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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.

The specific features of the field of deep intrusions and tectonics of the NR are studied. It is shown that the formation of copper–nickel deposits in the study area in the Early Triassic is associated with the evolution of the stress field in the crust over 50‒100 Ma. It is established that the specific features of the formation of the intrusive field at the initial stage are associated with the deep and lateral heterogeneity of the stress state that arose before the onset of magmatism in the Early Permian in the crust of the Khantay‒Rybninsky uplift and adjacent structures. The emergence of this heterogeneity, which has an inherited long-term nature, is due to the formation of uplifts (swells) in the region and the processes of denudation of the surface of these uplifts (amplitudes of 1.5‒2.5 km). Since the processes of surface denudation lead to the release of rocks that have experienced a supercritical flow at great depths, in the upper part and, partially, in the middle part of the crystalline crust of the Khantay‒Rybninsky uplift and adjacent territories there were prerequisites for the emergence of a stress state of horizontal compression. In the lower part of the crust of the Khantay‒Rybninsky uplift, as well as in the crust of the Norilsk‒Kharaelakh trough and the Tunguska syneclise, the horizontal extension regime was preserved. This difference in the stress state of the crust determined the specific features of the spatial heterogeneity of the development of volcanism and intracrustal magmatism of the Norilsk‒Kharaelakh trough and Tunguska syneclise. [ABSTRACT FROM AUTHOR]

Stability problems in rock stress fields were highlighted. It is a direct source of force for crustal deformation, rock destruction, and earthquake occurrence. Through large-scale international cooperation, the global GPS velocity field and world stress map were updated. Plates with the soul of a power source are no longer a bunch of rigid tectonics, and for the first time the dynamism of their movements and internal stresses are revealed. This paper describes the methods of in-situ measurement of stress, the principles of division of stress tensor regimes, and the basic features of stress maps. In response to the earthquake focal mechanism, the author has drawn a variety of 3D perspective drawings, so that readers can easily grasp the geologic meaning of the earthquake focal mechanism in a way that is easy to read and understand by looking at the drawings. Finally, the background of the local dynamics is analyzed with two examples comparing the similarities and differences between the measured stress maps and the earthquake focal mechanism.

Anomalously 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. Plain Language Summary: A dense seismic network operational from April 2019 to May 2023 has been continuously recording earthquakes occurring in and around Sikkim Himalaya. In this study, we have located the earthquakes occurring within 200 km radius of Sikkim Himalaya to determine which regions are seismically active. We further analyzed these earthquakes to deduce deformation in the source region, which comprises of how the accumulated stress in the Earth gets released. This study aided in mapping the fault zones and its sense of motion, which are responsible for the persistent occurrence of earthquakes. We provide the possible extent of the debated mid‐crustal Dhubri‐Chungthang Fault Zone, which traverses across the study region and is stated to orthogonally divide the arcuate Himalayas. Our study also provides evidence for earthquakes originating in the lower‐crust due to overlapping of parallelly dipping layers of the Moho. Earthquakes occurring in upper‐crust and along the Moho boundary attest to previously obtained results. Such complex multi‐fault dynamics increases the seismic hazard potential in Sikkim Himalaya. Key Points: High resolution local earthquake catalog for Sikkim Himalaya recorded at the longest running seismic networkDelineation of possible seismogenic extent of the highly debated Dhubri‐Chungthang Fault ZoneEvidence of lower crustal earthquakes along imbricated Moho [ABSTRACT FROM AUTHOR]

Copyright of Progress in Earthquake Sciences is the property of China Earthquake Administration, Institute of Geophysics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Berane Basin is a Miocene, northeast‐southwest oriented intramountain basin of the Dinarides, overlying the pre‐neotectonic basement of the Drina–Ivanjica unit, the East Bosnian–Durmitor unit and the Western Vardar Zone. The structural evolution and the tectonic regimes that controlled the formation of the Berane Basin are not fully understood. In this paper, we conducted field kinematic analysis by applying fault‐slip inversion to derive paleostress regimes and study the deformation phases that led to the formation of the Berane Basin. Observed deformation is related to the latest Oligocene‐Miocene extension in two directions, perpendicular and parallel to the Dinarides orogen. Such bi‐directional extension resulted in a complex fault pattern where, among observed normal, oblique and strike‐slip faults, those with oblique‐normal slip dominate. The observed faults likely form a system of mutually overprinting half‐grabens, mainly driven by orogen‐parallel extension associated with the large‐scale regional Skadar–Peć Fault, while orogen‐perpendicular extension has subordinate effects on the Berane Basin formation.

Abstract Anomalously 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.

