UMass Geomechanics

Slip rate distributions along faults can be determined from 3D models of geologic deformation. Such numerical generated distributions reveal that the average slip rate along the fault can differ from the rate at specific paleoseismologic sites. Cooke, Michele and Scott Marshall, 2006. Slip rates on faults within the Los Angeles Metropolitan region, GRL, vol. 33, L21212, doi:10.1029/2006GL027850..

The subsurface active fault configuration is poorly costrained in much of southern California. We can assess between alternative fault geometries, by evaluating fit to 1) geologic slip rates (Griffith and Cooke, 2004. Mechanical validation of the three-dimensional intersection geometry between the Puente Hills blind-thrust system and the Whittier fault, Los Angeles, California , BSS, vol 94 pp. 493-505.) and 2) uplift patern (Meigs, Cooke and Marshall, 2008. Using vertical rock uplift patterns to constrain the three-dimensional fault configuration in the Los Angeles Basin, BSSA, vol 98, pp 106-123, doi: 10.1785/0120060254)

Scott Marshall is currently working on interseismic models of the Los Angeles basin that will compare model predictions to observed GPS station velocities.

How does fault topology influence slip rates in the Ventura basin?

Marshall, Cooke and Owen, 2008. Effects of Non-Planar Fault Topology and Mechanical Interaction on Fault Slip Distributions in the Ventura Basin, CA BSSA,

The left image shows slip pattern along Northridge Hills fault and the right shows the slip pattern along the same fault when all the fault surfaces are modeled as planar. The geometry of fault intersections differs significantly for the models and fault configuration greatly influences the distribution of slip along interacting faults. In other words, 3D fault configuration matters and assumption of fault planarity will neglect significant components of deformation in the Ventura basin.