Geomorphologic mapping and analysis of fault activities along the northern margin of the Yanfan Basin, China

Abstract

The proximity of Beijing to active faults at the northeastern end of the Shanxi Rift System has heightened seismic concerns since the 1976 Tangshan M 7.8 earthquake. This study examines the 105-km-long northern margin fault of the Yanfan Basin in the rift system. Previous studies indicated that the alluvial fans and terraces along the fault have been displaced due to large earthquakes over the past ~30 ka. Analysis of 0.5 m resolution terrain data enabled the identification of six surface levels of alluvial fans and five river terraces. We measured 373 vertical displacements across these geomorphic features and grouped the distribution of these values into five categories based on their probability density. These groups correspond to repeated faulting events since ~14 ka, with data from prior paleoseismological studies aiding in dating these offsets. The most recent displacements are potentially linked to the 1484 M 6.8 Juyongguan and 1337 M 6.5 Huailai earthquakes. The ~2 m difference between the offset sets suggests that similar multiple seismic events could have caused each set. The empirical relationship between surface rupture length and earthquake magnitude for the recorded events indicates that the fault's complex geometry likely contributed to segmented ruptures during these events. This study highlights the need to scrutinize fault activity near densely populated regions.