Measuring Earthquake Intensity

There are two scales used to measure the magnitude and intensity of earthquakes.

Richter Magnitude Scale
Mercalli Intensity Scale

Richter Magnitude Scale:

The Richter scale of magnitude was created in 1935 by the American seismologist Charles F. Richter. It is based on the amplitude of the waves as measured by a seismograph. The measurement is adjusted to account for the distance between the seismograph and the epicenter of the quake. Richter magnitudes increase logarithmically, which means that each level is ten times more powerful than the one before it. The numbers on the Richter scale are linked to the amount of destruction caused by an earthquake at each level

Magnitude	Description
1	Not felt on the surface, but recorded by seismographs near the epicenter.
2	May be felt only slightly near the epicenter, if at all.
3	Minor quake, often felt near the epicenter, but causing little or no damage.
4	Light quake, felt but causing little or no damage.
5	Moderate quake, felt widely, can cause slight damage near epicenter.
6	Strong quake clearly felt over a wide area. Damage to poorly constructed buildings within 10 km.
7	Major earthquake, causes serious damage and possible loss of life up to 100 km from epicenter.
8	Great earthquake, which can cause destruction, loss of life over several 100 km from epicenter.
9	Rare great earthquake, major damage and loss of life over a large region even more than 1000 km from epicenter.

Mercalli Intensity Scale:

The Mercalli intensity scale was invented in 1902 by the Italian scientist Giuseppe Mercalli. It is based upon the observation of earthquake damage at a particular location. The intensity of a quake differs greatly from place to place. It depends upon such factors as the distance from the epicenter, the design and quality of construction of local buildings, and the type of surface beneath the buildings.

Number	Name	Description
I	Instrumental	Detected by seismographs, usually not felt.
II	Feeble	A few people might notice movement if they are at rest and/or on the upper floors of tall buildings.
III	Slight	Felt by many, often mistaken for a passing vehicle. Shaking felt indoors; hanging objects swing back and forth. People outdoors might not realize that an earthquake is occurring.
IV	Moderate	Most people indoors feel movement. Hanging objects swing, parked cars might rock. Dishes, windows, and doors rattle. The earthquake feels like a heavy truck hitting the walls. A few people outdoors may feel movement.
V	Rather strong	Almost everyone feels movement. Sleeping people are awakened. Doors swing open or closed, dishes are broken, pictures on the wall move. Cracked walls, trees disturbed.
VI	Strong	Felt by all. Many run outdoors. Slight damage occurs. Stronger shaking can cause people to fall over and walls and ceilings to crack. People walk unsteadily; windows break; pictures fall off walls. Furniture moves. Trees and bushes shake
VII	Very strong	Everyone runs outdoors. Poorly built buildings suffer severe damage. Slight damage everywhere else. Difficult to stand; plaster, bricks, and tiles fall; large bells ring. Drivers feel their cars shaking. Some furniture breaks. Loose bricks fall from buildings. People fall over.
VIII	Destructive	Tall buildings sway, furniture breaks, cars swerve. Everyone runs outdoors. Moderate to major damage. Minor damage to specially designed buildings. Chimneys and walls collapse. Drivers have trouble steering. Houses that are not bolted down might shift on their foundations. Tree branches break. Hillsides might crack if the ground is wet. Water levels in wells might change.
IX	Ruinous	Ground cracks, well-constructed buildings damaged, pipes break. All buildings suffer major damage. General panic; damage to foundations; sand and mud bubble from ground. Reservoirs suffer serious damage.
X	Disastrous	Landslides, ground cracks widely. Major damage. Most buildings and their foundations are destroyed. Some bridges are destroyed. Water is thrown on the banks of canals, rivers, and lakes. Railroad tracks are bent slightly.
XI	Very disastrous	Bridges and buildings destroyed, large fissures open. Almost all structures fall. Very wide cracks in ground. Railway tracks bend; roads break up; rocks fall. Underground pipelines are destroyed.
XII	Catastrophic	Rocks moved, objects thrown about. Total destruction. Ground surface waves seen. River courses altered. Large amounts of rock may move.

Or log in with...

Related article