Operational real‐time GPS‐enhanced earthquake early warning

Abstract

AbstractMoment magnitudes for large earthquakes (Mw≥7.0) derived in real time from near‐field seismic data can be underestimated due to instrument limitations, ground tilting, and saturation of frequency/amplitude‐magnitude relationships. Real‐time high‐rate GPS resolves the buildup of static surface displacements with theSwave arrival (assuming nonsupershear rupture), thus enabling the estimation of slip on a finite fault and the event's geodetic moment. Recently, a range of high‐rate GPS strategies have been demonstrated on off‐line data. Here we present the first operational system for real‐time GPS‐enhanced earthquake early warning as implemented at the Berkeley Seismological Laboratory (BSL) and currently analyzing real‐time data for Northern California. The BSL generates real‐time position estimates operationally using data from 62 GPS stations in Northern California. A fully triangulated network defines 170+ station pairs processed with the software trackRT. The BSL uses G‐larmS, the Geodetic Alarm System, to analyze these positioning time series and determine static offsets and preevent quality parameters. G‐larmS derives and broadcasts finite fault and magnitude information through least‐squares inversion of the static offsets for slip based on a priori fault orientation and location information. This system tightly integrates seismic alarm systems (CISN‐ShakeAlert, ElarmS‐2) as it uses theirPwave detections to trigger its processing; quality control runs continuously. We use a synthetic Hayward Fault earthquake scenario on real‐time streams to demonstrate recovery of slip and magnitude. Reanalysis of theMw7.2 El Mayor‐Cucapah earthquake tests the impact of dynamic motions on offset estimation. Using these test cases, we explore sensitivities to disturbances of a priori constraints (origin time, location, and fault strike/dip).