Remote Aquifer Response to the 18 November 1755 Cape Anne Earthquake

Abstract

The historic earthquake of 18 November 1755, the largest in the New England catalog, was felt widely throughout the American colonies and adjacent Canada (Street and Lacroix, 1979; Ebel and Kafka, 1991). Moderate damage—toppled stone walls, broken chimneys, cracks and liquefaction—was largely restricted to the lowland north of Boston near Cape Anne, with an inferred epicenter on the continental shelf to the east (42.70°N, 70.30°W. The earthquake has been assigned an epicentral Modified Mercalli intensity of 8 and a magnitude of 6.0. Abrupt, long-term changes in the flow rate and chemistry of water wells from five Connecticut colonial towns coincided with the earthquake and were interpreted as local responses to ground shaking up to 275 km from the 1755 epicenter (Figure 1; Thorson, in press). Based on reconstructions in Street and Lacroix (1979), these hydrologic changes took place in a zone having a MMI of V. Three of the towns (Franklin, Lebanon, and Lisbon) are in southeastern Connecticut (41.5°N, 72.00°W), terrain underlain by Paleozoic and late Proterozoic granitic and high-grade metamorphic rocks (Rodgers, 1985). A fourth town, Farmington (41.00°N, 72.83°W), lies an additional 50 km to the west within the Hartford Basin, a sediment-filled, early Mesozoic half-graben. The furthest town to experience groundwater changes (Bethlehem; 41.63°N, 73.20°W) is underlain by Ordovician schists. All five towns are mantled by glacial till and meltwater stream deposits, into which the colonial wells were dug. ### The Questionnaire In 1799, the newly formed Connecticut Academy of Arts and Sciences inaugurated a project to collect “every species of information... relative to the... Natural... history... of the State.” They created a questionnaire covering the breadth of post-Colonial life, ranging from town history and ecclesiastical affairs to race relations, soils, hydropower, the weather, and other phenomena, sending it to “informed” gentleman who were, more often than not, Yale-educated …