The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fau...The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone（Dangjiang segment） reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone（striking NW-NWW）, less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone（Dangjiang segment）. We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.展开更多
Our field investigation obtains new evidence of the later Quaternary activity and recent large earthquake ruptures of the Garzê-Yushu fault. The average left-lateral slip-rate along the fault is determined to be ...Our field investigation obtains new evidence of the later Quaternary activity and recent large earthquake ruptures of the Garzê-Yushu fault. The average left-lateral slip-rate along the fault is determined to be (12 ± 2) mm/a for the last 50000 years from both offset landforms and ages of the correlative sediments. This result is very close to the estimated average left-lateral slip-rate for the Xianshuihe fault, suggesting that the horizontal movement along the northern boundary of the Sichuan-Yunnan active tectonic block and the northeastern boundary of the Qiangtang active tectonic block has been basically harmonious during the later Quaternary period. Remains of ground ruptures of recent large earthquakes have been discovered along all 3 segments of the fault, of which, the 1896 rupture on the northwestern segment is at least 70 km long, and its corresponding earthquake could be of moment magnitude 7.3. The latest rupture on the middle segment of the fault has a length of about 180 km, and was produced by an unknown-age large earthquake that could have a moment magnitude of about 7.7. Along the southeastern segment of the fault, the latest unknown-age rupture is about 65 km long and has a maximum left-lateral coseismic displacement of 5.3 m, and its corresponding earthquake is estimated to be as large as about 7.3 of moment magnitude. Based on relevant investigation, an inference has been drawn that the later two large earthquakes probably occurred in 1854 and 1866, respectively. These demonstrate that the individual segments of the studied Garzê-Yushu fault are all able to produce large earthquakes.展开更多
The Longmen Mountains and adjacent regions on the eastern margin of the Tibetan plateau can be divided into three tectonic units: the eastern Songpan—Garzê fold belt, the Longmen Mountains (Longmen Shan) Thrust...The Longmen Mountains and adjacent regions on the eastern margin of the Tibetan plateau can be divided into three tectonic units: the eastern Songpan—Garzê fold belt, the Longmen Mountains (Longmen Shan) Thrust—Nappe belt and the Western Sichuan foreland basin that occupies the western part of the Sichuan basin. The Longmen Shan Thrust—Nappe belt is subdivided by six northwest\|dipping major listric thrusts, with accompanying duplexes and imbricate fans, into five large\|scale nappes (Chen & Wilson, 1996). In the inner Longmen Shan, the nappe units have incorporated both Mesoproterozoic basement and Sinian (Neoproterozoic) to Triassic cover sequences as “thick\|skinned" horses. Whereas, in the frontal Longmen Shan, Sinian to Cretaceous cover sediments have been stripped from the basement as “thin\|skinned" fold and thrust sheets, including extensively distributed klippen structures. Pre\|thrusting extension during Devonian to middle Late Triassic times resulted in syndepositional normal faults. Structural inversion of these faults initiated the “Peng Xian—Guan Xian basement complex", Jiuding Shan and Tangwangzhai nappes, during an early episode of the Indosinian Orogeny (Norian to Rhaetian). This was followed by episodic thrusting during latest Triassic to Early Cretaceous times to develop the Guan Xian—An Xian and Southeastern Marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the Thrust—Nappe belt. Differential thrusting occurred across the Thrust—Nappe belt during a Late Miocene reactivation of the pre\|existing faults.展开更多
基金supported by the China Earthquake Administration Research Fund(Grant No.DZJ2016-18)the National Natural Science Foundation of China(Grant No.41602222)
文摘The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes（M 〉 7）. The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone（Dangjiang segment） reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone（striking NW-NWW）, less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone（Dangjiang segment）. We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.
文摘Our field investigation obtains new evidence of the later Quaternary activity and recent large earthquake ruptures of the Garzê-Yushu fault. The average left-lateral slip-rate along the fault is determined to be (12 ± 2) mm/a for the last 50000 years from both offset landforms and ages of the correlative sediments. This result is very close to the estimated average left-lateral slip-rate for the Xianshuihe fault, suggesting that the horizontal movement along the northern boundary of the Sichuan-Yunnan active tectonic block and the northeastern boundary of the Qiangtang active tectonic block has been basically harmonious during the later Quaternary period. Remains of ground ruptures of recent large earthquakes have been discovered along all 3 segments of the fault, of which, the 1896 rupture on the northwestern segment is at least 70 km long, and its corresponding earthquake could be of moment magnitude 7.3. The latest rupture on the middle segment of the fault has a length of about 180 km, and was produced by an unknown-age large earthquake that could have a moment magnitude of about 7.7. Along the southeastern segment of the fault, the latest unknown-age rupture is about 65 km long and has a maximum left-lateral coseismic displacement of 5.3 m, and its corresponding earthquake is estimated to be as large as about 7.3 of moment magnitude. Based on relevant investigation, an inference has been drawn that the later two large earthquakes probably occurred in 1854 and 1866, respectively. These demonstrate that the individual segments of the studied Garzê-Yushu fault are all able to produce large earthquakes.
文摘The Longmen Mountains and adjacent regions on the eastern margin of the Tibetan plateau can be divided into three tectonic units: the eastern Songpan—Garzê fold belt, the Longmen Mountains (Longmen Shan) Thrust—Nappe belt and the Western Sichuan foreland basin that occupies the western part of the Sichuan basin. The Longmen Shan Thrust—Nappe belt is subdivided by six northwest\|dipping major listric thrusts, with accompanying duplexes and imbricate fans, into five large\|scale nappes (Chen & Wilson, 1996). In the inner Longmen Shan, the nappe units have incorporated both Mesoproterozoic basement and Sinian (Neoproterozoic) to Triassic cover sequences as “thick\|skinned" horses. Whereas, in the frontal Longmen Shan, Sinian to Cretaceous cover sediments have been stripped from the basement as “thin\|skinned" fold and thrust sheets, including extensively distributed klippen structures. Pre\|thrusting extension during Devonian to middle Late Triassic times resulted in syndepositional normal faults. Structural inversion of these faults initiated the “Peng Xian—Guan Xian basement complex", Jiuding Shan and Tangwangzhai nappes, during an early episode of the Indosinian Orogeny (Norian to Rhaetian). This was followed by episodic thrusting during latest Triassic to Early Cretaceous times to develop the Guan Xian—An Xian and Southeastern Marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the Thrust—Nappe belt. Differential thrusting occurred across the Thrust—Nappe belt during a Late Miocene reactivation of the pre\|existing faults.
