Module 15

How many earthquakes are felt each year?

1,000,000

True or False: On seismograms, seismic waves recorded from more distant facilities are closer together than those recorded from facilities close to the epicenter.

False

True or False: S-waves do not enter the core because they cannot travel through solids

False

True or False: S-waves do not enter the core because they cannot travel through solids.

False

True or False: Surface waves are the first to arrive at a seismic station.

False

What happens to a rock that undergoes elastic deformation once the stress is removed?

It returns to its original shape.

What is true about the modified Mercalli scale?

It uses Roman numerals on the scale and It is used to measure earthquake intensity.

In constructing travel-time curves, scientists use the average travel times of ______.

P-waves S-waves

What numerical rating system measures the energy of the largest seismic wave?

Richter scale

Famous California strike-slip fault

San Andreas

_________ waves are useful to scientists because they contribute to scientists' understanding of Earth's interior.

Seismic

If a tsunami develops during an underwater earthquake, what will most likely occur?

Severe destruction will occur in some coastal areas.

True or False: Seismologists have reasoned that Earth's outer core must be liquid based on the disappearance of S-waves.

True

True or False: Studies of how waves reflect deep inside Earth show that Earth's inner core is solid.

True

True or False: The P-wave shadow zone does not receive direct P-waves.

True

True or false: Factors such as whether or not the ground is consolidated and what type of material buildings are made of have a strong effect on the amount of damage an earthquake can cause.

True

On the Richter scale, which term describes the height of the seismic waves?

amplitude

Magnitude is measured on the Richter scale using differences in

amplitude of seismic waves.

decreases the volume of a material

compression

Because seismic waves travel through Earth's interior, scientists have been able to:

construct models of Earth's interior and understand Earth's interior.

Which type of earthquake generally causes the least amount of damage?

deep-focus

What knowledge is needed to learn whether a fault ruptures at regular intervals and generates similar earthquakes?

earthquake-recurrence rates

Seismograms and travel-time curves are used to help scientists locate an earthquake's __________ and the time of occurrence.

epicenter

Any fracture or system of fractures along which Earth moves is called a(n) _________

fault

Fracture along which movement occurs

fault

Fault surface along which movement takes place

fault plane

Factors that effect the intensity of an earthquake include the amplitude of the seismic waves and the depth of the _____.

focus

What is stress?

force per unit area

All seismometers include a ___________ that is anchored to the ground and vibrates during an earthquake.

frame

What do scientists use to evaluate an area's seismic risk?

history of an area's seismic activity

What can the difference in travel times between P- and S-waves be used to determine?

how far away the epicenter was

The Eastern Japan earthquake in 2011 caused this building to sink and then collapse. Which process was responsible for weakening the soil underneath the building?

liquefaction

What is a measure of the energy released during an earthquake?

magnitude

All seismometers include a ________ suspended from a wire or spring

mass

What is strain?

measure of the deformation of rocks

Which scale rates the types of damage and other effects of an earthquake as noted by observers during and after its occurrence?

modified Mercalli scale

Which scale uses Roman numerals to designate the degree of earthquake intensity?

modified Mercalli scale

What is the rating scale that measures the energy released by an earthquake, taking into account the size of the fault rupture, the amount of movement along the fault, and the rocks' stiffness?

moment magnitude scale

An area that has already experienced past earthquakes is _________ likely to experience a future earthquake than an area that has never had an earthquake.

more

Which type of fault occurs when rocks on one side of a fault move down relative to the other side?

normal

Fracture caused by horizontal tension

normal fault

What type of structural failure occurs when the supporting walls of the ground floor fail and cause the upper floors, which initially remain intact, to fall and collapse as they hit the ground or lower floors?

pancaking

Which seismic hazard is a form of structural failure?

pancaking

What do rocks undergo when stress builds up past the elastic limit?

plastic deformation

Squeezes and pulls rock in the same direction as the wave travels

primary wave

Scientists use the history of earthquakes in an area, and the rate at which stress builds up in the rocks to determine the

probability of an earthquake's occurrence.

Which type of fault occurs when rocks on one side of a fault move up relative to the other side?

reverse

Fracture that forms as a result of horizontal compression

reverse fault

Causes rock to move at right angles to the direction in which the wave travels

secondary wave

sections located along faults that are known to be active, but which have not experienced significant earthquakes for a long period of time.

seismic gaps

A paper or computer record of earthquake vibrations is called a ________

seismogram

What is the record produced by a seismometer?

seismogram

What instrument is used to measure horizontal or vertical motion during an earthquake

seismometer

an instrument that records earthquake vibrations.

seismometer

causes a material to twist

shear

In areas with sand that is nearly saturated with water, which term describes what happens when seismic vibrations cause the ground to behave like a liquid?

soil liquefaction

When seismic waves reach boundaries between materials they change ______.

speed and direction

What is the total force acting on crustal rocks per unit of area?

stress

Which factor is studied to determine the rate at which stress builds up in rocks to help forecast an earthquake?

stress accumulation

Fracture caused by horizontal shear

strike-slip fault

Causes rock to move both up and down and from side to side

surface wave

pulls a material apart

tension

What are earthquake hazards?

the factors that determine the severity of damage produced by an earthquake

What data are used to determine the distance from the epicenter of an earthquake to the seismic station that recorded the seismogram?

the separation of P-wave and S-wave lines

In order to have data from seismic stations overlap at one spot and pinpoint the location of an earthquake's epicenter, there must be data from at least ______ stations.

three

S-waves ________ through Earth's mantle.

travel

A large ocean wave generated by vertical motions of the seafloor during an earthquake is called a(n) __________

tsunami

What is a large ocean wave generated by vertical motions of the seafloor during an earthquake?

tsunami