Earthquakes
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What are the possible results of brittle failure in the Earth’s crust?
earthquakes, joints, faults
What is an earthquake’s focus?
the place where energy is released (on the fracture, etc.)
What is an earthquake’s epicentre?
the place on the Earth’s surface directly above where the energy is released
What happens when the stress on the crust exceeds elastic reound?
stored energy is released suddenly, resulting in brittle failure - if it fractures, earthquake
What parts of an earthquake can be felt/seen?
ground motion, landslides, scarps, after shocks, tsunamis
What part of an earthquake causes the most damage?
indirect results of ground motion - falling debris, landslides…
Why are landslides so dangerous?
cut off area from outside world - cut utilities, dam rivers, break roads
How do the intensities of after shocks compare to the actual earthquake, and why do they cause damage?
less intense; hit things that were damaged by main earthquake
What is a scarp?
fault surface where it intersects the earth
How is earthquake intensity measured?
Mercalli Intensity Scale - by asking people what they felt
Why is measuring earthquakes with intensity bad?
intensity is independent of amount of energy released ; varies based on the time and place; hard to measure if no one was present; can’t compare between earthquakes
What is used instead of intensity to measure earthquake strength?
magnitude - the energy released
What scale is used to measure magnitude?
Richter scale
What type of scale is the Richter scale?
exponential - each magnitude quake produces 10 times more ground motion than the magnitude - 1
What does measuring magnitude allow one to do that couldn’t be done by measuring intensity?
comparison of earthquake
What are the 3 notable magnitudes on the Richter scale?
M1: just able to record; M5: damage begins M8.5: maximum magnitude
What does the energy relassed (magnitude) of an earthquake really represeent?
the potential destructive power of an earthquake
What decides the actual destruction caused by an earthquake?
where the energy was released
What does a seismometer do?
generates a seismograph
How does a simple seismometer work?
earth moves while pen (fixed by spring) does not, so pen draws wiggly lines to represent ground motion
Where do seismometers work best?
in places without competing energy (traffic, people, etc.)
What does a typical seismograph look like?
small oscillations for P wave; larger oscillations for S-wave; huge oscillations for Surface-wave; decreases except for spikes (aftershocks)
What effect does fault size (amount of sliding/fault surface area) have on earthquake size?
bigger faults make bigger earthquakes (based on magnitude) - pretty linear with magnitude
What effect does earthquake size (magnitude) have on the length of time the earthquake lasts?
bigger earthquakes last a longer time