ALAN L. KAFKA, Weston Observatory, Department of Geology and Geophysics, Boston College, Weston, MA 02493, email@example.com
The hypothesis that seismicity delineates areas where future large earthquakes are likely to occur is tested to investigate the extent to which it applies to earthquake catalogs from a variety of regions. In all tectonic environments analyzed, large earthquakes do indeed seem to occur preferentially in areas of previous seismicity. This finding seems intuitively reasonable, and the results are hardly surprising. We can, however, ask more of the data. Do the data, for example, allow us to infer the percentage of large earthquakes expected to occur in areas near previous seismicity? Can we quantify what we mean by large earthquakes occurring in areas "near" previous earthquakes? Are the results of the previous studies generally applicable to any seismically active regions, or are they artifacts of those particular data sets and analysis procedures? This study addresses these types of questions. Based on regional analyses, I find that, on average, at least two-thirds of the large earthquakes in a region tend to occur near previous small earthquakes, and the percentages do not appear to be statistically different for regions in different types of tectonic environments. On a whole Earth scale, the percentage of large earthquakes that occur near concentrations of previous seismicity is higher than it is for the specific regions. Also, unlike in the regional cases, there is rather strong evidence in the whole Earth analysis that the nature of tectonic processes in a region does have an effect on the results. The effect of different tectonic environments may indeed be present on both scales, but the scatter in the currently available regional data may be too great for that effect to be seen.