Spain's Earthquake

On May 11, a magnitude 5.2 earthquake struck southeastern Spain, near the town of Lorca, some 30 miles southwest of Murcia. Lying near the boundary of the African and Eurasian Plates, which runs through the Mediterranean Sea, this area is prone to quakes, most of which are relatively weak. Unfortunately, the epicenter of this earthquake was shallow (less than a mile deep), leading to significant structural damage and the death of at least ten citizens.

About 50 million years ago, the Tethys Sea began to close and the African Plate drifted northward, triggering a collision with the Eurasian Plate that is crumpling up the Alps and associated ranges of southern Europe. Within another ten million years, the East African Rift began to develop, the Red Sea opened and the northward movement of Africa shifted to a northwesterly direction relative to the Eurasian Plate. Today, along the southern coast of Spain, the African Plate is both colliding with and slipping past the Eurasian Plate, a tectonic scenario very similar to events on the South Island of New Zealand and along the San Andreas fault in Southern California.

Of interest, the May 11, 5.2 magnitude earthquake occured two hours after a weaker, 4.4 magnitude quake in the same area. Aftershocks are typically weaker than the parent quake as pressure is distributed down the primary and secondary faults that connect with the epicenter. Apparently, this pressure shift triggered a rupture at another site where friction between the plates was already nearing its point of tolerance.