Are sentences correct?

Re: Are sentences correct?
(1) Less than half of the people think an earthquake will ever occur within this decade.

"The" people? What people? The people questioned in a survey? The people of Peru? You would not use the definite article "the" in this way. i.e. not specifying who "the" people are. You should delete "the", but in reality such a sentence would contain information about who was questioned, e.g. "Less than half of the people questioned in a survey of Californians think..."

Sentence (1) is the only one which correctly uses "ever".

(2) More than half of the people think an earthquake will ever occur within this decade.

No. "Ever" used in that way is coupled with a negative formulation.

(3) Most people think an earthquake will ever occur within this decade.

See above.

Are sentences fine?

Delete "ever" from (2) and (3).

Re: Are sentences correct?

Re: Are sentences correct?
(1) Less than half of the people think an earthquake will ever occur within this decade.

Actually, I have changed my mind about this sentence. None of these sentences should have the word "ever" in them. "Ever" means, well, ever. The infinite future, or if not that, then the indefinite future.

Will the universe ever end?

-- or --

Will the universe end within (or during) the next decade?

-- but never --

Will the universe ever end within the next decade?

You cannot mix the indefinite time span of "ever" and the definite time span of "the next decade".



Following on from what I wrote above, you could write

More than half of people think an earthquake will occur within this decade.

-- or --

Less than half of people think an earthquake will occur within this decade.

-- or --

Less than half of people think an earthquake will ever destroy Los Angeles. (doubt about indefinite future). Also no "the" before "people".

When we use "ever" in conjunction with a prediction or question about the future, the word can indicate a degree measure of doubt.

I wonder if my mother ever give up drinking.

Will you ever learn to respect your father?

Will my dog ever stop chewing my slippers?

Thanks, Contrex.