Brittle and Non-Brittle Events in a Continuum-Granular Earthquake Experiment

TL;DR

This study uses a laboratory earthquake fault experiment with granular media to analyze the distribution of brittle and non-brittle events, revealing distinct statistical behaviors and effects of normal force on event types.

Contribution

It provides the first detailed measurement of spatial and temporal moment distributions of brittle and non-brittle events in a granular fault model.

Findings

Non-brittle events follow an $M^{-3/2}$ power law distribution.

Brittle events have a broad, peaked moment distribution.

Increasing normal force results in more brittle events and broader moment distribution.

Abstract

We report moment distribution results from a laboratory earthquake fault experiment consisting of sheared elastic plates separated by a narrow gap filled with a two dimensional granular medium. Local measurement of strain displacements of the plates at over 800 spatial points located adjacent to the gap allows direct determination of the moments and their spatial and temporal distributions. We show that events consist of localized, larger brittle motions and spatially-extended, smaller non-brittle events. The non-brittle events have a probability distribution of event moment consistent with an $M^{-3/2}$ power law scaling. Brittle events have a broad, peaked moment distribution and a mean repetition time. As the applied normal force increases, there are more brittle events, and the brittle moment distribution broadens. Our results are consistent with mean field descriptions of statistical models of earthquakes and avalanches.