Transcript Earthquake Lab Walkthrough

Do Now – In Notebooks
1. In what order do earthquake waves appear
on a seismogram?
2. How many points are needed to determine
the epicenter of an earthquake? Why?
Measuring Earthquakes
• How can we use seismic data to determine the
magnitude of an Earthquake?
• How do we know where an earthquake occurred?
Steps to Locating an
Earthquake’s Epicenter
1. P waves move faster than S waves so they
arrive at seismometers first. Determine the
time between the P and S wave arrivals using
seismic data. We use 3 seismic stations to
locate epicenters.
P Wave
S Wave
Fresno, CA
2. Using the time between P and S waves,
determine the distance the waves traveled
on the Earth’s surface using the S-P line
graph.
3. Determine the
scale on the map
being used. (100
km = X mm) Using
a ruler, measure
how many mm’s
there are in 100
km on the map
4. Calculate the distances for all three seismic
stations. (Scale down from km to mm)
Formula:
Measured (mm) = X mm
100 km
distance (from pg. 2)
*Make sure to cross multiply and divide
5. Using a compass draw the areas around the
seismic station showing where the EQ could
have originated.
– You are using the numbers you just calculated in
step 4!
– Open the compass to the mm you calculated
using a ruler
– Put the pointy end of the compass on the city for
that station and carefully draw a circle
– The cities are listed on page 1 of the packet,
under the seismograms
6. Using triangulation (using 3 angles) locate
the epicenter. The epicenter will be where all
3 circles intersect.
Epicenter
How can we calculate the magnitude
on our Epicenter Packets?
1. Determine the amplitude for each seismogram
• Amplitude – Highest point of a wave
Fresno, CA
2. Plot the amplitude
and the distance in
km for each
station.
3. Draw a line (using a
ruler) connecting
those two points.
4. Repeat for stations
2 and 3
5. The area where
all three lines
cross over the
middle line,
indicates the
magnitude of
the Earthquake
and the number
on the Richter
Scale