The Bermuda earthquake of March 24, 1978: A significant oceanic intraplate event

Abstract

The Bermuda earthquake (M ∼ 6) occurred near the westerly extension of the Kane Fracture Zone roughly 370 km southwest of the island of Bermuda. It is one of the largest oceanic intraplate earthquakes to occur off the eastern coast of North America. Because of its size and location, it has provided an excellent set of WWSSN body waves. They can be used to infer its depth and faulting parameters by waveform modeling techniques. The results indicate a north‐northwest striking thrust mechanism (strike = N20°W, dip = 42°NE, rake = 90°) with the hypocenter located at a depth of 11 km, which for an oceanic crust places it predominantly in the mantle. The event had a seismic moment of 3.4 × 1025 dyne cm, and its time history was modeled with a symmetric trapezoidal time function 3 s in duration. The north‐northwest strike of the event is in good agreement with the bathymetry of the area, the epicenter being close to the southwestern edge of the Bermuda Rise. The strike of the event is also close to that of the inferred extensions of the present ridge fracture zones in the region. The presence of such fracture zones is indicative of local weak zones in the lithosphere. The Bermuda earthquake most likely is associated with one of these zones of weakness and is the result of the application of present day stress imposed on the region by the North American plate in the direction of its absolute motion. This is an important event in terms of understanding and estimating seismic hazard on the eastern seaboard of North America.