Dear Steve
you are handling this really well. 4.2 is a pretty big aftershock.
according to
this article, which i found quite informative:
Quote:
Quake Highlights East Coast Fault Lines
Missouri, Virginia, New York are home to significant seismic zones.
By Will Oremus | Posted Tuesday, Aug. 23, 2011, at 4:20 PM EDT
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“Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast.”
Easterners curious about their local earthquake risk shouldn’t get too hung up on the precise location of fault lines, yet another USGS explainer points out: “In California, a large earthquake can generally be associated with a particular fault because we have watched the fault break and offset the ground surface during the earthquake. In contrast, east of the Rockies things are less straightforward, because it is rare for earthquakes to break the ground surface. In particular, east of the Rockies, most known faults and fault lines do not appear to have anything to do with modern earthquakes. We don't know why.”
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the above article contains several links to more technical information. here are two of them:
San Andreas-like fault found in eastern U.S.
U.S. Fault Lines GRAPHIC: Earthquake Hazard MAP