Holocene activity evidence on the southeast boundary fault of Heqing basin, middle segment of Heqing-Eryuan fault zone, West Yunnan Province, China
The Heqing-Eryuan fault is an important part of the active fault system in the Northwestern Yunnan Province, China. Thus, the study on the nature, characteristics and activity history of this fault can provide not only the basis for seismic safety and engineering evaluation, but also the important information for the characteristics, history and patterns of the structural deformation of the southeastern margin of the Tibetan Plateau. Trench and faulted landforms investigations could provide effective paleoseismic methods to obtain the recent parameters of active faults. Using these methods, this study makes some breakthroughs on the recent activity of southeast boundary fault of the Heqing basin, middle segment of Heqing-Eryuan fault zone. Results indicate that the average vertical slip rate and left-lateral slip rate of the segment are about 0.28 mm/a and 1.80 mm/a respectively since the Late Pleistocene. The trench near the Beixi Village at the southeast boundary fault of the Heqing basin reveals that there have been at least three paleoearthquake events during the Holocene (~8 ka BP). The vertical displacement and sinistral strike-slip distance of a single paleoearthquake are ~20 cm and ~1.2 m, respectively. The estimated paleoearthquake magnitudes with Ms7.0, and the recurrence interval at 2-5 ka, as well as the latest activity time during 800- 290 cal yr BP, are of great significance for preventing and mitigating regional earthquake disasters.
KeywordsHeqing-Eryuan fault zone Paleoearthquake Holocene activity Sinistral strikeslip Heqing basin
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We thank Profs. XU Xi-wei, RAN Yong-kong, ZHANG Shi-min, TIAN Qin-jian and CHANG Zufeng for assistance in field investigation and Dr. ZHAO Jun-xiang for OSL dating. We are grateful to the staffs of Earthquake Bureau of Heqing County, Yunnan Province, China for the trench excavation and the Earthquake Administration of Yunnan Province, China for the airphoto collection. We also thank Prof. HUANG Zhong-xian for improving the English writing and two anonymous reviewers for valuable comments, which helped to improve this manuscript. This work was supported by the National Natural Science Foundation of China (Grant No. 41171001, 41471002, 41402184), the 1:50000 Active Fault Mapping of Heqing- Eryuan fault (Grant No. 201108001-20) and a research grant from the Institute of Crustal Dynamics, China Earthquake Administration (Grant No. ZDJ2013-17).
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