AuthorMcFarland, Phillip Kenneth
AdvisorBennett, Richard A.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction, presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractContinuous global navigation satellite system (cGNSS) ground tracking station data are commonly used in the study of active tectonics to measure crustal deformation at plate boundaries. In this work, surface crustal velocities for 29 cGNSS stations from the southern central Andes are presented in a South-America-fixed frame for a transect across the Puna Plateau, Eastern Cordillera, and Santa Barbara System for the time span between two major megathrust earthquakes: the 27 February 2020 Maule and the 1 April 2014 Iquique earthquakes. The surface crustal velocities exhibit a systematic decrease in magnitude from roughly 35 mm/yr near the Peru-Chile trench to less than 1 mm/yr within the stable craton. The contribution to the velocity field due to loading on the Nazca-South America (NZ-SA) subduction interface was modeled using back-slip on elastic dislocations to approximate a fully locked interface from 10 to 50 kilometers depth. For this modeling, an ensemble of models was generated by iterating over the percentage of NZ-SA convergence accommodated at the subduction interface. Velocity residuals calculated for each model demonstrate that locking on the NZ-SA interface is insufficient to reproduce the observed velocities. In order to fully fit the velocity field, a supplemental back-arc décollement model was employed comprising an edge dislocation for which parameters were estimated using the velocity residuals for each forward model of the subduction interface ensemble using a Bayesian approach. The best fit to the thrust-perpendicular velocity field was realized with 70 ± 5 % of NZ-SA convergence accommodated at the subduction interface and a slip rate of 9.1 ± 0.9 mm/yr on the fold-thrust belt décollement. The locking depth for the décollement was estimated to be 14 ± 9 km, which places the down-dip extent of the locked zone 135 ± 20 km from the thrust front. The thrust-parallel component of the velocity field was fit by a constant shear strain rate of -19×〖10〗^(-9) yr¬-1, equivalent to clockwise rigid-block rotation of the back arc at a rate of 1.1 /Myr.
Degree ProgramGraduate College