Among natural disasters, earthquakes are the most difficult to predict in advance. Fortunately, innovations in base vibration control technology continue to evolve in Japan. One example is Tokyo Skytree. At 634 meters (2080 feet) in height, the Skytree is the world’s tallest radio tower. The lofty structure reduces vibrations caused by earthquakes through its core column (shinbashira) vibration control system, which shares features with traditional architecture.
“In addition to supporting the structure, the shinbashira passing through the center of the Skytree tower functions as a counterweight. The shinbashira moves independently of the tower, counterbalancing and suppressing swaying motions during an earthquake,” explains Atsuo Konishi, the structural designer of Tokyo Skytree working for Nikken Sekkei Ltd, which designed the tower. In fact, this structural technique resembles the design of the five-story pagoda at Horyu-ji Temple, constructed about 1,400 years ago, making it Japan’s oldest wooden building. During this long history, there are no records of the Horyu-ji pagoda ever collapsing due to earthquakes. This is attributed to a central pillar called the “shinbashira” inside the pagoda, which provides an independent counterweight that cancels out vibrations during an earthquake.
“Since the natural environment of Japan places severe demands on high-rise structures, the investigation of ways to withstand earthquakes has a long history,” comments Konishi. “Whenever you visit, please relax and have a good time at Tokyo Skytree, which is a safe structure incorporating the best of Japanese technology.”
Tall structures are not the only things that benefit from advances in earthquake countermeasures. Technical innovations progress daily to ensure the earthquake-readiness of the Shinkansen, the high-speed rail that links cities throughout Japan. The East Japan Railway Company (JR East) introduced the Earthquake Early Warning System for the Shinkansen in 1998, which detects preliminary tremors from seismographs located along the tracks, the seafloor, and inland, and then brings trains to an emergency stop by interrupting the electric supply. This prevents major accidents during an earthquake.
“Since then, we have continued to strengthen structures such as train stations and viaducts against earthquakes, and in order to prevent derailment we are also installing off-track prevention guides and rail turnover prevention devices,” says Takashi Shimoyama, deputy general manager, Facilities Department of JR East. Thanks to these advances, when the Great East Japan Earthquake struck the Tohoku area in 2011, all 27 trains in operation throughout the Tohoku Shinkansen were safely brought to a stop without derailing.
From November 2017, a new system has been introduced, with the potential for sensing tremors up to 20 seconds earlier than the conventional method. This advance utilizes seafloor seismograph data acquired from the Seafloor Observation Network for Earthquakes and Tsunami built and operated by the National Research Institute for Earth Science and Disaster Resilience (NIED). JR Central and JR West plan to introduce similar systems in turn. Shinkansen drivers also practice emergency shutdown skills regularly in sophisticated simulators. Shimoyama adds, “Safety measures never end. Improving the safety of our trains is an ongoing concern.”
In Japan, the growth of reliable technology continues daily, building on the experience of past earthquakes and the unflagging efforts of innumerable persons. The effort to achieve the utmost safety continues.