Right-lateral Strike-slip Fault Research Articles

Internal deformation of the North Andean Sliver in Ecuador-southern Colombia observed by InSAR

Summary In the Northern Andes, partitioning of oblique subduction of the Nazca plate beneath the South American continent induces a northeastward motion of the North Andean Sliver. The strain resulting from this motion is absorbed by crustal faults, which have produced magnitude 7 + earthquakes historically in the Andean Cordillera of Ecuador and southern Colombia. In order to quantify the strain in that area, we derive a high-resolution surface velocity map using InSAR time-series processing. We analyzed 6 to 8 years of Sentinel-1 data and combined different satellite line-of-sight directions to produce a reliable velocity map in the East direction. We use interpolated GNSS data to express the velocity map with respect to Stable South America and remove the long-wavelength pattern due to the post-seismic deformation following the 2016 Mw 7.8 Pedernales earthquake. The InSAR velocity map finds high E-W shortening strain rates along N-S trending structures within the Western Cordillera and the Interandean valley, with little deformation taking place east of them. This result strengthens the previous proposition of a ∼350 km long Quito-Latacunga tectonic block, forming a restraining bend in the overall right-lateral strike-slip fault system accommodating the northeastward escape motion of the North Andean Sliver. However, the high spatial resolution provided by InSAR indicates that previously proposed boundaries for this block need to be revised. In particular, InSAR results highlight high strain rate (>300 nstrain/yr) along undescribed active structures, south and west of the proposed limits for the Quito-Latacunga block, respectively in Peltetec and Ibarra regions. Interestingly, the two areas with the largest strain rates spatially correlate with the proposed areas of large historical earthquakes. Modeling of the InSAR and GNSS velocities in these areas suggests shallow coupling and high slip rates on structures which, previously, were not identified as active. We also demonstrate a slow-down of the shallow aseismic slip on the Quito fault after the Pedernales earthquake, suggesting that stress changes following large megathrust events might trigger transient slip behaviors on crustal faults. The high-resolution strain map provided by this work provides a new basis for future tectonic models in the Ecuadorian and southern Colombian Andes, and will contribute to the seismic hazard assessment in this highly populated area of the Andes.

Structural and stratigraphic history of the southern domain of the Indian Mountain Deformed Zone, southeastern New Brunswick, Canada: Tournaisian (Lower Carboniferous) tectonic ‘pop-up’ and collapse

The southern domain of the Indian Mountain Deformed Zone (IMDZ) in southeastern New Brunswick marks a major right-lateral strike-slip fault belt active during late Tournaisian (Lower Carboniferous) sedimentation. The rocks of the Sussex Group, representing a depositional cycle from subsidence to basin inversion, occupy this zone and lie unconformable on crystalline basement, the latter representing a partially exhumed portion of the adjacent (to the south) buried Westmorland uplift. Deformation is related to early reverse faults/thrusts, later strike-slip faults. and latest normal faults. The Gorge Fault zone in the southern domain of the IMDZ demonstrates many essential features of the entire zone. The offset of The Gorge Fault zone increases to the east. In the west it forms a blind thrust and asymmetric anticline whereas in the east it expands into a reverse fault/thrust complex. A progressive evolution from reverse faults/thrusts to strike-slip fault movement resulted in a tectonic pop-up, culminating in gravitational collapse along normal faults with listric profiles that flatten out within 100–200 metres of the present erosion surface. Megabreccias formed during deposition of the Sussex Group are contemporary with reverse fault/thrusts. The geometry of the various faults is best explained by progressive deformation within an overall right-lateral strike-slip regime under general shear, with early formed features rotating both congruently and incongruently to the main IMDZ boundaries. Further complexity is a consequence of many reverse faults/thrusts and normal faults occurring close to a free surface and the latter a response to gravitational instability of the pop-up structure controlled by topography. A revised stratigraphy for the Sussex Group in the Indian Mountain Deformed Zone and its interpretation is integral to constructing the structural history. Two units, Stilesville Formation and Briggs Cross Formation, are formally defined here.

