Development characteristics and formation analysis of Baixiang earth fissure on North China plain

摘要

The Baixiang earth fissure is a typical earth fissure developed on the North China Plain, about 12km in length, with NE40 degrees trending, distinct linear emergence, and in good agreement with the South Baixiang fault. Its formation was the result of internal tectonic factors and external dynamic factors. The trenching and drilling data show that the strata in the earth fissure development zone have a striking two-element structure: the upper thick silty clay formation and the lower thick sand formation, providing the necessary space for the development of an earth fissure. The seismic exploration data show that the width of the developed earth fissure zone is determined by the fault structure buried at a certain depth under the strata and the horizontal stretching of the overburden. Constrained by such geological structure and stratal properties, a series of small tensile cracks are developed at different depths in the development zone. They are further affected by phenomena, such as formation compression and collapse, which are caused by groundwater seepage and sediment laden water migration in the lower sand formation under the influences of external factors (such as groundwater withdrawal and man-made concentrated irrigation). These cracks hence cut through to the earth surface and a cascade of cracks in a certain direction form linear surface fissures. This study importantly reveals the correlation mechanism between the various factors of earth fissures and the transformation mechanism of regional tectonic movements from deep to surface.