The Brave New World of Real-time GPS for Hazards Mitigation

Real-time GPS position streams are desirable for a variety of seismic and tsunami monitoring and hazard mitigation applications. We report on progress in our development of a comprehensive real-time GPS-based seismic monitoring system for the Cascadia subduction zone. This system is based on 1 Hz point position estimates computed in the ITRF08 reference frame. Convergence from phase and range observables to point position estimates is accelerated using a Kalman filter based, in-line stream editor that produces independent estimations of carrier phase integer biases and other parameters. Positions are then estimated using streamed satellite clock and orbit products from the International GNSS Service (IGS). The resulting positions show typical RMS scatter of 2.5 cm in the horizontal and 5 cm in the vertical with latencies below 2 seconds. To facilitate the use of these point position streams for applications such as seismic monitoring, we broadcast real-time positions and covariances using custom-built aggregation-distribution software based on RabbitMQ messaging platform. To demonstrate the power of this approach, we have developed a Java-based front-end that provides a real-time visual display of time-series, displacement vector fields, and map-view, contoured, peak ground displacement. This Java-based front-end is available for download through the PANGA(.org) website. We currently analyze 120 PBO and PANGA stations along the Cascadia margin and San Andreas system in California along with another 50 from the circum-Pacific. We are gearing up to process all available west-coast real-time stations. These will serve as milestones towards our over-arching goal of extending our processing to include all of the available real-time streams from the Pacific rim. In addition, we have developed a Kalman filter to combine CWU real-time PPP solutions with those from Scripps Institute of Oceanography's PPP-AR real-time solutions as well as real-time solutions from other analysis centers, which may be distributed via the RabbitMQ system and merged locally at redundant institutions. These combined products have been shown to improve the robustness and reliability of real-time point-position streams, and form the basis for a geodetic earthquake and tsunami monitoring system.