On behaviour and scaling of small repeating earthquakes in rate and state fault models

Journal Article · 10 June 2019 · Geophysical Journal International

DOI: https://doi.org/10.1093/gji/ggz270 · OSTI ID:1529538

Chen, Ting  ^[1]; Lapusta, Nadia ^[2]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. California Inst. of Technology (CalTech), Pasadena, CA (United States)

With abundant seismic data for small repeating earthquakes, it is important to construct a dynamic model that can explain various aspects of related observations. We report on small repeating earthquakes on a fault governed by rate- and state-dependent friction laws. The earthquakes occur on a velocity-weakening patch surrounded by a much larger velocity-strengthening region. The whole fault is subject to long-term tectonic loading. The model with a circular patch and the aging form of rate- and state-dependent friction laws has been shown to reproduce the scaling of recurrence time versus seismic moment for small repeating earthquakes in a previous study. In this work we investigate the behaviour of small repeating earthquakes in related models under different scenarios, including several forms of the state evolution equations in rate- and state-dependent friction laws, rectangular velocity-weakening patch geometries, quasi-dynamic versus fully dynamic representation of inertial effects and 2-D versus 3-D simulations. We discover that the simulated scalings between the recurrence time and seismic moment for these different scenarios is similar while differences do exist. We propose a theoretical consideration for the scaling between the recurrence time and seismic moment of small repeating earthquakes. For patch radii smaller than or comparable to the full nucleation size, the scaling is explained by the increase of seismic to aseismic slip ratio with magnitude. For patch radii larger than the full nucleation size, the scaling is explained by the model in which the recurrence time is determined by the earthquake nucleation time, which is in turn determined by the time for aseismic slip to penetrate the distance of the full nucleation size into the patch. The obtained theoretical insight is used to find the combinations of fault properties that allow the model to fit the observed scaling and range of the seismic moment and recurrence time.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: National Science Foundation (NSF); United States Geological Survey; USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation
• Grant/Contract Number: 89233218CNA000001; EAR-1520907; 1724686; G10AP00031; G16AP00117
• OSTI ID: 1529538
• Report Number(s): LA-UR-18-29324
• Journal Information: Geophysical Journal International, Vol. 218, Issue 3; ISSN 0956-540X
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United States
• Language: English