module 6/7- earthquakes

Question 1

where do most earth quakes occur? why?

Answer 1

• at plate margins (divergent, convergent, transform)
• at faults
  -stress acting on rocks cause strain. when strain is greater than strength of rock, there is a sudden break or movement. This releases energy as sesmic waves

Question 1

what is an earthquake

Answer 1

a motion of trembling of the ground caused by a sudden displacement of rock

Question 2

what is a fault

Answer 2

-break in rock
- planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements; can be surface or buried

Question 3

how are sesmic waves generated

Answer 3

waves of energy produced by an earthquake

Question 4

stress vs strain

Answer 4

stress: (force/unit area)
strain: deformation or bending in response to stress
stresses acting on rock cause strain

Question 5

focus vs epicenter

Answer 5

• focus: point of inital movement on a fault, where sesmic wabes originate
• epidenter: point of earths surface directly above the focus

Question 6

types of sesmic waves

Answer 6

• body wave (travel through earth, p and s)
  -surface waves (travel on earths surface)

Question 7

p waves

Answer 7

-compressional
-very fast (4-7km/sec)
-rock vibration parallel to direction of wave propagration
-can pass through solids and liquids

Question 8

s waves

Answer 8

-shear
-move up and down
- slower (2-5km/s)
-rock vibration perpendiclar tp direction of wave propagation
-cannot pass through liquids

Question 9

Rayleigh waves

Answer 9

-rolling waves
- very destructive
- similar to wave motion in ocean

Question 10

love waves

Answer 10

• horizontal movements
  -tock vibration perpendicular to direction of wave propagation

Question 11

what hazards are caused by earthquakes

Answer 11

• ground shaking casuses collapsed structures, ground vibrations are amplified in some structures
• surface faulting: breaks at faults(caused by tectonic plates)
• landslides- mountainous areas are affected
• liquifaction- shaking caused liquification of sediments (structures collapse)
• fire: causes shaking of natural gas lines, gas stations, or snapped electrial wires
• tsunamis- very large, very fast waves

Question 12

how can we tell if we are at risk of earthquakes in eastern north america?

Answer 12

• old fault lines could be potential site

Question 13

can be predict earthquakes

Answer 13

-no
-we can predict where they might occur, but not when

Question 14

which areas of canada are at risk from earthquakes

Answer 14

-pacific coast (BC)
- yukon
- nort west territories
- at any old fault lines

Question 15

wht do we know about earthquales in the caribbean and the global south

Answer 15

• caribbiean- oriente fault (in atlantic ocean, whch have decreased earthqukes)
• global south near ring of fire (increased earthquakes)

Question 16

what is a shaow zone

Answer 16

an area where no p or s waves are detected

Question 17

what are sesmic waves dected with

Answer 17

-seismometer
- seismograph: records motion, globlal network of seismograph stations
- seismogram: paper record on which p waves and s waves can be differentiated

Question 18

how do seismometers locate earthquakes

Answer 18

• p waves are faster and arrive first and then s waves arrive
• the greater the distance travelled, the greater the time difference
• time travel cure produced
• use time travel cure which determiens distance to epicenter
• need three or more stations to locate epicenter because one staion can give you magnitude but not direction

Question 19

how can we determine focus

Answer 19

• through further anaylsis of sesmiograms
• shallow focus (less than 70km)
• intermediate focus (70-350 km)
  -deep (350-670 km)

Question 20

how do we determine size of an earthquake

Answer 20

• Modified Mercalli Scale 9I-XII): meansures how much damage is caused, the intensity of the earthquake, human-centered; has biases; tells us what happens ; perception of destruction measured. descriptive words used, no exact numbers
• Richter scale: base 10 log for every increase; measures amplitude of “squiggle” on sesmiograph which reps the magnitude of the earthquake
• moment magnitude: an earthquake magnitude calculated from the strength of the rock, surface area of the fault rupture, and the amount of rock displacement along the fult

Question 21

how do tsunamis form

Answer 21

• displcemnt of sea floor in an earthquake
• water rushes in and overcorrents
  -creates long, low waves