Earthquakes. They occur as the result of the release of pressure along a fault. They are most common along tectonic plate boundaries, but can occur almost anywhere. Although usually lasting only seconds, they can result in extensive damage to buildings, gas and water pipes, power and communication lines, and roadways. Besides the immediate, obvious threat presented by earthquakes, they can also serve as triggers for several other natural hazards. In fact, the primary cause of damage in modern earthquakes is fire, which is usually started by broken gas pipes and power lines. Slope failures can easily be triggered by the energy release associated with earthquakes. When earthquakes occur in an ocean or large lake, a tsunami may be formed and a flood may surround coastlines. Earthquakes often occur along with volcanic activity, which presents a variety of additional threats.

What are Earthquakes?

An earthquake is a trembling or shaking movement of the Earth's surface, typically caused by movement on faults, quasi-planar zones of deformation within its uppermost layers. The solid earth is in slow but constant motion. Ĺearthquakes occur when the resulting stress exceeds the capacity of Earth materials to support it. This condition is most often found at the boundaries of the tectonic plates into which the Earth's lithosphere can be divided.

How do they occur?

Scientists have developed a theory called plate tectonics in order to explain why most earthquakes occur. According to this theory, Earth's outer shell is consisted of about 10 large rigid plates and 20 smaller ones. Each plate is formed by a section of Earth's crust and a portion of the mantle, the thick layer of hot rock below the crust. Scientists call this layer of crust and upper mantle lithosphere. The plates move slowly and continuously on the asthenosphere, a layer of hot, soft rock in the mantle. As the plates move, they collide, move apart, or slide past one another.

The movement of the plates strains the rock at and near the plate's boundaries and produces zones of faults around them. Along the segments of some faults, the rock locks in place and cannot slide as the plates move. Stress builds up in the rock on both sides of the fault and causes the rock to break and shift in an earthquake.

When an earthquake occurs, the violent breaking of the rock releases amounts of energy that travels through Earth in the form of vibrations, which are called seismic waves. Seismic waves are spreading out, from the focus of the earthquake, in all directions and weaken gradually. This is the reason why the farthest a place is from the Earthquake's focus the less the ground shakes.

When and how often do they occur?

This is one of the most pressing and puzzling questions for scientists. There is no definite answer to that. It depends on the local geotectonic conditions. Researchers try to limit the recurrence interval for large earthquakes, so as to define the best possible way the hazard for a particular area. In order to achieve that, scientists use all the help they can get: seismology, geology, archaeology, etc.

What is their impact (positive - negative, short-term - long-term)?

Earthquakes occur every day on Earth, but the majority of them are minor and cause no damage. However, depending on their magnitude, earthquakes may produce heavy damages and human casualties. Large earthquakes can cause serious destruction and massive loss of life via a variety of destructive agents including:

• Fault rupture.
• Vibratory ground motion (i.e. shaking).
• Inundation (e.g. tsunami, dam failure).
• Various kinds of permanent ground failure (e.g. liquefaction, landslide).
• Fire or release of hazardous materials.

How does science cope with Earthquakes?

Scientific approach to earthquake hazards is double-sided:

Firstly, by fundamental research in the fields of seismology, earthquake geology, etc. scientists:

• Try to find out the earthquake's generation factors and understand the propagation of the earthquake rupture.
• Research the geological structure of a particular area in order to define earthquake hazard. Seismic zoning is based on fundamental research results.

Secondly, by applied research in the fields of civil engineering and engineering geology, scientists try to develop new construction methods and materials that will better withstand severe shaking. Building codes are constantly changing and adapting the most recent (newest) research results.

Selected RTD Projects to be presented in SHIELD's Exhibitions

      Click here for Earthquakes related RTD Projects