Distinguishing the Coseismic Phase of the Earthquake Cycle 
with Seismogeodesy

Dorian Golriz, Yehuda Bock, & Xiaohua Xu

Published August 15, 2020, SCEC Contribution #10700, 2020 SCEC Annual Meeting Poster #109

Inversions for earthquake source and fault slip distribution models rely on reliable static surface displacements from GNSS stations. Recent studies have also demonstrated the utility of peak-ground-displacement in rapid magnitude estimation. Determination of these crucial parameters requires the choice of an appropriate time window for the displacement time series. It is important to determine the most accurate earthquake time span, individually at each station, in order to avoid overestimating the coseismic moment by including early postseismic motion and the inclusion of multipath noise that bias peak-ground-displacement estimates. Most studies have considered the time span of the coseismic phase based on daily GNSS displacements. Others use regional seismic instruments to determine the start of seismic shaking but choose the time interval to be constant for all GNSS stations regardless of their hypocentral distance, geological setting, or azimuth relative to fault rupture. Here we calculate a measure of energy at seismic stations to properly bracket the earthquake period. We then interpolate these times to all GNSS stations in the area and differentiate between the earthquake’s coseismic and early postseismic motion. After we determine the relevant earthquake time interval at each station, we can reliably extract useful information regarding the earthquake source. We apply our methodology to a series of earthquakes over a range of magnitudes and fault mechanisms and find substantial differences with existing methods. As an example, we input our rapid coseismic estimates into a fault slip model for the 2019 Mw7.1 Ridgecrest earthquake and find more than 1 meter of slip taking place during the first hours of postseismic deformation compared to daily estimates of coseismic motion.

Citation
Golriz, D., Bock, Y., & Xu, X. (2020, 08). Distinguishing the Coseismic Phase of the Earthquake Cycle 
with Seismogeodesy. Poster Presentation at 2020 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy