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Bayesian Inference of Stress Evolution in Rate-and-state Governed Faults Constrained by Seismicity Rate Observations

Description: 

Distinguishing between competing mechanical theories of earthquake nucleation requires advancing our ability to resolve fine-scale temporal variations in stressing rates driving fault slip. An improved characterization of fault stressing rates can be achieved by analyzing the mechanical response to variations in seismicity rates of a representative crustal volume. Two main end-member hypotheses prevail in current earthquake science literature: the pre-slip model which emphasizes slow slip in promoting large ruptures, and the cascade model which relies on stress transfer between earthquakes and does not require a slow slip phase. If pre-slip occurs before earthquakes, it is expected to generate a seismicity rate above background levels before the mainshock, providing a potential indicator for identifying pre-slip processes.

Here we introduce a novel methodology to infer the timing and evolution of slow slip from seismicity rates based on rate-and-state friction law (Heimisson & Segall, 2018). The temporal evolution of stressing rates is modelled as an asymmetric ramp function, selected to capture various fault behaviors: acceleration, steady-state, and deceleration. From the rate-and-state model, we derive an integral form for R/r, the ratio of observed to background rate, and obtain its closed-form expression. Using a Bayesian framework, we estimate probability distributions for model parameters, such as the time and amplitude of shear stressing, frictional-stress parameter, and characteristic time. We can reliably reconstruct stress history from synthetic simulations. Using this framework, we reanalyze the 2008 Mogul seismic swarm near Reno, Nevada, where previous geodetic studies identified significant aseismic slip (Bell et al., 2012). Our model reveals two phases of elevated stress rates above background levels, interpreted as separate slow slip phases: the first from Jan 20 to Apr 18, and the second from Apr 19 to Apr 25. These results suggest that stress evolution before an energetic event can be inferred from seismicity rate observations, providing new insights into earthquake nucleation physics.

Session: Predictability of Seismic and Aseismic Slip: From Basic Science to Operational Forecasts [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Yu

Student Presenter: No

Invited Presentation: 

Poster Number: 43

Authors