Seismic hazard awareness - a historical perspective

Lisbon last year recorded the 250th nniversary of its 1755 earthquake on November 1. It was strongly felt at around 9:40 a.m. in Lisbon, south of Spain and Morocco. Without causing damage it was felt almost all over Europe, in the Azores and Madeira Islands. At around 11 the waves of a tsunami passed downtown over several buildings with its flow and reflux for a distance of 250 metres with the waters raised by five metres. Besides the damage caused by the seismic movement, a great fire burned for six days, increasing the number of deaths and material damage.

The devastating Lisbon earthquake and others in Europe, particularly those which occurred in Calabria in 1783 and Messina in 1908, stimulated renewed interest in the phenomenon of earthquakes and provoked an intellectual debate which helped scientific explanation finally to divorce itself from religious dogma.

The Lisbon earthquake is a devastating event which stimulated intellectual cross-disciplinary endeavour, from the likes of Voltaire, Rousseau and Kant.

The earthquake took place when churches were full of the devout attending Mass on All Saints' Day. This helped contemporary intellects to ridicule prevailing beliefs that earthquakes and other natural disasters were 'divine retribution'. Voltaire's poem on the disaster of Lisbon, pointed out the irony of devout Lisbon, while dancing continued in vice-ridden Paris.

Politicians, risk managers and emergency relief agencies still have much to learn from the pragmatism and efficiency demonstrated in the aftermath of the Lisbon seismic event. King Jose's secretary of state was completely in command from day one of the earthquake.

The first tasks were to dispose of the dead and feed the living. The stagnant pools were drained, with troops from the provinces helping to stem the tide of survivors swarming out of the city, ordering able-bodied men and skilled workers back into the city to help with fighting the flames, clearance of streets and demolition or repair of damaged structures.

Tents, huts and other temporary shelters were erected for the homeless, profiteering in wood was stopped and available supplies of timber were commandeered. Landlords of lodgings which had survived the earthquake were not allowed to raise rents, permitting also existing tenants to return to their properties. This description appears in total contrast to the relief organisation to the Katrina hurricane.

Assessment questionnaires - asking people how many shocks were felt and what kind of damage was caused were sent out. Some of the questions are the same as those asked nowadays.

The Lisbon earthquake had a tremendous impact on the development of seismology and indeed has been characterised as the starting point of modern seismology.

Differences between deep, intermediate and shallow earthquakes were identified and their ground effects were described mainly in a qualitative fashion. Earthquake catalogues were compiled in the aftermath of the Lisbon disaster.

It was recognised that the rebuilding should be supervised and unauthorised building in stone or brick was stopped. Engineers and architects were given charge of the subsequent planning and rebuilding of the new Lisbon. The Lisbon earthquake is further responsible for one of the earliest recorded building laws. It was proposed that no building should be taller than the street width and that they should be limited to a height of two storeys.

It is important to point out that these rules for structural configurations of masonry buildings have been recently implemented in modern seismic standards, as in the Italian seismic code 2003, where specific rules account for building heights (H) with respect to street widths (L) in zones of high (0.35g) and moderate (0.25g) seismicity (Malta's low seismicity hovers around 0.075g).

A so called timber cage (gaiola) using flexes at each corner to withstand lateral forces has been described as the first recorded development of a method for reinforcing masonry buildings to resist earthquakes.

Mortared stone provided another form of bracing and a shear wall was also designed to resist lateral deformations. Malta's present building practice is totally in violation of above centuries-old recommendations, as tying between structural members is practically non-existant and soft structures at ground level are the order of the day.

A few decades later in 1783 during the Calabrian earthquake it was noted that the only building left standing in the village of Filogaso was a wooden planked structure built according to the Lisbon regulations.

Following this event the authorities recommended that timbers in the roof should have transverse reinforcements in the form of diagonal members. Light-weight shingle roofs replaced the traditional tiles. The common adobe buildings were limited to one storey, and the use of small stones, good quality bricks and a suitable mortar was advised.

A timber framework was further prescribed encased in the masonry predating later earthquake-resistant design principles of tying the building together as a unit, together with symmetric construction demonstrated optimal building configuration.

There is even evidence that persons not adhering to the rules had their buildings demolished, at least in the following years. This demonstrates that checks and quality control were undertaken.

Following ground shaking in Calabria in 1854, the government of Naples developed a plan for iron reinforcement of buildings, the first to adopt the use of iron for earthquake resistant construction.

Following the 1908 Messina earthquake an engineering professor recommended that the first storey be designed for a horizontal force equal to 1/12th the mentioned weight, while the second and third storeys be designed for 1/8th of the building weight. This method which still survives today was the first example of seismic design implementing the equivalent static method.

In 1913 two types of protection were pointed out. The first, the compensation through insurance of property owners and the second, the inspections and quality control of buildings to prevent structural damage and loss of life. The present cover in Europe for natural disasters is as follows:

Countries where the state intervenes or participates in the insurance arrangements include Spain, France, Norway, The Netherlands, Switzerland and Turkey.

Countries where the state does not intervene include Germany, Austria, Belgium, Denmark, Finland, Italy, Poland, Portugal, Czech Republic, United Kingdom and Sweden.

The prevention of vulnerability for these natural hazards is mostly catered for by the provision of building codes and for a mandatory requirement for property to be covered by an insurance policy for damage caused by natural catastrophes.

Malta appears exposed to these perils which history has taught that although infrequent do strike with dire consequences. We do not know when but we have to prepare for it to mitigate losses. The major mitigation strategy involves the deployment of national structural integrity regulations.

These have been in draft form for the past 10 years, but the building regulations section relating to conservation of fuel, energy and natural resources is to be implemented at greater cost to the construction industry well in advance of the Structural Integrity Regulations. Further property insurance cover is only mandatory for acquiring banking finance.

dhcamill@maltanet.net

Architect D.H. Camilleri is Structural & Property Investments consultant

The article draws heavily on a paper presented at the IABSE Symposium Lisbon 2005 - "Dealing with Earthquakes: Lisbon and other Historical Lessons", by L. Di Sarno and M.D. Carter.

A workshop, entitled "Seismicity and Earthquake Engineering in the Extended Mediterranean Region", chaired by seismologist Dr Pauline Galea is to be held between April 24 and 27, at Le Meridien in St Julian's.

This is part of the RELEMR programme (Reduction of Earthquake Losses in the Eastern Mediterranean Region), sponsored by UNESCO and USGS. Mr Camilleri will present a keynote paper on "Outlining the Seismic Vulnerability of Malta's Buildings - is it an issue?"