A 3400-year-long paleoseismologic record of earthquakes on the southern segment of Anninghe fault on the southeastern margin of the Tibetan Plateau

The Anninghe fault (ANHF) is an active left-lateral strike-slip fault along the southeastern margin of the Tibetan Plateau. Previous studies suggested the ANHF was divided into two segments, which herein we named the northern and southern segments respectively. Multiple trenches were excavated on the northern segment, revealing well-constrained paleoseismic events by radiocarbon ages. However, until now there is no paleoseismic result on the southern segment, which terminates at the Zemuhe fault (ZMHF) around Xichang where there were multiple historical records of large earthquakes. In this paper, we used high-resolution images for mapping fault traces on the southern segment of the ANHF and found a small depression. Through trenching in the depression, five paleoseismic events are identified and named E1 through E5 from youngest to oldest at 1750 AD-present, 1430-1870 AD, 940-1150 AD, 700-1000 AD, and 1400-500 BC respectively. Comparing with the historical record earthquakes around Xichang, we suggest that the latest event E1 is associated with one of the 1850 AD and 1952 AD events, and event E2 is interpreted as the 1536 AD earthquake; event E4 is possibly associated with the 814 AD earthquake. The average recurrence interval of earthquakes on the southern segment is about 600-800 yr, the interval between E1 and E2 is 416 yr or 314 yr, and 386-596 yr between E2 and E3. The interval between E3 and E4 is shorter at 126-336 yr, but much longer at 1314-2214 yr between E4 and E5. These surface-faulting events on the southern segment of the ANHF appear to be unevenly spaced in time. Furthermore, integrating the paleoseismic sequence of the northern segment of the ANHF, the two segments appear to be ruptured individually or interactively triggered within a narrow time range, or co-ruptured during one paleoseismic event, indicating that the ANHF possibly shows a cascading rupturing behavior.