GEOLOGY

Detailed explanation-1: -By measuring the time interval between the arrivals of the P and S wave groups seismologists are able to calculate the distance between the seismograph and the origin of the earthquake. Magnitude is then derived from the amplitude of the waves on the seismogram and the distance of the earthquake from the seismograph.

Detailed explanation-2: -S waves are indicated by an abrupt change in wave amplitude. In the seismogram below, we see that the S wave arrived at about 34 sec after the P wave arrived. This time difference is called the S-P interval and is the lag time between the P and S wave.

Detailed explanation-3: -The arrival times of the P-and S-waves at different seismometers are used to determine the location of the earthquake. Assuming that we know the relative speed of P-and S-waves, the time difference between the arrivals of the P-and S-waves determines the distance the earthquake is from the seismometer.

Detailed explanation-4: -As the P and S waves travel out from an earthquake the P waves get progressively farther ahead of the S waves. Therefore, the farther a seismic recording station is from the earthquake epicenter the greater will be the difference in time of arrival between the P and S wave.

Detailed explanation-5: -Finding the Distance to the Epicenter Use the time difference between the arrival of the P and S waves to estimate the distance from the earthquake to the station. (From Bolt, 1978.) Measure the distance between the first P wave and the first S wave. In this case, the first P and S waves are 24 seconds apart.