Direction Of Compressive Stress Research Articles

Seismic anisotropy and stress-field variations along the Dead Sea Fault zone in northern Israel

Geological observations based mainly on stress (strain)-indicating meso-scale markers suggest that the local maximum horizontal compressive stress (SHmax) direction along the Dead Sea Fault (DSF) system in northern Israel changes considerably over short distances from a ∼ N-S, fault-parallel orientation in the south to an ∼E-W, fault-perpendicular orientation in the north. However, the association of the meso-scale markers to the present-day stress field is not well constrained as many of them could have formed at any stage during the DSF evolution. In this study, we use a large dataset of Shear-Wave Splitting (SWS) measurements, taken from local DSF-related earthquakes, to characterize the azimuthal seismic anisotropy of the upper-crust at this critical turning point of the DSF system, near the Lebanese Restraining Bend. The SWS directions commonly align parallel to the local SHmax as revealed by the meso-scale markers, supporting their association with the current stress field. In several stations, SWS fast directions indicate azimuthal anisotropy at high angles to the trace of the master fault, indicating that stress-induced anisotropy represents a more plausible mechanism for SWS than structure-controlled anisotropy. The SWS measurements suggest that a northward counterclockwise rotation of the crustal SHmax is present along this segment of the DSF, supporting previous notation on the transition from divergent to convergent strike-slip faulting in this area. Plain langauge summaryGeological observations based mainly on stress (strain)-indicating meso-scale markers suggest that the local maximum horizontal compressive stress direction along the plate-boundary Dead Sea Fault (DSF) system in northern Israel changes considerably over short distances. However, the association of the meso-scale markers to the present-day local stress field is not well constrained since many of them could have formed at any stage of the DSF evolution. In this study, we use a common method of measuring local seismic anisotropy called “shear wave splitting” (SWS) to characterize the directional-dependent seismic wave speeds in the upper crust. The SWS measurements are obtained from local seismic and micro-seismic DSF-related events, and characterize the upper-crust seismic anisotropy at this critical turning point of the DSF system. The SWS directions commonly align parallel to the maximum compression as revealed by the meso-scale markers, supporting their association with the current stress field. The SWS measurements suggest that a northward counterclockwise rotation of the crustal maximum compression is present along this segment of the DSF.

Evolution of tensile fractures in feldspar porphyroclast and its implication in paleostress estimation

Fractures are ubiquitous brittle features of the upper crust. Syntectonic granites are often replete with fractures of various attitudes, cross-cutting each other, which develop under the prevalent states of stress. In this article, we study the origin and mechanism of formation of tensile fractures restricted within rectangular alkali feldspar porphyroclasts found in Closepet granite (Dharwar Craton, India), and venture on the possibility of using them as potential paleostress marker. The study is conducted using finite-element-method (FEM) to assess the distribution of induced stresses within the porphyroclasts considering the geometry and varying mechanical properties of the porphyroclast and the embedding matrix. We infer that fractures in the porphyroclast develop due to amplification and concentration of far-field stresses within it. The direction of maximum principal compressive stress as indicated by the fractured porphyroclasts lies in close proximity to the paleostress direction derived from fault-slip analysis of adjacent bodies such as Chitradurga Schist Belt and Koppal syenite (Dharwar craton). Therefore, we advocate that fractured feldspar porphyroclasts are a reliable indicator of paleostress orientations.

Mapping of stress and structure controlled upper crustal anisotropy in Kumaon-Gharwal Himalaya

