Nepal: More than 80 percent of buildings in Nepal are not earthquake-resistant. Therefore, the rule of 'hiding under the table' like in Western countries may not apply in all cases.
Dr. Shiva Subedi
(The author is a seismologist working at the Nepal Academy of Science and Technology.)
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| Source: Google image |
• The Nepal government tries to spread knowledge and awareness about earthquakes by observing National Earthquake Safety Day on Magh 2 every year.
• The main cause of earthquakes in Nepal is the friction between the Indian and Tibetan plates, which is scientifically called the 'Main Himalayan Thrust'.
• The Gorkha earthquake of 2072 BS showed that a large earthquake can occur at any time and place and that an earthquake early warning system is necessary.
Every year on Magh 2, the Nepal government celebrates National Earthquake Safety Day. Its main objective is to spread knowledge and awareness about earthquakes at the public level. Such programs held in specific places may benefit only a few thousand people, but according to scientific studies, if an earthquake larger than 8 magnitude were to occur in Nepal, the damage could be beyond our imagination.
Even today, no school, college or university in Nepal teaches special studies about earthquakes. The few seismologists in Nepal have also returned from studying abroad. In order to help more people understand earthquakes, prepare for them, and reduce future human risks, frequently asked questions and their scientific reasons are mentioned here.
1. What is the reason for earthquakes in Nepal?
70 million years ago, there was an ocean between the Indian Plate and the Eurasian Plate in the place where Nepal is now. The Indian Plate was moving northward at a certain speed every year, and about 50 million years ago, it collided with the Eurasian Plate. When the two plates collided, the rocks on the upper part were compressed and mountains like Mount Everest were formed, while the Indian Plate began to penetrate under the Eurasian Plate.
Along with the Himalayas, another small plate was also formed to the north, which we call the Tibetan Plate. There is a friction point between the Indian Plate and the Tibetan Plate under the land of Nepal, which is the main source of earthquakes. In scientific language, this is called the ‘Main Himalayan Thrust’. The main cause of all earthquakes in Nepal is the friction between these two plates.
2. Why do tectonic plates move?
The movement of tectonic plates is based on the principle of heat transfer in physics. Where atoms with higher temperature (lower density) tend to rise, atoms with lower temperature (higher density) tend to fall. For example, when water is heated in a pot, hot water rises from the bottom and cold water from the top goes down.
The temperature of the Earth’s core is about 6,000 degrees Celsius, while the surface temperature is only about 20–30 degrees Celsius. This large temperature difference is enough for the movement of tectonic plates. The process of plate movement is very slow, but it has been going on continuously for millions of years. This process has created the current shape of the Earth’s surface.
3. What did the Gorkha earthquake teach us?
The 2072 Gorkha earthquake was not in the expected area for seismologists; They were expecting a big earthquake in the western part of the country. What it taught us was that a big earthquake can happen anytime and anywhere.
Usually, the biggest aftershock of an earthquake is one unit less in magnitude than the main shock, but the Gorkha earthquake (7.8/7.9) was followed by a powerful 7.3 earthquake. Studies showed that this was not just an aftershock but a new earthquake caused by the transfer of energy from the main earthquake. This taught us that the energy stored in one place can be transferred to another area and cause a new disaster.
It also became clear that the lack of earthquake-resistant structures would significantly increase the damage. This also confirmed the need for an ‘earthquake early warning system’ in Nepal.
4. What is the difference between the magnitude and intensity of an earthquake?
Magnitude is a measure of how much energy was released from the ground when an earthquake occurred. It is a constant number. A one-unit increase in magnitude means a 32-fold increase in energy. For example, an earthquake of magnitude 8 is 32 times more powerful than an earthquake of magnitude 7.
Intensity is a measure of the shaking felt at a particular location and the effects it has. The intensity of a single earthquake varies from place to place. It depends on the magnitude, distance from the epicenter, and the local terrain.
5. Why can't earthquakes be predicted?
Science has not yet been able to accurately predict earthquakes (date, time, and location). Earthquakes are sudden events, and the technology to accurately measure the energy stored deep within the Earth has not yet been developed. Saying that an earthquake of this magnitude may occur in the near future is a scientific estimate or risk analysis, but it is not possible to predict it precisely.
6. Are earthquakes only horizontal and vertical?
Earthquakes have both types of waves. The first ‘P-wave’ shakes the ground up and down, while the ‘S-wave’ shakes the ground left and right. Then come the ‘surface waves’ that spread across the surface. Therefore, an earthquake cannot be said to be only vertical or only horizontal. When you are close to the epicenter, all the waves seem to be happening at the same time, so the experience may be different.
7. Do only tall buildings collapse during an earthquake?
This depends on the height of the building and the frequency of the seismic waves. Low-rise buildings are more susceptible to high-frequency waves, while tall buildings are more susceptible to low-frequency waves. While high-rise apartments in Kathmandu were damaged in the 2015 earthquake, low-rise buildings outside Kathmandu also collapsed.
In essence, it is more important to consider whether a building is earthquake-resistant than whether it is tall or short. Buildings of any height that do not comply with building codes are at risk.
8. What to do during an earthquake?
• More than 80 percent of buildings in Nepal are not earthquake-resistant. Therefore, the Western-style ‘hide under a table’ rule may not apply in all situations.
• If you are outside, stay in an open area away from houses, trees, electricity poles, or structures that can collapse.
• If you are on the ground floor, if the building is not earthquake-resistant, get out to an open area as quickly as possible in a safe manner.
• If you are on an upper floor, if it is not possible to get out, take cover under a strong pillar, door frame, or table. Only go out when the shaking stops.
• Exercise restraint. Do not jump from a window or roof in a hurry. Use your hands or something to protect your head when going out.
writer- Dr. Shiva Subedi
(The author is a seismologist working at the Nepal Academy of Science and Technology.)
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