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In mainland China, approximately 86% of M≥7 earthquakes have occurred in the block boundary zone, which has been well explained by active block theory. However, a few large earthquakes have occurred within the active block, which provides us with an opportunity to better study the deformation of the Tibetan Plateau. The Litang Fault (LTF) is a strike-slip fault within the Sichuan-Yunnan Active Block and produced the 1948 Litang M7.3 earthquake. We presented the Holocene rupture behavior of the LTF based on detailed field investigations, paleoearthquake trenching, and radiocarbon dating. Specifically, we revealed 13 Holocene paleoearthquake events at four trenching sites and divided these events into 3 rupture cycles at the whole-fault scale. The seismic rupture behavior of the LTF is characterized by recurrent southeastward migration, and since the Holocene, the period of each rupture cycle has decreased rapidly from 8000 years to 500 years. Our results may provide geologic evidence for understanding the intrablock stress patterns and material transfer of the southeastern region of the Tibetan Plateau. The rapidly enhanced fault activity of the LTF since the late Holocene indicates that the LTF may have played an important role in accommodating the deformation of the southeastern region of the Tibetan Plateau.

The 2022 Luding Ms 6.8 earthquake has drawn attention to the Xianshuihe fault zone. Historically, there was an M 73/4 earthquake in this region in 1786. Because the surface rupture of this historic earthquake was not obvious, there is still much debate over the extent of the surface rupture, which is critical for comprehending tectonic activity and assessing seismic risk for the Xianshuihe fault (XSHF). In particular, the seismogenic structure of this earthquake was connected by three active left-lateral strike-slip faults—the Anninghe fault (ANHF), Daliangshan fault (DLSF), and XSHF—where a large earthquake could cause multi-fault rupture. Given these criteria, we report the results of a series of trenches excavated in the vicinity of the epicenter at the northern section of the DLSF, the northern section of the ANHF, the Zheduotang section, and the Selaha section of the XSHF. We find that 1) three palaeoseismic events have been revealed on the northern section of the ANHF: BE1, ∼1003 AD; BE2, 1000–1182 AD; and BE3, 1536 AD as M 7 earthquakes, and 2) two palaeoseismic events have occurred on the Selaha fault during the last 500 years. The first event corresponds to the AD 1725 Kangding M 7 earthquake, and the latest event may be the AD 1786 M 73/4 earthquake. 3) Three palaeoseismic events occurred on Zheduotang: ZD1, 1215 BC∼315 AD; ZD2, 830 BC∼705 AD; and ZD3, the 1955 AD Kangding M 71/2 earthquake. 4) The 1786 Kangding M 73/4 earthquake was probably a multi-fault rupture event, as evidenced by the trenching profile evidence, nearby offset geomorphic features, and historical earthquake data. Not only the Moxi fault, a seismogenic structure, but also the southern end of the Selaha fault to the north and the Shimian fault (DLSF) to the south simultaneously broke during this earthquake.

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The WNW-trending Yangda-Yaxu fault (YYF) is located in the interior of the Qiangtang block (QTB). The YYF cuts through the Nujiang suture and Lancang river suture zone and divides Nujiang fault (NF) and Lancangjiang fault (LCJF) into two sections with significantly different activity levels, suggesting that the YYF may function as a specific structure in this region. In addition, a recent work argues that the YYF plays an important role in strain partitioning in southeastern Tibet and poses a high surface-faulting risk to the Sichuan-Tibet railway. However, no M ≥ 5.0 earthquakes have been recorded, and no palaeoseismic research has been conducted along the fault, leading to limited knowledge regarding its rupture behavior, which is essential for understanding regional tectonic deformation and assessing the regional seismic potential. In this study, we constrained the timings and recurrence intervals of late Quaternary paleoseismic events along the YYF for the first time. Through trench excavations and exposure cleaning combined with radiocarbon dating, five faulting events were identified, namely, E1 through E5 from youngest to oldest (831–1,220, 3,307–6,703, 9,361–10,286, 12,729–14,651, and before 14,651 yr BP). The recurrence interval of major earthquakes along the YYF follows a quasi-periodic pattern with an interval of ∼4,000 yr. Combining the clear linear geomorphic features along the fault and the paleoearthquake results in this paper, we believe that YYF is a newly-generated active fault, and has a significant control effect on the late Quaternary evolution of the NF and the LCJF. Further analysis revealed that the YYF also plays an important role in accommodating crustal deformation.