Earthquakes

Question 1

Locating the epicenter of an earthquake:

How many seismometer stations does the method require?

Answer 1

Three seismometers are required to locate the epicenter

Question 2

Locating the epicenter of an earthquake:

What information does each seismometer record?

Answer 2

It measures the difference in arrival time between P and S waves, as well as their intensity

Question 3

Locating the epicenter of an earthquake:

How do you use this information to determine the distance of the seismometer from the earthquake?

Answer 3

Using the difference in arrival time between P and S waves, a circle is created showing the possible locations of the earthquake. Three seismometers are needed so the circles intersect, and a point of where the epicenter was is created.

Question 4

What is the magnitude of an earthquake? How does a magnitude 7.1 earthquake differ from a magnitude 5.5 earthquake in terms of quantity and ground shaking? (ex)

Answer 4

• Magnitude: the amount of seismic energy that an earthquake releases
• For every whole number, the magnitude goes up 10 times
• To find how much stronger an earthquake is than another, subtract the smaller quake from the larger one
• Ten to the power of this number is how much stronger the quake is
• For example, 7.1 - 5.5 = 1.6. 10^1.6 = 39.8 times stronger.

Question 5

Describe the kinds of dangers to human life that are created when an earthquake strikes

Answer 5

• Buildings can fall over and kill people, power lines can break and become live, and they can trigger tsunamis to hit coastal towns which can destroy houses and wash things away
• Plus fires can be created

Question 6

What should you do during an earthquake to ensure your safety?

Answer 6

Move away from anything that can fall on you, stay away from windows and power lines, and get under a table, desk, etc

Question 7

How do tsunamis form? How fast do they move? How large are they in the open ocean? How large are they when they approach land?

Answer 7

• When an earthquake is triggered at a convergent boundary (or by volcanic eruptions, underwater landslides, or asteroids), the overriding plate jolts up, suddenly pushing water up, too (called a megathrust)
• This wave of water rushes to the land at a speed of hundreds of kph where the front of it slows down due to the shallow water (friction with shore), but the back of it keeps moving fast
• This creates a bigger bulge upward, increasing the size of the wave (scrunching wave together)

Question 8

What are the shapes of P and S waves?

Answer 8

• P-waves pulse (similar to a soundwave), meaning they push rock in front of it forward
• S-waves push rock perpendicular to the wave (up, down, or either side).

Question 9

Which wave is faster?

Answer 9

P-waves are faster than S-waves

Question 10

Can both P and S waves move through all of the layers of the Earth?

Answer 10

• No, only P-waves can travel through all of the layers of the Earth (P-waves can travel through solids, liquids, and gasses)
• S-waves can only travel through the crust, mantle, and inner core because S-waves can only travel through solids.

Question 11

Which wave causes most of the damage during an earthquake? Why?

Answer 11

• S-waves cause more damage during an earthquake because S-waves push rock away from the wave (this causes most of the shaking)
• P-waves only compress the rock.

Question 12

For a given epicenter location, be able to identify what types of waves (P or S) would be detected by seismometers at other points on the Earth’s surface.

Answer 12

• Point the globe so the epicenter is facing directly upward, and estimate where 103-140 degrees away from the epicenter is
• Between 0-103 degrees, both types of waves are detected
• Between 103-140 degrees, no waves are detected (the “shadow zone”)
• Between 140-180 degrees, only P-waves are detected.

Question 13

Remember that earthquakes are closely associated with plate tectonics. So, remember the relationship between quakes and plate boundaries.

Answer 13

Earthquakes occur on plate boundaries, either at a convergent boundary where one plate is being subducted into the mantle, a divergent boundary, or a transform boundary where two plates slide by each other.

Question 14

How have seismologists used earthquake waves to learn about the internal structure of the Earth? Know how body waves move within the interior of the Earth (for example, how they are bent sharply at the core-mantle boundary).

Answer 14

• Waves bend when they reach different layers of the Earth because of differences in density, or don’t pass through them at all
• Scientists use blackout zones and the bent waves to know where layer boundaries of the Earth are, and what the density and material of these layers are

Question 15

Body Waves

Answer 15

A seismic wave that travels through the body of the Earth (through the Earth’s different layers).

