Himalayan Thrust Research Articles

Weak, Vertically Stronger Main Himalayan Thrust in the India‐Asia Collision

AbstractMegathrusts at convergent plate boundaries generate the largest and some of the most hazardous earthquakes on Earth. However, their physical properties, including those influencing fault slip accumulation and release and earthquake‐related surface displacements, are still poorly constrained at critical depths. Here, we combine seismic imaging and geodetic modeling to investigate the structure and mechanical behavior of the Main Himalayan Thrust fault (MHT) in the center of the 2015 Mw 7.8 Gorkha rupture in Nepal. Our results from two independent observations consistently suggest the presence of a channel associated with the MHT with high compliance (shear modulus as low as ∼4 GPa) and strain anisotropy (stiffer in the vertical orientation than in the horizontal), likely arising from a weak subducting layer with north‐dipping foliation. Such mechanical heterogeneity significantly influences the quantification of short‐term fault kinematics and associated earthquake potential, with implications on across‐scale dynamics of plate boundaries in Himalaya and elsewhere.

Application of Singular Spectrum Analysis to InSAR time-series for constraining the postseismic deformation due to moderate magnitude earthquakes: the case of 2019 Mw 6 Mirpur earthquake, NW Himalaya

Summary Detection and separation of the subtle postseismic deformation signals associated with moderate magnitude earthquakes from Interferometric Synthetic Aperture Radar (InSAR) time-series is often challenging. Singular Spectrum Analysis (SSA) is a statistical non-parametric technique used to decompose and reconstruct signals from complex time-series data. We show that the SSA analysis effectively distinguished the postseismic signal associated with the 2019 Mw 6 Mirpur earthquake from periodic and noise components. The SSA derived postseismic deformation signal is smoother and fits better to an exponential model with a decay time of 34 days. The postseismic deformation is confined to the southeast of the rupture area and lasted for ∼90 days following the mainshock. Inversion of the postseismic deformation suggests an afterslip mechanism with a maximum slip of ∼0.07 m on the shallow, up-dip portions of the Main Himalayan Thrust. The 2019 Mirpur earthquake and afterslip together released less than 12 per cent of the accumulated strain energy since the 1555 Kashmir earthquake and implies continued seismic hazard in the future.

Detection of a cracked and fluid-filled main Himalayan thrust (MHT) and its implications toward the genesis of earthquakes in the Uttarakhand Himalaya

The present study looks into the significant role of metamorphic and aqueous fluids in the mid-crustal Main Himalayan Thrust (MHT) in triggering strong to moderate earthquakes in the Kumaon-Garhwal Himalayas. Using seismic velocity tomograms, crack density (ε) and saturation rates (ξ) have been modelled using the crack theory. All three earthquakes in Uttarakhand with Mw ≥ 6.5 (viz., 1803 Mw7.8 Garhwal, 1991 Mw6.8 Uttrakashi and 1999 Mw6.5 Chamoli earthquakes) occurred within the MHT, which is depicted as a shallow north-dipping layer with low velocity. Our models show that these earthquakes occurred between 10 and 20 km depths where ε (∼0.011–0.012), ξ (∼0.386–0.392), and Vp/Vs (∼1.74–1.90) are all relatively high, indicating a greater possibility of aqueous/metamorphic fluids within the MHT than in the surrounding area. These fluids are suspected to be the trigger for earthquakes in the Uttarakhand Himalaya. As we drill deeper into the crust, we find that ‘ε’ decreases as a result of crack closure (≤0.011), while ‘ξ’ is predicted to increase (∼0.3–0.6) as a result of the presence of more wet and saturated cracks caused by the presence of partial melts (higher Vp/Vs: 1.74–1.92). Our modelling further verifies that the earthquakes in the Uttarakhand Himalaya are primarily driven by the existence of a highly conductive and weakened MHT with a greater concentration of metamorphic/aqueous fluid-filled cracks at depths ranging from 10 to 20 km. The ramifications of our research could significantly impact the earthquake hazard and risk in the Uttarakhand Himalayas.

