Earthquakes
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What are earthquakes
The shaking resulting from a rapid release of energy due to sudden movement in the lithosphere
List some causes of earthquakes
• movement of magma in volcano/volcanic eruption • underground explosions • mining • MOST: tension building up along fault lines in the crust due to the slow movement of tectonic plates
How do earthquakes occur
• friction causes moving plates to stick along plate boundaries • pressure increases till > friction • sudden release of kinetic energy
What is elastic rebound theory
• strained rocks during earthquake resumed their unreformed state after rapid energy release • what causes ground shaking
List fault types, what happens to crust, what happens to hanging wall
Normal fault: EXTENSION of crust Hanging wall goes down Reverse fault: COMPRESSION of crust Hanging wall up Strike slip fault: PARALLEL movement
Why do Benoiff zones stop at 700km
At this point the subduction crust melts into asthenosphere due to extreme heat and pressure
What are the types of waves
Body waves: P and S waves Surface waves: Rayleigh and love waves
What waves arrive first ?
• P waves: travel through solid and liquid • S waves • Surface waves
What do seismometers do and record?
They detect seismic waves They record the arrival time, frequency, amplitude of different waves DONT RECORD APPROACH DIRECTION
The ___ to earthquakes can be detected using ____ between _ waves and _ waves
Distance Lag time P S
What is the moment magnitude scale ?
• considers how the family moved and energy required to do so • calculates seismic moment
What’s the formula for moment magnitude ?
= rigidity of earth x average amount of fault slip x size of area that slipped
The MM scale is _____ a whole number increase represents ____ increase in measured amplitude = __ times more energy release
LOGARITHMIC TENFOLD INCREASE = 30 TIMES MORE ENERGY RELEASE
How is richer scale measured What does it measure
• measured using wave amplitude and distance to earthquake • measures the amount of energy released ONLY • underestimates energy release of large earthquakes
What is the mercalli scale
• measures intensity by obvserving effect on people environment local geology