Shear wave splitting analysis of local earthquakes provides valuable insights into the structure and stress controlled upper crustal anisotropy signatures. We examine these signatures at the Kumaon-Garhwal Himalaya and provides an excellent example of anisotropic crustal structure in the ongoing continent-continent collision settings between Indian and the Eurasian plates. A total of 256 local earthquakes were selected for the analysis (1.0 ≤ M ≤ 5.4) between January 2017 and February 2021, recorded at a dense network of 51 broadband stations. The result indicates the observed crustal anisotropy is parallel to stress-aligned micro-cracks far from the major Himalayan fault zones and structure parallel near the fault zones. The dominant fast polarization directions (FPD) in the Inner Lesser Himalaya (ILH) and Higher Himalaya, are consistent with the maximum compressive horizontal stress directions (SHmax), essentially influenced by the local stress field. Whereas in the Outer Lesser Himalaya (OLH) and Sub Himalaya, fast directions are sub-parallel to the structural trends, suggesting that the anisotropy is associated with the shear fabric from recent deformation episodes related to structural induced anisotropy. The computed normalized delay times show a mean value of 1 ms/km, within the OLH and Sub-Himalaya, while in ILH and Higher Himalaya, this value increases up to 5.3 ms/km. The associated crack densities are 0.0038 and 0.0207, with shear wave velocity anisotropy of 0.38% and 2.07% respectively. Significant scatter within the depth range of 10–15 km is observed in normalized delay times, suggesting the source of anisotropy within the upper crust.

Rigid widths of active block boundary faults and crustal layered anisotropy in the intersection of faults Honghe and Xiaojiang in the SE margin of the Tibetan Plateau

SUMMARYThe distribution of block boundary faults, both horizontally and vertically, has significant implications for crustal movements and structural variations. In the SE margin of the Tibetan Plateau, the south part of the Sichuan–Yunnan block is surrounded by the first-order block boundaries of the Honghe faults (HHF) trending NW–SE and the Xiaojiang faults (XJF) trending N–S. Crustal anisotropy provides valuable insights into the ongoing deformation and evolution. This study investigates the upper-crustal anisotropy at 26 stations, using local seismic waveforms from the temporary linear Honghe–Xiaojiang seismic broad-band Array (i.e. the HX Array) in 2017–2019 and regional permanent stations in 2012–2019. The PFS (i.e. polarization of fast S wave) shows an abrupt change in the Yimen region, which is the middle of the HX Array survey line between two large faults. The NW–SE dominant PFS orientations across the HHF agree well with the strike of faults and the direction of regional principal compressive stress, illustrating cracks or minerals aligned with the HHF, influenced by regional stress. The NE–SW dominant PFS orientations crossing the XJF differ from the faults strike or regional stress orientation, suggesting alignment with microcracks caused by the in situ principal compressive stress. The comparison between the upper-crustal and whole-crustal anisotropy demonstrates a noticeable PFS consistency across the two large faults, the HHF and the XJF. This observation implies that these two large faults may tectonically control a wide zone, with wide rigid widths of approximately 150 and 200 km, respectively. This study presents a new pattern indicating the control of deep physical properties on the boundary faults and uncovering the layered deformation in the upper and lower crust.

Self-toughening mechanism of the ZrO2 scale and the precipitation of Sn during the steam oxidation of ZIRLO™ at 1200 °C

The steam oxidation behavior of ZIRLO™ at 1200 °C was investigated using a thermogravimetric analyzer. The microstructure of the oxide was analyzed using SEM, EBSD, and FIB+TEM in depth. Very long “spaghetti-like” columnar oxide grains were formed owing to the intracrystalline diffusion of O2− and the high oxidation temperature. These grains extended from the oxide/matrix interface to a thin outer equiaxed grain layer. The special growth mechanism of the columnar grains determines the unique properties of the oxide scale, such that their structural integrity cannot be destroyed. Therefore, the oxidation kinetics followed a parabolic law throughout the oxidation process without breakaway behavior. Observations revealed the presence of twins, slip bands, and subgrains within the ZrO2 grains, which were identified as the primary manners of oxide deformation under stress. The residual stress and phase distribution along the thickness of the oxide were investigated using synchrotron radiation X-ray diffraction. The oxide was almost completely transformed into a m phase after oxidation. The compressive stress inside the oxide was relatively low, indicating that the stress was relaxed. Transformation toughening, plastic deformation, densely arranged columnar grains, and the absence of grain boundaries parallel to the direction of compressive stress constitute the self-toughening mechanism of the ZrO2 scale. Zr5Sn3, ZrSn2, and β-Nb second phase particles were observed at the ZrO2 grain boundaries and inside the ZrO2 grains. The outward diffusion of Sn in the liquid state and the peritectic reaction can result in the formation of voids at the edges of the second phase particles.

