Quiz 3 Topic 3

Question 1

What causes earthquakes?

Answer 1

Rocks have rough surfaces so they stick, when you add pressure you will get some slip and this will induce an earthquake.

Question 2

Where do earthquakes happen?

Answer 2

Plate boundaries and faults

Question 3

What is a seismograph?

Answer 3

Is a recording of measuring ground shaking

Question 4

Do earthquakes always happen at plate boundaries?

Answer 4

No, they can also occur at faults due to fracking

Question 5

What causes a plate boundary?

Answer 5

Movement in different directions and at different speeds produces plate boundaries.

Question 6

What is the diff between all 3 types of plate boundaries? Name em

Answer 6

Transform plate boundary- moves past each other
Divergent- away
Convergent- together

Question 7

What is a fault?

Answer 7

fault plane- surface of two sides of fault
hanging wall is on top, foot wall is on bottom
Faults are located at plate boundaries but also other places of the earth where stress builds and is released by faults
Faults are planar fractures in rocks where the rocks on either side have moved

Question 8

What are the three types of faults? Describe them

Answer 8

Strike-slip, normal and reverse faults (dip-slip faults) .
Strike slip- moving past eachother horizontally (happen when you have sheer)
normal fault- hanging wall goes down vertically and move outward
thrust fault- hanging wall goes up and onto foot wall (same as reverse fault but shallower angle)
reverse fault- blocks move together hanging wall climbs up foot wall

Question 9

Why do faults occur?

Answer 9

Faults occur because of directed stress which builds up in rocks.

Question 10

What are the three different types of stress?

Answer 10

compression, tension, and shear (slipping along a plane parallel to the stress)

Question 11

What does stress lead to?

Answer 11

strain (deformation)

Question 12

IF you keep stress what does that lead to in rocks?

Answer 12

Breakage, (fracture)

Question 13

What are the three stages strain takes place in?

Answer 13

Elastic Deformation
Fully reversible – stretch the spring a little and it springs back
Ductile Deformation
Irreversible – stretch the spring too much
and it won’t go back to its original shape
Brittle Deformation (Fracture)
Stretch the spring so much that it breaks.

Question 14

What are the scales that fractures can occur at?

Answer 14

can be at the scale of a plate boundayr, can be in a moutain, or can even be microscopic

Question 15

What is elastic rebound theory?

Answer 15

friction exists along the fault plane, so rocks on either side of the fault resist movement until strain overcomes the friction- resulting in an earthquake

Question 16

name four steps in an earthquake

Answer 16

stress is added (via sheer), rocks bend (ductile deformation) and store energy, rocks fracture and release energy (get earthquake) then rocks rebound to their deformed shape.

Question 17

Where does slip occur in a fault?

Answer 17

On the rupture zone

Question 18

what is the focus?

Answer 18

where the rupture starts.

Question 19

What is the epicentre

Answer 19

is on the surface above the focus

Question 20

Where do the biggest earthquakes occur?

Answer 20

At subduction zones

Question 21

Can shallow and intermediate earthquakes also occur at subduction zones?

Answer 21

yes, earthquakes happen at clusters at specific depths, this is because of mineralogical changes due to metamorphism of the rock. This is because water in the minerals gets released as they melt which weakens rock and earthquakes occur. The shallow earthquakes occur due to energy released from the rocks snagging on eachother.
The pattern of the clusters of earthquakes is called the Wadati-Benioff Zone. Can use these zones to see which way the subduction zone is dipping and angle of the dip.
the shallower the angle of the bed the stronger the earthquake!

Question 22

What type of plate boundaries usually have shallow earthquakes?

Answer 22

Transform and divergent boundaries are associated with shallow earthquakes.

Question 23

What are body waves?

Answer 23

Some seismic waves are generated at the focus and travel through the interior of Earth = body waves

Question 24

What are the two types of body waves?

Answer 24

p waves and s waves

Question 25

Describe p waves

Answer 25

stand for primary waves
Is like a slinky, you move the slinky and all the rings move with energy.
P waves are like that but they move in circles from the epicentre.
P waves do not cause much damage

Question 26

describe s waves

Answer 26

S waves stand for shear waves or secondary waves
Are analogous to a rope wiggling, move out in a sphere except instead of a pressure wave they shear all the rock around them.
slower then P waves,
S-wave ground motion is in both horizontal and vertical direction, can cause a lot of damage. More than P waves as they move in multiple dimensions.

Question 27

What are surface waves?

Answer 27

Is the arrival of body waves at the surface of the earth

Question 28

Are surface waves more or less destructive than body waves?

Answer 28

Surface waves tend to have the greatest amplitudes in near- surface layers of sediment and are the most destructive of the earthquake waves.

Question 29

What are the two type of surface waves?

Answer 29

rayleigh and love waves

Question 30

How do rayleigh waves move?

Answer 30

rotating waves along surfaces, create vertical displacement, are like ripples on water.
Energy moves in a rolling way through rock at the surface of earth.

Question 31

How do love waves move?

Answer 31

Are horizontal moving not up and down like rayleigh waves. Are side to side shearing.

Question 32

Recite all of table properties of seismic waves

Question 33

How are seismographs built?

Answer 33

Have ground movement, base, frame, and fix mass

Question 34

What does attenuate mean?

Answer 34

Earthquakes attenuate as they travel through Earth (the amplitude of the wave gets smaller

Question 35

If earth was completely homogenous how would waves travel?

Answer 35

If Earth was completely homogeneous, waves would travel along essentially straight paths.

Question 36

What do we actually see in the way waves travel?

