Tunnels and Earthquakes

25-11-23 00 / episode: 314

Wouldn't you feel afraid if you were in a tunnel and an earthquake happened? I'm sure that I would feel afraid but now that I've done my research I think my tone has changed. I live in Japan. Japan is on the Ring of fire, which is a big ring around the Pacific ocean where volcanoes and earthquakes happen a lot. I felt earthquakes here in Japan and they're pretty scary sometimes.

Introduction

Hi and welcome to the Les Perras podcast episode number 314. This episode is about tunnels and earthquakes.

Pretty scary

I remember my first earthquake in Japan. I didn't notice it. I only knew that an earthquake happened because the staff in the building said oh that was an earthquake.

I was pretty impressed because I thought these people are really sensitive to earthquakes.

But that shouldn't be surprising for people who grow up in an earthquake prone country.

Anyway a few weeks later I felt a real earthquake and what I mean is it was really big.

No it wasn't really big but it was much bigger than anything I've ever experienced in my life.

The whole building moved.

There was a big sound.

I can't quite describe the sound but it was big and deep and loud.

Earthquakes damage tall buildings

One of the worst places you want to be in an earthquake is in a tall building.

There's something called inertia.

This is the tendency of something that's not moving to stay not moving.

That means that tall buildings get shaken at the bottom and start to flex.

The top of the building doesn't move but the bottom of the building is moving because of the earthquake.

Eventually the top starts moving but it's not moving the same as the bottom.

So the whole building is flexing.

But these things are made of steel and concrete: they're not made to flex

Houses

The 1995 great hanshin earthquake displayed that on a smaller scale.

A lot of the houses had heavy tile roofs.

The heavy tile means it has a lot of inertia so it stays in one place.

The bottom of the house is being shaken by the earthquake and moved.

When the top of the house and the bottom of the house are not moving in the same direction

then things break and the houses fall down.

It was a very damaging situation.

Tunnels

Now tunnels are a different story.

Number one if you're tunnelling in really hard rock it's probably going to be even safer.

But being in the tunnel is already safe because the whole tunnel is moving at the same time because it's part of the Earth.

When the Shock Wave moves through the Earth the Earth itself is moving.

All of it is moving together.

This means that there's not very much damage in the tunnels.

Don't go crazy here.

It doesn't mean tunnels are perfectly safe.

It just means they're quite a bit safer than the buildings above ground.
There are cases where tunnels were damaged quite a bit in earthquakes here in Japan.

But for the most part tunnels come out okay.

If you had a choice to be in a tunnel or a skyscraper during an earthquake you should take the tunnel.

It's a lot safer.

It might not sound safe but we found over the years that tunnels are not that bad.

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