Research progress on Late Quaternary activity of the eastern foothill fault of Yulong Snow Mountain in Northwestern Yunnan and its tectonic implications

The northwest Yunnan rift zone develops along the western boundary of the Sichuan-Yunnan block. The N-S trending eastern foothill fault of Yulong Snow Mountain on the northern edge of the rift zone extends between the Yulong Snow Mountain and the Lijiang Basin. It is the innermost part of the western boundary of the Sichuan-Yunnan block. The formation mechanism and activity characteristics of the eastern foothill fault of Yulong Snow Mountain are not only related to the complex structural boundary issues on the western side of Sichuan and Yunnan, but also can explain the uplift process of the Yulong Mountain and the Haba Mountain. After the MS7.0 earthquake in Lijiang in 1996, the eastern foothill fault of Yulong Snow Mountain widely attracted attention. However, previous research results about the Late Quaternary activity of this fault were diverse, including normal faulting, strike-slip faulting, and thrusting. It indicates that although this fault is only 60 kilometers long, it belongs to a complex tectonic system. Understanding the activity characteristics and earthquake-generating behavior of this fault is of great significance for establishing a complex structural model in the western Sichuan-Yunnan block. This article summarizes previous research data, reinterprets the fault based on satellite images, analyzes the typical fault-related landforms and identifies clear evidence of a combination of normal faulting and sinistral strike-slip along the fault. Field investigations have further validated these interpretations. Based on the conclusions and analysis presented in this paper, we have summarized different regional tectonic models corresponding to the different activity properties of eastern foothill fault of Yulong Snow Mountain. Meanwhile, from the perspective of plateau expansion, it is believed that the complex fault combination in the western Sichuan-Yunnan block is new and is forming a new western boundary of the Sichuan-Yunnan block.