Which sequence correctly describes how scientists locate an earthquake epicenter?

Which sequence correctly describes how scientists locate an earthquake epicenter?

• A. Recorded by seismic network → estimate distance → triangulate the epicenter
• B. Estimate distance from a single station → draw circle
• C. Observe aftershocks → triangulate
• D. Use only felt reports to locate epicenter

Answer: (A)

Locating an epicenter relies on measurements from a network of seismic stations to turn arrival-time differences into distances and then intersect those distances to pinpoint the source. When an earthquake happens, P-waves and S-waves reach each station at different times. The difference in their arrival times gives an estimate of how far away the quake occurred from that station. That distance defines a circle around the station where the epicenter could lie. You need several stations, because each adds a circle, and where those circles intersect points to the epicenter. That combination of recording the event, estimating distances, and triangulating is the standard method. Using only one station leaves endless possible locations along a circle, aftershocks aren’t used to locate the main epicenter, and felt reports lack the precise geometric information needed to triangulate.