University of Memphis and University of Texas scientists are acquiring 300 km of high-resolution seismic reflection data and sub-bottom profile data along the Mississippi River, from Helena, Arkansas, to Caruthersville, Missouri using marine seismic methods. The study area is located in the Mississippi embayment, south of the enigmatic New Madrid seismic zone, an extraordinarily active seismic area in the heart of the North American continent, 2000 km from the nearest plate boundary. In this intraplate area, the high level of historic and instrumentally-recorded seismicity seems at odds with the flat topography of the Mississippi Embayment, low geodetically-determined velocity vectors, and a puzzling lack of substantial deformation in the post-Late Cretaceous sedimentary deposits of the Embayment. To reconcile this apparent paradox it has been proposed that the seismicity in the New Madrid seismic zone is either 1) episodic; 2) very young (at least in its present incarnation); or 3) migrates throughout a broad region at the continental or regional scale. In order to test these hypotheses the research team is conducting reconnaissance seismic profiling of a large portion of the embayment along the Mississippi River. Earthquake-induced liquefaction features that do not correlate with the New Madrid seismic zone events have been identified in the study area, suggesting that earthquakes have occurred in the embayment in the past. The seismic acquisition, calibrated to illuminate the shallow section, will provide unprecedented high-resolution images of the Mississippi River sediments and the suspected faults concealed under the subdued topography, providing detailed information on the partitioning of the deformation among key structures beyond the limit of the New Madrid seismic zone.
Although the theory of plate tectonics revolutionized our understanding of earthquake processes, it does not explain why earthquakes occur in regions distant from plate boundaries where deformation rates are low and where plate motions supply insufficient driving energy. This research project will use marine geophysical data acquisition techniques along the Mississippi River to examine the enigmatic New Madrid seismic zone of the central U.S. These techniques will allow very cost effective examination of the subsurface of a 300 km stretch of the Mississippi River Valley, where devastating earthquakes have occurred in the historic and prehistoric past. The data will also provide observational constraints on theoretical models proposed to explain seismicity in the middle of tectonic plates. The high-resolution seismic data acquired as part of this study will be suitable to diverse applications. The most important application will be in earthquake hazard assessment and earthquake loss and risk reduction in the mid continent. The data will be also valuable for understanding the impact of a earthquake on the Mississippi River navigation by evaluating the riverbed and slope stability. In addition, the data will be critical for ground water sustainability and water quality studies in large metropolitan areas, such as Memphis.
