Flashcards in Quiz 5 Deck (57):
What is a wave?
A disturbance that transfers energy from one place to another.
A vibration that travels through earth carrying the energy released during an earthquake
3 different types of seismic waves
-Compressional or Primary
-Shear or Secondary
Travel along the surface of the earth. Slowest of the three
Push pull motion. Fastest of the waves.
Travel slower than P-waves
How does a P wave cause the matter it is traveling though to vibrate?
Compressional waves, contraction and expansion
How does an S-wave cause the matter it is traveling through to vibrate?
Shear waves that push material at right angles
How do surface waves cause the matter it is traveling through to vibrate?
1st- rolling motion
2nd- shakes sideways with no vertical motion.
Why does matter vibrate when traveled through by seismic waves?
Because the seismic waves displace the earth.
What is the approximate velocity of a seismic wave?
Approximately how long does it take a seismic wave to get to the other side of the earth?
Which of the waves travel through liquid and which do not?
P waves through liquid.
S and Surface do not.
Point within the earth where movement begins
Point on the earth’s surface directly above the focus
What is a seismograph and how does it work?
An instrument for measuring waves. When the ground starts shaking, the instrument starts shaking but he mass inside remains still.
What is a seismograph recording or seismogram?
A recording of earth movement from a seismograph.
Why is there a delay between the arrival of a P-wave and the arrival of an S-wave from the same earthquake?
Because S waves are slower and cannot move through water and move through a perpendicular.
How is this delay used to determine the distance between an earthquake epicenter and a seismograph station?
Because P waves travel twice as fast as S waves, the interval between their travel time curves increases with distance. By measuring the time intervals, a scientist can determine the distance between an epicenter and station.
Seismograph recording from how many stations are required to determine the distance between a particular station and the focus?
1 to find the distance and get the richer magnitude.
3 to find the focus of the earthquake and the epicenter is directly above that in the surface.
How are seismograms used to determine the location of the focus of an earthquake?
It is a record of the ground motion at a measuring station as a function of time. Time is used to find the distance.
His is the direction of first movement recorded on a number of seismograph recordings used to determine the sense of first movement in a fault and the orientation of the fault?
First movement that hits the seismograph is either compressive or expansive.
Expansive: plate is moving away.
Compressive: moving towards.
What is the Richter Magnitude of an earthquake?
A measure of the amount of ground motion generated by an earthquake.
How is the Richter magnitude determined from a seismograph recording?
Determined by the amount of ground movement measured with a seismograph at a certain site.
Seismograph recordings from how many stations are required to determine the Richter magnitude of an earthquake?
For an increase in magnitude of one unit, what is the increase in the amount of ground motion?
One unit of moment magnitude higher is equivalent to 10 times the rupture area.
For an increase in magnitude of one unit, what is the increase in the amount of energy released?
A factor of 30 times greater
How many stations do you need to narrow down the sense of first movement as well as you can?
Many more than 3
What is the largest magnitude earthquake?
How does moment magnitude differ from Richter magnitude?
Moment magnitude uses newer technologies to get a more accurate result.
What’s a tsunami?
A large ocean wave that is caused by a sudden motion.
What is the approximate amplitude and wavelength of a tsunami as it traverses the open ocean?
Only a few centimeters high in the deep ocean.
What changes in a tsunami S it approaches land?
Half inch to 30 meters
How fasts does a tsunami travel?
500 miles per hour
Is the speed of a tsunami faster or slower than each three types of seismic waves?
Slower than all three
What are the 5 settings that are earthquake prone?
-Mid ocean trench
-Trench arc thrust
-Intraplate (earthquakes that don’t occur in the other 4 settings)
In which setting are magnitude 9 earthquakes possible?
In which three settings is the maximum magnitude 8?
Which setting has earthquake foci deeper than 60 km?
Trench arc thrust
Which of the earthquake prone setting is represented by the San Andreas fault?
Strike slip (Right Lateral)
Which of the earthquake prone settings is represented by the West Coast of Washington/Oregon?
Trench Arc (1700 year)
Which of the earthquake prone settings is represented by the Sumatra area (which produced the Great Sumatran Earthquake of 2004)?
Which of the earthquake prone settings is represented by northeastern Japan?
Why is seismic risk considered high in the Pacific Northwest even though no large earthquakes have occurred there historically?
Because it is located near a trench arc setting.
Are the series of New Madrid earthquakes from the 1810’s represented by any of these settings?
Intraplates (big ones)
On average, what is the length of time between large earthquakes on the portion of the SamAndreas fault near LA?
How long has it been since the last large earthquake along that portion of San Andreas? (LA)
How do we know that the outer core is liquid?
Because P-waves can travel through it but not S-waves
Why are there seismic shadow zones for P-waves? S-waves?
Results from S-waves being stopped entirely by the liquid core and P-waves being bent by the liquid core.
The bending of waves as they enter a material in which they travel faster or slower.
Why do seismic waves travel in curved paths through large portions of the earth?
Because they refract, which makes curve shape when going through denser materials.
The bouncing of waves off of interfaces.
The March 11, 2011 Tohoku earthquake off of Japan occurred on what type of fault?
The amount of movement of the earth as it vibrates in a normal mode after a large earthquake is about
1 mm to 1 cm
As it goes through the earth, an S-wave travels at a velocity approximately equal to a:
Jet plane at cruising altitude
An ______ wave causes the rock through which it passes to deform in a direction perpendicular to the propagation direction of he wave