Japan’s Century of Efforts to Tame Earthquakes

When the 9.0 magnitude earthquake occurred on March 11, 2011, Takashi Hosoda was inside a Tokyo skyscraper, but the educated architect was "not particularly worried" because contemporary Japanese structures are made to safeguard their inhabitants.

Tokyo no longer resembles the metropolis leveled by the 7.9 quake that killed 105,000 people in the Great Kanto Earthquake of 1923, which occurred a century earlier.

A towering megalopolis where reinforced concrete reigns has replaced the low-rise, mostly timber city that was twice devastated by US firebombing during World War II.

The September 1, 1923, disaster marked "the dawn of seismic design of structures in Japan", said Yoshiaki Nakano, an earthquake engineering expert from the National Research Institute for Earth Sciences and Disaster Resilience (NIED).

The following year Japan introduced its first building code for earthquake-resistant construction.

These standards have been constantly expanded since then, drawing on lessons from other major tremors in the archipelago, which accounts for around 10 percent of the world's earthquakes.

Japan's seismic building code is one of the most stringent in the world, Nakano told.

"Basically, the Japanese building requires a relatively higher strength" than elsewhere, he said, stressing the importance of meticulous monitoring of compliance.

"The system to supervise and check the design and the construction on-site is a very key factor to ensure the quality of the structure, the performance of the building during earthquakes," he said.

The 2011 earthquake triggered a deadly tsunami along the northeast coast but in Tokyo the damage was limited: high-rise towers oscillated alarmingly for several minutes but did not topple.

Early basic reinforced structures have been adapted with more sophisticated seismic safety measures found in modern towers.

Massive soft rubber cushions are installed under the foundations to isolate them from ground vibrations; shock absorbers are distributed throughout the floors; and some even have pendulums weighing several hundred tonnes installed at the top to counteract the movement of the building during a quake.

Built in 2014 and rising 247 metres (810 feet) above the city, the Toranomon Hills Mori Tower is fitted with such seismic anti-vibration systems, including 516 oil dampers, each comprising a thick cylinder 1.7 metres long.

"It stretches and shrinks repeatedly in case of an earthquake. It then starts getting warm, which means the energy of the quake transforms into heat and gets released," Kai Toyama, a structural engineering official at real estate giant Mori Building, told.

"As a result, the tremor of the whole building can be controlled."

After the Kobe earthquake in 1995 left more than 6,000 dead, emphasis was also placed on strengthening earthquake resistance standards for new wooden houses and upgrading older buildings dating from before the last major overhaul of the building code in 1981.

The Great Kanto Earthquake of 1923 was also "a wake-up call to Japan", Nakano noted. "Not only the engineers but also for people."

Since 1960, Japan has marked September 1 as national Disaster Prevention Day.

Every year on that day, countless schoolchildren, employees and civil servants -- including the entire government -- carry out simulation exercises in preparation for a major earthquake.

In Japan, many people stock emergency supplies at home, as do businesses and local governments. As of April 1, 2023, local authorities in Tokyo have stockpiled 9.5 million instant meals (comprising rice, noodles and biscuits) in about 400 warehouses.

These precautionary measures were intensified after the 2011 earthquake, which caused huge traffic jams in Tokyo and the suspension of public transport, preventing millions of people from returning home, said Hosoda, now head of disaster management at Mori Building.

Despite all of these precautions, some experts claim that Tokyo still faces a high risk of earthquakes, and an even greater risk of other natural catastrophes like floods.

There are still several clusters of ancient wooden homes joined to one another in the eastern districts of the city, which were constructed on prone to flooding and unstable soils.

Seismologist Masayuki Takemura bemoaned that the post-war reconstruction of Tokyo was "anarchic" and "prioritized economic development rather than the construction of a resilient city" during a recent news conference.

The building of residential zones on man-made islands and a "excessive concentration of skyscrapers" were other issues he mentioned that increased the chance of isolation in case of a natural disaster.

Furthermore, according to scientists, there is a 70% possibility that Tokyo may experience a significant earthquake in the next 30 years.

Source: AFP