Deformation Processes Adjacent to Active Faults -- Examples from Eastern California

Eitan Shelef, & Michael E. Oskin

Published 2010, SCEC Contribution #1225

Major seismogenic faults are embedded within narrow zones of inelastic off-fault deformation (OFD), where both distributed displacement and modification of rock properties occur. Active distributed displacement may affect slip-rate estimates, understanding of seismic energy radiation and geodynamic models. This study addresses the role of OFD in the displacement history and mechanical behavior of seismogenic faults, by multi-site study of deformed geologic features adjacent to 30-60 km long active strike-slip faults in the Mojave Desert. We find that distributed displacement accommodates ~20 % of the total displacement over zones of one to two km width. Displacement occurs mostly within 100-200 m of faults and decreases non-linearly away from the main fault. Distributed displacement is accommodated by a combination of block rotation and simple shear across secondary faults. Analysis of block dimensions show that blocks tend to decrease in size toward faults and that cumulative length of secondary faults is longer then the main fault by at least a factor of ten. Finally, we argue that distributed displacement is an active process and suggests that zones of diminished rigidity near faults may be at least in part driven by coseismic rupture propagation along secondary faults.

Citation
Shelef, E., & Oskin, M. E. (2010). Deformation Processes Adjacent to Active Faults -- Examples from Eastern California. Journal of Geophysical Research, 115. doi: 10.1029/2009JB006289.