IDENTIFICATION AND CLASSIFICATION OF LATERAL SPREAD FEATURES IN THE NEW MADRID SEISMIC ZONE

Between December 1811 and March 1812, the largest series of earthquakes ever recorded in United States struck the upper Mississippi Valley, 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 who’s characteristics and morphology appear similar to lateral spread features associated with the 1964 Alaska earthquake. However, to date, 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 tentatively identified several 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. Two types of lateral spreads appear to exist in the NMSZ; arcuate or “pancake” spreads and “fan-type” lateral spreads with a shape similar to alluvial fans. It is believed that both lateral spread types formed in response to liquefaction of underlying confined sand layers during ground shaking associated with the New Madrid earthquakes. The authors are employing geophysical methods, such as ground penetrating radar, electrical resistivity, and induced polarization, as well as trenches, standard penetration tests and cone penetrometer tests to determine if the suspect features are indeed lateral spreads.