Chapter 12: Problem 15

What is the relationship between an epicenter and the focus of an earthquake? Give an example from the Loma Prieta, California, earthquake.

Short Answer

Expert verified

The 'focus' of an earthquake is its starting point beneath the Earth's surface, while the 'epicenter' is the point on the Earth's surface directly above this focus. For the Loma Prieta earthquake, the focus was about 11 miles underground, and the epicenter was near Loma Prieta peak in the Santa Cruz Mountains.

Step by step solution

Understanding the terms

The 'focus' of an earthquake is the actual location beneath the Earth's surface where the quake starts, where rocks first move along the fault, and seismic (earthquake) waves originate. 'Epicenter' is the point on the Earth's surface directly above the focus. So in summary, earthquakes begin in the focus, and the seismic waves are felt first at the epicenter.

Applying the terms to the Loma Prieta earthquake

During the Loma Prieta earthquake that occurred in California in 1989, the focus was approximately 11 miles (18 kilometers) beneath the Earth's surface. The epicenter was near Loma Prieta peak in the Santa Cruz Mountains, approximately 9 miles northeast of Santa Cruz on a section of the San Andreas Fault.

Establishing the relationship

In the case of the Loma Prieta earthquake, the relationship between the epicenter and the focus is that seismic waves initiated in the deeper focus, and were felt first at the epicenter on the surface of the Earth. Thus, the epicenter serves as the initial point of contact for seismic activity on the Earth's surface, while the focus is the origin of the earthquake below the surface.

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What is the relationship between an epicenter and the focus of an earthquake? Give an example from the Loma Prieta, California, earthquake.

Short Answer

Step by step solution

Understanding the terms

Applying the terms to the Loma Prieta earthquake

Establishing the relationship

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