Late Quaternary Fault Activity of the Southern Segment of the Daliangshan Fault along the Southeastern Margin of the Tibetan Plateau and Its Implications for Fault Rupture Behaviour at Stepovers

Abstract

Stepovers have been widely suggested to be important structural boundaries that control earthquake rupture extent and therefore the size of earthquakes. Previous studies suggested that ~4-5 km wide stepovers are likely to arrest fault rupture. However, recent earthquake cases show that even much wider stepovers (e.g., ≥7-8 km wide) sometimes may not effectively impede seismic rupture propagation, which requires us to further explore cascading rupture mechanism of large earthquakes at wider stepovers. Here, we constrained slip rates and paleoseismic earthquakes of two fault sections that bound a constraining stepover with width of approximately 7-8 km along the southern segment of the Daliangshan fault along the southeastern margin of the Tibetan Plateau. Multiple landform offset and radiocarbon dating results constrained that the two fault sections show a moderate slip rate at approximately 5 mm/yr. Moreover, three or four paleoseismic events Z through W, in 1489 AD, 620-515 BC, 4475-3700 BC, and 6265-4510 BC, were revealed on the Jiaojihe fault section. Based on the aforementioned results, we suggest that the most recent seismic event might exhibit a jump over the restraining stepover, whereas ruptures of the older events might be arrested by the stepover. Furthermore, we suggest that moderate slip-rate faults might have similar potential with that of high slip-rate faults to rupture through wider stepovers, which increases us in understanding the generation of cascading ruptures on strike-slip faults and is helpful for evaluating seismic hazards.