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25-Second Determination of 2019 M7.1 Ridgecrest Earthquake Coseismic Deformation from Global GNSS Seismic Monitoring

We have developed a global seismic monitoring capability based on real-time measurements from ~ 1,000 GNSS receivers to rapidly characterize large earthquakes and, where relevant, tsunami. It complements traditional seismic monitoring by allowing moment release to be quantified while fault rupture unfolds. Position time series from stations distributed across six continents are continuously estimated within an earth center of mass-fixed reference frame and streamed as local north, east and vertical coordinates into a variety of seismic monitoring algorithms and also rebroadcast for third-party use. Average positioning latency, which includes satellite observable acquisition, telemetry and processing, averages about 1.4 seconds on our production system and 0.5 seconds on a development system. Ongoing efforts through 2020 will up the number of global stations to ~2500.

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.

While ~1 sec determination of GNSS coseismic offsets could not help ShakeAlert improve its initial magnitude assessment made several seconds after nucleation, high-M6 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 magnitude estimation for events whose duration and extent of rupture is difficult using only P-wave amplitudes.

Presenting Author: Timothy I. Melbourne

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