An earthquake is the
result of a sudden release of energy in the Earth’s
crust that creates seismic
waves. It is also called as a quake, tremor or temblor.
There are few different types of earthquakes. The most
common of earthquakes is tectonic earthquakes. These are produced when rocks
break suddenly in response to the various global forces. The second type of
earthquake is the one which accompanies volcanic eruptions. A volcanic
earthquake is defined as one that occurs in conjunction with volcanic activity,
but it is believed that eruptions and earthquakes both result from tectonic
forces in the rocks and need not occur together. While collapse earth quakes
are comparatively small earthquakes and they take place around underground
mines. This also referred to as the mine bursts that are caused by the pressure
induced within the rocks. And the last, the explosion earthquakes, that are
caused due to the nuclear explosions.
Earthquakes are caused mostly by rupture of geological faults, but also by other events
such as volcanic activity, landslides, mine blasts, and nuclear tests.
The epicenter is the place directly above it where the
seismic waves were felt while the focus of an earthquake is the place where an
earthquake occurred along the fault underground. The focus is where
an earthquake starts and epicenter is where the earthquakes are hit
the hardest.
An aftershock is a smaller earthquake that
occurs after a previous large earthquake, in the same area of the main shock
while a foreshock is an earthquake that occurs before a larger seismic event and is
related to it in both time and space.
A seismograph, or seismometer, is an instrument used to
detect and record earthquakes. It consists of a mass attached to a fixed base.
During an earthquake, the base moves and the mass do not. The motion of the
base with respect to the mass is commonly transformed into an electrical
voltage. The electrical voltage is recorded on paper, magnetic tape, or another
recording medium. This record is proportional to the motion of the seismometer
mass relative to the earth, but it can be mathematically converted to a record
of the absolute motion of the ground.
Magnitude is a measure of earthquake size and remains
unchanged with distance from the earthquake. Intensity, however, describes the
degree of shaking caused by an earthquake at a given place and decreases with
distance from the earthquake epicenter.
The Richter
magnitude scale was developed to
assign a single number to quantify the energy released during an earthquake. The scale is a base-10 logarithmic scale. The magnitude is
defined as the logarithm of the ratio of the amplitude of waves measured by a seismograph to arbitrary small
amplitude while Rossi–Forel scale is an arbitrary numerical scale of intensity of seismic
disturbances ranging from one for a barely perceptible tremor to 10 for an
earthquake of the highest intensity
Before an earthquake, attend earthquake drills, be
prepared for first aid kits, remove all heavy objects on top of cabinets and
put them at the bottom of the cabinets. During an earthquake, do not panic. If
there are kids, gather them together and stay with them, lay down on the
ground, and ran outside the house if you have time. After an earthquake, shut
off the main switch of the electricity, stay away from damaged buildings,
report damages immediately.
Source:
http://www.presstv.ir/detail/2013/05/15/303582/scientists-working-on-earthquake-forecasting-systems/
