Movers and shakers: Trying to understand earthquakes

Pauline Galea on what makes the earth shake • Video by Ray Attard

Tremors rattle the globe on a daily basis, some of them with no effect on us whatsoever, but others with devastating consequences on life and property.

It’s their unpredictable nature, apart from their power, that makes them so scary…

MaltaToday spoke to the head of the geosciences department at the University of Malta, Dr Pauline Galea, to understand somewhat what this frightening phenomenon is all about.

“It’s hard to give a simplified description, but essentially all earthquakes have their origins from movements that are constantly happening some 10 to 20 km into the earth’s crust,” Galea said.

She pointed out that these underground movements are completely normal, and they often involved huge masses of land coming into contact with each other. 

“The earth’s crust is made up of a veritable jigsaw puzzle of continental and oceanic plates that are constantly coming into contact with each other and sliding past each other, or even pulling apart from each other.”

“If we take the Mediterranean, for instance, the European and African continents are constantly pushing on each other,” Galea said, adding that earthquakes normally originated in areas known as fault zones.

“Some argue that the increasing temperatures at the core of the earth, are causing ever greater risks of earthquakes,” she said.

Asked whether there are any faults visible in Malta, Galea explained that many of the known faults around Europe were at the bottom of the sea, but that there were a few visible lines across the Maltese islands.

“There is a fault line in Qala, another one near the Victoria Lines, towards the San Pawl tat-Targa area, as well as one in the Ghar Lapsi area, known as ix-Xaqqa, which is exactly where the area gets its name from.”

The area known as Xaqqa, near Ghar Lapsi is one of the clearest visible examples of a fault line on the island

She explained that the latter area is believed to have caused the tremors felt towards the South of the island some weeks ago, on 30 July. Interestingly, Galea also pointed out that millions of years ago, this area was also believed to be connected to Filfla, and that the connection is believed to have sunk into the sea after some tremor in the area. 

“The Mediterranean is one of the zones that is at most risk around the world,” she said, explaining that the countries running the highest risk were peninsular areas like Greece, Italy, Algeria and Turkey.

“Malta is in the middle of all this activity, which means there is some risk. However, according to past studies we are far enough from all this activity so the risk of us experiencing earthquakes isn’t so high,” she said reassuringly. 

She explained that an earthquake which had its epicentre in Sicily, was the earthquake in 1693, which also happened to be one of the worst felt in Malta’s history.

“This was one of the earliest documented earthquakes near Malta, and it is believed to have reached around 7.4 on the Richter Scale,” she said, adding that it had even caused some damage to buildings in Valletta and Mdina Cathedral among others.

“So far, the tremors in Malta have never caused deaths, but the Sicily earthquake had killed some 20,000 people there,” she said, pointing out that tremors of such magnitude were rare in the Mediterranean.

“A particularly notable earthquake that had taken place in Messina, Sicily in 1908, had even caused a tsunami to reach our shores and cause some flooding in Msida,” she explained. “An even more recent series of tremors had taken place in 2011 when tremors were felt for three to four days around Easter Sunday originating from around 40 km East of Malta.”

Galea explained however, that the greatest fear now, if earthquakes of such magnitude were to strike, was that given today’s increase in population and density of construction, the danger to people might be higher.

“However, although it is not yet part of the law, many modern buildings are built to resist tremors of a certain magnitude,” she said. 

Talking about the University of Malta’s work in seismology, Galea said that researchers used seismometers, small instruments which were placed on the surface of rocks in somewhat isolated areas, to measure ground movement. 

“We currently have three different seismometers, one in Wied Dalam in Birzebbuga, another one to be placed  at the University itself and another one in Gozo. We also have a portable one, which is currently at Mdina,” she added. 

Galea also explained that the lab registered an average of one tremor a month at a distance of between 50 to 100 km from our shores, but that only one of these tremors (on average) would be perceptible to people in a year. 

“Although somewhat frequent, tremors in Malta are never strong enough to be a cause for alarm,” she said, adding that some geologists believed there was a possible link between the frequency and the strength of tremors. The theory goes that the further apart tremors were, the stronger they became, and that they were weaker if they happened more frequently. 

Discussing precautionary measures to be taken if such tremors were felt, Gauci said that if the tremors were particularly strong, people were encouraged to avoid places where heavy things could topple down or fall squarely on them, and to hide under a particularly sturdy table if tremors were worryingly strong. 

“It’s not possible to precisely predict when and where an earthquake will strike, but countries carry out risk evaluations to reflect these possibilities,” Galea said, pointing out that changes in building methods and preparations by the civil protection department were the order of the day. 

In fact, the CPD will be holding a large earthquake simulation process involving some 300 people next week. The scenario will test the department’s response in the case of a 7.6 magnitude earthquake hitting the island. 

“There are constant studies into the nature of the movements in the ground, as well as, what causes earthquakes and how buildings react to them.”

She added that a country’s risk assessment was based mostly on its history, and the number, frequency and strength of earthquakes in the past, and to establish patterns with nearby countries.