We present a new three-dimensional model of the major fault systems in southern California. The model describes the San Andreas fault and associated strikeslip fault systems in the eastern California shear zone and Peninsular Ranges, as well as active blind-thrust and reverse faults in the Los Angeles basin and Transverse Ranges. The model consists of triangulated surface representations (t-surfs) of more than 140 active faults that are defined based on surfaces traces, seismicity, seismic reflection profiles, wells, and geologic cross sections and models. The majority of earthquakes, and more than 95% of the regional seismic moment release, occur along faults represented in the model. This suggests that the model describes a comprehensive set of major earthquake sources in the region. The model serves the Southern California Earthquake Center (SCEC) as a unified resource for physics-based fault systems modeling, strong ground-motion prediction, and probabilistic seismic hazards assessment.

Far too few moderate earthquakes have occurred within the Los Angeles, California, metropolitan region during the 200-year-long historic period to account for observed strain accumulation, indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries-long interseismic period between much larger (moment magnitude, M(w), 7.2 to 7.6) events. Geologic slip rates and relations between moment magnitude, average coseismic slip, and rupture area show that either of these hypotheses is possible, but that the latter is the more plausible of the two. The average time between M(w) 7.2 to 7.6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years.

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[1] New paleoseismic results from Panama, conducted as part of the seismic hazard assessment for the expansion of the Panama Canal, have led to a reevaluation of the tectonic framework and geologic history of the isthmus of Central America. We propose a soft block indenter model wherein the collision of Central America and South America has resulted in significant internal deformation of the isthmus. Deformation is accommodated by both rapid slip on conjugate strike-slip faults within the isthmus, as well as the generally assumed flexure and northward buckling of Panama. The model is kinematically self-consistent in that there are little or no space problems created with 3 Ma of retrodeformation. Sparse GPS velocity data are consistent to within uncertainties with the new geologically constrained block model, supporting the rapid and extensive internal deformation of Panama. Together, the paleoseismologic and geodetic data suggest that central Panama is an area of high risk due to earthquakes, which is consistent with the historical occurrence of several moderate to large earthquakes in this region. However, this is generally counter to the current perception in central Panama where most people live and where there have been no large, damaging earthquakes for over 100 years.Citation: Rockwell, T. K., R. A. Bennett, E. Gath, and P. Franceschi (2010), Unhinging an indenter: A new tectonic model for the internal deformation of Panama, Tectonics, 29, TC4027,