Earthquake depth-energy release: thermomechanical implications for dynamic plate theory

TL;DR

This paper investigates the regional variations in seismic energy release up to 290 km depth, linking them to thermomechanical properties and implications for plate dynamics and faulting behavior.

Contribution

It introduces a thermomechanical model explaining seismic energy distribution and faulting patterns based on regional thermomechanical contrasts and shear localization.

Findings

Seismic energy release varies significantly with depth and region.

Shear localization occurs at specific angles, influencing fault types.

Adiabatic conditions are predicted in the mantle below 1000 km.

Abstract

Analysis of the global centroid-moment tensor catalog reveals significant regional variations of seismic energy release to 290 km depth. These variations reflect radial and lateral contrasts in thermomechanical competence, consistent with a shear-dominated non-adiabatic boundary layer some 700-km thick, capped by denser oceanic lithosphere as much as 100 km thick, or lighter continental tectosphere 170 to 260 km thick. Thus, isobaric shearing at fractally-distributed depths likely facilitates toroidal plate rotations while minimizing global energy dissipation. Shear localization in the shallow crust occurs as dislocations at finite angles with respect to the shortening direction, with a 30 degree angle being the most likely. Consequently, relatively low-angle reverse faults, steep normal faults, and triple junctions with orthogonal or hexagonal symmetry are likely to form in regions of crustal shortening, extension, and transverse motion, respectively. Thermomechanical theory also predicts adiabatic conditions in the mantle below about 1000-km depth, consistent with observed variations in bulk sound speed.