Active ages of metallogenic structures in the Liangyan lead–zinc deposit, northwestern Guizhou: Constraints from geometric, kinematic, and sphalerite Rb-Sr dating analyses

More than ten lead–zinc deposits formed under the control of the Yadu-Mangdong fault (YMF) are known to have undergone multi-stage activity. However, ore control processes in such fault zones are poorly understood, such as in the Liangyan deposit in northwestern Guizhou. The internal geometrical structure, mineralization, alteration, tectonic stress, and kinematics of the YMF were investigated in three sections (1605, 1655, and 1720) of the Liangyan deposit. The ore-forming age (214.8 ± 4.3 Ma) was obtained by rubidium-strontium dating of sphalerite. The YMF is defined by double-fault cores and superimposed faults that indicate at least three stages of deformation since the mineralization period. The first stage is characterized by the ore-bearing dolomitization ancient fault core formed in the Indosinian period. The principal compressive stress direction was northwest to southeast (NW-SE). The second stage of Yanshanian was the tectonic breccia fault stage (new fault core). The principal compressive stress was northeast to southwest (NE-SW). The third stage was dominated by superposed faults that destroyed the new fault core in the Himalayan period. The principal compressive stress direction was east to west (E-W). In summary, we established a model of evolution for the YMF since the metallogenic period. In conclusion, based on the above research, we consider that the YMF turning point of the Liangyan deposit is prone to orebodies. Additionally, the prospecting target should be concentrated in the footwall (NW-trending) and hanging wall (NE-trending) of the Liangyan deposit YMF model.

Seismic anisotropy in the upper crust around the north segment of Xiaojiang faults in the SE margin of Tibetan Plateau

The Xiaojiang faults located in the SE margin of the Tibetan Plateau is a fault system of left-lateral strike-slip, striking NS, between the 2nd-order Sichuan-Yunnan block and the 1st-order South China block. The Xiaojiang faults and the surrounding areas are characterized by strong tectonic movements and intense seismic activities. Using seismic data from January 2013 to November 2020 recorded at the stations of the temporary QiaoJia seismic Array (QJ Array), deployed by the Institute of Geophysics, China Earthquake Administration, this study investigates the upper crustal anisotropy by the shear-wave splitting analysis on small local earthquakes, discusses the deformation patterns in the upper crust in the north segment of the Xiaojiang faults, evaluates the stress distribution in the study area, and analyzes its relationship with the regional tectonic structure. Adopting the data processing technique of shear-wave splitting, a total of 875 effective records were obtained at 50 stations. The mean direction of polarizations of fast shear-wave (PFS) is 162° ± 44° in the study areaand the mean normalized time-delay is 4.96 ± 2.38 ms/km. Based on the spatial distribution of the PFS and the regional geologic structure, the study area is divided into two zones: the zone N and the zone S. The PFS in the zone N is scattered, but the dominant PFS direction is in NNW, which is consistent with the direction of the regional maximum principal compressive stress. In the zone N, there are a few smaller local areas (i.e., subzones A, B, C, and D) in which the orientations of the PFS are quite different from the surrounding area. In the zone S, the dominant directions at most stations are in nearly NS, consistent with the strike of the Xiaojiang fault. It reveals the detailed spatial distribution of seismic anisotropy in the upper crust, as well as in situ principal compressive stress, indicating the influence of the regional stress, the complex tectonic environment, and maybe also the impact of the South China block. It also reveals that there also might be an upper-crust scale of tectonic line at near 26°20′N under Xiaojiang faults, which coincides with the north-south tectonic boundary in the lithospheric anisotropy.

