Fault Segmentation and Paleoseismicity along the North Wutaishan Fault of the Shanxi Rift System, China

The Shanxi Rift System is prominent example of active, intracontinental seismicity and has been the location of multiple large and devastating earthquakes in the past. This includes the M ~8 Hongdong earthquake of 1303 where an estimated 800,000 people were killed. The Shanxi Rift System consists of a series of en echelon left stepping half graben basins located in the Shanxi Province of Northern China. This study reports preliminary results of paleoseismic investigations along the North Wutaishan Fault (NWTSF) at the Northeastern end of the rift system. The ENE-WSW striking NWTSF is 85 km long and bounds the Wutai Mountains and the Xinding basin. The last major earthquake in the region was M 7.5 in 512 A.D., though the precise location as well as the associated faulted section is unknown. High resolution, stereoscopic satellite imagery was used to produce a 5-meter pixel digital elevation model of the study area. These data then served as a basis for mapping the active fault trace. The NWTSF shows evidence of 6 main structure segments associated with fault bends and splays which may correspond with possible seismogenic segments. Earthquake recurrence along the eastern segment of the NWTSF is investigated using paleoseismic trenches. Paleoseismic indicators suggest at least 4 possible events with displacements ranging from 0.8 - 2 meters. This range of displacements suggests the NWTSF does fit with a characteristic earthquake recurrence model. The last event appears preserved in one trench as a colluvial wedge approximately 75 cm thick. This could suggest an original scarp height of up to 1.5 meters. If this reflects the mean surface displacement, this would imply a magnitude of ~7.2. Radiocarbon dating for this event is pending. Collectively, these results provide a view of earthquake recurrence in this part of the Shanxi Rift and provide a view of earthquake processes involved in intracontinental rifting.