Saturday, March 19, 2011

Earthmovers: Quakes in Mallorca

In the early morning of the 26th of July last year, at seven minutes before two, there was an earthquake in Alcúdia. Its epicentre was the Alcanada district. The tremor lasted no longer than a couple of seconds. It registered 2.5 on the Richter scale, but it was enough to cause alarm in Pollensa, Sa Pobla and Can Picafort.

This was a minor, insignificant event, but the earthquake in Japan, coming on the back of those in New Zealand and previously in Chile and Haiti, ones that created significant charitable efforts in Mallorca and Spain, have all raised awareness of potential threats to the island and to the mainland.

Earthquakes have tremendous power, not just through their unleashing of natural forces but also through their ability to scare the living daylights out of you. As a young child, I started to appreciate, in 1963, that the world was not always a very nice place. Makarios gave me nightmares, I thought Kennedy's assassination meant a world war and Russians exploding giant mushrooms over our heads, and I began to fear being swallowed by the earth suddenly breaking up. Skopje was that significant for me that my father, an engineer with an earthmoving-machinery manufacturer, was engaged in organising aid for the devastated, then Yugoslavian city. Coincidentally, the Skopje earthquake occurred in the early morning of the 26th of July.

The concern in Spain, arising from events in Japan, has been more sophisticated than my eight-year-old fears. Partly, it has to do with any threats to Spain's nuclear power stations. If tsunami is the main reason for concern, then the plants most vulnerable are those of Vandellòs near to Tarragona, along the Catalonian coast. In an act of reassurance, the Spanish Government has released a map which shows the degree and number of seismic observation facilities across Spain, there being one in Mallorca. Observation isn't, necessarily though, of much use when it comes to the unstoppable.

The map shows a concentration of observation units in the south of Spain and in Catalonia up towards the Pyrenees (as well as in the Canaries). With good reason. These are the parts of Spain most at risk from earthquakes. The most significant of recent earthquake activity has been in Barcelona (September 2004, a measure of 4.1) and Ciudad Real in Castille-La Mancha (August 2007, 5.1). The most devastating of earthquakes in modern times occurred in Granada in 1884. With an estimated magnitude of up to 7, it left 800 people dead. Modelling of potential earthquake risk places a similar level of magnitude affecting the likes of Santa Fe.

Spain, by comparison with countries further to the east in the Mediterranean, is at relatively low risk of suffering serious earthquakes, but the risk is still there. In Mallorca, there are specific fault lines, one between the Balearics and Alicante and another on the island itself, the Sencelles fault. The worst earthquake to affect Mallorca was one recorded in Palma in 1851. This registered VIII on the MSK scale, a different seismic system to the Richter scale; VIII representing "damaging". The earthquake was centred on Santa Eugenia and was attributed to the Sencelles fault.

Scientists from the University of Salamanca and the national museum of natural sciences published a paper in 2001 that traced earthquake activity in Mallorca**. They reported that the level of seismic activity was indeed low on the island; a mere 21 "events" between 1654 and 1996. But they pointed out that, despite the irregular and low occurrence, there had been some large earthquakes, such as the one in Palma in 1851. And the most serious ones (VII on the MSK scale) pre-dated the 1851 event; one also in Palma in 1660 and another centred on Selva but with impact on Alcúdia in 1721.

The fact that these more damaging earthquakes happened so long ago is no reason for being relieved. Quite the opposite. The scientists believe that "given the time elapsed ... it is reasonable to assume that the Sencelles fault has accumulated sufficient elastic energy to generate a new VIII MSK seismic event". And the most likely impact would be on Palma and its surroundings. A "damaging" event is characterised by, inter alia, large cracks and fissures, partial collapse or considerable damage to buildings.

Precise predictions of earthquakes are nigh on impossible. What can be predicted is that they will happen, some time. They are inevitable. But the inevitable can be delayed. In the eastern Med, in Israel, a major earthquake is almost 600 years overdue. It will happen, though. You just don't know when. This said, take a look at the dates above. There are no data relating to earthquakes before 1654, so no one can say with any certainty what the pattern was before then, but the gap between the two big Palma earthquakes was 191 years. We are now 160 years on from the last one. And nature, despite the coincidence of the 26th of July, doesn't deal in exactness. It deals in variance.

Don't go having nightmares.

** "Paleo and historical seismicity in Mallorca", Silva, González Hernández, Goy, Zazo, Carrasco, "Acta Geologica Hispanica", 2001.

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