A reassessment of the CSA S304 chi-factor for design of reinforced concrete masonry members: large-scale experimental investigation

An experimental investigation was conducted that consisted of 12 pairs of reinforced masonry specimens in which the two specimens were constructed with their longitudinal axes oriented parallel and perpendicular to the laboratory floor, respectively. This work was conducted to reassess the need for the χ-factor accounting for the direction of compressive stresses in masonry members in relation to the direction used to establish their masonry assemblage strength included in CSA S304-14— Design of Masonry Structures. Parameters investigated included block size and reinforcement ratio. Test results suggest that the χ-factor can be eliminated from future editions of CSA S304 but should be considered with caution: a review of the literature and the current tests show that, in some cases, voids may develop between the exterior webs of adjacent blocks and so may be the source of the reduction in the magnitude of the equivalent rectangular compressive stress block.

Shear wave splitting analysis of local earthquakes from dense arrays in Shimian, Sichuan

The Shimian area of Sichuan sits at the junction of the Bayan Har block, Sichuan-Yunnan rhombic block, and Yangtze block, where several faults intersect. This region features intense tectonic activity and frequent earthquakes. In this study, we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region. We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area. Although some stations returned a polarization direction of NNW-SSE, a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area. The polarization directions of the fast shear wave were highly consistent throughout the study area. This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults. The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures. The mean delay time between fast and slow shear waves was 3.83 ms/km, slightly greater than the values obtained in other regions of Sichuan. This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.

Structural diagenesis and high-quality reservoir prediction of tight sandstones: A case study of the Jurassic Ahe Formation of the Dibei gas reservoir, Kuqa depression, Tarim basin, NW China

• The paleo-tectonic stress was verified to be an important factor for porosity reduction in tight sandstones . • The structural diagenesis of tight sandstone of Ahe Formation was quantitatively characterized. • The favorable reservoir areas were predicted based on structural diagenesis and stress field simulation. Structural diagenesis is an important factor controlling the reservoir characteristics of the Jurassic Ahe Formation (J 1 a) of the Dibei gas reservoir in the northern structural belt of the Kuqa depression, which is mainly manifested as the compaction-attributed porosity reduction by the paleo-tectonic stress and structural fracture formation. Based on the analysis of the reservoir and tectonic stress characteristics, the control effects of the paleo-tectonic stress on porosity reduction and structural fracture characteristics of the Ahe Formation reservoir are quantitatively investigated. With numerical simulation based on the finite element method, the high-quality reservoir area of the Jurassic Ahe Formation of the Dibei gas reservoir is predicted. The results show that paleo-tectonic stress is an important element affecting reservoir physical properties and structural fracture characteristics of the Ahe Formation. The maximum paleo effective compressive stress is negatively linearly correlated with the average reservoir porosity, while it is positively exponentially correlated with the porosity reduction attributed to tectonic compaction. The direction of the maximum paleo effective compressive stress controls the dominant striking direction of structural fractures, and the stress magnitude determines the development degree of structural fractures. A clear positive exponential correlation is found between the maximum paleo effective compressive stress and both the areal density and plane porosity of fractures. The Well DX1-YN2-DB104 district and Well TZ4 district present high gas production, and the circular zone in the central-southern part of the study area has paleo-tectonic stress and reservoir characteristics similar to those of the above two districts. Thus, it is a potential favorable area for high gas production and should be considered a key exploration orientation of the Dibei gas reservoir.

Preferred orientation of calcium silicate hydrate and its implication to concrete creep

Calcium silicate hydrate (C–S–H) is the primary binding phase of cement-based and alkali-activated materials. The preferred orientation of C–S–H under non-hydrostatic pressure (e.g., uniaxial/biaxial load) is overlooked yet crucial in understanding concrete's multiscale mechanical performance. Here, we unveil the texture formation of C–S–H under compressive deviatoric stress, S, from 0 to ∼200 MPa, using high-pressure X-ray diffraction. Texture initiated at S < 12 MPa: the c-axis (normal to the basal plane) of C–S–H nanocrystallites preferentially re-oriented towards the direction of the principal compressive stress. Below S ∼100 MPa, the preferred orientation intensified through translation and rotation of C–S–H nanocrystallites; above ∼100 MPa, the texture stopped growing then weakened, suggesting internal transformations of C–S–H nanocrystallites. The time-dependence of the preferred orientation development is unveiled by the texture weakening after full unloading. The findings implicate that concrete creep under service loads is contributed by the intergranular preferential re-orientation of C–S–H nanocrystallites, not interlayer sliding or silicate chain breakage.

