Be aware of speed

Several published examples demonstrate that seismic control effectively reduce earthquake-induced shaking. Put simply, seismic control convert the seismic energy applied to a building by seismic motion into heat or other energy sources, absorbing it and damping the building's vibrations. The mechanism for converting seismic energy is based on the velocity of the vibrations caused by the earthquake, using dampers that respond to the velocity. Dampers include those that move viscous materials such as oil, and those that use friction between steel members. A more specialized system transfers the building's vibrations to weights placed on the roof, absorbing the seismic energy through their movement. Seismic isolation structures, which have expanded rapidly since the Great Hanshin-Awaji Earthquake, also effectively reduce shaking by employing numerous dampers that absorb vibration energy in addition to seismic isolation devices that cushion the vibrations. In this sense, seismic isolation structures can also be considered seismic control in a broad sense. This seismic control works to prevent damage to ceilings and furniture from falling over, and even after shaking occurs in high-rise buildings, it subsides relatively quickly.

Dealing with earthquake motion by focusing on speed is the highest achievement of earthquake-resistant design technology at present. A wide variety of specific devices and their effective placement methods have been developed. Taking this a step further, a system is also being developed to efficiently generate electrical energy from vibration energy. Of course, in this case, the vibration energy being targeted is not the rare earthquake motion, but vibrations that are constantly present, such as wind and waves.

Being aware of speed and controlling it well is also an important aspect of tsunami countermeasures for buildings, which became a new issue as a result of this earthquake. The force that a tsunami exerts on a structure is proportional to the flood height, but increases exponentially as the force and speed of the water increases. Therefore, in order to fight it as a force, you must properly grasp the speed. If there is a mechanism in place to weaken the force of the tsunami before it hits the structure, the force of the tsunami will be reduced, so creating such a mechanism well is also effective. Of course, if you decide that you must flee, your fleeing speed must be faster than the speed of the pursuer.

Controlling the speed and being conscious of the speed is also an important perspective for the business of reconstruction. Reconstruction plans that consider what the town should be like tend to be static and off-time. And there is probably no reconstruction plan that is convenient for everyone. A plan that has a weak time axis and cannot be agreed upon by everyone will not proceed easily. If we are conscious of the speed of reconstruction, we will place emphasis on the restoration of human activities. Here, human activity is, first and foremost, production. A wide range of productive activities, from agriculture, fishing, and industry to commerce, distribution, tourism, and education, must be quickly restored. To do this, the time axis of the seasons and market conditions will be important. I am worried that if the timing is off, we may not even be able to recover. These things may be at the level of recovery, but since there must have been a desire to do this in the future even before the earthquake, starting the recovery will lead to reconstruction. And if reconstruction starts and the speed becomes more conscious, reconstruction will probably progress at an accelerated pace.