SCEC Award Number 16100 View PDF
Proposal Category Individual Proposal (Data Gathering and Products)
Proposal Title Impact of atmospheric models in Southern California on InSAR contribution to the CGM
Investigator(s)
Name Organization
Rowena Lohman Cornell University
Other Participants Graduate student: Either Chelsea Scott or Kyle Murray
SCEC Priorities 1d, 1e, 5b SCEC Groups Geodesy, Transient Detection
Report Due Date 03/15/2017 Date Report Submitted 03/31/2017
Project Abstract
 Tropospheric phase delays pose a major challenge to InSAR (interferometric synthetic aperture radar)-based studies of tectonic deformation. One approach to the mitigation of effects from tropospheric noise is the application of elevation-dependent corrections based on empirical fits between elevation and interferometric phase. We quantify the effects of corrections with a range of complexity on inferred earthquake source parameters using synthetic interferograms with known atmospheric characteristics. We infer statistical properties of the stratified component of the atmosphere using pressure, temperature, and water vapor data from the North America Regional Reanalysis model over our region of interest in the Basin and Range province of the western United States. The statistics of the simulated atmospheric turbulence are estimated from InSAR and Global Positioning System data. We demonstrate potentially significant improvements in the precision of earthquake magnitude, depth, and dip estimates for several synthetic earthquake focal mechanisms following a correction for spatially variable atmospheric characteristics, relative to cases where the correction is based on a uniform delay versus elevation relationship or where no correction is applied. We apply our approach to the 1992 M5.6 Little Skull Mountain, Nevada, earthquake and demonstrate that the earthquake source parameter error bounds decrease in size after applying the atmospheric corrections. Our approach for evaluating the impact of atmospheric noise on inferred fault parameters is easily adaptable to other regions and source mechanisms.
Intellectual Merit As InSAR data coverage improves, researchers are attacking problems with more and more subtle signals - this comes along with added risk that spatially correlated noise sources will be mapped into fault motion, aquifer drawdown, etc. Our work (published with a more detailed workflow in Scott and Lohman, 2016) outlines a method for using synthetic data to assess potential biases and likely error bounds that should be placed on such products in the presence of the expected variations in the troposphere.
Broader Impacts This project supported the work of Chelsea Scott while she was a graduate student. She has now gone on to a postdoc with Ramon Arrowsmith at ASU. The work, programming and much of the idea for the work all came from Chelsea Scott - Lohman participated primarily through aid in writing and figure critiques.
Exemplary Figure Figure 1: Results of 100 earthquake simulations for each correction approach, fault geometry, and depth. Constraints on earthquake magnitude, depth, dip, and stress drop for a 30° dipping normal fault (first column), 60° dipping normal fault (second column), and a vertical strike-slip fault (third column) from applying no atmospheric correction (black), a correction for constant atmospheric properties (blue), and a correction for variable atmospheric properties (red). The black, blue, and red dots show the inferred median parameter value, and the error bars show the 16th to 84th percentiles (i.e., 1σ) of the resulting ensemble. The green lines show the input value of each respective parameter.