iPlex Lunch fall-2015

Relative stress magnitudes of plate margins and interiors as constrained by strike-slip fault spacing

Rigid plate motion on Earth implies that the plate interiors are mechanically strong and/or have lower stress than that along plate margins. Although the strength contrast between plate interiors and margins has been quantified, their relative stress magnitude has never been investigated. Here we use a mechanical model that relates active strike-slip fault spacing to fault strength to show that the average strength of faults, which places a bound on the magnitude of stress in the crust, is about a factor of two weaker in the continental interior of Asia than that along the San Andreas transform plate boundary in California. This result provides a critical insight into the dynamic state of plate tectonics on Earth: a higher stress regime along plate boundaries and a lower stress regime within plate interiors enable classical plate-like rigid-body motion on a continental scale. As fault strength is a key parameter in modeling continental deformation and the mechanical behavior of earthquakes, our approach also provides a new approach of estimating the absolute frictional strength of active strike-slip faults on Earth.