For the past several years, the USGS and research teams in California have been studying how they might do earthquake early warnings in the United States, but there is no system in place.
In a sense, there was a warning that wasn't recognized.
Two days earlier, the region was rattled by a 7.2 quake. Scientists now consider that a foreshock.
Image: A volunteer firefighter walks past a house pierced by a utility pole fallen after Friday's strong earthquake in Rikuzentakada, Iwate Prefecture, northern Japan on March 13, 2011.