RESEARCH ON RUPTURE CHARACTERISTICS AND GENESIS MECHANISM OF SEISMIC GROUND FISSURE IN HUANGCAOPING SECTION OF BATANG FAULT

Ground fissure is a kind of geological disaster and caused by linear fracture in surface rock and soil. The formation and development of tectonic ground fissures are closely related to the movement characteristics of active faults. The existing reports of tectonic ground fissures are mostly related to fault creep-slip movement, but the ground fissures formed by fault stick-slip(earthquake) are generally divided into seismic surface rupture zones. The main focus is on the investigation of their distribution characteristics. Research on the rupture characteristics and genetic mechanism of a single ground fissure is rare. In this paper, the ground fissure formed in Huangcaoping section of Batang fault is taken as the research object. The shallow-medium-deep geometric structure of ground fissures and their formation mechanisms have been revealed through field geological surveys, unmanned aerial vehicle surveying and mapping, field trenching, and geophysical prospecting. Batang fault forms a valley landform in Huangcaoping segment. The ground fissure in the valley shows a linear geomorphic scarp S₁ with a height of 0.26±0.03 m. The geological trench across the valley revealed 18 ground fissures densely developed under and on both sides of the steep slope. Based on the situation of ground fissures penetrating into the overlying strata, three active periods can be roughly divided, which may represent three seismic events since the Holocene on Batang Fault. Part of the ground fissure penetrated to the surface and connected with scarp S₁, which may be caused by Batang M 7 \raise0.7ex\hbox1 \!\mathord\left/ \vphantom 1 2\right. \!\lower0.7ex\hbox2 earthquake in 1870. The seismic reflection profile across the valley shows that the valley boundary is controlled by two listric faults which dip towards each other. The two faults together form a "Y" shaped tensile graben structure. In the graben, there is a near-vertical deformation zone of reflection layer, which roughly corresponds to the S₁. Since the Holocene, during the right-lateral strike-slip process of the Batang fault, a multi-level"Y"-shaped extensional graben structure has been formed near the surface. The ground fissures within the graben are densely developed, and the formation is closely related to the seismic activity of Batang fault. Therefore, the geometry of the ground fissure is controlled by Batang fault structure, and the active period corresponds to the strong earthquake activity of Batang fault. It is a typical seismic ground fissure.