Testing Contour Triggering In ShakeAlert Earthquake Early Warning

Deborah E. Smith, Jennifer R. Andrews, Jeff J. McGuire, & Minh Huynh

Published August 16, 2021, SCEC Contribution #11564, 2021 SCEC Annual Meeting Poster #247

The ShakeAlert system for the West Coast of the United States traditionally uses the epicenter of earthquakes to determine whether an event is within the reporting boundary. This works well for most cases; however, there is the potential for large earthquakes to start outside (but close to) the DM reporting boundary and for significant shaking to extend into the West Coast DM reporting boundary. To address this, the Software Management working group coded an option for generating ShakeAlert messages to the public if the EqInfo2GM contours of a specified MMI level overlap the DM reporting boundary. This allows ShakeAlert to effectively send messages based on ground motion shaking intensity in addition to the epicenter location.

The System and Testing Performance (STP) working group has assessed the performance of this new configuration option. STP did the following: 1) Curated a data set for testsuite 2.0 that includes events to test the contour triggering option. STP selected events with a ANSS or DM M4.5+ where the Shakemap MMI 3 contours either overlapped or came close to overlapping with the DM reporting boundary. 2) Tested the contour triggering option with initial Solution Aggregator (SA) and FinDer boundaries. 3) After Excom feedback, generated revised SA and FinDer boundaries and tested again with MMI 3 and MMI 4 contour triggering levels.

We confirm that the contour triggering option helps with significant earthquakes close to the reporting boundary. Two examples of particular interest, are the 2010 M7.2 El Mayor-Cucapah earthquake and the 2020 M6.5 Monte Cristo earthquake. For El Mayor-Cucapah, the contour triggering helps speed up the initial ShakeAlert message and for Monte Cristo, the contour triggering helps the DM not miss the event altogether. Further results of this replay testing will be presented. Potential drawbacks and risks of contour triggering will also be discussed.

Key Words
early warning

Smith, D. E., Andrews, J. R., McGuire, J. J., & Huynh, M. (2021, 08). Testing Contour Triggering In ShakeAlert Earthquake Early Warning. Poster Presentation at 2021 SCEC Annual Meeting.

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