Damage of reservoir rock induced by CO2 injection

The study of reservoir rock damage induced by gas injection is of great significance to the design of reservoir stimulation and the improvement of oil and gas recovery. Based on an example horizontal well in the Hudson Oilfield of the Tarim Basin and considering the multi-physics coupling effects among high-pressure fluid, rock deformation, and damage propagation during CO 2 injection, a three-dimensional finite element model for CO 2 injection in deep reservoir considering seepage-stress-damage coupling was developed. The evolution of reservoir rock damage under different CO 2 injection conditions was systematically investigated. The results show that tensile damage and shear damage are concentrated in the vertical direction and the horizontal maximum compressive principal stress direction, respectively, and the tensile damage is the main damage mode. At higher CO 2 injection rate and pressure, the damaged areas near the wellbore are mainly distributed in the direction of the maximum compressive principal stress, and the development of the damaged area near the wellbore will be inhibited by the formation and evolution of far-field damage. CO 2 injection aggravates the extension of tensile damage, but inhibits the initiation of shear damage, and eventually leads to the gradual transition from shear damage to tensile damage. Under the same injection conditions, CO 2 injection has superior performance in creating rock damage compared with the injection of nitrogen and water. The results in this study provide guidance for enhanced oil recovery in deep oil and gas reservoirs with CO 2 injection.

Active crustal deformation model of the Fen–Wei rift zone, North China: Integration of geologic, geodetic, and stress direction datasets

The Fen–Wei rift zone (FWRZ) of North China is an important zone of active crustal deformation representing a transition from extrusion tectonics related to the Tibetan Plateau to subduction tectonics related to the potential far-field influence of the west Pacific plate. In this study, we determined the kinematic constraints of active crustal deformation in the FWRZ, which are fundamental for forecasting seismicity. NeoKinema, a kinematic finite-element model, was employed to estimate the long-term fault slip rates, distributed crustal deformation field, and on- and off-fault strain-rate fields in the FWRZ by fitting updated geological fault slip rate, geodetic GPS velocity, and principal compressive stress direction datasets. Our results show that the FWRZ is a characteristic low-strain kinematic setting, with most active faults exhibiting slip rates of less than 1 mm/a. The total sinistral shear rate from the southern Ordos block to the Qinling Mountains is approximately 1 mm/a, indicating limited tectonic extrusion along the EW-trending Qinling Mountains. Additionally, the central Shanxi rift exhibits prominent dextral shear of ∼0.5 mm/a that decreases toward its north and south ends, corresponding to crustal extension of 1.1–1.2 mm/a in the Datong and Yuncheng basins, respectively. However, this significant crustal extension cannot be solely attributed to terminal effects caused by dextral shear in the central Shanxi rift. A comparison between predicted seismicity and historical earthquake records reveals some remarkable seismic gaps, particularly in the Datong, Hancheng, and Yuncheng basins, indicating higher seismic potential in these locations. This study provides insights into the long-term crustal deformation processes and regional seismic potential of the FWRZ.

Determining the regional tectonic stress field by remote sensing in the Bou Azzer inlier, Central Anti-Atlas, Morocco

