
Earthquake Intensity And Magnitutde
EARTHQUAKE INTENSITY
 The intensity of an earthquake can
be expressed in terms of the destruction it
causes. Eye witness accounts of earthquake damage
at the surface are matched to the Mercalli
Intensity Scale which consists of an arbitrary 12
step scale originally designed by Giuseppe
Mercalli. The scale relies on subjective
information from people who witnessed the
earthquake. From their information it is possible
to determine the epicenter and the relative
earthquake strength.

 The intensity of an earthquake at
any particular place depends not only on the
magnitude of the earthquake, but also on the
distance from the epicenter, depth of the focus,
and on the surface and subsurface geological
conditions.

 The intensity decreases outwards
from the focus, forming concentric zones of
declining intensity radiating out from the
epicenter.

 EARTHQUAKE MAGNITUDE

 The strength of an earthquake can
also be measured and expressed in terms of the
magnitude of energy released by the earthquake.

 Seismologist Charles Richter
devised his system based on the amplitude of the
seismic waves recorded by seismographs. When the
data from several seismometers are compared a
measure of magnitude can be realized within
minutes of the earthquake activity.

 The Richter scale is logarithmic.
An increase in magnitude of one unit corresponds
to a tenfold increase in the size of an
earthquake. Thus an earthquake of magnitude 6 is
ten times larger than one of magnitude 5, and a
hundred times larger than one of magnitude 4.
