What is a seismograph?

A seismograph is specifically designed to detect and record the vibrations caused by seismic waves produced during earthquakes. When an earthquake occurs, the seismic waves travel through the Earth's crust, and the seismograph captures these movements, allowing scientists to analyze the intensity, duration, and location of seismic events. This information is crucial for understanding the behavior of earthquakes and improving safety measures in affected areas.

The other options mention different types of measurements that are not related to seismic activity. For example, measuring air movement over the oceans or water movement pertains to meteorology and oceanography, not earthquake monitoring. Additionally, while forecasting Earth movement is a related field (seismology), a seismograph itself does not forecast; rather, it records seismic activity after it occurs. Thus, the device's primary purpose is accurately represented by the correct choice, which focuses on its function related to earthquakes.