Chapter 8

During the 1906 San Francisco earthquake, the movement of the Pacific Plate was approximately ________.

10 meters

Felt earthquakes usually last for ________.

10-60 seconds

In elastic rebound theory, what must occur to produce an earthquake?

Enough stress must build up over time on a fault to overcome friction.

The Mercalli Scale is a scale from ________.

I to XII that rates the structural damage due to an earthquake

Modern seismographs rely on ________ to record the ground motion from an earthquake.

Inertia

________ have the highest velocities

Primary waves (P-waves)

The velocity of seismic waves generally increases with depth in the earth.

True

Major earthquakes are often followed by somewhat smaller events known as ________.

aftershocks

The Richter magnitude of an earthquake is determined from the ________.

amplitude of the largest seismic wave

P waves ________.

are faster than S waves and surface waves

The position on Earth's surface directly above the earthquake source is called the ________.

epicenter

When an earthquake occurs, energy radiates in all directions from its source. The source is also referred to as the ________.

focus

Faults are "locked" because ________.

high confining pressure increases friction on the fault

Which of the following is determined by measuring the amplitude of waves recorded from an earthquake?

magnitude

Liquifaction, where normally solid material behaves more like a fluid during an earthquake, occurs because ________.

pore spaces between particles in unconsolidated sediments close and displace fluids

Overall, this type of seismic wave is the most destructive.

surface wave

On a typical seismogram, ________ will show the highest amplitudes.

surface waves

Aftershocks occur because ________.

the area surrounding a region that experienced a large earthquake needs time to adjust to the displacements on the main fault

The earth's major layers formed because ________.

the earth was heated after its formation resulting in melting and redistribution of major chemical compositions

If you are on a beach, you might recognize that a tsunami is approaching because ________.

the water will withdraw from the beach farther than usual

In the 1906 San Francisco earthquake, much of the damage was due to fires because ________.

water lines were badly damage so that firemen could not put out the fires

Structural damage from seismic vibrations would be worse ________.

where older buildings were built on a thick layer of sediment