Seismic Activity Flashcards
how are seismic waves created
when plates jerk past each other it sends out seismic waves
what is the focus
the place in the lithosphere where the earthquake starts, seismic waves spread out from here
what is the epicentre
the point on the earth’s surface where the earthquake is felt first, directly above the focus
what are the 3 main types of seismic waves
- primary waves = p waves
- secondary waves = s waves
- surface waves = Rayleigh and love waves
characteristics of p waves
- can travel through solids and liquids
- waves push and pull the earth in the same direction as the wave is travelling
- fastest type of wave
- 5000m/s rock(granite)
- 1450m/s liquid
characteristics of s waves
- can travel through solids not liquids
- move the earth at 90oC to the direction of travel
- slower than p waves, 1/3 of p waves
characteristics of love waves
- only travel through solids
- move the surface from side to side
- 90% of s wave velocity
characteristics of Rayleigh waves
- can travel through solids and liquids
- move the surface in a rolling motion
- 90% of s wave velocity
what can be used to measure earthquakes
seismometer,
what do seismometers measure?
the magnitude of earthquakes - the amoint of energy they release. they also measure the duration and direction of the vibrations
what are the two different scales to measure earthquakes?
the richter scale and the mercalli scale
what does the richter scale measure
magnitude of an earthquake
characteristics of the richter scale
- no upper limit, logarithmic (10x greater)
- each value represents about 30 times more energy released than the previous value
- don’t feel earthquakes at 1-2, major earthquakes are above
what does the mercalli measure
the impacts of an earthquake
impacts are measured using observations
what is the scale of the mercalli scale
1-12.
1 = earthquake only measured by instruments
12- earthquake causing total destruction
what is a tsunami
large waves caused by displacement of large volumes of water
how is a tsunami caused?
-triggered by underwater earthquakes
the earthquakes cause the seabed to move which displaces the water
-waves radiate out from the epicentre
-greater the movement of the sea floor, the greater the volume of water displaced - bigger wave produced
what can cause a tsunami other than earthquakes?
volcanic eruptions and landslides that slide into the sea can displace large volumes of water
characteristics of a tsunami in open, deep water
- high speeds, 500-950km/h
- long wavelength, 200km
- small amplitude, 1m
what happens to the wave of a tsunami as it enters shallower waters
waves get compressed (squashed together) and their energy becomes more concentrated
characteristics of a tsunami in shallower waters close to land
- slow down to less than 80km/h
- wavelength decreases to less than 20km
- amplitude increases to many metres
what happens just before the tsunami reaches the coast
-water withdraws down the shore (is called drawback)
looks like the tide is going in