Recent Holocene activity and regional tectonic significance of the northern segment of the red river fault zone

The Red River Fault Zone is a large-scale right-lateral strike-slip fault zone with relatively strong activity during the Quaternary Period. This fault, located on the southeastern margin of the Qinghai‒Tibetan Plateau, plays a key role in the extrusion, rotation and escape of the continental blocks constituting the Qinghai‒Tibetan Plateau. Furthermore, this fault represents the southwestern boundary of the Sichuan–Yunnan Block, which has experienced strong deformation and frequent seismic activity. The northern segment of the Red River Fault Zone is the most active part of the whole fault. However, surface erosion and vegetation coverage have obscured the activity of the northern segment; therefore, the study of its activity has obviously been insufficient. There is still controversy over whether all the secondary faults on the northern segment are active Holocene faults. Studying the activity characteristics of the northern segment, which is densely populated, is particularly important for seismic risk prevention in this area. Based on remote sensing interpretations and field geological surveys, this paper describes the latest activity characteristics of the Cangshan Piedmont Fault, Fengyi–Dingxiling Fault and Midu Basin Margin Fault, including their spatial distributions and kinematic characteristics. According to the ages of the offset strata in profiles, the above three secondary faults were all active in the late Holocene. The latest active age of the Cangshan Piedmont Fault was later than 543-494 cal BP, and two palaeoseismic events that occurred in this section during the Holocene occurred at 2700 and 473 cal BP. The latest active age of the Fengyi–Dingxiling Fault was later than 2760–2700 cal BP; in this section, one Holocene palaeoseismic event occurred between 1777 cal BP and 2730 cal BP, another occurred between 2730 cal BP and 5664 cal BP, and the third occurred between 6449 cal BP and 8360 cal BP. The latest active age of the Midu Basin Margin Fault was later than 558-510 cal BP, and two Holocene palaeoseismic events occurred later than 2318-2114 cal BP and 558-510 cal BP. Based on the results of this paper and previous studies, we believe that the Fengyi–Dingxiling Fault on the northern segment of the Red River Fault Zone is at risk for future strong earthquakes. Additionally, abundant geological and geomorphologic evidence suggests that the northern segment is dominated by normal faults, reflecting the local strain response to secondary clockwise rotation of the Sichuan–Yunnan Block along the boundary fault. This finding is in line with the eastwards extrusion and escape of materials on the Qinghai‒Tibetan Plateau caused by the northwards and northeastwards pushing of the Indian Plate. To a certain extent, these observations reflect the tectonic deformation coordination between block rotation and boundary fault slip in the Sichuan–Yunnan Block in the context of continental block extrusion on the Qinghai–Tibetan Plateau.

The 2013 Mw 6.2 Shonbeh (Kaki) earthquake (Zagros-Iran): seismo-tectonic implications for the Kazerun shear transition zone from high-resolution aftershock and InSAR data analysis

SUMMARY The aim of this study is to investigate the aftershock sequence data recorded by a dense temporary seismological network deployed in the epicentral area of the 2013 April 9 Shonbeh (Kaki) earthquake, located in the south of the Simply Folded Belt of the Zagros (Iran). For a comprehensive understanding, coseismic displacements of the Shonbeh earthquake have been investigated using Interferometric Synthetic Aperture Radar (InSAR) data. The epicentral distribution of high-resolution relocated aftershocks shows NW–SE and N–S trending of seismicity. The aftershocks are confined between ∼3 and ∼14 km depth, which implies that the rupture occurred mostly within the sedimentary cover beside the fault parameters retrieved from InSAR modelling. Projection of precisely located aftershocks on NE-oriented section and InSAR ground displacement data are consistent with both NW-trending NE- and SW-dipping fault segments. We observe a NNW–SSE right-lateral strike-slip motions that accommodate oblique convergence and differential motion between the North and Central Zagros. The spatial pattern and focal mechanisms of aftershocks are consistent with a distributed deformation between NW–SE trending reverse and N–S trending right-lateral strike-slip fault segments in the south of the Kazerun transition zone that accommodates a wide shear zone.

