Characteristics and formation analysis of earth fissure in Anren area in Wei River Basin, China

Since the 1950’s, 212 earth fissures have been discovered in the Wei River Basin. During a field survey in 2016, an additional 48 earth fissures were discovered in Anren area, northeast of the Wei River Basin. The characteristics and formation mechanisms of these fissures were studied through field investigations, measurements, trench excavation, and drilling. On-site investigations indicated that these earth fissures were distributed along a fault-controlled geomorphic boundary. Fissures trended at 60°–80° NE and were divided into five groups. Trenches revealed multiple secondary fissures, exposing severe soil ruptures in the shallow earth surfaces. Drilling profiles revealed that earth fissures dislocated several strata, and resembled synsedimentary faults. Seismic reflection profiles revealed buried faults beneath the earth fissures. The Anren area fissures formed in the following three stages: regional extension that initially generated multiple buried faults; seismic activity rupturing multiple strata, resulting in multiple buried fractures; and finally, erosion processes that propagated the buried fractures to the surface, forming the current earth fissures.