Link #99: Melting Soil Destroyed 3,500 Buildings in Niigata!

Jul 29, 2015

Link #99: Melting Soil Destroyed 3,500 Buildings in Niigata!

Liquefaction_at_Niigata — Niigata Earthquake, 1964. PD-PRE1978.

If you read our last article, then you know that the Leaning Tower of Pisa is leaning because of a loose and unstable subsoil layer. In fact, one side of the tower continued to sink for a good amount of its life.

While the sinking of the Leaning Tower of Pisa was gradual, there have been occasions in human history when buildings have toppled in a matter of minutes. The best example of this was Niigata in Japan in 1964 where melting soil resulted in the destruction of thousands of buildings in a matter of seconds.

What Happened in Niigata in 1964?

Niigata is a city located in north western Japan. The city is known for the damage it incurred due to an earthquake in 1964. The earthquake destroyed 3,534 buildings in Niigata and damaged more than 11,000 others.

It wasn’t the usual kind of damage that is seen in normal earthquakes. There were actually some regions where buildings just fell over without any other damage caused to them. The most interesting part was that the earthquake didn’t even originate in Niigata.

The central point of the earthquake, also known as the epicentre, was 50 kilometres to the north of the city. The earthquake actually occurred off the coast of Japan on the continental shelf. A continental shelf is a piece of land jutting out underwater into the sea.

How Can Melting Soil Destroy Buildings?

Foundation-House-Apt — Foundations of buildings by Blacklemon67, PD image.

The scientific name of melting soil is soil liquefaction. If you want to understand how melting soil destroy buildings, you need to think about how buildings are constructed. Every building is built on a foundation.

The standard foundation depth rests within the subsoil in most situations. Even buildings with extremely deep foundations are susceptible to soil liquefaction because they still rest on subsoil layer.

When the soil melts or liquefies, the building’s base shifts. Depending on the shift of the foundation, the building is either destroyed or, at the very least, damaged.

What Is Soil Liquefaction?

The_Leaning_Tower_of_Pisa — The Leaning Tower of Pisa. Image credit: McPig, (CC BY 2.0)

Soil liquefaction, in simple terms, is a process where layers of the soil in a region get unstable and loose. In other terms, the soil loses its stiffness which makes it difficult for the building’s foundation to be steady.

There are many different reasons that can cause soil liquefaction. In the majority of cases, external influences are responsible for the phenomenon of soil liquefaction. Things that can set soil liquefaction off include a sudden increase in moisture content, change in stress from external sources and earthquakes. The quality of the soil also makes a difference.

For instance, in the case of the Leaning Tower of Pisa, the tower sank for such an extended period of time because of two reasons. The first was that the soil it was built upon was loose and unstable from the very beginning. The second was that the foundation of the tower wasn’t deep enough.

In contrast, buildings got destroyed and damaged in Niigata because of the vibrations from an earthquake 50 kilometres away. The vibrations shook up the subsoil layer under the buildings and made it soft and loose. This resulted in the ground being incapable of holding the foundations of the buildings which just popped out of the ground.