E-larmS: Berkeley's Earthquake Early Warning Algorithm
What is ElarmS?
ElarmS is a robust earthquake early warning system that has successfully alerted on hundreds of events throughout California since it was developed in 2007. We have recently begun expanding ElarmS coverage into the Pacific Northwest (Washington and Oregon) and there are versions of ElarmS being tested in countries around the world, including Israel, Turkey, and Chile. ElarmS is one of the fastest earthquake early warning algorithms running in the world, and even sent out an alert for an earthquake before the damaging S-waves arrived at the surface!
ElarmS is a network-based earthquake early warning algorithm. It currently requires P-waves to be detected at 4 stations before it can issue an alert. Though we are experimenting with novel devices and methodologies to reduce the number of stations needed, we’ve found that 4 is a good number of stations to create robust alerts.
Since a production version of ElarmS began running in early 2016, it has detected 19 earthquakes with magnitude M>4 in California (see figure). For these events, the median estimated magnitude error was 0.3 magnitude units, the median distance error was 3.9km, and the median alert time (time between when the earthquake occurred and when the first alert was sent out) was just 7 seconds.
What Can We Do with Earthquake Early Warning?
The ElarmS earthquake early warning system is an incredibly useful tool that may one day be used to provide alerts of imminent earthquakes to people throughout the West Coast. Though warning times range from just a few seconds to tens of seconds, the warnings provided could be used to slow down high-speed trains, provide warnings people working in precarious conditions (for example, surgeons, construction workers, and those working with dangerous equipment and/or chemicals), divert aircraft that are about to land, and possibly trigger automatic shutdown of critical equipment. These warnings can also be used by the general public to give them time to take cover under a table and move away from unsafe situations (for example, large glass windows).
August 24, 2014
M6.0 South Napa Earthquake:
shakeAlert issues warning, alert from ElarmS
The above is a video capture of the warning received at the UC Berkeley Seismological Laboratory. It shows the 5 second countdown to the beginning of shaking in Berkeley and the expected shaking intensity in Berkeley which was 4 (shown IV) on the intensity scale and described as "light" shaking. The strongest shaking in Berkeley occured 10 seconds after the alert was received.
Warning time: The amount of warning time depends on the distance of the user from the epicenter of the quake; the greater the distance, the greater the warning time. For the Napa quake Berkeley got 5 sec warning, our users in San Francisco got 8 sec warning.
User actions: Our beta-testers across the San Francisco Bay Area received the alert at the same time as the Berkeley Seismo Lab. BART has implemented an automated train-stopping system. The system activated and would have stopped trains, however, at 3:20 in the morning there were no trains running. The alert was received in the 911 center in San Francisco and the the UC Police.
March 28, 2014
M5.1 La Habra Earthquake:
ShakeAlert issues warning across LA, alert from ElarmS
ElarmS provided the ShakeAlert for the M5.1 La Habra quake, the M4.4 Encino quake beneath the Santa Monica mountains (March 17, 2014) and the M4.2 Westwood quake (June 2, 2014), all in the Los Angeles region.
The above video shows a press conference at Caltech follwoing the La Habra quake. During the press conference ShakeAlert issues a warning for a small aftershock that is caught on camera.