EARTHQUAKE
1. Context
More than 1,500 people died and several hundred were injured after a major earthquake of magnitude 7.8 hit south-central Turkey and Northwest Syria on Monday early morning. Turkey’s President Tayyip Erdoğan said that authorities are yet to determine how high the death toll might rise as search and rescue operations are still going on.
2. What is an Earthquake?
An earthquake is an intense shaking of the ground caused by movement under the earth’s surface. It happens when two blocks of the earth suddenly slip past one another, according to USGS. This releases stored-up ‘elastic strain’ energy in the form of seismic waves, which spreads through the earth and cause the shaking of the ground.
3. How do exactly Earthquakes Occur?
- As we know, the earth’s outermost surface, crust, is fragmented into tectonic plates. The edges of the plates are called plate boundaries, which are made up of faults.
The tectonic plates constantly move at a slow pace, sliding past one another and bumping into each other. - As the edges of the plates are quite rough, they get stuck with one another while the rest of the plate keeps moving.
- Earthquake occurs when the plate has moved far enough and the edges unstick on one of the faults.
- The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.”
4. Earthquake waves
The release of energy during an earthquake generates waves which are called Earthquake Waves. Earthquake waves are basically of two types body waves and surface waves.
Body waves: They are generated due to the release of energy at the focus and move in all directions traveling through the body of the earth. Hence, the name body waves. The body waves interact with the surface rocks and generate a new set of waves called surface waves.
Surface waves: These waves move along the surface. The velocity of waves changes as they travel through materials with different densities. The denser the material, the higher the velocity. Their direction also changes as they reflect or refract when coming across materials with different densities.
There are two types of body waves. They are called P and S-waves.
P-waves or ‘primary waves’ move faster and are the first to arrive at the surface. The P-waves are similar to sound waves. They travel through gaseous, liquid, and solid materials.
P-waves vibrate parallel to the direction of the wave. This exerts pressure on the material in the direction of propagation. As a result, it creates density differences in the material leading to stretching and squeezing of the material.
S-waves or secondary waves arrive at the surface with some time lag. They can travel only through solid materials. This characteristic of the S-waves is quite important. It has helped scientists to understand the structure of the interior of the earth.
The direction of vibrations of S-waves is Perpendicular to the wave direction in the vertical plane. Hence, they create troughs and crests in the material through which they pass. Surface waves are considered to be the most damaging waves.
5. Measuring of Earthquakes
- The earthquake events are scaled either according to the magnitude or intensity of the shock.
- The magnitude scale is known as the Richter scale. The magnitude indicates the energy released during the quake. It is expressed in absolute numbers 0-10.
- The intensity scale is named after Mercalli, an Italian seismologist. The intensity scale indicates the visible damage caused by the event. The range of intensity scale is from 1-12.
6. Turkey and Syria lie in a seismically active region
- The region where the earthquake struck lies along a well-known seismic fault line called the Anatolia tectonic block that runs through northern, central, and eastern Turkey.
- It is a seismically active zone-though not as active as, say, the Himalayan region which is one of the most dangerous regions in the world from the perspective of earthquakes.
- Large earthquakes, of magnitude 5 or higher, have not been very frequent in recent years. According to USGS, only three earthquakes of magnitude 6 or more have happened in the region since 1970. The last major quake in this area came in January 2020.
- The seismicity in this region is a result of interactions between the African, Eurasian, and Arabian plates. The Arabian plate is known to be pushing northward, which results in a slight westward movement for the Anatolian plate, where Turkey is located.
- The earthquake happened around the near-vertical fault line on the eastern Anatolian block, close to the Syrian border.
7. Shallow Earthquakes cause much greater damage
- Earthquakes in Turkey emerged from relatively shallow depths which made them devastating. The first earthquake, of magnitude 7.8, originated 17.9 km below the earth's surface.
- All the subsequent ones, including one of 7.5 magnitudes, emerged from even closer to the surface.
- Shallow earthquakes are generally more devastating because they carry greater energy when they emerge on the surface.
- Deeper earthquakes lose much of their energy by the time they come to the surface. The deeper quakes spread farther though- the seismic waves move conically upwards to the surface even as they lose energy while traveling greater distances and hence cause less damage.
8. Can earthquakes be predicted?
- An accurate prediction of an earthquake requires some sort of a precursory signal from within the earth that indicates a big quake is on the way.
- Moreover, the signal must occur only before large earthquakes so that it doesn’t indicate every small movement within the earth’s surface. Currently, there is no equipment to find such precursors, even if they exist.
- Theoretically, it is possible to offer a lead time of a few seconds between the time of the origin of the earthquake and the time it reaches the Earth’s surface.
- Seismic waves travel significantly slower than the speed of light between 5 and 13 km
per second. So if the earthquake is detected as soon as it is triggered, information about it can be related a few seconds ahead of it reaching the ground. - Such systems are already in use in some locations to issue alerts about earthquakes. However, these are not predictions. The alerts are issued post-event.
- Attempts to find reliable predictors of earthquakes have not been fruitful so far. Scientists have been able to map the areas that are earthquake-prone, and are likely to generate earthquakes in the future, but there is no way to predict when.
For Prelims & Mains
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For Prelims: Earthquake, Tectonic plates, Hypocenter, Epicenter, Body waves, Surface waves, P-waves or ‘primary waves’, S-waves or secondary waves, Richter scale, and Seismic waves.
For Mains: 1. What is an Earthquake? How do exactly Earthquakes Occur? Discuss the effects of Earthquakes.
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Source: The Indian Express
