Seismographs
Today most scientists use the electromagnetic seismograph. There are 4 types of electromagnetic seismograph: The Short Period Seismograph, Heavy Seismograph, Long period seismograph and The Broadband Seismograph. The short period seismograph is used to measure local earthquakes while the long period seismograph is used to measure far away earthquakes. The broadband seismograph measures both types of earthquakes and this type is more commonly used.
The electromagnetic seismograph has 3 parts. The 3 parts are a seismometer, amplifier and display. On top of a spring is a case with a magnet inside. The out side of the box is lined with tiny coils of fine wire. The magnet moves when the case generates small electrical signals in the wire because of the movement of the earth beneath it. These movements are recorded either on a role of paper to create a seismogram or are sent to a computer for later analysis.
The electromagnetic seismograph has 3 parts. The 3 parts are a seismometer, amplifier and display. On top of a spring is a case with a magnet inside. The out side of the box is lined with tiny coils of fine wire. The magnet moves when the case generates small electrical signals in the wire because of the movement of the earth beneath it. These movements are recorded either on a role of paper to create a seismogram or are sent to a computer for later analysis.
The difference between the short period seismograph and long period seismograph is the different frequency. The short period seismograph only measurers seismic waves close together and quick. The short period seismograph magnifies the earth movements by several hundred thousand times. They can measure earthquakes too small to feel because of this. There is a problem with this. When the earthquake nearby is large enough it can not be read by the short period seismometer. To solve this problem there is the strong motion seismographs. These seismographs still measure close together and quick just with a magnification less than a 100x. Strong motion seismographs normally aren't on all the time. They are only triggered and turned on when the short period seismograph can't read the earthquake because it is too big. The long period seismograph reads lower frequency waves to get reading of far away seismic movement.