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The seismic intensity, seismogenic tectonics and mechanism of the Ms6.6 Damxung earthquake happened on October 6, 2008 in southern Tibet, China

Authors:
  • Institue of geomechanics, CAGS

Abstract

Field survey shows that the macro -epicenter of October 6, 2008 Ms 6.6 Damxung earthquake is located at northern Yangyi graben in the north section of the Yadong-Gulu rift. The maximum intensity of the Damxung earthquake is IX degree and lies at Yangyi village (29°43.3′N; 90°23.6′E). The main boundary normal fault of Yangyi graben is NNE-trending, dipping to east and located at west side of Yangyi basin. It is main seismogenic tectonics on the Damxung earthquake that control the site of macro-epicenter, pattern of the iso-seismal contours, distribution of meizoseismal region and aftershocks. The field observation and focal mechanism solutions from HRV and NEIC indicate that the Damxung earthquake of October 6, 2008 occurred as a result of normal faulting along the western boundary fault of Yangyi graben. The normal faulting that caused the earthquake is predominantly east-west oriented extensional deformation that is distributed in southern Tibet and ultimately arises from the convergence of the India plate northwards with respect to the Eurasia plate. Recendy, the frequent strong earthquake activity occurred around Qinghai-Xizang plateau as a result of the regional stress field adjustment after the Ms8.0 Wenchuan earthquake.
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... On October 6, 2008, an Mw 6.3 earthquake struck Dangxiong county, Tibet province, China, in the Yadong-Gulu rift of the southern Tibetan Plateau (Fig. 1). This event was a shallow destructive earthquake, causing the largest economic losses (about $411 million) and the most serious casualties (up to 10 people) in Tibet in the last 50 years (Wu et al., 2009;Zhang et al., 2008). Geological field observation in southern Tibet (Armijo et al., 1986) indicated that transverse extension of the Yadong-Gulu rift is significant, which can be explained by a series of normal faults dipping to the east and west. ...
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We present a study of the active tectonics of China based on an interpretation of Landsat (satellite) imagery and supplemented with seismic data. Several important fault systems can be identified, and most are located in regions of high historical seismicity. We deduce the type and sense of faulting from adjacent features seen on these photos, from fault plane solutions of earthquakes, and from existing field reports. In central China the three major east-west trending fault systems are left lateral strike slip faults. Movement on these faults appears to displace much of China eastward, out of the way of the converging Indian and Eurasian subcontinents. Moreover, these large eastward displacements are a key to the understanding of the tectonics both of southern China, where normal faulting and right lateral strike slip faulting occur in Yunnan in contrast with thrust faulting in Szechwan, and of northeastern China, where extensional tectonics and basaltic volcanism dominate. Hence we relate all of the recent tectonics of China to the convergence of India and Eurasia during the Cenozoic at a rate of about 5 cm/year. The continental lithosphere of Asia appears to behave like a rigid plastic medium indented by India. In this context the large strike slip faults are analogous to slip lines in the indented plastic material.
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Plane indentation experiments on unilaterally confined blocks of plasticine help us to understand finite intracontinental deformation and the evolution of strike-slip faulting in E Asia. Several large left-lateral strike-slip faults may have been activated successively, essentially one at a time. The experiments suggest that the penetration of India into Asia has rotated (approx= 25o) and extruded (approx= 800km) Indochina to the SE along the then left-lateral Red River fault in the first 20-30Ma of the collision. This process can account for the opening of the S China Sea before late Miocene time. Extrusion tectonics then migrated N, activating the Altyn Tagh fault as a second major left-lateral fault and moving S China hundreds of km to the E. As this occurred, Indochina kept rotating clockwise (as much as 40o), but the sense of motion reversed on the Red River and other strike-slip faults in the S. Opening of the Mergui basin and Andaman Sea (up to the present) also appears to be a simple kinematic consequence of the extrusion. Recent rifts in NE China and Yunnan may be considered incipient analogs of the S China and Andaman Seas. Other Tertiary tectonic features such as the sedimentary basins of the Gulf of Thailand may be explained as collisional effects, if one uses our experiments as a guide. The experiments also suggest that a major left-lateral strike-slip fault and rift system will propagate across the Tien Shan, Mongolia, and Baikal to the Sea of Okhotsk.-Authors
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A geological and geophysical context for the Wenchuan earthquake of 12 May
  • B C Burcmel
  • L H Royden
  • R D Van Der Hilst
BurcMel B C, Royden L H, van der Hilst R D, et al. A geological and geophysical context for the Wenchuan earthquake of 12 May, 2008, Sichuan, People's Republic of ChinaU]. GSA Today, 2008, 18(7): 4-11.