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How Japan spent more than a century protecting its architecture from earthquakes

How Japan spent more than a century protecting its architecture from earthquakes

(CNN) — Scenes of buildings reduced to rubble spread around the world this week after the 7.5-magnitude earthquake struck Ishikawa Prefecture, on Japan's west coast, on Monday.

The full extent of the damage remains unknown. According to authorities, at least 270 homes were destroyed in the area, although the final figure is likely to be much higher. This figure does not include, for example, Suzu or Wajima, a city with a population of more than 27,000 located just 32 kilometers from the epicenter, where firefighters are stationed. They said Public Broadcasting Corporation (NHK) reported that about 200 buildings had been burned.

These reports speak to the personal tragedies faced by many residents of the area. However, although no two earthquakes are directly comparable, earthquakes of similar magnitude in other parts of the world – such as the 7.6 magnitude earthquake that caused more than 30,000 buildings to collapse in Kashmir in 2005, for example – Often caused much greater destruction.

By contrast, Ishikawa may have emerged unscathed, according to Robert Geller, professor emeritus of seismology at the University of Tokyo. “Modern buildings seem to be holding up very well,” he told CNN the day after the Japan quake, noting that older buildings It was holding up very well. Older houses “with heavy clay tile roofs” appear to have fared worse.

“Most single-family homes, although damaged, did not completely collapse.”

The saying in seismic design is that earthquakes don't kill people; But the buildings. In one of the most earthquake-prone countries in the world, architects, engineers and urban planners have long tried to protect cities from major earthquakes through a combination of ancient wisdom, modern innovation and ever-evolving building codes.

A building in Osaka, Japan has been reinforced to protect it from earthquakes.  (Credit: Trevor Mogg/Alamy Stock Photo)

A building in Osaka, Japan has been reinforced to protect it from earthquakes. (Credit: Trevor Mogg/Alamy Stock Photo)

From large-scale “shock absorbers”, which swing like a pendulum inside skyscrapers, to spring systems or ball bearings that allow buildings to sway independently of their foundations, technology has advanced dramatically since the Great Kanto earthquake that destroyed large parts of Tokyo and Yokohama just over 100 years.

“But the innovations focus primarily on a simple, long-known idea: that flexibility gives structures the best chance of survival.” Many buildings, especially hospitals and critically important structures, rely on these (bearings) so that the building itself can sway. “, explains Miho Maziryu, an assistant professor of architecture and urbanism at the Massachusetts Institute of Technology (MIT), who analyzes Japan's culture of care in her upcoming book, “Design before disaster.”

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“In theory, it boils down to the idea that instead of resisting the movement of the ground, you let the building move with it.”

This principle has been used in Japan for centuries. For example, many of the country's traditional wooden temples have survived earthquakes (and likely succumbed to fires or wars), even when modern structures cannot. For example, the 55-meter-high Toji Temple, built in the 17th century near Kyoto, emerged intact after the 1995 Great Hanshin Earthquake, also known as the Kobe Earthquake, while many nearby buildings collapsed.

Five-storey 17th-century pagoda at Toji Temple in Kyoto.  (Credit: Ivan Marchuk/Alamy Stock Photo)

Five-storey 17th-century pagoda at Toji Temple in Kyoto. (Credit: Ivan Marchuk/Alamy Stock Photo)

Traditional Japanese architecture has much in common with its counterpart in neighboring Korea and China, although it differs in aspects that reflect the country's high incidence of earthquakes.

In particular, the remarkable survival rate of temples has long been attributed to “shinbashira,” central columns made of tree trunks that have been used by Japanese architects for at least 1,400 years.

Whether anchored to the ground, supported by a beam, or suspended from above, these columns bend and flex when the building's floors move in the opposite direction to their neighbors. The resulting swaying motion – often compared to that of a slithering snake – helps counteract the force of tremors and is aided by interlocking joints and loose supports, as well as wide roof eaves.

Learn from tragedies

Not all buildings in Japan today may look like pagodas, but skyscrapers do.

Although the country imposed a strict height limit of 31 meters until the 1960s, due to the risks posed by natural disasters, architects have since been allowed to build taller towers. Currently, Japan has more than 270 buildings with a height of more than 150 meters, which is the fifth country in the world in this classification, according to data from the Council on Tall Buildings and Urban Habitat.

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The use of steel structures that add flexibility to already rigid concrete has encouraged designers to develop extensive counterweights and “base isolation” systems that act as shock absorbers.

