Which phrase describes a feature of an earthquake’s epicenter?
A) starting point of an earthquake
B) place around the center of an earthquake
C) region directly above the focus
D) point about 100 kilometers deep in the lithosphere
The correct answer and explanation is:
Correct Answer: C) region directly above the focus
Explanation (300 words):
An earthquake originates from a specific point within the Earth where rocks suddenly break due to accumulated stress. This point is called the focus (or hypocenter). It is located beneath the Earth’s surface where the actual rupture occurs. Directly above this focus, on the Earth’s surface, lies the epicenter.
The epicenter is not the origin point of the earthquake in a physical sense—that would be the focus—but it is crucial because it is the surface location that typically experiences the most intense shaking. Seismic waves radiate outward from the focus, and by the time they reach the surface at the epicenter, the energy is often strong enough to cause significant ground movement, structural damage, and human impact.
Let’s briefly review the other answer options and why they are incorrect:
- A) starting point of an earthquake: This refers more accurately to the focus, not the epicenter. The focus is the true point of origin where the earthquake starts below the surface.
- B) place around the center of an earthquake: This is vague and misleading. “Around the center” lacks clarity and doesn’t define a specific geological feature.
- D) point about 100 kilometers deep in the lithosphere: While some earthquakes do occur at this depth (especially intermediate and deep-focus earthquakes), the epicenter is always on the surface, not deep within the Earth.
In summary, the epicenter is defined as the point on the Earth’s surface directly above the earthquake’s focus. This surface location is essential for seismologists to track and report earthquakes, and it is often where emergency services respond first due to the concentration of damage. Thus, the phrase that best describes the epicenter is:
“region directly above the focus.”