What information is contained in a seismogram?
The seismogram (or recording of an earthquake or several earthquakes) duplicate the ground motion at the station in magnified form. Generally, several different pulses of energy, representing different waves traveling through the Earth at different speeds & by different paths, appear for each quake. When an earthquake starts, the sudden shifting of rock along the fault causes two types of “body waves”, which propagate outward & downward from the hypocenter, starting at the same time. P (primary) waves & S (secondary) waves travel at different, for the most part known, speeds. (Think of throwing a rock into a pond, except instead of one type of wave, there are two.) In addition, “surface waves” may be generated, which travel along the surface of the Earth only. There are two basic types of surface waves: Rayleigh waves & Love waves. For earthquakes that are near the station (within about 120 km), we usually see only one P & one S wave, because the first waves travel a direct path throug
