Epicenter and Amplitude Notes
The distance of an earthquake from a seismograph can be determined from the seismogram. The difference between the arrival times of the P wave and the S wave (SP interval) is related to the distance to the earthquake's focus. By knowing the speeds of the P and S waves through the Earth, seismologists can create a chart relating the SP interval time to the foci distance. This chart provides the distance from the seismograph (observer) to the earthquake's epicenter. 

Procedure for Finding the Epicenter

Epicenter Example
 P wave arrival time= 0 seconds
 S wave arrival time= 37 seconds
 SP interval = 37  0 seconds = 37 seconds
 Follow the 37 second line across the SP graph until you reach the SP line. Drop down to the Xaxis and read the distance to the epicenter. Distance = 360 km.
Amplitude
The seismogram amplitude of the earthquake is found by measuring the peak value of the S wave traces. In the seismogram above, the amplitude is 180 mm.