5.1 earthquake: Prototype early-warning system works again

[n2doc]

By Rong-Gong Lin II
March 29, 2014, 12:02 p.m.
A prototype earthquake early-warning system worked again Friday night, giving seismologists in Pasadena about a four-second heads-up before shaking was felt from the magnitude 5.1 quake that struck near La Habra.

The system is being tested by a team of scientists on a U.S. Geological Survey project to create a statewide network.
USGS seismologist Lucy Jones has said the system works because while earthquakes travel at the speed of sound, sensors that initially detect the shaking near the epicenter of a quake can send a message faster -- at the speed of light -- to warn residents farther away that the quake is coming.

The system being tested by scientists at the USGS and Caltech previously gave officials at the Pasadena center about a two-second warning ahead of a magnitude 4.4 earthquake that struck near Westwood in March.

Once developed, the system could give downtown Los Angeles 40 to 50 seconds of warning that the “Big One” was headed from the San Andreas fault, giving time for elevators to stop at the next floor and open up, firefighters to open up garage doors, high-speed trains to slow down to avoid derailment and surgeons to take the scalpel out of a patient.


http://www.latimes.com/local/lanow/la-me-ln-earthquake-prototype-early-warning-system-20140329,0,6637333.story

[Control-Z]

1. I thought it was 4 - 6 seconds.

Would it really be 40 - 50 from San Andreas? Wow. That would be enough time to get to a safe place for many people. When it comes to earthquakes seconds really matter.

[defacto7]

2. I made another comment just now but I'll ask here too.

Has anyone noticed that several of those 2.5 to 4 tremors are only about 300 feet underground? USGS says .1km. I don't remember such shallow swarms. Relatively speaking, that is not very deep. Not sure if it matters, I'm just curious.

edit: 3 of them are .1km, 5 of them are .3km or less.