On November 14, 2001, an earthquake measuring a magnitude of 8.1 occurred to the west of the Kunlun Mountain Pass which is near the border between Xinjiang and Qinghai of China. Since its epicenter is located in an ar...On November 14, 2001, an earthquake measuring a magnitude of 8.1 occurred to the west of the Kunlun Mountain Pass which is near the border between Xinjiang and Qinghai of China. Since its epicenter is located in an area at an elevation of 4900 m where the environment is extremely adverse, field investigation to this event seems very difficult. We have performed interpretation and analysis of the satellite images of ETM, SPOT, Ikonos, and ERS-1/2SAR to reveal the spatial distribution and deformation features of surface ruptures caused by this large earthquake. Our results show that the rupture zone on the ground is 426 km long, and strikes N90-110°E with evident left-lateral thrusting. In spatial extension, it has two distinct sections. One extends from the Bukadaban peak to the Kunlun Mountain Pass, with a total length of 350 km, and trending N95-110°E. Its fracture plane is almost vertical, with clear linear rupture traces and a single structure, and the maximum left-lateral offset is 7.8 m. This section is the main rupture zone caused by the earthquake, which is a re-fracturing along an old fault. The other is the section from Kushuihuan to the Taiyang Lake. It is 26 km long, trending N90-105°E, with the maximum strike-slip displacement being 3 m, and is a newly-generated seismic rupture. In a 50 km-long section between the Taiyang Lake and the Bukadaban peak, no rupture is found on the ground. The eastern and western rupture zones may have resulted from two earthquakes. The macroscopic epicenter is situated at 65 km east of the Hoh Sai Lake. The largest coseismic horizontal offset in the macroscopic epicenter ranges from 7 m to 8 m. Based on the dislocation partition of the whole rupture zone, it is suggested that this rupture zone has experienced a process of many times of intensification and fluctuation, exhibiting a remarkable feature of segmentation.展开更多
The transitional pressure of quartz coesite under the differential stress and highly strained conditions is far from the pressure of the stable field under the static pressure. Therefore, the effect of the different...The transitional pressure of quartz coesite under the differential stress and highly strained conditions is far from the pressure of the stable field under the static pressure. Therefore, the effect of the differential stress should be considered when the depth of petrogenesis is estimated about ultrahigh pressure metamorphic (UHPM) rocks. The rheological strength of typical ultrahigh pressure rocks in continental subduction zone was derived from the results of the laboratory experiments. The results indicate the following three points. (1) The rheological strength of gabbro, similar to that of eclogite, is smaller than that of clinopyroxenite on the same condition. (2) The calculated strength of rocks (gabbro, eclogite and clinopyroxenite) related to UHPM decreases by nearly one order of magnitude with the temperature rising by 100 ℃ in the range between 600 and 900 ℃. The calculated strength is far greater than the faulting strength of rocks at 600 ℃, and is in several hundred to more than one thousand mega pascals at 700-800 ℃, which suggests that those rocks are located in the brittle deformation region at 600 ℃, but are in the semi brittle to plastic deformation region at 700-800 ℃. Obviously, the 700 ℃ is a brittle plastic transition boundary. (3) The calculated rheological strength in the localized deformation zone on a higher strain rate condition (1.6×10 -12 s -l ) is 2-5 times more than that in the distributed deformation zone on a lower strain rate condition (1.6×10 -14 s -1 ). The average rheological stress (1 600 MPa) at the strain rate of 10 -12 s -1 stands for the ultimate differential stress of UHPM rocks in the semi brittle flow field, and the average rheological stress (550-950 MPa) at the strain rate of l0 -14 - 10 -13 s -l stands for the ultimate differential stress of UHPM rocks in the plastic flow field, suggesting that the depth for the formation of UHPM rocks is more than 20-60 km below the depth estimated under static pressure condition due to the effect of the differential stress.展开更多
