What instrument network records earthquakes to determine epicenters?

• A. Seismic network
• B. Magnetic network
• C. Solar observatory
• D. Gravity meter

Answer: (A)

The main idea is that locating an earthquake relies on measuring ground shaking with multiple instruments. A seismic network uses seismometers spread out over a region to record when the waves from an earthquake arrive at each station. Because P-waves arrive before S-waves and the difference in arrival times increases with distance, you can estimate how far away the epicenter is from each station. Each station therefore defines a circle on the map, centered at that station with a radius equal to the distance to the epicenter. When you have data from at least three stations, the circles intersect at the epicenter. This triangulation is what lets us pinpoint the epicenter quickly and accurately. Other networks—magnetic, solar observatories, or gravity meters—don’t track earthquake waves to determine epicenters, so they aren’t used for locating earthquakes in the same way.