SCEC Award Number 15193 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Effective Friction Laws for Fault-Scale Earthquake Rupture and Ground Motion
Investigator(s)
Name Organization
Eric Daub University of Memphis
Other Participants
SCEC Priorities 3c, 3d, 6b SCEC Groups FARM, DRCV, CS
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 This project uses dynamic rupture simulations on heterogeneous, complex faults to investi-gate methods to quantify frictional weakening at a larger scale. We have developed a finite difference code for simulating dynamic earthquake rupture that allows for flexible handling of different friction laws. To quantify the heterogeneity of frictional weakening, we examine how the effective slip weakening distance, defined as the fault parallel slip at the time of the peak fault parallel velocity, varies in space, both along the fault strike as well as with distance from the fault. We find that frictional information can be extracted for off-fault points near the fault. This frictional length scale estimate increases with distance from the fault, and is approximately 1.5-2 times larger than the true value at a distance of one cohesive zone length away from the fault. This effective weakening distance also varies along strike, and is related to the topography of the complex fractal fault surface. Our results suggest that one way to capture small-scale heterogeneity is through a spatially variable slip weakening distance.
Intellectual Merit Development of methodologies for simulating large scale earthquakes in Southern California is one of the central science goals of SCEC. In parallel, SCEC researchers have also been at the forefront of investigating the basic small-scale frictional mechanisms responsible for fault weakening. However, these efforts involve vastly different length scales. To support these goals of SCEC, this proposal develops a method for quantifying how to rescale physics-based friction laws for use in large-scale simulations.
Broader Impacts The earthquake rupture simulation code developed under this award is used for education purposes through PI Daub’s graduate class Earthquake Source Physics. The course involves a significant numerical modeling project using the code, and graduate students have used the code to tackle a range of projects, including coupling geodynamic and earthquake rupture models, and constructing dynamic source models for the 2008 Chino Hills and 2013 Lushan earthquakes.
Exemplary Figure Caption: (a) Normalized effective slip weakening distance using low pass filtered seismograms, defined as the slip at peak velocity, as a function of distance from the fault. Distance is normalized by the cohesive zone length, illustrating that the effective slip weakening distance generally increases as the observation point is moved away from the fault. The progression from light to dark colors indicates position along strike, with light colors closer to the hypocenter. (b) Variation of the normalized effective slip weakening distance along strike. The plot shows the estimate one cohesive zone away from the fault trace, using the estimate obtained from the filtered seismograms. The slope of the fault trace is shown for comparison (positive slope indicates a restraining bend in the fault profile). Larger values of the effective weakening distance tend to occur at transition from releasing to restraining bends.