Active Faulting in Southern California

Mechanical Earthquake Cycle Models of the Los Angeles and Ventura Basins

Along with my collaborators, Michele Cooke (UMass) and Susan Owen (Jet Propulsion Lab), We have created some of the first mechanical models of active tectonics in southern California that use non-planar, geologically representative fault surfaces. These complex non-planar surfaces are part of the Community Fault Model, compiled by the Southern California Earthquake Center. So far, we have compared results from these models to geologic fault slip rates, fault slip distributions, and folding patterns. I am currently working on interseismic timescale versions of these models, so that I can directly compare model results to GPS data in southern California. I am also interested in using physics-based models, similar to these, to predict earthquake recurrence intervals and magnitudes.

Above: Shaded relief map of the Ventura region showing the complex non-planar fault traces. To view the three-dimensional modeled fault mesh, choose one of the two regions below. For instructions on how to navigate in 3D, read the opening page of the pdf file. For 3D capability, acrobat 7.0 or later is required (Apple's Preview or Foxit Reader will not work!) and a three-button or scrolling mouse is recommended.
Three-Dimensional Interactive Fault Mesh of The Ventura Region, CA Three-Dimensional Interactive Fault Mesh of The Los Angeles Region, CA

Miocene Faulting in Southeast Nevada

Fault Mechanics of Lake Mead Fault System

Along with my collaborators, Simon Kattenhorn (University of Idaho) and Michele Cooke (UMass), we are using mechanical models to better interpret field observations of the interelationship between strike-slip and normal faults in the Miocene Lake Mead fault system. So far, we have shown a clear mechanical relationship between strike-slip and normal faults along the left-lateral Pinto Rige fault. We proposed that a preference for west-dipping normal faults, such as are observed at Pinto Ridge, indicates a west-dipping detachment fault at depth. Because the extent of this proposed detachment is unclear, we need to get back out in the field and carefully map other near-tip regions of strike-slip faults the Lake Mead fault system.

Above: Various views of strike-slip faults in the Lake Mead fault system. (a-b) An exposure of the Bitter Spring Valley fault observed in a wash channel. (c) panoramic view of the Pinto Ridge fault. Note the laterally-mismatched Kaibab and Moenkopi Formations. (d-e) Exposure of the near-vertical Pinto Ridge fault surface.

Faulting and Fracturing on Icy Satellites

Fracture Mechanics on Europa

Along with Simon Kattenhorn, we made the first detailed geometric and morphologic descriptions of curved cracks, called cycloids, on Jupiter's icy moon, Europa. We argued that these enigmatic arcuate cracks arise due to the rotating diurnal tidal stress field and form kinks (cusps) due to small amounts of shearing during the tidal cycles. We also studied strike-slip faults on Europa and found similar kinks at the ends of many strike-slip faults. I am currently interested using the data that we have collected to create mechanical models of faults and cracks on the surface of Europa.

Above: High resolution images of the highly fractured icy surface of Europa. These images were taken by the Galileo spacecraft. The above images highlight the three most common morphologies of cycloids on Europa (a) trough (b) ridge (c) band.

A good way to get a quick sense of the kinds of tools that I use and the types of geophysical problems that interest me is to browse through some of my past poster presentations. These things take a long time to make, so why not post a few of them? Also, students may find these files useful when making his/her first research poster, as choosing a layout and color scheme can be rather challenging. I'm not advocating that my posters are greatly artistic, but posting the files here at least gives to new students something to compare. Some of my layouts were simple and some were rather complex. The differences were mainly based upon what kind of paper I was printing on and how good I knew the printer to be.

Marshall, S.T., Cooke, M.L. Owen, S.E. 2008. Geologic Slip Rates and Interseismic Deformation in the Ventura Region, Southern California Eos, Transactions of the American Geophysical Union.

Kattenhorn, S.A., Marshall, S.T., Cooke, M.L. 2008. Kinematically Coupled Strike-Slip and Normal Faults in the Lake Mead Strike-Slip Fault System, Southeast Nevada Eos, Transactions of the American Geophysical Union.

Marshall, S.T., Cooke, M.L., Owen, S.E. 2008. Simulating heterogeneous rock properties in crustal deformation models: preliminary results Southern California Earthquake Center Annual Meeting, Palm Springs, CA.

Cooke, M.L., Marshall, S.T., Dair, L., Kendrick, K., Dolan, J., DeGroot, R. 2008. Students and teachers from high schools for the deaf around the country explore the geologic hazards of southern California. Southern California Earthquake Center Annual Meeting, Palm Springs, CA.

Marshall, S.T., Cooke, M.L., Owen, S.E. 2007. Interseismic Deformation along Intersecting Faults: Application to the Greater Los Angeles Region, CA. Southern California Earthquake Center Annual Meeting, Palm Springs, CA.

Marshall, S.T., Cooke, M.L. 2006. Fault Trace Slip Distributions in the Ventura and Los Angeles Basins, California: Implications for Past and Future Paleoseismic Sites. Southern California Earthquake Center Annual Meeting, Palm Springs, CA.

Marshall, S.T., Cooke, M.L., Owen, S.E. 2005. Comparison of GPS data from the Ventura Basin, California to interseismic three-dimensional mechanical models. Eos, Transactions of the American Geophysical Union.

Marshall, S.T., and Kattenhorn, S.A. 2004. The importance of resolved shear stress and dilation at the instant of cycloid cusp formation on Europa. Eos, Transactions of the American Geophysical Union.