Earthquakes: causes, measurement and why early warning is not possible

Yesterday, a 7.7 magnitude earthquake occurred in central Myanmar, with the epicenter about 15km northwest of Sagaing city. Aftershocks spread to neighboring countries such as Thailand and southwest China. Because earthquakes rarely affect Thailand, buildings in Bangkok are not designed to withstand strong shaking and damage has resulted. Thai authorities also declared a state of emergency in the capital Bangkok afterward.

In Thailand, at least 10 people died in Bangkok because of the earthquake from Myanmar and more than 100 people are still trapped in the collapse of a high-rise building under construction. In Myanmar, statistics show that at least 144 people were killed and 732 people were injured. The Earthquake Risk Program and the US Geological Survey (USGS) estimate the number of deaths in this earthquake could range from 10,000 - 100,000 people, causing serious economic damage. And below is information that you may not know about earthquakes.

How do earthquakes happen?

There are many causes of earthquakes, of which the majority of earthquakes occur due to the movement of tectonic plates. Tectonic plates are large pieces of rock that form the Earth's outer shell. These patches vary widely in size, from very large to quite small. Researchers are still arguing about how many pieces make up the "puzzle" of the Earth's crust.

At the boundaries between plates, the impact of magma in the mantle causes the rock layer to melt, expand and push the plates to move apart or closer together a few centimeters each year. These movements, which have occurred over billions of years, are called plate tectonics. When moving, tectonic plates collide with each other. When stress accumulates to a certain threshold, the plates can suddenly break, causing pressure waves to spread to the Earth's surface in the form of an earthquake. When an earthquake occurs under the ocean, it can cause a tsunami, creating large waves at high speed, leading to devastating floods when it hits land.

How are earthquakes measured?

The intensity of an earthquake is often measured using the Richter scale, classified from 1-10 using a seismograph. Magnitude 1 earthquakes are very common and often cannot be felt, while magnitude 10 earthquakes are extremely rare and can cause catastrophic damage. Seismologists say earthquakes with a magnitude above 5 can cause significant destruction. Besides, there is another scale to measure earthquakes, the Moment Magnitude Scale. Although less common, it is favored by seismologists because it measures large earthquakes, with a magnitude above 8.0, more accurately than the Richter scale.

What are aftershocks?

Strong earthquakes are almost always accompanied by aftershocks. Aftershocks occur because the tectonic plates at the epicenter of an earthquake do not stop moving even after the main earthquake has ended - they continue to shift until they completely stabilize.

Aftershocks contribute to making the situation worse, because they cause buildings that were damaged in the earthquake to collapse, leading to more injuries and deaths. Aftershocks are usually strongest 2 days after the main earthquake, but sometimes aftershocks can continue for many years afterward.

Usually the intensity of the aftershock will be lower than the main earthquake. For example, if the main earthquake has a magnitude of 5, the aftershocks will have a magnitude of 4 or lower. However, this is not always true. Sometimes some aftershocks have equal or greater intensity than the main earthquake. For example, in 2023, the aftershock was almost equal in intensity to the main earthquake that occurred in Türkiye and Syria.

The difference between shallow earthquakes and deep earthquakes

An earthquake is considered shallow if it occurs less than 50km from the Earth's surface. Researchers say shallow earthquakes cause more destruction because these quakes propagate quickly, making the impact at the surface much stronger than earthquakes that occur deep underground, which take longer to reach the surface. Earthquakes that occur deeper than 300 km below the Earth's surface are considered deep earthquakes.

Can earthquakes be predicted?

Although there are now earthquake warning systems, they can only detect P waves - the first waves emitted from an earthquake a few seconds before the shaking occurs. According to experts, there is still no current technology that can predict earthquakes in the long term. "What is clear is that we have no means of predicting earthquakes. Unlike volcanoes, one can predict them for several days before the eruption." said Patricia Martinez-Garzon, an earthquake researcher at the German Geological Research Center.

With the same intensity, how is the destructive power of earthquakes different?

The 7.8 magnitude earthquake that occurred in Türkiye and Syria in February 2023 killed more than 50,000 people. Meanwhile, the number of deaths in earthquakes of magnitude 8.2 and 8.3 on the Richter scale that occurred in Chile in 2014 and 2015 was just under 20 people. Why is there such a big difference?

According to experts, the difference in the level of damage depends on two main factors: the depth of the earthquake and the design of the structure where it occurs. If an earthquake occurs in sparsely populated areas, the destruction will be less than in urban centers. And if the earthquake is deep, it also causes less damage, compared to a shallow earthquake of similar magnitude.

Besides, there is another important factor due to the design of the project. The basic principles of earthquake-proof design only appeared in the second half of the 20th century, so in many countries they have not yet been applied to building construction. In most earthquake-prone countries like Chile and Japan, structures will be built to comply with Seismic codes to minimize damage caused by natural disasters. Meanwhile, in most countries around the world, this has not been applied. During the 2023 earthquake, many structures in Türkiye and Syria collapsed because they had not been upgraded to standards, so the level of destruction was also more severe. According to DW