which are primary waves, and S waves, which are secondary waves. P waves go through anything, while S waves only go through rock as these are shearing-type waves. P waves represent mild elevations above the baseline noise. The baseline squiggles you see all the time are called microseisms. P waves are still slight but they are fast and indicate a possible earthquake. Above these are the S waves, which are the largest ones you will see. No S waves can still mean that an earthquake happened but that it happened too far away on the other side of the planet. P waves can travel through the earth's liquid parts but S waves cannot. This is how you know when an earthquake was nearby or not. S waves come after P waves. Surface waves are their own kind of wave. These only travel through rock and have a slow wavelength as a result. There are two kinds of surface waves: Raleigh waves and Love waves. Love waves move side to side across the wave's direction. Raleigh waves are elliptical. They are slower than Love waves but spread out wide. You'll see these last a long time after an earthquake.
MEASURING MAGNITUDE OF AN EARTHQUAKE There is only one magnitude for any given earthquake. It is not location-dependent. The Moment Magnitude Scale has been in use since 1970 all over the world. This is different from the intensity, which as mentioned, is location-dependent. Geologists use the Modified Mercalli Scale to measure local earthquake shaking activity. Magnitude scales for earthquakes are not linear; they are logarithmic. One point increase equals ten times the strength. The Richter scale is no longer in use as it was only valid in Southern California and does not put into play all of the seismographs in the world. The MMS or moment magnitude scale is used to measure rock movement on a fault line. It is excellent for measuring the magnitude of large earthquakes. There are differences among the different magnitudes and what they mean. Within the MMS, there are classes of earthquakes called earthquake magnitude classes.
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