Earthquakes

EARTHQUAKES___________________________________________________

Mechanism of destruction:-

Vibration energy transmitted through the earth’s surface from depth. Vibration causes damage and collapse of structures, which in turn may kill and injure occupants. Vibration may also cause landslides, liquefaction, rock falls and other ground failures, damaging settlements in the vicinity. Vibration may also trigger multiple fires, industrial or transportation accidents and may trigger floods through failure of dams and other flood retaining embankments.

Parameters of severity:-

Magnitude scales (Richter, Seismic Moment) indicate the amount of energy release at the epicenterвЂ"the size of an area affected by an earthquake is roughly related to the amount of energy released. Intensity scales (Modified Mercalli, MSK) indicate severity of ground shaking at a locationвЂ"severity of shaking is also related to magnitude of energy release, distance away from epicenter of the earthquake and local soil conditions.

Causes:-

Energy release by geophysical adjustments deep in the earth along faults formed in the earth’s crust. Tectonic processes of continental drift. Local geomorphology shifts.

Volcanic activity

Hazard assessment and mapping techniques:-

Past occurrence of earthquakes and accurate logging of their size and effects: tendency for earthquakes to recur in the same areas over the centuries. Identification of seismic fault systems and seismic source regions In rare cases it may be possible to identify individual causative faults. Quantification of probability of experiencing various strengths of ground motion at a site in terms of return period (average time between events) for intensity

Potential for reducing hazard:-

None.

Onset and warning:-

Sudden. Not currently possible to predict short-term earthquake occurrence with any accuracy.

Elements most at risk:-

Dense collections of weak buildings with high occupancy Non-engineered buildings constructed by the householder: earth, rubble stone and un reinforced masonry buildings.

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