Locating Buried Earthquake-Induced Liquefaction Deposits At Native American Cultural Sites Using Non-Invasive Geophysical Surveys

Geophysical surveys were conducted at culturally sensitive sites in the New Madrid seismic zone<br>(NMSZ) of the central United States to locate buried earthquake-induced liquefaction deposits for<br>paleoseismic study. Although recent seismicity of the zone is of low to moderate magnitude, studies of<br>prehistoric earthquake sequences suggest that very large earthquakes occurred in A.D. 900 ± 100 years<br>and A.D. 1450 ± 150 years, in addition to the well-known historic events of 1811-1812 that caused<br>widespread soil liquefaction in Mississippi Valley alluvial deposits. Dates for the prehistoric<br>earthquakes are derived from radiocarbon dating of charcoal and from the presence of Native American<br>cultural features and artifacts of distinct periods that are collocated with buried liquefaction features,<br>such as sand fissures and sand blows. Trench excavations are often necessary to establish stratigraphic<br>and structural relationships critical for determining the timing of these paleoliquefaction events. Because<br>many sites are located in culturally sensitive or federally protected areas, non-invasive methods that can<br>increase the likelihood of identifying potential excavation sites while minimizing destruction of the site<br>are highly desirable. Geophysical surveys conducted at numerous sites in the NMSZ demonstrate that<br>subsurface imaging techniques can be useful for siting trenches for paleoseismic study and for<br>identifying areas susceptible to liquefaction.