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Real-Time Gnss Point Positioning for Shakealert

Description: 

We have developed a real-time GNSS point positioning capability based on low-latency measurements from ~ 1000 Global Navigational Satellite System (GNSS) receivers to rapidly characterize large earthquakes and, where relevant, tsunami. For earthquake early warning applications such as ShakeAlert, the system can enhance traditional seismic monitoring by allowing moment release to be quantified as fault rupture unfolds. Position time series from all stations within the ShakeAlert footprint are continuously estimated within an earth center of mass-fixed reference frame and streamed as local north, east and vertical coordinates to ShakeAlert centers in Seattle WA and Berkeley and Pasadena, CA. Average positioning latency, which includes satellite observable acquisition, telemetry, and processing, averages about 0.5 seconds and average position variance within the ITRF reference frame of 4, 6 and 8 cm in the north, east and vertical components, respectively.

This system captured the 2019 Ridgecrest California M7.1 earthquake and determined its coseismic deformation of up to 70 cm on 12 nearby stations within 22 seconds of event nucleation. Those 22 seconds comprise the fault rupture time itself (roughly 5-10 sec), another ~5s for propagation delay between various regions of slip and GNSS stations, another 5-10s for dynamic displacements to dissipate such that coseismic offsets ‘settle down,’ plus another 1.4 seconds for telemetry and data analysis latency. Comparison of coseismic deformation estimated within 25 seconds to that determined with post-processing using several days of post-processing show that the real-time offsets were accurate to within 10% of the post-processed “true” offsets.

The GNSS-based high-M6 PGD magnitude at ~25 seconds could have nonetheless triggered or revised an alert before S-waves reached the LA Basin. This highlights how GNSS can improve earthquake early warning magnitude estimation for large events whose duration and extent of rupture precludes accurate assessment using only the first few seconds of P-wave amplitudes.

Session: Earthquake Early Warning Optimization and Efficacy

Type: Oral

Date: 4/20/2023

Presentation Time: 05:00 PM (local time)

Presenting Author: Walter M. Szeliga

Student Presenter: No

Invited Presentation: 

Authors