Toward a Continuous Monitoring of the Horizontal Displacement Gradient Tensor Field in Southern California Using cGPS Observations from Plate Boundary Observatory (PBO)

William E. Holt, & Gina Shcherbenko

Published 2013, SCEC Contribution #1779

We have developed a cGPS network-processing tool for detection of anomalous strain transients within the Plate Boundary Observatory network in southern California. Position estimates from cGPS are interpolated (through a joint inversion of strains and position estimates) to provide a model solution for the horizontal displacement gradient tensor field as a function of time. Regularization of the solution is achieved by adjusting a single isotropic strain variance parameter until the reduced chi-squared misfit between model and observed displacement approaches 1.0. Additional constraints are provided by a priori information on fault style and orientation, along with the application of Pacific-North America displacement boundary conditions. A geodetic reference solution is subtracted from the epoch solution and the significance of residual strains is tested using a t-statistic. Tests using synthetic cGPS observations, generated in the SCEC IV Transient Detection Exercise, show that anomalous strains associated with slow-slip over 6-8 week time frames, totaling less than 1 cm, can be detected with high confidence (assuming uncertainties in daily positions estimates of ± 3 mm). Analysis of PBO cGPS time series since July 2010 shows a complex field of significant anomalous strain, primarily associated with post-seismic processes.

Citation
Holt, W. E., & Shcherbenko, G. (2013). Toward a Continuous Monitoring of the Horizontal Displacement Gradient Tensor Field in Southern California Using cGPS Observations from Plate Boundary Observatory (PBO). Seismological Research Letters, 84(3), 455-467. doi: 10.1785/0220130004.