Finding the Epicenter Lab

Guiding Question: How can you locate an earthquake’s epicenter?

Hypothesis: To locate an earthquake’s epicenter you have to find out all the areas in which the earthquake was felt, and then take the average and the middle of all the locations. In the middle of all areas is the epicenter, where the earthquake’s seismic waves started

Data Table

City	Difference in P and S waves	Distance to Epicenter
Denver, Colorado	2 min 40 s	1600
Houston, Texas	1 min 50 s	1000
Chicago, Illinois	1 min 10 s	600

Analyze and Conclude

Drawing Conclusions: Observe the three circles you have drawn. Where is the earthquakes epicenter?

From looking at my three circles I can see that the earthquake’s epicenter is somewhere around Tennessee. I know this because all the circles around the areas in which the earthquake was felt intersect at around the same point. The circle around Chicago, Houston, and Denver all come close together and make a small triangle, around the earthquake’s epicenter.

Measuring: Which city on the map is closest to the earthquake's epicenter? How far in kilometers, is this city from the epicenter?

The city the closest to the epicenter on the map was Chattanooga, Tennessee. It is about in the exact center of where all the circles met, in the bottom middle of the triangle. Chattanooga is possibly from 50 kilometers to 0 kilometers away from the earthquakes epicenter. We can’t know for sure since my measurements probably weren’t exactly accurate, and an uneven move with my hand or a slip of the compass would have altered the exact location. This might have changed the epicenter, or the meeting point of the circles, where the triangle was formed.

Inferring: In which of the three cities listed in the data table would seismographs detect the earthquake first? Last?

Out of the cities Denver, Houston and Chicago, Chicago would have been the first to feel the earthquake. This is because it is only 600 kilometers away from the epicenter. The damage caused in Chicago would also be more than the damage in other cities. Denver would have felt the earthquake less, since it was 1600 kilometers away from the epicenter, and the damage would be minimal. Houston, with 1000 kilometers in between the earthquake, would have felt it and had damage smaller than Chicago but larger than Denver.

Estimating: About how far from San Francisco is the epicenter that you found? What would be the difference in arrival times of the P and S waves for a recording station in San Francisco?

My guess is that when the P and S waves are felt in San Francisco, there will be about a 5 minute 20 second difference. I got this number because San Francisco is about double the space away from Denver, Colorado, and therefore it should take double the time for the seismic waves caused at the epicenter in Tennessee to get to San Francisco. This also means that the earthquake was very weak and hardly felt, since the great distance causes the seismic waves to slow down. The earthquake would probably not even be felt, and damage would be tiny.

Interpreting Data: What happens to the difference in arrival times between P waves and S waves as the distance from the earthquake increases?

As the distance from the earthquake increases, more time is passing between the P and S waves. It takes more energy to get further away, and seismic waves lose energy as they travel. That is why earthquake’s P and S waves are closer together in areas closer to the earthquake where the earthquake’s damage and energy is larger, and why areas further away have less damage and energy.

Lately, no major earthquakes have happened in Italy. However, there have been a lot of small earthquakes, with an average of magnitudes of 2-3 on the Richter scale.

In Sweden there are even less earthquakes, but a small quake they have had lately was next to Kiruna and Oulu, with a magnitude of 3 on the Richter scale. They have also had other minor earthquakes.