EEE: 1.1: Introduction, Earthquake phenomenon

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INTRODUCTION:

      Nature’s forces influence on Human existence is immense.

      Even in the face of catastrophic phenomenon, human beings have tried to control and coexist with nature.

      Among all the disasters like earthquakes, floods, tornadoes, hurricanes, droughts and volcanic eruptions the least understood and most destructive are earthquakes.

      Due to this reason, earthquake demands serious attention

      Now let us try to understand the earthquake as a Civil Engineering perspective and treat it as an engineering challenge rather than merely a disaster.

EARTHQUAKE:

“A wave like motion generated by forces in constant turmoil under the surface layer of earth (Lithosphere) Travelling through the earth’s crust”  (or)

“A sudden violent shaking of the ground resulting from the sudden release of energy in the Earth’s lithosphere that creates seismic waves.

Ø  This sudden release of energy can be caused by

1.      Sudden dislocation of segments of the crust

2.      Volcanic eruptions

3.      Explosions created by Human beings

Ø  In the process of dislocation, vibrations called seismic waves are generated.

Ø   In the most generic sense, the word earthquake is used to describe any seismic event whether a natural phenomenon or event caused by humans that creates seismic waves.

EARTHQUAKE PHENOMENON:

☞   The earthquake phenomenon is still unclear and is understood by the case studies

☞   Every earthquake shall be a source of knowing earth’s interior and phenomenon of earthquake

☞   An earthquake is caused by tectonic plate movements getting stuck and putting a strain on the ground.

☞   Most naturally occurring earthquakes are related to the tectonic nature of earth. Such are called tectonic earthquakes

☞   The earth’s lithosphere is a patchwork of plates in slow but constant motion caused by release to space of heat in the earth’s mantle and core.

☞   The heat causes the rock to melt and flow with geological time scale so that the plates move slowly but surely.

☞   Plate boundaries lock as the plates move past each other, creating frictional stress

☞   When the frictional stress exceeds a critical value called local strength a sudden failure occurs

☞   The boundary of the tectonic plates along which failure occurs is called fault plane.

☞   When the failure at fault plane results in a violent displacement of the earth’s crust, the elastic strain energy is released and seismic waves are radiated, thus causing an earthquake.

☞   This process of stress, strain and failure is referred to as elastic rebound theory.

☞   It is estimated that only 10 percent or less of an earthquake’s total energy is radiated as seismic energy.

☞   Most of the earthquake energy is used to power the earthquake fracture growth and is converted into heat or is released to friction.

☞   Majority of earthquakes originate at depth not exceeding tens of kilometers.

☞   Earthquakes may also occur in volcanic regions and are caused there both by tectonic faults and by the movement of magma in volcanoes, such earthquake can be an early warning of volcanic eruptions.

☞   The attempts of understanding phenomenon of earthquake are still being continued by investigating the cases of earthquakes encountered in recent times.