Abstract

Most of the earthquakes in the New Madrid seismic zone correlate spatially with the Blytheville arch and part of the Pascola arch, which are interpreted to be the same structure. Both arches may have formed by diapirism along the axis of the Reeffoot rift. Seismic, geophys ical, and drill-hole data indicate that the rocks in the arches are highly deformed and fractured and have gross lithologic properties that make them weaker than rocks adjacent to the arches. The weaker rocks are inferred to fail seismically more readily than the stronger rocks adjacent to the arches.

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