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Finding an Earthquake's Epicenter

Subjects: Science: Earth Science; Social Sciences: Geography
Grades: 9-12


Brief Description

This lesson helps students understand the processes used to identify the location of an earthquake's epicenter and how the Richter magnitude of the earthquake is determined.



  • understand the economic, societal, and geological impact of earthquakes;
  • interpret a seismograph reading to determine distance to an earthquake's epicenter;
  • interpret a seismograph reading to determine the Richter magnitude of an earthquake;
  • pinpoint an earthquake's epicenter using a minimum of three seismograph readings.



earthquake, epicenter, Richter, Richter scale, seismograph


Materials Needed

  • computers with Internet access


Lesson Plan

Generate interest in earthquakes by showing the students pictures, simulations, and maps of historic earthquakes in the United States and around the world. Data, such as damage estimates in dollars, number of deaths, and Richter magnitude, show the importance of specific events and the reasons for studying the causes and characteristics. The following resources will be helpful: Direct the students to several Web sites showing the most current seismic activity. Students can view maps showing the location of the epicenter of a recent earthquake in the United States or another location, along with locations of past earthquakes in those areas. Links to actual seismograph readings (seismograms) recorded by the United States Geological Survey (USGS) are also displayed. The following resource will be helpful:

Instruct the students on how to determine the distance to an epicenter using one seismograph reading. This is accomplished using a time-travel graph, which is a graph that shows the relationship between the difference in arrival times of the primary seismic wave and the secondary seismic wave and the distance to the earthquake's epicenter. By interpreting the difference in arrival times of the two seismic waves, one seismograph reading can determine the distance to an epicenter. However, it does not determine the direction the seismic waves came from. Therefore, at least three seismographs are necessary to pinpoint an epicenter, which is accomplished by drawing a circle around each seismograph location at the correct distance. The location of an earthquake's epicenter is where the three circles come in contact with one another. The Richter magnitude of the earthquake is determined by measuring the amount of movement at an individual seismograph station. The following resources will be helpful:

Direct students to the Virtual Earthquake Web site, which is a tutorial to guide students through the process of determining earthquake epicenters and magnitudes, as discussed in the previous activity. This tutorial is both a problem-solving activity as well as an active learning activity. Students are first presented with the problem of determining the epicenter of a past earthquake. A student chooses an area of the world to study, then uses three seismograph readings and a time-travel graph to locate the epicenter and determine the Richter magnitude. Students must manipulate the data by reading seismographs, entering data, and drawing circles around stations. This activity is found at the following resource:



To practice the skills obtained in the previous activities, students will choose another location in the world and complete the tutorial again. Following tutorial completion, students will print out certificates of completion that contain their results. Use the certificates as a performance-based assessment.


Lesson Plan Source

Virtual Courseware, Geology Labs Online

Submitted By

Tim Leister, Garden Spot High School, New Holland, Pennsylvania


Links last updated 8/23/2011

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