of Shivnath-Salena Area, Using Stress Response Structure

The geological mapping of the Shivnath-Salena area and structure analysis of the same area were conducted in the LesserHimalayan sequence, Far West Nepal, unveiling the characteristics of kinematics and the associated stress field in the region. Thearea comprises of the Salena Formation and Chachura Formation. The Salena Formation is sandwiched between the PachkoraThrust and Dudulakhan Thrust, and the Chachura Formation occurs between the North Dadeldhura Thrust and Pachkora Thrust.The Salena Formation is composed of light grey and white quartzite and black slates that are intensely deformed, with folds. The Malena Anticline and the Lamalek Syncline are the intraformational folds observed in the study area. Superimposed folding was also observed. The Chachura Formation comprises Paleocene to Late Eocene green sandstone, grey and purple shale, and approximately 1 m thick grey fossiliferous limestone. This study interprets stress-response structures to show the tectonic stress field in the Salena Formation. Twenty-seven fault slip data (slickenside) were collected in the field and used to determine the stress regime by applying the stress inversion technique. The direction of the maximum principal stress axes is interpreted as NE-SW. The average value of the stress index R' is about 0.30, indicating an extensional tectonic stress regime in the study area. As σ1 is vertical, R = R' in the study area suggests normal faulting in an extensional regime.

Tectonic activity in Gulf of Guinea and Sub-Sahara West Africa: A validation of Freeth (1977) using focal mechanism solutions

Fault plane solutions for a group of 104; 4.0 ≤ Mw ≤ 7.1 earthquakes between January 1979 and December 2016, extracted from the Global Centroid Moment Tensor Project catalog. Were used to investigate the regional tectonic stress regime of the Gulf of Guinea region. The idea is to validate the theory of membrane tectonics put forward by Freeth (1977)[1] in which the tectonic of the Gulf of Guinea and the sub-Sahara West Africa region were described based on Freeth (1977)[1]. The tectonic of the Gulf of Guinea and the sub-Sahara West Africa region are based on the movement of the African plate, we emphasized the use of rigorous statistical tests to decide on the quality and variability of the earthquake focal mechanisms (FMSs) utilized for the stress tensor inversion analysis. To constrain our analysis, we have applied both the Algorithm of Michael and Gauss technique in our stress tensor inversion analysis of FMS obtained from the region, and the results are found to be coherent and in good agreement with each other. Both Michael (1984)[2] and Zalohar and Vrabec (2007)[3] techniques show that the regional tectonic stress regime of the Gulf of Guinea and the sub-Sahara West Africa is extensional, which is in good agreement with the work of Freeth (1977)[1]. However, our investigation concluded that the orientation of the extensional stress regime is the same as the orientation of the movement of the African plate, which is towards the Euro-Asia plate.

Mitigation of tunnel support design risks for hydropower projects within high tectonic stress regimes – an empirical analysis

Abstract The study for the design of tunnels in similar geological settings, providing insights into potential challenges that may arise during excavation and offering strategies for mitigating risks in District Kalam on the Ushu River, Khyber Pakhtunkhwa, Pakistan. The methodology involved geological mapping, rock sampling, discontinuity surveys, and laboratory testing for empirical analysis of tunnel parameters at the Weir House, Powerhouse, and tunnel alignment locations. Empirical analysis of tunnel parameters using three rock classification systems, rock mass rating (RMR), rock quality tunneling index, and rock mass index (RMi). Based on the classification, the rock quality was found to be fair, indicating favorable rock properties. The Q-system rated the rock as poor to fair, suggesting low discontinuity intensity, medium rock strength, or medium deformation modulus. According to the RMi, rock was rated as medium to strong, indicating low discontinuity intensity, high rock strength, or low deformability. The support design for the tunnel is based on empirical analysis, it recommends support design for the tunnel reinforcement elements such as rock bolts, wire mesh, and shotcrete lining. Overall, the tunnel is stable and does not have complex structure and weak zones.

