  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.
