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 ∼86% probability of occurring within 36 km of past earthquakes, and ∼60% probability of occurring within 14 km of past earthquakes.

Abstract The northeastern United States has one of the longest records of reported earthquake activity in North America (Fig. 1). Earthquake activity in this region was noticed by the early European settlers within the first few decades after their arrival. Since the early colonial days, the increasing population density throughout the Northeast led to more frequent reports of usually minor, but sometimes not-so-minor and occasionally even damaging earthquakes. Instrumental seismic monitoring began in the early 1900s, and routine reporting of the earthquake activity in the region began in 1938 with the initiation of the Northeastern Seismic Association (NESA) bulletins. The first telemetered regional seismic network was operated in northern New England by Weston Observatory from 1962 to 1968, but it was not until the early 1970s that the present regional networks were established. The number of seismic stations in the northeastern United States steadily increased between 1970 and 1974. By 1975, a number of institutions operating seismic networks in the region formed a cooperative group known as the Northeastern United States Seismic Network (NEUSSN; Fig. 2). The data recorded by the NEUSSN has enhanced our ability to study the regional seismic activity, and analysis of these data provides insight into the possible causes of earthquakes in this region. Since at present the northeastern United States is not located on or near a plate boundary, there is no obvious plate-tectonic interpretation of why earthquakes occur here. The present-day tectonic setting of the region is a passive continental margin. The nearest plate boundaries