Earthquakes are among the most devastating natural disasters known to humanity.
Things You Didn’t Know About Earthquakes
What is an Earthquake?
An earthquake is a sudden shaking of the Earth’s crust, which can vary in intensity (measured by the Richter scale) and is caused by the movement of tectonic plates or faults beneath the Earth’s surface, transmitting energy over great distances.
A single shock typically lasts no more than a few seconds, while the most severe earthquakes usually last a maximum of 3 minutes.
Buildings destroyed after an earthquake.
Causes of Earthquakes
Endogenous Causes
- Earthquakes caused by the collapse of underground caves and earthquakes due to natural landslides of large masses (this type of earthquake typically only shakes a narrow area and accounts for about 3% of total earthquakes worldwide).
- Volcanic earthquakes, primarily associated with explosive volcanic activity (this type of earthquake is usually not very strong – accounting for about 7%).
- Tectonic earthquakes (accounting for 90%) are related to the activity of tectonic faults, especially those at the edges of tectonic plates, tectonic movements in subduction zones; they are also related to magma intrusions into the Earth’s crust, disrupting the pre-existing pressure balance of surrounding rock, causing stress, which when released, results in an earthquake; and associated with the transformation of rock types from one crystalline form to another, causing volume contraction and expansion, leading to significant volume changes that also cause earthquakes.
Buildings destroyed after an earthquake.
Exogenous Causes: Include earthquakes caused by meteorite impacts on Earth.
Anthropogenic Causes: Earthquakes occur due to activities that alter the stress in rocks near the surface, particularly nuclear tests, artificial explosions underground, or the pressure exerted by the water column of reservoirs and hydroelectric lakes.
Devastation after an earthquake in Kesennuma city, Miyagi Prefecture, Japan. (Photo: AP).
The Danger Level of Earthquakes
Earthquakes can be a trigger for tsunamis. When an earthquake occurs beneath the ocean, seismic energy can displace a massive volume of water. Over hundreds of square kilometers, the displaced water can rise and fall, generating large waves that travel across oceans and make landfall. Sometimes, earthquakes can also activate volcanoes, even those that have been dormant for a long time. The fracturing of the Earth provides opportunities for magma to erupt. These phenomena, when combined, can lead to unpredictable disasters.
Due to the sudden occurrence of earthquakes and their dangerous nature, and since we cannot prevent them, the only way to cope is to minimize the damage caused by them.
Magnitude of Earthquakes
Destruction of buildings after an earthquake.
The magnitude of an earthquake, M, also known as Richter scale. Here’s how to understand the Richter scale:
- From 1 – 2: Not detectable.
From 2 – 4: Detectable but usually causes no damage.
From 4 – 5: The ground shakes, a rumbling sound is heard, with negligible damage.
From 5 – 6: Buildings shake, some structures may crack.
From 6 – 7: Minor damage to buildings.
From 7 – 8: Strong earthquakes destroy most ordinary buildings, with large cracks or subsidence on the ground.
From 8 – 9: Buildings are devastated, the ground may subside up to 1 meter, with significant collapses in mountainous areas along with widespread changes in topography.
Above 9: Extremely rare.
Earthquakes with M > 7 do not occur everywhere but are typically concentrated in certain regions known as seismically active zones.
The Impact of Earthquakes
- The direct effects of earthquakes are ground shaking, causing fractures, collapsing buildings, landslides, and avalanches. The severity of these effects depends on the intensity, distance from the epicenter, and geological and topographical conditions in the affected area.
- Earthquakes often trigger fires when they damage power lines and gas pipelines.
- Earthquakes occurring beneath the ocean can cause landslides or seabed deformation, which can generate tsunamis (large waves that travel across oceans and make landfall). Sometimes earthquakes can even activate volcanic activity, including those from long-dormant volcanoes…
Many significant earthquakes have occurred worldwide, causing immense damage to life and property. Japan is one of the most earthquake-prone countries, experiencing earthquakes of various magnitudes regularly.
