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intensity of the earthquake

The intensity of the earthquakes is valued according to the Richter scale (Charles Francis Richter 26/4/1900 - 30/9/1985) or the modified Mercalli scale (Giuseppe Mercalli 21/5/1850 - 19/3/1914). The first scale furnishes an evaluation (magnitude) of the quantity of freed energy, while the seconds scale assigns a degree to the effects on the environment. In the 1902 Mercalli proposed the first composed scale from 10 degrees, in succession the Americans H.O. Wood and F. Neumann modified it adding 2 degrees at the end of adapt it to the constructive customs in California conventions. For the same motive in Western Europe is in use the MCS scale (Mercalli, Cancani, Sieberg), but in Oriental Europe be used the MKS scale (Medvedv, Karnik, Sponheuer). For a real comparison of the intensity of the earthquakes, and not only of the effects, has stayed introduced the scale of the magnitudo or Richter. From notice that already the Cancani (1856-1904), had introduced a gradation not empirical, assigning at 1 of the own scale the value of 2.5 mm/s2, and at 12 the value of 10000 mm/s2.

Richter scale

This scale doesn't have divisions in degrees, inferior limits, (if not of the tools) and superior. The appraisal of the energy freed from a seism is associated to an index, by definition magnitudo, it has drawn to divide the decimal logarithm of the maximum ampleness of a shake and the logarithm of a shake champion. The zero of the scale is equivalent to a freed equal energy to 105 Joule.

Mercalli scale

degree tremor description 
I  instrumental  People do not feel any Earth movement.
II  lightest  A few people might notice movement if they are at rest and/or on the upper floors of tall buildings.
III  light  Many people indoors feel movement. Hanging objects swing back and forth. People outdoors might not realize that an earthquake is occurring.
IV  mediocre  Most people indoors feel movement. Hanging objects swing. Dishes, windows, and doors rattle. The earthquake feels like a heavy truck hitting the walls. A few people outdoors may feel movement. Parked cars rock.
V  strongly  Almost everyone feels movement. Sleeping people are awakened. Doors swing open or close. Dishes are broken. Pictures on the wall move. Small objects move or are turned over. Trees might shake. Liquids might spill out of open containers.
VI  much fort  Everyone feels movement. People have trouble walking. Objects fall from shelves. Pictures fall off walls. Furniture moves. Plaster in walls might crack. Trees and bushes shake. Damage is slight in poorly built buildings. No structural damage.
VII  strong  People have difficulty standing. Drivers feel their cars shaking. Some furniture breaks. Loose bricks fall from buildings. Damage is slight to moderate in well-built buildings; considerable in poorly built buildings.
VIII  violent  Drivers have trouble steering. Houses that are not bolted down might shift on their foundations. Tall structures such as towers and chimneys might twist and fall. Well-built buildings suffer slight damage. Poorly built structures suffer severe damage. Tree branches break. Hillsides might crack if the ground is wet. Water levels in wells might change.
IX  disastrous  Well-built buildings suffer considerable damage. Houses that are not bolted down move off their foundations. Some underground pipes are broken. The ground cracks. Reservoirs suffer serious damage.
X  most disastrous  Most buildings and their foundations are destroyed. Some bridges are destroyed. Dams are seriously damaged. Large landslides occur. Water is thrown on the banks of canals, rivers, lakes. The ground cracks in large areas. Railroad tracks are bent slightly.
XI  catastrophic  Most buildings collapse. Some bridges are destroyed. Large cracks appear in the ground. Underground pipelines are destroyed. Railroad tracks are badly bent.
XII  great catastrophe  Almost everything is destroyed. Objects are thrown into the air. The ground moves in waves or ripples. Large amounts of rock may move.

magnitude Richter
energy
joule
degree Mercalli
< 3.5
< 1.6 E+7
I
3.5
1.6 E+7
II
4.2
7.5 E+8
III
4.5
4 E+9
IV
4.8
2.1 E+10
V
5.4
5.7 E+11
VI
6.1
2.8 E+13
VII
6.5
2.5 E+14
VIII
6.9
2.3 E+15
IX
7.3
2.1 E+16
X
8.1
> 1.7 E+18
XI
> 8.1
.
XII

earthquake severity

Richter magnitude
earthquake effects
less than 3.5
Generally not felt, but recorded.
3.5-5.4
Often felt, but rarely causes damage.
under 6.0
At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions.
6.1-6.9
Can be destructive in areas up to about 100 kilometers across where people live.
7.0-7.9
Major earthquake. Can cause serious damage over larger areas.
8 or greater
Great earthquake. Can cause serious damage in areas several hundred kilometers across.
magnitude Richter
TNT equivalent
-1.5
6 ounces
1
30 ounces
1.5
320 pounds
2
1 ton
2.5
4.6 tons
3
29 tons
3.5
73 tons
4
1000 tons
4.5
5100 tons
5
32000 tons
5.5
80000 tons
6
1 milion tons
6.5
5 milion tons
7
32 milon tons
7.5
160 milion tons
8
1 bilion tons
8.5
5 bilion tons
9
32 bilion tons
10
1 trilion tons
12
160 trilion tons

presumed that one ounce of TNT exploded below ground yields 640 million ergs of seismic wave energy


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