EARTHQUAKES

Question 1

• Earthquake:

Answer 1

the ground shaking cases by stresses released in Earth

Question 2

o Factors that determine destructiveness

Answer 2

 Location, magnitude, depth, distance from epicenter, secondary effects, architecture

Question 3

EQ stresses

Answer 3

seismic waves (kinetic energy), displacements along the fault (kinetic energy), heat and other energy

Question 4

megathrust EQs

Answer 4

plate boundary EQ
up to M9 occurs every 200-800 years
causes large tsunamis

Question 5

• Understand why most earthquakes IN Canada occur on the west coast

Answer 5

o Subduction zone at a convergent Boudry
 North America plate w/ Juan de Fuca plate and pacific plate
 North American plate EQs
* Large damage potential  closer to surface =more shaking
 Juan de Fuca plate EQs
* Deeper and very frequent

Question 6

o Quantitative 1-10

Answer 6

measures magnitude
richter scale
moment magnitude scale

Question 7

 Richter’s scale

Answer 7

based on aptitude of seismic waves, which is related to energy released
* Not really used by geologists, despite being well known

Question 8

 Moment magnitude scale:

Answer 8

is based on the amount of fault slippage produces, the size of surface area that ruptured, and the nature of the materials that faulted, which is more accurate than Richter’s scale

Question 9

qualitative

Answer 9

1-12 intensity
 Modifies Mercalli scale

Question 10

 Modifies Mercalli scale

Answer 10

what we feel
* 1: felt by very few
* ~5: general panic
* 12: total destruction

Question 11

o Magnitude

Answer 11

 Characterizes an EQs relative size
 Each whole number represents a tenfold increase in the measured amplitude and 32 times more energy release

Question 12

• Use plate tectonics to predict where earthquakes occur, and how earthquake depth and magnitude is ties to different types of plate tectonic boundaries.

Answer 12

o Materials respond differently (strain) to stress. Brittle deformation leads to an earthquakes
o Deep focus at convergent boundaries
o Intermediate focus at transform boundaries?
o Shallow focus at divergent boundaries

Question 13

o Subduction zone earthquakes (convergent boundaries)

Answer 13

 Largest possible earthquakes/ deep focus (meteorite impacts can be larger)
 Convergent boundaries
 Type of stress here: compression
 Type of faults: reverse (or thrust)
 Three locations of earthquakes
* #1: subduction interface earthquakes.
o Can be huge @ M9.4) megathrust EQs
* #2 EQs in the subducting or overriding plate
o Moderate size, largest = ~M7
* #3 Benioff earthquakes
o Very deeps: 100s of km)
o Little/ no damages at surface
o Deeper focus as moved down the Benioff zone
 Megathrust rupture zone located on the coast of Vancouver island
* 12-30 minutes from EQ till initial tsunami waves arrive
* Last one: jan 26 1700 @ M9 (records in Japan and first nations(oral) )

Question 14

o Continent- continent convergent Eq zones

Answer 14

 Very large (not as large as subduction) up to ~M8
 Convergent boundaries
 Type of stress: compression
 Type of fault: reverse (or thrust)
 India= thrust fault

Question 15

o Divergent EQ zones

Answer 15

 Small to moderate EQs usually less than M5
 Most are underwater
 Type of stress: tension/extension
 Type of fault: normal
 Ex: east African rift, mid Atlantic ridge
* Rift valley forms

Question 16

o Transform boundaries

Answer 16

 Oceanic (majority) very small Eqs
 Continental- shallow mostly small earthquakes, some larger usually up to M6 or M7
 Type of stress: shear
 Type of fault: strike-slip
 Ex: San Andreas fault, Queen Charlotte fault

Question 17

o Body waves

Answer 17

 P- wave (primary/ pressure)
* Particles move parallel to the direction wave propagates
* Can travel through all matter
* Is the fastest
 S- waves ( shear/ secondary)
* Particles move perpendicular to direction wave propagates

