Abstract
Earthquake early warning (EEW) systems provide a few to tens of seconds of warning before shaking hits a site. Despite the recent rapid developments of EEW systems around the world, the optimal alert response strategy and the practical benefit of using EEW are still open-ended questions, especially in areas where EEW systems are new or have not yet been deployed. Here, we use a case study of a rail system in California’s San Francisco Bay Area to explore potential uses of EEW for rail systems. Rail systems are of particular interest not only because they are important lifeline infrastructure and a common application for EEW around the world, but also because their geographically broad yet networked infrastructure makes them almost uniquely well suited for utilizing EEW. While the most obvious potential benefit of EEW to the railway is to prevent derailments by stopping trains before the arrival of shaking, the lead time for warnings is usually not long enough to significantly reduce a train’s speed. In reality, EEW’s greatest impact is preventing derailment by alerting trains to slow down or stop before they encounter damaged track. We perform cost-benefit analyses of different decision-making strategies for several EEW system designs to find an optimal alerting strategy. On-site EEW provides better outcomes than source-parameter-based EEW when warning at a threshold of 120 gal (the level of shaking at which damage might occur) regardless of false alarm tolerance. A source-parameter-based EEW system with a lower alerting threshold (e.g., 40 gal) can reduce the exposure to potentially damaged track compared to an on-site system alerting at 120 gal, but a lower alerting threshold comes at the cost of additional precautionary system stops. The optimal EEW approach for rail systems depends strongly on the ratio of the cost of stopping the system unnecessarily to the potential loss from traversing damaged tracks.
Highlights
The original idea for Earthquake early warning (EEW) is generally credited to a piece by Dr J
We considered a rail system based on the Northern California Bay Area Rapid Transit (BART) system as an example of a special type of infrastructure network where it is critical not just to forecast shaking at the user’s current location and at distant parts of the track that the train will later encounter in its route
Rather than focusing on a specific application, we instead present an example of our framework in which we evaluate the utility of different EEW system designs assuming the theoretical performance of an ideal system with zero noise, data latency, or computational delays, quantifying the maximum possible risk reduction from EEW
Summary
The original idea for EEW is generally credited to a piece by Dr J. The first practical implementation of an EEW system began nearly a hundred years later, in 1965, when a M6.1 earthquake led what is the Japan Railways Group (JR) to install seismometers every 20–25 km along the Shinkansen bullet train tracks to issue an alert to slow trains if horizontal accelerations exceeding 40 gal were observed (Saita and Nakamura, 2003). The Coastline Detection System was later upgraded and replaced with the Urgent Earthquake Detection and Alarm System (UrEDAS) (Saita and Nakamura, 2003). In 2004, JR replaced the UrEDAS with another new EEW system that estimates source parameters, while continuing its ground-motion-based system of stopping trains if acceleration, bandpass filtered between 0.5 and 5 Hz, exceeds a given threshold (Yamamoto and Tomori, 2013)
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