DESTRUCTIVE EARTHQUAKES AND TSUNAMI WARNING SYSTEM

The Portuguese coast has been affected several times in the past by strong earthquakes that generated tsunamis severely damaging the city of Lisbon. The most significant event known was the Lisbon earthquake of 1 November 1755. It is generally assumed that the location of this event was the Gorringe Bank region in the North Atlantic. This ridge, located 200 km south-west of the Portuguese shore, was also the location of the 28 February 1969 magnitude M(s) = 7.9 earthquake (Fukao, 1973), that generated a tsunami of small amplitude clearly recorded at the tidal stations of the Portuguese south and south-west coasts. The need to reduce the social and economic impact of an event of this type, greatly amplified by the urban concentration of coastal areas, led to the research project 'Destructive Earthquakes and Tsunami Warning System in SW Portugal'. This project, sponsored by the European Economic Community and the public Portuguese research funding agencies, has been conducted by the Geophysical Centre of the University of Lisbon, since April 1988. The main targets of the project are: the installation of a pilot warning system against tsunamis, based on two ocean bottom stations, comprising a 3 component seismometer and a bottom mounted pressure sensor, linked by cable to a surface buoy. This buoy is equipped with a data acquisition and data transmission system. Seismic and water level data will be collected on an almost real-time basis and will be transmitted to Lisbon via satellite; the refinement of existing geological models, in order to clarify the genesis of the bank and the seismic activity in this area; the installation of an adequate network of seismic monitoring stations in order to better locate off shore earthquakes (Fig. 1); the evaluation of seismic and tsunami risk around the Iberian Peninsula.