The point where the vibration of earthquake begin is called

Options

A. hypo centre
B. focus
C. epicentre
D. both (a) and (b)

Explanation

To solve the question, "The point where the vibration of an earthquake begins is called," we will analyze the options provided and identify the correct term.

### Step-by-Step Solution:

1. **Understanding Earthquake Terminology**:
- An earthquake is caused by the sudden release of energy in the Earth's crust, which generates seismic waves.

2. **Identifying Key Terms**:
- **Hypocenter**: This term refers to the actual location within the Earth where the earthquake originates.
- **Focus**: This is another term for the hypocenter, indicating the point where the seismic waves begin.
- **Epicenter**: This is the point on the Earth's surface directly above the hypocenter. It is where the effects of the earthquake are usually felt most strongly.

3. **Analyzing the Options**:
- Option 1: Hypocenter
- Option 2: Focus
- Option 3: Epicenter
- Option 4: Both A and B (Hypocenter and Focus)

4. **Determining the Correct Answer**:
- Since both "hypocenter" and "focus" refer to the same point where the earthquake vibrations begin, the correct answer can be either of these terms. However, since the question specifically asks for the point where the vibration begins, "focus" is the most commonly used term in this context.

5. **Final Answer**:
- The point where the vibration of an earthquake begins is called the **Focus** (Option 2).