Locating an Epicenter and Earthquake from Seismographs To locate an epicenter, records from three different seismographs are needed. Ideally, this activity should be done using a globe.

When projected onto a flat map, the circles showing distances to the epicenter become distorted. For this reason, the method used here is an approximation.

Problem how can you determine the location of an earthquake’s epicentre?

Materials

• Pencil

• drawing compass

• World map or atlas

• Photocopy of map on page 241

Skills Measuring, Interpreting Maps, Interpreting Graphs

Procedure

1. These three seismograms recorded the same earthquake, in New York City, Seattle, and Mexico City. Use the travel-time graph to determine the distance that each station is from the epicenter. Record your answers in a data table like the one shown.

2. Refer to a world map or atlas for the locations of the three seismic stations. Place a small dot showing the location of each of the three stations on the photocopy of the map on the next page. Neatly label each city on the map.

3. On the map, use a drawing compass to draw a circle around each of the three stations. The radius of the circle, in miles, should be equal to each station’s distance from the epicenter. Use the scale on the map to set the distance on the drawing compass for each station. CAUTION: Use care when handling the drawing compass.

# Locating an Epicenter and Earthquake from Seismographs Analyze and Conclude

1. Using Graphs How far from the epicenter are the three cities located?

2. Calculating what would the distances from the epicenter to the cities be in kilometers?

3. Interpreting Maps what is the approximate latitude and longitude of the epicenter of the earthquake that was recorded by the three stations?

4. Drawing Conclusions on the New York seismogram the first P wave was recorded at 9:01 UTC. UTC is the international standard on which most countries base their time. At what time (UTC) did the earthquake actually occur? Explain.

Go Further Use the Internet or the library to find the locations of recent earthquake epicenters. Make a data table displaying the location, date, and magnitude of ten recent earthquakes. Report your findings to the class.