GEODETIC DETECTION OF ACTIVE DEFORMATION IN THE NEW MADRID SEISMIC ZONE

SMALLEY, R. JR, ELLIS, M.A., PAUL, J., CERI, University of Memphis, Memphis, TN 38152, smalley@ceri.memphis.edu, ellis@ceri.memphis.edu, jpuchkys@memphis.edu.

During the winter of 1811-1812, three earthquakes within three months shook the entire eastern half of the United States. These earthquakes caused liquefaction over a wide area and to distances far greater than any other historic earthquake in North America. The earthquakes occurred near the small town of New Madrid, MO, in the central United States, more than 2,000 km from the nearest plate boundary. The origin and geologic significance of these earthquakes, however, is highly contentious. Paleoseismic studies show liquefaction due to strong ground shaking has occurred at least three and possibly four times in the past 2,000 years. The scale of the liquefaction generated by these events was similar to that generated by the 1811-1812 New Madrid earthquakes and is consistent with recurrence statistics derived from regional seismicity. We have detected ongoing deformation associated with microseismically active faults in the New Madrid area using continuous GPS network data. The design of this sparse, 11 station network was optimized for detecting deformation at scales from the very near field (fault scale) to regional distances (100's km). Strain rates are of the order of 10e^-7 per year, comparable to strain rates in active plate boundary zones, were detected in the near field. These results have significant implications for the definition of seismic hazard and for processes that drive intraplate seismicity.