Most people know what the Richter scale is, the famous evaluation method for determining the intensity of an earthquake, but do you know what the Mercalli scale is? This scale is also used to evaluate earthquakes and is a complement to the Richter scale, but what is the difference between the Richter and Mercalli scale?
What is the difference between the Richter and Mercalli scale?
Every time there is an earthquake, the radios, televisions and newspapers give an account of its intensity, placing them at a point on the Richter scale. This scale allows us to know the intensity of the earthquake, being able to foresee the possible consequences that a certain seismic movement can cause in a certain area. However, and there have been many cases, an 8.8 earthquake on the Richter scale in Japan can be much less destructive than a 6.2 in Italy. It is at this point that we should talk about the Mercalli scale.
The difference between the Richter scale and the Mercalli scale is that the former measures the seismic movement itself, while the latter measures the damage that this movement has caused. If the first measures the magnitude of the earthquake, the second measures its intensity, that is, Richter tells us the amount of seismic energy that has been released by the earthquake while Mercalli informs us about the effects that the release of that energy has caused in a specific territory, that is why we say that both scales complement each other.
Factors involved in the Mercalli scale
Since the Mercalli scale measures the effects of the earthquake, the factors involved in the measurement are many and different. Below we will explain the main variants that help us determine the effects of an earthquake in a territory:
- The energy of the earthquake, that is, the intensity of the seismic movement based on the Richter scale.
- The distance to the faultwhere the earthquake arose is another indication, since the closer it is, the more destructive the earthquake is.
- Depending on the way in which the waves reachthe place the intensity varies.
- The type of material and the geological characteristicsof the soil.
- The sensation that the earthquake leftin the population and in the place, this is also measurable with the physical damage it has caused in the place, collapsing buildings or bursting pipes.
Like the Richter scale, the Mercalli scale also has different levels with which we can get an idea of the level of destruction that an earthquake has caused. The difference between the Richter scale and the Mercalli scale can also be seen at this point, since the second has up to 12 levels and the first only reaches up to 10.
Levels on the Mercalli scale
The levels on the Mercalli scale range from the barely perceptible jolt to total destruction, below we explain them all:
- Grade I:Even in favourable conditions to do so, few people are capable of feeling a small shock.
- Grade II:Only some people who are still, at rest and mostly in the high areas of buildings can notice a shaking.
- Grade III:The shaking is clearly felt indoors, especially on high floors, although it does not pass as a small tremor. The sensation is like the vibration caused by a train passing by.
- Grade IV:If it is daytime, many people notice it inside the houses, but few outside. If it is at night some may wake up to the sound of windows, doors and dishes, even parked cars can sway ostensibly.
- Grade V:In this grade everyone already feels it, if not many who wake up if it happens at night. Dishes and crockery, window panes and unstable objects can break.
- Grade VI:Shaking can cause panic and force people to leave their home, relatively heavy furniture can be moved and cause slight damage to some structures. In this article we explain how you should act in the event of an earthquake.
- Grade VII:At this level everyone notices the power of the earthquake, even people who travel in motorized vehicles. In well-made and well-equipped constructions there is no damage, in ordinary ones there is little damage, but in poorly built it can be considerable.
- Grade VIII:Damage in well-designed structures, collapses in ordinary structures and total destruction in bad ones are already noted. Monuments, tall posts, chimneys, furniture fall and those who drive vehicles lose their control.
- Grade IX:The pipes projected on the ground break, the foundations of the buildings come out and small collapses occur even in those of good construction.
- Grade X:At this level the surface of the ground is already cracking, bending even the rails of the railways and displacing the margins of rivers and mountains. Wooden buildings are also beginning to give way.
- Grade XI:Few structures manage to stand, the ground cracks considerably, destroying bridges, pipes, buildings and sinking and collapsing large areas.
- Grade XII:This is the maximum destruction that an earthquake can cause, that is, to destroy everything: disturb the level levels of rivers, seas and lakes, throw objects upwards.
As you have seen, many of the devastating effects of an earthquake have more to do with being prepared and enjoying good building structures than with the strength of it, that is why earthquakes more or less high on the Richter scale can be in different positions on the Mercalli scale.