SCEC Award Number 14127 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Contributions to the CGM and non-secular motion representation
Investigator(s)
Name Organization
Thomas Herring Massachusetts Institute of Technology
Other Participants Michael Floyd
SCEC Priorities 1d, 1e, 5b SCEC Groups Geodesy, SDOT, Transient Detection
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
We are undertaking the tasks of collating, analysing and combining processed time series to produce Community Geodetic Model (CGM) final products. This necessarily includes formalizing metadata documentation formats for distribution in the eventual CGM. We are also exploring advanced techniques for determining the variable nature of seasonal fluctuations in geodetic time series, as well as accounting for correlations between components and sites. Lastly, we have started to investigate techniques for the consistent and precise recovery of secular velocities in the presence of time-dependent deformation such as post-seismic decays. This is especially important but challenging in the case of little or no pre-earthquake data, such as for the 1992 Landers, 1994 Northridge and 1999 Hector Mine earthquakes. Accurate recovery of secular geodetic velocities requires accounting for on-going post-seismic motions, such as after the Parkfield, El Major-Cucapah and South Napa earthquakes, even where pre-earthquake data are available so that newer data may be incorporated into on-going motion estimates.
Intellectual Merit Our research is contributing to the development of the Community Geodetic Model through data acquisition, organization and analysis. These activities are targeted at developing an understanding of the complex deformation modes California and the relationship of this deformation to earthquake occurrence. Our current analysis of continuous GPS solutions is very technical as we assess the agreement and differences between results generated by different analysis groups. Once this phase is completed and we will be able to generate with confidence a combined time series motion model for California with realistic assessments of the noise and systematics in the series.
Broader Impacts The opportunity presented by the South Napa earthquake in particular, with the rich geodetic data set acquired, is unique even by California standards. High-quality pre- and post-earthquake measurements allow us to map zones of differing co- and post-seismic behavior on the fault plane with high spatio-temporal evolution. We may then infer whether such processes occur on other faults throughout California, how such processes may be related to physical characteristics, such as frictional variations, and their influence on the earthquake cycle as we currently understand it. Continued exploitation and study of such examples anywhere in California is therefore highly valuable to the SCEC community and beyond.
Exemplary Figure Figure 2: Left: Current GPS velocity solution relative to the Pacific plate in the North San Francisco Bay Area, which contributes denser GPS data to the Community Geodetic Model in this region. Velocities do not include data from after the 2014-08-24 South Napa earthquake (red star; discussed below). Right: Displacement of near-field survey GPS sites (except P199 and P200) operated continuously from within one day of the South Napa earthquake. Time series are plotted from the day of the earthquake relative to their pre-earthquake velocities shown in the left-hand figure and fit with a logarithmic decay function x=a ln⁡(1+((t-t_"eqk" )/τ)).