(CNN) — There were scenes of buildings reduced to debris around the world this week after a 7.5-magnitude earthquake struck Ishikawa Prefecture on Japan’s west coast on Monday.
The full extent of the damage is still unknown. According to officials, at least 270 homes were destroyed in the area, although the final figure is likely much higher. This figure does not include, for example, Suzu or Wajima, a city of more than 27,000 residents located just 32 kilometers from the epicenter, where firefighters said about 200 buildings were destroyed, according to public broadcaster NHK. She was burnt.
These reports tell of the personal tragedies that many residents of the area face. However, while no two earthquakes are directly comparable, earthquakes of similar strength in other parts of the world – such as the 7.6 magnitude earthquake that caused the collapse of more than 30,000 buildings in Kashmir in 2005, have often caused much greater destruction. Are.
In contrast, according to Robert Geller, professor emeritus of seismology at the University of Tokyo, Ishikawa may have emerged safely. “The modern buildings look great,” he told CNN the day after the Japanese earthquake, adding that the older buildings, with their “heavy clay tile roofs,” looked even worse.
“Most single-family homes, although damaged, did not completely collapse.”
An adage in seismic design says that earthquakes don’t kill people, they kill buildings. And in one of the most seismic countries in the world, architects, engineers and urban planners have long tried to protect cities from major earthquakes through a combination of ancient knowledge, modern innovation and constantly evolving building codes.
From massive “shock absorbers” that swing like pendulums inside skyscrapers, to spring or ball-bearing systems that allow buildings to shake independently of their foundations, technology progressed dramatically. This is because the Great Kanto Earthquake destroyed large parts of Tokyo and Yokohama. More than 100 years ago.
But the innovations first focus on a simple and long-known idea: that resilience offers structures the best chance of survival. “Many buildings, particularly hospitals and critical mass structures, rely on these (bearings) of rubber to allow the building itself to sway,” explains Miho Mazereuw, associate professor of architecture and urban planning at the Massachusetts Institute of Technology (MIT). who analyzes Japan’s culture of preparedness in his upcoming book, “Design Before Disaster.”
“Conceptually, it’s based on the idea that, instead of resisting the Earth’s movement, you have to let the building move with it.”
This principle has been used in Japan for centuries. For example, many of the country’s traditional wooden pagodas have survived earthquakes (and are more likely to succumb to fire or war), even when modern structures have not. For example, the 55-meter-high Toji Temple Pagoda, built in the 17th century near Kyoto, survived the 1995 Great Hanshin earthquake, also known as the Kobe earthquake, intact, while many nearby buildings collapsed.
Traditional Japanese architecture has much in common with neighboring Korea and China, although it differs in aspects that reflect the high incidence of earthquakes in the country.
In particular, the pagoda’s remarkable survival rate has long been attributed to “shinbashira”, central pillars made from tree trunks and used by Japanese architects for at least 1,400 years.
Whether anchored to the ground, supported by a beam, or suspended from above, these pillars bend and flex as the building’s floors move in the opposite direction to their neighbors. The resulting undulating motion – often compared to a slithering snake – helps to counteract the force of the shock and is aided by interlocking joints and loose supports as well as the wide rafters of the roof.
learn from tragedies
Not all buildings in today’s Japan look like pagodas, but skyscrapers do.
Although the country had a strict height limit of 31 meters in place until the 1960s, architects have since been allowed to build taller, due to threats posed by natural disasters. According to data from the Council on Tall Buildings and Urban Habitat, there are currently more than 270 buildings taller than 150 meters in Japan, ranking it fifth in the world.
The use of steel skeletons that add flexibility to already rigid concrete has encouraged designers to develop massive counterweights and “base isolation” systems that act as shock absorbers.
The real estate company behind Japan’s new tallest building, which opened in Tokyo’s Azabudai Hills development last July, says its earthquake-resistant design features – including massive shock absorbers – will “protect businesses” in case of an earthquake. will be allowed to continue operating”. In 2011, the record magnitude 9.1 Tohoku earthquake shook the country.
But in many places without skyscrapers, like Wajima in Japan, earthquake resistance has focused more on protecting everyday buildings: homes, schools, libraries and shops. And in this sense, Japan’s success has been a question of technology as well as politics.
For one thing, Japanese architecture schools have ensured—perhaps because of the country’s history of natural disasters—that students are trained in both design and engineering, explains Mazeriouw, who also directs MIT’s Urban Risk Lab. Do, which is a research organization that studies seismology and earthquakes. The climate risks that cities face.
“Unlike most countries, Japanese architecture schools combine architecture with structural engineering; in the US they teach structural engineering classes, but they are very superficial,” he said, adding that in Japan the two subjects “are always united.”
Over the years, Japanese authorities have tried to learn from each major earthquake that has hit the country, and researchers have conducted detailed studies and updated building regulations accordingly.
The process dates back to at least the 19th century, Mazeriouw says, describing how the widespread destruction of new European-style brick and stone buildings in the Mino-Owari earthquake of 1891 and the Great Kantō earthquake of 1923 led to new ideas on urban planning. Laws should be made. and urban buildings.
The piecemeal development of building regulations continued throughout the 20th century. But a code introduced in 1981 called “Shin-taishin” or new amendment to earthquake-resistant construction standards – a direct response to the Miyagi earthquake three years earlier – marked a before and after.
The new standards, which set stricter requirements for the load-bearing capacity of new buildings and require more “story drift” (how much floors can move relative to each other), among many other things, have proven so effective. Pre-built homes up to the 1981 standard (known as “Qi-Taishin” or “pre-earthquake resistance”) may be much more difficult to sell and more expensive to insure.
The first real test of the rules came in 1995, when the Great Hanshin earthquake caused widespread destruction in southern Hyogo Prefecture. The results were overwhelming: according to the Global Fund for Disaster Reduction and Recovery, 97% of the collapsed buildings were built before 1981.
Innovation and preparedness
The 1995 earthquake triggered a national campaign to retrofit old buildings to 1981 standards, a process that municipal authorities have encouraged through subsidies. Innovation has continued over the decades and Japanese architects are often at the forefront of seismic design.
For example, Kengo Kuma, one of the country’s best-known architects, collaborated with textile company Komatsu Matere in 2016 to develop a curtain made of thousands of braided carbon fiber rods that would anchor the company’s headquarters to the ground like a tent. Is. campaign (photo above). More recently, he co-designed a kindergarten building with an earthquake-resistant checkerboard wall system in southern Kochi Prefecture.
Elsewhere, prominent Japanese architects such as Shigeru Ban and Toyo Ito have pioneered the use of cross-laminated timber (CLT), a new type of wood that proponents believe could change the way skyscrapers are constructed. Is.
Advanced computer models also allow designers to simulate seismic conditions and build accordingly. However, the limits of most disaster-resistant buildings have never been tested.
“There are a lot of tall buildings and a lot of effort has been put into designing them to be safe, but those designs are mostly based on computer simulations,” says Geller of the University of Tokyo. “We won’t know whether these simulations are accurate until a big earthquake happens. If even one of those skyscrapers collapses, it could cause a lot of damage.”
So, the question that has long worried Japanese engineers and seismologists remains: What would happen if a major earthquake directly hit a city like Tokyo, with officials in the Japanese capital warning that there is a 70% chance in the next 30 years. Is ?
He added, “Tokyo is probably pretty safe.” “But until the next big earthquake actually hits, there’s no way to know for sure.”
CNN’s Eric Cheung and Saki Toi contributed to this report.