Question

Which statements concerning how geologists locate an earthquake’s epicenter are accurate? Check all that apply.

Geologists use seismic waves to locate the center of an earthquake.
The epicenter of an earthquake is located at the same place as the seismograph.
Geologists use data from two data stations to determine the location of an earthquake.
Geologists use data from three or more data stations to determine the location of the epicenter.
A seismograph measures the difference between the arrivals of P waves and S waves.

Answer 1

Correct choices:
- Geologists use seismic waves to locate the center of an earthquake. — True. Seismic (P and S) waves recorded at stations are used to find where the quake originated (hypocenter/epicenter).
- Geologists use data from three or more data stations to determine the location of the epicenter. — True. Distances from three stations are needed to triangulate a single epicenter location.
- A seismograph measures the difference between the arrivals of P waves and S waves. — True (practically). A seismograph records the arrival times of P and S waves; the time difference is measured from that record to compute distance to the quake.

Incorrect:
- The epicenter of an earthquake is located at the same place as the seismograph. — False. The seismograph is just a recording station, usually far from the epicenter.
- Geologists use data from two data stations to determine the location of an earthquake. — False. Two stations give two possible locations (ambiguous); a third is needed to pinpoint the epicenter.