What is an earthquake?
An earthquake occurs when there is sudden slip of two opposing tectonic plates after a huge rise in pressure across the fault line. The forces exerted are far greater than that caused by an atomic bomb. The initial earthquake is often followed by after-shocks which can continue for several days.
Earthquakes in El Salvador are very frequent indeed as there is an active fault line along the coast and additionally the country lies in the vicinity of three tectonic plates moving at different speeds. The two major earthquakes over the last century have been in 1986 and 2001.
Why do earthquakes happen?
Earthquakes are paradoxically part of the safety mechanism of pressure release that prevents the global crust from disintegrating completely. Fault lines are situated in the proximity of volcanoes which are also part of the pressure release mechanism of our planet. Tectonic plates move at varying speeds and the differential in movement between the various tectonic plates leads to a rise in the pressure gradient across the fault line. The pressure reaches a critical point at which time the slippage occurs causing the sudden release of energy.
Secondary effects of earthquakes…
There are many secondary effects of earthquakes including mud slides, boulder slides, floods and tsunamis and fires. Immediate effects for people in an earthquake zone include collapse of buildings and entrapment. Disruption of water, gas and electricity is a common feature after earthquakes. After shocks can cause further damage and possible collapse of already weakened buildings and structures. Roads and railways are often damaged and service severely disrupted. Buildings and structures built on soft material, such as alluvial deposits or volcanic ash are much more prone to collapse as the ground shaking is intensified compared with buildings sited on firm ground or rock.
Prediction of earthquakes..
It is difficult to predict earthquakes precisely but the modern technology is assisting in ascertaining pressure build up across fault lines. This is achieved by using networks of Global Position Sensing (GPS) and the satellites detect microscopic crustal deformation on an atomic time clock. The information received from the GPS networks can be processed by mathematicians and the strain pattern demonstrated. This gives a high indication of vulnerable areas on the earth’s crust.
Mitigation & Preparedness for earthquakes
Local knowledge of earthquake vulnerability is essential and mitigation can be achieved by sound building policies with good planning in areas of low ground shaking and with substantial re-enforcement. Additionally the local population should be educated particularly the children regarding measures to be taken in the event of an earthquake including taking cover under a firm table or crouching below a doorway lintel.
New Zealand is a lead country in earthquake mitigation and the population is well educated and all public buildings registered for adequate re-enforcement