Question

An earthquake with a hypocenter depth exceeding 300 km is known as:

• A. Shallow-focus earthquake
• B. Intermediate-focus earthquake
• C. Deep-focus earthquake
• D. Surface-focus earthquake

Hint:

Depth>300 km = deep-focus earthquake; occurs mostly in subduction zones.

Answer 1

The Correct Option is C

To classify an earthquake based on its hypocenter depth, we examine standard seismological definitions of earthquake depth categories.

1. Understanding Hypocenter Depth:
The hypocenter (focus) is the actual point of earthquake origin within the Earth, while the epicenter is its surface projection.

2. Standard Depth Classification:
Earthquakes are categorized by depth into three main types:

3. Depth Categories:
- Shallow-focus: 0-70 km depth
- Intermediate-focus: 70-300 km depth
- Deep-focus: >300 km depth (correct answer)
- "Surface-focus" is not a standard classification

4. Characteristics of Deep-Focus Earthquakes:
- Occur in subduction zones at 300-700 km depths
- Result from phase changes in subducting slabs
- Generally cause less surface damage
- More frequent in Pacific Ring of Fire

5. Why Other Options Are Incorrect:
- Shallow earthquakes dominate tectonic activity
- Intermediate-depth marks transition zone
- No recognized "surface-focus" category exists

6. Scientific Significance:
Deep-focus earthquakes help scientists study: - Lower mantle properties
- Slab dynamics in subduction zones
- High-pressure mineral phase changes
- Stress distribution at depth

Conclusion:
An earthquake with hypocenter depth exceeding 300 km is properly classified as a deep-focus earthquake.

Final Answer:
The correct option is: deep-focus earthquake.