The North China Block mainly consisting of the Ordos and North China Plain sub-blocks, is one of the most intriguing regions jointly controlled by the India-Eurasia collision and the westward subduction of the Pacific-Philippine plate (e.g.,
We establish a continuous GPS transect crossing the central Altyn Tagh fault at 90°E with eight years of observations. GPS velocities along this profile and another one crossing the fault at 86°E suggest a fault slip rate of 12.4 ± 0.7 mm/yr, but with asymmetric straining of adjacent terrain. On the south side, ∼8.2 mm/yr of left‐lateral shear is absorbed across a region ∼210 km from the fault, but only ∼4.2 mm/yr is found on the north side. This estimate of slip rate is ∼30% larger than the consensus estimate of previous models. By treating the deforming regions as elastic plates with different thicknesses overlying a substrata that obeys a linear Maxwell viscoelastic constitutive relationship, we infer a viscosity of ∼5.1 × 1019 Pa s (between 3.5 and 9.1 × 1019 Pa s at 1‐σ) on the south side, beneath northern Tibetan Plateau. This low viscosity, compared to some estimates for the asthenosphere, concurs with the Tibetan Plateau being underlain by a relatively hot and weak lower crust and upper mantle. The effective elastic thickness on the south side is 16.5–20 km, which is significantly smaller than that of the Tarim Basin of >60 km.
Slip from paleoearthquakes is preserved in geomorphology in the form of displaced landforms. By recovering the surface slip distribution of displaced landforms along a fault, we can constrain the earthquake rupture histories and recurrence characteristics on the fault, thus benefiting seismic hazard assessment. In this study, 1‐m‐resolution airborne Light Detection and Ranging data were obtained along about 185 km of the Sertengshan Piedmont Fault, which is a dip‐slip normal fault located at the northern margin of the Hetao Graben around the Ordos Block in Northern China. A total of 601 vertical displacements were measured on different geomorphic surfaces along the fault strike. Through statistical analysis of the displacement measurements, it is inferred that at least five to seven large earthquakes have ruptured this fault, displaying a remarkably regular slip increment of ∼2 m. Compared with the slip, the recurrence intervals of paleoearthquakes exposed by previous paleoseismic excavations are less regular, which may be due to the different recording capacity of geomorphic and paleoseismic markers. By recovering the surface slip distributions of several recent events, we identified several large full‐rupture earthquakes that may have broken two adjacent segments together and smaller partial‐rupture events that have ruptured only a part of the segment, thus suggesting a bimodal rupture behavior for the fault. Our estimates indicate that rupturing of the Sertengshan Piedmont Fault may yield a large earthquake of Mw 7.1–7.5, leading to significant seismic hazards in the densely populated Hetao Graben area.
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