Tools for GNSS application to tectonics

Jay W. Parker, Michael B. Heflin, & Andrea Donnellan

Published August 12, 2019, SCEC Contribution #9438, 2019 SCEC Annual Meeting Poster #215

We propose a common set of tools for regional GNSS time series analysis. To retrieve regional time-limited sets of time series for earthquakes and other phenomena simple scripting elements reduce the varieties of center-specific formats to a selection of stations matching limits in time and space and an array of detrended E,N, U time series values, based on current databases at any center among JPL, NGL, SIO, and PBO. In order to study tectonics, detrended series RMS apart from earthquakes are reduced by removing stations with any component RMS greater than three times the smallest station RMS. Stations are also removed if occupancy is below 95%, with missing data linearly interpolated using nearest values of that single-component time series. SVD-based principal components analysis (PCA) is used to remove regional common mode error (CME), known to corrupt earthquake-based jumps in the medium to far field. Comparison of common mode error during tectonically quiet times among different centers helps identify processing strategies that reduce CME. Standard products include time series corrected for CME, spatial and temporal modes of PCA, autocorrelation and spectra of PCA time series, tabular and KML maps of CME-corrected jumps and PCA modes. Removing CME from large earthquake regions presents a challenge, as PCA cannot separate the earthquake-related signals from the CME. We implement a strategy in four steps: first, eliminate nontectonic stations based on several years of time series before the earthquake. Second, create a set of stations forming a halo about the earthquake, by using the previous passing stations for a time period including the earthquake and finding those that meet the RMS threshold requirement. Perform PCA using this halo set. The CME for the halo set is the same CME present in the full, earthquake affected set. Third, construct a CME series from the halo set and subtract it from each time series in the full set. Fourth, compute jumps using this corrected set. In this way a CME-free earthquake jump set is produced for graphical display and use in inversion.

Key Words
Earthquake,geodesy,common mode error

Citation
Parker, J. W., Heflin, M. B., & Donnellan, A. (2019, 08). Tools for GNSS application to tectonics. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy