Three- Dimensional Models of Active Faulting in Southern California
Numerical models allow us to explore the interaction between active faults within the three-dimensional fault system. If we want to predict future earthquakes, we have to understand what the active fault configuration is at depth in Southern California and how the faults work together accomodate plate motions.
fault model of the Los Angeles Basin modified from the
Southern California Earthquake Center
Community Fault Model for 3D modeling with POLY3D, a Boundary Element
Click on image at the right to view interactive 3D image of active faults in the Los Angeles basin with earthquake hypocenters. Earthquake magnitude increases with warmer colored points. (You need to have installed a VRML plug-in for your web browser to be able to manipulate the image.)
|Los Angeles basin faults||Ventura basin faults|
This research has been funded by the US Geological Survey's National Earthquake Hazard Reduction Program (NEHRP) and by the Southern California Earthquake Center (SCEC).
Slip rates on faults can be determined from 3D models of geologic deformation.
Cooke, Michele and Scott Marshall, 2006. Slip rates on faults within the Los Angeles Metropolitan region, Geophysical Research Letters, vol. 33, L21212, doi:10.1029/2006GL027850..
Model slip rates are red circles and grey bars show geologic rates. The models matches the available slip rates and can provide slip rates along faults for which paleoseisimc data is not available.
How does fault topology influence slip rates in the Ventura basin?
Marshall, Cooke and Owen, in press. Effects of Non-Planar Fault Topology and Mechanical Interaction on Fault Slip Distributions in the Ventura Basin, CA Bulletin of the Seismological Society of America,
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.
Evolution of the San Gorgonio Knot along the southern San Andreas fault
2D mechanical efficiency analysis of the Los Angeles Basin:Cooke, Michele and Ayako Kameda, 2002. Mechanical Fault Interaction within the Los Angeles Basin: A Two-Dimensional Analysis using Mechanical Efficiency, Journal of Geophysical Research: vol.I107(B7), doi:10.1029/2001JB000542 (PDF file)
Comparing Mechanical and Geodetic Models of Los Angeles Basin Faults:
Fault geometry validation
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 , Bulletin of the Seismological Society of America, vol 94 pp. 493-505.
Vertical thickening or escape tectonics in the Los Angeles basin?
Griffith and Cooke, 2005. How sensitive are fault slip rates in the Los Angeles basin to tectonic boundary conditions? Bulletin of the Seismological Society of America, vol. 94, pp. 1263-1275. (PDF file)
North-south contraction accompanied by negligible east-west contraction best matches fault slips in the Los Angeles basin.
Fault System Evolution
Olson and Cooke. 2005. Application of Three Fault Growth Criteria to the Puente Hills Thrust System, Los Angeles, California, USA Journal of Structural Geology, vol. 27, pp. 1765-1777. (PDF file)
3D Patterns of strain energy density outline the lateral growth of the Puente Hills echelon thrust fault system.
Three-dimensional VRML models of strain energy density around the faults at each stage of evoltuion:
Step 1: Whittier and Chino faults
Step 2: Whittier, Chino and Coyote Hills faults
Step 3: Whittier, Chino, Coyote Hills and Santa Fe Springs faults
Step 4: Whittier, Chino, Coyote Hills, Santa Fe Springs and Los Angeles faults