Late Pleistocene slip rate of the central Haiyuan fault constrained from optically stimulated luminescence, 14C, and cosmogenic isotope dating and high-resolution topography

Abstract

To better constrain the long-term millennial slip rate of the Haiyuan fault in its central part, we revisited the site of Daqing, where there are multiple paired offset terraces. We used 0.1-m-resolution terrestrial light detection and ranging (LiDAR) and uncrewed aerial vehicle imagery to survey the offset terraces, quantify their geomorphology, and map the fault trace. From these observations, we refined the geomorphological interpretation of the site, measured terrace riser offsets, and determined their relation to terrace formation. The well-constrained age of the highest terrace, T3, at 13.7 ± 1.5 ka, determined from a combination of surface and subsurface optically stimulated luminescence, 14C, and terrestrial in situ 10Be cosmogenic radionuclide dating, associated with an offset of 88 m, yields a late Pleistocene minimum slip rate of 6.4 ± 1.0 mm/yr. The less-well-constrained offset (72 ± 3 m) of the T3/T2 riser base and the age (>9.3 ± 0.6 ka) of terrace T2 yield a maximum slip rate of 7.7 ± 0.6 mm/yr. The smallest offset of a gully incised into T1 of 6.0 ± 0.5 m is potentially associated with the most recent slip event that occurred in the last millennia. Overall, these offsets and ages constrain a geological rate of 5−8 mm/yr (preferred rate >6.4 mm/yr), similar to geodetic estimates. Our collocated high-resolution topography and precise chronology make it possible to reveal the geomorphic complexities of terrace riser offsets and their postformational evolution, and to show how previously determined geological rates along the fault were both under- and overestimated.