Paleoseismological evidence for segmentation of the Main Himalayan Thrust in the Darjeeling-Sikkim Himalaya

Whether the Main Himalayan Thrust can host a single surface-rupturing event in the Himalaya with a rupture length of > 700 km remains controversial. Previous paleoseismological studies in the Darjeeling-Sikkim Himalaya (DSH) suggested medieval surface-rupturing earthquakes, correlating them with the eleventh–thirteenth century events from Nepal and Bhutan and extending the coseismic rupture length > 700 km. Conversely, there is no rupture evidence of the 1714 Bhutan and 1934 Bihar–Nepal earthquakes in the DSH, resulting in a discrepancy in the rupture extent of the great earthquakes. Consequently, we conducted a paleoseismological investigation across a ~ 10 m-high fault scarp on the Himalayan Frontal Thrust at Chenga village, DSH, revealing a surface-faulting event during 1313–395 BCE. We suggest that the DSH is a 150 km-long independent segment bounded by a transverse ridge and fault and has a recurrence interval of ~ 949–1963 years, which is significantly larger than Nepal (~ 700–900 years) and Bhutan Himalaya (~ 339–761 years).

Complex Lesser Himalayan tectonics in the Darjeeling-Sikkim Himalaya: New perspectives from a fold-duplex model

This study provides a comprehensive account of the modes of crustal shortening in the Lesser Himalayan Sequence (LHS) of the Darjeeling-Sikkim Himalaya (DSH). The distributed ductile deformation episodes are integrated with the localized thrusting events in the LHS. The LHS records four major episodes of buckle folding in distributed ductile deformations. From field-based structural correlations, it is demonstrated that multiple orders of third-generation orogen-parallel (F3) and late-stage orogen-perpendicular (F4) folds have resulted in complex interference patterns, varying from plane non-cylindrical (Type 1) to non-plane non-cylindrical (Type 2). Continued N–S shortening in the DSH produced a crustal-scale thrust with ramp-flat geometry, locally known as the Daling Thrust (DT) under the influence of a mechanically weak coal-shale-bearing Gondwana layer, which can be compared with the present-day Main Himalayan Thrust (MHT). The thrust ramp eventually shifted towards the foreland during the India-Asia collision. A fold-duplex model is proposed to explain the potential mechanism of forelandward basal ramp migration. Our model suggests that the southern shallower Main Himalayan Thrust (MHT) flat is susceptible to creeping aseismically due to the influence of coal-shale rheology. In contrast, the mid-crustal ramp and the presently active frontal splay faults (e.g., Main Frontal Thrust, MFT) are potentially seismogenic. These findings have important implications for the interpretation of the MHT seismic cycles.

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

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

Evidence for an Imbricated Lower Crust and Its Role in Accommodating Crustal Shortening in Sikkim Himalaya

AbstractGeometrical heterogeneity of the subducting Indian continental crust along the Himalaya‐Tibet collision zone remains enigmatic. Mass budget estimates describing shortening across the orogen are partly derived from observations made from seismic imaging of the deep earth. Here, using data from 38 broadband seismic stations covering Sikkim Himalaya, we produce high resolution seismic images in order to fill crucial gaps in our understanding of the evolution of Himalayan collision zone. We used 12,288 high quality receiver functions computed using waveforms of earthquakes having magnitude >5.5 in the distance range of 30°–100°. Our results reveal a highly imbricated and heterogeneous crust beneath Sikkim Himalaya. The Main Himalayan Thrust (MHT) responsible for large scale earthquakes in the Himalayan collision zone is not so distinct in the migrated images, but intermittent. A dominant cluster of earthquakes at shallower depths is associated with the MHT, marked by negative amplitude arrivals. The Moho is found to be gently dipping, reaching depths of ∼60 km beneath the Higher Himalaya compared to ∼40 km in the Himalayan foredeep. Interestingly, the Moho in this part of Himalaya has offsets and overlapping segments, indicating crustal imbrication in response to active shortening. Clusters of lower crustal earthquakes coincide with the junction of offsets in the Moho.

