Focal Mechanisms for Subcrustal Earthquakes Beneath the Gibraltar Arc

Abstract

AbstractIntermediate deep earthquakes are usually associated with active subduction, and show mostly dip‐slip faulting mechanisms aligned with the downgoing oceanic lithosphere. Forty‐two new focal mechanisms from 50‐ to 100‐km depth beneath the Gibraltar Arc and Alboran Sea show different characteristics. The most abundant solutions are strike‐slip mechanisms, in agreement with relative plate motion between Nubia and Eurasia. Additional reverse faulting mechanisms indicate compression in direction of absolute plate motion, reproducing the basal drag of the mantle on the hanging lithosphere. In turn, no signature of ongoing subduction was found. Migrated sections of P wave receiver functions suggest that a significant part of intermediate deep seismicity is produced within the stalled remnants of Jurassic age, oceanic lithosphere that once formed the connection between the Alpine Tethys and the central Atlantic and later has been buried beneath the Gibraltar Arc.