Malta is often considered an earthquake-free zone, but can we afford to be complacent when building our homes? Local seismologists and civil engineers investigate.

The Magħlaq fault

On January 11, 1693 a major earthquake with an estimated magnitude of 7.4 on the Richter scale struck about 170 kilometres from Malta. It devastated south-eastern Sicily, destroyed buildings and killed almost two-thirds of Catania’s population. Historical documents record serious damage in Malta to buildings in Valletta, Mdina, Rabat and elsewhere.

Major earthquakes in the central Mediterranean are rare. Research suggests that a similar earthquake on the same fault could occur every few hundred years. However, where does one draw the line between consigning such events to history and planning for a possible earthquake?

Malta is often considered an earthquake-free zone, but can we afford to be complacent? In 1693, only a small part of the Maltese archipelago was built up and the population was around 50,000 to 100,000. Fast-forward to the present and the population is close to 400,000 and over one-third of the island is built up.

The integrity of a building during an earthquake is affected by materials used, structural systems, short and tall building heights and layout, position in a block and building-to-ground interface

How will today’s buildings, especially unreinforced masonry buildings, react to an earthquake similar to that of 1693? What is the effect of adjoining buildings? What is the effect of having a clay layer beneath the surface? What features of local buildings are vulnerable and do we need to modify our construction practices? And how will earthquakes of different intensities affect our island?

Seismologists and civil engineers at the University of Malta are investigating these questions within the EU-funded project SIMIT (Italia-Malta Operational Programme 2007-2013) led by the regional Civil Protection Department of Sicily, with other partners being the Malta Civil Protection Department and the Universities of Palermo and Catania. SIMIT is a multi-disciplinary endeavour, which ultimately will explore the ways in which civil protection ­departments can support each other through sound scientific knowledge of earthquake hazard and risk. Sicilian and Maltese seismologists are crafting earthquake scenarios based on accurate ­computer simulations.

Seismic equipment

In an effort to obtain rapid information and an understanding of earthquake activity, the Seismic Monitoring and Research Unit (SMRU) within the Department of Physics at the University of Malta has recently invested in state-of-the-art equipment to improve real-time earthquake monitoring and alerts in the central Mediterranean. The seabed of the Sicily Channel, which lies between Sicily and Africa, is frequently seismic. In the last decade, over 170 earthquakes have occurred within 100 kilometres off the coast of Malta.

The SMRU is installing two new, permanent seismic stations, one in central Malta and another in Gozo, in addition to the one at Wied Dalam, creating a real-time networked system. This will improve earthquake coverage, allowing more accurate identification of earthquake epicentre location and knowledge about their causes. They are also investigating how Maltese rocks may affect the intensity of earthquake shaking. This will help to create seismic hazard maps of Malta and surrounding areas, which provide estimates of how strongly a particular area is likely to shake during an earthquake.

To understand what makes a building vulnerable requires seismologists or geophysicists who understand how the surface layers of the ground respond to earthquakes, and civil and structural engineers who know how the building will respond to this shaking. The interaction between the structure and the ground is a very critical aspect.

Malta has a dense urban landscape. Local buildings have been constructed over a span of thousands of years with different construction methods and a great variety in building types that influence a building’s seismic vulnerability. The integrity of a building during an earthquake is affected by materials used, structural systems, short and tall building heights and layout, position in a block and building-to-ground interface.

The Faculty for the Built Environment of the University of Malta is developing a list of sensitivity indicators in order to evaluate the vulnerability of a building to earthquakes. The methods used are being developed from similar techniques used in other countries with a high earthquake risk but adapted to the local situation.

However, the methods employed in other countries cannot be directly transposed to the local building stock due to inherent variations in local building typologies which need to be taken into account, including the incidence of soft stones and transfer slabs in lower floors with overlying load-bearing structures and lack of transverse lateral restraint, the occurrence of terraced development of varying heights and the characteristics of the aggregate of buildings in a block. To assess and calibrate the seismic vulnerability of the local built environment, local researchers refer to load-bearing masonry buildings in other regions and the past ­experiences of other countries.

The SIMIT project has funded the purchase of advanced numerical software to model building components, buildings and the aggregate of buildings in a block. By combining this numerical modelling with information about earthquake ground shaking, different scenarios can be evaluated for any type of local building to assess its seismic vulnerability to collapse.

To determine full seismic risk requires knowledge of the seismic hazard of the region, its exposure and the seismic vulnerability of the buildings. The SIMIT project is ­intended to lead to a better understanding of the seismic vulner­ability of buildings and the built environment to seismic action in Malta, although considerably more research work and financial support is needed for this purpose. This task requires the expertise of geophysicists and seismologists collaborating with civil and structural engineers, materials engineers and construction workers since, without this important research, we would just be building in the dark.

An in-depth article on the Maltese seismologists’ work was published in Think, the University of Malta’s research magazine. The article, Rocking the Islands, is available on www.um.edu.mt/think. Italia-Malta Programme – Cohesion Policy 2007 – 2013. A Sea of Opportunities for the Future.