Most earthquakes occur at Plate Boundaries The deepest
earthquakes occur at subduction boundaries
Slide 3
The focus of an earthquake is the source, or where it
originates. The epicenter is the point on the Earths surface
directly above the focus.
Slide 4
Seismographs are used to record the various types of seismic
waves that are generated during an eathquake. (see picture above
right in packet to see how one looks/works)
Slide 5
P- Waves (elastic) push and pull the ground Travel through
solids, Liquids & gases S-Waves (shear) move the ground up and
down. Only travel through solids
Slide 6
L-waves (Rayleigh/Love waves)- rolling surface waves; arrive
last Only travel through solids
Slide 7
Slide 8
Seismographs record results on seismograms The difference in
arrival times of p and s waves= lag time Using lag time we can find
the distance to the epicenter
Slide 9
The further away the seismograph station, the greater the lag
time.
Slide 10
Which city is located farthest from the epicenter? (use picture
at left in packet) What is the difference between arrival times of
the first P and S waves in the seismogram above (in the
packet)?
Slide 11
Used to record the distance (measured in km) from the recording
center to the epicenter of an earthquake
Slide 12
The difference in arrival times of p and s waves= lag time
Slide 13
When the first P-wave arrives 4 minutes before the first
S-wave, the earthquake occurred _________ km from the recording
station.
Slide 14
Using seismograms from 3 record stations and a travel-time
graph, we can establish the location of the earthquake
_______________________.
Slide 15
How far from the epicenter is each of these three cities?
Slide 16
Why do seismologists need to plot data from three recording
centers?
Slide 17
We need 3 seismograph stations to find the epicenter of an
earthquake. With one, it could be anywhere on the circle. With two,
it could be either two areas they touch. With three, its where they
all meet!
Slide 18
This is where the crust is under stress and potential energy is
stored.
Slide 19
Measure of how much energy is released. Richter scale is used
to plot, from 1 10, how strong an earthquake is. Each increase in 1
equals 10 times more energy released.