Present‐day convergence between Caribbean and North American plates is accommodated by subduction zones, major active thrusts and strike‐slip faults, which are probably the source of the historical large earthquakes on Hispaniola. However, little is known of their geometric and kinematic characteristics, slip rates and seismic activity over time. This information is important to understand the active tectonics in Hispaniola, but it is also crucial to estimate the seismic hazard in the region. Here we show that a relatively constant NE‐directed shortening controlled the geometry and kinematics of main active faults in southern central Hispaniola, as well as the evolution of the Quaternary stress regime. This evolution included a pre‐Early Pleistocene D1 event of NE‐trending compression, which gave rise to the large‐scale fold and thrust structure in the Cordillera Central, Peralta Belt, Sierra Martín García and San Juan‐Azua basin. This was followed by a near pure strike‐slip D2 stress regime, partitioned into the N‐S to NE‐SW transverse Ocoa‐Bonao‐La Guácara and Beata Ridge fault zones, as well as subordinate structures in related sub‐parallel deformation corridors. Shift to D2 strike‐slip deformation was related to indentation of the Beata Ridge in southern Hispaniola from the Early to Middle Pleistocene and continues today. D2 was locally coeval by a more heterogeneous and geographically localized D3 extensional deformation. Defined seismotectonic fault zones divide the region into a set of simplified seismogenic zones as starting point for a seismic hazard modeling. Highest peak ground acceleration values computed in the Ocoa Bay establish a very high seismic hazard. Key Points: Active faults in central southern Hispaniola are controlled by NE‐directed shorteningQuaternary stress regime evolution includes a compressional D1 followed by a strike‐slip D2, locally coeval with an extensional D3Modeling establishes a very high seismic hazard zone centered in the Ocoa Bay [ABSTRACT FROM AUTHOR]

Abstract Present‐day convergence between Caribbean and North American plates is accommodated by subduction zones, major active thrusts and strike‐slip faults, which are probably the source of the historical large earthquakes on Hispaniola. However, little is known of their geometric and kinematic characteristics, slip rates and seismic activity over time. This information is important to understand the active tectonics in Hispaniola, but it is also crucial to estimate the seismic hazard in the region. Here we show that a relatively constant NE‐directed shortening controlled the geometry and kinematics of main active faults in southern central Hispaniola, as well as the evolution of the Quaternary stress regime. This evolution included a pre‐Early Pleistocene D1 event of NE‐trending compression, which gave rise to the large‐scale fold and thrust structure in the Cordillera Central, Peralta Belt, Sierra Martín García and San Juan‐Azua basin. This was followed by a near pure strike‐slip D2 stress regime, partitioned into the N‐S to NE‐SW transverse Ocoa‐Bonao‐La Guácara and Beata Ridge fault zones, as well as subordinate structures in related sub‐parallel deformation corridors. Shift to D2 strike‐slip deformation was related to indentation of the Beata Ridge in southern Hispaniola from the Early to Middle Pleistocene and continues today. D2 was locally coeval by a more heterogeneous and geographically localized D3 extensional deformation. Defined seismotectonic fault zones divide the region into a set of simplified seismogenic zones as starting point for a seismic hazard modeling. Highest peak ground acceleration values computed in the Ocoa Bay establish a very high seismic hazard.

The Kodki fault zone comprises a unique fault system along the Median High (MH) zone in the Kachchh Mainland Uplift (KMU) region of the Kachchh Rift Basin (KRB). The structural and paleostress investigation of the Kodki fault zone shows a typical style of bed-parallel slip (BPS) due to repeated reactivation of the normal faults. The fault growth is accompanied by the reactivation of one or both of the fault segments followed by offset due to BSP. In sections where both fault planes reactivate, and propagate past one other forms a bulk between coinciding fault segments that display typical characterization of relay zones. These structures in the Kodki fault section differ from the conventional relay zone in the strata. The thickness of BPS surfaces along the strata equals the fault's throw at the time of the BPS event. Geometrical restoration of the Mesozoic cross-sections exposed across the selected fault displays repeated BPS forming a complex intersecting structure along the Kodki fault zone. Further, the paleostress analysis determines E-W to WNW-ESE maximum extensional stress inhibits recurrences from the reactivation of faults with the MH zone.

The spatio-temporal changes in the fluvial system and landform of the central Kachchh Mainland region are caused by distinctive ongoing tectonic deformations. The present study aims to decipher ongoing tectonic processes resulting modification of landscape in the Central Mainland Kachchh region during the Late Quaternary period. The region marks the presence of several neotectonic features along the faults indicating rejuvenation of the landform due to tectonic activity. The paleostress analysis of the faults indicates normal faulting due to WNW-ESE, E-W to WSW-ENE directed radial to pure extension. The OSL dates from the strath terrace section confirm accommodation of Quaternary sediments from ∼42ka till ∼32ka. The presence of abandoned channels and obstructed tributary channels across the fault plane deciphers reactivation of extensional fault planes at ∼42ka, constituting accommodation space for sedimentation on the downthrown block forming several sag-fill deposits. The sedimentation ceased after ∼32ka due to regional Kachchh Mainland Uplift (KMU) upliftment triggering vertical incision of channels forming several strath and fluvial terraces. The paleostress analysis and dynamic modification of landform depict reactivation of the hinge faults on the structural Mesozoic bend of the basement high known as the ‘Median High’.

In remote northern regions, lacking deep geothermal exploratory boreholes, a theoretical approach to provide a first-order estimate of the stress regime seems a useful tool. Literature data was used in this context to evaluate the orientation of the stress components and empirical relationships were applied to calculate their magnitude in a community of Nunavik, northern Quebec. A Monte Carlo-based sensitivity analysis was carried out due to the uncertainty of the input parameters. Mohr–Coulomb friction and slip tendency analyses were additionally undertaken to assess the stress state and potential reactivation of existing fractures. The results highlight how the poor knowledge of the stress field has an important impact on the design and development of engineered geothermal energy systems in the Canadian off-grid community of Kuujjuaq.

