|
|
Earthquake Intensity - The Mercalli Scale
- 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 sub-surface geological
conditions.
-
- The intensity decreases outwards
from the focus, forming concentric zones of
declining intensity radiating out from the
epicenter.
Modified Mercalli
Intensity Scale
Intensity I
Instrumental |
Not felt by
people, only detected by seismographs. |
Intensity II
Feeble |
Felt only by a
few people at rest, especially on upper floors of
buildings. Delicately suspended objects may
swing. |
Intensity III
Slight |
Felt noticeably
indoors; like the vibrations due to a passing
truck. Standing motor cars may rock slightly |
Intensity IV
Moderate |
Felt indoors by
many people, outdoors by few. Dishes, windows,
doors rattle. May awaken some sleepers. Standing
cars rocked noticeably. |
Intensity V
Rather strong |
Felt by nearly
everyone, many awakened. Some dishes and windows
broken; occasional cracked plaster; unstable
objects overturned. Some disturbance of trees,
poles and other tall objects |
Intensity VI
Strong |
Felt by all; many
frightened and run outdoors. Some heavy furniture
moved; some falling plaster or damaged chimneys.
Damage slight. |
Intensity VII
Very strong |
General alarm;
people run outside. Walls crack; chimneys fall.
Considerable damage in poorly designed
structures. Noticed by persons in moving
vehicles. |
Intensity VIII
Destructive |
Considerable
damage in ordinary substantial buildings with
partial collapse. Fall of chimneys, factory
stacks, columns, monuments, walls. Heavy
furniture overturned. Changes in well water. Car
drivers seriously disturbed. |
Intensity IX
Ruinous |
Considerable
damage with partial collapse of substantial
buildings. Buildings moved off foundations;
ground cracks conspicuous. Underground pipes
broken. |
Intensity X
Disastrous |
Ground cracks
badly; landslides on river banks and steep
slopes; rails bent. Many buildings destroyed. |
Intensity XI
Very disastrous |
Broad fissures in
ground; major landslides and earth slumps;
floods. Few buildings remain standing; bridges
destroyed. Nearly all services (railways,
underground pipes, cables) out of action. |
Intensity XII
Catastrophic |
Total
destruction. Ground rises and falls in waves;
lines of sight and level distorted. Objects
thrown into the air. |
|
Innovative Technologies
Freeplay Eyemax NOAA windup radio
Innovative Technologies
QuakeAlert Electronic Earthquake Alarm
Innovative Technologies
Freeplay X-Ray Windup Flashlight
|