Focal Mechanisms for Subcrustal Earthquakes Beneath the Gibraltar Arc

Abstract

Earthquakes below 50‐km depth are usually associated with active subduction, and the direction of faulting is aligned with the orientation of the subduction zone. Faulting in 42 earthquakes beneath the Gibraltar Arc and Alboran Sea shows different characteristics. The most abundant solutions show horizontal slip, in agreement with relative plate motion between Africa and Europe. Further solutions are associated with shortening and suggest compression from the basal drag of the Earth's mantle on the moving plates. In turn, no signature of active subduction was found. Images of the Earth's interior from teleseismic waves suggest a relation between the earthquakes and a stalled remnant of ~150‐Ma‐old oceanic material that once formed the connection between two oceans and later has been buried beneath the Gibraltar Arc.