The real estate company behind Japan's tallest new building, which opened in Tokyo's Azabudai Hills district last July, says its anti-seismic design features – including extensive shock absorbers – “will allow businesses to continue operating” in the event of a strong earthquake. Such as the 9.1 magnitude Tohoku earthquake that shook the country in 2011.

But in many places in Japan without skyscrapers, such as Wajima, earthquake resistance has focused more on protecting everyday buildings: homes, schools, libraries and shops. In this sense, Japan's success was as much a matter of politics as of technology.

For one thing, Japanese architecture schools — perhaps because of the country's history of natural disasters — have been keen to train students in both design and engineering, explains Mazerio, who also runs MIT's Urban Hazards Laboratory, a research organization that studies earthquakes and environmental impacts. Climate risks facing cities.

Tokyo lay in ruins after the Great Kanto Earthquake of 1923. (Credit: Hulton Deutsch/Corbis/Getty Images)

Tokyo lay in ruins after the Great Kanto Earthquake of 1923. (Credit: Hulton Deutsch/Corbis/Getty Images)

“Unlike most countries, Japanese architecture schools combine architecture and structural engineering; in the United States they teach structural engineering classes, but they are very superficial,” he said, adding that in Japan both disciplines are “always combined.”

Over the years, Japanese authorities have also tried to learn from each of the country's major earthquakes, and researchers have conducted detailed studies and updated building regulations accordingly.

This process dates back to at least the 19th century, says Mazerio, explaining how the widespread destruction of new European-style brick and stone buildings in the 1891 Mino-Owari earthquake and the 1923 Great Kanto earthquake led to new laws on urban planning and urban buildings .

The gradual evolution of building systems continued throughout the twentieth century. But a law introduced in 1981 known as Shin Taishin, or New Amendment to Earthquake-Resistant Building Standards — a direct response to the Miyagi earthquake three years earlier — marked a before and after.

The new standards, which set more stringent requirements for the load-bearing capacity of new buildings and require greater “floor drift” (the amount of floors that can move relative to each other), among many other things, have proven so effective that pre-built homes – The 1981 standards (known as “Q-taishin” or “pre-earthquake resistance”) are harder to sell, and more expensive to insure.

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The first real test of the regulations came in 1995, when the Great Hanshin Earthquake caused widespread devastation in southern Hyogo Prefecture. The results were astonishing: 97% of collapsed buildings were built before 1981, according to the Global Fund for Disaster Reduction and Recovery.

Innovation and preparation

The 1995 earthquake launched a national campaign to adapt old buildings to 1981 standards, a process that municipal authorities encouraged through subsidies. Innovation has continued in the decades since, and Japanese architects are often at the forefront of seismic design.

For example, Kengo Kuma, one of the country's most famous architects, collaborated with textile company Komatsu Materi in 2016 to develop a curtain made up of thousands of braided carbon fiber rods that anchors the company's headquarters to the ground like a tent. Image above). Most recently, he was involved in the design of a kindergarten building in the southern Kochi prefecture using an earthquake-resistant checkerboard wall system.

Elsewhere, prominent Japanese architects, such as Shigeru Ban and Toyo Ito, have pioneered the use of cross-linked timber (CLT), a new type of wood that proponents believe could change the way skyscrapers are built.

An anti-seismic column used in the design of an old wooden house in Miyama, Kyoto Prefecture.  (Image source: Eric LaForge/Art in All of Us/Corbis/Getty Images)

An anti-seismic column used in the design of an old wooden house in Miyama, Kyoto Prefecture. (Image source: Eric LaForge/Art in All of Us/Corbis/Getty Images)

Advanced computer models also allow designers to simulate seismic conditions and build accordingly. However, the limits of most disaster-resistant buildings have not been tested.

“There are a lot of high-rise buildings and a lot of effort has been put into designing them to be safe, but these designs are mostly based on computer simulations,” says Geller of the University of Tokyo. “We may not know whether or not these simulations are accurate until a large earthquake hits. If just one of these skyscrapers collapses, it could cause severe damage.”

Therefore, the question that has long worried Japanese engineers and seismologists remains: What would happen if a large earthquake directly shook a city like Tokyo, something that the Japanese capital authorities have warned has a 70% probability within the next thirty years. ?

“Tokyo is probably reasonably safe,” he adds. “But there's no way to know for sure until the next big earthquake actually hits.”

CNN's Eric Cheung and Saki Toy contributed to this report.