Present-day strain accumulation in the Liupan Shan area, northeastern margin of the Tibetan Plateau by GPS observations

Abstract

We derived a new GPS site velocity field by integrating the data of ten newly built stations across the Liupan Shan Fault, in the northeastern margin of the Tibetan Plateau and those of pre-existing sites in this area for the period of 1999 - 2015. The GPS velocity field in a Eurasian plate-fixed frame shows a clockwise rotation around the Ordos cratonic block. Relative to the Ordos block, GPS sites generally move northeastward. The inferred GPS velocity profile across the Liupan Shan Fault shows that fault-normal velocities decrease from west to east from 5.4 ± 0.9 mm yr-1, at the central of the Lanzhou block to 0.1 ± 0.8 mm yr-1 at the western Ordos craton. We estimated the locking degree and the slip deficit rate on the Liupan Shan Fault using the tectonic elastic block model. Modeling results show that the Liupan Shan Fault is characteristic of segmentation in terms of locking degree and slip deficit rate. The southern segment has the largest locking degree, with complete locking to the depth of 13 - 15 km; the locking degree in the central segment is smaller than that of the northern and southern segments. On average, the slip deficit rate at the northern segment is larger than that of the Southern and central segments. We estimate the maximum magnitude of an expected earthquake based on the moment budget since the last large earthquake of M 6.7 in 1921. If the accumulated energy was completely released by a single earthquake, the expected maximum magnitude would be Mw 6.7. The model prediction suggests a high potential for seismic hazard in the Liupan Shan area.