Question 18

surface waves

Answer 18

 Rayleigh wave: vertical and horizontal motion parallel to wave travel direction (like ocean wave)
 Can travel through all matter

Question 19

o Seismograph: the basic idea

Answer 19

 Mass suspended by a spring
 Seismograph moves, the mass does not
 Motion causes pen to move

Question 20

EQ detectors

Answer 20

 P waves arrive first
* Twice as fast as the others
* Over 300km (our distance from the subduction zone)
* P waves will take 60 sec to arrive
* Surface waves will take 100 sec to arrive
* If we can detect p waves, we have enough time to “take shelter”

Question 21

o Seismograph readings

Answer 21

 Three seismographs gives us triangulation
 The earthquake epicenter is where the three circles meet

Question 22

o EQ forecasting

Answer 22

 Scientists cannot yet predict EQs due to the complicated nature of subsurface stress and strain
* They use probability

Question 23

 Long-term forecasts

Answer 23

(10- few thousand years)

Question 24

 Medium range predictions

Answer 24

(few years to a few months)

Question 25

 Short range predictions

Answer 25

(few days or hours)

Question 26

paleoseismology

Answer 26

uses past earthquake data to predict future occurrences
o Areas which are overdue for an earthquake are in a seismic gap and have built up strain

Question 27

• Paleo earthquakes:

Answer 27

rock records also show past EQs through disrupted sediment layering
o The faults

Question 28

o Measurements

Answer 28

(tiltmeters and radon detectors)

Question 29

 Measure dilatancy

Answer 29

increase in volume due to built up stress in a rock

Question 30

 Tiltmeters:

Answer 30

measures tilting and swelling (dilatancy) of rocks

Question 31

 Seismographs: BC has 30, 200 all over Canada

Answer 31

japan more than 4000

Question 32

 How we perceive earthquakes depends

Answer 32

• Magnitude
• Foundation (ground) material
• Duration
• Building construction
  o In general
   Brick and concrete- bad
   Wood, steal, and reinforces concrete – good

Question 33

5 EQ hazard types

Answer 33

ground shaking
liquefaction
fire
tsunami
landslides

Question 34

landslides

Answer 34

 very common after EQs
 Usually, people blame these deaths on the EQs not the landslide but
 Very common in BC and mountains around the world
 After EQs landslides can increase for up to 10 years

Question 35

tsunami

Answer 35

 Can be caused by vertical motion of tectonic plates (or landslide, or meteorites, or volcanoes)

Question 36

fire

Answer 36

 Shaking breaks gas and electrical lines (often at the same place)
 Van- secondary fire hydrant system- connected to ocean incase mountain connection fails

Question 37

liquefaction

Answer 37

 Shaking causes wet loose (unconsolidated) soils to liquify (act like a liquid)
 Ground loses cohesion and flows
 Bad for buildings
 Richmond and delta are at major risk to liquification since the ground is mostly loose sediments

Question 38

o Ground shaking

Answer 38

 Buildings may fall down
 Most deaths and injuries in EQs are from building collapse
 Bedrock is much more stable than sediments
 Building materials
* Wood is better than brick since it is flexible
* Building codes need to meet seismic standards in EQ prone areas

Question 39

o Interplate

Answer 39

EQs between two plates, initialed near plate boundaries

Question 40

o Intraplate

Answer 40

EQs that are large and damaging, located within a single plate, and can occur far from plate boundaries

Question 41

short term predictions

Answer 41

o Chinese scientists made the first successful prediction of major EQ in 1975 based on foreshocks: M7.5 haicheng earthquake
o Other precursory phenomena include pre-seismic deformation of the ground surface, emission of radon gas seismic gaps along faults, and anomalous animal behaviour

Question 42

• EQ planning

Answer 42

o Development o hazard-reduction programs
o Engineering and land-use adjustments to earthquake activity
o Development of a warning system