Stress field and tectonic regime of the Eastern Mediterranean from inversion of earthquake focal mechanisms

The formal stress inversions of 1258 earthquake focal mechanism solutions reveal the presence of six distinct stress regimes. However, the predominant tectonic regimes comprise normal faulting (39%), strike-slip faulting (29%), thrust faulting (25%), and unspecified oblique faulting (7%). The division of the study area into zones based on structural and deformation patterns has provided valuable insights into the variations in the stress field and tectonic processes within this seismically active region. For each designated zone, reduced stress tensors were derived using the improved right dihedron method and the rotation optimization technique implemented by the Win-Tensor software.The stress field derived from the entire dataset is characterized by R′ = 1.0 and an NW-SE SHmax orientation, strongly influenced by the tectonic stress regime of the Hellenic Arc. In specific regions such as CYS, CEM, and WEM, the prevailing tectonic regimes is characterized by a predominant compressive setting with a stress index (R' = 2.0 to 2.5). This pattern aligns with neotectonic deformation associated with the subduction of the African Plate beneath the Eurasian Plate. The EMZ Zone exhibits a strike-slip tectonic regime with an R' of 1.50, primarily influenced by the Dead Sea Transform Fault. This fault accommodates differential motion between the African and Arabian plates in the NNE direction, resulting in left-lateral strike-slip motion along the plate boundary. The mean slip tendency values, varying between 0.62 and 0.66, suggests that the faults in the study area are appropriately oriented for slip or shear displacement, indicating an elevated probability of reactivation.

Seismotectonic Stress Regime and Airborne-Gravity Lineament Investigation of the Caribbean region and its Kinematic implications

The tectonic stress regime of the Caribbean region has been studied by stress tensor inversion analysis for the area bounded by Latitudes 17.32o to 23.79o N and Longitudes 81.47o to -60.56o E. A total of two hundred and twenty (220) fault plane solutions (FPS), made up of the seismic (earthquake) events that have occurred in the region of the study were found on the data catalog of the project website of the global centroid moment tensor, were employed in this study. To characterize the stress regimes of the region of study, the classification of the region based on the global moment tensor project is as follows: Cuba-zone, Haiti-zone, Dominican-republic, Monapassage, Puerto Rico, Virgin-Island and the Leeward Island. The gravity geophysical method revealed the presence of multiple or swarms of fractured lines within the same geographical range of study which might have developed over the years as a result of the interaction and coupling effect of the plate boundaries that have close proximity to the region of study. The seismicity pattern indicates that none of the provinces or countries located within the Caribbean region is devoid of large-magnitude earthquake occurrences capable of wreaking severe havoc on the immediate environment. Obviously, our stress tensor inversion result indicates two types of stress regimes namely compression and the strike-slip with different orientations. Cuba-zone, Haiti-zone, Dominican Republic, Monapassage, and Leeward Island are governed mainly by compression stress regimes. In contrast, the strike-slip stress regimes mainly govern the Puerto Rico and the Virgin Island.

Two-step exhumation of Caucasian intraplate rifts: A proxy of sequential plate-margin collisional orogenies

Intraplate structural deformation is diagnostic of tectonic stress regime changes linked to plate interactions and can result from superposed tectonic events whose single contributions are hardly distinguishable. In this paper, we present a set of integrated thermochronologic inverse models along a 140 km-long transect across the central Greater Caucasus and the adjacent Adjara-Trialeti fold-and-thrust belt of Georgia, two intraplate orogens produced by structural inversion of parallel continental rift zones located on the Eurasian plate. Our dataset allows to distinguish discrete and superposed deformation episodes and quantify their respective contributions to orogenic exhumation. The integration of (U-Th)/He analysis on apatite and zircon, fission-track analysis on apatite, and peak-temperature determinations (clay mineralogy, organic matter petrography, Raman spectroscopy) shows that structural inversion was punctuated by two incremental steps starting respectively in the latest Cretaceous and the mid-Miocene. Latest Cretaceous partial inversion of the Greater Caucasus is documented here for the first time and placed in a geographically wider context of coeval deformation. The two episodes of intraplate structural inversion, exhumation, and sediment generation are chronologically and physically correlated with docking of (i) the Anatolide-Tauride-Armenian terrane (Late Cretaceous - Paleocene) and (ii) Arabia (Miocene hard collision) against the southern Eurasian plate margin. Intraplate deformation in the Caucasian domain was triggered by far-field propagation of plate-margin collisional stress which focused preferentially along rheologically weak rift zones.

