Performance of the ShakeAlert Earthquake Early Warning System During the Ridgecrest Sequence

Angela I. Chung, Deborah E. Smith, Jennifer R. Andrews, Maren Böse, Jeff J. McGuire, Men-Andrin Meier, Igor Stubailo, & Richard M. Allen

Published August 14, 2019, SCEC Contribution #9607, 2019 SCEC Annual Meeting Poster #274

On July 4, 2019 an earthquake sequence began near Ridgecrest, CA. The sequence began with a M4.0 earthquake followed 30 minutes later by a M6.4 earthquake. Less than 36 hours later, a M7.1 earthquake shook the Los Angeles region. This mainshock was the largest continental earthquake to occur in the West Coast in nearly 20 years.

ShakeAlert is a US West Coast-wide earthquake early warning system that has been under development since 2006 and is a collaboration between the USGS and partner institutions California Institute of Technology, University of California Berkeley, University of Oregon, University of Washington, and ETH. A production prototype version of the system officially came online in 2016 and has been detecting earthquakes and creating alerts since that time.

The ShakeAlert earthquake early warning system detected and created alerts for more than 180 M≥3.5 earthquakes in the four weeks following the M6.4 foreshock. This sequence included both the largest earthquake and the most intense aftershock sequence that the production ShakeAlert system has encountered thus far.

The system rapidly detected both the M7.1 and the M6.4 main events within 8 seconds and accurately located them to within 3 km of their true hypocenters. While the magnitude of the M6.4 event was successfully estimated in real-time, the size of the M7.1 event was underestimated by 0.8 units.

Although alerts were created by the ShakeAlert system for the two largest earthquakes, with each alert providing 48 sec of warning at LA City Hall, those alerts were not pushed out to users of the ShakeAlert pilot user City of LA’s ShakeAlertLA cell phone app due to the fact that ground motions predicted by ShakeAlert did not surpass the necessary alerting thresholds. In this presentation we will discuss the performance of ShakeAlert system during the Ridgecrest Sequence from detection to alert.

Key Words
Earthquake Early Warning

Citation
Chung, A. I., Smith, D. E., Andrews, J. R., Böse, M., McGuire, J. J., Meier, M., Stubailo, I., & Allen, R. M. (2019, 08). Performance of the ShakeAlert Earthquake Early Warning System During the Ridgecrest Sequence. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes