CHPTR 10 Earthquakes and Earth's Interior Flashcards
hypocentre/focus
location where the fault initially breaks or explosion happens
epicentre
point on surface directly above hypocentre
Plates move how many cm per year
1-10cm
Earthquakes convert elastic energy to
kinetic energy and heat energy
foreshocks
small tremours before major earthquakes
elastic rebound
rocks spring back to original shaped
occurs during earthquake
causes of earthquakes
movement of faults
- underground nuclear explosions
- oil + gas extraction
creeping fault
moves a few cm per year
seismology
study of earthquakes
seismograph
instrument that measures ground movement as earthquake occurs
seismogram
record of an earthquake made on a seismograph
seismologist
person who studies seismology
body waves
travel through earth
- p waves
- s waves
surface waves
travel along or just below the surface
- love waves
- rayleigh waves
which has greater amplitude surface or body waves
surface
Sequence of waves from slowest to fastest
Surface waves, S waves, P waves
P-wave
primary wave
particle motion parallel to direction of travel
(like a sound wave)
S-wave
shear wave
particle motion normal to direction of travel
(like a sine graph)
Which wave type cannot travel through liquid
S-wave
Rayleigh Wave
- retrograde elliptical particle motion
(circular movement)
Love Wave
- horizontal motion
How does depth influence surface waves
amplitude decreases with depth
what can you tell from one station reporting data of receive p and s waves
distance
what can you tell from three stations reporting data of received p and s waves
epicentre location
How to read travel Time curve for distance
- measure arrived time
- difference between p-wave and s-wave arrival time
- look for a vertical difference on the graph that matches the arrival time
- follow that line down to the x-axis
How to find the time that the earthquake occurred at using a travel time curve
- First solve for the distance to the Earthquake
- circle the where the p or s wave crosses the vertical line marking your distance
- subtract their time from their respective arrival time.
ie. if at 200km, it takes the P-wave 40s to arrive, subtract 40 from the time of the P-waves arrival
Where do most earthquakes occur
Pacific ocean
Wadati-Beinoff Zones
dipping seismic zones in a subduction zone
Earthquake intensity
qualitative measurement of the damage caused by an Earthquake
Earthquake Magnitude
quantitative measurement of energy released by an earthquake
Modified Mercalli Scale
Measurement of earthquake intensity based on how it affects people
Richter scale
Measurement of the magnitude of an earthquake
Increase in magnitude corresponds to what increase in amplitude
10x
increase in magnitude corresponds to what increase in energy
30x
Worst magnitude of Earthquake, we have seen
9
Seismic moment magnitude scale
uses area of the fault that slips and offset of area to compute magnitude
post glacial rebound + relation to earthquakes
- large ice sheets made depressions
- ice melted quickly
- as surface moves to return to existing shapes, there is movement along faults
What year was the last Cascadia earthquake
1700
What was minimum magnitude of the 1700 Cascadian earthquake
M8
liquefaction
- stable soil is held together by friction
- shaking increases space between grains; no structure; soil flows like liquid
- buildings and sink
What earthquake occured in 2004, causing a tsunami
Indonesia
Tsunami negative wave
- water pushed away from shore first
- retreat rise cycle
- there is warning
Tsunami positive wave
- water pushed directly to shore
- rise, retreat, rise cycle
- little warning
aftershock
big earthquake puts other areas into stress, aftershocks are the Earth trying to adjust itself
- smaller earthquakes following the main earthquake
What Earthquake occurred in 2008 and resulted in landslides
Sichuan Earthquake
earthquake precursors
short term and long term changes within the earth prior to an earthquake that assist in prediction
Which is faster; radio waves or p waves
radio waves
How far can we image with seismic waves
20-30km
What happens to the path of p waves through the earth
as pressure increases, p-wave velocity increases; they move away from the normal
moho
boundary between the Earth’s crust and mantle
moho depth
30-40km; up to 80 under the himilayas
P-wave shadow
If you send waves straight through the earth; the p-waves will refract (due to the outer core) in such a way that they will not be seen everywhere on the other side of the Earth
Distance to the outer core of the Earth
3000km
Which has a larger shadow zone; p-waves or s-waves
s-waves since they cannot go through the liquid outer core
How deep are Earthquake foci of convergent boundaries
> 100km
(Its going deep into the Earth)
how deep are Earthquake foci of divergent boundaries
30<km
(Its not going into the Earth at all)
how deep are Earthquake foci of divergent boundaries
30<km
(Its not going into the Earth at all)
Maximum depth of Earthquake focus
600km
Most common plate boundary in the Pacific
convergent
where are most of the worlds convergent plate boundaries
the Pacific ocean (big subduction zones all alone the West coast)
Most common plate boundary in the Atlantic
divergent