Question 16

Focus

Answer 16

The exact area where an earthquake occurs in the body of the Earth

Question 17

Earthquake magnitude

Answer 17

The scale that seismologists use to determine how much an earthquake shakes the ground. Magnitude is recorded on a logarithmic scale

Question 18

Elastic Rebound

Answer 18

• A theory explaining how energy is spread during earthquakes, how two plates at a transform fault slide past each other, get caught on each other, deform, and suddenly snap back into their natural form
• The sudden movement and displacement of rock and energy is what causes the earthquake

Question 19

Epicenter

Answer 19

The spot on the Earth’s surface directly above where the earthquake happened

Question 20

Focus

Answer 20

The exact area where an earthquake occurs in the body of the Earth

Question 21

Megathrust

Answer 21

• Happens at convergent boundaries, and the cause of tsunamis
• The overriding plate snaps back
• A type of earthquake you can get at convergent boundaries that can often result in a tsunami

Question 22

P-wave

Answer 22

• Also known as a primary wave, these seismic waves can pass through solids, liquids, and gasses, and push the rock in front of it forward (compressing the rock like a pulse)
• They are the first to arrive at any place during an earthquake
• More rigid rock = moves faster

Question 23

Plastic

Answer 23

If you put stress on rock that is plastic it will deform, and when you let go it will remain in this shape (you cannot break rock that is plastic, it will just flow and deform)

Question 24

Richter Scale

Answer 24

A way of measuring the seismic energy or the magnitude that an earthquake releases, for every number it goes up, a ten times bigger earthquake occurs (the scale that measures magnitude)

Question 25

Rigid

Answer 25

If you put stress on an object it will deform, and when you let go it will go back to its original state

Question 26

S-wave

Answer 26

• Also known as a secondary wave, this type of wave can only pass through solids (not liquids and gasses, meaning S-waves can’t travel through the outer core - only solids resist a change in shape
• S-waves are substantially slower than P-waves at a 60% velocity of them, and cause most of the damage in an earthquake

Question 27

Seismometer

Answer 27

An instrument that seismologists use to record seismic waves created by an earthquake

Question 28

Shadow zone

Answer 28

An area that is 103-140 degrees away from the epicenter of an earthquake where neither P or S-waves are recorded

Question 29

Surface Waves

Answer 29

-Seismic waves that travel throughout the surface of Earth like ripples on water, as opposed to all of the Earth’s layers
-Form from motion along a shallow fault or from the conversion of energy from P and S waves
-Cause the most damage in an earthquake
-Slowest moving type
-Love waves: move rock side-to-side and perpendicular
Rayleigh waves: move rock moves in an elliptical, rolling motion

Question 30

Tsunami

Answer 30

• A wave or series of waves generated by the displacement of a huge volume of water by an earthquake, a landslide, a volcanic eruption, or an asteroid impact
• Continental debris in the rocks – evidence of past tsunamis in the Pacific Northwest
• 1958, Alaska tsunami 1700 ft - rocks fell into inlet
• Asteroid impact can generate wave 1-2 miles high

Question 31

Earthquake

Answer 31

• A vibration of the Earth caused by the breaking of rocks in the lithosphere as energy is released along the fault
• Shallow focus = most damage

Question 32

Speed of P wave from epicenter to other layers

Answer 32

• Increases speed - mantle denser than crust

- Outer core is less rigid - slows down

Question 33

Wind wave vs tsunami (on open ocean):
Wavelength
Velocity
Wave period
Wave height

Answer 33

Wavelength (distance between crests):
WW: 50-100 meters
Tsu: 100s of km

Velocity:
WW: 5-100 km/hr
Tsu: Hundreds of km/hr

Wave Period (time between waves hitting):
WW: 5-20 sec
Tsu: 20-60 min

Wave Height:
WW: A few cm to 100 ft
Tsu: 3 ft

Question 34

Number of earthquakes at certain numbers on the Richter scale

Answer 34

< 2: millions per year 
2-3: 300,000 
3-4: 50,000 
4-5: 5-6,000 
5-6: 800 
6-7: 250 
7-8: 18 
8-9: 1-2