Abstract

The focus of this study is to identify and characterize specific features related to historic or prehistoric earthquakes south of the southern terminus of the New Madrid seismic zone in eastern Arkansas. Aerial photography, field surveys, and trenching reveal the existence of several liquefaction features (sand blows) and linear structures as far as south of Marianna, Arkansas. This is more than 100 km from the currently active segments of the New Madrid seismic zone. Radiocarbon dating indicts that the event(s) that generated some of these features took place about 5500 years B.P. The discovered liquefaction features are significant because they are at a considerable distance from present-day earthquake activity. The implication of this is that they either represent a new earthquake source not previously recognized or that they are related to an earthquake(s) of very large magnitude in the source region of the New Madrid seismic zone. These liquefaction features have very large dimensions (∼110 by 60 m), resembling features in the immediate vicinity of the New Madrid seismic zone, implying that regardless of where the source region was, the ground shaking had to be severe in order to generate them. Detailed investigation of these features may have important implications for earthquake risk mapping in the central United States, as they may provide important constraints on the southern terminus of the New Madrid seismic zone and the magnitude of the characteristic earthquake in the region.

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