The southeastern Spain earthquake of 11 May, 2011, occurred within the plate boundary region that separates the Eurasia and Africa (Nubia) plates. At the longitude of the earthquake, the Africa plate moves NW with respect to the Eurasia plate with a velocity of 6 mm/yr.
Earthquakes in different parts of the plate-boundary region separating Africa and Eurasia may occur as the result of strike-slip or normal faulting, in addition to the reverse/thrust faulting that is expected as the most direct consequence of the convergence of two major plates. The diversity of faulting styles over the plate-boundary region may reflect the motions of crustal blocks that are situated within the broader plate-boundary zone and that move slowly relative to one another to accommodate the NW/SE convergence of the major plates.
The epicenter of the 11 May earthquake is situated near a major fault, the Alhama de Murcia fault. However, significant field work in the epicentral region of the earthquake will be necessary to confidently determine if the earthquake occurred on a segment of the Alhama de Murcia fault or on a nearby fault.
In recent decades, the larger shallow-focus shocks of southeastern Spain have had magnitudes of about 5.
Shocks of this size occurred near the epicenter of the 11 May earthquake in February 1999 and August 2002. The distributions of damage associated with several shocks that occurred before the twentieth century imply that these shocks had magnitudes in the 6.5-7 range.
Iberia and the Mahgreb also experience occasional deep-focus earthquakes of magnitude greater than 6 that occur at depths of over 600 km in lithosphere that was subducted along the plate boundary millions of years ago.
Some text and pictures: courtesy USGS and EMSC