Earthquakes 2

Question 1

List and describe the three main types of stress

Answer 1

All forces are opposite and…

1. Compression
   - act towards each other
2. Tension
   - act away from each other
3. Shear Stress / Transverse
   - act parallel but across a plane

Question 2

What are the 3 types of plate boundaries?

Answer 2

1. Divergent
2. Convergent
3. Transform Boundary

Question 3

Faults are

Answer 3

large brittle fracture in a rock body
- movement range is mm to km

Question 4

What is the point of origin for many earthquakes?

Answer 4

faults

Question 5

What are faults called based on their movement range?

Answer 5

Fractures: mm to cm
Faults: m to km

Question 6

What are plate/tectonic margins?

Answer 6

contact / boundary between plates
- like very large faults but we refer to them as margins

Question 7

Hanging wall block vs footwall block

Answer 7

Hanging: block above the fault
Foot: block below the fault

&laquo_space;Refer to slides for diagram&raquo_space;

Question 8

Normal Fault

Answer 8

• blocks move AWAY
• HW moves down relative to FW (and vice versa)
• caused by tension

Question 9

Reverse Fault

Answer 9

• blocks move towards
• HW moves up relative to FW
• caused by compression

Question 10

Thrust Fault

Answer 10

• motion similar to reverse fault except low angle + large displacement
• blocks move towards
• HW moves up relative to FW
• caused by compression

Question 11

The Rocky Mountains are likely made by what type of faults?

Answer 11

thrust faults

Question 12

Strike-Slip Fault

Answer 12

• vertical fault, no FW or HW
• motion is lateral (like traffic)
• caused by shear stress

Question 13

What are the types of strike slip faults? How can we tell?

Answer 13

Left lateral and right lateral

&laquo_space;slides for pic&raquo_space;
face the fault, whichever way it moved is the name

Question 14

The type of stress determines what type of ____ we have

Answer 14

boundary

Question 15

describe continental plates

Answer 15

• felsic / granite
• light colour
• relatively thick
• less dense
• float high

Question 16

describe oceanic plates

Answer 16

• mafic / basalt
• dark colour
• relatively thin
• more dense
• float low

Question 17

what phase is the asthenosphere?

Answer 17

solid but deforms plastically + mobile

Question 18

Do plates move independently of each other?

Answer 18

oui

Question 19

Divergent plate margins movement + type of stress

Answer 19

• starts with a rift or rift valley in a continent
• plates move apart
• tension stress

Question 20

What happens at a divergent margin?

Answer 20

• extensive volcanism begins
• continental crust thins
• oceanic crust forms at bottom of rift
• starts a new ocean basin
• becomes mid-ocean ridge where new oceanic crust is created and older is pulled away

Question 21

Divergent margins are associated with what hazards?

Answer 21

volcanism and many small earthquakes

Question 22

Convergent margins movement

Answer 22

• plates moving together
• oceanic plates more dense so they will subduct

Question 23

What are the 3 variations of convergent margins?

Answer 23

1. oceanic-oceanic
2. oceanic-continental
3. continental-continental (NO subduction)

Question 24

What is subduction

Answer 24

when plates are pushed together, the denser oceanic one goes down to mantle

-> older = colder = more dense

Question 25

Convergent margins: What will happen if subduction occurs?

Answer 25

1. extensive volcanism - island arcs if ocean-ocean - intermediate if continental 2. mountain building 3. many earthquakes - small to large to very large, megathrust (9.0 +) ex/ Tokyo

Question 26

Mountain building occurs at what type of margins?

Answer 26

convergent

Question 27

Convergent margins: what will happen if no subduction occurs?

Answer 27

(i.e. no oceanic plates involved) - mountain building - many earthquakes (up to 8+) - little to no volcanism

Question 28

Transform Boundaries

Answer 28

- move laterally - shear stress - like traffic - no space problems = no mountains form

Question 29

What happens as a result of transform boundaries?

Answer 29

- little to no volcanism - many earthquakes (moderate to large) but NOT as big as convergent margins

Question 30

Do convergent margins have bigger earthquakes or transform boundaries?

Answer 30

convergent margins

Question 31

What will happen to plate margins if the stresses change?

Answer 31

boundaries may change as well! - plate margins react to stress, and all margins are interrelated

Question 32

Can boundaries change?

Answer 32

yah

Question 33

Do mountains form on transform boundaries?

Answer 33

nah

Question 34

Are divergent margins threatening?

Answer 34

generally not

Question 35

Subduction occurs when what type of crust is involved?

Answer 35

oceanic only!

Question 36

Subduction occurs when what type of crust is involved?

Answer 36

oceanic only!