ShakeAlert EEW System Improvements, Recent and Upcoming, Tested by the STP Working Group and the SP Working Group

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

Submitted August 14, 2020, SCEC Contribution #10614, 2020 SCEC Annual Meeting Poster #058

ShakeAlert is a distributed West Coast earthquake early warning project that includes collaboration from a variety of institutions. The goal is to generate estimates of earthquake source parameters and ground motions as quickly and as reliably as possible. The System and Testing Performance (STP) Working Group in ShakeAlert is tasked with examining candidate algorithm performance and determining if the performance is improved over the current production algorithm. The System Performance (SP) Working Group examines production system performance and develops recommendations for the STP working group. Two key improvements to ShakeAlert have recently been tested, one by STP and the other by SP.

The first tested improvement (by STP), which is now in production, was a change to the Solution Aggregator (SA) to improve large magnitude earthquake performance. It was noted in Ridgecrest and in replayed Japanese events that the previous SA underestimated the magnitude for ~M6.5+ events, due to the weighting scheme between point-source algorithm EPIC and finite-fault algorithm FinDer. This weighting scheme was revised to prefer the magnitude from FinDer for M6+ events if the FinDer magnitude was larger than the EPIC magnitude. The effect of this new weighting scheme was then tested with a suite of West Coast earthquakes, selected large Japanese events, and the M6.4 and M7.1 Ridgecrest data. These tests demonstrated that the new SA now provides a more appropriate large magnitude estimate.

The second tested improvement (by SP), which is currently being examined, is the effect of turning on existing SA and Decision Module (DM) configuration parameters. The current ShakeAlert system sends out alerts only for events whose epicenters are within the DM reporting boundary. This leaves out events like the recent Monte Cristo Nevada M6.5 event, whose epicenter was just outside the reporting boundary but the ground motion contours of interest intersected the reporting region. The SA and the DM already have the ability to determine if an alert should be sent out by the intersection of ground motion contours with the DM reporting boundary. Hence in testing, this contour feature was turned on via configuration changes and regional West Coast events from the past 5 years were replayed through the entire suite of algorithms.

Key Words
earthquake early warning, seismology, ShakeAlert, West Coast, earthquake detection,

Smith, D. E., McGuire, J. J., Chung, A. I., Andrews, J. R., Meier, M., & Böse, M. (2020, 08). ShakeAlert EEW System Improvements, Recent and Upcoming, Tested by the STP Working Group and the SP Working Group. Poster Presentation at 2020 SCEC Annual Meeting.

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