SAN JUAN, Puerto Rico (AP) — The two powerful earthquakes that struck Venezuela’s northern coast, killing more than 180 people, were an event known as a “doublet.”

Doublet earthquakes happen when a pair of similar-sized quakes hit close in location and time, according to the U.S. Geological Survey. On Wednesday evening, a 7.2 magnitude quake hit first, followed by a magnitude 7.5 just 39 seconds later.