Lateral electrical conductivity variations along the Main Himalayan thrust in the northwestern Himalayas: Insights from 3D Magnetotelluric forward modeling

Understanding the arc parallel variation on the geometry of the Main Himalayan Thrust (MHT) is as important as understanding the arc perpendicular variation in the Himalayas. The geometric variability of the MHT holds significant implications for the occurrence of major and great earthquakes. Three-dimensional magnetotelluric (MT) forward modeling enables the investigation of potential crustal models along the MHT in northwest Himalayas. MT impedance tensors were computed utilizing the 3D forward modeling code MTD3FWD. Previously established MT resistivity and seismic velocity models from various sectors of the northwestern Himalayas were employed as inputs for generating the resistivity mesh necessary for 3D forward modeling. The computed impedance tensors by 3D forward computation were cross-referenced with the original published MT data to validate their accuracy. A lateral resistivity cross section is also derived from the 3D forward model along the sub-Himalaya and lesser-Himalaya region to study the lateral heterogeneity. The lateral resistivity cross-section reveals significant heterogeneity within the crust, marked by both high and low-resistive structures and a possible lateral ramp along the MHT. The geometry of the lateral MHT showcases a gradual incline within the Himachal sector and a steep ramp within the Garhwal and Kumaun sectors in the northwestern Himalayas. The crustal architecture exhibits distinct nearly-vertical resistive and conductive features beneath the study area. Consequently, the crust within this region is characterized by considerable heterogeneity, influenced by a network of subsurface faults and ridges. The Delhi Haridwar Ridge, which exhibits high resistivity, plays a significant role in dictating the lateral dip of the MHT and exerting control over seismic activity patterns in the region.

A future scenario earthquake and ground motion hazards for Kathmandu, Nepal

Since Nepal is an earthquake-prone country due to the collision of the Indian and Eurasian plates, it is crucial for its capital of Kathmandu to evaluate ground motion hazards from a future large earthquake. For this purpose, we constructed a realistic scenario earthquake with realistic rupture parameters in a likely location. To obtain the location, a new distribution of the rupture zones of large historical earthquakes along the Main Himalayan Thrust (MHT) was obtained by integrating the distribution from a previous study and the results of trench surveys. Global Navigation Satellite System observations indicated that the plate boundary is strongly coupled from the southern boundary of the MHT to a depth of approximately 10 km and there is almost no lateral change in the coupling. This implies that all regions along the MHT have similar rates of strain increase. Therefore, it is most probable that the rupture zone of the oldest previous event will rupture as a scenario earthquake. In the new distribution, the 1255 earthquake is the oldest. However, large earthquakes occurred in 1934 and 2015 within its rupture zone. Thus, we adopted the area obtained by removing the 1934 and 2015 rupture zones from the western part of the 1255 rupture zone. The relationship between the rupture area size and seismic moment of the 2015 earthquake lies between the scaling formulas for crustal earthquakes and plate-boundary earthquakes, but is closer to the former. Therefore, using this and the scheme for characterized source models, we determined realistic rupture parameters. We then simulated broadband ground motions in Kathmandu using these rupture parameters, our 3-D velocity structure models, and a hybrid method combining the finite-difference method and the stochastic Green’s function method. We obtained the peak ground accelerations (PGAs) of simulated ground motions, and calculated the seismic intensities in the Modified Mercalli intensity scale from the PGAs as indexes of hazards for Kathmandu. Intensities IX coincide with the center of the Kathmandu Valley, and intensities VIII and VII are found in the area surrounded by the sedimentary boundary and the southernmost part of the valley.Graphical abstract

Assessing the geometry of the Main Himalayan thrust in central Nepal: A thermokinematic approach

