Due to the recent events that have hit our country we have again found ourselves face to face with a catastrophic event, unfortunately known in Italy: the earthquake. But what exactly is it?
Earthquake derives from the Latin terrae motus, meaning "movement of the earth" and we can all understand the reason for this name. Using the technical terms of geophysics, its synonyms are earthquake or earthquake (from the Latin Tellus, Roman goddess of the Earth). In concrete terms, they are sudden vibrations or settlements of the earth's crust, caused by the sudden movement of a rock mass underground.
- The earthquake intensity measurement scales: Richter and Mercalli
- The 10 most devastating earthquakes in history
- The map of the earthquake-prone areas in the world
- User questions and comments
The earthquake intensity measurement scales: Richter and Mercalli
To measure the devastating force of an earthquake they are used two different reference systems.
- La Richter scale devised by the US seismologist classifies the so-called magnitude of an earthquake. In practice it allows you to know the amount of energy released by the shock and its destructiveness. It is obtained by measuring the amplitude of the ground oscillations thanks to the recordings made by the seismographs.
- La Mercalli scale takes its name fromItalian seismologist of the same name. It classifies the intensity of an earthquake according to its own visible effects on buildings. Only from the 4th degree onwards the tremors are felt by the majority of the population and there are minor injuries to buildings. From the 7th degree the damage created to the structures is serious. The maximum degree of this scale is 12th and involves the total destruction of every human work.
The Richter Scale, therefore, provides a decidedly more objective evaluation compared to the Mercalli, as the damage that human constructions can suffer also strongly depend on where, how and on the basis of which typology they are built. For example, a strong earthquake in a large metropolis will suffer much more damage to buildings than an earthquake of the same magnitude in an uninhabited desert area.
The values of the Richter Scale
- Grade 1 - Magnitude 0: Very mild earthquake
- Grade 2 - Magnitude 2,5 / 3: Shock felt only in the immediate vicinity
- Grade 3 - Magnitude 4/5: Can cause damage locally
- Grade 4 - Magnitude 5: The energy released is equal to that of the atomic bomb dropped on Hiroshima in 1945
- Grade 5 - Magnitude 6: Destructive earthquake in a restricted area of 10 km radius
- Grade 6 - Magnitude 7: Destructive earthquake in a restricted area of 30 km radius
- Grade 7 - Magnitude 7/8: Great destructive earthquake, equal to the San Francisco earthquake of 1906
- Grade 8 - Magnitude 8,4: Close to the maximum known ever released
- Grade 9 - Magnitude 8,6: Highest degree of magnitude known up to now. The energy produced by the earthquake is 3 million times higher than that generated by the atomic bomb dropped on Hiroshima in 1945
The values of the Mercalli scale
- Grade I - Inaudible: Not felt by people except in special circumstances. Only detected by tools.
- Grade II - Very light: Felt indoors only by a few people, mostly in the upper floors of houses and by people in a particularly favorable position.
- Grade III - Light: Felt indoors where hanging objects wobble. Vibrations as if light trucks pass by. Its duration can be estimated. It may not be recognized as an earthquake.
- Grade IV - Moderate: Suspended objects oscillate for a long time. Vibrations as if heavy trucks pass by, or sensation of a sharp blow like that of a heavy ball against a wall. Stationary cars swing. Windows, plates, glasses and doors vibrate. At the upper limit of grade IV, the wooden walls and window frames crack.
- Grade V - Strong enough: Also felt externally. People who sleep wake up. Liquids fluctuate and sometimes overflow. Small unstable objects move and tip over. The doors open and close. Shutters and paintings are moving. Pendulum clocks stop (or start running if they are stopped) and change period of oscillation. Rubble falls from the walls.
- Grade VI - Strong: Felt by all. Windows, plates and glasses break. Books fall off the shelves and pictures on the walls. Furniture moves or turns over. Fragile constructions crack. Small bells (such as those of churches and schools) ring. The trees and bushes sway.
- Grade VII - Very strong: Difficult to balance. Also felt by those who are driving a car. The furniture breaks. Fragile chimneys are destroyed at the base. Plasters, bricks not well fixed, cornices fall. Some cracks in the stone constructions. Waves are formed, the water in the puddles becomes cloudy with mud. Small landslides and depressions in sand and gravel banks. Big bells ring. Concrete irrigation channels are damaged.
- Tier VIII - Ruinous: Driving cars are difficult. Damage to stone buildings; partial collapse. Some damage to stucco and some brick walls. Swings or collapses of chimneys, chimneys, monuments, suspended tanks. The buildings sway on the foundations; the partitions fall. The statues fall from the pedestals. The branches of the trees break. The flow and temperature of springs and wells change. Cracks form in moist, steeply sloping soil. You can have victims.
- Grade IX - Destructive: General panic. Heavily damaged stone buildings, sometimes with total collapse; heavily damaged brick constructions. Buildings collapse or are displaced from the foundations. Heavy damage to tanks. Underground pipes break. Conspicuous cracks form in the ground. In alluvial areas, sand and mud are sprayed into the air: sand craters are formed. The victims begin to be numerous.
- Rank X - Completely Destructive: Most buildings are destroyed. The wooden structures, even if well built, and the bridges are destroyed. Severe damage to dams, irrigation canals and embankments. Large landslides. Invasion of water from canals, rivers, lakes, etc. Sand and mud are displaced horizontally on the beaches and in the flat regions. The rails are slightly curved.
