Subduction delivers crustal material to the mantle, playing a primary role in geochemical cycling. Although flattening, primary inherited chaotic fabrics, and fault migration through subducting sediments or the frontal prism may build mélange sections that are much thicker (to several kilometers), this thickness does not describe the active fault at any depth. Subduction zones are ultimately responsible for spectacular explosive volcanic eruptions, the planet’s greatest earthquakes, and some of our most valuable concentrations of economic ores. At subduction zones, two tectonic plates are pulled towards each other. Thin sharp faults representing earthquake slip surfaces or other discrete slip events are found within and along the edges of the tens-of-meters-thick fault strands. Subduction zones are one of the three types of tectonic plate boundaries. The total thickness encompassing all simultaneously active strands increases to ∼100–350 m at ∼1–2 km below seafloor, and this thickness is maintained down to a depth of ∼15 km. We describe a general geometric model for subduction thrust décollements, which includes multiple simultaneously active, anastomosing fault strands tens of meters thick. We have compiled direct measurements of the thickness of subduction thrust faults from active and ancient examples observed by ocean drilling and field studies in accretionary wedges.

The thickness of an active plate boundary fault is an important parameter for understanding the strength and spatial heterogeneity of fault behavior.

Subduction boundary