The formation of strath and strath terrace is closely related to tectonic uplift in the drainage basin. Based on the investigation of straths at Yandantu and Changcaogou on the eastern segment of the northern margin f...The formation of strath and strath terrace is closely related to tectonic uplift in the drainage basin. Based on the investigation of straths at Yandantu and Changcaogou on the eastern segment of the northern margin fault of Altun, and in combination with the paleoclimatic data, the tectonic uplift since late Epipleistocene as revealed by stream terraces at the two places is discussed. At Yandantu, three levels of stream terraces(T 1, T 2 and T 3)have developed since 16ka BP, where T 1, T 3 and T 2 are fill terraces and the buried major straths are exposed. The ages of three treads are dated to be about 16.1ka BP, 12.8ka BP and 6.2ka BP, respectively. The three terraces reflect three tectonic uplift events, while the ages of the treads represent the occurrence time of these events. The stream is still beveling the bedrock and widening the channel at present, and the modern strath is being generated. The uplift rate is 4.8～4.5mm/a since 16.1 ka BP in this area. From 12.8ka B.P to 6.2ka BP, The uplift rate was 6.4mm/a. The uplift rate is 3.1mm/a since 6.2ka BP. At Changcaogou, four levels of stream terraces(T 1, T 2, T 3 and T 1′)have developed since 7ka BP. All of them are fill terraces. There are buried straths under the deposits. The buried major strath is exposed on T 3 and T 2 and the minor strath on T 1′and T 1. The ages of treads of the three terraces (T 3, T 2 and T 1′) are 7 ka BP, 3 ka BP and 2.5 ka BP, respectively. The four terraces reflect two uplift events induced by tectonic activities. One occurred in about 7 ka BP, and the other in 3ka BP. The uplift rate is 5.9mm/a since 7.0 ka BP at Changcaogou. From 7ka BP to 3ka BP, the uplift rate was 7.0mm/a, and since 3ka BP till now, the uplift rate is 4.7 mm/a.展开更多
In order to study quartz-coesite transition under the conditions of differential stress, experiments of quartzite deformation were carried out using a triaxial testing system with a Griggs type solid medium pressure v...In order to study quartz-coesite transition under the conditions of differential stress, experiments of quartzite deformation were carried out using a triaxial testing system with a Griggs type solid medium pressure vessel. Analyses on the plastically-deformed samples under optical microscope and Raman spectra show that fine-grained coesite was present in the region of samples adjacent to the pistons at temperatures of 950-1000℃, confining pressure of 1.3 GPa, differential stress of 1.5-1.67 GPa, and total strain of 75%-81%. It is evident that the transition pressure of quartz-coesite at differential stress and intensely-strained conditions is far lower than the pressure for coesite stability at isostatic pressure. In other words, the stress condition of coesite occurrence is not unique. The decrease in confining pressure for quartz-coesite transition under differential stress conditions is controlled by a combined effect of the maximum principal stress that provides a high stress environment, and differential stress that causes sample deformation. Coesite was produced in the plastically-deformed samples in this study, but it can occur in both semi-brittle and plastic deformation regimes as seen in previous studies. Phase transition in semi-brittle deformation regime is caused by local mechanical instability induced by shear deformation, and phase transition in plastic flow regime is due to strain instability induced by the presence of a high dislocation density within intensely-deformed quartz crystals.展开更多
基金the special project"Monitoring Research of Major Seismic Disasters”(No.2002DIA10001)of the Minister of Science andTechnologythe National Natural Science Foundation of China(grant 40374013) the Joint Foundation ofEarthquake Science(No.102096).
文摘On November 14, 2001, an earthquake measuring a magnitude of 8.1 occurred to the west of the Kunlun Mountain Pass which is near the border between Xinjiang and Qinghai of China. Since its epicenter is located in an area at an elevation of 4900 m where the environment is extremely adverse, field investigation to this event seems very difficult. We have performed interpretation and analysis of the satellite images of ETM, SPOT, Ikonos, and ERS-1/2SAR to reveal the spatial distribution and deformation features of surface ruptures caused by this large earthquake. Our results show that the rupture zone on the ground is 426 km long, and strikes N90-110°E with evident left-lateral thrusting. In spatial extension, it has two distinct sections. One extends from the Bukadaban peak to the Kunlun Mountain Pass, with a total length of 350 km, and trending N95-110°E. Its fracture plane is almost vertical, with clear linear rupture traces and a single structure, and the maximum left-lateral offset is 7.8 m. This section is the main rupture zone caused by the earthquake, which is a re-fracturing along an old fault. The other is the section from Kushuihuan to the Taiyang Lake. It is 26 km long, trending N90-105°E, with the maximum strike-slip displacement being 3 m, and is a newly-generated seismic rupture. In a 50 km-long section between the Taiyang Lake and the Bukadaban peak, no rupture is found on the ground. The eastern and western rupture zones may have resulted from two earthquakes. The macroscopic epicenter is situated at 65 km east of the Hoh Sai Lake. The largest coseismic horizontal offset in the macroscopic epicenter ranges from 7 m to 8 m. Based on the dislocation partition of the whole rupture zone, it is suggested that this rupture zone has experienced a process of many times of intensification and fluctuation, exhibiting a remarkable feature of segmentation.