Abstract Since the 2015 Gorkha earthquake in Nepal, the relationship between the geometry of megathrusts and the control it exerts over the nucleation and propagation of major earthquakes has become an important topic of debate. In this study, we integrate new geologic mapping, a newly interpreted cross section from the Daraundi valley of central Nepal, two published cross sections from the neighboring Marsyangdi and Budhi Gandaki valleys, and a suite of 270 thermochronometric ages to create an integrated and validated three-dimensional kinematic model for the central Nepal Himalaya. We use this model to investigate the assertion that the westward propagation of the Gorkha rupture was restricted by deep-seated structures in the Main Himalayan thrust. The integrated kinematic model based on these cross sections indicates that the ~30 km southward step in the Main Central thrust system mapped in the Daraundi valley, along with the corresponding step in the distribution of reset muscovite (Ar-Ar) ages, is not the result of a lateral structure in the modern Main Himalayan thrust. Instead, the step in the surface geology is the result of a considerably shorter Trishuli thrust sheet in the Daraundi transect (~30 km compared to between 105 and 120 km in the other transects). The corresponding southward step in the distribution of reset muscovite Ar-Ar ages is the result of the Lesser Himalayan duplex being completely translated over the Main Himalayan thrust ramp, elevating and exposing rocks heated to >400 °C farther south in the Daraundi transect. Our integrated model also highlights the 10–15 km of out-of-sequence thrusting that occurs on the Main Central thrust system across central Nepal. Importantly, these out-of-sequence thrusts sole directly into the modern Main Himalayan thrust ramp, and, together with the distribution of reset zircon (U-Th)/He and apatite fission track ages, show that the modern ramp is distinctly linear from east to west, with no support for a lateral structure at the ramp or to the south.

Geodetic plate coupling and seismic potential on the main Himalayan thrust in Nepal

We model interseismic plate coupling distribution on the Main Himalayan Thrust (MHT) in Nepal through the inversion of secular GNSS velocity data. To complement previously published data, we compile velocity data from ten additional continuous stations to improve spatial resolution in central and mid-western Nepal. A regional non-planar structural model is adopted to reproduce the MHT fault plane. In general, the coupling pattern seems nearly binary, indicating that transition from full coupling to decoupling is occurring sharply in very narrow zones. In eastern Nepal (> 84.5ºE), plate coupling is very strong from the surface to intermediate depths, including the source region of the 2015 Mw 7.8 Gorkha earthquake. Geodetically estimated slip deficit rates are consistent with the rupture history of great earthquakes in the east revealed by geomorphological observations. In the west (< 83.0ºE), a weakly coupled zone extends laterally at intermediate depths, whereas the coupling in the shallower part remains very strong. Although the slip deficit rate in the west is significantly smaller than that in the east, seismic moment accumulated, since the last complete rupture in 1505 may be capable of generating a future great event. In central Nepal, estimated slip deficit rates are comparable with those in the east, and no great event has been documented over the past several centuries. Thus, the seismic risk may be most urgent in central Nepal. The development of local seismicity and crustal deformation should be carefully monitored.Graphical

Present-day quantification of seismic coupling along the décollement level beneath the Potwar Plateau region in Pakistan western Himalaya

Using GNSS horizontal surface velocities and Sentinel-1 interferometry line-of-sight velocities, we quantify the current velocity field of the Potwar Plateau Salt Range fold-and-thrust belt. From this velocity field indicating a creep of the Potwar Plateau along the Main Himalayan Thrust, we inferred a weak subhorizontal décollement level formed by a massive Precambrian salt layer. To the south of the Plateau, the Salt Range is uplifted along the Salt Range Thrust, conditioned by the presence of an inherited normal fault. The Kalabagh Fault, which forms the western boundary of the Salt Range and Potwar Plateau, exhibits a creep rate of 3.3 mm/yr. Numerical modelling enabled us to characterise the slip distribution and coupling along the faults, showing the presence of a large asperity along the décollement level beneath the Potwar Plateau and several asperities along the eastern part of this basal thrust. The model also indicated an alternation of coupled and decoupled zones along the Kalabagh Fault, suggesting that this strike-slip fault can be characterised by creep and the occurrence of earthquakes and/or slow slip events. Considering the lack of instrumental and historical large-magnitude earthquakes in this area, the Main Himalayan Thrust and Kalabagh Fault are likely to be affected by earthquakes of magnitude Mw larger than 7.5. A slip rate of 20 mm/yr is modelled along the southern and superficial parts of the Salt Range Thrust, which is larger than the 14 mm/yr slip rate along the Main Himalayan Thrust at depth. This observation suggests the existence of a southward flow of massive salt along the Salt Range Thrust.

