The December 18,2023,M_(S)6.2 Jishishan earthquake occurred along the northeastern margin of the Qinghai-Xizang Plateau within the Laji-Jishi Shan Fault Zone(LJSFZ),a complex thrust-dominated tectonic belt.To identify...The December 18,2023,M_(S)6.2 Jishishan earthquake occurred along the northeastern margin of the Qinghai-Xizang Plateau within the Laji-Jishi Shan Fault Zone(LJSFZ),a complex thrust-dominated tectonic belt.To identify the seismogenic fault and better understand the regional tectonic framework,we integrated high-resolution Digital Elevation Models(DEMs)derived from GF-7 stereo satellite and Unmanned Aerial Vehicle(UAV)photogrammetry,relocated aftershock sequences,and conducted detailed field investigations.Our results identify four Late Quaternary thrust faults(F1-1 to F1-4),among which the Zhaomuchuan fault(F1-3),a NE-dipping back-thrust,aligns closely with the main-shock and aftershock distribution and exhibits clear Holocene activity.Seismic relocation reveals a NEdipping seismogenic zone at depths of 5-12 km,consistent with a shallow reverse-faulting mechanism under WSW-ENE oblique compression.Structural analysis and cross-sectional profiles suggest that fault F1-3 propagates into a mid-crustal detachment surface,forming a foreland-vergent thrust-nappe system.Importantly,the rupture of this secondary fault,rather than the locked primary boundary fault F1-1,indicates stress transfer and localization within a critically tapered wedge,consistent with global analogs of back-thrust-dominated earthquakes.These findings underscore the seismotectonic complexity of the LJSFZ and highlight the significant seismic hazard posed by subsidiary structures in compressional settings.展开更多
The present study area involves part of a deformed coalesced fan located along the Himalayan Frontal Thrust(HFT)on the east of river Tista near the India-Bhutan border.The area is marked by two spectacular E-W trendin...The present study area involves part of a deformed coalesced fan located along the Himalayan Frontal Thrust(HFT)on the east of river Tista near the India-Bhutan border.The area is marked by two spectacular E-W trending south-sloping scarps namely the Matiali(ca.60 m)and Chalsa(ca.90 m)Scarps and a north-sloping E-W trending Thaljhora(ca.80 m)Scarp.Our work comprises of a comparative study of geomorphology and geologic history in the adjacent interfluves of Jaldhaka-Gathia and Neora-Murti rivers to understand the tectonic history of the area.We mapped the Jaldhaka-Gathia river interfluve at a 1:25,000 scale and report a hitherto unidentified northerly sloping small scarp of ca.5 m height named the Nagrakata Scarp.This scarp was identified using satellite images,DEMs,and total station survey.We interpret that the two northsloping,E-W trending scarps(Thaljhora and Nagrakata Scarps)are manifestations of steep limbs of anticlines over blind south-dipping back thrusts.Together they form a wrinkle-ridge pair behind the north-dipping HFT,which is manifested by south-sloping Chalsa Scarp.We propose a plausible geomorphic model interpreting that deformation along the small fan in the Jaldhaka-Gathia interfluves is younger compared to fan deposition and deformation in the adjacent Mal-Murti interfluve.The most recent geomorphology of the Jaldhaka-Gathia interfluve is controlled by tectonism associated with the thrust below the Nagrakata Scarp where the youngest deformation episode is recorded to at around^6 ka and is likely related to motion on a splay off of the thrust beneath the Thaljhora Scarp.展开更多
A family of geophysical lineaments have been identified in ~15,000 km^2 in central Kerala between9 30'N to 10 45'N and 76 00'E to 77°30′E,integrating geophysical data with geological and geomorpholog...A family of geophysical lineaments have been identified in ~15,000 km^2 in central Kerala between9 30'N to 10 45'N and 76 00'E to 77°30′E,integrating geophysical data with geological and geomorphological features. The characteristics of these lineaments in the magnetic and gravity fields and their derivatives have been analysed. The evolution of the lineaments has been traced to the temporal phases of global evolution of the region. A group of these faults have formed by reactivation of the deep-seated distensional fractures associated with and accompanying dyke emplacements during the episodic breakup of Gondwana at ~90 and 65 Ma under distinctive mantle thermal regimes. It is possible that reactivation of these distensional faults may have started during the cooling interval of time between the two distensions in the 90 and 65 Ma and post 65 Ma periods and later in the Cenozoic, when the lineaments were enlarged to their present dimension, possibly under the influence of forces that led to the uplift of the western Ghats. These may extend down to the crust-mantle interface. A cluster of youngergeophysical lineaments has been generated by reactivation along the weak planes of transformation of the charnockitic rocks of the Precambrian. They seem to have a strike-slip character. They are devoid of any dyke association and were formed on a cold crust. They may be confined to the upper-middle crust.They were generated in the high intensity intra-plate palaeo-stress fields of the triple forces arising from(1) the back-thrust from the Himalayan Collision;(2) the impact of epeirogenic forces and related isostatic uplift of the Western Ghats and(3) the flexural isostatic uplifts due to surface loads of late Mesozoic basaltic lavas and Cenozoic sedimentation in the coastal rifted basins in late Cenozoic, probably in the time span of 20 Ma to the present, when the palaeostress fields were most intense.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42277152,42041006)the Fundamental Research Funds for the Central Universities,Chang'an University(300102262910)+2 种基金supported by the International Science and Technology Cooperation Program of China(202406560140)Shaanxi Province Science and Technology Innovation Team(Ref.2021TD-51)the innovation team of Shaanxi Provincial Tri-Qin Scholars with Geoscience Big Data and Geohazard Prevention(2022)。
