This collapse of the Azure Window in Dwejra, Gozo, on the morning of March 8 was recorded by the seismic station in Xlendi of the Seismic Monitoring and Research Group (SMRG) at the University of Malta. The seismic station, which is just around 3.5 kilometres away from Dwejra, recorded the impact of the rocks from the collapsed window falling on the sea bed at 9.32am.
The seismic stations record signals from a wide range of sources, including ‘urban noise’, such as traffic and machinery, natural phenomena such as wind, ocean noise and crashing waves, as well as earthquake signals and quarry blasting. Different types of signals have their own ‘signature’ in terms of frequency content, waveform, time of day, and so on.
The waveform from the Azure Window rock collapse was different from urban noise as well as from earthquake signals and quarry blasts. In terms of energy, it may be compared to a very small earthquake, of a magnitude of less than 2.0.
Although urban and artificial noise signals are very common, signals from rock collapses are not so common. In August 2015, the seismic station at Wied Dalam had also recorded the cliff collapse in Delimara.
The SMRG also operates two other stations in Malta.