One cannot avoid a seism but the main objective is to envisage the place where the future earthquake will occur.
The Earth moves at a rate of more than one million jolts per annum. Of course, this telluric activity is not, in the majority of the case, perceptible with the man.
Our history is marked fatal seisms which underline the brittleness of our planet and consequently, of our company.
To include/understand the operation of a seism:
An earthquake does not strike randomly. Some essential scientific points make it possible to better include/understand the phenomenon.
The world seismic activity is perceived better thanks to the theory of the plate tectonics. The Earth's crust consists of several plates of a hundred kilometers thickness which move the ones compared to the others. But, this displacement is done by with blow. The seisms are born with the level from the zones from contact from these plates.
The dynamics of the plates:
The most important plates are: American, the Eurasian, African, theAustralian one and the Antarctic.
These plates are associated with secondary plates: Somali, Arabic, plate of Nacza, Coconuts, the Caribbean and Philippines.
These rigid plates are subjected to tensions so strong that they undergo brutal ruptures regularly.
The enormous quantities of energy released during these ruptures are at the origin of the earthquakes.
Zones of intense seismic activity:
The hot areas with the earthquakes are:
The médio-oceanic dorsals which account for 1 or 2 km under the surface of the oceans
The zones of subduction which give place to violent one seisms. The latter are centered up to 700 km of depth on the tilted level of the oceanic crust.
One speaks about subduction when a oceanic plate plunges under another plate
Zones of transforming faults the length whose the plates slide. Example: the fault of San Andreas in California.
The zones of collision which are the collision between two continents
Hearth and epicentre of a seism
The hearth or hypocentre is the point of origin of the rupture of the Earth's crust.
The epicentre is the point of surface being with the vertical of the hearth. It is there that the jolt is maximum.
Magnitude of the seism:
The magnitude quantifies the power of the earthquake. This scale of power was worked out by Charles Francis Richter and was used as from 1935. This scale is graduated from 1 to 9.
The energy of a seism is transmitted starting from the hearth via elastic waves: the waves P or primary educations which are longitudinal and the waves S or secondaries which are transverse.
The propagation velocity of the waves varies from 2 to 14 km/s.
To envisage the earthquakes
There exist harbingers which are a prelude to with the seisms:
Variation of the local magnetic field
Increase in the circulation of subterranean water
Reduction in the resistivity of the rocks
Light deformations of the surface of the ground
In the areas at the risks, plus the last seism is far, plus the risk is large that new occurs.
The seismic cycle is very variable. It can run out of tens or the hundreds of years between two ruptures strong magnitude.
Means of detection and recording exist:
The seismographs which make it possible to amplify the most negligible movement of the ground
The networks “WWSSN” (American) and géoscope (French) which are measuring devices recording all the components of the movement of the ground on two complementary wavebands.
Interferometry: catches of sight by satellites which give the modifications of terrestrial surface.
To date, no earthquake could be envisaged. Best protection remains related to constructions.
The choice of the establishment and the solidity of the foundations are paramount. Without implementation of the paraseismic provisions, many deaths will be still to regret.
Last earthquake. The Seism in Asia
The giant waves generated by a powerful seism off Indonesia broke Sunday, December 26 on the South Asia, after having devastated villages of fishermen and tourist resorts, in particular in India, in Sri Lanka and in Thailand.
This seism, most violent which has occurred in the world for forty years, with a magnitude of 8,9 on the open scales of Richter, has occurred in broad island of Sumatra.
It caused a series of tidal wave and vaguenesses reaching ten meters in height sometimes submerged thousands of kilometers of coasts in India, in Sri Lanka, in Malaysia, in Indonesia, in Thailand and in Maldives.
The assessment is very heavy since one advances the figure of a million deaths. The scientists had however sounded alarm. The populations would have had between 3 and 5:00 to evacuate the most dangerous zones. Who are the persons in charge? Why the governments didn't inform the populations?
his questions I am well afraid which it will never have inswers .