Micro Quakes Preventing Large-Scale Event In India: ExpertsFeb 13, 2023 | Pratirodh Bureau
Micro tremors have been helping release tectonic stress and protecting India from a devastating event, experts said and asserted that the country has seen a paradigm shift towards effective response and mitigation.
They said India is well-prepared to deal with the fallout of large-scale earthquakes as it has a dedicated, well-equipped and trained force in the form of the National Disaster Response Force (NDRF).
The impact of a large-scale earthquake can also be reduced if people and institutions strictly comply with the bylaws and codes to build resilient structures, they said.
“The triple junction on India’s western side near the border with Pakistan is continuously releasing stress due to the occurrence of micro-level earthquakes. There are a few earthquakes of magnitude 4 and 5 as well,” said OP Mishra, director at the Ministry of Earth Sciences’ National Centre for Seismology.
A triple junction is a point where three tectonic plates meet and interact. These are important areas of geological activity and can be sites of significant seismic and volcanic activity.
The movement of the plates can cause significant build up of stress and strain in the Earth’s crust that is eventually released in the form of earthquakes.
“Triple junctions are rigid and compact and withstand a lot of stress. If it breaks, the entire stress is released, causing a lot of damage,” Mishra explained.
There are two triple junctions in Turkiye. One of them is where the Arabian Plate, the African Plate and the Anatolian Plate meet. The breaking of this junction led to the massive earthquake that devastated Turkiye and Syria, leaving more than 25,000 dead, he said.
“Since there had been no small earthquakes in this region, a lot of stress accumulated there. Turkiye saw several powerful earthquakes within 24 hours because the couple zone area was quite big and it took time to break away,” Mishra said.
A couple zone is a region where two tectonic plates horizontally slide past each other.
“India is located in a seismically active region but we are lucky that we have a lot of micro earthquakes occurring every day. So the store-up energy is being released,” the scientist said.
He added that the impact of a large-scale earthquake can be reduced if people and institutions strictly comply with the bylaws and codes to build resilient structures.
According to experts, the resonant frequency of a building can play a critical role in determining the level of damage it experiences during an earthquake.
Buildings have natural frequencies of vibration, also known as resonant frequencies, which are determined by their mass, stiffness and size. The ground motion during an earthquake can excite these natural frequencies, causing the building to vibrate at its resonant frequency.
If the frequency of the ground motion matches or is more than the resonant frequency of a building, the structure will experience significant amplifications of the ground motion, leading to more intense shaking and potentially causing significant damage.
“The frequency of the buildings in the affected region in Turkiye was less than the frequency of ground motion. Hence, the structures collapsed like a pack of cards,” Mishra said.
India is divided into four seismic zones based on the potential for earthquake activity in each region.
According to the Ministry of Earth Sciences, 59 per cent of India’s land mass is prone to earthquakes. Zone V is seismically the most active region, while Zone II is the least. Around 11 per cent of the country’ area falls in Zone V, 18 per cent in Zone IV and 30 per cent in Zone III and the remaining in Zone II.
The zones are used to guide building codes and construction practices.
Mishra said the ministry is further unifying the country’s seismic hazard zonation map through seismic microzonation studies. At present, 30 cities with a population of five lakh and above and falling under seismic zones III, IV and V are being covered under the project.
The existing zonation map does not consider physical properties, heterogeneity and soil behaviour, among others, and compromises many engineering parameters, he said.
“The parameters will be shared with the Bureau of Indian standards (BIS) and the Ministry of Urban Affairs and municipalities will utilise them to create a new design code,” Mishra said.
On India’s disaster preparedness and response, experts said the country has a dedicated, well-equipped and trained force — the NDRF — which has the wherewithal to reach the right place at the right time.
“The NDRF and the National Institute of Disaster Management (NIDM) under the overall guidance of the National Disaster Management Authority (NDMA) is also carrying out capacity development of the entire country and reaching down to the community level with the help of all stakeholders, including public enterprises, private organisations and NGOs,” said Major General Manoj Kumar Bindal, former executive director at National Institute of Disaster Management, Ministry of Home Affairs.
Every state has its own disaster management authority and disaster response force.
There is a total paradigm shift towards effective response and mitigation. Now, India is increasing the resilience of communities to enable people to rebound after a disaster. The country is very well prepared to deal with such emergencies, he said.
“Though new buildings are being sanctioned based on designs that adhere to seismic codes, the issue that we are facing is more than 90 per cent of the existing buildings are based on old technology and most of them are non-engineered structures, especially in rural areas,” Major Gen Bindal said.
So it’s a massive work to convert the old, non-engineered structures that do not adhere to seismic codes, like in Delhi, to earthquake-proof buildings, he added.
The NDMA has now issued guidelines for training masons and retrofitting existing buildings, starting with critical infrastructure belonging to the government and private institutions such as schools and colleges.
A strict monitoring mechanism is required for the new buildings and a massive exercise is needed to map out each and every existing building. The government may consider relocating some structures that are extremely dangerous, the expert said.
He said it is not possible to do structural stability tests of each building as there are few structural engineers.
“The problematic areas are where the plans do not exist but the building looks good. A structural audit is needed for such structures and it’s a long-drawn process,” Major Gen Bindal said.
Asked what could happen if a large-scale earthquake event, like the one in Turkiye, strikes the Himalayas, he said the destructive potential of an earthquake depends on several factors, including depth and proximity to populated areas.
“It is not necessary that an earthquake of magnitude of 7 and above will cause massive damage in the Himalayas. However, if we take the worst-case scenario, an earthquake of this magnitude will lead to massive landslides, damage to roads, villages, flash floods etc. The effect on the urban areas will depend on the epicentre of the earthquake. It depends on which direction the ripples travel,” Major Gen Bindal said.
“So, a lot of simulation is being done and models being made and land use planning is being done accordingly. The problem comes when someone doesn’t follow the plans,” he added.