木曜日は、マリーのはてな日記/Marie the Scientist
「地震はどうして起きるの？/Why do earthquakes happen?」
Why do earthquakes happen?
Early this morning, there was an earthquake.
“Marie, it’s an earthquake.”
“I know Mom, I’m scared.”
We quickly turned on the TV.
The report said It was a three on the shindo scale in our town and the magnitude was 4.5.
Why do we have earthquakes?
And what are those numbers?
I asked my science teacher at school.
“Ms. Sato, I was so scared this morning.
Why do earthquakes happen?”
“An earthquake tells us that our earth is alive and active.”
“Earth is alive?
What do you mean?”
“First, let’s learn about the inside of earth.”
“You know earth is round like a ball.
The core or the very center of earth is made of different metals.
Then outside the core, there is another layer called the mantle.
It’s hard rock and it’s very thick.”
“So do we live on the mantle?”
“No, there are more layers, Marie.
The top layer is the surface of earth.
It’s divided into about ten big plates.”
“The core, the mantle, and the plates.
How do they make earthquakes?”
“Earthquakes happen because the mantle moves.”
“But the mantle is thick rock.
Does it move?”
The mantle is always moving very slowly.
When it moves the plates move, too.
At some places, different plates meet.
Earthquakes often happen at such places.
Marie, do you think Japan has many earthquakes?”
“Yes, some of them are really big.”
Japan is known for having many earthquakes.
We can feel between one and two thousand earthquakes in a year.”
“That’s a lot.”
“And do you know why?
That’s because our country is on top of four different plates.
They are the Pacific Plate, the North American Plate, the Eurasian Plate, and the Philippine sea Plate.”
“Oh, I have another question.
What are magnitude and shindo?”
“Magnitude shows how powerful an earthquake is.
The Great East Japan Earthquake in 2011 was magnitude 9.0.”
“Shindo is a Japanese way of majoring how much shaking there is in one place.
If that place is close to the center of the earthquake, the ground shakes more and the shindo is bigger.”
“I’m afraid of big earthquakes.
Will one happen in our town someday?”
“Maybe, we don’t know when a big earthquake may happen.
So let’s prepare for it.”
Today, I learned that we have to be prepared.
Because we live in a country with many earthquakes.
I’m going to have a meeting with Mom and Dad about what to do at home.