Dr. Bruce Shaw
Earth Institute Contact: Dr. Bruce Shaw
Geometrical and material heterogeneities in faults have been viewed as a crucial feature affecting earthquake behavior. More recently, the role of stress heterogeneities has begun to be recognized as a potentially central feature, particularly with the demonstration that stress heterogeneities alone already can produce a remarkably rich and complex set of earthquake-like behaviors on uniform planar faults. What is missing is an understanding of how the two types of heterogeneities, the static geometrical and material heterogeneities, and the dynamic stress heterogeneities, might combine and interact to produce even more realistic behavior.
This research seeks to further develop a line of modeling which extends elastodynamic simulations to nonplanar geometries. Specifically, the aim is to develop simulations of rough fault geometries. By studying long sequences of events on the faults, the dynamical attractor develops, and thus the interaction of stress heterogeneities with any geometrical heterogeneities can be examined. Having developed the technology, a set of applications which connect the model with observations will be pursued. Three projects are proposed:
o One concerns the examination of normal stress effects on friction. Classical formulations of friction incorporate normal stress through a simple multiplicative dependence on its instantaneous value. This zeroth order approximation has been shown to be inadequate in reproducing experiments, where non-instantaneous memory effects are observed. In the rough fault context we will need a better formulation of the normal stress dependence, and an examination of potential formulations and their implications will be done. This work has broad implications for a wide variety of scientific and technological fields where dynamic friction arises.
o A second project concerns the interaction of geometrical and dynamic heterogeneities, and their expression in earthquake behaviors. The relationship between geometrical heterogeneities and rupture initiation and arrest will be one expression examined. This work has major implications for earthquake hazard estimation based on geometrically defined segmentation. Stress effects.
o A third project concerns aftershocks. While the time delay of aftershocks have clear explanations, the spatial distribution has yet to be successfully reproduced. Most puzzling are the aftershocks which apparently occur on the fault surface which has just ruptured. Jim Dieterich has suggested rough faults may be the key to resolving this puzzle. This project would explore this hypothesis. This work has important implications for understanding aftershocks, and for short term earthquake hazard estimates based on aftershock probabilities, during which relative hazard rates rise many orders of magnitude above background rates.
In addition to the broader impacts mentioned above, from dynamic friction effects relevant across a range of engineering and technological fields, and seismic hazard estimation used in policymaking and construction, this work will further the educational mission of the NSF, through support of a graduate student. It will additionally support the aim of enhancing diversity in science, as the Ph.D. student planned for the research is female.
Cross Cutting Themes:
Hazards and Risk