Geometry, kinematics and morphotectonics of the Yanqing-Huailai active faults (northern China)

Field studies along the Huailai and Yanqing mutually parallel neotectonic f ault zones lead to a description of morphotectonics and palaeoseismicity, a s well as the geometry and segmentation of these structures. The study emph asizes the kinematics of the region. The faults belong to the tectonic inte raction between the Shanxi rift system and the North China fault system. Al though the general strike of the zones is NE-SW, the Yanqing fault is divid ed into five segments of NNE-SSW, ENE-WSW and E-W trends, and the Huailai f ault into three segments of ENE-WSW and E-W trends. They are mainly pure di p-slip normal faults, while less often they show oblique-slip components. T he mesostructural quantitative palaeostress analyses (local neotectonic-act ive stress pattern) indicate a regional NNW-SSE-oriented extension (sigma(3 )), locally deviated to N-S, NW-SE, WNW-ESE, depending on the fault segment strike. The great deviation of fault strikes from the mean and their relat ion with the basement joint and thrust systems lead to the hypothesis that the neotectonic faults, which have a capacity for strong earthquakes, follo w pre-existing inherited structures. (C) 1999 Elsevier Science B.V. All rig hts reserved.