Seismogram Interpretation

How to Read Seismogram

We have already known that there are two types of seismic waves propagating inside the Earth: P waves or compressional waves which travel faster than the second types S waves or shear waves.

The first arriving pulse labeled as “P” is a P wave that followed a direct path from the earthquake to the seismometer.

Another P wave labeled as pP went upward from the Earthquake, refelcted off the Earth’s surface and then traveled to the seismometer. The depth of the earthquake can be found from the time difference between the direct P and pP phases (only if the seismic velocity model near the source is known).

P wave that went downward from the source, “bottomed”, reflected at the surface and repeated the process is marked as PP.