UNIVERSIDADE
DO ALGARVE
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September 2005, Joaquim Luis
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A little insight over the recent S. Miguel seismic activity
It has been claimed by the authorities that the recent increase of the seismic activity at the São Miguel island is of tectonic origin. However, IMHO it is far from obvious that this is the right explanation. I base this opinion only from the seismicity data obtained at the ISC catalog because unbelivably no other type of data is available to the scientific comunity, namely the seismic wave-forms. But let us see what the seismicity shows when analized in terms of seismic swarms. Displayed bellow are 9 swarms together with attempts to fit to each one a modified Omori law. As can be seen, the swarms show a dispersion arround the central part of the island and for none of them is it possible to aceptably fit and Omori behaviour. Also the time-magnitude relations shows that the swarms have no associated main event. Therefore, and not forgeting that we are dealing with a volcanic active zone, the more likely explanation is obviously that the mentioned seismicity is of volcanic origin.
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