Seismic structure of the 2015 Mw7.8 Gorkha earthquake revealed by ambient seismic noise and teleseismic surface wave tomography

The destructive 2015 Mw7.8 Gorkha earthquake occurred in the Main Himalayan Thrust due to the collision of the Indian and Asian plates, which provides a unique opportunity to understand the deep dynamic processes and seismogenic mechanisms of strong earthquakes. We construct a regional-scale shear-wave velocity model of the crust and uppermost mantle using ambient seismic noise and teleseismic surface wave at periods of 5–100 s around the Gorkha earthquake region. The new shear-wave velocity model exhibits prominently lateral heterogeneities in the Gorkha earthquake areas. We observe a high-velocity (high-V) zone around the Gorkha main shock in the Main Himalayan Thrust, indicating the existence of a high-strength asperity that sustains the stress accumulating. The aftershocks are primarily located in the low-velocity (low-V) anomalies and enclosed by two high-V anomalies, which appear to act as structural barriers that influence the spread of the aftershocks. Prominent low-Vanomalies from the lower crust to the mantle lithosphere are observed along the north–south trending rifts, suggesting the hot materials upwelling due to the tearing of the northward subducting Indian lithosphere. These observations may indicate that seismic velocity heterogeneity could play an essential role in earthquake initiation and the rupture process.

Magnetotelluric Imaging of the Central Himalayan Crust Away From Rift Zones

AbstractImaging the crustal structure and state of the Himalayan Orogenic Belt (HOB) is of great significance for understanding crustal deformation and its tectonic response in the collision front of the Indian‐Eurasian plates. To avoid the influence from the anomalies underneath the north‐south trending rifts, a three‐dimensional electrical resistivity model across the central HOB was obtained between the Dingjie‐Shenzha and Yadong‐Gulu rifts. No lower‐crustal conductor was found in the southern Lhasa Terrane, and the lower crust with a moderate resistivity value of approximately 100 Ωm is interpreted to be the residue of previous partial melting beneath the Gangdese porphyry copper deposits. The middle crust between the Main Himalayan Thrust and Southern Tibet Detachment System is electrically resistive to the north of the north Himalayan gneiss domes (NHGD) belt and conductive to the south. The middle crust in the northern Himalayas may have undergone partial melting and crystallization during southward migration and duplexing. There is a strong deep‐shallow coupling relationship in the central HOB, where an increase in the underthrusting angle of the Indian crust has resulted in a southward turn of the NHGD belt.

3-D coseismic displacement mapping of the 2015 Mw7.8 Gorkha earthquake using multi-viewed InSAR

After the 2015 Mw7.8 Gorkha earthquake, geodetic measurements have been extensively used to constrain slip kinematics, fault geometry of the Main Himalayan Thrust (MHT) and earthquake cycle deformation. However, the spatially dense coseismic 3-D displacements remain largely unresolved, owing to the side-looking geometry of SAR images and sparse GPS observations. We improved 3-D displacements by incorporating a strain model in a Bayesian framework, utilizing all available coseismic interferograms and azimuth offsets from Sentinel-1 and ALOS-2 satellites. The coseismic strain map shows that major landslides in large slope areas are spatially consistent with extensional strain. The vertical component illustrates a spatial pattern different from interseismic and postseismic uplift, hinting at diverse contributions from various tectonic uplift processes in the frontal mountain belt. The spatial relationship between the interseismic strain and coseismic deformation suggests a partial release of the accumulated strain, implying a remaining notable seismic hazard around Gorkha.

