Based on the data from repeated precise leveling and across-fault deformation measurements carried out in recent 30 years and the analyzed results from GPS observations made in recent years along the northeastern marg...Based on the data from repeated precise leveling and across-fault deformation measurements carried out in recent 30 years and the analyzed results from GPS observations made in recent years along the northeastern margin of Qinghai-Xizang block, and combined with the geological structures and seismic activities, some characteristics in regional tectonic deformation and strong earthquake development are studied and approached preliminarily. The results show that: a) The space-time distribution of current tectonic deformation in this area is inhomogeneous with relatively intensive tectonic deformation in the vicinity of main boundary faults and weak deformation in the farther areas. The intensity of vertical differential movement and the deformation status vary with time, and the horizontal movement and deformation are characterized by apparent compression and strike-slip. b) The tectonic stress field generated by the NE-trending continuous compressive movement of Qinghai-Xizang block due to the northward press and collision of India plate is the principal stress for the tectonic deformation and earthquake development in this area. The evolution of space-time distribution of tectonic deformation and seismicity is closely related to the block activity and dynamic evolution of regional tectonic stress field. c) The vertical deformation uplift and high-gradient deformation zones and the obvious fault deformation anomaly appeared along the boundaries of tectonic blocks can be considered as the indicators of hindered block motion and intensified tectonic stress field for strong earthquake development. Usually, the above-mentioned phenomena would be followed by the seismicity of M6.0, but the earthquake might not occur in the place with the maximum movement. The zones with the fault deformation anomaly characterized by tendencious accumulation acceleration turning and the surrounding areas might be the positions for accumulation of strain energy and development and occurrence of strong earthquakes.展开更多
Based on leveling data in 1972 -2011 and relative-gravity data in 1993 -2011, we obtained a longterm vertical crustal-deformation rate of 1.62mm/a and a relative-gravity variation rate of 0.62 × 10^-8 ms^-2a^-1 f...Based on leveling data in 1972 -2011 and relative-gravity data in 1993 -2011, we obtained a longterm vertical crustal-deformation rate of 1.62mm/a and a relative-gravity variation rate of 0.62 × 10^-8 ms^-2a^-1 for the northeastern margin area of Qinghai-Tibet plateau. After removing the contributions from the observed vertical movement and inferred surface denudation, we obtain a gravity-variation rate of 0.73 × 10^-8 ms^-2a^-1 attributable to the mass changes beneath the crust. This positive change suggests that the total mass under the observation stations was gradually increasing. We consider this result to be the gravitational evidence of underplating beneath the study area, and propose that the underplating was caused by collision betwen the Indian plate and Tibetan plateau and by gravitation-potential induced deviatoric stress.展开更多
基金Foundation item: The Development Program on National Key Basic Researches under the Project Mechanism and Prediction of Continental strong Earthquakes (G1998040703)
文摘Based on the data from repeated precise leveling and across-fault deformation measurements carried out in recent 30 years and the analyzed results from GPS observations made in recent years along the northeastern margin of Qinghai-Xizang block, and combined with the geological structures and seismic activities, some characteristics in regional tectonic deformation and strong earthquake development are studied and approached preliminarily. The results show that: a) The space-time distribution of current tectonic deformation in this area is inhomogeneous with relatively intensive tectonic deformation in the vicinity of main boundary faults and weak deformation in the farther areas. The intensity of vertical differential movement and the deformation status vary with time, and the horizontal movement and deformation are characterized by apparent compression and strike-slip. b) The tectonic stress field generated by the NE-trending continuous compressive movement of Qinghai-Xizang block due to the northward press and collision of India plate is the principal stress for the tectonic deformation and earthquake development in this area. The evolution of space-time distribution of tectonic deformation and seismicity is closely related to the block activity and dynamic evolution of regional tectonic stress field. c) The vertical deformation uplift and high-gradient deformation zones and the obvious fault deformation anomaly appeared along the boundaries of tectonic blocks can be considered as the indicators of hindered block motion and intensified tectonic stress field for strong earthquake development. Usually, the above-mentioned phenomena would be followed by the seismicity of M6.0, but the earthquake might not occur in the place with the maximum movement. The zones with the fault deformation anomaly characterized by tendencious accumulation acceleration turning and the surrounding areas might be the positions for accumulation of strain energy and development and occurrence of strong earthquakes.
基金supported by the National Natural Science Foundation of China(40874035)
文摘Based on leveling data in 1972 -2011 and relative-gravity data in 1993 -2011, we obtained a longterm vertical crustal-deformation rate of 1.62mm/a and a relative-gravity variation rate of 0.62 × 10^-8 ms^-2a^-1 for the northeastern margin area of Qinghai-Tibet plateau. After removing the contributions from the observed vertical movement and inferred surface denudation, we obtain a gravity-variation rate of 0.73 × 10^-8 ms^-2a^-1 attributable to the mass changes beneath the crust. This positive change suggests that the total mass under the observation stations was gradually increasing. We consider this result to be the gravitational evidence of underplating beneath the study area, and propose that the underplating was caused by collision betwen the Indian plate and Tibetan plateau and by gravitation-potential induced deviatoric stress.