Tectonic geomorphology and Quaternary slip history of the Fuyun fault, southwestern Altai Mountains, central Asia

The northwest-trending Altai Mountains of central Asia expose a complex network of thrust and strike-slip faults that are key features accommodating intracontinental crustal shortening related to the Cenozoic India-Asia collision. In this study, we investigated the Quaternary slip history of the Fuyun fault, a right-lateral strike-slip fault bounding the southwestern margin of the Altai Mountains, through geologic mapping, geomorphic surveying, and optically stimulated luminescence (OSL) geochronology. At the Kuoyibagaer site, the Fuyun fault displaces three generations of Pleistocene–Holocene fill-cut river terraces (i.e., T3, T2, and T1) containing landslide and debris-flow deposits. The right-lateral offsets are magnified by erosion of terrace risers, suggesting that river course migration has been faster than slip along the Fuyun fault. The highest Tp2 terrace was abandoned in the middle Pleistocene (150.4 ± 8.1 ka uppermost OSL age) and was displaced 145.5 +45.6/–12.1 m along the Fuyun fault, yielding a slip rate of 1.0 +0.4/–0.1 mm/yr since the middle Pleistocene. The lower Tp1 terrace was abandoned in the late Pleistocene and aggraded by landslides and debris flows in the latest Pleistocene–Holocene (36.7 ± 1.6 ka uppermost OSL age). Tp1 was displaced 67.5 +14.2/–6.1 m along the Fuyun fault, yielding a slip rate of 1.8 +0.5/–0.2 mm/yr since the late Pleistocene. Our preferred minimum slip rate of ~1 mm/yr suggests the Fuyun fault accommodates ~16% of the average geodetic velocity of ~6 mm/yr across the Altai Mountains. Integration of our new Fuyun slip rate with other published fault slip rates accounts for ~4.2 mm/yr of convergence across the Chinese Altai, or ~70% of the geodetic velocity field.

Detailed Active Fault Map of the Spin Ghar Fault System and Related Seismicity in Eastern Afghanistan

The Spin Ghar fault system is one of the major active structures in northeastern Afghanistan, stretching ~130 km east-west along the Spin Ghar Mountains in the Jalalabad Basin. The fault system includes a group of strike-slip and oblique-slip thrust fault strands only 25 km from Jalalabad City. However, there is no existing detailed map of the fault traces, which is essential for mitigating seismic hazard from future seismicity. We therefore studied the fault-related geomorphology based on the interpretation of satellite images and shaded-relief topography. To identify exposed lithologies within the area we used true colour and false colour composite (FCC), band rationing and principal component analysis (PCA) on multispectral imagery. The Spin Ghar fault system is marked by both continuous and discontinuous linear and arcuate fault scarps developed in piedmont alluvium and along the Spin Ghar Mountain front. We also recognised scarps cutting bedrock terrain. Several deformed surfaces of Neogene-Quaternary age are observed along the fault strands in the Jalalabad Basin. The basin is also traversed by a series of east-west arcuate folds that suggest the area is undergoing south-north compression. The Quaternary faulting and seismicity demonstrate the kinematics of faulting in eastern Afghanistan. Our observations suggest that the east-west–trending right-lateral strike-slip and oblique-slip thrust faults are active and are important components of the seismic hazard in the eastern Afghanistan.

