Optimizing alerts by tuning the PLUM prediction radius for the ShakeAlert System

Elizabeth S. Cochran, Jessie K. Saunders, Sarah E. Minson, Julian Bunn, Debi Kilb, Annemarie S. Baltay, Colin O'Rourke, Mitsuyuki Hoshiba, & Yuki Kodera

Published August 13, 2021, SCEC Contribution #11385, 2021 SCEC Annual Meeting Poster #248

We optimize performance of the Propagation of Locally Undamped Motion (PLUM) Earthquake Early Warning (EEW) algorithm in the U.S. ShakeAlert System by testing a range of distances used to forecast ground motions. EEW systems, such as ShakeAlert, must balance the primary goal of providing timely alerts for moderate to strong ground shaking while limiting precautionary alerts (alerts for ground motions too low to be of concern). PLUM forecasts ground motion directly from real-time observations of ground motion without estimating the source parameters of the earthquake. PLUM is already operational in the Japan Meteorological Agency’s EEW system, and currently is under consideration for inclusion in ShakeAlert. PLUM forward-predicts observed ground motions to nearby prediction sites within a defined radius without any attenuation. PLUM was originally developed in Japan where alerts are issued to districts with sizes ranging from approximately 500 to 5,000 sq. km, and uses a prediction radius of 30 km. In contrast, ShakeAlert uses a generally smaller alerting grid of 0.2 by 0.2 degree cells (~500 sq. km). Given this contrast in alert region size, we test a range of prediction radii (20-100 km) to examine whether PLUM’s alert performance for ShakeAlert can be optimized. We compare predicted ground motions from PLUM to ShakeMap-reported ground motions for a set of 22 U.S. events of magnitude 4.4 - 7.2 and evaluate available warning times. We find that ideal performance depends on the user’s tolerance for precautionary alerts. Users with high tolerance for precautionary alerts (have a low cost of taking action relative to their expected damage averted by taking the action) and who experience damage at lower ground motions (low target threshold) achieve optimal performance when a larger prediction radius (60-100 km) is implemented. In contrast, users who have low tolerance for precautionary alerts and high target ground motions achieve better performance for smaller prediction radii (30-60 km). Setting the PLUM forward-prediction radius to 60 km balances the needs of many users and provides warning times of up to ~20 sec.

Key Words
earthquake early warning, ground motion alerting

Cochran, E. S., Saunders, J. K., Minson, S. E., Bunn, J., Kilb, D., Baltay, A. S., O'Rourke, C., Hoshiba, M., & Kodera, Y. (2021, 08). Optimizing alerts by tuning the PLUM prediction radius for the ShakeAlert System. Poster Presentation at 2021 SCEC Annual Meeting.

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