Testing self-organized criticality by induced seismicity

TL;DR

This paper explores how the self-organized criticality (SOC) hypothesis explains earthquake clustering and induced seismicity, showing that small perturbations can trigger significant earthquakes in the crust, indicating widespread seismic hazard.

Contribution

It demonstrates that induced seismicity supports the SOC model by showing small stress changes can trigger large earthquakes, expanding understanding of seismic hazards.

Findings

Pore pressure and mass transfer changes can trigger earthquakes up to magnitude 7.0.

Stress variations of >0.01 MPa can sustain seismic activity.

Seismic hazards are more widespread than areas with frequent earthquakes.

Abstract

We examine the hypothesis proposed in recent years by several authors that the crust is in a self-organized critical (SOC) state by exploring how the SOC concept can help in understanding the observed earthquake clustering on relatively narrow fault domains and the phenomenon of induced seismicity. We review the major reported cases of induced seismicity in various parts of the world and find that both pore pressure changes (+/-p) and mass transfers (+/-m) leading to incremental deviatoric stresses of <<1 MPa are sufficient to trigger seismic instabilities in the uppermost crust with magnitude ranging up to 7.0 in otherwise historically aseismic areas. Once triggered, stress variations of at least 1 order of magnitude less but still larger than the ~0.01 MPa tidal stress are enough to sustain seismic activity. We argue that these observations are in accord with the SOC hypothesis as they show that a significant fraction of the crust is not far from instability and can thus be made unstable by minute perturbations. Not all perturbations, however, trigger seismic activity; this is also compatible with the SOC hypothesis which embodies naturally the existence of large heterogeneities in the stress field. In conclusion, the properties of induced seismicity and their rationalization in terms of the SOC concept provide further evidence that potential seismic hazards extend over a much larger area than that where earthquakes are frequent.