What is an "earthquake"?
An earthquake is any shaking of the ground - usually intense shaking of the ground - caused by either natural sources or by humans. The most common types of earthquakes are those caused by ruptures of geologic faults or earthquakes associated with volcanic activity.

1.什么是地震？
任何地动-通常是强烈的地动，无论是由自然力引起还是由人为引起，都叫地震。最常见的地震是那些由断层或者是火山活动引起的。