In November 2010, ten months after a magnitude 7.0 earthquake flattened huge sections of Port-au-Prince, Haiti, a team of geologists commissioned by the United Nations set out to make the first detailed soil map of the city. Armed with sledgehammers and vibration sensors, the scientists surveyed how soils throughout Port-au-Prince either amplify or muffle seismic vibrations. The resulting map can now be used to guide reconstruction efforts. In this Science Bulletins feature, learn how geologists and engineers in Haiti and San Francisco are improving our resilience to powerful shifts of Earth's crust.