Paleoearthquake sequence in the eastern segment of the Serteng Shan frontal fault (Hetao graben, North China) during the last 50 ka

Abstract

To better constrain the paleoseismicity and assess the seismic hazard, we investigated the eastern segment of the Serteng Shan frontal fault along the northern margin of the Ordos Block. The Ordos Block in northern China has a stable interior but is surrounded by seismically active faults. Several historical earthquakes with magnitude ≥M7 have ruptured along the northern boundary of the Ordos Block. Using excavated trenches, the eastern segment of the Serteng Shan frontal fault along the northern margin of the Ordos Block was investigated. Seven events were identified based on distinct geological markers, such as colluvial wedges. To constrain the timing of these events, 28 samples were collected and dated using the optically stimulated luminescence (OSL) method. The dating indicates show that all seven events occurred after ∼90 ka, with the five most recent events occurring after 50 ka. Based on OxCal modeling results, the most recent event is inferred to have occurred at 7.0 ± 1.1 ka. The penultimate and preceding events occurred at approximately 25.0 ± 2.2 ka, 35.6 ± 1.5 ka, 41.3 ± 1.9 ka, and 46.2 ± 2.4 ka, respectively. The minimum recurrence intervals are approximately 5 ka, or multiples thereof, resulting in longer intervals of up to ∼20 ka. Combining the displacement of the T6 terrace and their corresponding ages, a uniform vertical slip rate of 0.15 ± 0.02 mm/yr over the last 90 ka is estimated. The slip rates and recurrence intervals indicate that the eastern segment of the Serteng Shan fault experiences a low rate of surface-rupturing earthquakes. This behavior could be explained by the effect of unloading of a mega-paleolake in the Hetao Basin at ∼50 ka. These results provide new constraints on long-term slip behavior and inform seismic hazard assessment.