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The Richter and Mercalli Scales

Seismologists have devised two scales of measurement to enable them to describe and record information about earthquakes in quantitative   terms.   The most widely known measurement is the Richter scale, a numerical logarithmic scale developed and introduced by American seismologist Charles R. Richter in 1935.

The purpose of the scale is to measure the amplitude of the largest trace recorded by a standard seismograph one hundred kilometers from the epicenter of an earthquake. Tables have been formulated to demonstrate the magnitude of any earthquake from any seismograph. For example, a one-unit increase in magnitude translates into an increase of times thirty in released energy. To put that another way, each number on the Richter scale represents an earthquake ten times as strong as one of the next lower magnitude. Specifically, an earthquake of magnitude 6 is ten times as strong as an earthquake of magnitude 5.

On the Richter scale, earthquakes of 6.75 are considered great and 7.0 to 7.75 are considered major. An earthquake that reads 4 to 5.5 would be expected to have caused localized damage, and those of magnitude 2 may be felt.

The other earthquake-assessment scale, introduced by the Italian seismologist Guiseppe Mercalli, measures the intensity of shaking, using gradations from 1 to 12. Because the effects of such shaking dissipate with distance from the epicenter of the earthquake, the Mercalli rating depends on the site of the measurement. Earthquakes of Mercalli 2 or 3 are basically the same as those of Richter 3 or 4; measurements of 11 or 12 on the Mercalli scale can be roughly correlated with magnitudes of 8 or 9 on the Richter scale. In either case, the relative power or energy released by the earthquake can be understood, and the population waits to hear how bad the earthquake that just passed really was.

It is estimated that almost one million earthquakes occur each year, but most of them are so minor that they pass undetected. In fact, more than one thousand earthquakes of a magnitude of 2 or lower on the Richter scale occur every day.

(Taken from: Barron’s Educational Series)

Earthquakes: What are the Richter and Mercalli scales?

Each year our planet is rocked by more than 50,000 earthquakes, of which approximately 99% are earthquakes too small to pose a real danger. In contrast, the remaining 1% consists of demonstrations that can be a source of serious harm if they occur in populated places. Did you know that many of the worst earthquakes in history have happened in the last century?, What we will be saying the Earth?. Nothing good, surely.

Most earthquakes do not come to light, or even out of the archives of the seismological center. They are events that go to swell the statistics to shape theories of forecasts of seismic events. However, despite all this information, you can not determine exactly how and when earthquakes will occur. It is one of the great unfinished business of science.
What we can know, more or less certain, is the energy released (Richter scale) and the destructive effects (Mercalli scale) of different possible earthquakes. Come on, we can assess what can be catastrophic but we can not avoid them. Anyway. Let’s see.
Mercalli Scale
Using this index we can determine the potential effects of earthquakes. Low levels of the scale are associated with how people feel the tremor, while higher grades are associated with structural damage.
Level I – Very weak. It is unlikely that a person can detect
Level II – Weak. Perceived by those people who are at rest and / or concentrates, especially on the upper floors of buildings. Hanging objects may swing.
Level III – Slight. It may be noted on the upper floors. At street level would be similar to the vibration that produces a small truck tonnage.
Level IV – Moderate. Would equate to the vibration generated by the passage of heavy trucks. It is noticeable to most. Some objects such as doors or walls may crack slightly. Those who have a very mild sleep may be awakened.
Level V – Somewhat stronger. At this point it really gets ugly. The vibrations are now considering, walking is difficult, falling objects and walls may crack.
Level VI – Strong. This is where you usually start to panic people, where many go into the street and it is difficult sustain standing. There may be structural damage to buildings which are suited to seismic tremors.
Level VII – Very strong. Those poorly designed structures fall to the ground, while good buildings, although damaged, can still stand.
Level VIII – Destructive. The buildings built specifically to withstand earthquakes damaged remarkable. By vibration furniture out of their holes, possible collapse of cities due to the inability to walk and move.
Level IX – ruined. Widespread panic. Buildings designed to withstand severe earthquakes damaged. Some buildings are out of their bases.
Level X – Disastrous. Rails bent, thousands dead. Few buildings remain standing.
Level XI – Very disastrous. Probably no building would be on foot, the area would be devastated. Few survivors.
Level XII – Catastrophic. Total destruction. Probably no survivors. The terrain would change its appearance.
Richter Scale
The Richter scale measures the energy released by an earthquake. To give you a rough idea here are some examples:
The first, those who are below 3 are virtually undetectable from the seismological point of view. In this scale, the earthquake generates an intensity equivalent to that of a conventional bomb or gas explosion. Sounds very appealing, but in reality, apart from hardly noticeable, the effect is minimal.
4 to 5 would be talking about an energy equivalent to the explosion of 200 tons of TNT. The damage would be minimal and the earthquake can be detected by humans.
5 to 6 hard start to feel the effects on building structures. On this scale we might get, for example, the earthquake in El Calvario (Colombia), 2008.
From 6 to 7. On this scale it gets more serious. The effects of an earthquake of this level could cause the destruction of an area of 100 km from the epicenter. The earthquake in Haiti in 2010, is on this scale. The energy released would equate to four times the power of “the Tsar Bomba, the most powerful bomb ever exploded. In total about 200 kilotons.
7 to 8. The energy released in this range would amount to approximately 450 joint blast bombs like Hiroshima. The devastation in the area is full if not have adequate facilities. An earthquake of this type could be the one that devastated Pisco (Peru) in 2007.
8 to 9. Are earthquakes that can destroy areas hundreds of miles. An example would be the recent earthquake in Mexico City 1985. It is clear that a greater extent it depends on what country you are prepared to endure.
From 9 to 10. On this scale we have from the strongest earthquakes which data are available (Valdivia Earthquake, 1960, and Chile 2010) to the impact of a meteorite than 2 km in diameter that impacts to 90000 km / h. In the case of earthquake, if the country is ready, could be arranged, in the case of the meteorite that God we caught confessed.
12 to 13. The energy released in these scales would mean the end of life on earth. Come to mean the planet’s internal breakdown or, for instance, the impact of a meteorite like the one that collided with the Yucatan Peninsula. The energy released would be something like the equivalent of the simultaneous explosion of two million artifacts as “the Tsar Bomba.”
Over 13. At this level the energy released is unknown. It would be similar to the one generated the collision of Earth and Mars.
Source: http://www.visitrockypoint.com/earthquakes-what-are-the-richter-and-mercalli-scales

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