Reevaluation of the Late Pleistocene Slip Rate of the Haiyuan Fault Near Songshan, Gansu Province, China

International audienceWell-constrained fault slip rates are important for understanding strain partitioning within a fault system and the associated seismic hazard. The Haiyuan fault is a significant active strike-slip fault in the northeast margin of the Tibetan Plateau with ongoing controversy over its late Pleistocene slip rate. Previous work by Lasserre et al. (1999) suggested a slip rate of 12 ± 4 mm/year, which is higher than recent geodetically determined rates on adjacent fault sections. We reanalyze and reevaluate the slip rates benefiting from new high-resolution airborne Light Detection and Ranging data at their two sites, located north of the Songshan village. Based on this data, we revise field-mapped offset constraints. At the Majia Wan site, we document a sinistral displacement of 130 ± 10 m of the crest and 93 ± 15 m of the base of T1/T2 terrace riser, respectively. At the Xuanma Wan site, the offset of T4/T1′ terrace riser is updated to be 68 +3 / −10 m. Combining new geochronology dates, we assess the abandonment age of T2 as 26.0 ± 4.5 ka and T1 as 9,445 ± 30 year. These data suggest a slip rate between 5.0 +1.5 / −1.1 and 8.9 +0.5 / −1.3 mm/year since~26 ka, based on the upper terrace and lower terrace reconstruction, respectively. Our reevaluation supports that apparent slip rate discrepancies in northern Tibet possibly share a systematic bias due to the use of lower-terrace reconstruction to interpret the age of offset