The bending mechanism of Anping ground fissure in the Hebei Plain, North China

The Anping fissure is one typical and particular ground fissure in the North China Plain. This study was carried out in Anping area with geological means, such as surveying, mapping, trenching and drilling. The geological structure and disasters were analyzed by both qualitative and quantitative methods. The main conclusions are as follows: (1) Anping ground fissure is the local manifestation of regional tectonic stress field and is basically folding directional, hidden and intermittent. (2) Under the control of Shen-rao fault, Anping ground fissure was exposed and expanded by water-related human activities, and then was cracked by small- and medium-sized earthquakes. (3) The forming process followed the bending-cracking rules. The uplifting force from deep in the earth bent the entire overlying strata. The tangential stress below the ground surface counterbalanced the horizontal stress of soils, even breaking through their tensile strength and inducing cracks. The fissure was periodic and wavery, because the cracking force was proportional to the uplifting force but inversely proportional to the stratigraphic depth.