SOPAC Refined Model Documentation

Site coordinates, velocities and time series are created by a SOPAC refined model (Nikolaidis, 2002) that takes into account offsets (co-seismic or otherwise), linear velocity, and annual and semi-annual fluctuations (for stations that have at least two years and one year of data, respectively). For stations that experience post-seismic relaxation, an exponentially decaying term is also estimated. In some cases where a station experiences coseismic and post-seismic deformation, changes in the linear velocity are also estimated. These parameters can be viewed via the refined model terms utility.

Input data provided to the model are the daily processed site positions calculated at SOPAC using the GAMIT and GLOBK software packages. Coordinates from the most recent SOPAC weekly processing run are available, and are generated using data for that week only. Conversely, products from the refined model (e.g., coordinates) are calculated based on the entire timeseries for a site.

All parameters are estimated with full white noise + flicker noise covariances based on a noise analysis of the GPS position time series. Their uncertainties can thus be considered realistic estimates, based on our data analysis.

For sites in the western United States, filtered coordinates are available. This includes sites in the BARGN, BARD, EBRY, PANGA, and SCIGN permanent GPS networks, and western U.S. sites in the CORS network.

The regional filtering is carried out in space domain. By stacking the time series from a group of core sites, a time series containing common noises for the region can be derived, which will then be subtracted from individual time series to improve positional estimates. Unfiltered time series are also available for these sites. For all other sites, only unfiltered time series are available. No regional filtering is performed for these sites.

Regionally filtered/unfiltered model terms for all processed sites are available by downloading the cleaned neu filtered/unfiltered time series tar file at http://garner.ucsd.edu/pub/timeseries. In this tar file, each "siteClean[Flt|Unf].neu.Z" file header contains the refined model terms for each site.

Please contact the webmaster if you have any questions.

Reference:

Nikolaidis, R., Observation of Geodetic and Seismic Deformation with the Global Positioning System, Ph.D. Thesis, University of California, San Diego, 2002

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