During a recent ONR experiment on the Northwest Atlantic continental shelf (i.e. New England Bight), a series of earthquakes occurred roughly 120 km from the 40 km × 20 km experimental area. A strong signal from these earthquakes was received by near-bottom vector sensors (the intensity vector acoustic recorders, IVARs) and high-bandwidth ocean-bottom seismometers (OBXs) embedded in the thick muddy sediments characteristic of the area. The events are roughly 30 seconds in duration, and are low-frequency (from 3 to 40 Hz). As such, energy is observed well below the acoustic cut-off frequency of the continental shelf. Correlating the arrivals to the USGS epicenter show these arrivals are supersonic in water, with group velocity >5 km/s. These arrivals appear to be leaky waves propagating within the rock below the ocean seafloor, distinct from the well-known T-phase of oceanic earthquakes that propagate at speeds close to the sound speed in seawater. The frequency dependence of the potential and kinetic energy of these arrivals suggest the field is evanescent, in both the water column and upper sediments. Spectral properties of the arrivals are shown to correspond to the water depth and sediment layering.