SCEC Award Number 14138 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Long-term behavior of faults with heterogeneous strength
Investigator(s)
Name Organization
Nadia Lapusta California Institute of Technology
Other Participants Junle Jiang, graduate student
SCEC Priorities 3c, 3e, 6b SCEC Groups FARM, CS, SoSAFE
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 Dynamic rupture simulations suggest that fault heterogeneity can strongly influence dynamic rupture and earthquake patterns. Its effects are typically studied in simulations of isolated dynamic events. To study the long-term effects of heterogeneity, we simulate earthquake sequences and slow slip in fault models with laboratory-derived friction laws, including enhanced co-seismic weakening due to shear heating. We find that large earthquake events can penetrate into deeper creeping regions, if enhanced co-seismic weakening is activated. Such deeper penetration results in much diminished concentration of seismicity at depth in the interseismic period; the seismicity would be expected otherwise to concentrate at the bottom of the seismogenic zone. This simulated behavior is consistent with observations on some major fault segments with large historical events. In simulations, fault segments hosting such deeper-penetrating earthquakes are characterized by deeper coseismic slip, larger spatial extent of ground motion, and time-dependent locking depths. One important implication is that using interseismic geodetic observations alone may underestimate the rupture extent of such earthquakes. Variability in arresting depth is determined by the combination of permeability and shear zone width that controls the efficiency of thermal pressurization, and also by dynamic properties of earthquake rupture. In addition, presence of nucleation-promoting spots affects recurrence times of larger events, and hence their slip and arresting depth. Further analysis suggests that the statistics of the resulting microseismicity is related to variations in fault coupling and stress. Hence the statistics is potentially useful for constraining fault properties at rheological boundaries.
Intellectual Merit The main goal of this work is to study how dynamic rupture behavior and earthquake patterns evolve in the presence of fault heterogeneity over long-term fault slip, using laboratory-derived friction laws including enhanced coseismic weakening due to shear heating. To study the long-term effects of heterogeneity, we simulate earthquake sequences and slow slip in fault models with laboratory-derived friction laws, including enhanced co-seismic weakening due to shear heating. Such simulations reveal how prior slip affects earthquakes and how large earthquake ruptures interact with fault heterogeneity. We focus on exploring the variability in earthquake slip and arresting depth in fault models with depth-dependent fault properties and incorporation of both flash heating and thermal pressurization of pore fluids. Our simulations reveal that deeper penetration is indeed possible for realistic physical properties based on laboratory and field studies. Variability in arresting depth is determined by the combination of permeability and shear zone width that controls the efficiency of thermal pressurization, and also by dynamic properties of earthquake rupture. In addition, presence of nucleation-promoting spots affects recurrence times of larger events, and hence their slip and arresting depth. Further analysis suggests that the statistics of the resulting microseismicity is related to variations in fault coupling and stress. Hence the statistics is potentially useful for constraining fault properties at rheological boundaries.
Broader Impacts Large-scale dynamic rupture simulations carried out by SCEC teams have the potential to provide novel and critical information for the assessment of seismic hazard in Southern California. The results of this project, when further developed, would (a) provide better understanding of the long-term behavior of faults, including nucleation conditions and seismicity at rheological boundaries; (b) provide better assessment of seismic hazard and evaluation of possible extreme events, based on physical models and integrations of laboratory, field and seismological studies; and (c) contribute to the development of realistic scaling laws for large events. A student and a postdoctoral fellow have gained valuable research experience by participating in the project and interacting with the SCEC community.
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