Integrating Geodetic Data For Earthquake Warnings in the Western U.S.

Researchers: J. R. Murray, J. O. Langbein, and S. E. Minson, U.S. Geological Survey, B. W. Crowell and D. A. Schmidt, University of Washington, R. Grapenthin, New Mexico Tech, K. Hodgkinson, UNAVCO, T. Melbourne, Central Washington University, and D. Melgar, University of Oregon

Written by Linda Rowan
3 January 2019

Summary

Real-time Global Navigation Satellite System (GNSS) ground-based sites can measure displacements on the Earth’s surface and these geodetic data have the potential to improve earthquake warnings. Here, the benefits of including GNSS in a warning system are outlined and three different algorithms for integrating geodetic data into the USGS’s ShakeAlert system are identified. Independent development of the algorithms has shown they can improve warnings, a systematic and rigorous testing of the algorithms is now required to quantify that improvement.

Observations

The United States is developing an earthquake early warning system called ShakeAlert along the West Coast. The U.S. Geological Survey is developing the system and is working with many universities as well as UNAVCO to build, operate and maintain the system. A prototype system uses the first few seconds of seismic waveforms recorded by seismic instrumentation to determine the earthquake’s location, magnitude and origin time. Recent large earthquakes, e.g., the 2011 Tohoku earthquake and the 2010 El Mayor Cucapah earthquake, have shown that relying on the first seconds of the waveform can lead to an underestimation of the earthquake magnitude. The growth of continuous, high-rate GNSS networks around the world in the past decade has provided data that shows GNSS can measure large displacements and be used to rapidly determine an accurate magnitude and other earthquake characteristics, even before the fault has finished rupturing.

On the West Coast of the U.S., large magnitude earthquakes (>M7) are likely and a Tohoku-like earthquake and tsunami is possible along the Cascadia Subduction Zone that slices beneath Northern California, the Pacific Northwest and parts of Canada. Adding geodetic data for large events to any warning system would help to mitigate damage as the information it provides would yield more accurate estimates of impending ground shaking. UNAVCO operates and maintains ~640 real-time GNSS sites on the West Coast of the U.S. The U.S. Geological Survey is using these data to develop methods for integrating the geodetic data into ShakeAlert.