Holocene paleoearthquakes of the Maoergai fault, eastern Tibet

Much work about fault activity and seismic hazard assessment has been conducted on major boundary faults of eastern Tibet, whereas seismic activity on faults between subblocks is poorly understood. The Maoergai fault, ~ 200 km northwest of and parallel to the Longmen Shan, is the eastern branch of the Longriba fault zone that divides the Bayan Har block into the Aba and Longmen Shan subblocks. Field investigation indicates that the Maoergai fault is a purely right-lateral strike–slip fault active in the Late Quaternary. Our trenches, combined with radiocarbon dating and Bayesian analysis, show that three Holocene paleoearthquakes ruptured the Maoergai fault at ~ 8510 ± 420, ~ 7100 ± 70, and ~ 5170 ± 80 cal yr BP, respectively. This suggests that the fault fits a cluster model with an average recurrence interval of ~ 1700 years and has a high potential of large earthquakes (Mw ~ 7.2–7.4) in the near future. Our results also indicate that an apparent fault scarp on a sloping tread provides an alternative site for paleoseismic studies to determine coseismic horizontal displacement on a strike–slip fault, and using the age of the upper terrace to determine strike–slip rate by displaced terrace riser is probably closer to the true value in streams with insufficient capacities of lateral erosion. This study provides useful information for the earthquake risk and fault behavior in eastern Tibet.

► The Maoergai fault is a purely dextral strike-slip fault.
► Holocene paleoearthquakes on the Maoergai fault are firstly reconstructed.
► Terrace with a sloping tread can be used to determine strike-slip coseismic offset.