Earthquake Early Warning Testing: Using New Synthetics

Deborah E. Smith, Robert W. Graves, & Jeff J. McGuire

Submitted August 30, 2026, SCEC Contribution #15459, 2026 SCEC Annual Meeting Poster #TBD

The West Coast ShakeAlert Earthquake Early warning system has been sending public alerts since October 17, 2019, and has been successfully generating real-time earthquake messages. In order to assess continuing algorithm development and proposed improvements, ShakeAlert has a System Testing and Performance (STP) platform. The overarching principle is that proposed changes should improve either the warning time and/or accuracy of location and magnitude estimates while minimizing additional complexity to the system and alerting. Performance analysis must balance these competing goals. To properly assess the value of proposed software changes, STP replays a suite of waveforms (recordings of moderate to large earthquakes plus a few synthetic earthquakes) through 4-8 instances of the algorithm stack and evaluates with metrics from Cochran et al. (2017). These metrics are focused on point source parameters such as estimated magnitude, location, and origin time. In addition, proposed software is run on a set of test machines that are configured like the production system to process real-time data for a minimum period of 2 weeks.

Because well recorded large earthquakes on the West Coast are relatively rare, we currently test ShakeAlert using a robust data set of M6+ shallow crustal and M7+ shallow subduction zone earthquakes from Japan. However, in order to test the system with large events having the appropriate West Coast geometry, geology, and station distribution, one needs to generate realistic synthetics. Initially, we are focusing the use of synthetics on high-hazard areas like San Andreas fault, PNW Cascadia subduction zone, and the Hayward fault. For example, we have been working with the new PNW Cascadia subduction zone synthetics from Audrey Dunham for seismic and geodetic data. And we are also working with others for additional California scenarios.

Citation
Smith, D. E., Graves, R. W., & McGuire, J. J. (2026, 08). Earthquake Early Warning Testing: Using New Synthetics. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology