Earthquake Distance Calculator

Find the distance to the epicenter using P-wave and S-wave arrival times.

1. Seismic Data
S-P Time Delay (Lag) sec

Time between first tremor and secondary shaking.

2. Crust Type / Velocity
Geological Setting
Distance to Epicenter
201.6
Kilometers
125.3 mi Distance (Miles)
~33s Total Travel Time
Seismogram Visualizer
P-Wave vs S-Wave

How does this work?

When an earthquake occurs, it releases energy in different types of seismic waves. The two most important for finding the epicenter are:

  • P-Waves (Primary): These are compressional waves. They travel the fastest (about 6 km/s in the continental crust) and arrive at the seismograph first.
  • S-Waves (Secondary): These are shear waves. They travel slower (about 3.5 km/s) and arrive second.

The Calculation: Because P-waves and S-waves travel at different speeds, the gap in time between their arrivals (the "lag time") increases the further you are from the earthquake. By multiplying the lag time in seconds by a velocity constant (typically around 8.4 km/s for average crust), seismologists can determine exactly how far away the earthquake originated!