Characteristics structures of the mélange zones in the Ukrainian Carpathians

Mélange is characterized by the block-in-matrix fabric in which rigid blocks of different sizes, lithologies, and ages are distributed in a ductile matrix. Though mélange is a significant component of orogenic belts, in the Ukrainian Carpathians, mélanges of tectonic origin have not been reported. We have described the mélange zones widespread in the Pieniny Klippen Belt, Marmarosh Klippen Zone, and the inner nappes of the Outer Ukrainian Carpathians, as well as the typical deformation structures developed within them.
 The mélange matrix is characterized by a scaly fabric formed by cleavage surfaces and somewhere arranged in S-C structures. Lenticular clasts within the matrix show their long axis aligned to the tectonic foliation. Rotation of the boudins occurs against the shear direction following the formation of the S-C structures. The rigid clasts somewhere demonstrate sigma-type rotation structures. Some blocks within the mélange are highly fractured up to tectonic breccias.
 The study of tectonic slicken-sides and other deformation structures within the Pieniny belt demonstrates the presence of regular stress fields correlated with the geodynamics of the Carpatho-Pannonian region. The main stress field indicates the SW-NE regional compression related to the formation of Carpathian nappes and S-N — trending dextral strike-slip faults. Our study in the Priborzhava quarries records the Oash right-lateral strike-slip fault zone. In the Pieniny Klippen Belt some oblique normal faults of the Carpathian direction are related to the Transcarpathian Depression formation. The study showed that the mélange zones in the inner part of the Ukrainian Carpathians were formed largely due to strike-slip movements. In contrast, in the outer part of the Carpathian orogen, they formed mainly due to thrusting.

Seismotectonic aspects of the Ms 7.3 1948 October 5 Aşgabat (Ashgabat) earthquake, Türkmenistan: right-lateral rupture across multiple fault segments, and continuing urban hazard

SUMMARY The Ms 7.3 1948 Aşgabat earthquake was one of the most devastating earthquakes of the 20th century, yet little is known about its location, style and causative fault. In this study, we bring together new seismic and geomorphic observations with previously published descriptions of surface rupture and damage distributions to determine the likely source of the earthquake. We determine the epicentre and focal mechanism of this earthquake from digitized historical seismograms and the relocation of regional seismicity to show that the earthquake most likely nucleated close to the city of Aşgabat. The earthquake ruptured a right-lateral strike-slip fault to the southeast of the city, which has a clear long-term expression in the landscape, and also likely reactivated a subparallel concealed thrust along the Gyaursdag anticline east of the city. The earthquake potentially also ruptured a right-lateral segment northwest of Aşgabat, which does not have an identifiable expression in the landscape. Using high-resolution satellite imagery and digital elevation models we investigate the geomorphology of active faulting around Aşgabat and adjacent parts of the Köpetdag (Kopeh Dagh) mountain range front, showing that there are significant strike-slip and oblique strike-slip segments adjacent to the city that apparently did not rupture in 1948, and yet show clear geomorphic expression and potential right-lateral displacement of Parthian-era (∼2000 yr) and post-Sassanian era (∼1500 yr) archaeological remains. Luminescence dating of displaced fluvial terraces west of Aşgabat yields a vertical displacement rate of 0.6 mm yr−1, though the strike-slip rate remains undetermined.

Geomorphic interpretation on the formation of strike-slip basins along the Northern Sumatran fault

This study describes geomorphic expressions and constructs the schematic evolution of the Northern Sumatran Fault based on the development of transverse drainage basins and streams. This fault is a 400-km NW-SE right-lateral strike-slip fault with three segments, namely the Aceh and Seulimeum Faults in the northern section and the Tripa Fault in the southern section. The two faults at the northern section are sub-parallel and they link at the southeast termination of the latter fault. The examination on the geomorphic expressions comprised the fault configuration, stream deflections, and the delineation of landforms based on their genesis and geometry. This study applied drainage basin relief ratio (Rh), drainage basin volume-to-area ratio (Rva), and transverse stream profile analysis (normalized stream profile, qualitative interpretation of the profile shapes, stream concavity index (SCI), stream gradient, and knickpoint distribution) for investigating the development of transverse drainage basins and streams. For constructing the schematic evolution, this study evaluates drainage maturity level from the applied methods to interpret relative timing of basin formation. This study suggests that the Aceh and Tripa Faults constituted the initial configuration and they propagated to the southeast and northwest, respectively, before merging. The Seulimeum Fault, which formed subsequently, propagated to the northwest after merging with the Aceh Fault at its southeast termination. This study also infers that fault section with lower drainage maturity coincides with greater numbers of earthquakes.

