SEISMICALLY-INDUCED LATERAL SPREAD FEATURES IN THE WESTERN NEW MADRID SEISMIC ZONE

Between December, 1811, and March, 1812, the largest series of earthquakes recorded in United States struck the Upper Mississippi Embayment, centered near New Madrid, Missouri. The region was subjected to repeated episodes of wide-scale liquefaction, ground subsidence and uplift, as well as landslides and earth movement towards channels. In his 1912 report on the New Madrid earthquakes, Myron Fuller described numerous features that exhibited characteristics and morphology similar to lateral spread features associated with the 1964 Alaska earthquake. However, prior to this report, no lateral spread features have been substantially verified and characterized within the New Madrid Seismic Zone (NMSZ).

The authors have undertaken an investigation focusing on the identification of areas of seismically-induced landslippage, including lateral spread features, along Crowley’s Ridge in the western NMSZ. To date the authors have identified anomalous features along Crowley’s Ridge as lateral spread features through the use of topographic algorithms. Lateral spreads, like other types of landslippage, exhibit fairly specific topographic signatures that can be identified on contour maps. It is believed that the lateral spread features formed in response to liquefaction of underlying confined sand layers during ground shaking associated with the New Madrid earthquakes. The authors are using digital map products in combination with Geographic Information Systems programs to find and delineate areas with topographic signatures representative of lateral spread features. For verification of the features, the authors are employing geophysical and field methods, including ground penetrating radar and electrical resistivity to determine if the suspect features are indeed lateral spreads.