The 1994 Northridge earthquake was one of the costliest natural disasters in U.S. history. Fifty-seven people died, more than 8,700 were injured, and property damages amounted to billions of dollars. In the 25 years since the 6.7 quake shook Southern California at 4:30 a.m. on Jan.17—collapsing buildings, bridges and freeways—what have we learned?