Earthquake Epicenter Triangulation
Enter P-wave and S-wave arrival times at three seismograph stations. The tool calculates the distance from each station and draws overlapping circles. The point where all three circles intersect is the earthquake epicenter.
Computed Results
How Seismic Triangulation Works
P-waves and S-waves
Earthquakes produce two main body waves. P-waves (primary) are compressional waves that travel at about 6 km/s through the crust. S-waves (secondary) are shear waves moving at roughly 3.5 km/s. Because P-waves travel faster, they always arrive at a seismograph first. The difference in arrival times grows with distance from the epicenter.
The S-P Distance Formula
The distance from a station to the epicenter is calculated from the S-P time difference using: d = (t_S - t_P) x V_P x V_S / (V_P - V_S). With V_P = 6.0 km/s and V_S = 3.5 km/s, the factor simplifies to 8.4 km per second of S-P delay. A 10-second S-P difference means the epicenter is about 84 km away.
Three-Station Triangulation
Each station defines a circle centered on itself with radius equal to the computed distance. One station alone only narrows the epicenter to a circle. Two stations give two possible intersection points. Three stations uniquely identify the epicenter as the single point where all three circles overlap. Stations should be spread far apart for an accurate fix.
Richter Scale Basics
The Richter scale measures earthquake magnitude on a base-10 logarithmic scale. A magnitude 5 earthquake releases about 31 times more energy than a magnitude 4. Most earthquakes people feel are in the 3-5 range. Magnitude 6-7 can cause significant damage. Events above magnitude 8 are major earthquakes capable of affecting large regions. Magnitude is estimated from ground motion amplitude corrected for distance.
Real Seismic Networks
Global seismic networks like the USGS and IRIS maintain hundreds of stations worldwide. Modern seismographs record ground motion in three components (vertical, north-south, east-west) with precision below a nanometer. Automated algorithms triangulate epicenters within minutes of an event. Dense regional networks can locate small earthquakes to within a few kilometers.
