A tremendous number of earthquakes occur every year around the world. The primary tool seismologists use to locate the source of each quake is a network of seismometers. Seismometers are instruments designed to be sensitive enough to feel even the smallest motion of the waves coming from distant locations on Earth. By understanding how seismic waves travel these records of ground motion, called seismograms, can be interpreted to enable us to locate the earthquake’s source.
In this activity, students use recent 3-component seismograms (recordings of motion on the N/S, E/W, and up/down axis) to locate quakes. Students identify P and S waves in their seismograms and measure the time between arrival of the P and S wave. Students then use this time to look-up the distance the epicenter is away from the station using the travel-time-curve. By combining their information with the results from at least three other students using seismograms recorded at different locations, the location of the epicenter can be determined.
While seismologists have not used this method of locating quakes since the advent of computers, it is an excellent exercise to get students familiar with the information contained within seismograms and excited about earthquakes as part of the Earth system.
By the end of this activity, the student will be able to:
- Identify P and S waves on three-compontent seismograms,
- Determine the distance of an epicenter from a seismic station using travel time curves,
- Locate the epicenter of an earthquake by triangulation, and
- Calculate the time of origin of an earthquake based on seismic data