EARTHQUAKES:
TO CONTROL OR TO PREDICT? | |
Facing
natural disasters (hurricans, earthquakes, etc.) mankind has always had two alternatives:
try in same way to control the phenomenon or to recognize that nature is more
powerfull and only to predice (it implies a passive resignation attitude when
allowing the phenomenon occurs) |
HOW EARTHQUAKES HAPPEN?
The cortex is formed
by tectonic plates that float in the "magma" (hot and semiliquid rocks).
The contact zone between two plates is called "fault". If the plates
slip slightly one over the other (or in other words, if the friction were light)
we would have an amount of shakes... slight and harmless. Unluckily in the faults
there is a great friction that keeps them in its place, while the vortices of
magma ("convection currents") produce a continual pushig which is shown
as increasing pressure.
So, when the accumulated forces exceed the friction,
there is a violent shake because of a strong movement of the plates. That is what
can be called an earthquake. On other side, to
settle a city is preferable that the climate and the natural means of transport
be favorurable. This leads us to coasts, valleys and riversides, it means... on
the faults. Effect? A 40% of the cities in the world are in seismic zones. Just
one quake can cause thousands of deaths:
* 1976, Tangshan, China: 250 000
deaths
* 1978, Iran: 15 000 deaths
* 1985, Mexico City: 30 000 deaths
* 1988, Armenia: 25 000 deaths, etc. |
| | ¿What
to do in front of earthquakes? i) To ban the
construction of cities on the faults. In other words, should be inhabited Chile,
Japan, etc.
ii) If the first choice is rejected, let us build antiseismic
cities. The problem? It is difficult to ask a poor country to invest in antiseismic
technology. Also, if the antiseismic technology were the latest one, it would
hardly bear a greater than 8 degrees Richter seism.
As a consequence, "To
Avoid" is rejected. We still can Control and Predict. iii)
To control the seisms?
As explained before, the problem of earthquakes is
a FRICTION problem. If the faults were well lubricated, the plates would slide
as slowly that we wouldn't notice it (except by the topographical changes). According
to the Figure, |  |
the fault could close in A and C, pushing out water of deep wells.
Then, that water could be pumped to the B well (as a way of lubricant) what would
cause a little seism. In this way, a violent earthquake would be avoided dissipating
the pressure with a series of practically imperceptible little seisms. Imagination?
We have the technology to do it... but is extremely expensive (may be in a 100
years more). |
|
iv) To
Predict the Seisms?
We have the last choice: to predict the seisms to evacuate
in time the cities. However, to make the prediction useful, it must have a good
precision. It´s not useful to state that in the following 5 years a big
earthquake is going to happen. Are we going to evacuate the city for 5 years?
Let us see another set: "We are going to have an earthquake next tuesday".
The city is evacuated and nothing happens. The next day people come back to their
houses and the earthquake occurs, causing many deaths. Despite of being wrong
in just one day, the prestige of the predictable model used would be destroyed.
The (valid) argument that every science has a margin of error would hardly satisfy
the deaths relatives.
| What
can we do?
Following with the topic of prediction, nowadays there
are two possible alternatives:
i) Accumulated pressures calculation
Through
satellites with interferometers and lasers the changes in the shape of the planet
can be meassured with great precision and also detect the little movements that
in its surface occurs. In this way it is possible to get a complete map of the
deformations of the planet, what means (thanks to the Matter Continual Mechanics)
a map of tensions.
A computarized analysis of the point to point tensions
would allow us to know beforehand the time when the accumulated pressure could
overcome the friction.
At last we could have a chronograme of earthquakes.
Unluckily the leaders of opinion think that the space technology is a waste of
money.
| |
ii) Zones
of Seismic Silence ("Gaps")
In may of 1985, two Geologists showed
that a zone of the Saint Andreas Fault had been suspiciously calmness. What meant
that a huge pressure was being accumulating. The prediction was that a earthquake
was going to happen in that place. And that was what happened. Motivated by the
success, the Geologists discovered that in other four times the earthquakes had
been preceeded by a period of "seismic silence". |
Zones of Seismic Silence in Chile
* 450 Km of coast in the
North zone, from Ilo (Perú) to Camarones
* From Matanzas to Constitución
* For the next 20 years: an earthquake like the one in 1928 in Talca
* La
Ligua - Papudo, with a period of 15 years
* Central zone: an earthquake like
that in 1985 before 2070 END OF THE SERIES |
| |
