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Abstract: We investigated the mesoscopic and microscopic structural features of the Keumwang fault zone, Korea, to determine the effect of different protoliths (crystalline granitic gneiss and mudrock) on fault zone structure including discrete shear surfaces, shear bands, foliation, porphyroclasts and calcite veins. Overall, in crystalline rock, the shear deformation tends to be localized to a fault core or several fault gouge-dominated layers within the fault zone. The cataclastic flow appears to become stronger toward the fault core. Most of the shear deformation appears to be partitioned between slip on discrete shear surfaces and shear bands, and cataclastic flow, including syntectonic alteration in the fine-grained matrix of fault rocks. In contrast, within mudrocks, shear deformation tends to be relatively uniformly distributed within the entire fault zone. Shearing generates continuous S-foliations throughout the whole fault zone. Most of the shearing is accommodated by slip along these foliations and on discrete shear surfaces distributed within the entire fault zone. [Copyright &y& Elsevier]

Abstract: Recurrence characteristics of a Quaternary fault are generally investigated on the basis of field properties that are rapidly degraded by chemical weathering and erosion in warm humid climates. Here we show that in intense weathering environments, mineralogical and micromorphological investigations are valuable in paleoseismological reconstruction. A weathering profile developed in Late Quaternary marine terrace deposits along the southeastern coast of the Korean Peninsula was disturbed by tectonic movement that appears to be a simple one-time reverse faulting event based on field observations. A comparative analysis of the mineralogy, micromorphology, and chemistry of the weathering profile and fault gouge, however, reveals that both the microfissures in the deformed weathering profile and larger void spaces along the fault plane were filled with multi-stage accumulations of illuvial clay and silt minerals of detrital origin, suggesting a repetition of fissuring and subsequent sealing in the weathering profile as it underwent continuous mineralogical transformation and particle translocation. We reconstruct a sequence of multiple faulting events unrecognized in previous field surveys, which requires revision of the view that the Korean Peninsula was tectonically stable, during the Late Quaternary. [Copyright &y& Elsevier]