Tectonic stress regime and faulting style analysis due to sequence of earthquakes in Western Nepal

The current study examines the source mechanism and the regional stress regime of a sequence of moderate-sized earthquakes between October 2022 and October 2023. ISOLA-GUI-a Matlab coded program has been used to estimate Moment Tensor Solution to understand the source mechanisms of the earthquakes in the region. The earthquakes are recorded at the broadband station arrays of the regional seismological network around the Tehri region, installed by the Indian Institute of Technology Roorkee in India. The study focuses on earthquakes with epicentral distances of less than 10°. The investigation aims to comprehend the source process by estimating the focal mechanisms utilizing regional waveform data and then inverting the acquired focal mechanism of these earthquakes to comprehend the active stress regime in the region. The obtained source mechanism reveals a predominance of a double-couple mechanism in faulting and hence, suggests that the majority of the seismic energy is released through shear motion along a defined fault plane. By revealing the complex interaction of geological forces in the Himalayan belt, this investigation will help us to better understand the distribution of stress and deformation patterns beneath the Earth's crust. The main emphasis lies on assessing stress distribution through the utilization of earthquake focal mechanism data and employing the Stress Inversion technique using the WinTensor program. The result of stress inversion suggests that the maximum compressive stress is plunging horizontally, while the minimum compressive stress is oriented vertically. Hence revealing a thrust stress regime in Western Nepal, trending in the NNE- SSW direction corroborating the ongoing tectonic processes associated with the collision of the Indian plate with the Eurasian plate.

Contemporaneous Thick- and Thin-Skinned Seismotectonics in the External Zagros: The Case of the 2021 Fin Doublet, Iran

In this work, we propose a geodetic model for the seismic sequence, with doublet earthquakes, that occurred in Bandar Abbas, Iran, in November 2021. A dataset of Sentinel-1 images, processed using the InSAR (Interferometric Synthetic Aperture Radar) technique, was employed to identify the surface deformation caused by the major events of the sequence and to constrain their geometry and kinematics using seismological constraints. A Coulomb stress transfer analysis was also applied to investigate the sequence’s structural evolution in space and time. A linear inversion of the InSAR data provided a non-uniform distribution of slip over the fault planes. We also performed an accurate relocation of foreshocks and aftershocks recorded by locally established seismographs, thereby allowing us to determine the compressional tectonic stress regime affecting the crustal volume. Despite the very short time span of the sequence, our results clearly suggest that distinct blind structures that were previously unknown or only suspected were the causative faults. The first Mw 6.0 earthquake occurred on an NNE-dipping, intermediate-angle, reverse-oblique plane, while the Mw 6.4 earthquake occurred on almost horizontal or very low-angle (SSE-dipping) reverse segments with top-to-the-south kinematics. The former, which cut through and displaced the Pan-African pre-Palaeozoic basement, indicates a thick-skinned tectonic style, while the latter rupture(s), which occurred within the Palaeozoic–Cenozoic sedimentary succession and likely exploited the stratigraphic mechanical discontinuities, clearly depicts a thin-skinned style.

Geodynamics and tectonic stress model for the Zagros fold–thrust belt and classification of tectonic stress regimes

