Holocene Activity of the Xigeda Fault and Its Implications for the Crustal Deformation Pattern in the Southeastern Tibetan Plateau

Intra-block faults generally attract less attention because little slip occurs on them. However, some of them can host strong earthquakes and thus their faulting behaviors are also significant for assessing seismic risk and understanding crustal deformation patterns. The Xigeda fault is one of the intra-block faults in the southeastern Tibetan Plateau and has generated two M > 6 earthquakes in the past 70 years. Nevertheless, little is known about its faulting behavior, seismic hazard, and tectonic role. Focusing on this problem, we conducted field investigations, trench excavations, and shallow seismic exploration to characterize its fault activity. Our work reveals that the Xigeda fault slips left-laterally at a rate of 0.8-1.6 mm/yr with a thrust component through high-resolution landforms measuring and sample dating. The paleoseismic investigations determine the latest surface rupturing event along the Xigeda fault occurred between 1580 CE and 1970 CE, which is further determined as the 1732 earthquake with a reevaluated magnitude of 7.0-7.5. Therefore, the Xigeda fault is confirmed to be active in the Holocene and can generate M >= 7.0 earthquakes. Moreover, the Xigeda fault, along with the Yuanmou fault, makes up the shortage of slip rates between the Anninghe and Zemuhe faults and plays an important role in partitioning the slip along the Xianshuihe-Xiaojiang fault system and accommodating the crustal deformation in the Sichuan-Yunnan block. Additionally, our work suggests a crustal deformation pattern for the southeastern Tibetan Plateau that most of the crustal deformation within tectonic blocks is still expressed by slipping along significant intra-block faults.