Morpho-Sedimentary evidence of the Huoshan Fault’s late Cenozoic right-lateral movement in the Linfen Graben, Shanxi Graben System, North China

Abstract

The Huoshan Fault, being of NEN strike, is one of the most important faults in the Shanxi Graben System of North China; it is the location of the 1303 A.D. Hongtong earthquake (MS = 8.0). The late Pleistocene and Holocene offset of some gullies that cross the fault and some fault scratches have proved its right lateral movement during the late Quaternary; however, until now, geological evidence to support the movement in the Neogene and early Quaternary was scarce. Our work provides further crucial evidence that supports both its movement in the late Cenozoic and the total right-lateral displacement since the Pliocene. The difference in the outcrop heights of the Pliocene sediment along the fault, the difference in the geomorphological development along the fault, the inconsistency in the lithological composition of the Pliocene proluvial gravels with the rock types within the catchments of the current upper stream, and the offset of the Pliocene alluvial gravels all completely indicate that the fault has always moved right-laterally since the Pliocene. Additionally, this evidence indicates that the accumulative displacement is up to 12.5 km. Based on the horizontal and vertical displacement of the fault since the Pliocene, the time-averaged horizontal slip rate of the fault is estimated to be about 3.5 mm/a, while the ratio of the horizontal to vertical offsets is about 3.8; these data are roughly close to the results that were acquired from the Holocene and the present movement of the fault. This similarity in the tectonic movement parameters may imply that the intensity as well as the configuration of the regional stress field has remained constant, and that no significant changes have taken place since the Pliocene.