A 08: Earthquakes and Earth's Interior

Earthquake wave that pushes and pulls rocks in the direction of the wave; also known as compression wave

P wave

Which seismic waves travel most rapidly?

P waves

The moment magnitude scale is used to estimate the _____.

energy that an earthquake releases

The location on Earth's surface directly above the focus, or origin, of an earthquake

epicenter

When an earthquake occurs, which type of energy is released from rocks along a fault?

elastic energy

* How are earthquakes measured against the Richter scale?

The Richter scale depends on the amplitude of the largest seismic wave recorded on a seismogram. A ten-fold increase in the amplitude is registered as an increase of 1 on the Richter scale.

The hypothesis that explains the release of energy during an earthquake is called the _____.

elastic rebound hypothesis

The amount of shaking produced by an earthquake at a given location is called the _____.

intensity

Where is the epicenter of an earthquake?

on the surface, directly above the focus

According to the elastic rebound hypothesis, what produces an earthquake?

rocks are subjected to great forces, then suddenly break

vibrations that travel through Earth carrying the energy released during an earthquake

seismic waves

The record made by a seismograph

seismogram

An instrument that records seismic waves

seismograph

A seismic wave that travels along the surface of Earth

surface wave

When an earthquake strikes, which type of seismic wave causes the most destruction?

surface waves

The San Francisco earthquake of 1906 occurred along what fault?

the San Andreas fault

What does a seismograph directly measure?

the arrival and strength of seismic waves

* How are an earthquake's fault, focus, and epicenter related?

An earthquake's focus is located along a fault beneath Earth's surface. The focus is the point within Earth where an earthquake starts. The epicenter is the location on the surface directly above the focus.

From fastest to slowest, the three types of seismic waves are _____.

P waves, S waves, and surface waves

* Why do scientists prefer the moment magnitude scale over the Richter scale?

Richter scales are useful to measure only small, shallow earthquakes recorded within a certain distance from the epicenter. A moment magnitude scale is more precise than a Richter scale. It also gives a measure of the energy released during an earthquake.

A seismic wave that shakes particles perpendicular to the direction the wave is traveling

S wave

Elastic rebound is similar to what happens when you release _____.

a stretched rubber band

A small earthquake that follows the main earthquake

aftershock

How can the arrival and progress of an earthquake be recognized on a seismogram?

by wavy lines of characteristic shapes

The slow continuous movement that occurs along some fault zones is referred to as _____.

creep

Small foreshocks that precede a major earthquake can occur _____.

days or years before the major earthquake

A seismogram shows that P waves travel _____.

faster than S waves

A fracture in Earth along which movement has occurred

fault

Moment magnitude estimates the amount of energy an earthquake releases and is derived from the amount of displacement along _____.

fault

The point within Earth where an earthquake originates

focus

When an earthquake occurs, energy radiates in all directions from its source, which is called the _____.

focus

A small earthquake that often precedes a major earthquake

foreshock

Which is NOT a factor in calculating the moment magnitude of an earthquake?

magnitude of past earthquakes in the area

Scientists use the _____ scale to measure the extent of shaking, or intensity, of an earthquake.

modified Mercalli

A more precise measure of earthquake magnitude than the Richter scale that estimates the energy released by an earthquake

moment magnitude

A seismograph records an earthquake. Which feature of the seismogram indicates the distance to the epicenter?

the time lag between the arrival of P waves and S waves

Which is NOT true about S waves?

they change the volume of of material by compression and expansion

What is the minimum number of seismic stations needed to determine the location of an earthquake's epicenter?

three

In 1989, a major earthquake struck northern California. To locate the epicenter of the earthquake, scientists could have studied seismographic data that was recorded in _____.

three locations, each far away from California