Stress measurement in rocks is an essential parameter in Earth and petroleum sciences. In hydrocarbon exploration and production from oilfields, a lack of sufficient knowledge on the initial stress field for the fracturing of formations limits proper simulation of the production process.To date, only a limited number of studies have investigated the state of stress in the Zagros Mountains. In this paper, well-established analytical techniques were used to determine the stress state in the Zagros Mountains. First, the Angelier method was used to invert earthquake data in different structural domains. Second, the pattern of crustal stresses was analyzed, and four classes of stress regimes were identified. The stress patterns were reconstructed for five distinct structural domains (zones 1–5). In all five zones, the compressive stress was normal to the main structures (fold axis and fault trace with NW‒SE strike). It can be inferred that the structural pattern in the sedimentary cover of the Zagros fold-and-thrust belt (ZFTB) is controlled by R1 (Regime 1) and R4 for zones 1 and 2; R3 for zone 3; R1 and R2 for zone 4; and zone 5. The reconstructed stress patterns are consistent with the observed strike-slip faulting and compressional tectonic deformation regimes. The patterns indicate that deformation in the ZFTB can be explained by a dextral transpressional tectonic model. First-order NE–SW compression stress controls the main convergence tectonics within the Zagros Mountains. Two subordinate compression directions were also identified: one oriented in a dextral main compression direction (N 241°–243°) and another in a sinistral (N135°–177°) and minor extension (N201°–229°). Classification and modeling of the stress regimes identified both thrusting and strike-slip systems; the former controls the Main Zagros Reverse Fault (hereinafter MZRF), and the latter results in a transpressional tectonic regime.

Cenozoic tectonic evolution of the Bohai Bay Basin: Constraints from strike-slip activities of the Wangjiagang fault zone, NE China

The Wangjiagang (WJG) fault zone is regarded as the northward propagation of the Tan-Lu fault zone (TLFZ) in the Bohai Bay Basin (BBB). We used three-dimensional seismic and borehole data, as well as structure and isopach maps, to describe the structural properties and tectonic development of the WJG fault zone. The properties and thickness of the mechanical layer are the principal factors of differences in the deformation of the strike-slip fault zone. Extensional tectonics and strike-slip faulting occurred in WJG. Not only does strike-slip faulting regulate sand body distribution, but it also plays a critical role in oil migration. WJG provides a record of the tectonic evolution of the BBB and how it responded to plate interactions around the Pacific-Eurasian-Indian plates and/or the strike-slip faulting of the TLFZ. The BBB extended in the early Paleocene as a result of relative relaxation between the Pacific and Eurasian plates and the upwelling of the asthenosphere mantle. Before and after the late Eocene (ca. 42 Ma), the tectonic stress regimes at a nearly N-S-oriented extensional to dextral strike-slip faulting along TLFZ coincided with the strike-slip faulting of the pre-existing fault in WJG. The Pacific Plate's change in direction and rate of subduction, as well as the far-field effect of a hard collision between the Indian and Eurasian plates, caused the TLFZ's two walls to move in opposite directions. The resulting force couple caused a strong simple shear in the TLFZ and adjacent areas, including the WJG fault zone.

The submarine Azores Plateau: Evidence for a waning mantle plume?

The submarine Azores Plateau in the Central Northern Atlantic has generally been considered to represent a large igneous plateau formed some 10 Ma by widespread volcanism, however a lack of age progression amongst the younger submarine and subaerial volcanism, an irregular distribution of platform-related magmas east and west of the Mid-Atlantic Ridge, a strong tectonic stress regime, and a lack of abundant tholeiitic compositions that reflect initial, high degrees of melting is not easily explainable in the framework of a classic, long-lived mantle plume model. Here, we present new bathymetric and seismic data from the submarine Azores Plateau obtained during cruises M113/1 and M128 with the German R/V Meteor. Our new data combined with prior geochemical and petrological studies indicate that the majority of the western Azores Plateau may indeed have formed during the arrival of a short-lived mantle melting anomaly at 10 Ma. However, our new data also indicate that volcanism <2 Ma is extremely localized and along structural features that result from plate reorganisation in the vicinity of the diffuse triple junction of the Eurasian, Nubian and North American plates, and that much of the easternmost Azores Plateau is magmatically inactive. Our model implies not only that the actual flood basalt province of the Azores is only some 30% of what has been previously estimated but may not have formed from a typical large-scale, long-lived mantle plume. Instead, excess melting as evident from the anomalously shallow water depth and the presence of islands in the Azores may be the result of a volumetrically small-scale melting anomaly in the upper mantle which is in its waning stages as evident from the localised distribution of magmatic activity at <1 Ma. Our model also solves the conundrum of a potential asymmetry of the recent submarine and subaerial volcanism both east and west of the Mid-Atlantic Ridge which instead is the result of an interacting upper mantle anomaly and the complex plate tectonic domain in the vicinity of the triple junction of the Eurasian, Nubian and North American plates.