The mechanical earth model (MEM) has recently been considered in the oil and gas industry due to its importance in predicting the safe and stable range of drilling mud, better understanding the effective parameters in wellbore instability, safe drilling and reduce exorbitant costs on the industry and understanding the geomechanical properties of the reservoir. The MEM includes a logical set of information related to geology, stress field, mechanical properties of rock (elastic modulus and rock failure properties) and pore pressure which can be employed as a tool to quickly update information for use in drilling and reservoir management. In this paper, a MEM was constructed using well logging data for a well in one of the oil-fields as a case study and calibrated using laboratory results and drilling reports. According to the results obtained from the minimum horizontal stress values and the maximum horizontal stress range, as well as the occurrence of tensile failures in the wellbore, it was found that the stress regime prevailing in the study field is a strike-slip fault regime. The results also show that shear failure occurs in the direction of minimum horizontal stress and tensile failure occurs in the direction of maximum horizontal stress.

This research assessed stress regimes and fields in eastern Iran using fault-slip data and the tectonic events associated with these changes. Our stress analysis of the brittle structures in the Shekarab Mountains revealed significant changes in stress regimes from the late Cretaceous to the Quaternary. Reconstructing stress fields using the age and sense of fault movements showed that during the late Cretaceous, the direction of the maximum horizontal stress axes (σ1) under a compressional stress regime was ~N290°. This stress regime led to the uplifting of ophiolites and peridotites in eastern Iran. During the Eocene, the σ1 direction was NE-SW. The late Eocene and Oligocene stress states showed two distinct transpression and transtension stress regimes. This transition from transpression to transtension in the eastern Shekarab Mountains was the consequence of regional variations in stress regimes. The Quaternary stress state indicates that the tectonic regime in the Quaternary is strike-slip and the σ1 direction is ~N046°, which coincides with the current convergence direction of the Arabia–Eurasia plates. Our paleostress analysis revealed that four distinct stress regimes have been recognized in the area, including compressional, transtensional, transpressional, and strike-slip regimes. Our findings indicated that the diversity of the tectonic regimes was responsible for the formation of a variety of geological structures, including folds with different axes, faults with different mechanisms, and the current configuration of the Sistan suture zone. [ABSTRACT FROM AUTHOR]

The study of brittle deformation of the collisional mountains can explain its shallow crustal tectonic evolution and the palaeostress regime. The Main Boundary Thrust (MBT) zone in the western Arunachal Himalaya displays imbrication in the Permian Gondwana sequence between the MBT‐1 (/Bome Thrust/MBT‐Upper) in the north and MBT‐2 (/MBT‐Lower) in the south with consistent northerly dip. The Lower Gondwana rocks occur in the footwall of the MBT‐1 with the Proterozoic Bomdila Group in the hangingwall. The upper Gondwana rocks constitute the hangingwall sequence for the MBT‐2 with Neogene Siwalik rocks in the footwall. This article analyses palaeostress using brittle fractures in the Gondwana rocks that crop out for ~120 km2 in the study area. The fault‐bounded imbricate zone depicts eight brittle shear indicators and four sets of joints (J1 and J2: inclined and J3 and J4: subvertical). The signatures of the inherited pre‐Himalayan extensional deformation are preserved in the Lower Gondwana Miri Formation. The Bichom and Bhareli rocks exhibit brittle deformation features of the Himalayan Orogeny under strong ~N‐S compression. The palaeostress analysis of all joint sets indicates three phases of brittle deformation in the Gondwana and Siwalik rocks of the area. The subvertical joint sets and normal faults in the Miri Formation indicate a north‐northwest (NNW)‐directed extensional phase of the pre‐Himalayan origin. The inclined joint sets of the Bichom and Bhareli formations of the Gondwana sequence depict Himalayan orogeny with ~N‐S compressional phases. The third phase of brittle deformation in the Siwalik sequence depicts an east‐west (~E‐W) extension. The arc‐parallel extension in the frontal fold belt of the Arunachal Himalaya may be due to oblique India‐Asia collisional tectonics. [ABSTRACT FROM AUTHOR]

The eastward expansion of the Tibetan Plateau has resulted in different earthquake types in the eastern Tibetan Plateau, but the mechanism remains unclear. Here, we construct a three-dimensional visco-elastoplastic finite element model considering the topography to investigate the influence of fault geometry and rheological heterogeneity on stress fields. In our best-fitting model, the minimum principal stress is nearly vertical around the southern Huya fault zone, which is adjacent to the Longmen Shan fault zone, due to the significant mid-lowerWE crust lateral rheological heterogeneity, and the thrust stress regime accounts for the reverse fault and thrust-dominated earthquakes. In this scenario, the eastward horizontal motion of the mid-lower crust is obstructed and facilitates thrust faulting, suggesting the limited eastward expansion of the Tibetan Plateau. In contrast, the northern Huya fault zone, one of the terminal branches of the East Kunlun fault, accommodates the continuous eastward extrusion of the East Kunlun fault, where the stress regime under a more homogenized crust favors the strike-slip faulting process, along with the dominant strike-slip earthquakes. Moreover, the best-fitting of stress regime explains the thrust-dominated 2008 Ms. 8.0 Wenchuan and 2013 Ms. 7.0 Lushan earthquakes on the Longmen Shan fault zone. Combining geophysical and geodetic observations and model analyses, we propose that the hybrid deformation mode in the eastern Tibetan Plateau is accommodated by upper crustal shear and thrusting deformation and mid-lower crustal thickening driven by the gravitational potential energy gradient. Our results elucidate the mechanism for differences in strong historical earthquakes and, more importantly, isolate the effect of fault geometry from those of heterogeneous viscosity on crustal deformation and stress heterogeneity in the eastern Tibetan Plateau. • We model the three-dimensional stress regime in the eastern Tibetan Plateau. • The stress regime well explains the spatial differences of earthquake types in Huya fault. • The best-fitting model isolates the effect of fault geometry from heterogeneous viscosity on crustal deformation. • The eastern Tibetan Plateau experiences the present-day limited eastward expansion. [ABSTRACT FROM AUTHOR]

