G-larmS is an earthquake early warning algorithm for big quakes (magnitude > 7). It builds on the alert provided by E-larmS using geodetic data, and tracks the geographic extent of the fault rupture.
It is being developed and implemented by the UC Berkeley Seismological Laboratory in collaboration with Ronni Grapenthin at New Mexico Tech. It is currently being real-time tested along the U.S. west coast for inclusion in ShakeAlert.
G-larmS development started in 2010 with the realization that real-time GPS data was accurate enough to be used for real-time earthquake information [Allen and Ziv, 2011]. Following the M9 Tohoku-Oki earthquake in Japan, the need for better real-time information about really big earthquakes became clear [Colombelli et al. 2013]. Real-time testing of G-larmS began in 2014 [Grapenthin et al. 2014a], and the algorithm performed well for the M6 Napa earthquake [Grapenthin et al. 2014b]. Since then testing has been extended to the west coast ShakeAlert region.
Technical details about the system can be found in our publications
Animation illustrating G-larmS assessment of the August 24, 2014, magnitude 6 Napa earthquake. The map shows the baselines being used to detect deformation associated with the earthquake. The purple bar illustrates the amount of slip estimated on the Napa fault. Top right shows the magnitude estimation, and lower right shows the time history of four baselines. This is a rerun of the data with no latencies. The realtime system provided the first magnitude estimate 24 sec after the origin time. With improvements to the code, we would now expect this information 12 sec after the origin time. G-larmS is designed to add additional information to alerts for big earthquakes (magnitude > 7). As a magnitude 6 earthquakes, Napa represents the lower limit of when geodetic data can provide information about an earthquake.