A systematic compilation of earthquake precursors

A survey of published scientific literature was undertaken to identify and catalog observed earthquake precursors. The earthquake precursors selected for analysis included electric and magnetic fields, gas emissions, groundwater level changes, temperature changes, surface deformations, and seismicity. For each of these precursors, the published scientific literature was searched to document the statistics of each reported earthquake precursor (spatial extent, time, duration, amplitude, signal/noise ratio), to analyze dependence of the observable for each precursor on earthquake magnitude, and to explore proposed physical models to explain each earthquake precursor. Some general characteristics were observed for these precursory phenomena. First, the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes. Also, the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake. Finally, the precursory anomalies tend to occur close to the eventual epicenter of the earthquake. In general, the physical models indicate that all of the precursory phenomena are related to deformation that occurs near the fault prior to the main earthquake. While the models provide plausible physical explanations for the precursors, there are many free parameters in the models that are poorly resolved.