Individual places and topics of interest
Earthquakes and Tsunamis
As described in Chapter 4, convergence between the African and Eurasian plates is still continuing today, although at a more sedate pace than in the collision phase of Chapter 3.
A fair amount of the plate movement is today taken up by shear along the Trans-Alboran Shear Zone, and one evidence and consequence of this is in the recent earthquake activity. The map opposite shows in yellow dots the main earthquakes from the first part of 2016. All of them plot along the TASZ and have epicentres relatively shallow in the crust - generally less than 30km deep. Looking a little further back in time though there have been some major, more deep-seated earthquakes with epicentres over 600km deep - well into asthenospheric Mantle. A noteworthy one occurred in Nigüelas, south of Grenada as recently as 2010. The origin of these quakes is debated by academics. For some it is evidence that active subduction is still occurring below the Gibraltar Arc; for others, the tremors are coming from remnant sinking or even splitting of a formerly subducting slab (sketch at bottom left). Earthquakes can also generate tsunamis, and the western Mediterranean has had its fair share of those as shown opposite. In fact, according to the website tsunami-alarm-system.com, one in ten of the world's tsunamis occur in the western Med. Incidentally, the infamous Lisbon earthquake and tsunami of 1755 that killed scores of thousands of people had its epicentre in the Atlantic, and was due to plate motions west of Gibraltar, not directly connected with our story. |