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