Estimation of horizontal stresses from wellbore failures in strike-slip tectonic regime: A case study from the Ordovician reservoir of the Tinzaouatine field, Illizi Basin, Algeria

We present a geomechanical analysis of the Ordovician reservoir from the Tinzaouatine field situated in the prolific Illizi Basin, eastern Algeria. The sandstone reservoir has a hydrostatic pore pressure gradient (9.95 MPa/km). We analyzed a cumulative of 300 m of acoustic image log data and identified the coexistence of B-quality extensive drilling-induced tensile failures (DITFs) and compressive failures, i.e., breakouts (BOs), indicating a mean maximum horizontal stress ([Formula: see text]) orientation of N140°E. We used a combined BO and DITF-based solution to estimate horizontal stress magnitudes when the two failure types coexist. Based on the C-quality minifrac measurements, we interpreted the minimum horizontal stress ([Formula: see text]) gradient as 17.4–17.47 MPa/km, whereas the new approach indicates an [Formula: see text] range of 17.31–18.67 MPa/km. Using the BO width and DITF-based approaches, we inferred an [Formula: see text] gradient range of 28.37–38.59 MPa/km within the studied reservoir. Based on the relative stress magnitudes, we infer a strike-slip tectonic stress regime in the studied field.

Rock Properties and Modelled Stress State Uncertainties: A Study of Variability and Dependence

The safety and sustainability of subsurface applications requires a profound knowledge of the local stress state which is frequently assessed using 3D geomechanical-numerical models. Various factors lead to generally large uncertainties in these models. The variabilities in the rock properties as one of the sources of uncertainties and their influence on the modelled stress state is addressed herein. A generic 3D geomechanical-numerical model is used to investigate the influence of different distributions of variability and their effect on different stress states. The variability in rock properties clearly affects the uncertainties in the stress state in a positive correlation with differences that depend on the affected component of the stress tensor. The basic observation is that largest uncertainties are observed in the normal components of the stress tensor where the variabilities apparently are most effective. The same rock property variabilities affect the shear components uncertainties to a significantly lesser extent. Variabilities in the Young’s modulus and the Poisson’s ratio chiefly affect the uncertainties in sigma _{xx} and sigma _{yy}. The density variability, however, leads to highest uncertainties in sigma _{zz}. In general, variabilities in the Young’s modulus are most effective, followed by the Density and then the Poisson’s ratio. Furthermore, an influence of the tectonic stress regime on how the variability in the rock properties affects the stress state is observed. At the same time only a small effect is observed for different stress magnitudes. The eventual uncertainties in a modelled stress state depend not only on the uncertainties in the rock properties but also whether the uncertainties are found mainly in the Young’s modulus, the Poisson’s ratio or the Density. These findings indicate the importance to regard variabilities in rock properties as a source for significant uncertainties in geomechanical-numerical models. It is proposed to use the derived relations for an inexpensive quantification of uncertainties by means of a post-computation assignment of uncertainties to a stress model.

The integrated history of repeated caldera formation and infill at the Okataina Volcanic Centre: Insights from 3D gravity and magnetic models

