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Rapid Line-Source and Ground-Motion Estimates for Earthquake Early Warning Using FinDer Version 2

Maren Böse, Deborah E. Smith, Claude Felizardo, Men-Andrin Meier, Thomas H. Heaton, & John Clinton

Published August 14, 2017, SCEC Contribution #7557, 2017 SCEC Annual Meeting Poster #081

Characterizing earthquakes in real-time, for applications like earthquake early warning, requires a flexible modeling approach that can accommodate a small earthquake becoming large as fault rupture evolves over time. Hence, we present a modeling strategy that generates a set of output parameters and uncertainty estimates that are consistent with both small/moderate (≤M6.5) and large earthquakes (>M6.5). Our approach treats earthquakes over the entire magnitude range (M2 to M9) with a consistent line-source methodology, where the dimensions of large earthquakes could exceed several tens to hundreds of kilometers in length and the dimensions of small earthquakes could be very small (< 100 m) which approximates point-source behavior. The extent of the assumed line-source is estimated from the level and distribution of high-frequency peak ground acceleration (pga) amplitudes observed in a local seismic network. High-frequency motions are well-suited for estimating rupture extent, because they are mainly controlled by their distance to the rupturing fault. Observed ground-motion patterns based on pga data are compared with theoretical templates calculated from empirical ground-motion prediction equations. Based on a matching technique, the best line-source and uncertainties are determined in less than a second. This algorithm extends earlier work by Böse et al. (2012, 2015) for large finite-fault ruptures. We give a summary of the new algorithm, including its offline performance for large finite-fault ruptures (M6.0 and M7.0) and its real-time performance for 100 real-time detected local earthquakes (2.2≤M≤5.1) in California. Both the rupture length and the strike are well constrained within a few seconds (<10 s) of the event origin, for most events. For example, with the Kumamoto earthquake, even for sites with eventual accelerations of ~10% g, accurate ground motion prediction levels, based on distances from the FinDer estimated rupture, are reached ≥ 10s before a threshold acceleration of ~4% g (Intensity 5) is exceeded. For more distant sites, with lower eventual ground-motion amplitudes, accurate predictions are available with approximately one minute warning time. It is only the sites closest to the epicenter that would not receive a warning. The FinDer method could also be useful for resolving fault plane ambiguities of focal mechanisms, thus identifying rupturing faults for earthquakes as small as M2.5.

Key Words
earthquake early warning, ground-motion prediction, finite-fault ruptures, focal mechanism

Böse, M., Smith, D. E., Felizardo, C., Meier, M., Heaton, T. H., & Clinton, J. (2017, 08). Rapid Line-Source and Ground-Motion Estimates for Earthquake Early Warning Using FinDer Version 2. Poster Presentation at 2017 SCEC Annual Meeting.

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