文摘The December 18,2023,M_(S)6.2 Jishishan earthquake occurred along the northeastern margin of the Qinghai-Xizang Plateau within the Laji-Jishi Shan Fault Zone(LJSFZ),a complex thrust-dominated tectonic belt.To identify the seismogenic fault and better understand the regional tectonic framework,we integrated high-resolution Digital Elevation Models(DEMs)derived from GF-7 stereo satellite and Unmanned Aerial Vehicle(UAV)photogrammetry,relocated aftershock sequences,and conducted detailed field investigations.Our results identify four Late Quaternary thrust faults(F1-1 to F1-4),among which the Zhaomuchuan fault(F1-3),a NE-dipping back-thrust,aligns closely with the main-shock and aftershock distribution and exhibits clear Holocene activity.Seismic relocation reveals a NEdipping seismogenic zone at depths of 5-12 km,consistent with a shallow reverse-faulting mechanism under WSW-ENE oblique compression.Structural analysis and cross-sectional profiles suggest that fault F1-3 propagates into a mid-crustal detachment surface,forming a foreland-vergent thrust-nappe system.Importantly,the rupture of this secondary fault,rather than the locked primary boundary fault F1-1,indicates stress transfer and localization within a critically tapered wedge,consistent with global analogs of back-thrust-dominated earthquakes.These findings underscore the seismotectonic complexity of the LJSFZ and highlight the significant seismic hazard posed by subsidiary structures in compressional settings.
基金the Fast Track Project for Young scientists granted to Chandreyee Chakraborty Goswami by the Department of Science and Technology, Government of India (Grant No. SR/FTP/ES-47/2013)
文摘The present study area involves part of a deformed coalesced fan located along the Himalayan Frontal Thrust(HFT)on the east of river Tista near the India-Bhutan border.The area is marked by two spectacular E-W trending south-sloping scarps namely the Matiali(ca.60 m)and Chalsa(ca.90 m)Scarps and a north-sloping E-W trending Thaljhora(ca.80 m)Scarp.Our work comprises of a comparative study of geomorphology and geologic history in the adjacent interfluves of Jaldhaka-Gathia and Neora-Murti rivers to understand the tectonic history of the area.We mapped the Jaldhaka-Gathia river interfluve at a 1:25,000 scale and report a hitherto unidentified northerly sloping small scarp of ca.5 m height named the Nagrakata Scarp.This scarp was identified using satellite images,DEMs,and total station survey.We interpret that the two northsloping,E-W trending scarps(Thaljhora and Nagrakata Scarps)are manifestations of steep limbs of anticlines over blind south-dipping back thrusts.Together they form a wrinkle-ridge pair behind the north-dipping HFT,which is manifested by south-sloping Chalsa Scarp.We propose a plausible geomorphic model interpreting that deformation along the small fan in the Jaldhaka-Gathia interfluves is younger compared to fan deposition and deformation in the adjacent Mal-Murti interfluve.The most recent geomorphology of the Jaldhaka-Gathia interfluve is controlled by tectonism associated with the thrust below the Nagrakata Scarp where the youngest deformation episode is recorded to at around^6 ka and is likely related to motion on a splay off of the thrust beneath the Thaljhora Scarp.
文摘A family of geophysical lineaments have been identified in ~15,000 km^2 in central Kerala between9 30'N to 10 45'N and 76 00'E to 77°30′E,integrating geophysical data with geological and geomorphological features. The characteristics of these lineaments in the magnetic and gravity fields and their derivatives have been analysed. The evolution of the lineaments has been traced to the temporal phases of global evolution of the region. A group of these faults have formed by reactivation of the deep-seated distensional fractures associated with and accompanying dyke emplacements during the episodic breakup of Gondwana at ~90 and 65 Ma under distinctive mantle thermal regimes. It is possible that reactivation of these distensional faults may have started during the cooling interval of time between the two distensions in the 90 and 65 Ma and post 65 Ma periods and later in the Cenozoic, when the lineaments were enlarged to their present dimension, possibly under the influence of forces that led to the uplift of the western Ghats. These may extend down to the crust-mantle interface. A cluster of youngergeophysical lineaments has been generated by reactivation along the weak planes of transformation of the charnockitic rocks of the Precambrian. They seem to have a strike-slip character. They are devoid of any dyke association and were formed on a cold crust. They may be confined to the upper-middle crust.They were generated in the high intensity intra-plate palaeo-stress fields of the triple forces arising from(1) the back-thrust from the Himalayan Collision;(2) the impact of epeirogenic forces and related isostatic uplift of the Western Ghats and(3) the flexural isostatic uplifts due to surface loads of late Mesozoic basaltic lavas and Cenozoic sedimentation in the coastal rifted basins in late Cenozoic, probably in the time span of 20 Ma to the present, when the palaeostress fields were most intense.
