A study of the symbiotic relationship between tectonic fissures and faults in the Fenwei Graben System, China

The Fenwei Graben System is an important extensional fault-depression zone, which is the tectonic boundary between the Ordos Block and the South China Block and the North China Block. The graben system presents an “ S ” shape, with a total length of 1200 km and a width of 30–60 km and an overall strike of NNE. Due to complex tectonic background and active faults, nearly 612 ground fissures develop in these basins, and more than 90% of these ground fissures are tectonic fissures, which are closely associated with fault activities. To reveal the plane symbiotic phenomena, profile symbiotic modes and symbiotic mechanism between tectonic fissures and faults in the Fenwei Graben System, the developmental characteristics were investigated in detail by surveying, mapping, trenching and drilling in the study area. The main conclusions are as follows. (1) The tectonic fissures of the Fenwei Graben System are mainly distributed along the margin faults of basins, the boundary faults between blocks and the hidden faults within blocks, causing serious damages to farmlands, houses and roads. The symbiosis between these fissures and faults is obvious on the surface. (2) The profile symbiotic morphology includes vertical extension type, syncline and anticline “y” type, and stepped type. (3) The symbiotic mechanisms include vertical growth, lateral rupture and clustery derivation. (4) The activities of underlying faults give impetus to the formation and expansion of tectonic fissures. The exposure of the fissures makes underlying faults continue to develop in the form of surface fractures.