module 6/7- earthquakes Flashcards
where do most earth quakes occur? why?
- 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
what is an earthquake
a motion of trembling of the ground caused by a sudden displacement of rock
what is a fault
-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
how are sesmic waves generated
waves of energy produced by an earthquake
stress vs strain
stress: (force/unit area)
strain: deformation or bending in response to stress
stresses acting on rock cause strain
focus vs epicenter
- focus: point of inital movement on a fault, where sesmic wabes originate
- epidenter: point of earths surface directly above the focus
types of sesmic waves
- body wave (travel through earth, p and s)
-surface waves (travel on earths surface)
p waves
-compressional
-very fast (4-7km/sec)
-rock vibration parallel to direction of wave propagration
-can pass through solids and liquids
s waves
-shear
-move up and down
- slower (2-5km/s)
-rock vibration perpendiclar tp direction of wave propagation
-cannot pass through liquids
Rayleigh waves
-rolling waves
- very destructive
- similar to wave motion in ocean
love waves
- horizontal movements
-tock vibration perpendicular to direction of wave propagation
what hazards are caused by earthquakes
- 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
how can we tell if we are at risk of earthquakes in eastern north america?
- old fault lines could be potential site
can be predict earthquakes
-no
-we can predict where they might occur, but not when
which areas of canada are at risk from earthquakes
-pacific coast (BC)
- yukon
- nort west territories
- at any old fault lines
wht do we know about earthquales in the caribbean and the global south
- caribbiean- oriente fault (in atlantic ocean, whch have decreased earthqukes)
- global south near ring of fire (increased earthquakes)
what is a shaow zone
an area where no p or s waves are detected
what are sesmic waves dected with
-seismometer
- seismograph: records motion, globlal network of seismograph stations
- seismogram: paper record on which p waves and s waves can be differentiated
how do seismometers locate earthquakes
- 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
how can we determine focus
- through further anaylsis of sesmiograms
- shallow focus (less than 70km)
- intermediate focus (70-350 km)
-deep (350-670 km)
how do we determine size of an earthquake
- 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
how do tsunamis form
- displcemnt of sea floor in an earthquake
- water rushes in and overcorrents
-creates long, low waves