Maars are volcanic craters excavated by the interaction of magma and groundwater in subsurface phreatomagmatic explosions. Maar craters display a variety of shapes and sizes, but commonly display elongation. This paper explores the relationship between the orientation of maar elongation and regional stress indicators. The orientations of maar elongation, regional faults, and nearest neighbor lineaments containing maars were measured in seven volcanic fields: Auckland, Lamongan, Newer Volcanics Province, Pali Aike, Pinacate, San Pablo City, and Serdán Orientale. Common maar orientations were observed in several fields, and compared with faulting and nearest neighbor lineaments. It was found that the distribution of maars was commonly correlated with regional stress indicators (in lineaments), but the orientation of elongation of those maars did not always correlate with stress indicators. Maars not aligned with stress indicators were likely influenced by more local effects, including changes to the subsurface stress regime from the ongoing eruption.

This study provides a multi-disciplinary overview of the seismology and geodetic data with tectonics analysis in order to provide an evaluation of stress trajectories, and probabilistic fault rupture hazard assessment. Based on the different scenarios obtained from the comparison of several overviews and their interpretation, we investigated the kinematics and active tectonics of different structural zones. In this study, the magnitudes and directions of seismic and geodetic strain rates (SSR and GSR) were evaluated using reliable earthquake focal mechanisms and all available GPS data (1999–2015) in the structural subzones of northern Iran, where have experienced more than 14 strong instrumental earthquakes (Mw ≥ 6). In addition, a tectonic stress model was inferred from the Focal Mechanism Stress Inversion (FMSI). The new crustal stress map was proposed by the weighted average analysis of the SSR, GSR, and FMSI. N35.5° E and N104° E were estimated for the Alborz and Talesh mountains, respectively. The numerical analysis of stress regimes confirms the slip partitioning mechanism of oblique shortening on the sub-parallel thrusts and strike-slip faults in the area. Four main stress regime categories were defined, including thrust (49.37%), strike-slip (39.24%), thrust with a strike-slip component (2.53%), normal (1.27%), and unknown faulting (7.59%). Seismic and geodetic moment rates (SMR and GMR) and their comparison were also calculated in order to evaluate the function of these parameters in determining the seismicity arrangement. The ratio of the seismic/geodetic moment rates for the area is ~70.7%. This ratio for the Alborz, western Koppeh-Dagh, north part of Central Iran, South Caspian Basin, and Talesh is ~0.9, 0.3, 11.9, 0.3, and 57.3, respectively, which indicates the most elastic energy has been released in the Talesh and the north part of Central Iran. The comparison of geodetic moment rates in the subzones of the area indicates that geodetic deformation is high in the Central Alborz (networks 8, 9, 17) and western Koppeh-Dagh (networks 5, 13). [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the high in situ stresses, dynamic disasters occurred frequently in the Huainan mining area, China. Our understanding of the in situ stresses in this area is still insufficient. In this study, the in situ stresses of 18 sections in two boreholes in the Xinji No. 1 coalfield were measured using the hydraulic fracturing method, and the distribution of in situ stresses in the Huainan mining area were investigated. The relationship between in situ stress and geological structure in the Huainan mining area was summarized and the limitation of fault friction strength on in situ stress was discussed. The result showed that the maximum horizontal principal stress (σH) at Xinji No. 1 mine was 13.95–25.23 MPa, the minimum horizontal principal stress (σh) was 12.16–21.17 MPa. The average azimuth of the maximum horizontal principal stress was N83.61°E. The statistical results showed that the in situ stresses in Huainan mining area were characterized by a strike-slip faulting regime. Both the horizontal and vertical principal stresses increased approximately linearly with the increase of burial depth. The orientation of the maximum principal stress in the study area is closely related to the tectonic movement and the ratio of maximum principal stress to minimum principal stress was primarily limited by the friction strength of the faults. The outcomes of this research can provide some reliable engineering parameters and benefit the roadway layout and support design in the Huainan mining area. [ABSTRACT FROM AUTHOR]

