REGIONAL FRACTURE PATTERNS OF THE SOUTHERN KOREA

The Korean Peninsular has undergone four cycles, at minimum, of deep-crustal deformation, metamorphism, and magmatism, the Songrim Disturbance (Triassic to early Jurassic), the Daebo Orogeny (Jurassic to early Cretaceous), the Bulguksa Disturbance (late Cretaceous to early Tertiary) and the Yunil Disturbance (Tertiary). These tectonic events probably resulted in producing the predominant NE-SW trend and some others within the peninsular.

Previous studies provide fracture maps at different scales (from local areas to the entire Korea) and some fracture analysis, based on rather general and qualitative analysis. Recently, however, detailed and quantitative fracture analyses have been carried out to classify and characterize these fractures developed in the peninsular, and to understand these fracture systems as a whole.

This study produced a combined regional fracture map of the southern Korea from the regional fracture maps published in journals and research reports, analyzed the fractures in terms of length, orientation and density of the fractures, and suggests a fracture classification system of the southern Korea.

Orientation analysis of the fractures shows three dominant peaks at NNE, NW and WNW trends, revealing that the NNE set is predominantly great in population and length of the member fractures relative to the other sets. The regional fractures in the southern Korea were classified into four orders by the trace length (F₁, the longest, to F₄, the shortest), and the fractures of each order are self-similar with respect to the orientation. F₁ fractures are recognized only in the tectonic provinces that record evidences of Quaternary fault, probably indicating that it is the result from the slip accumulation through multiple deformation. Besides, the distributions of fracture density and size seem to be well correlated with the distribution of tectonic provinces and physical properties of local geology.