Are the dangers to constructions within the Himalayas and north-eastern states from earthquakes overestimated? Scientists, structural engineers, representatives from a number of authorities ministries are anticipated to deliberate and report again to the Cabinet Secretariat within the coming weeks.
This follows a ‘withdrawal’ earlier this month by the Bureau of Indian Standards (BIS) of a set of up to date standards that building initiatives ought to include to protect towards collapse when impacted by earthquakes.
The withdrawal was prompted – as The Hindu reported on March 7 – by an order from Cabinet Secretariat, that mentioned the brand new requirements “materially affected … ongoing and future infrastructure projects including metro rail projects,” and {that a} “holistic and comprehensive review of the revised IS 1893 be conducted, taking into account the perspectives of all stake holders.”
However a decade price of research – commissioned and accredited by the federal government – and involving scientists from probably the most reputed establishments in India with experience in geology, seismology, geotechnical engineering and structural engineering are unambiguous: the potential harm to all constructions, whether or not residential buildings, bridges, industrial constructions or water tanks, dams, energy crops within the Himalayan states are far increased than the present danger assessments, which in flip feed into current building codes throughout the nation.
The IS 1893 –Criteria for Earthquake Resistant Design of Structures- is a five-part doc revealed by the Bureau of Indian Standards (BIS), that gives the obligatory tips that engineers and designers should comply with to make sure buildings and infrastructure can survive seismic exercise.
India’s seismic zoning maps delineate the nation into 4 zones (Zone 2II, III 3, IV4 and V5). Zone 2 II is the calmest a part of India’s seismic panorama. The floor beneath you would possibly shake noticeably throughout your lifetime, however the forces concerned are comparatively modest. The 2016 model of India’s seismic zoning map – the one which was to have been outmoded by the now withdrawn 2025 avatar – assigns a design acceleration of 0.10g in Zone II, which means engineers anticipate the sideways power on a building to be not more than about 10% of the downward pull of gravity throughout the strongest believable earthquake within the space.
Zone V is a essentially completely different proposition. The design acceleration is at the least 0.36 g, or three and half instances increased than Zone II. At these forces, the bottom is lurching sideways with a power equal to one-third of gravity. Unsecured furnishings topples, folks can not stand with out holding on to one thing, and buildings expertise forces that may buckle metal columns, shatter concrete, and trigger flooring to pancake onto each other if not designed suitably. This is the zone assigned to areas alongside the Himalayan entrance and components of northeast India — areas sitting instantly on or adjoining to one of the crucial energetic tectonic plate boundaries on Earth, the place the Indian plate is driving into the Eurasian plate and the place magnitude 8 earthquakes have occurred inside dwelling reminiscence. These proportions – 10%, 36% – are often expressed as 0.10g and 0.36g and known as ‘peak ground acceleration’ (PGA) values in seismic zoning language.
At a distance of, say, 20 km from the fault — shut sufficient to be within the zone of robust shaking however circuitously on the rupture — a magnitude 6 earthquake on rock would possibly produce PGA values within the vary of 0.15 to 0.30g used. A magnitude 7 earthquake – which releases about 32 instances extra power – on the identical distance would usually produce PGA values within the vary of 0.40 to 0.80g. At very shut distances, say 10 km, a magnitude 7 can produce PGA values exceeding 1.0g. So, the ratio is roughly an element of two.5 to three.5 in PGA for a one-unit improve in magnitude on the identical distance.
Prior to the BIS withdrawal, was a 2024 paper within the peer-reviewed Indian Journal of Earth System Sciences that radically up-ended how India – because the Sixties – has accounted for the chance from earthquakes in building design, proposed a brand new methodology to estimate earthquake hazard danger and making it consonant with how the remainder of world computes it and, inevitably – and finally controversially – elevated the PGA values that underlie present building codes.
This wasn’t a purely tutorial research however was the result of a mission commissioned in 2019, by the National Disaster Management Authority (NDMA), of the Ministry of Home Affairs, to the Indian Institute of Technology, Madras and Bureau of Indian Standards (BIS) to convey India in control with the remainder of the world and create a ‘probabilistic risk hazard assessment map’ for India. This was preceded by two different initiatives, one from 2007-11 (funded by the NDMA) and one other from 2013-17 funded by the Department of Science and Technology – all of which had been supposed to maneuver India’s earthquake hazard evaluation in direction of a probabilistic frame-work.
The NDMA had accepted this research, following which its outcomes had been revealed by the BIS in IS 1893 (Part 1) as a 2025 replace of India’s design earthquake hazard and zoning map, which was then withdrawn.
The authors of the paper, comprise scientists from a few of India’s most respected establishments such because the Indian Institutes of Technology in Mumbai and Chennai, the Atomic Energy Regulatory Board, and Geological Survey of India amongst others.