- Grade XI - Catastrophic: The dams break. The rails are strongly curved. Underground pipes are rendered completely unusable. Chasms open up in the ground. Communications are down. It has a large number of victims.
- Degree XII - Completely Catastrophic: Nearly total damage. Large boulders of rock moved. The morphology of the landscape is altered. Objects thrown into the air. It does not resist any artifact. It can cause thousands of casualties.
The 10 most devastating earthquakes in history
Earthquakes have practically always existed, even before humans appeared on Earth. Our planet continues to shake, but in the course of history there have been many devastating earthquakes for humanity, some not even registered by educated men of the time. The most devastating so far studied have been 10:
- Valdivia, Chile - May 22, 1960 - magnitude 9.5
The earthquake caused a crazy-sized tsunami, with waves up to 25 meters high. The toll of the disaster was around 3.000 victims and 2 million displaced.
- Prince William Sound, Alaska - March 28, 1964 - magnitude 9.2
The quake caused a tsunami that, pushing south, reached the coast of California. The toll was of massive damage to inhabited centers and more than a hundred victims.
- Sumatra, Indonesia - December 26, 2004 - magnitude 9.1
Many of us will remember it. The violent tsunami sowed death and destruction from the African coast to Southeast Asia. The toll was over 200 victims and several tens of thousands of missing people, as well as considerable damage to the economic and social fabric of the affected areas.
- Kamchatka, Russia - November 4, 1952 - magnitude 9.0 -
This earthquake caused a massive tsunami that reached various locations in the Pacific Ocean, causing extensive damage but, fortunately, no victims.
- Sendai, Japan - March 11, 2011 - magnitude 8.9-9.0
It was the most powerful earthquake ever recorded in the area and was followed by a swarm of over forty quakes with a magnitude greater than 5.0. In a country like Japan, prepared to deal with earthquakes of a certain intensity, the greatest damage was actually caused by the subsequent and consequent tsunami. Thousands of victims, millions of displaced people and extremely dangerous damage to the reactors of two nuclear power plants.
- Ecuador - January 31, 1906 - magnitude 8.8
Off the coast between Ecuador and Colombia, an 8.8 magnitude quake occurred. The earthquake also destroyed San Francisco, caused a tsunami that shook many places in the Pacific and caused several hundred victims.
- Coast of Maule, Chile - February 27, 2010 - magnitude 8.8
The earthquake caused damage in many cities of the country. The quake was also distinctly felt in Argentina, up to Buenos Aires. The official toll spoke of 452 victims and about 2 million displaced persons.
- Sumatra, Indonesia - March 28, 2005 - magnitude 8.7
Shortly after the disastrous tsunami of 2004, Sumatra and the Indonesian archipelago were again hit by a very violent shock. The approximate toll was enormous, about 1.300 dead, mostly concentrated on the western island of Nias.
- Rat Islands, Alaska - February 4, 1965 - magnitude 8.7
The Rat Islands are located in a highly seismic area but are not inhabited. For this reason, the 8.7 magnitude earthquake that struck them, causing a tsunami with waves up to 10 meters high, did not cause victims or significant damage.
- Assam and Tibet - August 15, 1950 - magnitude 8.6
The earthquake in Tibet caused destruction and over 1.500 victims.
Based on the statistics, the earthquake with the heaviest death toll was the one that hit Haiti in January 2010: nearly 300 estimated dead, 300 injured and about one million displaced. Numbers from true apocalypse for a small state already severely tried by poverty.
But which are the nations most at risk of earthquakes? Let's find out together.
The map of the earthquake-prone areas in the world
Here's in order i 10 states most at risk of seismic in the world:
- New Zealand
- Dominican Republic
- Costa Rica
In addition to these seismically dangerous nations, the earth can turn into a bloodthirsty killer in 5 cities in the world:
- Los Angeles (USA)
La San Andreas fault it is a kind of underground sword of Damocles. According to the Geological Society of the United States, the risk of the Los Angeles area experiencing an earthquake of magnitude 6.7 or greater by 2038 exceeds a 66% chance.
But what is even more scary is the 7% chance of a magnitude 8 seismic event in the next 30 years!
- Tehran (Iran)
La Northern Anatolian fault, one of the three largest in the world, keeps Iran and its capital in suspense. Tehran is built on a relatively recent sediment, which is extremely dangerous in the event of an earthquake. Tehran became a metropolis very quickly and without particular attention to anti-seismic measures.
The chances of a telluric event of magnitude 6 or higher occurring in the next decade are estimated at 90%.
- Istanbul (Turkey)
Turkey is certainly not new to violent earthquakes. The government has invested huge resources to improve the structural conditions of the old buildings in Istanbul, but most of its inhabitants live in hastily built houses without taking into account anti-seismic safety requirements.
According to a 2000 study, the chances of a magnitude 7 earthquake occurring in the city by 2030 is 60%.
- Lima (Peru)
Various earthquakes hit the capital of Peru, some even violent, but none were more like the devastating one of 1746. It is precisely this fact that worries experts. The South American tectonic plates and that of Nazca are constantly on a collision course with each other and the risk of violent tremors and tsunamis is always dangerously high.
- Tokyo (Japan)
The sea, the volcanoes, the location in the middle of the ocean: all factors that make Japan a sensitive target for any kind of environmental disaster. The capital, then, rises right above an important active fault of the Pacific Ocean.
Much of the country rests on the Belt of Fire, responsible for 9 out of 10 earthquakes in the world.