Abstract Based on 54 sets of well test data of 29 coalbed methane (CBM) wells, the distribution characteristic of in situ stress in the eastern part of the southern Junggar Basin and its control on permeability (K), reservoir pressure (Po), and gas content (G) were discussed systematically. The results show that three types of in situ stress regime exist and are converted corresponding to a certain depth, (1) σv > σh); (2) 600‐1050 m is the stress transition zone (σH ≈ σv > σh); and (3) >1050 m is the normal fault regime (σv > σH>σh). Regionally, with depths σv > σh type in the western Miquan, σH ≈ σv > σh type in the middle Fukang, and σv > σH > σh type in the eastern Jimushaer, respectively. Controlled by stress regime and vertical belting, coal K shows a trend of “remarkably decreased, rebounded increase and greatly decreased,” and two decreasing stages ( 1050 m) are mainly influenced by horizontal stress and vertical stress, respectively. Taking a burial depth of 1000‐1150 m as a boundary, the relationship between G and depth converts from “continually increasing” to “gradually decreasing,” which is in good agreement with the converted interface of stress regime from σH ≈ σv > σh type to σv > σH > σh type. Taking the converted interfaces of G (1000‐1150 m), K (800 m), and the prediction depth of the weathered zone (400 m) into consideration, CBM development potential in the study area can be divided into three grades, that is, (1) 400‐800 m (high K and medium G), (2) 800‐1150 m in Miquan and 800‐1000 m in Fukang (medium K and high G), and (3) >1150 m in Miquan and >1000 m in Fukang (low K and poor G). Overall, a key CBM development breakthrough will most likely be made in the study area within the scope of 600‐800 m due to the better G and higher K.

NW Iran-SE Turkey is a tectonically active zone related to the Arabia-Eurasia convergence, but the active stress state in this zone has not yet been clearly studied. To improve the knowledge of present-day stress state in this region, optimum reduced stress tensor was analysed. For this, a large number of earthquake focal mechanisms (277) were collected. The analyses show most mechanisms exhibit strike-slip to thrust faulting. These data indicate that this region is dominated by an N158° maximum horizontal compressive stress (SHmax) belonging to a transpressional tectonic regime. In the scale of the study area, the relative magnitude of the intermediate and minimum principal stress axes do not differ much (ϕ = 0.09). Brittle deformation in this area is dominantly accommodated by a combination of strike-slip and thrust faulting (Aϕ = 1.82 to 2.30). The analyses reveal that two sets of faults show a high tendency to slip and reactivate. These sets contain NW-SE-striking right-lateral and NNE-SSW-striking left-lateral faults. The results of this study may help to study the active seismicity, tectonic activity, and seismic risk in this region. [ABSTRACT FROM AUTHOR]

The Mexican subduction zone, the Gulf of California spreading center, as well as the triple junction point around the Jalisco and the Michoacán Blocks, represents the most active seismogenic belts inducing seismic hazard in the Jalisco-Colima-Michoacán region. Herein, considering such seismotectonic setting, we develop a new seismic source model for the surrounding of Jalisco-Colima-Michoacán to be used as an input in the assessment of the seismic hazard of the region. This new model is based on revised Poissonian earthquake (1787–2018) and focal mechanism (1963–2015) catalogs, as well as crustal thickness data and all information about the geometry of the subducting slabs. The proposed model consists of a total of 37 area sources, comprising all the three different possible categories of seismicity: shallow crustal, interface subduction, and inslab earthquakes. A special care was taken during the delimitation of the boundaries for each area source to ensure that they represent a relatively homogeneous seismotectonic region and to include a relatively large number of earthquakes that enable us to compute as reliable as possible seismicity parameters. Although the sources were delimited following the standard criteria of assessing the probabilistic seismic hazard, they are also characterized in terms of their seismicity parameters (annual rate of earthquakes above Mw 4.0, b-value, and maximum expected magnitude), mean seismogenic depth, as well as the predominant stress regime. The proposed model defines and characterizes regionalized potential seismic sources that can contribute to the seismic hazard at the Jalisco-Colima-Michoacán region, providing the necessary information for seismic hazard estimates. [ABSTRACT FROM AUTHOR]

The paper represents a multidisciplinary investigation of the relation between seismicity, active stress field and geological structure for the West of Romania. The study is based on revised and updated catalogues of earthquakes (3572 events) and focal mechanisms (89 solutions). The large spatio-temporal variations of the stress tensor parameters, b-value (b=0.74-0.81) and fractal dimensions of seismicity (D=1.05-2.34) highlight both clustering patterns along active fault systems and scattered epicentres within planes or volumes. A tectonic model with at least three blocks bordered by active faults is proposed controlling SHmax trend: it rotates clockwise in time and 3D space by up to 900 along with the changes of the stress regime from the compressional to extensional and activity migration between two major and complex fault systems. Low b-values characterize the regardless of the size of data source, but the smaller source/dataset, with or without aftershocks included, ensures a more realistic estimation of seismic hazard that is confirmed by seismic history (Tr_Mw5.5 = 76 years). Key words: active tectonics, earthquakes, focal mechanisms, stress regime, seismic hazardThe paper represents a multidisciplinary investigation of the relation between seismicity, active stress field and geological structure for the West of Romania. The study is based on revised and updated catalogues of earthquakes (3572 events) and focal mechanisms (89 solutions). The large spatio-temporal variations of the stress tensor parameters, b-value (b=0.74-0.81) and fractal dimensions of seismicity (D=1.05-2.34) highlight both clustering patterns along active fault systems and scattered epicentres within planes or volumes. A tectonic model with at least three blocks bordered by active faults is proposed controlling SHmax trend: it rotates clockwise in time and 3D space by up to 90° along with the changes of the stress regime from the compressional to extensional and activity migration between two major and complex fault systems. Low b-values characterize the regardless of the size of data source, but the smaller source/dataset, with or without aftershocks included, ensures a more realistic estimation of seismic hazard that is confirmed by seismic history (Tr_Mw5.5 = 76 years). [ABSTRACT FROM AUTHOR]

