Earthquake engineering

Definition:
• An Earthquake is a sudden and rapid shaking of the ground due
to passage of vibrations beneath caused by transient disturbance
of elastic or gravitational equilibrium of rocks.
• The scientific study of earthquakes is called Seismology.
• Earthquakes are measured using observations from seismometers.
• Seismic waves are recorded on instruments called seismographs.
• The time, locations, and magnitude of an earthquake can be
determined from the data recorded by seismograph stations.

RICHTER MAGNITUDE SCALE:
• The Richter magnitude scale was developed in 1935 by Charles F.
Richter.
• Earthquakes with magnitude of about 2.0 or less are usually called
micro earthquakes; are generally recorded only on local
seismographs.
• Events with magnitudes of about 4.5 or greater, are strong enough
to be recorded by sensitive seismographs all over the world.
• Great earthquakes have magnitudes of 8.0 or higher.
• On the average, one earthquake of such size occurs somewhere in
the world each year.

CAUSES :
Natural Causes of Earthquake:
• Tectonic Movement
• Volcanic Activity
• Pressure of gases in the interior
• Landslides and avalanches
• Faulting and folding in the rock beds are responsible for causing
minor earthquakes.

Man-made Earthquakes:
• The impounding of large quantities of water behind dams
disturbs the crustal balance.
• The shock waves through rocks set up by the underground
testing of Atom bombs or Hydrogen bombs may be severe to
cause earthquake.

EFFECTS:
Destructive Effects:
• Earthquake causes dismantling of buildings, bridge and other
structures at or near epicenter.
• Rails are folded, underground wires broken.
• Earthquakes originate sea waves called Tsunamis.
• Earthquakes result in the formation of cracks and fissures on the
ground formation.
• The earthquakes cause landslides.
• Landslide due to earthquake may block valleys to form lakes.

SEISMIC BELT:
• Narrow geographic zone on the Earth's surface along which most
earthquake activity occurs.
• The outermost layer of the Earth (lithosphere) is made up of
several large tectonic plates.
There are three main seismic belts in the world ：
1. Circum-Pacific seismic belt
2. Alpine-Himalayan seismic belt
3. Ridge seismic belt

Earthquake engineering

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Earthquake engineering