2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 321-4
Presentation Time: 2:15 PM


FRIEDRICH, Anke M., Department of Earth and Environmental Sciences, University of Munich, Luisenstr. 37, Munich, 80333, Germany, KÜBLER, Simon, Department of Earth and Environmental Sciences, Ludwig Maximilians University, Luisenstrasse 37, Munich, 80333, Germany and STRECKER, Manfred R., Institut für Erd- und Umweltwissenschaften, University Potsdam, K.-Liebknecht-Str.24/25, Haus 27, Golm-Potsdam, 14476, Germany, friedrich@lmu.de

Earthquake-rupture parameters are typically derived from large-offset faults. As a result, small faults are often ignored in seismic hazard assessment of continental interiors. We mapped the brittle process zone of a small bedrock fault recorded in a thin muddy-gravel deposit, and document permanent textural and structural evidence for near-surface rupturing. Gravels, which were systematically rotated and fractured, indicate particulate to cataclastic flow mechanisms at high strain-rates, consistent with the regional stress field. The contrasting sense of gravel-rotation invokes elastic rebound of underlying crustal rocks. Coseismic stress is transmitted across the basement-sediment interface kinematically and dynamically, and then dissipated in the sediments, documenting the fault's arrest. This provides a mechanism for the "shallow slip-deficit" above blind faults. Mixed-gravel textures are a high-resolution paleoseismological tool to extend mappable limits of active faults, which leads to improved earthquake magnitude, hazard, and zoning estimates.