It is well known that studies on palaeo-seismicity at present are generally accomplished byanalyzing the scale and episode of wedge-shaped seismic colluvial deposits along fault zones. Asan example,this paper has inve...It is well known that studies on palaeo-seismicity at present are generally accomplished byanalyzing the scale and episode of wedge-shaped seismic colluvial deposits along fault zones. Asan example,this paper has investigated the seismic landslides along the Changma fault zone, analyzed their modes of combination, intrinsic structural characteristics and ages,and thereby studied palaeo-seismic events on that fault zone.The Changma fault zone is an important active fault zone in the northwest of the Qilianmountains. It trends about west-northwest on the whole, and is composed of west-northwest,east-northeast-and n ort h-nort h west-ire nd in g fan its. It w as form ed in t h e Ca led onia n p eriod ofthe Palaeozoic era and had had obvious activities in all of the Hercynian, Yanshan and Himalayanperiods. DUring the Quaternary period, especially in the late Pleistocene, it has experiencedmany times of intense left-lateral strike-slip movements. The Changma Ms￣7. 5 earthquake occurred on December 25, 1932, and produced a series of seismic landslides and collapses alongpiedmont areas of the basement fault (Figure la).展开更多
Based on field investigations and indoor systematic research of the 1879 South Wudu M8.0 earthquake conducted in recent years, the magnitude, damage, seismic intensity, co-seismic fracture of the earthquake, as well a...Based on field investigations and indoor systematic research of the 1879 South Wudu M8.0 earthquake conducted in recent years, the magnitude, damage, seismic intensity, co-seismic fracture of the earthquake, as well as its seismogenic tectonics and preparation process, have been studied. The paper summarizes the results of studies on location of the earthquake’s macroscopic epicenter, magnitude and co-seismic fracture, with emphasis on the distribution range, type, extent and mechanism of its co-seismic fractures. The research reveals that, (1) the major part of the meizoseismal area of the South Wudu earthquake is located between Wudu and Wenxian in southern Gansu Province. It extends in a NEE direction, its shape is elliptical with the major axis about 70km long and the minor axis 30km. The macroscopic epicenter is located in the vicinity of Baoziba, in the east of the meizoseismal area; (2) three co-seismic fracture belts developed in the meizoseismal area, scattering northeastwards and converging southwestwards; (3) the major fracture belt extends from Baishuijiang at Hanan on the west, to the the bank areas of Bailongjiang river on the east, such as Gushuizi, Toufang and Daoqizi, etc.; (4) the co-seismic fractures consist of earthquake fissure, scarp, bulge, landslide, barrier lake and so on, among which landslides are the most obvious phenomenon; (5) according to the location, geometry and mechanism of the fracture, it is assumed that the co-seismic fracture zone of the South Wudu earthquake is the product of left-lateral strike-slip, associated with a dip-slip in the Hanan-Daoqizi-Maopola fault zone; (6) based on the size of the co-seismic fracture and the observed amount of displacement of the seismogenic fault of the South Wudu earthquake, the magnitude of this event is estimated to be M8.0.展开更多
文摘It is well known that studies on palaeo-seismicity at present are generally accomplished byanalyzing the scale and episode of wedge-shaped seismic colluvial deposits along fault zones. Asan example,this paper has investigated the seismic landslides along the Changma fault zone, analyzed their modes of combination, intrinsic structural characteristics and ages,and thereby studied palaeo-seismic events on that fault zone.The Changma fault zone is an important active fault zone in the northwest of the Qilianmountains. It trends about west-northwest on the whole, and is composed of west-northwest,east-northeast-and n ort h-nort h west-ire nd in g fan its. It w as form ed in t h e Ca led onia n p eriod ofthe Palaeozoic era and had had obvious activities in all of the Hercynian, Yanshan and Himalayanperiods. DUring the Quaternary period, especially in the late Pleistocene, it has experiencedmany times of intense left-lateral strike-slip movements. The Changma Ms￣7. 5 earthquake occurred on December 25, 1932, and produced a series of seismic landslides and collapses alongpiedmont areas of the basement fault (Figure la).
文摘Based on field investigations and indoor systematic research of the 1879 South Wudu M8.0 earthquake conducted in recent years, the magnitude, damage, seismic intensity, co-seismic fracture of the earthquake, as well as its seismogenic tectonics and preparation process, have been studied. The paper summarizes the results of studies on location of the earthquake’s macroscopic epicenter, magnitude and co-seismic fracture, with emphasis on the distribution range, type, extent and mechanism of its co-seismic fractures. The research reveals that, (1) the major part of the meizoseismal area of the South Wudu earthquake is located between Wudu and Wenxian in southern Gansu Province. It extends in a NEE direction, its shape is elliptical with the major axis about 70km long and the minor axis 30km. The macroscopic epicenter is located in the vicinity of Baoziba, in the east of the meizoseismal area; (2) three co-seismic fracture belts developed in the meizoseismal area, scattering northeastwards and converging southwestwards; (3) the major fracture belt extends from Baishuijiang at Hanan on the west, to the the bank areas of Bailongjiang river on the east, such as Gushuizi, Toufang and Daoqizi, etc.; (4) the co-seismic fractures consist of earthquake fissure, scarp, bulge, landslide, barrier lake and so on, among which landslides are the most obvious phenomenon; (5) according to the location, geometry and mechanism of the fracture, it is assumed that the co-seismic fracture zone of the South Wudu earthquake is the product of left-lateral strike-slip, associated with a dip-slip in the Hanan-Daoqizi-Maopola fault zone; (6) based on the size of the co-seismic fracture and the observed amount of displacement of the seismogenic fault of the South Wudu earthquake, the magnitude of this event is estimated to be M8.0.
