回答
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Earthquakes are scary because you never know when one might happen.
地震に対する「怖い」は、scary やさらに強い意味（非常に恐ろしい）の terrifying が自然な言い回しです。
「起こる」の英訳は happen ですが、地震が起こることに限定して言うこともできます。strike や hit が使えます。
回答
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It's really scary because you never know when an earthquake will occur.
「地震がいつ起こるかは絶対にわからないから本当に怖い」という言い方にしてみました。「scary」（「怖い」）という表現は日常的に使う表現です。「you never know」（「誰にも絶対にわからない」）という表現もよく使います。ご参考にしていただければ幸いです。
回答
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I am very terrified of an earthquake.
terrified is another word for scary.
terrifiedは、scaryの類義語です。
回答
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Earthquakes take us by surprise which is terrifying, we never know when they are going to hit.
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We live everyday with caution as we never know when an earthquake will occur
Earthquakes take us by surprise which is terrifying, we never know when they are going to hit.
Take us by surprise – there isn’t much of a warning before they occur.
Going to hit – another way of saying ‘when they are going to occur’.
When something takes you by surprise, you are not expecting it and can leave you shocked. In this instance we are talking about an earthquake, when you are unsure of when it will hit, you live life a bit cautiously.
"Take us by surprise –警告や前触れがなく突然何かが起こる事
ヒットになる - 「起こるとき」と言う別の方法。
Going to hit – 「起こるとき」という意味で
‘when they are going to occur’とも言えます。
なんの前触れもなく何かが起こると、予期してなかっただけにショックが大きいです。
この場合は地震ですね。いつ地震が来るか分からないので日々の
生活も少し緊張するという意味合いです。"
回答
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It is frightening to note that an earthquake can occur at any time.
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It is so scary to note that an earthquake can happen at any moment when you least expect it.
Earthquakes are natural phenomenons that occur when you least expect them. You may be seating at your office desk when it suddenly strikes, or you may be in your bath tub, or you may be in a shop when you suddenly feel the ground shaking and everything else around you rocking. It is a scary thought especially if you have been affected before.
So you may say:
It is frightening to note that an earthquake can occur at any time.
or
It is so scary to note that an earthquake can happen at any moment when you least expect it.
Earthquakes(地震)は自然災害ですので予期せぬ時に起こります。
会社のデスクに座っている時かもしれませんし、お風呂に入っている時、もしくは買い物中に突然地面が揺れ出すかもしれません。そしてもし以前、地震の被害にあったことがあれば余計に怖いでしょう。
It is frightening to note that an earthquake can occur at any time.（地震がいつ起こるかわからないと考えると怖いです。）
It is so scary to note that an earthquake can happen at any moment when you least expect it. （予期せぬ時に地震がいつ起こるかもしれないと考えると怖いです。）
回答
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Earthquakes are unpredictable and that is scary!
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We never know when can earthquake occurs and it is very scary.
You can say :
Earthquakes are unpredictable and that is scary!
We never know when can earthquake occurs and it is very scary.
---> When something is unpredictable, you don't know when it might happen.
You can also say :
Earthquakes catch us by surprise and we are really scared.
Earthquakes are unpredictable and that is scary!
地震は予知出来ないから、怖いですよね！
We never know when can earthquake occurs and it is very scary.
地震はいつ起きるのか分からないので、とても怖いですよね。
→何かが「unpredictable」というときは、予想ができない、いつ起こるかわからないということです。
他の言い方としては：
Earthquakes catch us by surprise and we are really scared.
地震は突然やって来て、私たちをすごく怖がらせます。
回答
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An earthquake can happen any time! And you'll be frightened!
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Be aware that a disastrous earthquake can happen without notice!
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The scariest thing about earthquakes is that they are always a surprise.
Superlative expressions:
The scariest thing that ever happened to me was when I fell out of a tree!
The worst thing about golf is that you can get caught in a thunderstorm.
The most wonderful thing about summer is the beautiful flowers in the garden.
最上級の表現：
私が木から落ちたときが、今まで私に起こった最も恐ろしいことです。
ゴルフに関する最悪の事は、雷雨に巻き込まれうることです。
庭の美しい花々は夏の最も素晴らしいことのひとつだ。
回答
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Earthquakes are always unexpected.
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Earthquakes are scary because they are unpredictable.
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Earthquakes always take us by surprise.
We would say that earthquakes are always, "unexpected," or, "unpredictable," to describe that it's something we can know about in advance and prepare for. "To take us by surprise," also means that they can't be predicted and always come when we least expect them.
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