Some quakes hit busy cities or small villages where somebody can tell you about it, but even if a quake hits far away from people, it sends out waves to all parts of the globe. You can use your seismograph to record these waves and determine how far away the epicenter is from your seismogram. To pinpoint the exact location of a quake, you need at least three seismographs. Be a geologist again and try locating the epicenter of an earthquake. This activity did not tell you where the earthquake actually hit.
Many people can remember at least one large quake.
Some of these waves are headed in your direction. By the time they reach you, most of these waves are too weak for you to feel any shaking. However, a good seismograph would show you that weak seismic waves are silently vibrating the ground underneath your feet every day. Since all large earthquakes send P and S seismic waves through the interior of the earth, you should be able to receive these waves from every part of the globe. Many years ago, however, geologists noticed something strange.