The spatial distribution of seismicity is often used as an indicator of zones where future large earthquakes are likely to occur. This is particularly true for intraplate regions, where geology is more enigmatic in terms of delineating seismically active areas. In this study, we investigate whether this tendency for future earthquakes to occur near past earthquakes can be treated as a real, measurable, physical phenomenon. The goal of this study is to systematically investigate the tendency for past seismicity to delineate zones where future large earthquakes are likely to occur. The method used is called "cellular seismology" and it involves constructing circular zones of a given radius around each epicenter in a past earthquake catalog. The percentage of future earthquakes that occurred within these circular zones is systematically analyzed to investigate the likelihood of future earthquakes occurring near past earthquakes.
Three decades of global data (1973-2002) from the National Earthquake Information Center (NEIC) were used for this study Different tectonic environments were analyzed including eight sub-regions of the Earth (all of equal shape and surface area), and smaller, specific tectonic environments, including: Alaska, Australia, Japan and the Interior of the North American Plate. The cellular seismology method was applied to each of the regions. Differences in tectonic environment were investigated to determine their effect on the extent to which past seismicity delineates zones where future large earthquakes are likely to occur. Analysis of the time dependence of these forecasts indicates that the ability to forecast does not decrease over the 30 years of data available. This suggests that the 30 years of NEIC data currently available provides a statistical basis for forecasting locations of future earthquakes, at least on the time scale of the next few decades. Additional monitoring should further elucidate the effect of tectonic environment on the tendency for seismicity to delineate zones where future large earthquakes occur, as well as the time dependency of this phenomenon.
