The University of Malta completed the second phase of the Geophysical investigations that will establish a geological model which will guide the conceptual design of the proposed tunnel between the islands, Transport Malta said today.

Researchers used a multibeam echo sounder to create a 3D map of the seabed.  They emit an acoustic pulse at a particular frequency which hits the seabed and is reflected back.  The software registers the time it takes and since the speed of sound in water is known, can calculate the depth of the sea-bed.  This system emits 500 of these impulses at one go.  Thus by moving with the boat the researchers mapped bands of the bottom at a very high resolution.

The first phase gave details of the geological structure of up to 400 metres below the seabed. Scientists deployed a 300-metre-long cable with a series of specialised receptors.  An ‘air gun’ released bursts of compressed air every few metres.  The compressed air was reflected back to the receptors.  

Different geological layers reflect back different frequencies.  Scientists can thus determine the geological formations that lie beneath the surface and determine possible cracks.  For several days, the vessel Midas express navigated between the islands repeating this process.