How many seismic stations are needed to triangulate an earthquake's epicenter?

How many seismic stations are needed to triangulate an earthquake's epicenter?

• A. 4
• B. 2
• C. 5
• D. 3

Answer: (D)

Locating an earthquake’s epicenter relies on overlaying distance estimates from multiple seismic stations. Each station records the timing difference between P-wave and S-wave arrivals, which lets scientists estimate how far away the quake happened. With two stations, you get two distance circles centered on each station. Those circles can intersect in up to two points, or not at all, so the exact epicenter isn’t uniquely determined. Three stations add a third distance circle; when the data are consistent, all three circles intersect at a single point, giving a unique epicenter on the map. Additional stations further improve accuracy and help constrain depth, but three stations are the minimum needed for a unique epicenter.

Locating an earthquake’s epicenter relies on overlaying distance estimates from multiple seismic stations. Each station records the timing difference between P-wave and S-wave arrivals, which lets scientists estimate how far away the quake happened.

With two stations, you get two distance circles centered on each station. Those circles can intersect in up to two points, or not at all, so the exact epicenter isn’t uniquely determined. Three stations add a third distance circle; when the data are consistent, all three circles intersect at a single point, giving a unique epicenter on the map. Additional stations further improve accuracy and help constrain depth, but three stations are the minimum needed for a unique epicenter.