Comments on Malik et al., 2023. Geological evidence of paleo-earthquakes on transverse rightlateral strike slip fault along the NW Himalayan front: Implications towards fault segmentation and strain Partitioning. Journal of Asian Earth Sciences 244, 105518. https://doi.org/10.1016/j.jseaes.2022.105518

Comments on Malik et al., 2023. Geological evidence of paleo-earthquakes on transverse rightlateral strike slip fault along the NW Himalayan front: Implications towards fault segmentation and strain Partitioning. Journal of Asian Earth Sciences 244, 105518. https://doi.org/10.1016/j.jseaes.2022.105518

Replies to comments raised by Singh T., and Rajendran C.P. On paper “Geological evidence of paleo-earthquakes on a transverse right-lateral strike-slip fault along the NW Himalayan front: Implications towards fault segmentation and strain partitioning” by Malik et al. (2023), [JAES, 244, 105518

Replies to comments raised by Singh T., and Rajendran C.P. On paper “Geological evidence of paleo-earthquakes on a transverse right-lateral strike-slip fault along the NW Himalayan front: Implications towards fault segmentation and strain partitioning” by Malik et al. (2023), [JAES, 244, 105518

Preliminary Results from a Dense Short-Period Seismic Deployment around the Source Zone of the 1886 M 7 South Carolina Earthquake

Abstract The 1886 magnitude ∼7 Summerville, South Carolina, earthquake was the largest recorded on the east coast of the United States. A better understanding of this earthquake would allow for an improved evaluation of the intraplate seismic hazard in this region. However, its source fault structure remains unclear. Starting in May 2021, a temporary 19-station short-period seismic network was deployed in the Summerville region. Here, we present our scientific motivation, station geometry, and quality of the recorded seismic data. We also show preliminary results of microearthquake detections and relocations using recordings from both our temporary and four permanent stations in the region. Starting with 52 template events, including two magnitude ∼3 events on 27 September 2021, we perform a matched filter detection with the one year of continuous data, resulting in a catalog of 181 total events. We then determine precise relative locations of a portion of these events using differential travel-time relocation methods, and compare the results with relocation results of 269 events from a previous seismic deployment in 2011–2012. We also determine focal mechanism solutions for three events from 27 September 2021 with magnitudes 2.0, 3.1, and 3.3, and infer their fault planes. Our relocation results show a south-striking west-dipping zone in the southern seismicity cluster, which is consistent with the thrust focal mechanism of the magnitude 3.3 earthquake on 27 September 2021 and results from the previous study based on the temporary deployment in 2011–2012. In comparison, the magnitudes 3.1 and 2.0 events likely occur on a north–south-striking right-lateral strike-slip fault further north, indicating complex patterns of stress and faulting styles in the region.

Fault Geometry, Slip Distribution, and Potential Triggering of the 2022 Mw 6.2 Deadly Afghanistan Earthquake Revealed from Geodetic and Weather Data

Abstract The 22 June 2022 Mw 6.2 Khōst, Afghanistan, earthquake struck killing more than 1700 people and devastating the region. For studying this earthquake, we computed the coseismic deformation fields of the earthquake using the Sentinel-1 Terrain Observation with Progressive Scans Interferometric Synthetic Aperture Radar (InSAR). The InSAR results show that the maximum coseismic displacement in the satellite line of sight direction reaches up to 39 cm. We determined the geometric parameters of the fault and coseismic slip distribution from these InSAR measurements. The best-fitted fault model shows that the rupture occurred on a right-lateral strike-slip fault with a strike of 203.7° and a dip of 68°. The most slip is concentrated at a shallow depth within the upper 10 km with the maximum slip of ∼3 m at 2.5 km depth. The maximum slip produced by this earthquake is significantly larger than the slip produced by several other similar earthquakes with similar magnitudes, implying that the focused shallow slip is likely the reason for the significant damage in the earthquake. The heavy rainfall was recorded during the earthquake period, which resulted in complicated fringes in coseismic interferograms close to the earthquake in time. Because a positive spatial and temporal correlation with the earthquake occurrence can be seen, the rainfall may have potential contributions to the earthquake, which deserves additional analysis in future. Combined with the potential effects of the 2015 Mw 7.5 Hindu Kush deep-seated earthquake, the seismicity in Afghanistan is the result of the ongoing subduction of the Indian plate beneath the Eurasian plate along their west boundary.

Active faults studies in Delhi and national capital region (NCR): Inferences from satellite data and field investigations

In recent years, the National Capital Region (NCR) of Delhi has experienced several earthquakes ranging in magnitude from 1.0 to 6.7. According to the last 50 years of earthquake data, the majority of earthquakes in the NCR have occurred near the Mahendragarh Dehradun Fault (MDF) and the Sohna Fault (SF). The region is bounded by a number of subsurface Ridges, Faults, and Lineaments, which are also influenced by the active plate boundary of the Indian and Eurasian plates. Active fault mapping is critical for the precise identification and marking of active fault traces in the NCR area for a precise seismic hazard assessment. We used high resolution Cartosat-1 stereopair data obtained from NRSC, Hyderabad, and Anaglyph (A 3D representation of the surface) and DEM prepared with ENVI software to map the active faults. We identified 12 sites in the NCR region based on satellite data interpretation, primarily along the MDF and Sohna Fault and their extensions. The presence of tectono-geomorphic markers along the MDF and Sohna Fault, such as warped surfaces indicative of fault scarps, stream offsets, gully erosion, and sag ponds, suggests active tectonic movement along these faults, most likely in the recent geological past. We believe the MDF is a right-lateral strike-slip fault with a compressional component on the western side and an extensional component on the eastern side. It acts as a segment boundary between compressional and extensional boundaries. We also identified the right lateral Nuh-Jhirka fault (NJF), which can be the Sohna Fault’s southern extension from Nuh to Jhirka. The western limb of the Delhi Mega fold has also seen a few right-lateral strike-slip movements that have extended up to the eastern bank of the Yamuna River, where the river reflects the base-level change and tight meandering on its upward side and a straight pattern on its downward side. This fault is known as the Delhi Fault (DF). The findings are preliminary, and further research would be required to create a detailed active fault map of the Delhi-NCR region to conduct a precise Seismic Hazard Assessment (SHA) of the region.

Flexural-slip folding in buckling phases of orogenic belts: Insight into the tectonic evolution of fault splays in the East Iran orogen

Introduction: The East Iran orogen has experienced multiple buckling phases resulting in the formation of strike-slip fault splays. The geometric and kinematic characteristics of these splays are influenced by folding mechanisms. This study focuses on investigating the structural characteristics and tectonic evolution model of the Khousf splay, located in the northern terminus of the Nehbandan right-lateral strike-slip fault system.Methods: Field visits and geometrical properties from map views were used to analyze the structural features of the Khousf splay. The splay was found to consist of a multi-plunging anticline and syncline, referred to as the Khousf anticline and Khousf syncline, respectively. Flexural slip was identified as a significant mechanism for the formation of these structures. Structural evidence, including parasitic folds, active folds, and strike-slip duplexes, suggested that flexural slip occurred on discrete movement horizons among the rock units.Results: Analysis of the parasitic folds in the cores and limbs of the Khousf anticline and syncline revealed M, W, Z, and S shapes, with complex slicken-line patterns observed on faults parallel to the beds at the limbs. The analysis results indicated strain partitioning and inclined left- and right-lateral transpressional zones. Shortening estimates obtained from profiles in the Shekarab inclined transpressional zone were approximately 33%, 65%, and 68% for NE-SW, N-S, and NW-SE profiles, respectively. In the Arc area, which is the core of the anticline, shortening estimates from NE-SW and N-S profiles ranged from 14% to 10%. Structural analysis of the folds in this area revealed broad, close, semi-elliptical, and parabolic shapes, suggesting that secondary folds with NW-SE axis directions have been superimposed on the first-generation folds with E-W axis directions in the Khousf refolded splay.Discussion: The findings of this study highlight the structural characteristics and tectonic evolution model of the Khousf splay in the northern terminus of the Nehbandan right-lateral strike-slip fault system. The results suggest that flexural slip played a crucial role in the formation of the multi-plunging anticline and syncline in the Khousf splay. The presence of parasitic folds and complex slicken-line patterns on faults indicate the complexity of deformation processes. The observed strain partitioning and inclined transpressional zones suggest a complex tectonic history in the study area. The superimposition of secondary folds with different axis directions on first-generation folds adds further complexity to the structural evolution of the Khousf refolded splay. Overall, this study provides new insights into the structural characteristics and tectonic evolution of the Khousf splay in the East Iran orogen.

