L'Aquila Earthquake - Followup
Tuesday, April 7, 2009 1:59:49 PM
There has been a lot of fuss about a so-called prediction of the quake. I would like to remind you what earthquake prediction is about. An earthquake prediction is a prediction that an earthquake in a specific magnitude range will occur at a specific place at a specific time. As Amphibol (in German) rightly reminds us, an earthquake was predicted to occur at Sulmora about 30 km from L’Aquila on Sunday 29 March - but it didn’t! A week later, however, on Monday 6 April an earthquake did occur, but at L’Aquila. What would have happened if the inhabitants of Sulmora had been evacuated or had fled to L’Aquila for shelter. Just think about it - and let’s face it, so far measurements of radon emissions are more or less worthless as earthquake prediction tool for all the other reasons we have heard the last couple of days.
In my post yesterday I mentioned that the quake occurred at a normal fault. When continents (like Africa and Europe) collide you would normally expect compression of the crust, but normal faulting is an expression of extension. I didn’t go into this apparent paradox, and I no longer need to as Kim Hannula at All of My Faults Are Stress Related did that extremely well in her post here.
Finally a satellite image of central Italy that shows the rugged topography in the vicinity of L’Aquila.
Lower elevations are shown in green, while higher elevations are light brown and off-white. The steepness of the mountain slopes is indicated by shading: darker shading means steeper slopes. L’Aquila is nestled in the central Apennine Mountains, which run the length of Italy like a spine. The mountains are crisscrossed by dozens of faults. Faults are not always visible at the surface, but in this part of the Apennines, many of them are revealed by steeply sloped fault scarps. A major fault system is revealed by a scarp running north-northwest from the Focino Plain nearly to L’Aquila, passing along the eastern foothills of Mt. Velino and Mt. Ocre. L’Aquila is wedged between a pair of parallel faults running toward the northwest and a long, broken fault extending toward the east.