A Transferable Strain-Rate-to-PGA Scaling Relation for DAS-Based On-Site Earthquake Early Warning

Abstract Earthquake early warning (EEW) systems provide crucial seconds for protective actions and automated responses. Distributed acoustic sensing (DAS) transforms fiber-optic cables into dense seismic sensor arrays, creating new opportunities for EEW. Although submarine cables can provide additional warning time for regional EEW of offshore megathrust earthquakes, urban telecom cables could support on-site EEW by increasing sensor density in urban areas and across critical infrastructure, yet their potential remains underexplored. A key challenge is that DAS records strain rate rather than the particle motion parameters used in conventional EEW. Using long-term operating downhole fiber observations at the Milun fault Drilling and All-inclusive Sensing site in eastern Taiwan, we establish and present a direct, empirical scaling relation between DAS-derived peak strain rate in the first 3 s of P waves and the peak ground acceleration recorded by a collocated seismometer, with a correlation coefficient of 0.93. Validations using DAS experiments in a building basement and at Sakurajima Volcano, Japan, demonstrate that this scaling relation is transferable across different cable settings and tectonic regions after amplitude calibration. This calibration can be achieved using a single correction term in the regression to jointly account for site amplification and potential biases related to cable orientation and coupling, and bootstrapping analysis shows that only five to six events are needed to constrain this term. Our results demonstrate the potential of widely distributed telecom cables to augment on-site EEW systems and contribute to the development of more resilient cities.