The occurrence of many seismic events in energy production projects is caused by fluid injection-induced reactivation of critically stressed faults. The distribution of local stress regime has a significant influence on natural earthquakes, while its role in controlling injection-induced fault slip behavior and seismicity magnitude remains poorly understood. In this paper, we present a three-dimensional hydro-mechanical coupled fault reactivation study using unified pipe-interface element method (UP-IEM). The accuracy and reliability of the numerical method are evaluated and confirmed by numerical verification and actual observation data in Pohang EGS project, South Korea. The relationship between fault aseismic slip, seismic slip and seismicity magnitude is analyzed. Results show that both aseismic and seismic slip have different spatiotemporal distribution with the variation of stress regime. The seismic slip zone will exceed the pressurized area with the increase of initial slip tendency under the strike-slip-faulting stress regime ( σ H > σ v > σ h ). Compared with fluid pressure, the seismic slip is mainly determined by a sudden increase of the shear stress at the aseismic slip zone boundary. In addition, the location of the microseismic events moves towards the fluid pressure propagation front. The larger slip area and seismicity magnitude are easier to be induced under strike-slip-faulting stress regime than thrust-faulting stress regime ( σ H > σ h > σ v ). The tensile failure and higher permeability of the fault induced at injection phase for normal-faulting stress regime ( σ v > σ H > σ h ) leads to a greater seismogenic hazard at the shut-in stage. • A 3D injection-induced fault reactivation model is developed using UP-IEM. • The aseismic slip dominates the slip budget regardless the stress regime. • Seismicity is mainly controlled by sudden shear stress growth at aseismic zone edge. • The magnitude of the slip area and seismicity is normal-fault > strike-slip-fault > thrust-fault. [ABSTRACT FROM AUTHOR]

Based on 54 sets of well test data of 29 coalbed methane (CBM) wells, the distribution characteristic of in situ stress in the eastern part of the southern Junggar Basin and its control on permeability (K), reservoir pressure (Po), and gas content (G) were discussed systematically. The results show that three types of in situ stress regime exist and are converted corresponding to a certain depth, (1) <600 m is the strike‐slip fault regime (σH > σv > σh); (2) 600‐1050 m is the stress transition zone (σH ≈ σv > σh); and (3) >1050 m is the normal fault regime (σv > σH>σh). Regionally, with depths < 1050 m, stress regime also changes from west to east, that is, σH > σv > σh type in the western Miquan, σH ≈ σv > σh type in the middle Fukang, and σv > σH > σh type in the eastern Jimushaer, respectively. Controlled by stress regime and vertical belting, coal K shows a trend of "remarkably decreased, rebounded increase and greatly decreased," and two decreasing stages (<600 m and > 1050 m) are mainly influenced by horizontal stress and vertical stress, respectively. Taking a burial depth of 1000‐1150 m as a boundary, the relationship between G and depth converts from "continually increasing" to "gradually decreasing," which is in good agreement with the converted interface of stress regime from σH ≈ σv > σh type to σv > σH > σh type. Taking the converted interfaces of G (1000‐1150 m), K (800 m), and the prediction depth of the weathered zone (400 m) into consideration, CBM development potential in the study area can be divided into three grades, that is, (1) 400‐800 m (high K and medium G), (2) 800‐1150 m in Miquan and 800‐1000 m in Fukang (medium K and high G), and (3) >1150 m in Miquan and >1000 m in Fukang (low K and poor G). Overall, a key CBM development breakthrough will most likely be made in the study area within the scope of 600‐800 m due to the better G and higher K. [ABSTRACT FROM AUTHOR]

Microscopic kink-bands in platy minerals are a common occurrence at impact craters. The geometry of kink-bands formed in biotite due to an impact cratering experiment on Maggia gneiss was analyzed to see if they might be utilized to deduce the shock wave propagation direction. Here, we investigated the kink-bands in a vertical profile just below the impact point. The intensity of kinking decreases from top to bottom, indicating higher strains near the crater floor. The high asymmetry of kink-bands indicates their formation due to dynamic deformation. We used three methods, viz., the kink-band triangle plot, the contraction-neutral-extension (P-B-T) axes method, and the rotational optimization, to determine the principal stress directions. The shock-wave propagation directions can be deduced from σ 1 orientation. All three approaches indicate a top-bottom orientation of the σ 1 (maximum principal stress direction), which matches the σ 1 orientation during the experiment. Furthermore, we examined the left and right oblique profiles to verify the relationship of kink-band orientations with the variation in angles between the point source and the foliations. The kink-bands in all the profiles show geometric relationship to σ 1. Therefore, the present study underlines the ability of kink bands as a potential indicator of shock-wave propagation directions. • Microscopic kink-bands are formed due to impact experiment on gneiss. • The high asymmetry of kink-bands indicates their formation due to dynamic deformation. • The three used paleostress calculation techniques indicate a top-bottom orientated σ 1. • The estimated σ 1 matches with the σ 1 orientation during the experiment. • The kink-band orientations show a geometric relationship to σ 1. [ABSTRACT FROM AUTHOR]