Answer 36

We see P shadow zones and well as S shadow zones

Question 37

What do the shadow zones tell us about the interior of the earth?

Answer 37

It tells us that the interior of the earth must have layers of materials with different properties

Question 38

Why do we get a P wave shadow zone?

Answer 38

Velovity of p waves change as it interacts with rocks of different properties, travels slowly through solid inner core, and then travel faster in liquid outer core.
P waves can travel through liquids and solids and velocities of the wave will change based on the density of the rock as well as depth as density of rock increases as the depth increases, s wave is a shear wave, p waves are compressional waves.
The change in p waves as it travels through diff materials results in an area with no p waves, when it hits the solid inner core it speeds up again and then will wave again.

Question 39

Why do we get an s wave shadow?

Answer 39

As liquid has no sheer strength they cannot transmit S waves

Question 40

What is the modified mercalli scale?

Answer 40

IS a qualitative description of what earthquake feels like.
This is an intensity scale, how it feels and the impacts of the earthquake.
The further up you go in this scale the worse the destruction is.
Goes upto 12

Question 41

What is the richter magnitude scale?

Answer 41

Consists of an amplitude scale, measures time between wave arrivals, measures distance from the epicentre to get magnitude of earthquake.

Question 42

What are the limitations of the richter magnitude scale?

Answer 42

For amplitude we’re measuring biggest peak on seismogram, when waves travel further from epicenter they attenuate (get smaller) so we apply a correction factor to the wave. On the richter scale 0 is calibrated at 100 km from the epicenter. This scale does not take inot account how long the ground shakes for. Is bad at measuring big earthquakes, this scale only takes into account the amplitude of the wave not the shaking of the ground. It also doesn’t work well for deep earthquakes as as waves trave up surface they attenuate, so the surface waves end up not being that big. Also really bad at measuring earthquakes with an epicenter that’s very far away from the seismonitor. Everyscale we use is generally imperfect bcuz it only focuses on the amplitude of the wave.
It doesn’t take into account differences in rock types, you can see changes in lithology over a space of a few metres, changes in lithology affect you waves velocity, for ex surface waves get amplified in loose sediments. And this is not included in the richter scale as the richter scale was developed for California and it’s lithology,so therefore it can’t be used everywhere even though certain countries have diff rock types so the scale won’t be exact place to place. They adjust the richter scale according to it’s local area to make up for this error when using it in diff places and call it a local magnitude scale.

Frequency is also missing as well as time from the richter scale.

Question 43

What is each level in the richter scale represent?

Answer 43

Each level in the richter scale is an order of magnitude, this is because amplitude varies extremely differently, so instead of expressing the actual numbers we use magnitudes in order for ease. The richter scale is also logarithmic, every time you increase the magnitude by 1, a 10X greater amount of amplitude occurs and 33X more energy occurs.

Question 44

Why do we convert amplitude into magnitude?

Answer 44

Do this to compare simple numbers

Question 45

What are the energy changes between each step in the richter scale?

Answer 45

Minor earthquakes happen all the time
One step up is a light earthquake, going to the feeling of tornado, from 5-6 feel an atomic bomb, upper than that is nuclear energy feeling

Question 46

What is the moment magnitude?

Answer 46

is MW equal to Average slip of fault (= amnt distance rock has moved) times the ruptured area on the fault, times the rigidity of the faulted rock (how spongy rock on either side of fault is) the larger the area of slip the bigger the earthquake, the greater the amount of distance rock has moved bigger the earthquake, the less spongy the rock- the bigger the earthquake.

Question 47

What number gets recorded in earthquake history?

Answer 47

moment magnitude

Question 48

Can we predict where earthquakes will happen? When they will happen?

Answer 48

Can predict where earthquakes will happen (ex plate boundaries/faults), but cannot predict when they will happen due to not being able to predict changes in rock in subsurface, any computer that could do this would take a really long time to happen and by that time earthquake will happen

Question 49

What are secondary hazards associated with earthquakes?

Answer 49

Changes in ground level (due to fault ruptures that come to the surface), landslides (due to rumble from earthquakes moving metastable rocks), fires (can be caused by ruptured gas lines, fallen power lines), liquefaction, and tsunamis

Question 50

How does liquifaction work?

Answer 50

Need loose sediment for this (has no cohesion, for ex no clay) need water saturation (all pores filled with water) and then need ground shaking.
When you have a loose sediment and shake it it will compress, the grains will support it, in an earthquake the squeezing motion of sediment put pressure on water in pores in respponse the water produces pore pressure equal to the pressure of the shaking of the grains this will push grains apart and the whole thing behaves like a fluid (quick sand).

Question 51

What causes tsunamis?

Answer 51

These happen when you have displacement in the oceans, some type of movement in sea floor which causes waves (can be earthquake, nucelar blast or underwater land slide)
Wave in the middle of the ocean will not be big at all, but as the tsunami heads towards land it will ride up the ramp towards land, due to friction water slows down and wave sstart to pile upm on eachother which causes height of wave tp be much much higher as frequency increases (waves are much closer to each other). Often called tidal waves, since they look like tides but don’t have to do anything with tides and are much much bigger.

Question 52

Describe some of the diff ways engineers make earthquake resistant buildings?

Answer 52

Braces stop deformation in buildings, braces are designed to be ductile without fraction, earthquakes hit weakest link (breaks). Good as it avoids links which will fracture.

Sheer walls, strongest and stiffest of all buildings

Dampers- is not a brute fort system, has water here to reduce earthquake vibrations via sloshing.

Seismis proofing- is best move for earthquakes- puts base isolation system in it, stop building from moving.