Monday, January 25, 2010

Earthquakes and El Salvador

The horrible devastation from the earthquake in Haiti necessarily prompts one to reflect on El Salvador's vulnerability to a similar event. Over the past 60 years, El Salvador has been hit by five earthquakes, which collectively have killed more than 2500 Salvadorans and destroyed the homes of hundreds of thousands.

From USGS:

* May 6, 1951 - Magnitude 6.2 - Fatalities 400
* May 3, 1965 - Magnitude 6.3 - Fatalities 125
* October 10, 1986 - Magnitude 5.5 - Fatalities 1,000
* January 13, 2001 - Magnitude 7.7 - Fatalities 852
* February 13, 2001 - Magnitude 6.6 - Fatalities 315

The most recent earthquake to shake the country and Guatemala was felt on Monday, January 18, when a tremor of magnitude 6.0 in Guatemala could be felt in El Salvador, shaking nerves but causing no damages.

Taking measures to mitigate the risk of a catastrophe like Haiti requires resources and attention. Unfortunately, El Salvador's limited resources and perhaps a lack of political will has resulted in too little attention to such efforts. A paper exploring El Salvador's earthquake susceptibility prepared by experts after the 2001 earthquakes had the following conclusions:

The lack of extensive structural damage in reinforced concrete buildings due to these earthquakes should not be interpreted as a vindication of the success of the current seismic design code in El Salvador nor its predecessors, since regardless of their technical merits these codes have generally been applied only sporadically. The lack of major structural damages and collapse of large buildings appears to be more closely related to the nature of the ground motions generated than the quality of engineering design or construction.

Particularly in San Salvador there is now a real danger of complacency regarding the capacity of existing buildings, despite the fact that it is widely known that many buildings have been left damaged by the 10 October 1986 earthquake and these may have been further weakened by the 2001 earthquakes. Destructive moderate magnitude earthquakes occur in San Salvador on average every 20-25 years (Harlow et al., 1993) and the next event, whose due date draws ever closer, could cause terrible damage and loss of life in the overcrowded and expanding capital.

The most devastating impact of the 2001 earthquakes has been the triggering of hundreds of landslides in volcanic soils, which have buried houses and blocked roads, causing most of the deaths in these earthquakes and bringing massive disruption: the Pan-American Highway remained closed for more than 10 months due to the la ndslide at Las Leonas. The number of landslides triggered by these earthquakes, the size of the slides and their geographical distribution, all indicate increasing susceptibility of the terrain when compared to patterns in previous earthquakes, with no ind ication that this was due to precedent rainfall. The hazard of earthquake- and rainfall-induced landslides in the volcanic soils that dominate much of El Salvador, and particularly the most densely populated areas, urgently requires attention. The identification of zones of high landslide hazard is an important component of any programme of mitigation, but relocation to lower hazard zones will often not be an option in this densely populated country with a long history of conflicts over land ownership....

Seismic risk in El Salvador clearly cannot be viewed in complete isolation from other risks, including those due to other natural hazards such as floods and volcanic eruption but also anthropogenic risks such as pollution, deforestation, crime, poverty, disease and social conflict. The failure to tackle the challenges of seismic risk, or even to hold back its increasing levels, is not due to lack of awareness amongst Salvadorians of the very high earthquake hazard that affects their country. Rather the lack of effective measures against earthquake hazards reflects the fact that there are many urgently pressing needs on limited resources, exacerbated by the weakness of central and local government. A pessimistic view of the situation may conclude that earthquake risk mitigation will only be possible following the solution of other major social problems in El Salvador. An alternative view holds that recognition of the interaction of seismic vulnerability with other features of vulnerability, including institutional vulnerability, means that concerted programs of seismic risk mitigation could provide a vehicle and a stimulus to the solution of many other issues, including the current concentration of more than half of the population in one third of the national territory. El Salvador will need external assistance, both in terms of material resources and technology transfer, to make this vision a reality.


chishi said...
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chishi said...

The paper on the equakes in E.S. must be interesting, and there are several truths we may derive from this quote, on how resilience of buildings in E.S. is allegedly not a result of compliance to construction seismic codes:

"The lack of major structural damages and collapse of large buildings appears to be more closely related to the nature of the ground motions generated than the quality of engineering design or construction".

No code will ever prepare you for the movement of the earth when its intensity or length is too much for structures to bear.

On the other hand, the construction industry in E.S. is light years from that in Haiti. Haiti's materials and constructions were lacking in quality and in technical strength in their designs. A total absence of state and codes.

While undoubtedly codes should be strengthened in E.S. and observed better and enforced completely, there are buildings and houses which have already survived 3 or more earthquakes and their subsequent seismic periods.

When they fall during a massive earthquake it will not be because codes were not observed, it will be because even a japanese built building could fall during an event that is unstoppable and unpredictable.

E.S. is, thank God, far away from having a Haiti like construction industry. We are not even close from being a failed state as poor Haiti is.