The Colorado Plateau, southwestern United States, has played an important role in the geologic evolution of the Pacific-North America plate boundary zone. Unlike most other parts of the western U.S., the Colorado Plateau has remained largely intact during most of its geologic history. Indeed, the area shows little to none active earthquake faults. However, earthquakes do happen within the Colorado Plateau, and some very large ones have occurred in southern Arizona and northern Mexico.
This project uses precise GPS measurements to establish how the crust of the Colorado Plateau moves relative to stable North America. Interpretation of the horizontal velocities tells the investigators whether the area moves as a coherent block or is internally deforming. In case of the former little earthquake activity is expected, and in case of the latter the seismic hazard in the region may be higher than currently thought. The deformation implied by the GPS data and earthquake data is compared in order to assess whether the earthquake activity can be related to the deformation measured in this project or whether they are due to other processes, such as gravitational collapse.
To perform the measurements, 33 new GPS stations are installed in Arizona, southern Utah and southeastern Nevada. These stations complement and densify the long-running continuous GPS stations of NSF EarthScope's Plate Boundary Observatory. The additional stations are needed to create well-constrained models to describe the region's present-day tectonics. With a well-constrained model of the deformation can the origin of the motion and deformation of the Colorado Plateau be investigated. Some of the models that are considered include a rigid motion of the plateau causing opening of the Rio Grande Rift, crustal extension encroaching into the plateau due to evolving mantle processes, and the effect of Pacific plate motion on the deformation of the southern Basin and Range.
Many of the new GPS stations are installed in National Parks and Monuments, as well as in State Parks. The investigators provide educational material to inform the parks on the active tectonics of the region and the aim of the project. The goal of these outreach activities is to educate the parks' visitors that the geologic wonderland they are in is actively changing due to geologic processes. Measurements are made for four years and the project involves training of a graduate student. The outcome of this project may be used in a reassessment of the seismic hazard in the region?s urban centers.
