How many seismic stations are needed to determine the epicenter of an earthquake?

How many seismic stations are needed to determine the epicenter of an earthquake?

• A. 4
• B. 2
• C. 5
• D. 3

Answer: (D)

Triangulation using multiple seismic stations is how scientists determine the epicenter. Each station records when the P-wave and S-wave arrive. The difference between those arrival times grows with distance from the source, so from that time gap you can estimate how far the epicenter is from that station. That distance defines a circle on the map around the station where the epicenter could lie. With two stations, you have two circles that can intersect in two possible points (or none), which leaves ambiguity about the exact location. Adding a third station produces a third circle, and the single point where all three circles meet pinpoints the epicenter on the surface. More stations help reduce errors and improve precision.

Triangulation using multiple seismic stations is how scientists determine the epicenter. Each station records when the P-wave and S-wave arrive. The difference between those arrival times grows with distance from the source, so from that time gap you can estimate how far the epicenter is from that station. That distance defines a circle on the map around the station where the epicenter could lie. With two stations, you have two circles that can intersect in two possible points (or none), which leaves ambiguity about the exact location. Adding a third station produces a third circle, and the single point where all three circles meet pinpoints the epicenter on the surface. More stations help reduce errors and improve precision.