Lake Level Changes and Holocene Extension Rate Across the NS-Trending Peiku Co-Gyirong Faults, Southern Tibet

Precise studies of Quaternary extension rates across NS-trending normal faults in southern Tibet are important to understand the recent tectonic evolution of the high plateau. As one of the six main, southernmost Tibetan rifts, the similar to NS-trending Peiku Co-Gyirong rifts and intervening horst (PGR), co-involve the west-dipping Gyirong normal fault (GF) and the east-dipping Peiku Co normal faults (PKF). Using unmanned aerial vehicle (UAV) high-resolution topographic data, C-14 dating of lake shorelines, and Be-10 cosmogenic exposure dating of alluvial surfaces, we assess the offsets and constrain the ages of fans and lake level variations at four sites along these rift faults. Across the PKF's southern segment, our measurements at three sites are consistent with offsets of similar to 4.7-6.5 m during the last similar to 12.3 ka. Across the GF, a larger total offset of similar to 8.5 m accrued since similar to 10.4 ka. Using the average, exposed, 60 degrees dip angle of the PKF implies a total Holocene EW extension rate of 0.72 +/- 0.08 mm/yr across the PGR. Overall, our results are in keeping with published extension rates of similar to 0.6-1.7 mm/yr across other southern Tibetan rifts, supporting the inference that the total, similar to EW, late Quaternary extension rate throughout southern Tibet is 9 +/- 2 mm/yr. That there has been no surface faulting since at least similar to 6.9 ka implies that the Gyirong County area, west of Peiku Co, may be at risk of Mw approximate to 6.9? event. Plain Language Summary Quantifying ongoing extension rates across the Tibet Plateau is key to understand its recent tectonic evolution. The active, NS-trending, Peiku Co-Gyirong normal faults bound one of the main six rifts of southernmost Tibet. Using unmanned aerial vehicle (UAV) DEMs and 10Be and radiocarbon dating, we measured alluvial fan offsets and dated lake shorelines at 4 sites along these faults. Across the southern PKF, our results at three different locations imply vertical throws of similar to 4.7-6.5 m since similar to 12.3 ka. Across the GF, we measure larger throws of similar to 8.5 m since similar to 10.4 ka. Using the 60 degrees fault dip-angle observed in the field, a total extension rate of 0.72 +/- 0.08 mm/yr across both faults is obtained, consistent with rates across other southern Tibet rifts. This supports the inference that the total late Quaternary extension rate across all of southern Tibet is 9 +/- 2 mm/yr. That the Peiku Co fault has not ruptured since similar to 6900 years implies that it might produce an earthquake of Mw similar to 6.9, and hence pose considerable risk to the similar to 17,000 people living in Gyirong County.

Automated summary

Accurate study of Quaternary extension rates along NS-trending normal faults in southern Tibet is crucial to comprehend the recent tectonic evolution of the high plateau. Through the use of UAV data, C-14 dating, and Be-10 cosmogenic exposure dating, this study assessed offsets and constrained ages at four sites along the Peiku Co-Gyirong rifts and intervening horst. The results show consistent offsets of approximately 4.7-6.5 m since around 12.3 ka along the Peiku Co normal faults, and a larger total offset of around 8.5 m since around 10.4 ka along the Gyirong normal fault. The overall findings support the inference that the total late Quaternary extension rate throughout southern Tibet is approximately 9 +/- 2 mm/yr, highlighting the risk of a potential Mw 6.9 earthquake in the Gyirong County area.