关键词: 青藏高原东北缘, 日月山断裂, 晚第四纪活动, 滑动速率

Abstract: The northeastern edge of the Tibetan Plateau is the forefront of the northeastward expansion of the Tibetan Plateau, which is the ideal place to study the deformation of the plateau as well as the far-field deformation associated with continental collision between the Eurasia and India plates. Within the northeastern margin of the Tibetan Plateau, there are two major fault systems: one is the left-lateral strike-slip fault systems in almost EW trending, including the Kunlun, Haiyuan and Western Qinling faults, the other one is the righ-lateral strike-slip fault systems in NNW trending, including the Elashan, Riyueshan faults, which are sub-parallel to each other. Since the Riyueshan fault is one of the major right-lateral strike-slip fault within the northeastern margin of the Tibetan Plateau, its activity is of great significance for understanding the plateau expansion. Previous studies mainly focus on its northern part which has been believed to be active during Holocene. However, its southern part is believed to be active during Late Pleistocene, which is not active since Holocene. Therefore, there are little studies focus on the late Quaternary activities of the southern part of the Riyueshan fault, hence, our understanding about the characteristics of the late Quaternary activity is insufficient. During our preliminary field survey along the Southern Riyueshan fault, we found distinct deformation of Holocene landforms, such as the young alluvial fan, terrace risers and channels, which indicate its late Quaternary activity. In this study, we firstly analyze the fault geometry of the Southern Riyueshan fault based on high-resolution Superview-1 remote sensing images and utilized in field. Based on fault geometry characteristics, fault strike orientation etc., we dived the Southern Riyueshan fault into Guide (generally trending in NW 20°)and Duohelmao (generally in NS striking) segments from north to south. During our field investigation, we found two typical sites for slip rate studies, Rixiaolongwa site on the Guide segment and Niemari sites along the Duohemao segment, respectively. We collected high-resolution images using UAV, then generated high-resolution DEM of these two sites. By measuring the multi-level offset and corresponding dating results of the terrace riser, we obtained three levels and two levels of displacement and dating data at Rixiaolongwa and Niemari sites, respectively. By applying Monte Carlo method, we obtained the corresponding slip rates for the Guide and Duohemao segment to be 3.37+0.55 -0.68mm/yr and 2.69+0.41 -0.38mm/yr, which is comparable with the previous suggested slip rate of Northern Riyueshan fault. Finally, we discussed the role of the Riyueshan fault in the tectonic deformation of northeastern Tibetan plateau.

Key words: Southern Riyueshan fault, Northeastern margin of Tibetan Plateau, Late Quaternary activity, Slip rate