A Seismogram of the 1906 Earthquake

Above is a seismogram recorded in Gottingen, Germany, 9100 kilometers away. It shows how the ground moved in Germany as a result of the 1906 San Francisco earthquake. Time advances from left to right. Small wiggles, beginning 1/2 inch from left end, signal arrival of first compressional (P) waves. Large wiggles half way along represent arrival of slower-traveling shear (S) waves. The part of the record shown here spans about 1600 seconds or 26 minutes. The instrument subsequently went off-scale when surface waves arrived.

Compare the above 1906 seismogram to one recorded on the same instrument at the same location after the 1989 Loma Prieta earthquake.