Discussion on Initiation Time of the Latest Tectonic Movement in Break-up Region of the North China Craton

The break-up region of the North China craton is an area where historically destructive earthquakes have frequently occurred. The focal mechanism solutions and earthquake surface rupture zones indicate that these historical earthquakes were dominated by the newly-formed seismogenic strike-slip faults, which are incompatible with the crustal extensional tectonics. This research firstly examines the high-resolution seismic reflection profile and borehole stratigraphy on the hanging wall of the Xiadian fault, which resulted in the 1679 Sanhe-Pinggu M8.0 earthquake ruptures along the western boundary of the Dachang concealed sag. Then, two unconformity contacts (UC1 and UC2) are distinguished by careful checks on structural and stratigraphic features from a cross section of the Late Pleistocene lacustrine at the southern piedmont of the Daqingshan. Combined with the results of active fault mappings with 1:50 000 scale and urban active fault detection in recent years, we conclude that the listric normal faults, which represent crustal extension in the Early Cenozoic, had been weakening in the Pliocene to the Early Quaternary, and had ceased activity by the early Late Pleistocene. The Daqingshan tectonic movement has initiated since the middle of the Late Pleistocene, representing the latest tectonic movement in break-up region of the North China craton, in which new strike-slip faults have formed under a shear-strain crustal condition owing to continuous eastward extrusion of the Qinghai-Tibet Plateau and strong eastward push on the southwestern margin of the Ordos block. These new points of view have important academic value for understanding mechanism of earthquake occurrence and dynamics of the latest crustal deformation in intra-plate.