Modeling low-frequency earthquakes on a rate-and-state fault

Zhichao Shen, & Nadia Lapusta

Published August 13, 2018, SCEC Contribution #8462, 2018 SCEC Annual Meeting Poster #191

Benefitting from the dense seismic networks deployed over the past two decades, the discovery of low-frequency earthquakes (LFEs) has enhanced our vision of the fault slip behavior. Compared to regular earthquakes of the same magnitude, LFEs are depleted in high frequency signals but are inferred to still represent shear slip. Seismologically, LFEs are characterized as events with small magnitudes (Mw0.3 ~ Mw2.6), long durations (0.2 s ~ 0.5 s), and low stress drops (1 kPa ~ 30 kPa). Given these observations, two views are possible regarding the origin of LFEs. One is that the sources of LFEs are regular earthquakes, but their seismic measurements are biased by strong near-source attenuation. The other is that the source process of the LFEs is conceptually different. In this work, we show that LFE-like events can be produced on rate-and-state faults with sub-critical velocity-weakening (VW) patches and typical rate-and-state properties, supporting the second view. For the sizes d of the VW patch that are 0.7-0.95 of the theoretical estimate h* of the nucleation size, the slip on the patch accelerates significantly, but to peak slip rates that 1-3 orders of magnitude below the slip rates of 0.1-1 m/s typical for traditional earthquakes. The seismological analysis of the synthetic seismograms produced by such sources results in source parameters similar to those inferred for the natural LFEs, for the models with certain parameter selections, e.g. the effective normal stress of 25 MPa, steady-state velocity weakening of 0.002, characteristic distance of 160 microns, and d/h* = 0.93-0.96. Our current work is directed towards exploring the range of fault properties that would result in observable LFEs.

Key Words
low-frequency earthquakes, rate-and-state fault, sub-critical velocity weakening patch

Citation
Shen, Z., & Lapusta, N. (2018, 08). Modeling low-frequency earthquakes on a rate-and-state fault. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)