Geodynamic models of Indian continental flat slab subduction with implications for the topography of the Himalaya-Tibet region

The slab structure and high elevation of the Himalaya-Tibet region and their underlying mechanisms have been widely discussed. Many studies interpret a flat slab segment of Indian continental lithosphere located below the overriding plate, but interpretations of the northward extent of the flat slab differ substantially, with minimum estimates placing the boundary at the northern margin of the Himalaya (Indus-Yarlung Tsangpo suture), and maximum estimates placing it at the northern boundary of Tibet. In this study, we investigate for the first time if a flat slab segment of subducted buoyant Indian continental lithosphere below the Himalaya-Tibet region is geodynamically feasible and we quantify its northward extent, as well as its contribution to the high topography of the region. We conduct three large-scale fully-dynamic (buoyancy-driven) analogue experiments to simulate the subduction of the Indian continent. Our preferred, and geodynamically most feasible, model shows a continental flat slab extending northward up to ~ 320 km from the Himalayan thrust front, in agreement with recent estimates. Furthermore, it suggests that the positively buoyant flat slab segment of the Indian continent contributes some ~ 1.5–2 km to the high topography of the Himalaya-Southern Tibet region by providing an upward force to elevate the overriding Eurasian plate.

Stress Evolution of the Main Himalayan Thrust Fault Induced by the Mw 7.8 Gorkha Earthquake

ABSTRACT The Mw 7.8 Gorkha earthquake that occurred in 2015 is the largest thrust event in the middle of the main Himalayan thrust fault zone (MHT) in the past 81 yr. Its impact on the regional tectonic stress state and future seismic risks is a significant scientific issue worthy of in-depth analyses. In this study, we inverted the planar fault-slip model (the planar model), the flat-ramp fault-slip model (the flat-ramp model) and the double flat-ramp fault-slip model (the double flat-ramp model) to analyze the effect of the fault geometry, based on the steepest descent method (SDM) and the layered earth model. Compared with the flat-ramp model, the planar model exhibits a wider slip distribution in the down-dip direction of the main rupture zone, whereas the double flat-ramp model shows a larger coseismic slip on the middle ramp at the depth of 7.5–11.5 km. Those slip differences produce larger stress shadow areas in the above models, but for a blind thrust event induced by a low-dip thrust fault, this does not significantly change the distribution mode of coseismic Coulomb stress change (ΔCFS) in the three models. Namely, there is an obvious stress release in the main rupture but an obvious stress loading in the up-dip and down-dip directions of the main rupture zone. Based on the Burgers rheological model, we calculated the postseismic viscoelastic Coulomb stress change (V−ΔCFS) and the cumulative Coulomb stress change (C−ΔCFS) induced by the Gorkha earthquake in the flat-ramp model and comparatively analyzed the evolution pattern of coseismic and postseismic stresses. Our results indicate that the variation trend of postseismic stress in the lithosphere is opposite to that of the coseismic ΔCFS. The postseismic viscoelastic relaxation promotes the slip of the flat-ramp structure at the depth of 10–25 km, and the stress unloads in the shallow and deep part simultaneously. As a blind thrust event, the coseismic ΔCFS still plays a dominant role in the shallow part after 50 yr, whereas the loading C−ΔCFS in the deep part of the MHT is greatly weakened by the postseismic V−ΔCFS. Seismic risks still exist in the unruptured area on the west side of the mainshock and the shallow Main Frontal thrust.

