Paleoearthquakes along the northeastern segment of the Yabrai range-front fault in the Alashan Block, northeast of the Tibetan Plateau

Abstract

The Yabrai range-front fault (YRF) is a large-scale fault within the Alashan Block, located northeast of the Tibetan Plateau, which has undergone several surface rupture events on the southwestern and middle segments since the late Quaternary. As no relevant research has been conducted on the northeastern segment, paleoseismic data for this area are lacking, which restricts our overall understanding of the spatiotemporal and intensity distribution of strong earthquakes on the YRF. To address this problem, we conducted investigations based on trench wall interpretation and stratigraphic optically stimulated luminescence ages. Four paleoearthquakes were identified in the middle of the northeastern segment, and occurred after 11.6 ± 0.7 ka and between 11.6 ± 0.7 to 6.9 ± 0.5, 6.9 ± 0.5 to 4.8 ± 0.6 and 4.8 ± 0.6 to 3.9 ± 0.7 ka, respectively. Three paleoearthquake events, one of which occurred at around 23.6 ± 1.6 ka, were identified at the northeastern end of the fault. According to the spatiotemporal distribution of the ruptured events on the YRF, the middle segment may be a long seismic gap (~8 ka), and combined with the status of tectonic stress concentration, this segment can be regarded as a zone of high seismic probability with the ability to produce a magnitude 7.2 earthquake. Furthermore, from the late Pleistocene to early Holocene, cascading ruptures may have occurred on the middle and northeastern segments of the YRF, with magnitudes approaching 7.3. In terms of tectonic relationships, we suggest that the YRF and the Langshan piedmont fault are two independent faults even though they are connected.