Estimation of the Maximum Magnitude of Normal Faults and Seismic Risk in the Southern Tibetan Rift Zones

Hu Guiming; Xu Yueren; Liu Han; Yuan Ruimin; Lu Lingyu

doi:10.3799/dqkx.2025.055

Abstract：In the southern Tibetan rift zones,there are several approximately north-south trending rifts distributed from west to east.As important tectonic extensional zones within the blocks,these rifts have developed a series of normal faults and experienced multiple strong earthquakes.Since the Late Quaternary,this region has exhibited intense tectonic activity with frequent earthquakes causing serious disasters.For instance,the January 7,2025 Mw7.1(CENC:Ms6.9)Tingri earthquake demonstrated the characteristics of"small earthquake with major disaster consequences".To assess the seismogenic potential of normal faults within the rift zones and understand their disaster-inducing competence,this study divides 92 normal fault zones based on geometric characteristics and statistically analyzed fault trace lengths.Under the assumption of full-length surface rupture along fault traces during earthquakes,combined with empirical relationships between normal fault rupture length and moment magnitude,we estimated the maximum potential magnitudes of normal faults in the rift zones.Results indicate that these normal faults have upper seismogenic limits ranging from Mw6.5 to Mw7.5,with numerous historical seismic gaps.While generally demonstrating strong seismogenic competence,they exhibit an eastward-increasing strength pattern.Bounded by major fault zones to the north and south,and considering multiple historical seismic gaps along the southern magethrust(particularly in the context of accelerated Coulomb stress loading following the 2015 Nepal Mw7.8 earthquake and potential interaction/triggering effects between major boundary faults),the normal faults south of Yarlung Tsangpo River,especially those in the Tingri-Nyalam and Xiongqu fault,show high potential for future strong earthquakes.