In this activity, students study seismograms from three different seismic stations that recorded the magnitude 9.0 Sumatra earthquake of December 26, 2004. By comparing the arrival times of the P and S waves on each seismogram, they can determine the distance from the epicenter to each station and accurately map its location. Using this information, they also calculate the position of the quake-generated tsunami at one-hour intervals and estimate the time before its arrival. Discussion topics explore some of the ways people can lessen the impact of future tsunamis. Links to additional resources such as images, news reports and eyewitness accounts, and satellite imagery, are included.