SCEC Award Number 18174 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Optimizing and further developing simulations of sequences of earthquakes and aseismic slip
Investigator(s)
Name Organization
Nadia Lapusta California Institute of Technology
Other Participants PhD student Valère Lambert
SCEC Priorities 5a, 1e, 2e SCEC Groups FARM, CS, SDOT
Report Due Date 03/15/2019 Date Report Submitted 04/26/2019
Project Abstract
 Fault processes involve both sequences of dynamic events (earthquakes) and complex patterns of quasi-static (aseismic) slip. For physics-based predictive modeling of destructive large dynamic events, it is important to consider sequences of earthquakes and aseismic slip (SEAS), because prior slip events, in-cluding aseismic slip, may determine where earthquakes would nucleate, as well as modify stress and other initial conditions before dynamic rupture. Furthermore, such simulations provide a framework for determining physical properties consistent with a range of observations including geodetically recorded surface motions, microseismicity, past (including paleoseismic) events, and thermal constraints, and hence inform us about the current state of a fault segment or system and potential future rupture scenari-os. However, simulating long-term slip histories is quite challenging because of the variety of temporal and spatial scales involved. We have been developing a boundary-integral methodology (BIM) for simu-lations of SEAS; in part, we have expanded our BIM methodology to include along-fault diffusion and compared the accuracy and efficiency of different variable time-stepping schemes. We have also partici-pated in the code comparison initiated by Drs. Erickson and Jiang. In addition, we have developed a benchmark for future code comparison, on interaction between two seismogenic (velocity-weakening) fault segments separated by a velocity-strengthening barrier, a problem of high relevance to the issue of rupture jumps between segments and UCERF. Our findings show that quasi-dynamic treatment of wave-mediated stress changes and using oversized cells significantly affects the long-term behavior of the model, including the probability of jumps.
Intellectual Merit Our study aims to verify, optimize and develop codes that simulate earthquakes sequences and aseismic slip, including the problems of earthquake jumps between segments. Our goal is two-fold: (i) improve the boundary-integral approach for simulations on planar faults by incorporating a range of physical in-gredients, including representations of fluid flow, fault roughness, and off-fault inelasticity and (ii) in-corporating inelastic bulk and complex geometries more rigorously, through finite element approaches such as PyLith and/or the combination of PyLith and our BIM approaches.
Broader Impacts
The results of this project, when further developed, would (a) provide better understanding of the long-term behavior of faults; (b) provide better assessment of seismic hazard and evaluation of possible ex-treme 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. Two graduate students and an undergraduate research student have gained valuable research experience by participating in the project and interacting with the SCEC community.
Exemplary Figure Figure 2: Slip history for 4000 years of simulated earthquake sequences illustrating the variabil-ity in the rate of ruptures jumping across a velocity-strengthening barrier for the same fault properties, but including vs. excluding inertial effects (a vs. b) and properly resolving the simu-lation vs. using over-sized cells (b vs. c). Contours in blue represent earthquakes that rupture across both strands whereas contours in red represent events that remain isolated on a single segment. The histograms on the left show the occurrence of events with different magnitudes throughout the 4000-year sequence of each simulation; the use of oversized cells results in more complexity in terms of the presence of small events produced (Lapusta, 2018; Lambert and Lapusta, 2019).