Geological evidence of paleo-earthquakes on a transverse right-lateral strike-slip fault along the NW Himalayan front: Implications towards fault segmentation and strain partitioning

Geological evidence of paleo-earthquakes on a transverse right-lateral strike-slip fault along the NW Himalayan front: Implications towards fault segmentation and strain partitioning

Analysis of Tectonic Influence on Morphological Formation: Case Study of Gapura Pemalang Area

Tectonic activity is closely related to the formation of landforms (morphology) in a region. The study area exhibits morphology controlled by normal fault tectonics, with blocks consisting of highlands and lowlands. This study aims to determine the extent of tectonic influence (normal faulting) on the morphology in the location. The quantitative geomorphological analysis method is used to obtain data on the level of tectonic activity present in the research area. Based on this method, it causes the formation of morphology and geological structures that affect the current surface forms. The methods used to calculate the tectonic influence are the Ratio of Valley Floor Width to Valley Height (Vf) and Mountain Front Sinuosity (Smf). Based on the results of the case study, the average Vf is 0.19, indicating class one tectonic activity and a high uplift level with V-shaped valleys. Meanwhile, the average Smf is 1.45, indicating strong tectonic activity associated with wide plains, narrow valleys, and steep hills. Based on these results, the study location falls into the category of strong tectonic activity, supported by field geological data showing right-lateral strike-slip faults and left-lateral normal faults intersecting each other.

Coseismic Rupture Behaviors of the January and March 2022 MW > 5.5 Hala Lake Earthquakes, NE Tibet, Constrained by InSAR Observations

On 23 January and 25 March 2022, two MW > 5.5 Hala Lake earthquakes characterized by right-lateral strike-slip faulting occurred around the Elashan Fault in Northeastern Tibet, marking the two largest events since the 1927 MW 6.2 Hala Lake earthquake. Since no surface rupture related to the two earthquakes has been reported, the seismogenic faults and coseismic rupture behaviors of the two events are still unknown. The occurrence of the two events provides a rare opportunity to gain insight into the seismogenic structure and rupture behavior of the less studied region, further helping us accurately evaluate the regional seismic hazard. Here, we first exploit Interferometric synthetic aperture radar (InSAR) data to obtain the coseismic deformation associated with the two earthquakes and then invert for the fault geometry and detailed coseismic slip of the two events. Coseismic modeling reveals that the January and March 2022 earthquakes ruptured two buried west-dipping moderate-angle and high-angle right-lateral strike-slip faults, respectively. Most of the slip of the January event occurred at depths from 1.7–7.6 km, while the majority of the slip associated with the March event occurred at depths from 2.5–10 km, which may have been restricted by the intersections between the January and March Hala Lake seismogenic faults. By a comprehensive analysis of the coseismic inversions, stress changes, and early postseismic signal, we suggest that the significant fault dip difference (~30°), highlighting a fault segmentation, stops the rupture propagation from one fault segment to another and that fluid migration may encourage the restart of the rupture of the later event, which requires further investigation. Moreover, Coulomb stress modeling shows stress loading on the eastern segment of the Daxueshan–Shule Fault and the northern segment of the Elashan fault, which we should pay more attention to.

