How skyscrapers are built in Japan
Building to Withstand Earthquakes
• • • • • • • May 2025 • • • • • • •
The building philosophies for earthquake resiliency in Tokyo and San Francisco are quite different. Some of it has to do with Japans philosophical outlook, “the green reed which bends in the wind is stronger than the mighty oak which breaks in a storm.” This wisdom is attributed to Confucius.
In the West, the phrase, “ be like the Willow and not the Oak” is more common. This outlook emphasizes the importance of resilience and adaptability over rigidity and resistance when facing challenges. Like a green reed that bends with wind without breaking, those who are adaptable can navigate difficult situations with greater ease. Oaks, while strong, can be brittle and break under intense pressure, representing the negative consequence of inflexibility.
However, Japanese builders have implemented this philosophy into their structures.
SEISMIC ISOLATION IN JAPAN (Base Isolation Above)
If a structure is able to absorb the energy of an earthquake, engineers in Tokyo believe, it will be resistant to failure. In order to do this, the Japanese builders use several techniques to minimize earthquake damage. One way is through seismic isolation.
The buildings or structures are put on a form of bearing or shock absorber – sometimes as simple as blocks of rubber about 30-50cm (12 to 20 inches) thick – to resist the motions of the earthquake. Wherever the building columns come down to the foundation, they sit on these rubber pads.
JAPANESE EARTHQUAKE DAMPER
Another strategy is to damper throughout the height of the building. For example, a tall building can move as much as five feet in an earthquake but if dampers are located, on every 2nd floor, all the way up to the top, this allows the building to be able to absorb more shock without failing. (See diagram above)
MESH STRUCTURES IN JAPAN
Other buildings use mesh structures which can prevent buildings from buckling and distributes the energy more evenly. Fortunately, using this style of design can also create very attractive buildings too.
EARTHQUAKE OCCURRENCE
Earthquakes in Japan are getting stronger. In California, it is estimated that there is a 95% chance of a serious earthquake occurring in the next 100 years.
HOW SKYSCRAPERS ARE BUILT IN SAN FRANCISCO
As you would expect, skyscrapers in San Francisco are built like the oak tree. Instead of numerous appliances to absorb or damper buildings, construction in San Francisco primarily depends on rebar and concrete to build strong modern skyscrapers. Skyscrapers built in this fashion are robust, however, the earthquake resiliency strategy is very different from that in Japan.
Before 1990, as many as 4,000 buildings in San Francisco were built with no rebar to resist side-to-side shaking. These buildings were usually built as office spaces or multi-family houses. In other countries, e.g., New Zealand and Mexico, similar buildings have collapsed in severe earthquakes.”
WHERE SAN FRANCISCO EARTHQUAKE STRATEGY FAILS
Before 1990, as many as 4,000 buildings in San Francisco were built with no rebar to resist side-to-side shaking. These buildings were usually built as office spaces or multi-family houses. In other countries, e.g., New Zealand and Mexico, similar buildings have collapsed in a severe earthquakes.
TILT-UP CONSTRUCTION
Another type of building vulnerable to damage during an earthquake is so-called tilt-ups and are typically warehouses, grocery stores, or manufacturing facilities. The problem with these buildings, is that the walls and the roof are not always secured together adequately. If the wall and roof separate, the failure can be catastrophic.
INSPECTION AND MONITORING IN TOKYO
Japan has a strict earthquake code and inspection measures in place. In addition, buildings are required to have safety inspections after an earthquake. This provides confidence for the public and owners of the building both. Buyers in Japan are required to provided legal documentation from independent inspectors attesting to the earthquake resiliency of their purchase.
1981 IN JAPAN
For buildings constructed before 1981, a Developer or Seller is required to disclose any seismic upgrading on the property. If not, the Buyer must provide the necessary seismic upgrading, including the cost of improvement. This provides leverage to the Buyer when purchasing unimproved property!
1981 to 2000 IN JAPAN
After the Miyag Earthquake of 1978, seismic standards were upgraded. Now, developers must confirm compliance with improved earthquake standards. Also, the Buyer has the responsibility to be sure the property meets post-1981 retrofitting standards.
POST 2000 BUILDINGS IN JAPAN
At this point in time, all seismic standards are cutting edge and meet the latest standards of code enforcement. Developers/Sellers must provide certificates stating the state of the art practices are in place for the building they sell. The Buyer has the mandate to verify that post-1981 standards and retrofitting were incorporated.
IN JAPAN BUYER CONFIRMATION IS REQUIRED AT PURCHASE
Buyers are entitled to receive proof the property is in compliance with seismic safety standards signed by a certified engineer. Most importantly, two Certificates of Compliance are provided to the Buyer. One is the Certificate of Inspection and the other is the Certificate of Completion. Furthermore, Sellers of the real estate agents are compelled to report any problem with the building due to earthquakes.
INSPECTION AND MONITOR IN SAN FRANCISCO
San Francisco is far behind Tokyo in inspection and monitoring of buildings for earthquake resiliency. As mentioned before, the City has 4,000 buildings that are likely to fail in an earthquake. However, this list is may be incomplete. Legislation under consideration by the Board of Supervisor (BOS) at the May 2025 meeting, will be to schedule research and inspections for questionable buildings. The cost to inspect each of these buildings can be between $300 to $3,200.
Should this legislation pass, the City would have a better idea of how buildings would fare in an earthquake. Currently, there seems to be a controversy as to whether this information should be available to the people who live and work in these buildings. The City hopes they can prod owners to upgrade their earthquake resilience when this information is available. Supervisor Melgar, who sponsored this legislation, believes those who visit, work or live in the City, should know if their buildings are safe.
Today, the ordinance does not require retrofitting but does provide a standard for these improvements. For now, the program is voluntary for earthquake readiness; however, Supervisor Melgar says, if the City identifies a substandard building and owners are not resolving the issues quickly enough, legislation would become mandatory.
The cost of retrofitting non-compliant concrete buildings could be between $50-$200 per square foot. At that point, perhaps San Francisco will have an inspection and monitoring systems as effective as those in Japan. We can only hope so!
FOOTNOTES:
1. https://www.bbc.com/future/article/20190114-how-japans-skyscrapers-are-built-to-survive-earthquakes
2. https://housingjapan.com/blog/why-japans-earthquake-resistant-buildings-are-the-future-of-real-estate/
3. https://www.sfchronicle.com/sf/article/earthquake-risk-concrete-buildings-retrofit-20267310.php
Glenn Rogers, RLA,
President, Coalition for San Francisco Neighborhoods (CSFN)
Landscape Architect, License 3223
May 2025
