Earthquake Distance Calculator

Epicenter distance from P-wave and S-wave arrival times.

S-P time interval (seconds)

P-wave velocity (km/s)

S-wave velocity (km/s)

Tab to move between fields

Distance to epicenter (km)

252

Distance (miles)156.59

Distance (degrees)2.27

P-wave travel time (s)42

S-wave travel time (s)72

Verified S-P interval (s)30

How to Use This Calculator

Read the seismogram and measure the S-P time interval — the gap in seconds between the first P-wave and first S-wave arrival.
Enter the P-wave velocity (km/s) for the local crust; the default 6.0 km/s is a typical continental average.
Enter the S-wave velocity (km/s); 3.5 km/s is standard for continental crust.
The calculator returns the Distance to epicenter (km). Use readings from three stations to triangulate the exact epicenter location.
Check the Verified S-P interval output — it should match your measured interval, confirming consistent inputs.

How the result changes with S-wave velocity (km/s)

S-P time interval (seconds): Time difference between S-wave and P-wave arrivals on the seismogram.
P-wave velocity (km/s): Compressional wave speed. Typical crustal average is ~6.0 km/s.
S-wave velocity (km/s): Shear wave speed. Typical crustal average is ~3.5 km/s.

Distance to epicenter (km): Estimated distance from the seismograph station to the earthquake epicenter.
Distance (miles): Epicentral distance converted to miles.
Distance (degrees): Epicentral distance in degrees of arc (~111.19 km per degree).
P-wave travel time (s): Time for the P-wave to travel from the epicenter at the given velocity.
S-wave travel time (s): Time for the S-wave to travel from the epicenter at the given velocity.
Verified S-P interval (s): Cross-check: S travel time minus P travel time (should match your input).

Identify Input Parameters
S-P time interval (seconds) = 30, P-wave velocity (km/s) = 6, S-wave velocity (km/s) = 3.5 = 3 input(s) provided
Calculate Distance to epicenter
Distance to epicenter = (vp * vs / (vp - vs)) * spInterval
252 = 252
Calculate Distance
Distance = distanceKm * 0.621371
156.59 = 156.59
Calculate Distance
Distance = distanceKm / 111.19
2.266 = 2.266