Purpose. This paper deals with the determination of the regional stress field direction of the Bou Azzer inlier using the remote sensing tool. Methods. CIn this study, we use an approach to digital mapping by remote sensing, including the steps of pre-processing and processing of Landsat-8 OLI images. Then, an automatic extraction of lineaments based on directional filtering has been performed. To determine the main directions of major mean fractures, these results have been supplemented and confirmed by an integrated model, including a synthesis of bibliographic works and field studies. Findings. The directional rosette analysis results show four systems of major directions namely, N0°, N45°, N90° and N135°. The regional stress field in the study area, according to tectonic history, is characterized by a horizontal compression tectonic regime, as indicated by several systems of strike-slip faults with a high tendency to deformation. Thus, the abundance of brittle and ductile microtectonic indicators confirms the direction of the main compressive stress N°30. The direction of the three-dimensional stress field: σ1: N°30, σ2: N°120, σ3: Vertical component. Originality. The present study allows to determine the regional stress field direction of the Bou Azzer inlier, in particular, in areas affected by complex tectonics of various scales, as well as in hard-to-reach areas. Practical implications. In mining practice, the study of stability using 2D and 3D geotechnical numerical modeling of underground mine workings is essential. The stress field direction is an important input parameter to develop more realistic decision support models, as well as to ensure the safety of people and materials at the Bou Azzer mine.

Upper crustal anisotropy in the Southeastern Sichuan Basin, China from shear-wave splitting measurements

The Sichuan basin which embodies salt and shale gas resources, is characterized by low seismicity. Seismicity in the southeastern Sichuan basin increased dramatically in recent years, including a series of moderate to strong earthquakes. We investigate seismic anisotropy in the upper crust by performing shear wave splitting analyses on local earthquakes recorded at seventeen stations around the Changning-Xingwen area, southeastern Sichuan basin between January 2016–February 2021. We perform an automatic shear wave splitting analysis and obtain 2926 high-quality splitting measurements by examining 5174 local earthquakes. The delay times range between 0.08 and 0.20 s, and the anisotropy magnitude ranges between 1.9% and 5.5% with a mean of 4.2%, indicating that the study area has significant strength of anisotropy. The fast polarization directions are highly variable reflecting a combined effect of complex local structure and stress field in this area. In the southeastern part of the study area, fast directions are aligned parallel to NW- and NE-oriented surface structures, suggesting structural anisotropy. In the northwestern part of the study area, fast-polarization directions align parallel to the strike of folds and the direction of maximum horizontal compressive stress, probably reflecting the combination of both stress- and structural-controlled anisotropy. Whereas at these stations of central part, fast directions tend to align parallel to the direction of maximum horizontal compressive stress, suggesting stress-induced anisotropy. We examined the temporal variation of seismic anisotropy associated with the 2019 MS 6.0 Changning earthquake. The significant changes in splitting parameters during the Changning earthquake period may only reflect the spatial changes in seismic anisotropy.

Depth-dependent crustal azimuthal anisotropy in the Salton Trough, southern California

We present new crustal models of azimuthally anisotropic P-wave velocity, isotropic P-wave velocity (Vp), isotropic S-wave velocity (Vs) and Vp/Vs ratio for the Salton Trough. High Vp/Vs ratio is revealed at depths of 2–8 km along the San Andreas Fault, implying the possible presence of fluids. High Vp and high Vp/Vs ratio (>1.8) structures of the mid-lower crust beneath the Salton Trough possibly reflect the underplated gabbroic rocks as a result of the extension-induced partial melting of the upwelling asthenospheric materials. The fast velocity directions (FVDs) generally correlate with the direction of the maximum horizontal compressive stress except that fault-parallel FVDs are found at main fault traces. However, the FVDs in the Salton Trough show complex features. The northern Slaton Trough basin (the northern Salton Sea basin and Coachella Valley basin) is dominated by NW-SE FVDs, which are possibly due to the active compression happening there. E-W oriented FVDs predominate the upper crust of the southern Salton Trough basin (the southern Salton Sea basin and Imperial Valley basin), possibly due to faulting and/or block rotation. As the depth increases (12–18 km), the FVDs to the south of the Salton Sea have an overall rotation and gradually become NW-SE. The depth-dependent variation of anisotropy orientation may be attributed to a large band of underlying heat source that probably causes a change of stress field by imposing thermal stress on overlying rocks. In all, our velocity models suggest that faults in the Salton Trough may bear a high risk of mechanical failures due to the complexities of stress distribution and geological structures as well as the presence of a large volume of fluids and heat.

