EARTHQUAKES

Tremors, slides and flows

Geology is not content with explaining the living nature of the planet. It is also concerned with forecasting its "caprices". The multi-disciplinary European LESSLOSS project with its some 50 partners is focusing on earthquakes and landslides.

Coulée de boue de Boulc-en-Diois, dans la Drôme (France). © BRGM im@gé/Michel Saint-Martin
Mudslide at Boulc-en-Diois, in Drôme (France) © BRGM im@gé/Michel Saint-Martin
Séisme de Gölcük, en Turquie (17 août 1999). Le bâtiment incliné a pris cette position en raison d’un phénomène de liquéfaction des sols de fondation. L’autre, construit selon une typologie poteauxpoutres en béton armé est détruit en torsion. © BRGM im@gé/Pierre Mouroux
© BRGM im@gé/Pierre Mouroux
© BRGM im@gé/Pierre Mouroux
Earthquake at Gölcük, in Turkey (17 August 1999). The leaning building adopted this position due to the liquefaction of the foundation soil. The other building, constructed using beams and pillars in reinforced concrete, suffered a torsion effect. © BRGM im@gé/Pierre Mouroux
Coulée de lave au piton de la Fournaise (île de la Réunion), dans les années 1980. © BRGM im@gé/François Michel
Lava flow at the Piton de la Fournaise (Réunion Island), in the 1980s. © BRGM im@gé/François Michel
Conception et assemblage d’un capteur sismique. ©CNRS Photothèque/Emmanuel Perrin
Design and assembly of a seismic sensor. © CNRS Photothèque/Emmanuel Perrin
Après le tsunami du 26 décembre 2004 (Indonésie), la mission «Tsunarisque» cherche à comprendre les raisons du désastre pour permettre une meilleure prévention. © CNRS Photothèque/Frank Lavigne
Following the tsunami of 26 December 2004 (Indonesia) the Tsunarisque project is seeking to understand the reasons for the disaster to permit better prevention. © CNRS Photothèque/Frank Lavigne

News travels fast - and never before as fast as in our world of instant, "real-time" communication. In the course of a year, scarcely a week passes without pictures and reports of some natural disaster - whether earthquake, landslide, flood or forest fire - on one of the world's continents. This media coverage has one undoubted benefit: the general public is much more aware of the risk of natural disasters and their consequences, and expects decision-makers and officials to implement safety measures. Although they are essentially inevitable and in most cases unpredictable in nature, natural events can nevertheless be anticipated and their effects mitigated to a degree.Will it one day be possible to give a reliable warning of a particular earthquake?

Perhaps... but not on the basis of the present state of knowledge. For several decades now, scientists have been searching in vain to discover abnormal physical phenomena that could herald such events. A number of lines of inquiry have been pursued, such as systematic observations of level changes and radon rates in underground water, scarcely perceptible increases in elevation, variations in the speed at which shock waves travel across the Earth's surface, disturbance to the electromagnetic environment, and even the behaviour of certain animal species.

Elusive warning signs

In the 1970s, China carried out intense observation campaigns of this kind and claimed what is still regarded as being a unique feat in history: the announcement, 24 hours in advance, of an earthquake measuring 7 on the Richter scale which occurred on 4 February 1975 in the Haicheng region. But this "textbook case of empiricism", based on a rapid cross-referencing of earthquake warning signs, proved to be a one-off. What is more, light has never been shed on a number of details, notably in terms of the victims and destruction averted. No substantial scientific lesson was ever drawn from this experience and the very next year China was hit by the Tang Chang earthquake - probably the most deadly in history with a death toll of 600 000, while images of this year's Sichuan earthquake remain a very vivid memory.

In the late 1980s, three Greek researchers - Varotsos, Alexopoulos, and Nomikos - proposed a forecasting model to which they lent their initials (VAN) based on a system of recording electro-seismic signals (ESS). The decoding of these signals is believed to have made it possible to announce in advance the 1988 and 1993 earthquakes that shook their country. The reproducibility and reliability of their measurements and conclusions have never been scientifically recognised, however. They also sparked a political and scientific controversy as, given the many uncertainties linked to an earthquake, what significance can be lent to a forecasting "experiment"? Given the huge scale of the safety measures needed - such as the evacuation of supposedly threatened populations and the resultant paralysis - advance knowledge that such a cataclysmic event is imminent without knowing exactly at what moment it will occur is in fact of no value as a "management tool".

The mitigation option

Given the randomness of nature, it is best to concentrate more on "protection" policies designed to prepare populations so as to mitigate and minimise the consequences of these disasters that are inherent to the Earth's capricious nature. In 2004, the EU therefore financed the creation of an integrated research project, known as LESSLOSS, dedicated to mitigating - that is, reducing the effects of - seismic risk and landslides.

