1 Institute of Geology, China Earthquake Administration, Beijing 100029, China 2 Development Research Center of China Geological Survey, Beijing 100037, China
Earthquake fault framework and seismotectonics of the Songpan-Garze region since 1900
1 Institute of Geology, China Earthquake Administration, Beijing 100029, China 2 Development Research Center of China Geological Survey, Beijing 100037, China
摘要Based on 4 781 observed faults (>2 km length) from a 1:200 000 scale digital geologic map and 5 220 recorded seismic events since the year 1900, 993 earthquake faults are identified within the triangular Songpan-Garze study region. The study area is delineated by the nearly EW-trending East Kunlun fault zone to the north, the NW-trending Xianshuihe fault to the south and the NE-trending Longmenshan thrust belt to the east. Seismicity changes along these earthquake faults, spanning four 10-year intervals since 1970, show that following a strong earthquake swarm, which occurred in the Huya area in the mid-1970s, seismic activity increased from north to south, and migrated eastward along each major strike-slip fault zone. GPS observation data before 2008 indicate a displacement rate across the Xianshuihe fault zone to the south of ~6.5-8.6 mm/a, whereas across the East Kunlun fault zone to the north it was ~1.8-2.2 mm/a. The May 12, 2008 MS8.0 Wenchuan earthquake, which occurred in the southeast corner of the study region, was the result of stable, high-speed left-lateral displacement along the Xianshuihe fault zone, and a sharp eastward bend of the fault trend in response to the presence of crystalline rocks in the Kangding area. Therefore, the 110-year established seismotectonic framework of the Songpan-Garze region can be defined by a network of various earthquake faults and the structural relations of the local earthquake activities.
Abstract：Based on 4 781 observed faults (>2 km length) from a 1:200 000 scale digital geologic map and 5 220 recorded seismic events since the year 1900, 993 earthquake faults are identified within the triangular Songpan-Garze study region. The study area is delineated by the nearly EW-trending East Kunlun fault zone to the north, the NW-trending Xianshuihe fault to the south and the NE-trending Longmenshan thrust belt to the east. Seismicity changes along these earthquake faults, spanning four 10-year intervals since 1970, show that following a strong earthquake swarm, which occurred in the Huya area in the mid-1970s, seismic activity increased from north to south, and migrated eastward along each major strike-slip fault zone. GPS observation data before 2008 indicate a displacement rate across the Xianshuihe fault zone to the south of ~6.5-8.6 mm/a, whereas across the East Kunlun fault zone to the north it was ~1.8-2.2 mm/a. The May 12, 2008 MS8.0 Wenchuan earthquake, which occurred in the southeast corner of the study region, was the result of stable, high-speed left-lateral displacement along the Xianshuihe fault zone, and a sharp eastward bend of the fault trend in response to the presence of crystalline rocks in the Kangding area. Therefore, the 110-year established seismotectonic framework of the Songpan-Garze region can be defined by a network of various earthquake faults and the structural relations of the local earthquake activities.
基金资助:the Major Project of Chinese National Program for Basic Research and Development (2008CB425703) and the International Cooperation Ministry of Science and Technology Key Project (2008DFA20700)