Texture and morphology of veins and their relationship to gold mineralization in the Penjom deposit, Malaysia

AbstractPenjom deposit is an orogenic gold deposit located in the Central Belt of Peninsular Malaysia. Gold mineralization is associated with various styles and textures of quartz‐carbonate veins hosted within the metasedimentary as the main host rock and felsic igneous rock including minor volcanic rock. Vein textural features and morphologies have been investigated based on macroscopic and microscopic characteristics to understand the process of veins formation, and the relationship with gold mineralization. At the hand specimen scale, veins show a variety of textures that are either primary or superimposed. Primary textures are comb, massive anhedral buck quartz veins, and laminae veins or vein septa representing early vein introduction without vein modification. Extension veins that are normally concordant to maximum compressive stress direction show either a common comb texture within these veins or buck texture inside thick veins. Secondary textures are ribbon, stylolites, breccias, and late spider veinlets that overprint early veins formed during repeated structural episodes. Later stage deformation events superimposed on the existing veins texture results in intensely deformed veins. The interrelationship of structure, vein‐type and texture, gold and sulfide mineralogy have been correlated to constrain the episodes of gold mineralization in the Penjom deposit. Characteristics of vein textures indicate physio‐environment under confining lithostatic pressure where fluids filled the space through crack and sealing mechanism. Vein systems and gold mineralization events that have been correlated with the D2D3 (fold‐fault) deformation events and inferred to be temporally related to the late‐stage regional orogenic event dated Late Triassic‐Early Jurassic that affected Peninsular Malaysia.

Characteristics of crustal stress field in Tienshan area

Based on 1143 focal mechanisms in Tienshan area from 1900 to 2019, according to the world stress map classification criterion, the main types of focal dislocations are thrust and strike slip; The results of parameter statistics show that the nodal plane of focal mechanism solution is basically consistent with the main tectonic strike in Tienshan area, and the orientation of P axis is perpendicular to the main tectonic strike in Tienshan area, which shows the horizontal nearly NS thrust. The direction of the maximum principal compressive stress is 175.1°, the minimum principal stress direction is 67.8°, the plunge angle of the maximum principal compressive stress axis is 4.3°, the plunge angle of the minimum principal compressive stress axis is 75.8°, the relative stress ratio R is 0.80, and the stress state is compressional, which indicates that the area is in the background of compressional orogeny.

The 2018 phreatic eruption at Mt. Motoshirane of Kusatsu\u2013Shirane volcano, Japan: eruption and intrusion of hydrothermal fluid observed by a borehole tiltmeter network

We estimate the mass and energy budgets for the 2018 phreatic eruption of Mt. Motoshirane on Kusatsu–Shirane volcano, Japan, based on data obtained from a network of eight tiltmeters and weather radar echoes. The tilt records can be explained by a subvertical crack model. Small craters that were formed by previous eruptions are aligned WNW–ESE, which is consistent with the strike of the crack modeled in this study. The direction of maximum compressive stress in this region is horizontal and oriented WNW–ESE, allowing fluid to intrude from depth through a crack with this orientation. Based on the crack model, hypocenter distribution, and MT resistivity structure, we infer that fluid from a hydrothermal reservoir at a depth of 2 km below Kusatsu–Shirane volcano has repeatedly ascended through a pre-existing subvertical crack. The inflation and deflation volumes during the 2018 eruption are estimated to have been 5.1 × 105 and 3.6 × 105 m3, respectively, meaning that 1.5 × 105 m3 of expanded volume formed underground. The total heat associated with the expanded volume is estimated to have been ≥ 1014 J, similar to or exceeding the annual heat released from Yugama Crater Lake of Mt. Shirane and that from the largest eruption during the past 130 year. Although the ejecta mass of the 2018 phreatic eruption was small, the eruption at Mt. Motoshirane was not negligible in terms of the energy budget of Kusatsu–Shirane volcano. A water mass of 0.1–2.0 × 107 kg was discharged as a volcanic cloud, based on weather radar echoes, which is smaller than the mass associated with the deflation. We suggest that underground water acted as a buffer against the sudden intrusion of hydrothermal fluids, absorbing some of the fluid that ascended through the crack.

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

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