Does seismicity delineate zones where future large earthquakes are likely to occur in intraplate environments?
Does seismicity delineate zones where future large earthquakes are likely to occur in intraplate environments? (in Continental intraplate earthquakes; science, hazard, and policy issues, Seth Stein (editor) and Stephane Mazzotti (editor))
Special Paper - Geological Society of America (2007) 425: 35-48
The spatial distribution of seismicity is often used as one of the indicators of zones where future large earthquakes are likely to occur. This is particularly true for intraplate regions such as the central and eastern United States, where geology is markedly enigmatic for delineating seismically active areas. Although using past seismicity for this purpose may be intuitively appealing, it is only scientifically justified if the tendency for past seismicity to delineate potential locations of future large earthquakes is well-established as a real, measurable, physical phenomenon as opposed to an untested conceptual model. This paper attempts to cast this problem in the form of scientifically testable hypotheses and to test those hypotheses. Ideally, thousands (or even millions) of years of data would be necessary to solve this problem. Lacking such a long-term record of seismicity, I make the "logical leap" of using data from other regions as a proxy for repeated samples of seismicity in intraplate regions. Three decades of global data from the National Earthquake Information Center are used to explore how the tendency for past seismicity to delineate locations of future large earthquakes varies for regions with different tectonic environments. This exploration helps to elucidate this phenomenon for intraplate environments. Applying the results of this exercise to the central and eastern United States, I estimate that future earthquakes in the central and eastern United States (including large and damaging earthquakes) have approximately 86% probability of occurring within 36 km of past earthquakes, and approximately 60% probability of occurring within 14 km of past earthquakes.