The Earth shook, but it wasn't an earthquake
The East Coast boom issue dates to at least the winter of 1977-78, when similar shock waves hit many communities. The military denied responsibility, so rumors and speculations abounded: secret weapons tests; operations of spacecraft or submarines; giant methane bubbles erupting from the seafloor. Lamont seismologists hypothesized that small earthquakes were emanating from areas lacking adequate instrumentation; or oil companies might be igniting explosives offshore to explore for petroleum reserves. David Simpson, then Lamont's head of seismology, set out an array of portable seismometers near Cape May, N.J., where many complaints came from, but got little useful information. "This was a big mystery that lasted for months," said Lamont seismologist emeritus John Armbruster. "It shows the frustrations of dealing with a culture of military secrecy."