SCEC Award Number 16038 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Towards consensus time series analysis for the Community Geodetic Model
Investigator(s)
Name Organization
Thomas Herring Massachusetts Institute of Technology Michael Floyd Massachusetts Institute of Technology
Other Participants Lei Wang
SCEC Priorities 1d, 1e, 5b SCEC Groups Transient Detection, SDOT, Geodesy
Report Due Date 03/15/2017 Date Report Submitted 03/15/2017
Project Abstract
 The SCEC Community Geodetic Model (CGM) relies on consensus regarding the processing and ingestion of geodetic data, primarily GPS and InSAR. We focus on the GPS component of the CGM. A number of processing centers, many of which are based in southern California, produce time series on an operational basis. We have developed tools to read and combine each of these time series into a single product. Our combined time series are now available for distribution in any agreed manner and we are able to produce updates to the time series at any time, or on a regular basis, as required by the SCEC CGM. In anticipation of the existence of a web portal or other centralized access area for the SCEC CGM, we have proposed and continue to work on developing an "extended" time series format, which may be used to include one or more models derived from any chosen approach to time series analysis. These may then be removed by any user as they wish, depending on their analysis needs and intention to remove perturbations such as displacements due to earthquakes or offsets due to equipment changes within their own analysis.
Intellectual Merit A community set of geodetic data, both GPS and InSAR, is a core product for any solid Earth deformation project. The benefit of producing a “community” product is that the efforts of those most knowledgeable about the aspects of the data are able to exercise their expertise, leaving those who are less concerned with data acquisition and product generation to focus on the analysis for scientific gain. Furthermore, such a product serves as the basis for other analytical work regarding changes to the background time series or velocity product. Such perturbations have already been explored during SCEC Transient Detection Exercise. There is generally much debate about how best to produce any geodetic product but it is often by combining, and therefore averaging, several different products that the most stable and reliable results are achieved rather than relying on any one product stream. This is the approach we have taken with our contribution to the SCEC CGM with GPS time series and we believe that the best combined product results. Our analyses to date have raised a number of fundamental questions about the approach taken by processing centers and the accuracy of their resulting products, although we have also shown that, given similar treatment regarding fits and transformations to the fundamental time series, products are generally perfectly equivalent within their level of uncertainty.
Broader Impacts The primary benefit of the CGM, as with all SCEC's Community Models, is to provide a simple and accessible product to the scientific community and public at large. The CGM in particular, and especially the GPS component of it, directly contributes to SCEC’s facilities, in that it is a distributable product that anyone can use at any time for any purpose. Civil and industrial partners may use the fundamental geodetic products, or products derived relative to the CGM such as outputs from the Transient Detection Exercise. These may inform both long- and short-term (in the case of, say, an earthquake) decisions regarding hazard and response. Furthermore, the readily available products, if well known and used in the public sphere, support the maintenance of the networks of instruments that measure, and centers that process, the data. Lastly, simple geodetic products can also serve as intuitive data sets that may be used and studied at all levels of education in schools and universities.
Exemplary Figure Figure 1 Combined InSAR and GPS data for the coseismic phase of the South Napa earthquake. The majority of GPS sites (yellow vectors) near the rupture (bold red line) are survey GPS sites. Continuous GPS sites are further afield, around the periphery of this figure’s boundary. Modified from Floyd et al. (2016).
Floyd, M. A., Walters, R. J., Elliott, J. R., Funning, G. J., Svarc, J. L., Murray, J. R., Hooper, A. J., Larsen, Y., Marinkovic, P., Bürgmann, R., Johanson, I. A., & Wright, T. J. (2016). Spatial variations in fault friction related to lithology from rupture and afterslip of the 2014 South Napa, California, earthquake. Geophysical Research Letters, 43(13), 6808-6816. doi: 10.1002/2016GL069428. SCEC Contribution 7126.