A massive 6.1 aftershock outside of Port-au-Prince sent refugees and relief workers shrieking and running into the streets Wednesday morning. The tremor was the strongest of the aftershocks to hit the area since the 7.0 quake that devastated Port-au-Prince eight days ago. According to The Washington Post, the quake hit Port-au-Prince with a "rolling, side-to-side motion" that lasted several seconds, followed by a cascading roar that was "presumably the collapse of another building." According to CNN, such strong aftershocks can be dangerous because buildings damaged by the first earthquake are already unstable. The Associated Press says the epicenter was 35 miles northwest of Port-Au-Prince and 13.7 miles underground.