Why a megaquake warning in Japan could be a warning for India too

medium nocaption118360215Japan is bracing for a devastating megaquake, with a new government advisory warning that a 9-magnitude tremor and tsunami could kill 2.98 lakh people and cause $2 trillion in damages.This is the second advisory issued by the Japanese government about the Nankai Trough megaquake, the first was in August last year after a 7.1 magnitude earthquake occurred at the edge of the Nankai Trough. The Japanese government estimates the next megaquake has a 75-82% chance of happening in the next 30 years.Japan has been preparing for this for over a decade.What’s the Nankai Trough megaquake?The megaquake — meaning earthquakes stronger than 9 on the Richter scale — will occur along a 900 km undersea trench off Japan’s Pacific coast where two tectonic plates meet. The Philippine Sea oceanic plate is slowly slipping below (or, subducting) Japan’s continental plate, the Eurasian plate. The plates produce enormous amounts of energy through this tectonic movement, which is periodically released in the form of massive earthquakes.The Nankai Trough runs from Shizuoka to the southern tip of Kyushu island.medium nocaption119980823The South China Morning Post reported that the last Nankai Trough quake was in 1946, when about 1,400 people died from the 8.1 magnitude earthquake.“The Nankai Trough is a well-studied tectonic feature that has a well-documented history of earthquakes,” says Prof Kusala Rajendran, a seismologist, former IISc professor and co-author of ‘The Rumbling Earth’. “It has been struck by major earthquakes every 100 to 150 years on average and the current forecast is based on a large amount of a variety of data.”How bad could the damage be?A Nankai Trough megaquake could wipe out $1.81 trillion from Japan’s economy, trigger tsunamis, flatten cities, and kill up to 3 lakh people, the report warns. The quake would be felt in 764 municipalities across 31 of Japan’s 47 prefectures and the resulting tsunami could be at least three metres (10 feet) tall and even reach as high as 34 metres in certain parts. The government’s report says about 2,15,000 people could be killed by the tsunami, 73,000 would die in collapsed buildings and another 9,000 in resulting fires. The fires could damage about 2.35 million buildings.The tsunami death toll can be brought down to 94,000 if 70% of people would evacuate immediately. The government has also accounted for anywhere between 26,000 and 52,000 casualties in ‘disaster-related’ incidents such as conditions at evacuation centres.Casualties would be highest on a winter night with strong winds—fewer people would be ready to evacuate.The expected economic damage was 270.3 trillion yen, which is nearly half of the country's total gross domestic product (GDP). Japan is also likely to see 1.23 million evacuees or 1% of its total population. medium nocaption119980903medium nocaption119980926A decade of preparationJapan is one of the most seismically active countries in the world, straddled across four major tectonic plates. It sees at least 1,500 earthquakes a year and accounts for 18% of the world’s earthquakes.In March 2011, Japan recorded its largest earthquake: a 9-magnitude undersea temblor. It triggered a tsunami, which left 18,500 dead or missing, and resulted in the Fukushima nuclear disaster.Over the next couple of years, the Japanese government released projections for the Nankai Trough megaquake. Back then, the country estimated 3,23,000 deaths and 2.386 million completely destroyed buildings.Japanese daily Asahi Shimbun noted that over the past decade, the country has seen an aging and shrinking population, an increase in high rise buildings, vacant houses, and inflation, increasing risks. There is, however, a bright side to all this. In 2008, 79% of Japanese houses were earthquake reinforced, reported Asahi Shimbun. This number increased to 90% in 2023. “The rate of seawalls constructed rose from about 39 percent in 2014 to about 65 percent in 2021. The rate of municipalities where disaster prevention drills have been conducted increased from about 79 percent in 2018 to around 86 percent in 2024,” it added.In 2014, Japan announced measures that aimed to reduce the Nankai Trough megaquake deaths by 80% and damage by 50% over a decade. Even though they failed to reduce the casualties quite as sharply, the government will now be reviewing mitigation measures, reported Asahi Shimbun.“A statement in one of the Japanese reports recommends that in order to prevent damage, it is important to fix shelves in buildings and introduce new systems to check if there are any problems with the structure of buildings,” says Prof Rajendran. “Further, it adds that it is important to keep preparing and practicing evacuation plans with family and friends.”medium119981075Japan is preparing for the worst. But how ready is India for its own megaquake?Scientists warn that a powerful earthquake (>8.0 magnitude) in the Himalayas — dubbed the ‘Great Himalayan Earthquake’ — is overdue, which could have devastating consequences for Delhi and northern India. “Research has identified certain segments of the Himalaya (the Garhwal-Kumaon, for example), where earthquakes are due to occur, based on model calculations the stresses that are accumulating and the prolonged quiescence (inactivity) along specific segments.” says Prof Rajendran. Geophysicist Roger Bilham has emphasised that the question is not if but when. Bilham said that the Himalayas have been experiencing major earthquakes ‘every few hundred years.’ In the past 2,000 years, the Himalayan region has seen several earthquakes at a regular interval. Most of these tremors have been of magnitude 8.7. But he cautioned that in the past 70 years or so, the Himalayas have not reported any earthquake above the intensity of 8 on the Richter scale. In fact, Prof Rajendran explains that India has never had an earthquake stronger than 9.0. “The 2004 Sumatra earthquake that affected us mostly by the tsunami was of magnitude 9.2, but it was not sourced in India,” she adds.“The last great Himalayan earthquake (more than magnitude 8.0) occurred in Assam in 1950, close to the China border,” she explains. “The one closer to home occurred near the Bihar-Nepal border in 1934. Both these caused heavy damage in India.”medium nocaption118351702Could we be dangerously unprepared?There are several ways India can prepare for the Himalayan megaquake. Prof Rajendran recommends practicing building codes and retrofitting weaker structures. “Instead of paying compensation for losses, the government should support earthquake resistant designs, give incentives for such efforts and also provide insurance,” she says. “I am not aware of any such steps taken systematically to mitigate earthquake damage, even in the most seismically active Himalaya.” “Today my worry goes beyond that. The level of constructions that are happening in the Himalaya could potentially weaken many structures and an earthquake could also trigger landslides,” she warns. “We need to worry about the future Himalayan earthquakes, more than ever before.”While Japan refines its disaster drills, India risks being caught completely unprepared. The Great Himalayan Earthquake isn’t a question of if—but when.With inputs from Reuters