Measuring ‘p-waves’ to warn the public of impending quakes

Earthquakes, unlike other natural disasters, often hit without warning. But some countries have systems to give residents a heads-up before one strikes. Despite a history of deadly quakes in California, the U.S. has no widespread warning system. The NewsHour’s Cat Wise reports on ShakeAlert, a project in development in Southern California that measures initial waves before a strong shaking.