Abstract Leak-off and formation integrity test data from the central part of the Bavarian Foreland Molasse Basin have been investigated in detail to infer information about the stress regime of the Cenozoic basin fill. The detailed analysis of leak-off test data from the Bavarian Foreland Molasse Basin and lithology-dependent analysis of leak-off test and formation integrity data is the first of its kind in a published study. Only test data from shale-rich sequences have been considered. All data yield minimum principal stresses that are smaller than an estimated vertical stress range. In combination with critical stress and frictional equilibrium theory, the data indicate that the stress regime in the greater Munich area and possibly the far-field stress regime of the Bavarian Foreland Molasse Basin are most likely of an extensional nature (normal-faulting stress regime). Under the assumption of frictional equilibrium, a friction coefficient between 0.2 and 0.4 best explains failure in shale-dominated sections of the central part of the Bavarian Foreland Molasse Basin and can be used to estimate the minimum horizontal stress S Hmin. However, even in the spatially restricted domain of the greater Munich area the stress regime might vary towards a strike-slip stress regime; most likely in the vicinity of fault zones and/or due to variations in mechanical rock strength. The results of this study have great impact and relevance to improved planning of drilling campaigns, future numerical modelling and the general understanding of the evolution of the Bavarian Foreland Molasse Basin. Additional leak-off tests and extended leak-off tests are recommended to fully unravel the spatial variation and geologic control factors of the stress regime of the entire Bavarian Foreland Molasse Basin. Highlights • Leak-off test and formation integrity test data have been analyzed in detail. • A normal-faulting stress regime is most likely present in the greater Munich area. • A friction coefficient between 0.2 and 0.4 can be used to estimate S Hmin in shales. • Lithological composition is key in analyzing formation integrity and leak-off tests. [ABSTRACT FROM AUTHOR]

To study the effects of the tectonic stress environment on the tectonophysical features of deformed coal, No.8 Mine in the Pingdingshan mine area is used as a study area and the relationship between the development of deformed coal, distribution of fractures, formation of deformed coal and tectonic stress environment are analyzed. The results indicate that the thickness of the bedrock layer should be included in the analysis of the tectonic stress environment for a region of intense tectonic activity. Although the reverse faulting stress regime can control the development of deformed coal, the C seam is extremely sensitive to the stress regime. The most advantageous direction of the deformed coal fractures is consistent with the regional maximum principal stress, and the development of fractures is closely related to the evolution of the tectonic stress environment. The fracture density of the E seam presents a uniform distribution, yet that of the C seam is completely heterogeneous. Superposition and compounding of the tectonic communities evidently increase the fracture density of the deformed coal. There is a relatively apparent boundary between the different types of deformation, which gradually transform from brittle to ductile with a decreasing lateral pressure coefficient. A generalized deformation pattern of the deformed coal is proposed and can be divided into frictional sliding and solid flow. [ABSTRACT FROM AUTHOR]

The Tunisian domain is formed following the convergence between Nubia and Eurasia which is responsible for folding and still active faulting. We used 62 earthquake focal mechanisms to constrain the present stress field of the Tunisian domain. The results show that the tectonic regime is compressional with a dominant direction NW-SE maximum horizontal principal stress direction. The focal depth distribution indicates that Northern Tunisia is an area of convergence with a thin crust and a shallow Moho. However, in the central and southern Atlas, the presence of focal mechanisms with strike-slip faulting shows that this zone is a deep seismogenic area with a thick crust.These results are consistent with the neotectonic and seismotectonic stress field determined by other studies. The neotectonic deformations of Tunisia are like the past deformations guided by the convergence between the African and the Eurasian plates. [ABSTRACT FROM AUTHOR]

Northwestern Iran is one of the seismically active regions with a high seismic risk in the world. This area is a part of the complex tectonic system due to the interaction between Arabia, Anatolia and Eurasia. The purpose of this study is to deduce the stress regimes in the northwestern Iran and surrounding regions from stress inversion of earthquake focal mechanisms. We compile 92 focal mechanisms data from the Global CMT catalogue and other sources and also determine the focal mechanisms of 14 earthquakes applying the moment tensor inversion. We divide the studied region into 9 zones using similarity of the horizontal GPS velocities and existing focal mechanisms. We implement two stress inversion methods, Multiple Inverse Method and Iterative Joint Inversion Method, which provide comparable results in terms of orientations of maximum horizontal stress axes SHmax. The similar results of the two methods should make us more confident about the interpretations. We consider zones of exclusion surrounding all the earthquakes according to independent focal mechanisms hypothesis. The hypothesis says that the inversion should involve events that are far enough from each other in order that any previous event doesn't affect the stress field near the earthquake under consideration. Accordingly we deal with the matter by considering zones of exclusion around all the events. The result of exclusion is only significant for eastern Anatolia. The stress regime in this region changes from oblique to strike slip faulting because of the exclusion. In eastern Anatolia, the direction of maximum horizontal stress is nearly north-south. The direction alters to east-west in Talesh region. Errors of σ 1 are lower in all zones comparing with errors of σ 2 and σ 3 and there is a trade-off between data resolution and covariance of the model. The results substantiate the strike-slip and thrust faulting stress regimes in the northwest of Iran. [ABSTRACT FROM AUTHOR]

