Malta is deemed as the European country facing the highest stress on its water resources. Our islands have a semi-arid climate with approximately 550 millimetres of annual rainfall and  a very high population density. Consequently, 80 per cent of Malta’s groundwater is used for agriculture by direct abstraction from aquifers via boreholes or underground galleries.

The groundwater in Malta is rigorously monitored by a network of direct borehole readings run by the Energy and Water Agency (EWA). These readings are highly accurate, however, they require drilling deep holes in the rocks to reach the water tables, and in order to have a good coverage, many boreholes are necessary across the islands, making it increasingly challenging to maintain.

Scientists from the Seismic Monitoring and Research Group at the University of Malta have come up with a novel, cost-effective approach to monitor the aquifers that does not depend on drilling such holes. They are using ambient seismic noise, which is made up of continuous vibrations of the ground surface and shallow rock layers due to natural and anthropogenic sources such as wind, waves and traffic. These vibrations travel through the rock at a speed which depends on the rock properties.

The seismic noise recorded on seismographs recorded by the Malta Seismic Network can therefore provide information on the shallow seismic wave velocity structure beneath the network, which in turn is influenced by the water content and distribution. Changes in the water content, such as, the replenishing and depletion of aquifers due to seasonal effects or anthropogenic intervention, result in changes in the velocity structure.

This can be measured in an automated manner, complementing on-site, single-measurement investigations (e.g. borehole). Therefore, the continuous recording of seismic networks can be used to track real-time changes in the reservoirs, extending significantly the present-day coverage of aquifers limited to borehole measurements.

Preliminary analyses on the seismic data show promising results that agree with the borehole data. This research is being conducted by Matthew Agius and Masters student Luca Laudi, led by principal investigators Sebastiano D’Amico and Pauline Galea for the project SIGMA (Seismic Imaging of Groundwater for Maltese Aquifers). SIGMA is addressing a national policy priority in the water sector. The project outcome will hopefully benefit environmental sustainability through better water management. 

Project SIGMA is financed by the EWA under the National Strategy for Research and Innovation in Energy and Water (2021-2030).

Matthew Agius is a seismologist and a postdoctorate researcher.

Sound Bites

•        An earthquake can have a negative magnitude because the calculation is based on a logarithmic scale. A 10-fold drop in amplitude decreases the magnitude by 1. If an amplitude of 20 millimetres corresponds to a magnitude 2 earthquake, then 10 times less (2mm) corresponds to a magnitude of 1; 100 times less (0.2mm) corresponds to magnitude 0; 1000 times less (0.02mm) corresponds to magnitude -1.

•        Normally, it’s not the shaking ground itself that claims lives during an earthquake. It’s the associated destruction of human-made structures and the instigation of other natural disasters such as tsunamis, avalanches and landslides. Not only is it important to have a plan for yourself in the case of an earthquake but your pets need a disaster plan as well. Create an earthquake plan for the animals around so if disaster strikes, you’ll be prepared. Sign up for Save Our Pets.

For more science news, listen to Radio Mocha on www.fb.com/RadioMochaMalta/.

DID YOU KNOW?

•        The deepest earthquake ever recorded struck 751 km beneath Japan in 2015.

•        Quakes on the planet Mars are called marsquakes, on the moon they are called moonquakes.

•        Icy parts of the Earth system, the cryosphere, also have quakes, they are called icequakes.

•        Seismometers are so sensitive that they can detect human-made explosions such as nuclear and quarry blasts, as well as record the storms and automobile traffic.

•        The largest recorded earthquake in the world was a magnitude 9.5 in Chile on May 22, 1960.

For more trivia, see: www.um.edu.mt/think.