Abstract

Sand dikes and sills in glaciomarine sediments record two liquefaction events in Newbury, Massachusetts, the meizoseismal area of the A.D. 1727, felt-area magnitude 5.0, earthquake. During the 1727 earthquake, Newbury experienced ground shaking on the order of modified Mercalli intensity VII and underwent ground failure typical of liquefaction. According to accounts of the earthquake, ground cracks with separations of up to 0.6 m formed; sand and water vented through at least ten ground cracks; land was locally elevated; and firm ground was changed to quagmire. Crosscutting relations and radiocarbon dating of woody material associated with liquefaction features exposed by trenching indicate that at least two moderate to large earthquakes have occurred in the Newbury area in the past 4 ka. The relatively unweathered, younger features are consistent in style and location with ground failure described for the 1727 earthquake. The more weathered, older features probably formed during a prehistoric earthquake. Glaciomarine and other deposits that may be prone to liquefaction are widely distributed in northeastern North America; they provide the opportunity to develop criteria for identifying paleoliquefaction events and to better determine earthquake hazard in the region.

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