PALEOSEIMOLOGY AND LATE QUATERNARY SLIP RATE OF THE YOUSHASHAN FAULT AT SOUTHWESTERN MARGIN OF QAIDAM BASIN |
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| Authors: | XU Jian-hong HUI Xu-hui CHENG Hong-bin ZHANG Xiao-liang SHANG Si-qi |
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| Affiliation: | 1.The Second Monitoring and Application Center, China Earthquake Administration, Xian 710054, Shaanxi, China;2.State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China |
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| Abstract: | The Youshashan Fault lies in the south flank of Yingxiongling anticline, southwestern margin of Qaidam Basin. The Yingxiongling anticline is one of the most active neotectonics, situated at the front of folds expanding southward in the Qaidam Basin. Research on the paleoseimology and Late Quaternary slip rate of this fault is important for hazard assessment and understanding tectonic deformation in this area. We excavated a 27-m-long trench across the Youshashan fault where a pressure bridge formed on the Holocene alluvial fans, measured a profile of the fold scarp created by the fault west of the Youshashan mountain, and collected several samples of finer sands for luminescence dating. Analysis of these data shows that(1) The Youshashan Fault is a Holocene active feature. The fold scarp in the basin indicates that this fault has been active along a same surface trace since at least mid-late Pleistocene. At least two paleoseismic events are revealed by trenching, both occurred in Holocene. The latest event Ⅱ in the trench happened after 500a. The current information fails to confidently support that it is the 1977 Mangya M6.4 earthquake, but cannot excludes the possibility of it is related to this earthquake. The other event Ⅰ occurred about between 1 000a to 4 000a. Erosion after the event Ⅰ prevents us to constrain the event age and to identify more events further. (2)The vertical slip rate of the Youshashan fault is about(0.38±0.06)mm/a since mid-late Pleistocene. Comparing with relative speeds of GPS sites across the Yingxiongling anticline suggests that the Youshashan fault is an important structure which is accommodating crustal shortening in this region. |
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| Keywords: | southwestern margin of Qaidam Basin Youshashan fault paleoseismology slip rate folding scarp |
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