New paleoseismic events reveal decamillenial recurrence time for large earthquakes (M 7) along the Yuguang Graben Fault in North China

Paleoseismic studies are critical for the assessment and prediction of large earthquakes (M >= 7). These studies involve excavating and analyzing evidence from surface-rupturing earthquakes. However, they often face limitations in spatiotemporal resolution. The Yuguang Graben, located in the northern Shanxi Grabens of North China, contains an abundance of Quaternary loess that can be utilized for extending paleoseismic records. Fine-grained deposits of loess contrast sharply with gravel deposits of the colluvial wedge, making the wedge shape apparent. To enhance our understanding of earthquake behavior in the Yuguang Graben, we excavated a trench on terrace T2 of the Songzhikou segment of the Yuguang Graben Fault (YGF). We used LiDAR to obtain a high-resolution orthophoto of the trench wall. Through OSL dating of colluvial wedges and loess, we identified at least four large paleoseismic events with a magnitude of M >= 7 that occurred along the YGF. These events took place at >77.6 +/- 5.1, 63.9 +/- 5.1, 51.0 +/- 4.3, and 37.3 +/- 0.3 kyr, respectively. Combined with previous paleoseismic studies, we identified seven paleoseismic events since the late Pleistocene. These findings reveal that earthquakes occurring on YGF follow a quasiperiodic pattern with an average recurrence interval of about 12 +/- 3 kyr. The elapsed time of the most recent earthquake near the recurrence interval suggests an increased risk of a large earthquake along the YGF. We also analyzed earthquake clusters generated by neighboring faults in the active northeastern boundary of the Ordos block. Our analysis indicated that fault interactions can affect the recurrence interval of earthquakes along single faults, while regional seismic activity tends to concentrate in time during a seismically active period. These observations underscore the importance of expanding paleoseismic records and exploring regional seismic hazards to gain a more comprehensive understanding of earthquakes.