ElarmS EEW Performance

ElarmS is the UC Berkeley's algorithm contributing to the demonstration earthquake early warning system in California, CISN ShakeAlert. In the August 24, 2014 South Napa earthquake, ElarmS' first alert was sent to the Decision Module of the ShakeAlert system, with a magnitude of 5.7, 5.1 sec after the rupture started. The alert was based on P-wave triggers from four stations and took 3.3 s to produce after the waves arrived at the seismic station nearest to the epicenter (6.5 km). The latencies of the four stations contributed to the first ranged from 0.27 to 2.62 seconds, contributing to a total delay of 2.3 sec, with a concommitant increase in the blind zone, the region with no warning. Overall the magnitude estimate and event location were stable from the initial alert onwards. We will report on the development of the magnitude estimate as a function of time, as well as the performance of ElarmS as data from additional stations were integrated into its estimates of the quake's location and magnitude. We will highlight, in particular, the configuration of ElarmS and the requirements on earthquake early warning station density and data feeds that allow the very rapid reporting of earthquake parameters for earthquake alert systems.