What information does a seismograph primarily record?

• A. The exact epicenter coordinates.
• B. Weather conditions at the time.
• C. Arrival times and amplitudes of seismic waves.
• D. Soil moisture content.

Answer: (C)

A seismograph records how the ground moves when seismic waves pass through the Earth. The most important information it provides is the arrival times of different waves (such as P-waves and S-waves) and the amplitudes of those waves at the recording site. The arrival times tell you how long the waves took to reach the instrument, which, when data from multiple stations are combined, allows scientists estimate how far the epicenter is and ultimately locate it. The amplitudes reflect how strong the shaking was at that location, relating to the event’s magnitude at that site. Weather conditions and soil moisture aren’t measured by a seismograph, and determining exact epicenter coordinates requires readings from several stations, not a single one.