Earthquakes, Faults, and Crustal Geophysics of Southern California: Towards Operational Earthquake Forecasting

We analyze the waveform relocated (1981 to 2011) catalog of more than 500,000 earthquakes. This seismicity, with five mainshocks of M>6.5, reflects regional plate-boundary tectonics and other crustal deformation processes. The plate boundary is expressed as a system of late Quaternary faults or principal slip zones (PSZs) that accommodate major earthquakes. There are numerous smaller slip surfaces adjacent to the PSZs, which accommodate background seismicity as well as in some cases aftershocks. The plate tectonic strain loading dominates the dynamic process and causes the largest earthquakes along the PSZs, moderate-sized events in their immediate vicinity, and small earthquakes across the whole region. To analyze the seismicity rate in the context of this fault system, we measure the Euclidian distance from every hypocenter to the nearest PSZs. In addition, we assign crustal geophysical parameters such as heat flow values and shear or dilatation strain rates to each epicenter. Stress drop values are available for a subset of ~60,000 events. We extend our catalog by adding these parameters to the standard earthquake parameters of each event such as date, location, depth, magnitude, seismic moment, and error estimates. We use this extended catalog to investigate seismogenic thickness and fault zone width as well as earthquake scaling. We also discuss our current development of an operational earthquake forecasting system. We are implementing the current understanding of earthquake clustering in automatic algorithms to determine probability gains in near real-time to provide emergency managers with improved situational awareness about increased likelihood of future large earthquakes.