Exhumation of the Cuonadong Sn–W–Be polymetallic deposit, Tethyan Himalaya: Implications for exploration

The Cuonadong Sn–W–Be polymetallic ore deposit is the first rare-metal deposit related to leucogranites with giant mineralization potential to be discovered in the Himalayan Orogen. However, the post-mineralization exhumation and preservation processes of this deposit have not yet been studied in detail, although these factors are key to the exploration and evaluation of rare-metal deposits in the Himalaya. Geophysical data have revealed that a hidden fault (i.e., the Jisong secondary fault) cuts the southern part of the Cuonadong ore deposit. In order to determine the effects of the Jisong secondary fault on the exhumation of the Cuonadong deposit, we undertook zircon and apatite (U–Th)/He dating, apatite fission-track dating, and forward and inverse thermal history modeling of the footwall and hanging wall of the Jisong secondary fault. Our results show that the Cuonadong deposit experienced two stages of rapid, post-mineralization exhumation at ca. 10–9 and ca. 5–4 Ma, separated by a period of differential exhumation at ca. 9–5 Ma. These exhumation events were likely caused successively by the arc-shaped Nading Fault, normal faulting on the Jisong secondary fault, and thrusting on the Main Himalayan Thrust, although climate-related erosion may have also had a role in the exhumation. Owing to normal displacement on the Jisong secondary fault, the Cuonadong ore deposit underwent differential exhumation of 300–700 m. This implies that the eastern part of the deposit is more favorable for exploration than its western part if the deposit has the same mineralization depth. This study demonstrates that low-temperature thermochronological methods can be useful in the exploration for rare-metal deposits in the Himalayan Orogen.

Estimation of active surface deformation using PSInSAR technique of the Central Himalayan region

The Kumaun Himalaya is considered as the most active part of the Central Seismic gap in the Indian Sub-continent. In this paper, we presented active surface deformation rates of the Kumaun region from February 2017 to February 2021 using the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSI) technique. The cumulative displacement that occurred during the span of 4 years is ±55 mm, whereas the Line of Sight (LOS) deformation velocity rate ranges is ±7 mm/yr. Apart from PSI, we also estimated the b-value of the Kumaun region from 1803 to 2021 (399 events) and its value is 0.54 ± 0.03. A distinct NE-SW trend of b-value is observed where earthquakes with M > 6 occurred towards NE of this trend. The PSI-derived deformation reveals that the central part of the Inner Lesser Himalaya along with the Main Central Thrust (MCT) zone is dominated by uplift. The zone between the Munsiari Thrust (MT) and MCT in the central region shows the maximum uplift ranging 5–7 mm/yr which exactly lies above the mid-crustal ramp of the Main Himalayan Thrust (MHT). Our results are well corroborated with available observations of geodetic strain and peak ground acceleration values. However, the deformation patterns and high-velocity rates in the central part of the study area between MT and MCT indicate the accumulation of high stress.

Holocene paleoearthquakes activity in the Nieru graben, southern Tibet

The Yadong-Gulu Rift (YGR) is the longest and most prominent rift in southern Tibet. While 14 large historical earthquakes have occurred on the northern-central segment of the YGR, historical or paleoearthquake records along the southern segment remain poorly understood. The spatial discrepancy of large earthquakes has significant implications for assessing seismic hazards along the entire YGR. To address this knowledge gap, this study presents the paleoseismic events for the first time in the Nieru graben located along the southern segment of the YGR. The excavation of a paleoseismic trench reveals two Holocene earthquakes with calibrated radiocarbon dates constraining the timing of the two events to be after 4084-3954 cal yr BP. The paleoearthquake had a magnitude of M 7. The study shows that the southern segment of the YGR experienced strong paleoseismic events, except for the Relong graben. Considering the high present extension rate of the southern rifts and the magnitude of the paleoseismic events along the Nieru graben, the southern segment of the YGR holds the potential for producing large earthquakes. Furthermore, the ongoing tectonic deformation in the area, coupled with stress changes from large earthquakes on Himalayan thrust faults, may increase the likelihood of future rupture along the active faults in the Nieru graben.