Drawing on the expertise of 46 partners (one third of which were companies), this project was in some respects the "headquarters" of human research on mitigation. Gian Michele Calvi, Project Coordinator and Director of the European Centre for Training and Research in Earthquake Engineering at the University of Pavia (IT), believes that "the multi-disciplinary approach is essential. Scientists, engineers, sociologists, telecommunication experts, seismologists, mathematicians, town planners, etc. must combine their efforts to combat earthquakes. This is the only way to be able to effectively quantify and reduce the risk."

"Within such a consortium, this type of project has the advantage of making the partners aware of the full extent of the seismic problem rather than leaving them to remain within the confines of their chosen field of study," adds André Plumier, of University of Liège (BE), who coordinated the working group Reducing the vulnerability of construction materials. "These partnerships also open the door, at the time of the general assemblies, to a genuine community of researchers in this field."

Site effect

Like earthquakes, which they often accompany, landslides are caused by movements in the upper layer of the Earth's crust. A key aspect here, therefore, is the diagnosis of the "site effect", i.e. the knowledge on a caseby- case basis, in a given geographical situation, of the way in which different terrain reacts to seismic tremors. We know, for example, that geosolid formations (rocks) transmit seismic movements without modifying them while less rigid clay or sandy sedimentary soils can amplify the seismic shocks.

But landslides can also occur independently of earthquakes, causing comparable destruction. Taken in isolation, they can, however, be monitored by means of more predictable geomorphologic signals, such as minute ground movements or the circulation of underground water in microcracks. These changes are the result of stress linked to the weight of rock and sediment as well as the gulleying effects of water - clearly less complex than the mechanisms at work in the tectonic plates deep below the Earth's surface. A global positioning system (GPS) tool is invaluable in this field. Another recent innovation in analysing slight ground movements is based on Lidar (light detection and ranging) - a technology that uses laser light to establish topographical and bathymetric data of extreme precision.

Digital tools

At the same time, our knowledge of plate tectonics is also increasing, in particular of what happens at their boundaries, by crossreferencing multi-disciplinary data acquired both through ex-post studies of recent tremors and their effects and archaeo- or paleoseismology.

This data enables us to better identify geographically and physically certain very high-risk areas and to define potential values of macro-seismic intensity. As a result, we now possess geographical information systems (GIS) presenting an ever-more detailed seismic mapping of the Earth.

These systems draw on a growing volume of geological data on the nature and behaviour of surface soil and on human infrastructure, such as housing, industry and engineering works. An important line of research pursued by the LESSLOSS project concerned advanced two-dimensional (2D) or 3D modelling methods for evaluating a seismic movement. A simulation in the Grenoble basin in the French Alps showed that seismic waves leaving from the boundary of the tectonic break provoke an amplified movement of longer duration at the basin level.

Paraseismic progress

Research on common construction materials such as reinforced concrete or steel has brought considerable safety improvements over recent decades in the field of paraseismic construction. During recent earthquakes in countries such as Japan - which suffered the Kobe quake in 1995 - or in California, the resistance of the vast majority of buildings and engineering works bear testimony to this progress. One of the LESSLOSS lines of research, pursued by the Italian National Agency for New Technologies, Energy and the Environment (Ente per le Nuove tecnologie, l'Energia e l'Ambiente) in particular, sought to develop new systems of energy dissipation that are in fact the only way of reducing an earthquake's impact. In conventional buildings, horizontal earthquake-resistant dampers of low hardness are used.

Other studies are seeking to create, for more sophisticated buildings, dampers on rubber mountings, slide blocks linked to hypothesis elements, or friction pendulum systems. A major innovation is being developed for electro-inductive dampers that convert mechanical energy into electrical currents dissipated by heat. Such a device could strengthen the stability of major infrastructure works such as bridges and viaducts. Other techniques, based on the use of reinforced polymer fibres, are applicable to existing major engineering works.

Paraseismic research also extends beyond the way of designing the "container" and has the mission of protecting building "content", especially in the case of companies with risk equipment.

Didier Buysse


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Italy on the front line

With more than 100 000 deaths due to earthquakes during the last century, Italy is the European country most affected by seismic risk. It has therefore had to develop a vast system for monitoring its three active volcanoes - Etna, Vesuvius and Stromboli - that pose a continuous threat to the densely populated areas that lie at their feet. In certain areas spatial planning and urbanisation have another threat to contend with, that of landslides. 10 years ago, the Sarno landslide left 150 dead. Since then, a vast project known as IFFI (Inventory of landslide phenomena in Italy) has shown that almost 6% of Italy could be regarded as unstable and presenting a real risk.

"In addition to the number of victims, earth movement disasters have many serious financial and economic consequences for the communities rendered vulnerable at all levels of the complex system of society," explains Gian Michele Calvi. "The mitigation of the effects and the response to crisis situations must therefore be part of a holistic and integrated approach. LESSLOSS has responded to the challenge of drawing on the expertise of all the players, including town planners, computer experts, economists, sociologists, geologists and engineers."



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