| Northeastern Tibetan Plateau is plateau deformation frontier zone, it is very sensitive to deformation of the plateau, which has undergone expansion and extrusion of nearly EW to NW direction. Study area is located in the Qaidam- Qilian block internal activity by the East Kunlun fault and Qilian- Haiyuan breakage main boundary fault control, the formation of a secondary structure sandwiched between blocks inside the main boundary fault. Riyueshan fault zone is a Holocene fault activity, its seismic activity on the northeastern margin of the Tibetan Plateau what implications, how it affects their uplift of the Cenozoic basins, as well as the relationship between the conversion Lajishan fault zone, these issues are worth indepth study and discussion.Based on the above, the paper focuses on the formation of the Riyueshan fault zone, stratum and geomorphology, geometry attribution, kinematic characteristics and of plaeo-seismic studies, and the fault of the seismic hazard has been some qualitative understanding, reached the following basic conclusions :1)Near the Riyueshan fault zone, its stratigraphic, landform have different performance in secondary fault segments. In study area, the oldest strata is Presinian sub-group on border garang subgroup, widely distributed in the Riyueshan West in HaErgai river sides and DaTongshan area, lack of Silurian stratigraphic on Devonian and Carboniferous strata in the fourth missing Pleistocene sediments.Geomorphological aspects of the fault landform surface is divided into five geomorphic surfaces, that is the bedrock mountains, granite platform, Lat-Tertiary basin surface, Alluvial ground station ground and river terraces, use HuangShuiHe terraces contrast, the establishment of a zone Quaternary time scale, and has been three tectonic activity since the late Pleistocene.2) Order by district, faults and fault bifurcation tendency changes, the western part of the Riyueshan fault zone can be divided into five segments, from northwest to southeast were the DaTonghe segment, ReShui segment, Dezhou segment, Haiyan segment and Riyueshan segment. Between the fault segment to the right column of the order form plume spread between fault segments form a different scale pull partitions, the longest stage area about 8.5km, at its widest point about 0.77 km, fusiform.3) by sliding displacement comparing the paragraphs that since the late Pleistocene RiYueshan fault segments activity more consistent and comprehensive analysis of each segment displacement, horizontal displacement Riyueshan fault zone can be divided from the old to the new 815-1360 m, 400- 550 m, 260-300 m, 90-180 m, 42-77 m, 20-36 m, 10-15.5m, 3.5-8m. According to research data age,late Pleistocene contrast obtained 24ka-29 ka, 10ka-11 ka and 2-7ka, obtained three tectonic movement rates were: 0.75-1.36mm/a, 0.95-1.48mm/a and 0.78-1.78mm/a. Vertical sliding displacement is divided into three, namely: 6.03-15.78 m, 3.01-6.78 m and 0.34-2.99 m, vertical slip rate is 0.22-0.6mm /a, 0.29-0.65 mm /a and 0.08-0.66 mm /a.4) In the Riyueshan fault Dezhou section and Haiyan segment, We excavate 4 paleo-earthquake trenches, trenches 5 sectional. Through inter-trench ancient seismic event comparative analysis, revealed a total of 4 paleoseismic events that occurred in the Late Pleistocene, the use of test data and geochronology combined with previous data obtained to obtain since the late Pleistocene paleoearthquakes recurrence interval of about 3360 a BP, consistent with previous results of the latest research and the most recent events have been dating for about 2000 a, with strong seismic hazard, shall be increased by the fault zone near the attention. |
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