At Radford University we have two seismographs. A slinky seismograph measures vertical movement (P-waves). A Lehman seismograph (coming soon) will measure horizontal movement (S-Waves). When the seismometer is disturbed, the magnets induce a current in coils. The current is read by Amaseis, a data logging software. Potential earthquakes are analyzed with WinQuake.
A potential earthquake from the Slinky seismograph. Note the large spike where the P-wave initially started, and a smaller spike when the slower S-waves arrived. Because the Slinky seismograph is a vertical seismograph, the P-waves are much easier to spot.
Earthquake analyzed by WinQuake. The software calculates the time difference between P- and S- wave arrivals, and determines an approximate radius where the center of the earthquake occurred. This particular event correlates with a 4.0 in Maine on October 16.