Abstract

A comprehensive compilation and reassessment of intraplate seismicity in the Atlantic Ocean Basin is presented for the years 1918 through 1990. Of the 846 earthquakes whose original bulletin epicenters were located in Atlantic Ocean crust and were at least 2° from active plate boundaries, 289 were found to be reliably intraplate. A significant number (237) of the original epicenters were actually mislocated interplate earthquakes that located to active plate boundaries upon relocation, or whose 95% confidence locations determined through Monte Carlo simulations intersected seismically active boundaries. Many of these erroneous locations, particularly in regions surrounding the Mid-Atlantic Ridge, frequently appear in global seismicity maps. The resulting reliable catalog of intraplate seismicity is not randomly distributed but shows significant clustering in space and time. Much of the seismicity is associated with the locations of hot spots, such as the Bermuda, Canary, and Cape Verde Islands. Seismicity is also clustered around other tectonic features, such as the diffuse plate boundary between North America and South America, and the fossil spreading ridge between Greenland and North America. While we did not examine intraplate earthquakes within 2° of the Mid-Atlantic Ridge and some of our unreliable near-ridge earthquakes may be truly intraplate, we do not find an indication within our “reliable” data set of an increase in intraplate seismicity with increased proximity to the Mid-Atlantic Ridge beyond our 2° limit.

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