Earthquakes & Early Warning
Earthquakes are one of the natural hazards that cannot be forecasted. It is not possible to
say where and when such event may occur. In this case early warning are restricted to the
delimitation of zone presenting higher risk requesting appropriate infrastructures and tool
for the evaluation of the victims for quick and appropriate response after the event.
Geographical Information Systems (GIS) may help in evaluating both aspects.
Maps showing risks
The risk is a function of two components, one depending from the frequency and
magnitude of the event occurrence and the other from the vulnerability of the population.
In the case of earthquakes, the vulnerability could be evaluated using 5 indicators:
The population density, the quality of the construction, the type of soil (Quarternary
rocks are less stable and amplify the shakes), the Global Domestic Product (GDP), may
help to evaluate the capacity of one country to protect its population and to react after a
disaster. Most of the victims from natural disasters are located in poor countries as shown
on the map "Earthquakes since 1980 having caused 1000 or more Deaths". War in a
country could also increase the risk by preventing aid organisations to access the
population in need.
Data source: Council of the National Seismic System (CNSS)
Data analysis, mapping and printing: UNEP/GRID-Geneva, June 2000
The frequency and magnitude of hazards could be used to compute the probability of
being struck by an earthquake at a certain location.
The above map delineates the probability of occurrence for earthquakes having a
magnitude higher than 5.4 on Richter scale, within a distance of 200 km. This figures are
based on the last 20 years as recorded by the Council of The National Seismic System
(CNSS).
Models
If models for forecasting earthquakes worldwide are not available, it is possible to build
predictive models providing an estimatino of the number of victims and injured persons
after an earthquake. The inputs required are the population density distribution, the type
of soil, the quality of buildings (the GDP could be used as an estimation in case this
information is missing), the intensity of the earthquake and exact location of the
epicenter, its depth and orientation of the active fault. Such model could really help aid
organisation and local governments to evaluate the situation after an earthquake, leading
in improved efficiency on the terrain.
However the figures should be taken with care as it also depend of the time of the day, if
the people are outside, if they are woring or if they are sleeping: the situation will be
completely different. So such model could be a help but it will be very difficult to
achieve a real performant tool.
The following map shows the earthquakes causing the worst number of victims in the last
20 years, in relation with the density of the population. The vulnerability to earthquakes
depends obviously from the density of the population but also to the level of
infrastructure. Prevention could consist on selecting appropriate ground for building and
avoiding sismic area or at least smooth ground which accelerate the earthquakes.