New Delhi | Anurag Mishra: The National Capital Region (NCR) -- which includes Delhi, Noida, Ghaziabad, Gurugram and Faridabad -- has witnessed more than 15 earthquakes since April, causing fear and panic among people. The earthquakes were all of mild and medium intensity failed to cause much damage. However, experts say that these small and medium intensity earthquakes are a sign that a major earthquake might struck Delhi-NCR and have appealed people to prepare for the situation. Though some geologists believe that these mild and medium earthquakes are reducing the chances of a major earthquake in the region.
Professor Chandan Ghosh of the civil engineering department of IIT Jammu said that Delhi falls in the northern region. It is in Zone-4 in terms of earthquake, so it is sensitive. Earthquake centers are also changing due to changes in environment. This is happening due to change in tectonic plates. Delhi is close to the Himalayas, which was formed by mixing of tectonic plates such as India and Eurasia. Due to the movement in these plates, areas like Delhi-NCR, Kanpur and Lucknow are the most prone to earthquakes. Sohna, Mathura and Delhi-Moradabad are the three fault lines near Delhi, due to which the possibility of major earthquake cannot be ruled out.
However, it is also being said that small earthquakes may also reduce the chances of a major earthquake. The Delhi Ridge region is a low danger area, while the medium risk areas are - South West, North West and West. The most threatened areas are the North Eastern region.
Professor Ghosh said that at present there is no scientific basis to reach to a conclusion based on fault line movement, ground vibration, building response in Delhi-NCR.
Meanwhile, professor ML Sharma of IIT Roorkee said that it would be wrong to make any assessment about the frequent earthquakes in Delhi-NCR. These earthquakes are coming due to fault lines present in Delhi-NCR. Sometimes this frequency increases and sometimes it decreases. It is better that we should adopt anti-earthquake prevention measures instead of assessing the magnitude of the earthquakes. Retrofitting of old buildings, places should be done on priority.
Professor Durgesh C Rai, convener of National Information Center of Earthquake Engineering, IIT Kanpur, said that just because the local fault cess are jolting the national capital, it does not mean that Delhi-NCR will witness a major earthquake. He said that earthquakes intensifying in the Himalayan belt could affect Delhi-NCR, and if this happens continuously then there will be a situation to worry. In such a situation, the most important thing is that we make our houses anti-earthquake.
University of Delhi Professor R.B. Singh said that 90 percent of earthquakes are caused by the movement of tectonic plates. The first point is the need to pay attention to the buildings in Karol Bagh, Old Delhi areas. This can prevent any future mishap. Secondly, these frequent earthquakes can be considered as a sign of a major earthquake. But at present, there is no such technique that can be used to assess when an earthquake will occur and what will be its magnitude. Many scientific and cultural underpinnings (such as the behavior of birds) etc. are also not clear. We have to develop the synthetic articular radar technique, which is a remote sensing technique that can be used to assess the occurrence and scale of the earthquake.
Broadly, three levels of risk are now certain. First earthquake intensity, second time interval. Because usually an earthquake takes 35 to 40 seconds, and if this earthquake were to last two minutes, it could cause terrible damage. Third, the economic social status of the region or country because rich individuals or countries always build good quality buildings.
Why do tremors come again and again?
In areas where there is a high risk of earthquakes, stress in the lower surfaces of the earth increases in hundreds of years. This is caused by the movement of tectonic plates, but the effect of stress is not only sudden but slowly. First the earth remains calm for a long time, then the layers start moving for some time and this process is repeated again and again. Nepal is located at the place where the activity of the layers of the earth is highest. Every year the Indian plate slips under the Eurasian plates by about four centimeters. This is a very high speed for the plates of any continent to move. This is also the reason for the increasing height of the Himalayas.
Delhi standing on danger line due to haphazard development
Delhi has developed in a very clumsy way. The construction of colonies here is quite dense. Also, there is a lot of illegal construction in Delhi. Two-thirds of the capital's population live in illegally constructed houses. A few years ago, the building collapsed in Laxmi Nagar without earthquake raises a questions over the quality of the buildings. Areas on the banks of the Yamuna in Delhi come under the maximum danger.
Making old houses Earthquake resistant
Chandan Ghosh said that many years ago anti-earthquake construction techniques were not available. Hence these techniques could not be used in the buildings, bridges etc. that were built then, but now that this danger is increasing and we have such techniques, then there should be an initiative in this direction and people should adopt these techniques in sensitive areas to make their houses safe nand earthquake resistant.
