When a magnitude 4.8 earthquake struck northern New Jersey's Tewksbury township on April 5, it triggered widespread alarm as the biggest event since 1884. Based on existing models, it should have done substantial damage at its epicenter, but that didn't happen. Meanwhile, relatively distant New York City shook much harder than expected, causing damage, albeit minor. Outsize shaking extended all the way to Virginia and Maine. A new study suggests why this happened, calling into question some assumptions about regional earthquake hazard.