Characterizing Brittle Deformation, Damage Parameters, and Clay Composition in Fault Zones: Insights from the Chelungpu, Taiwan and Mozumi, Japan Fault Zones

Angela Isaacs
Utah State University, Department of Geology
Logan, Utah
[email protected]

Six outcrop sites along strike of the Chelungpu Fault (CF), Taiwan are compared with core samples through the CF zone and the Mozumi fault zone, Japan to evaluate how mesostructural and microstructural scale fault properties and clay mineralogy change as a function of strike, structural depth, and in different components of a fault zone. Characterization of core and outcrop samples will determine fluid flow properties and processes, and determine seismological processes at each study site. X-ray diffraction analysis shows an increase in smectite towards the CF at or very near the surface, and an increase in illite toward the fault at depth. Weathering and increased fluid flow in the exhumed fault zone plays an important role in the composition of the clay, but is enhanced in the clay gouge because of fabrics created by faulting. Weathering profiles will be used to determine the effects of weathering on clay gouge. The abundance of gouge, the dominance of smectite in outcrop samples, and the intensity of fault related damage at meso and microstructural scales are increased in southern portions of the CF. The southern portion of the CF is probably older and has accumulated more damage relative to the north. The Chelungpu and Mozumi faults provide a valuable opportunity to characterize shale and clay-rich fault zones. Studies of fault zone properties provide important constraints for geologic modeling, and clay mineralogy and microstructures may control the role of fault core and damage zone as conduits or barriers to fluid flow.

AAPG Search and Discovery Article #90033©2004 AAPG Foundation Grants-in-Aid