SCEC Award Number 14171 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Earthquake Cycles Near Sedimentary Basins
Investigator(s)
Name Organization
Eric Dunham Stanford University
Other Participants Kali Allison (graduate student, Stanford University)
SCEC Priorities 3f, 4e, 2e SCEC Groups FARM, CS, Simulators
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 Variations in frictional properties along faults, like the transition from velocity-weakening to velocity-strengthening at depth, provide a leading order control on the location and timing of ruptures. Much insight has been gained by modeling the entire earthquake cycle with realistic friction laws, though with a few notable exceptions, these simulations have all been conducted in uniform elastic half-spaces. Yet substantial variations occur also in off-fault material properties, with potentially important consequences on earthquake sequences. Most notably in Southern California, many active faults pass through or near sedimentary basins, regions of greatly reduced elastic moduli.

In this project, we seek to answer the general question, how do sedimentary basins influence the occurrence of earthquakes on nearby faults? Preliminary SCEC-funded cycle modeling by our group [Erickson and Dunham, 2014] has shown that basins can both arrest and facilitate ruptures; earthquake sequences for faults cutting through basins exhibit an alternating sequence of sub-basin events (ruptures nucleating at depth that terminate at the bottom of the basin) and surface-rupturing events (ruptures nucleating at depth that penetrate through the basin all the way to the surface).

Over the past year, we developed a parallel, C++ code to investigate earthquake cycles with heterogeneous material properties. This new code is an order of magnitude faster than our previous code. We have more fully searched parameter space to confirm that deep, compliant basins give rise to sub-basin/surface-rupturing event cycles. Both the LA Basin and Salton Trough lie within this interesting part of parameter space. We have also imported material properties from the SCEC Community Velocity Model and begun simulations of ruptures on the Imperial Fault.
Intellectual Merit Sedimentary basins are common throughout Southern California, and many active faults pass near or through basins. Our work demonstrates the important influence that compliant sedimentary layers play on earthquake occurrence. Developing an understanding of what types of ruptures are expected, as a function of lithology, will permit us to predict whether certain fault segments are likely to exhibit creep or should participate in large, surface-rupturing events. Developing earthquake cycle simulation capabilities that properly account for elastic heterogeneity are required to address these questions. Such simulation tools are also the first step toward incorporating more realistic material response, including off-fault plasticity and viscoelasticity, which are presently neglected in most simulators.
Broader Impacts This project supported a female graduate student (Kali Allison) and involves collaboration with a female junior faculty member (Brittany Erickson). Our simulations also advance simulator capabilities.
Exemplary Figure Figure 1: System behavior as a function of basin depth and rigidity, with velocity-weakening properties extending through basin. Deep, compliant basins give rise to sequences of alternating sub-basin and surface-rupturing events. Also shown are properties of the LA Basin and Salton Trough; both are within this interesting part of parameter space. [Allison, Erickson, Dunham, work in progress, 2015]