Salair–Gornaya Shoria Junction (Northwestern Central Asian Orogenic Belt): Deep Structure and Tectonics from Magnetotelluric Data

Abstract —The Salair fold-thrust orogenic belt (Salair orogen, Salair) is located in the northwestern Altai–Sayan fold area within the Central Asian Orogenic Belt. The Salair orogen is an allochthon overriding the Kuznetsk Basin on a system of imbricate thrusts. The southern flank of the Salair thrust system is tectonically juxtaposed against the Gornaya Shoria terrane which differs markedly from Salair in its geological setting. The Salair and Gornaya Shoria terranes are separated by the Nenya-Chumysh Basin, a deep Mesozoic trough. The Salair orogen is composed of Cambrian–Early Ordovician island arc volcanic and sedimentary rocks, widespread garnet amphibolites and gneisses of the Angurep complex in its southern flank, and the Shalap subduction-related melange in the Alambai ophiolite suture. The southern Salair orogen and its junction with Gornaya Shoria have been imaged down to the lower crust by magnetotelluric (MT) soundings, which is an efficient tool for investigating the deep structure and tectonic history of orogenic areas. The MT surveys were performed at 25 stations on a 120 km long profile. MT data revealed an up to 70 km wide low-resistivity zone (a conductor) traceable till a depth of 20 km between the Salair and Gornaya Shoria terranes. The low-resistivity zone has a complex structure with its outer and interior boundaries dipping almost vertically. The conductor lies under several major geological structures: the Shalap melange, the Nenya-Chumysh Basin, and the NE trending Altai–Salair right-lateral strike-slip fault. The Altai–Salair fault, along which the Salair allochthon was displaced relative to Gorny Altai and Gornaya Shoria, joins the Salair system of imbricate thrusts. The Nenya-Chumysh Basin at the Salair–Gornaya Shoria junction is a deep trough having an asymmetric transversal profile with a steep western side and a shallower-dipping stepped eastern side. The southeastern flank of the basin is a wide area of thin sediments over the Paleozoic basement dipping gently in the northwestern direction. The revealed deep structure of the Nenya-Chumysh trough is consistent with its tectonic model implying an Early Cretaceous basin superposed over an early Jurassic pull-apart basin. Early Mesozoic motions on major faults is a regional-scale phenomenon known from many areas of southern West Siberia.

Airborne geophysics and remote sensing of an Nimas-Khadra area, southern Arabian shield: New insights into structural framework and mineral occurrences

The Shwas-Tayyah and Khadra belts belonging to the Asir terrane include potential mineralization zones, hosted in intensely deformed Precambrian basement rocks. Analysis of geophysical aeromagnetic data and satellite images, constrained by field data, highlights the deep hierarchy and structuring of the An Nimas-Khadra area in its regional litho-structural setting and geodynamic evolution. The N-S and NNE-SSW major trends, with other E-W, NE-SW and NW-SE minor directions, were identified. The Tarj, Ibran, and Junaynah close to N-S oriented master shear zones, delimit and cross the Al Lith-Bidah, Shwas-Tayyah and Khadra belts; they characterize the Asir composite terrane. Structural and kinematic models were highlighted, showing the control of intense deformations on the basement structures. The deep-seated faults are linked to wide tectonic movements induced by regional E-W to ENE-WSW contractional orogenic episodes. The tectonics induced genesis of the accreted terrane rocks with differentiated belts and shear zones. The resulted structures seem to be in accordance with the Riedel model that includes conjugate movements of right-lateral strike slip faults and right-oblique reverse faults.Correlation of geophysical and geochemical analyses is a crucial technique used for better assessment and valorization of mineral resources. The spatial association between the interpreted lineament patterns and mineralization rates testifies the tectonic deformations-mineral deposits relationship. The AHP-based MCDM statistical support model highlights the mining interest areas. The MCDM allows further spatial statistical evaluation and reveals new prospective metal occurrences in the Shwas-Tayyah and Khadra belts. N-S and NNE-SSW lineament networks show the highest mineralization rates, suggesting their priority for more detailed prospections. The metallic mineral deposits have to be related to prominent steeply dipping and brittle-ductile shear zones.