When a major earthquake strikes, seconds count. In the
devastating 2011 Japan earthquake, a sensor embedded in the
ground detected the first signs of movement and immediately sent
out an alert at the speed of light. Within seconds, text
messages warning of impending shaking went out to roughly 50
million people. Many people in Tokyo, 200 miles away from the
epicenter, knew the quake was coming before they felt the
shaking about 30 seconds later. Trains were able to slow down or
stop, and not a single car derailed. FOR THE RECORD: Earthquake
warning system: An article in the Jan. 29 Section A about a
proposal to create an earthquake early warning system in
California said that a study published in January was the latest
to predict a catastrophic quake on the San Andreas fault. The
study did not make that prediction, but it did raise the
possibility that a quake along that fault line could be large
enough to be felt across the entire state. Join our live video
discussion here at 3 p.m. PT On Monday, a group of