Multistage collapse caldera create complex geological structures that are often buried by kilometers of pyroclastic infill and late stage lava domes, making study of their origins difficult from outcrop alone. Here we present new gravity and aeromagnetic data compilations derived from terrestrial, lake and airborne surveys to investigate the buried internal structure of the Okataina Volcanic Centre (OVC) and interpret its stages of development. Magnetic highs (1300 nT) are caused by a combination of thick lava flows and domes that infill the collapse structures, and a deeper feeder structure/dyke complex that extends below the basement to at least 6 km depth. Magnetic lows caused by hydrothermal alteration are associated with topographically low areas near the topographic and structural collapse margins suggesting fluid circulation within the caldera exploits both deep and shallow structures. Several large rhyolite lava flows contain low magnetisation rims reflecting the glassy outer carapace and crystalline core.The gravity data show a − 62 mGal residual gravity low associated with the OVC, with the steepest gradients occurring inside the topographic margins. The gradient of the gravity low is stepped towards its lowest point near the outlet of Lake Tarawera. Each step is interpreted as relating to the buried structural collapse margins of the Utu, Matahina, Rotoiti and possibly Kawerau, catastrophic caldera forming eruptions, creating an overlapping and nested caldera structure, however there is no evidence for an OVC encircling ring structure. Buried caldera margins associated with oldest Utu eruption may play a role in the location of the youngest Tarawera eruptions. We propose smaller amplitude gravity lows that extend outside the topographic margins of the caldera are related to lateral magma migration to the south-west, exploiting regional tectonic stress regimes, towards eruption vents within the caldera. 3D gravity inversion, including models numerically constrained by a 3D magnetotelluric model, suggest a caldera depth of 5000 ± 500 m that accumulated over multiple collapse episodes along with rifting induced subsidence in the past 550 ka.Our multiphysics approach to investigating caldera structure has revealed buried structural margins and their relationships to eruptive vents and hydrothermal features at the OVC. Detailed geophysical models of caldera structure are rare globally, and our findings are consistent with analogue and numerical models of caldera formation that accompanies the most violent volcanic eruptions on Earth.

Relationships between Payenia volcanism and deep-seated structural controls: Insights from geophysical methods at Nevado volcanic field, Mendoza, Argentina

The Nevado Volcanic Field (NVF), in southern Mendoza foothills, is part of the Payenia Volcanic Province, a large Quaternary retro-arc volcanic area composed principally of basaltic lava flows and monogenetic volcanoes. Monogenetic volcanism location, distribution and evolution are extremely sensitive to previous rheological discontinuities or faults affecting their basement. With the aim of exploring the subsurface configuration and contributing to a better understanding of this volcanism, we analysed and interpreted aeromagnetic and gravity datasets in addition to structural and volcanic alignments information. Our results show that location of volcanism would have been mainly controlled by NW-SE trending structures. These structures would extend at least to middle crust levels. On the other hand, a secondary control might be related to crustal domains with different densities, which could have affected magma propagation to the surface, hence, controlling the spatio-temporal distribution of volcanoes. The complex interplay between these factors would be responsible for the distribution of volcanic centres. Finally, we discuss the implications of these controls concerning the tectonic stress regime contemporaneous with volcanic activity.

Zircon Th/U ratios suggest a post-collision extensional setting for the Permian Ni-Cu sulfide deposits in the Eastern Tianshan, NW China

Magmatic Ni-Cu sulfide deposits have been discovered in orogenic belts worldwide. However, the optimal period for extensive basaltic magmatism generating Ni-Cu sulfide mineralization during the development of orogenic belts has not been well addressed. Zircon Th/U may be correlated with end-member tectonic stress regimes (continental extension vs. compression) that correlate with distinct magmatic conditions. Here, zircon Th/U ratios from the Permian Huangshan-Jingerquan Ni-Cu metallogenic belt in the Eastern Tianshan are revisited, including magmatic zircons from mafic and felsic rocks and detrital zircons from sedimentary rocks. These zircons are filtered to minimize the effect of amagmatic conditions (e.g., metamorphism, alteration, inclusion and metamictization). After filtration, zircon Th/U ratios in the Huangshan-Jingerquan belt are likely linked to the silica content of the host melt and crystallization temperature under zircon growth with fractionating melts. They display high Th/U ratios (up to 2.5) and δEu values (up to 1.35) during the early Permian. In contrast, the others with low Th/U (most < 1.0) ratios and δEu (<0.8) appear in the pre-Permian except the late Devonian. This indicates that the crust in the region was thickened induced by collision at the end of late Carboniferous and then extended during the early Permian. Conclusively, we suggest that the post-collision extensional setting is the preferred stage for the Permian short-lived (<5 Ma) Ni-Cu sulfide deposits during the development of the Tianshan Orogenic Belt.

