# How earthquakes organize stress

## TL;DR

Earthquakes redistribute stress in the Earth's crust, leading to self-organized systems and consistent stress distributions.

## Contribution

The paper introduces the concept of stress redistribution as a central mechanism of self-organization in earthquake systems.

## Key findings

- Earthquakes redistribute stress and strain energy, organizing fault systems into reproducible states.
- Stress distributions are consistent and can be used to track changes and distinguish fault systems.
- Subduction zone faults synchronize through stress interaction, while complex continental systems do not.

## Abstract

Earthquakes organize the stress in the crust by redistributing it through slip events. As a result, fault systems evolve to preferred, reproducible states as evidenced by natural experiments that measure statistical distributions of stress from failure, strain energy, and scale-dependent rock strength. Knowing the mathematical form, and even establishing existence of the distributions has proven to be a powerful tool for tracking changes, characterizing systems and explaining rupture behavior. If the primary role of earthquakes in the system is to redistribute stress, then self-organization is a central feature of the Earth’s crust.

Stress is not uniform in the Earth. Therefore, we must use natural experiments to measure the distribution of stresses and related quantities, rather than single values. For instance, dynamic triggering shows that faults are uniformly distributed over their loading cycles in Southern California. The probability that a fault ruptures across a barrier measures the in situ energy distribution. Fault roughness reflects the distribution of strength. These natural experiments produce observable distributions that are surprisingly consistent and suggest some degree of self-organization in the Earth’s crust. Once established, the functional form of the distributions can be used to track changes in response to earthquakes as well as to distinguish fundamentally different fault systems. Transient fault locking before stress release in laboratory experiments can be interpreted as a consequence of self-organization of fault stress. The robust self-organization of multiple variables in earthquake systems suggests that the most consequential mechanical outcome of earthquakes may be the redistribution of stress and the strain energy associated with it. The low friction on a fault during seismic slip as inferred by temperature measurements of the Tohoku earthquake is consistent with dissipation playing a secondary role to this redistribution process. Through stress redistribution and interaction, subduction zone faults tend to synchronize, perhaps due to their geometric simplicity, while the continental system of Southern California cannot synchronize, perhaps due to the complexity of the fault network. Earthquakes organize stress in the crust and produce a suite of well-defined, consistent distributions.