Hilmar Bungum and Dominik Lang, NORSAR/ICG
In the wake of the disaster at Haiti on January 12 questions are naturally posed why this earthquake happened, why it could not be predicted and why it became so disastrous. Can it happen again and if so, where, what is being done and what can be done to prevent such disasters in the future? These questions will be briefly addressed in the following.
Global. It is now common knowledge that most of the larger earthquakes occur along the borders between 8 to 10 large crustal (tectonic) plates (and many smaller ones) which move relative to each other. Many would also know that these movements are typically in the range of a few centimeters per year and that the energy that drives them originates from the hot interior of the Earth. These are geologically controlled processes that are unaffected by man. We therefore have to learn to live with earthquakes, which however does not mean that we should accept disasters like the one in Haiti.
The Caribbean constitutes a separate (smaller) tectonic plate that covers the region from Venezuela in the south to Hispaniola (Haiti and the Dominican Republic) in the north and from Mexico in the west to the Lesser Antilles in the east. Many of the plate borders in this region are so-called subduction zones that are associated with a considerable tsunami hazard in addition to the shaking itself, and when active volcanoes as well as hurricanes moreover are quite frequent it is easily seen that this region is very much exposed to natural hazards and associated risks.
Hispaniola comprises a number of large faults (red lines) which produce earthquakes regularly, and it was one of these that ruptured this time, 240 years since the last big earthquake at Haiti. The red area indicates where the intensity was the strongest (level IX or larger). Source: NORSAR.
Hispaniola. The border between the Caribbean and the North American plates runs north of Hispaniola but south of Cuba, and the island contains a number of prominent fault systems with significant earthquake activity in particular to the east, in the Dominican Republic. A long fracture zone runs east-west through the southern parts of Port-au-Prince, with an average movement of 0.7 mm/year. Over 250-300 years enough energy will then have been stored to allow for an earthquake of magnitude 7.0, which fits quite well with an earthquake of that size in Haiti in 1770. This earthquake is well documented, with an intensity of X (10) on a scale to XII (12), just like the present one.
Haiti. The effects of the Haiti disaster are likely to be a lot more serious than what most countries with similar disasters experience, caused by the fact that the country was so poor and fragile in the first place. This will be seen most clearly when TV cameras are shut off and rescue teams have gone home. The society will have to be completely restructured, politically and economically, the reconstruction is expected to be rapid, of low quality, and with many provisional buildings and associated slums. The effects on the gross national product are likely to be seen for tens of years.
Earthquake prediction. As indicated above this earthquake was (statistically) expected, even though no one could say if it could occur now or in 20 years from now. Earthquakes can still not be predicted in terms of time, place and magnitude, but what one can do is to estimate, with a reasonably good reliability, the earthquake hazard on a statistical (probability) basis. Simply speaking, where a large earthquake once has occurred a new one of similar size will eventually occur, which means that we are able to predict the level of shaking that a building will be expected to be exposed to during its life time. This is essentially what we need as a basis for building rules and regulations, and if such had been developed and effectively implemented everywhere then earthquakes would have been a manageable problem on a global basis. Unfortunately, it is not that simple.
An overview of earthquakes since 1900 shows a great scatter in the level of casualties, but the underlying data also illustrates a steady increase with time. A future catastrophe with more than 500,000 casualties is not impossible. Source: Roger Bilham, University of Colorado.
What is going on? The situation is that we for a long time now have had a negative development with respect to earthquake damages and catastrophes, and at an accelerating pace. This development is, since earthquakes occur at their own stable pace, related to an increasing vulnerability, tied first of all to population increase, urbanization and associated slum development. More than half of the world population now lives in cities, we have about 200 cities with more than 2 million inhabitants, and 55% of these are located in earthquake-prone areas. About 25% of these are so-called megacities with more than 8 million inhabitants, and it is this dramatic development which first of all explains the rapid increase in earthquake disasters.
What can happen? This development is very serious and there are realistic models which predict earthquake catastrophes with up to 0.5 million casualties. The most exposed regions here are the earthquake belt from the Mediterranean through the Middle East, Iran, Pakistan, the Himalayas, China, to Japan, the Philippines and Indonesia, plus the west coast of the Americas (both south and north). It can take 50 years until this mega disaster strikes, but it can also happen tomorrow.
What is being done? There is a lot of good work going on at present to counter and mitigate this development, and the key here is to develop knowledge about earthquake hazard and to use this for reducing vulnerability, physical (building related) as well as societal. This is however a political challenge more than an engineering task, with increase of public awareness, education and capacity building as central elements. Since the capital interests will ensure the safe construction of large and expensive buildings, the real challenge here will focus on simple low-cost buildings where most people live, especially in developing countries. Traditional building styles are often death traps; it is the buildings that kill and not the earthquakes. Suitable solutions, however, are well known and they do not have to be expensive.
Whose responsibility? Earthquake catastrophes are essentially a socio-economic problem, and it could be said that such disasters are also man-made. But it would be a misunderstanding to believe that we cannot solve this problem until all countries are developed. We have enough knowledge but we are missing leaders who can see farther than to the next election. The problem is that we need to look 10 to 20 times ahead, since what is special with earthquakes is that they at a given location are quite rare but devastating. We can therefore not trust the local societal memory; in this case it is the global knowledge that has to be applied to each local region. This calls for political will and determination.
The key for reducing earthquake damages is to reduce vulnerability, building-related as well as societal, based on an underlying knowledge of earthquake hazard. A number of well-proven preventive measures can be activated for this mitigation purpose. Source: NORSAR.
A slightly different version of this popular note in Norwegian language was published in Aftenposten, January 20, 2010.
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