"The Big One is coming," Rep. Adam Schiff said at a news conference in Pasadena. "We don't know when, and the only question is: Will we be prepared?"
Known as ShakeAlert, the system is designed to notify the public, government officials and hospitals about a significant temblor before the shaking occurs.
Up to a minute of advance notice will be provided for some of the largest quakes, Rep. Judy Chu said. For other magnitudes, individuals will receive alerts between 10 and 20 seconds beforehand.
"That may not sound like a lot, but think about what can be done in 20 seconds," Chu said, noting that surgeons can safely pause operations; trains and elevators can be stopped; and gas lines can be shut down to reduce the risk of fire.
As of Wednesday, half the number of sensors needed for the system to be fully operational have been installed.
However, Doug Given of the USGS said there already is "a lot of capability in the system as it exists today -- to the point where it can definitely be used."