How to build a earthquake proof house
Retrofitting is recognized by the Bureau of Indian Standards and any civil engineer can apply this technique to a building. For this, old buildings which are not built on pillars, lanter bands are inserted in the doors and windows above where the roof starts. The corners of the four walls of the building are joined together by a lanter band. The difference is that lanter bands use iron rods, which are much stronger. Professor Vasant Matsagar of IIT-Delhi says retrofitting is a better method, but it is necessary that retrofitting of old buildings also be done. For this, many measures have been taken in Bhuj.
What kind of buildings are safe
It is generally believed that the buildings standing on the pillar are completely safe. However, if a seismic structure is put in its foundation in a pillar building, then it becomes 90-95 percent earthquake resistant. Base isolation techniques are being adopted to make old buildings earthquake resistant in New Zealand. In this, a structure of mantle is erected around the bottom of the foundation of the building, which confines the vibration of the earthquake to the lower part.
IIT Jammu professor Chandan Ghosh said that when the earthquake strikes, the biggest danger is to the buildings which are not standing on the pillars. The building standing on the pillar vibrates simultaneously during the earthquake, while the four walls of the building without pillar move separately, so buildings start falling down. Retrofitting attaches to buildings without pillars to a great extent and the walls do not move separately.
What is microzone
Microzoning has been done in Delhi and the city is divided into nine parts according to the intensity of earthquakes. Among them, three areas, including densely populated Yamunapar, are the most dangerous. Five zones are medium risk, one zone is safe.
According to the risk of earthquake, the country is divided into four parts, zone-2, zone-3, zone-4 and zone five. Of these, the least threatened is Zone 2 and the highest risked is Zone-5. All the states of North-East, Jammu and Kashmir, Uttarakhand and parts of Himachal Pradesh fall under Zone-5. Delhi falls in Zone-4, central India falls under relatively low danger zone of Zone-3, while most of the south falls in Zone-2 with limited danger, but it is a thicker classification.
There are some areas in Delhi which can be as dangerous as Zone-5. Thus, there may be many places in the south states which may be hazardous like zone-4 or zone-5. Other Zone-5 may also have some areas where earthquake risk is very low and they are less hazardous like Zone-2.
What is Earthquake microzoning
Microzoning means micro classification. In this, the surface structure of the ground is investigated. Actually, when an earthquake occurs, the future of the house depends to a large extent on the structure of the land as well. For example, if the building is built on a damp surface, ie on the ridge area or on any soil that absorbs water for a long time, then the danger is greater. On the other hand, where the soil is dry or sandy, or the rocks are below, it has different effects during an earthquake. In microzoning, soil samples are collected by drilling into the ground every 200 to 500 meters in the field and after scientific investigation it is decided how sensitive the location is.
The Richter scale is a mathematical measure of earthquake intensity. This is called the Richter Magnitude Test Scale. It is a small scale that measures the intensity of earthquake waves. The Richter scale measures earthquake waves on the scale of one to nine, but nine is no end point, it can also go up. By the way, no earthquake above this has occurred ever. The Richter scale was discovered in 1935 by Charles Richter, a scientist working at the California Institute of Technology in collaboration with Beno Gutenberg.
Basis of Measurement
Under this scale, the intensity of earthquake per scale increases by 10 times and the energy released during an earthquake increases by 32 times per scale. This simply means that the intensity of an earthquake measuring 3 on the Richter scale would increase 10 times on 4 Richter scale.
Earthquakes in the past few days in Delhi-NCR
3 July - 4.5 Richter Scale - Delhi
8 June - 2.1 Richter Scale - Delhi
3 June - 3.2 Richter Scale - Faridabad
1 June - 3 Richter Scale- Rohtak
1 June - 1.8 Richter Scale- Rohtak
29 May - 2.9 Richter Scale- Rohtak
29 May - 4.5 Richter Scale- Rohtak
15 May - 2.2 Richter Scale- New Delhi
10 May - 3.4 Richter Scale- Delhi
06 May - 2.3 Richter Scale- Faridabad
03 May - 3.0 Richter Scale- Delhi
16 April - 2.0 Richter Scale- Delhi
13 April - 2.7 Richter Scale- Delhi
12 April - 3.5 Richter Scale- Delhi
Many earthquakes measuring high on Richter scale were recorded throughout the year in the world:
Earthquakes of magnitude 6.0 to 6.9 are recorded about 120 times a year and can prove to be quite fatal in a range of up to 160 km. Earthquakes ranging in magnitude from 7.0 to 7.9 can cause massive devastation over a large area and are recorded about 18 times in a year.
Seismic tremors ranging from 8.0 to 8.9 on the Richter scale can cause severe havoc over an area of hundreds of kilometers, which is felt once a year. An earthquake of scale from 9.0 to 9.9 can wreak havoc in an area of thousands of kilometers, which occurs almost once in 20 years. On the other hand, an earthquake of 10.0 or more was not felt till date.
Posted By: Talib Khan