Development of a Geodetic Component for the U.S. West Coast Earthquake Early Warning System

Abstract

An earthquake early warning (EEW) system, ShakeAlert, is under development for the West Coast of the United States. This system currently uses the first few seconds of waveforms recorded by seismic instrumentation to rapidly characterize earthquake magnitude, location, and origin time; ShakeAlert recently added a seismic line source algorithm. For large to great earthquakes, magnitudes estimated from the earliest seismic data alone generally saturate. Real-time Global Navigation Satellite System (GNSS) data can directly measure large displacements, enabling accurate magnitude estimates for M w 7 events, possibly before rupture termination. GNSS-measured displacements also track evolving slip and, alone or in combination with seismic data, constrain finite-fault models. Particularly for large-magnitude, long-rupture events, GNSS-based magnitude and rupture extent estimates can improve updates to predicted shaking and thus alert accuracy. GNSS data processing centers at ShakeAlert partner institutions provide real-time streams to the EEW system, and three geodetic EEW algorithms have been developed through the ShakeAlert collaboration. These algorithms will undergo initial testing within ShakeAlert's computational architecture using a suite of input data that includes simulated real-time displacements from synthetic earthquakes and GNSS recordings from recent earthquakes worldwide. Performance will be evaluated using metrics and standards consistent with those adopted for ShakeAlert overall. This initial assessment will guide method refinement and synthesis of the most successful features into a candidate geodetic algorithm for the ShakeAlert production system. In parallel, improvements to geodetic networks and streamlining approaches to data processing and exchange will ensure robust geodetic data availability in the event of an earthquake.Electronic Supplement: Table listing recent earthquakes for which high sample-rate (≥ 1 Hz) processed Global Positioning System data and seismic data have been gathered for use in testing geodetic earthquake early warning algorithms and a summary of ground-motion metrics adopted by ShakeAlert, the U.S. West Coast EEW system, for evaluating new or updated components before adoption in the production system, and a schematic diagram of the real-time Global Navigation Satellite Systems data flow for ShakeAlert.

Peak Ground Displacement Saturates Exactly When Expected: Implications for Earthquake Early Warning

“…Visual examination of these derived displacement waveforms suggests that there may be significant artifacts inherent to the double‐integration process, particularly during dense aftershock sequences where long‐period noise and residual tilts in the accelerometer are not adequately removed by the application of high‐pass filter at 0.075 Hz. A potential solution for more accurate estimates may be to incorporate geodetic data, which is currently being explored for the ShakeAlert system (Murray et al, ). While beyond the scope of this study, the Bayesian framework we develop here should in principle be applicable to compute time‐dependent uncertainties in geodetic EEW systems, which can reliably measure the peak static and dynamic ground displacement but issue significantly slower alerts due to their dependence on S waveform data.…”

A Framework for Evaluating Earthquake Early Warning for an Infrastructure Network: An Idealized Case Study of a Northern California Rail System

“…In recent years, different EEW approaches have proliferated, such as algorithms that utilize geodetic data (Murray et al, 2018) or store seismogram filter banks (Meier et al, 2015). JMA has updated their source parameter algorithm using the Integrated Particle Filter (IPF) method and complemented that approach with the ground-motion-based Propagation of Local Undamped Motion (PLUM) method.…”

Quantifying the Value of Real‐Time Geodetic Constraints for Earthquake Early Warning Using a Global Seismic and Geodetic Data Set

“…Three of these are currently being tested for implementation into ShakeAlert: G‐larmS, BEFORES, and G‐FAST (Crowell et al, 2016; Grapenthin et al, 2014a; Minson et al, 2014). In this work, we will focus on performance of the G‐larmS algorithm (see Murray et al, 2018, for a comparison) and make the data freely available so that other algorithm developers can conduct similar evaluations. The Geodetic Alarm System (G‐larmS) was the first operational real‐time geodetic system in the United States (Grapenthin et al, 2014a), and has been running in real time since the beginning of May 2014.…”