“These PGA values are not derived based on any quantitative earthquake hazard assessment and are abysmally low, especially for the higher earthquake zones. For example, the regions of the Himalayan plate boundary and northeast India with the potential to produce earthquakes exceeding magnitude 8.0 are covered by earthquake zones IV and V with design PGA values of 0.24 and 0.36g, respectively, whereas the 1897 Great Shillong Plateau earthquake in northeast India is reported to have resulted in PGA values more than 1.0g,” the report of their research. They argue that acceleration values in India are too conservative by worldwide requirements. “The design accelerations in similar areas worldwide are taken to be two times (or more) compared to that in the existing zone map of India. Therefore, there is a need to revise India’s current earthquake-resistant design code on the basis of an adept quantitative technique such as hazard analysis,” mentioned a multi-author research led by STG Raghukanth, CVR Murty, Bhargavi Podili, KP Sreejaya and KP Sreejaya CVR Murty of IIT Madras. There are a number of different authors from different institutes and organisations.
In earlier assessments, a area was assigned a Zone IV or Zone V classification solely retrospectively, that’s, after it had skilled a major earthquake. The surrounding areas, which regularly had been as inclined, had been assumed to be at decrease danger regardless that proof had constructed up over many years that they had been usually areas with pent up pressure that hadn’t been launched. The present framework additionally didn’t account for native soil situations – that would amplify the waves emanating from the centre growing the forces a building was topic to – and the existence of a community of 168 monitoring stations – most of them within the Himalayas – that relayed knowledge on even small earthquakes of magnitudes of two and three and their related power waves from the Indian neighbourhood too together with Afghanistan and Xinjiang. “The earth is a dynamic system. Every 50 years or so, PGA values change by about 10%. Age affects the human body, and similarly the earth,” mentioned OP Mishra, former directorDirector, National Centre for Seismology (NCS), India’s official repository of earthquake knowledge, “In a probabilistic assessment you account for a variety of factors that might influence shaking and that serves as a reference point for builders… India has stated its commitment to be disaster resilient by 2047.” Dr Mishra was a part of a BIS committee to revise the code.
The historic document for nice earthquakes in India is extraordinarily brief relative to their recurrence intervals. The authors cite 4 nice Himalayan earthquakes because the late 1800s — the 1897 Shillong, 1905 Kangra, 1934 Bihar-Nepal, and 1950 Assam-Tibet occasions. But these 4 occasions occurred on completely different segments of the plate boundary. Any particular person phase would possibly expertise an incredible earthquake solely as soon as each 250 to 500 years, in response to the authors’ estimates. India’s instrumental seismic document is barely a century outdated, and the historic document, whereas longer, is patchy and incomplete. A 500-year recurrence occasion has an inexpensive chance of occurring throughout a building’s 50-year design life (roughly 10%), however might not have occurred in any respect throughout the obtainable commentary interval for a given fault phase. The conventional strategy has no mechanism for accounting for this.
Over 79% of India’s inhabitants lives on roughly 57% of its land, beneath the specter of average to extreme earthquake hazard. By 2046, the city inhabitants is projected to exceed the agricultural inhabitants, the research notes underlining the need for up to date acceleration values.
The new map assigns PGA values of 0.15g, 0.3025g, 0.4535g, 0.6050g, and 0.75g for zones II by way of VI almost doubling the hazard estimates within the increased zones and bringing them nearer to what comparable areas internationally are designed for. It’s these values which have seemingly rattled companies such because the Delhi Metro Rail Corporation and the National Dam Safety Authority.
The new map additionally introduces a fifth zone Zone VI, for areas the place PGA estimates exceed 0.60g. This captures probably the most seismically energetic areas (components of the Himalayan plate boundary and northeast India) that had been beforehand all lumped collectively in Zone V at an insufficient 0.36g. It additionally attracts on a a lot richer dataset and methodology than any predecessor: an earthquake catalogue of 69,519 occasions spanning from 2600 BC to December 2019 (de-clustered down to twenty-eight,770 mainshocks), 33 36 outlined seismogenic supply zones, a number of floor movement fashions. “The assessments are scientific., however a figure, like 0.75g represents a worst worst-case scenario. The practice is usually to halve the PGA value as a representative of what is likely and then – depending on the criticality of the structure – plan the structure,” mentioned a authorities division official, who declined to be on document.
“Recent evidence shows that 95% of those who die in earthquakes are those who live in 1-3 storey houses that are inadequately designed,” mentioned a scientist who was concerned within the train however declined to be recognized. “The 0.75 factor is also a lower number. While there are consultations in the offing on what design adjustments may be made, it is quite clear that the risks we have now computed are closer to reality.” Pakistan and Nepal, this particular person added, use values near 0.75g, and in addition to the United States and Japan routinely calculated values of 1g or extra, relying on the area at stake, he added.
An official of the NDMA who was aware of developments across the zoning map mentioned that the scientific evaluation outcomes had been a results of “too pure science.” He mentioned that whereas the NDMA had certainly thought of the report, the issue that cropped up was that advisable acceleration values “were too high” and would considerably pressure authorities public spending. “On one hand we have the situation that a large proportion do not follow even the existing (2016) codes. Then with these stringent numbers, steel, cement costs will go up manifold – where there is money to build four schools or clinics in a village, only one will be made. Finally, it doesn’t give builders the freedom to do their own assessments and compute the PGA risks. This ended up being too theoretical an exercise.” The NDMA didn’t reply to requests for an official remark.
Published – March 21, 2026 07:45 am IST