DOI: 10.5281/zenodo.4926527
title: Southern California Earthquake Center (SCEC) Community Geodetic Model (CGM)

description: Overview
Measuring accurately the relative movement of the surface of the Earth is a critical constraint on the slow and broad tectonic loading and unloading to which faults respond, and is one of the few observations of the solid Earth that may be made directly without inference. High-precision geodetic observations, such as from Global Navigation Satellite Systems (GNSS), which includes the Global Positioning System (GPS), and interferometric synthetic aperture radar (InSAR), allow measurement of fault motions between, during and in the aftermath of earthquakes and other related tectonic phenomena, densely in both space and time.
The Community Geodetic Model (CGM) provides velocities and time series of observed points on the Earth's surface over Southern California using data from a number of contributing researchers, institutions and analysis centers. The GNSS products provide high temporal resolution (nominally daily measurement points for continuous stations) in three dimensions at specific observation sites and the InSAR products provide high spatial resolution (approximately one point per tens of m on the ground, depending on exact specifications of data and processing). Combined, they provide the ability to study crustal deformation over a wide range of distances and periods.
The CGM differs from other SCEC Community Models in that it is constantly extending with time as new data are acquired daily, so it is not static.
The CGM version 1 (2016; doi:10.5281/zenodo.4926528) was a collection of time-independent (velocity-only) geodetic products gathered from published papers. The GNSS velocities were then combined and modeled by a Working Group researching methods and contributing interpolated deformation fields. The main goal of the CGM version 2 is to add time-dependent (time series) products to both the GNSS and InSAR products. For the GNSS, this is done by ingesting survey and (mostly) continuous time series from five analysis centers in the U.S.: the Geodetic Facility for the Advancement of Geoscience (GAGE); the Nevada Geodetic Laboratory (NGL) at the University of Nevada, Reno (UNR); the NASA Jet Propulsion Laboratory (JPL) and Scripps Orbital and Permanent Array Center (SOPAC) contributions to the MEaSUREs ESESES project; and the U.S. Geological Survey (USGS). Like the various contributions to the CGMv1 GNSS velocities, these time series are rigorously adjusted to be self-consistent, before a weighted mean is calculated to produce the consensus products. Much of the InSAR contribution is a consensus from research by the SCEC community within the CGM (InSAR) Working Group, whose individual contributions are listed below and in more detail in the README.txt file in the top directory of the archive. The CGMv2 is therefore a "union" or "superset" of survey and continuous GNSS and InSAR time series.
Please see https://www.scec.org/research/cgm for more information.
Version: CGMv2.0.0
This is the second major release of the CGM (version 2.0.0) and is distributed as a zip-file. See below and in the README.txt file for information about the directory structure and contents of the entire zipped archive. Much of the SCEC5 activity was focused on the assembly of GNSS and InSAR time series for measuring temporally variable motions, expanding the CGMv1 with the time dimension. The CGMv2.0.0 is a time-dependent set of products, consisting of time series and velocities of the Earth's surface measured by GNSS and InSAR.
Directory Structure and Contents
data/gnss/pos/The CGMv2.0.0 GNSS time series in "pos" format (plain text), relative to various reference frames described below. Header lines in each file provide information about the nominal reference coordinates and data columns. Files named "*.wmrss_*" are the continuous stations (weighted mean with rescaled sigma) and files named "*.final_" are the survey sites.
data/gnss/pos/igb14/ The International GNSS Service's (IGS's) revised realization of ITRF2014
data/gnss/pos/nam14/ North America defined by Altamimi et al.'s (2017) ITRF2014 plate motion model
data/gnss/pos/pcf14/ The Pacific defined by Altamimi et al.'s (2017) ITRF2014 plate motion model
data/gnss/pos/nam17/ North America defined by Kreemer et al. (2018)
data/gnss/vel/The CGMv2.0.0 GNSS velocities in a CSV file similar to GAGE's "vel" format (plain text), relative to the same reference frames described above. Header lines in each file provide information about the data columns.
data/insar/The CGMv2.0.0 InSAR line-of-sight consensus time series and velocities for four ESA Sentinel-1 tracks (ascending tracks 64 and 166, and descending tracks 71 and 173) over Southern California, in an HDF5 format designed for the CGM. A description of and reader for the HDF5 files may be found here.
data/insar/contrib/Individual contributions to the InSAR time series and velocity products, as described below and in more detail in the top-level README.txt file.
Contributors
The GNSS time series are a weighted mean, after restoration of global scale if processed using Gipsy (JPL, NGL/UNR and USGS) and self-consistent alignment of reference frame, of the following GNSS analysis centers, whose products are publicly available at the embedded hyperlinks:

The Geodetic Facility for the Advancement of Geoscience (GAGE) (Herring et al., 2016)
The Nevada Geodetic Laboratory at the University of Nevada, Reno (Blewitt et al., 2018)
NASA's Jet Propulsion Laboratory contribution to the MEaSUREs ESESES Project
SOPAC's contribution to the MEaSUREs ESESES Project
The United States Geological Survey (Murray and Svarc, 2017)
Zheng-Kang Shen's (UCLA) survey time series
Z.-K. Shen processed the raw data from the SCEC survey-mode GPS data archive to provide the corresponding time series and velocities. A. Gonzalez Ortega provided processed time series from CICESE's REGNOM network of continuous GNSS stations. M. Floyd and T. Herring designed the download, alignment and combination of the publicly available continuous GNSS archives, listed above, in various reference frames.
Contributions from individuals and institutions within the SCEC community to the CGM (InSAR) products are:

K. Wang contributed time series and velocity solutions
K. Guns and X. Xu contributed time series and velocity solutions
Z. Liu contributed time series and velocity solutions
S. Sangha, M. Govorcin and D. Bekaert contributed time series and velocity solutions
G. Funning contributed time series and velocity solutions
E. Tymofyeyeva calculated the combination of contributed solutions to generate the consensus product
K. Materna contributed time series and velocity solutions, and wrote the translation tools for converting to and from HDF5 format, as designed by all InSAR contributors listed immediately above plus M. Floyd
Three groups (K. Guns and X. Xu; Z. Liu; and S. Sangha, M. Govorcin and D. Bekaert) independently processed interferograms from common raw datasets using different processing approaches.
E. Tymofyeyeva coordinated and led the InSAR Working Group.
M. Floyd coordinated and led the wider CGM Working Group.
All contributed to the design of the HDF5 format in which the InSAR products are distributed.
description: The CGMv2.0.0 was supported by the Southern California Earthquake Center. SCEC5 was funded by U.S. National Science Foundation Cooperative Agreement EAR-1600087 and U.S. Geological Survey Cooperative Agreements G17AC00047 and G22AC00070. The research was partly carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).