文摘The transitional pressure of quartz coesite under the differential stress and highly strained conditions is far from the pressure of the stable field under the static pressure. Therefore, the effect of the differential stress should be considered when the depth of petrogenesis is estimated about ultrahigh pressure metamorphic (UHPM) rocks. The rheological strength of typical ultrahigh pressure rocks in continental subduction zone was derived from the results of the laboratory experiments. The results indicate the following three points. (1) The rheological strength of gabbro, similar to that of eclogite, is smaller than that of clinopyroxenite on the same condition. (2) The calculated strength of rocks (gabbro, eclogite and clinopyroxenite) related to UHPM decreases by nearly one order of magnitude with the temperature rising by 100 ℃ in the range between 600 and 900 ℃. The calculated strength is far greater than the faulting strength of rocks at 600 ℃, and is in several hundred to more than one thousand mega pascals at 700-800 ℃, which suggests that those rocks are located in the brittle deformation region at 600 ℃, but are in the semi brittle to plastic deformation region at 700-800 ℃. Obviously, the 700 ℃ is a brittle plastic transition boundary. (3) The calculated rheological strength in the localized deformation zone on a higher strain rate condition (1.6×10 -12 s -l ) is 2-5 times more than that in the distributed deformation zone on a lower strain rate condition (1.6×10 -14 s -1 ). The average rheological stress (1 600 MPa) at the strain rate of 10 -12 s -1 stands for the ultimate differential stress of UHPM rocks in the semi brittle flow field, and the average rheological stress (550-950 MPa) at the strain rate of l0 -14 - 10 -13 s -l stands for the ultimate differential stress of UHPM rocks in the plastic flow field, suggesting that the depth for the formation of UHPM rocks is more than 20-60 km below the depth estimated under static pressure condition due to the effect of the differential stress.
文摘The formation of strath and strath terrace is closely related to tectonic uplift in the drainage basin. Based on the investigation of straths at Yandantu and Changcaogou on the eastern segment of the northern margin fault of Altun, and in combination with the paleoclimatic data, the tectonic uplift since late Epipleistocene as revealed by stream terraces at the two places is discussed. At Yandantu, three levels of stream terraces(T 1, T 2 and T 3)have developed since 16ka BP, where T 1, T 3 and T 2 are fill terraces and the buried major straths are exposed. The ages of three treads are dated to be about 16.1ka BP, 12.8ka BP and 6.2ka BP, respectively. The three terraces reflect three tectonic uplift events, while the ages of the treads represent the occurrence time of these events. The stream is still beveling the bedrock and widening the channel at present, and the modern strath is being generated. The uplift rate is 4.8～4.5mm/a since 16.1 ka BP in this area. From 12.8ka B.P to 6.2ka BP, The uplift rate was 6.4mm/a. The uplift rate is 3.1mm/a since 6.2ka BP. At Changcaogou, four levels of stream terraces(T 1, T 2, T 3 and T 1′)have developed since 7ka BP. All of them are fill terraces. There are buried straths under the deposits. The buried major strath is exposed on T 3 and T 2 and the minor strath on T 1′and T 1. The ages of treads of the three terraces (T 3, T 2 and T 1′) are 7 ka BP, 3 ka BP and 2.5 ka BP, respectively. The four terraces reflect two uplift events induced by tectonic activities. One occurred in about 7 ka BP, and the other in 3ka BP. The uplift rate is 5.9mm/a since 7.0 ka BP at Changcaogou. From 7ka BP to 3ka BP, the uplift rate was 7.0mm/a, and since 3ka BP till now, the uplift rate is 4.7 mm/a.
基金supported by the National Natural Science Foundation of China(Grant No.40002020)the Institute of Geology,China Earthquake Administration(Grant No.2005B0010).
文摘In order to study quartz-coesite transition under the conditions of differential stress, experiments of quartzite deformation were carried out using a triaxial testing system with a Griggs type solid medium pressure vessel. Analyses on the plastically-deformed samples under optical microscope and Raman spectra show that fine-grained coesite was present in the region of samples adjacent to the pistons at temperatures of 950-1000℃, confining pressure of 1.3 GPa, differential stress of 1.5-1.67 GPa, and total strain of 75%-81%. It is evident that the transition pressure of quartz-coesite at differential stress and intensely-strained conditions is far lower than the pressure for coesite stability at isostatic pressure. In other words, the stress condition of coesite occurrence is not unique. The decrease in confining pressure for quartz-coesite transition under differential stress conditions is controlled by a combined effect of the maximum principal stress that provides a high stress environment, and differential stress that causes sample deformation. Coesite was produced in the plastically-deformed samples in this study, but it can occur in both semi-brittle and plastic deformation regimes as seen in previous studies. Phase transition in semi-brittle deformation regime is caused by local mechanical instability induced by shear deformation, and phase transition in plastic flow regime is due to strain instability induced by the presence of a high dislocation density within intensely-deformed quartz crystals.
