Abstract

It is generally assumed that faults in mid-plate regions, such as central and eastern United States (CEUS), unless historically active, are inactive and/or lack a potential for large earthquakes. The Meers fault in Oklahoma, located in an historically aseismic area, is a spectacular exception to this rule. Paleoseismic studies of this fault show that the most recent large event occurred about 1200 years ago, had a magnitude of more that MS = 7 or 7.5, a surface rupture of 40 km length, and several meters of net displacement on a major left-lateral fault (Ramelli and Slemmons, in press).

At least four fault zones in other parts of CEUS indicate that the Meers faulting event is not unique, including: (1) New Madrid epicentral region with three events of about MS = 8 in 1811 and 1812 with surface faulting and deformation (Russ, 1982), (2) Washita Valley fault (Cox and VanArsdale, 1986), (3) Kentucky River fault (VanArsdale, 1986), and possibly (4) faulting near Pierre, South Dakota (Nichols and Collins, 1987). Moreover, such midplate active faults are not unique, for there are at last four similar examples of historical seismogenic faulting (McCue and others, 1987) with earthquakes of up to 6.9 magnitude.

Most active fault zones can be dearly demonstrated to be parts of branching or interconnected tectonic systems, implying transfer of stress and strain along zones of deformation. We speculate that tectonically active mid-plate fault zones may also be parts of much longer, interconnected active systems, rather than isolated “hot spots” of activity resulting solely from the response of local crustal flaws to a regional stress field.

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