Earthquakes!

What are Earthquakes?

The shaking or trembling caused by the sudden release of energy.

Usually associated with faulting or breaking of rocks.

Where Do Earthquakes Occur and How Often?

~80% of all earthquakes occur in the Pacific Ring of Fire.more than 150,000 quakes that are strong

enough to be felt are recorded each year.

Where Do Earthquakes Occur and How Often?

Earthquakes

8.1 What Is an Earthquake?

• Focus is the point within the Earth where the earthquake starts.

• Epicenter is the location on the surface directly above the focus.

Focus and Epicenter

• Faults are fractures in Earth where movement has occurred.

Faults

The Focus and Epicenter of an Earthquake:

• The point within the Earth where faulting begins is the focus.

• The point directly above the focus on the surface is the epicenter.

Cause of Earthquakes

8.1 What Is an Earthquake?

• An aftershock is a small earthquake that follows the main earthquake.

• A foreshock is a small earthquake that often happens before a major earthquake.

Aftershocks and Foreshocks

The Effects of Earthquakes:• Building collapse• Fire• Tsunami• Deaths• landslides

8.3 Destruction from Earthquakes

• With many earthquakes, the greatest damage to structures is from landslides or the sinking of the ground triggered by vibrations.

Landslides

Fire• In the San Francisco earthquake of 1906, most of the destruction was caused by fires that started when gas and electrical lines were cut.

Tsunamis

8.3 Destruction from Earthquakes

• is a tidal wave or series of large waves caused by an earthquake under the ocean where a slab of the ocean floor is displaced vertically along a fault.

• A tsunami also can occur when the vibration of an earthquake sets an underwater landslide into motion.

• Tsunami is the Japanese word for “seismic sea wave.”

Movement of a Tsunami

Tsunami in India 2004

The end of part 1…

Earthquakes (part 2)!

What are Seismic Waves?

Seismic waves are waves of energy that travel through the Earth.

Two types:1. Body waves

P and S2. Surface waves

R and L

Body Waves: P and S waves P or primary waves

Are the fastest waves. They travel through

solids, liquids, and gases.

The land shakes in the same direction as the wave.

S or secondary waves Are slower than P

waves. They only travel through

solids. They move the land

perpendicular to the wave.

Surface Waves: R and L waves

Surface Waves: Especially damaging to buildings. They are slower than body waves. R or Rayleigh waves move in a rolling pattern. L or Love waves move in a side-to-side pattern.

Review: Faults

Faults are fractures in Earth where movement has occurred.

Earthquake Fault Lines:

…Ahh, we’re done taking notes for this bimester!