Ervin, C. Patrick
M.S. (Master of Science)
Department of Geology
Earthquakes--Missouri--New Madrid region; Seismology--Missouri--New Madrid region
The northern Mississippi Embayment has been characterized as a seismological enigma due to the occurrence and historical severity of seismic activity. This study tries to provide insight as to periodicity of seismic activity and possible factors responsible for this activity by correlation of gravity, seismic and hydrologic patterns. The Maximum Likelihood method of spectral analysis was used to detect dominant periodicities in energy release for long-term (1914-1983) and short-term (July 1976-June 1984) earthquake data sets from a 1.5° x 1.6° earthquake window centered over New Madrid, Mo. Periodicities of long-term data, consisting of 3 mb and greater earthquakes, revealed dominant cycles of 35 and 3.7 years in energy release. Short-term data using events of all magnitudes, revealed cycles of 4.6 and 6.5 months. Short-term release rates are 3.5 times below the long-term, suggesting a possible increase in energy release in the near future. The energy equivalent of a 5.3 mb event would return the rate to the average value. Patterns of gravity change in the area were both cyclic and abrupt. Stations along the Mississippi River exhibited correlations with change in river stage, although patterns that might be used as precursors to seismic activity were not observed. Correlations between short-term, monthly, seismic activity and stage suggested a six month lag between stage and both events and energy release. Although river loading may be the primary factor inducing the variations, it is probably not the only mechanism. Unrelated variations in gravity and seismic data still remain unexplained.
Mento, Dean J., "Spectral analysis of earthquake data and correlations with gravity and hydrologic changes in the New Madrid Seismic Zone" (1985). Graduate Research Theses & Dissertations. 5007.
viii, 137 pages
Northern Illinois University
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