This Wednesday is the drill, do you know what determines the Mercalli intensity of an earthquake?

Do you know what Mercalli intensity is in an earthquake? The question arises from the earthquake drill to be held in the Dominican Republic this Wednesday, October 20, with a magnitude of 7.7 on the Ritcher scale and IX of Mercalli intensity.

This intensity is named after the Italian physicist and priest Giuseppe Mercalli, who developed a modified scale to determine the intensity and damage of geological events, ranging from 1, very mild, to XII, which is catastrophic.

The director of the National Center of Seismology of the Autonomous University of Santo Domingo, Ramon Delanoy, explains that the main factors that influence an earthquake to have a greater Mercalli intensity than another, despite being of the same magnitude, are the soil and the structures of the physical plants.

Since the epicenter of the earthquake drill will be in Santiago de los Caballeros, at a distance of 9.4 kilometers and a depth of 10.50 kilometers, it is expected that the damage will be significant and the intensity will reach IX.

Why in Santiago the Mercalli intensity is IX? “Because it is close to the area where it is being suggested, due to the characteristics of the soil of that province and of the whole area of the Cibao Valley with very unstable soil, and where the seismic wave can last a long time in one place and as it is difficult to cross the medium, then a lot of energy is released there, and that is why higher intensities are produced”.

Ritcher and Mercalli Scale

The geologist explained that when an earthquake occurs, it releases an amount of energy, which is calculated on the Richter scale (the American geologist Charles Francis Richter) “and at any point that one measures approximately the energy of the earthquake, the magnitude will be the same wherever it is calculated. While the Mercalli intensity is a suggestive measure of the tremor. That is to say, how people feel it, how it manifests itself in the structures and many times an earthquake of magnitude 5 can produce an intensity of more than 5 or 6 and even 7, it could be because it will depend on how far it is from the buildings, the type of constructions and the soil”.

In detailing that the intensity of earthquake damage is not always in proportion to the magnitude or energy released, the expert gave several examples such as the most recent earthquake of 4.6 degrees that occurred a few weeks ago in the country, which was felt in the Eastern region and Greater Santo Domingo.

“It was of moderate magnitude and because of how people felt it, we could say that the Mercalli intensity was 4, but usually an earthquake of 4 does not produce an intensity of 4, but less.

He said that an earthquake can occur 50 kilometers away from a town and not cause damage, but being 100 kilometers away from another town it can destroy buildings and cause more damage due to the vulnerability of the soil, the constructions and if it has rained a lot in areas with slopes and where there are structures.

About the drill

The director of the National Seismology Center stressed the importance of the earthquake drill which is coordinated by the relief agencies, in which they participate, to educate and help the Dominican population, so that they can prepare, or learn how to react to the occurrence of an earthquake, what to do at the time, after and how to prepare before the tremor.

He recommended citizens to have a first aid backpack as they do when there is a hurricane threat.

The earthquake rehearsal, which includes a tsunami warning, will take place at 10:00 a.m. and will simulate the collapse of buildings, people trapped in rubble, evacuations will be carried out throughout the country and other actions.

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