Shear fractures, dip-slip, strike-slip faults and their striations are preserved in the pre- and syn-rift rocks at Gulf of Suez and northwestern margin of the Red Sea. Fault-kinematic analysis and paleostress reconstruction show that the fault systems that control the Red Sea-Gulf of Suez rift structures develop in at least four tectonic stages. The first one is compressional stage and oriented NE-SW. The average stress regime index R' is 1.55 and S oriented NE-SW. This stage is responsible for reactivation of the N-S to NNE, ENE and WNW Precambrian fractures. The second stage is characterized by WNW dextral and NNW to N-S sinistral faults, and is related to NW-SE compressional stress regime. The third stage is belonging to NE-SW extensional regime. The S is oriented NW-SE parallel to the normal faults, and the average stress regime R' is equal 0.26. The NNE-SSW fourth tectonic stage is considered a counterclockwise rotation of the third stage in Pliocene-Pleistocene age. The first and second stages consider the initial stages of rifting, while the third and fourth represent the main stage of rifting. [ABSTRACT FROM AUTHOR]

The Longmaxi shales are the major hydrocarbon source rocks for Sichuan Basin and adjacent regions in China. Tectonic stress field is important in controling the migration and accumulation of shale gas. In the present study, natural fractures in the Nanchuan region of Sichuan Basin were extensively studied and analyzed with the Rotational Optimization Method (ROM) to reconstruct paleostress fields and their transformation processes. The dominant strikes of natural fractures were in the NW-SE, NE-SW, NWW-SEE and NEE-SWW directions with high-angle oblique or vertical (70~90°) dip angles. Paleostress reconstructions indicated that the Late Yanshanian and Late Himalayan stress fields controlled the tectonics in the Nanchuan region. The orientation of the maximum principal stress (σ) during the Late Yanshanian and Late Himalayan period was ~NW-SE and ~NE-SW trending, respectively. In addition, the majority of stress regimes during the two tectonic stages were strike-slip regimes (SS). Remote effects of the westward subduction of the paleo-Pacific plate activated the Xuefengshan tectonic zone and generated the Late Yanshanian paleostress field. Later, the change in the stress field was due to the variation of tectonic activity intensity in the Xuefengshan and Dabashan tectonic zones. The paleotectonic stress fields and their transformation processes comprehensively influenced the migration and accumulation of hydrocarbons in the Nanchuan region. [ABSTRACT FROM AUTHOR]

The slip vector on a fault is an important parameter in the study of the movement history of a fault and its faulting mechanism. Although there exist many graphical programs to represent the shear stress (or slickenline) orientations on faults, programs to quantitatively calculate the orientation of fault slip based on a given stress field are scarce. In consequence, we develop Slicken 1.0, a software to rapidly calculate the orientation of maximum shear stress on any fault plane. For this direct method of calculating the resolved shear stress on a planar surface, the input data are the unit vector normal to the involved plane, the unit vectors of the three principal stress axes, and the stress ratio. The advantage of this program is that the vertical or horizontal principal stresses are not necessarily required. Due to its nimble design using Java SE 8.0, it runs on most operating systems with the corresponding Java VM. The software program will be practical for geoscience students, geologists and engineers and will help resolve a deficiency in field geology, and structural and engineering geology. [ABSTRACT FROM AUTHOR]

This work applies a three-dimensional (3D) multiscale approach recently developed by Nguyen et al. ( Int. J. Greenhouse Gas Control, 2016, 46:100-115; Greenhouse Gases: Sci. & Technol. , DOI: 10.1002/ghg.1616) to analyze a complex CO 2 faulted reservoir that includes some key geological features of the San Andreas and nearby faults. The approach couples the STOMP-CO2-R code for flow and reactive transport modeling to the ABAQUS ® finite element package for geomechanical analysis. The objective is to examine the coupled hydro-geochemical-mechanical impact on the risk of hydraulic fracture and fault slip in a complex and representative CO 2 reservoir that contains two nearly parallel faults. STOMP-CO2-R/ABAQUS ® coupled analyses of this reservoir are performed assuming extensional and compressional stress regimes to predict evolutions of fluid pressure, stress and strain distributions as well as potential fault failure and leakage of CO 2 along the fault damage zones. The tendency for the faults to slip and pressure margin to fracture are examined in terms of stress regime, mineral composition, crack distributions in the fault damage zones and geomechanical properties. This model in combination with a detailed description of the faults helps assess the coupled hydro-geochemical-mechanical effect. [ABSTRACT FROM AUTHOR]

The increasing number of earthquakes in recent decades in Northwestern Iran and the determination of the epicenters of these events makes possible to estimate accurately the changing tectonic regime using the Win-Tensor inversion focal mechanism program. For this purpose focal mechanism data were collected from various sources, including the Centroid Moment Tensor catalog (CMT). The focal mechanism and fault slip data were analyzed to determine change in the stress field up to the present day. The results showed that two stages of brittle deformation occurred in the region. The first stage was related to Eocene compression in NE-SW direction, which created compressional structures with NW-SE strike, including the North and South Bozgush, south Ahar and Gushedagh thrust belts. The second brittle stage began in the Miocene with NW-SE compression and caused developing thrusts with N-S trends that were active presently. These stress regimes were created by the counter-clockwise rotation of the Azerbaijan plateau caused by movement on strike slip faults and continuous compression between the Arabian plate, the south Caspian basin and the Caucasus region. Pliocene-Quaternary activity of the Sabalan and Sahand volcanoes as well as recent earthquakes occurred as a result of this displacement and rotational movement. The abundance of hot springs in the Ardebil, Hero Abad and Bostanabad areas also bore witness to this activity. [ABSTRACT FROM AUTHOR]