Using earthquakes to constrain stress in the Earth

The magnitude and orientation of stress in the Earth determine how the Earth deforms. It is a first-order feature that one must quantify when considering loads on the Earth’s surface, flow within the Earth’s crust and mantle, or the nucleation and rupture of earthquakes.

However, the absolute value of stress in the Earth has remained controversial for many decades because most of our observations only provide constraints on stress changes. Plausible absolute stress distributions vary widely, as illustrated below.

Observations and models of lithospheric loading, and laboratory measurements of rock friction, suggest that the lithosphere supports significant long-term shear stresses, on the order of hundreds of megapascals. However, alternative observational and modelling approaches imply much lower shear stresses, on the order of megapascals to tens of megapascals. These low stresses are consistent with the presence of the strong dynamic weakening observed in large earthquakes (something) and with observations of earthquake modulation by small-magnitude tidal stresses (something). An outstanding question concerns the relationship between large-scale stress distributions, the mechanics and properties of slip on individual faults, and the degree of lateral and temporal heterogeneity in fault stress over both individual ruptures and entire earthquake cycles. 

In this project, you will improve our understanding of stress in the Earth. You will (1) add two new observational constraints on stress state and (2) consider how (or whether) rheological models can accommodate your and others’ observations. 

For more detailed information, visit the institution website.