Slip Distribution and Footwall Topography of the Yanggao-Tianzhen Fault (Northern Shanxi Graben): Implications for the Along-Strike Variations in Fault Activity and Regional Deformation

Spatial patterns in fault activity were examined along the Yanggao-Tianzhen Fault (YTF) in the northern Shanxi Graben, North China. First, we reconstructed the distribution of fault slips and quantified slip rates at seven sites along the fault, based on satellite image interpretation, field investigation, topographic surveying, and optically stimulated luminescence dating. The T-3 terraces and their contemporaneous alluvial fans with a best-estimate age of 31.7 +/- 1.4 kyr were used as strain markers to estimate slip magnitudes. We determined vertical slip and dip-slip rates of similar to 0.10-0.31 mm/yr and similar to 0.11-0.37 mm/yr, respectively, at the surface. Assuming fault dips of 40 +/- 10 degrees at seismogenic depths, we predicted extension rates of similar to 0.17-0.55 mm/yr. This suggests that at least 10% and up to 28%-54% (95% confidence interval) of the total extension of the northern Shanxi Graben is inhomogeneously partitioned by different sections of the YTF. We also evaluated the along-fault relative tectonic activity by analyzing of five widely used geomorphic indices: hypsometric integral, basin elongation ratio, asymmetric factor, valley-floor-width-to-height ratio, and mountain front sinuosity. The determined fault slip rates and geomorphic indices demonstrate that the most prominent fault activity center occurred in the middle of the fault, and that fault activity wanes toward the fault tips. Moreover, the fault activity is highly heterogeneous and fluctuates along the fault strike, which may be attributed to either fault segmentation and linkage or the possible strike-slip component of motion along the fault. Further exploration of fault kinematics and paleoseismic history is warranted.