The 27 September 2021 Earthquake in Central Crete (Greece)—Detailed Analysis of the Earthquake Sequence and Indications for Contemporary Arc-Parallel Extension to the Hellenic Arc

The Arkalochori village in central Crete was hit by a large earthquake (Mw = 6.0) on 27 September 2021, causing casualties, injuries, and severe damage to the infrastructure. Due to the absence of apparent surface rupture and the initial focal mechanism solution of the seismic event, we initiated complementary, multi-disciplinary research by combining seismological and remote sensing data processing, followed by extensive field validation. Detailed geological mapping, fault surface measuring accompanied with tectonic analysis, fault photorealistic model creation by unmanned aerial system data processing, post-seismic surface deformation analysis by DInSAR image interpretation coupled with accurately relocated epicenters recorded by locally established seismographs have been carried out. The combination of the results obtained from these techniques led to the determination of the contemporary tectonic stress regime that caused the earthquake in central Crete, which was found compatible with extensional processes parallel to the Hellenic arc.

Quaternary tectonic history of seismically active intraplate Kachchh Rift Basin, western India: A review

Since the recorded historical period, the Kachchh Rift Basin (KRB) has encountered numerous moderate to large magnitude earthquakes. According to the series of seismicity research so far, there are several important points of debate regarding the tectonic history and evolution of the KRB, especially during the Quaternary period. Therefore, the main objective of the present research is to inspect and perceive the association amongst the strain build-up, earthquake provenance, landform evolution and progression as archived by the Quaternary deposits of the KRB. The previous studies demonstrated the evolutions of various landforms, such as the uplifted fluvial terraces, formation of the gorges, uplifted alluvial fan sequences, which can be ideally used to reconstruct the neotectonic history along active faults of KRB. Considering this, the analysis of the accessible and supportive data, including geochronology provided by earlier studies along with some new dataset for a superior knowledge on the Quaternary tectonic forces prevailing in the KRB, have been carried out. Furthermore, we also emphasized the differences and directions for future potential research issues. The observations of variability in uplift rates across the various active faults in the KRB suggest a complex geological history during the Quaternary period. The results show that the vertical uplift rate along the significant active faults range from 0.8 to 2.8 mm/yr, demonstrating the variable tectonic stress regime prevailing in the KRB. The uplift rates constricted from geomorphic and chronological aspects suggest that the tectonic movements within the Kachchh intraplate region is regulated by the fault segments and the present tectonic stress field is in accordance with the encompassing tectonic stress field associated with the northward movement of the Indian plate corresponding to the Eurasian plate.

Temporal evolution of the focal mechanism consistency of the 2021 Yangbi MS 6.4 earthquake sequence in Yunnan

Using the Cut And Paste (CAP) method, we invert the focal mechanism of 38 moderate earthquakes (MS ≥ 3.0) recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum spatial rotation angle. Our results indicate that the MS 6.4 mainshock is induced by a lateral strike slip fault (with a rake angle of ∼ −165°) and a little normal-faulting component event along a nearly vertical plane (dipping angle∼ 79° and strike ∼138°). Combining our results with high resolution catalog, we argue that the seismogenic fault of this earthquake sequence is a secondary fault western to the major Weixi-Qiaohou-Weishan fault. The focal mechanism evolution can be divided into three periods. During the first period, the foreshock sequence, the focal mechanism consistency is the highest (KA<36°); during the second period which is shortly after the mainshock, the focal mechanism shows strong variation with KA ranging from 8° to 110°; during the third period, the seismicity becomes weak and the focal mechanism of the earthquakes becomes more consistent than the second period (18°<KA<73°). We suggest that the KA, to some extent, represents the coherence between local tectonic stress regime and the stress state of each individual earthquake. Furthermore, high focal mechanism consistency and high linearity of seismic distribution may serve as indicators for the identification of foreshock sequence.