Resolving simulated sequences of earthquakes and fault interactions

Valere R. Lambert, & Nadia Lapusta

In Preparation May 3, 2020, SCEC Contribution #10089

Physics-based numerical modeling of earthquake source processes aims to combine available real-world data and physical principles to improve our understanding of fault behavior, with the loftier dream of developing models that have predictive power for quantities of interest for seismic hazard, such as the probability of an earthquake rupture jumping from one fault segment to another. Fault network-scale earthquake simulators aim to examine the long-term statistics of earthquake ruptures spanning multiple fault segments, and have been shown to be capable of reproducing frequency-magnitude statistics of some fault populations. However, due to computational limitations, these simulators must employ a number of simplifications, including inertial (wave-mediated) effects and the use of large computational cells. Here, we examine the sensitivity of numerical earthquake sequence simulations to choices in numerical discretization and approximations for inertial effects, using a simplified 2D model of a crustal fault with two co-planar fault segments separated by a relatively strong velocity-strengthening barrier. We find that the use of over-sized cells and quasi-dynamic approximation for inertial effects can qualitatively alter the long-term history of fault interactions, and particularly the rate of two-segment ruptures. Moreover, we find that reproducing earthquake frequency-magnitude statistics and static stress drops does not provide sufficient constraint for the rate of two-segment ruptures, which can range from 0 to 1 for models with comparable statistics. Our results emphasize the need to examine the sensitivity of numerically-derived solutions to the choice of numerical procedure and physical assumptions, particularly when assessing their predictive value for seismic hazard assessment.

Lambert, V. R., & Lapusta, N. (2020). Resolving simulated sequences of earthquakes and fault interactions. Journal of Geophysical Research: Solid Earth, (in preparation).