An earthquake measuring 4.0 on the Richter scale was registered 110 kilometres south of Faro on Monday morning, August 1st, but nothing seems to have been felt on the mainland.
The event occurred at 04:48 and followed Sunday’s 3.5 earthquake off the west coast that saw people running into the street in the Peniche area due to the loud booming noise created.
Both of the earthquake epicentres were in one of Portugal's oil concession areas, playing to the fears that oil drilling activity will only increases such instances.
Studies in Spain and in the USA have linked oil drilling activity, especially fracking, to increases in seismic activity (not earthquakes) and the concern is that the rock below Portugal’s ocean floors, already notable for its earthquake potential, may be disturbed by drilling which could trigger a sizeable event.
‘Seismic risk’ is one of the warnings being given by Portugal’s anti-oil and gas organisations which in recent weeks have grown in strength and supporter numbers.
As for the area to the south of Faro, a 2013 report ‘Tsunamigenic earthquakes in the Gulf of Cadiz: fault model and recurrence,’ stated
“Whatever main active tectonic engine is at work in the Gulf of Cadiz, this area is recognised as the major source of large earthquakes that can generate destructive tsunamis that affect the whole North-East Atlantic.
"Recognizing this, Portugal has been developing a Tsunami Warning System (the PtTWS) following the recommendations issued by the Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas.
“This is the responsibility of the Instituto Português do Mar e da Atmosfera, (IPMA), which is the national institution operating on a 24-7 basis that is responsible for the Portuguese seismic network.
“Starting from a seismic detection, the operator evaluates the tsunami threat level to the coastal areas and issues appropriate messages to the Portuguese Civil Protection agency. After receiving information on the sea level, the tsunami threat is re-evaluated and messages are updated accordingly. One critical component of the PtTWS is the tsunami scenario database and the Tsunami Analysis Tool that help the operator to make decisions during the course of the event.”
Two questions remain, will oil and gas drilling affect the stability of the oil and gas concession areas that already are noted as seismic hot spots; is the Algarve prepared if there is a major event?
Certainly, with the slap-dash approach of government to the environmental impacts that an oil or gas industry could have on the Algarve and west coast areas adjoining concession areas, there may be little confidence that these matters have been taken seriously with the exception of computer generated disaster scenarios showing the expected death toll in low-lying areas should a tsunami hit the Portuguese coast.
Those fearing a repeat of the 1755 earthquake and subsequent tsunami that destroyed Lisbon and wreaked havoc across the Algarve, there are words of comfort from the same publication:
"The Gulf of Cadiz is known to be the source area for the 1 November 1755 destructive earthquake and tsunami that affected Portugal, southwestern Spain and northern Morocco.
"The magnitude of this event has been estimated to be Mw∼8.7 and the occurrence of large earthquakes in this area dominate the seismic hazard in the bordering countries. However, given the very long seismic cycle associated with these extreme events (more than 1000 years) the uncertainty about the recurrence period for large earthquakes and tsunamis generated offshore is extremely high."
