Earth Institute News
about Manhattan Earthquake 01/17/01
This is a seismogram of the earthquake of January 17, 2001 recorded at the Lamont-Doherty Earth Observatory in Palisades NY.
Time proceeds from the left to the right with first quiet before the earthquake; then the arrival of the p-wave followed by an increased amplitude as the s-wave arrives. These two waves have come from the quake epicenter in New York City to Lamont through the earth starting at the same moment but traveling at different speeds; thus they arrive offset in time.An earthquake is a slip on a fault which generates a shearing motion that produces the s-waves (secondary or shear waves). The earthquake also pushes and pulls in different directions generating the p-waves (primary or compressional waves). The p-waves arrive faster because rock is stronger under compression in comparison to under shearing motion.
Like the difference in time between lightning and thunder, the distance from the event can be inferred from the difference in arrival times, in the case of an earthquake, arrivals of the p-waves and s-waves.
Recordings from the Lamont seismic network
can be observed near real-time by visiting the website: