The Earth's response to large earthquakes does not end when the seismic shaking dies away. Large earthquakes substantially change forces (stresses) within the Earth, and by measuring and modeling the response to these changes, we can learn about the mechanical properties of deep fault zones and the material that surrounds them. This time-dependent and transient response of the Earth produces postseismic deformation, which we will measure using high-precision GPS. A key challenge of postseismic deformation studies is to separate the effects of the two main mechanisms, afterslip or continued slip on the deep fault plane, and viscoelastic relaxation within the mantle and/or lower crust. In the first few years after the earthquake, these two mechanisms can produce similar deformation at the surface of the Earth, but they decay with time at different rates. In this project, we will use a long record of data (up to 15 years) following the 2002 Denali fault earthquake to develop a complete model for the postseismic deformation following this earthquake. This improved mechanical model will allow us to better understand the forces that drive tectonic deformation in Alaska, and the interaction between earthquakes.
We will carry out GPS surveys of a dense network of sites surrounding the 2002 fault rupture. These data will provide important spatial resolution to complement the sparse continuous GPS network from the Plate Boundary Observatory, which provides critical information about the time evolution of the postseismic deformation. We will carefully examine the observed deformation to identify observations that can be explained entirely or mostly by a single postseismic mechanism, if possible, which makes it easier to constrain model parameters. We will recalculate a new coseismic slip distribution using a finite element code that can utilize the full 3-D inferred elastic Earth structure, including the subducting slab, so that we can most accurately compute the postseismic response to the slip. We will develop 3D finite element models and other models to explain the observed deformation, and evaluate how these models would respond to other stress changes like the 1964 earthquake, or glacial unloading. We will share information about the Denali fault, earthquakes in Alaska, and the results of this project with the public through interaction with Denali National Park. The Park hosts about 400,000 visitors each year and coordinated outreach efforts with the Park offer a chance to reach a broad audience.
