Loma Prieta earthquake occurred on small, subsidiary faults within a few hundred meters of the mainshock rupture plane. On other fault segments like the San Andreas fault near Parkfield, most of the earthquakes occur on the San Andreas fault. It is difficult to automate this decision process, and it would be misleading to imply on the basis of only distance that an earthquake occurs on a named fault. The Central and Southeast U.S. region covers a large area of relatively diffuse, low rate seismicity. Principal areas of activity include the New Madrid Seismic Zone, the East Tennessee, and Southern Appalachian Seismic Zones, and South Carolina.
Earthquakes do occur throughout the entire region.
Due to the relatively low rate of seismicity, ground cover, deep soil, etc, most faults within the region aren't even mapped. Thus, unlike other recenteqs systems, we have elected not to show faults. We are responsible for seismic monitoring within this region and defer to our neighbors for information on earthquakes outside the region.