Gather three seismograms from different seismographs, preferably in different world regions. Measure the distance between the first P wave and first S wave and mark it on your chart. Distance is measured over time.
Use the seismic chart to determine the distance from your seismogram. Using the chart on your map to determine distance per inch or centimeter, set the compass to the distance from your reading.
Create a circle on the map, with your reading as the center point - this gives you the maximum distance of the radius of the epicenter.
To measure the strength (magnitude) of the quake, read the height (amplitude) of the strongest wave and mark the point on the chart. Using a ruler on the chart, draw a line from the time marking to the strength marking. The middle line, magnitude, is determined where the distance and amplitude meet.
Repeat steps one through four for the other two seismograms. Where the three circles meet is your epicenter. The magnitude chart should match on all three.