Earthquakes and Seismic Waves

At what point do seismic waves first reach the surface?

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Geologists use seismic waves to locate an earthquake's epicenter.

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What kind of movement is produced by each of the three types of seismic waves?

>P waves seismic waves that compress and expand the ground like an accordion >S waves A type of seismic wave that moves the ground up and down or side to side >surface waves seismic wave that moves rock particles up and down in a backward rolling motion and side to side in a swaying motion

P waves (Primary waves)

>first waves to arrive are >Seismic waves that compress and expand the ground like an accordion. >The crust vibrates forward and back along the path of the wave >travel through both solids and liquids

The effects of an earthquake increase with magnitude.

>magnitudes below 3 scarcely noticable >magnitude below 5; small and little damage >magnitude 5-6 : moderate damage >magnitude above 6: can cause great damage >magnitude 8 or above are rare

S Waves (secondary waves)

>seismic waves that vibrate from side to side as well as up and down. >shake the ground back and forth. When these waves reach the surface, they shake structures violently. >cannot move through liquids

surface waves

>type of seismic wave that forms when P waves and S waves reach Earth's surface. >move more slowly than P and S waves >produce severe ground movements >some make ground roll like ocean waves while other shake buildings from side to side.

What is an earthquake's magnitude?

A number geologists assign to an earthquake based on the earthquake's size

moment magnitude scale

A scale that rates earthquakes by estimating the total energy released by an earthquake >can be used to rate earthquakes of all sizes, near or far

S waves

A type of seismic wave that moves the ground up and down or side to side

What type of data do geologists use to locate an earthquake's epicenter?

Geologists use seismic waves to locate an earthquake's epicenter. > they measure the difference between the arrival times of the P waves and S waves. The farther away an earthquake is, the greater the time between the arrival of the P waves and the S waves.

When do P waves arrive at the surface in relation to S waves and surface waves?

P waves are primary waves they are the first set of waves. Next is the S waves witch stands for secondary and comes after the P waves. Last is the Surface waves witch move along the surface and go last.

How do scientists tell how far the epicenter is from the seismograph?

Scientists measure the difference between the arrival times of the P waves and S waves. The farther away an earthquake is, the greater the time between the arrival of the P waves ans S waves.

How does the energy of an earthquake travel through Earth?

Seismic waves carry energy from an earthquake away from the focus, through Earth's interior, and across the surface

How does energy from an earthquake reach Earth's surface?

Seismic waves carry energy from an earthquake away from the focus, through earth's interior and across the surface.

magnitude

The measurment of an earthquake's strength based on seismic waves and movement along faults.

epicenter

The point on the surface directly above the focus is called the _______________.

How is magnitude measured using the Richter scale?

The richter scale is a rating of an earthquake's magnitude based on the sixe of the earthquake's seismic waves. The seismic waves are measured by a seismograph. A seismograph is an instrument that records and measures seismic waves.

True/ False

There are at least 20 different measures for rating earthquakes, each with its strengths and shortcomings. (true)

During the 20th century, only two earthquakes measured above 9 on the moment magnitude scale.

These earthquakes occured in Chile in 1960 and in alaska in 1964

seismograph

a device that records ground movements caused by seismic waves as they move through Earth

Richter Scale

a scale that rates an earthquake's magnitude based on the size of its seismic waves

The level of damage caused by an earthquake varies depending on the magnitude of the earthquake

and the distance from the epicenter.

What evidence do geologists use to rate an earthquake on the moment magnitude scale?

data from seismographs, showing what kind of seismic waves and how strong. this information also helps scientists infer how much movement occurred along the fault and the strength of the rocks that broke when the fault slipped

Mercalli Scale

developed to rate earthquakes according to the level of damage at a given place. >12 steps I-III People notice vibrations like those from a passing truck. Unstable objects disturbed. IV-VI Slight damage. People run outdoors. VII-IX Moderate to heavy damage. Buildings jolted off foundations or destroyed. X-XII Great destruction. Cracks appear in ground. Waves seen on surface.

How do scientists locate the epicenter of an earthquake?

geologists use seismic waves to locate an earthquake's epicenter

focus

is the area beneath Earth's surface where rock that is under stress breaks, triggering an earthquake.

What are the advantages of using the moment magnitude scale to measure an earthquake?

it allows us to estimate the total amount of energy released, which allows us to compare earthquakes more accurately.

The Richter scale provides accurate measurements for small, nearby earthquakes. But it does not work well for

large or distant earthquakes.

surface waves

seismic wave that moves rock particles up and down in a backward rolling motion and side to side in a swaying motion

P waves

seismic waves that compress and expand the ground like an accordion

Which type of seismic wave causes the ground to roll like ocean waves?

surface waves

earthquake

the shaking and trembling that results from the movement of rock beneath Earth's surface.

What are the scales used to measure the strength of an earthquake?

there are three commonly used methods of measuring earthquakes: the Mercalli scale, the Richter scale, and the moment magnitude scale