The concealed active tectonics and their characteristics as revealed by drainage density in the North China plain (NCP)

Abstract

Drainage density, defined as river length per unit area, is an important tool to reveal the concealed active tectonics in the Quaternary-covered North China plain (NCP). The distribution of high-drainage density is characteristic of zonation and regionalisation. There are two sets of belts with high-drainage densities, which trend at 45–50 and 315–320°. The different locations and trends of these belts make it possible to divide the NCP into three regions. They are Beijing–Tianjin–Tangshan region in the north, Jizhong–Lubei region in the middle and Xingtai region in the south. Similarly located regions can be defined using contours of deformation data from geodetic-surveys from 1968 to 1982. Belts of high-drainage density are spatially coincident with seismotectonic zones and overlie concealed active faults. These active structures strike at an angle of ≈15° to that in the Eocene–Oligocene, a discordance, which may be an indication of an evolution of the fault pattern through time in the NCP during the Cenozoic. The current phase has more important consequences regarding seismic hazards in the NCP.