SCEC Award Number 21180 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Toward kinematic earthquake cycle models with a 3D viscous mantle rheology model for Southern California
Investigator(s)
Name Organization
Kaj Johnson Indiana University
Other Participants
SCEC Priorities 3g, 1a, 1c SCEC Groups SDOT, CXM, Geodesy
Report Due Date 03/15/2022 Date Report Submitted 11/15/2024
Project Abstract
 In 2021 we were funded to examine the influence of 3D mantle viscosity model son the present-day geodetically determined surface velocity field by building viscoelastic cycle models for southern California. We proposed to expand a fault-based model with an elastic crust over viscous mantle developed previously by PI Johnson to the entire southern California region. In previous studies we have used 1D, layered viscous models to construct earthquake cycle models. In this current work, we also develop 3D mantle viscosity models. The objective of this work is to examine the influence of often-neglected modeled time-dependent mantle flow on present-day predictions of surface deformation.

This project ended up being much more difficult than anticipated, yet we continue to develop earthquake cycle model calculations for southern California. In the middle of this project, we decided we had to abandon the use of computer code PyLith for these calculations. PyLith does not yet have a stable implement of gravitational restoring forces, and we could only run calculations without gravity. Instead, we have spent a substantial amount of time in the last three years developing a workflow to utilize Fred Pollitz visco3D spectral element codes into our earthquake cycle models. We have also continued our use of semi-analytical layer-cake (1D) viscoelastic cycle models to examine the influence of mantle relaxation on present-day strain rates in California.
Intellectual Merit We have developed a workflow to compute earthquake cycle deformation models using Greens functions computed with visco3d, the fully three-dimensional implementation of the Pollitz spectral element code which computes deformation in a gravitating spherical earth. This workflow can be used to generate viscoelastic Greens functions and earthquake cycle simulations for California.
Broader Impacts This project helped fund the PhD research of Indiana University graduate student Elizabeth Sherrill.
Exemplary Figure Figure 1.

Illustration of a viscoelastic earthquake cycle model for subduction zones consisting of elastic plates overlying viscoelastic mantle. This model can also be generalized to other tectonic settings (e.g., California’s transform system).
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