What do you call the instrument used to measure  and record earthquakes, explosions, and volcanic eruptions?

The instrument used to measure and record earthquakes, explosions, and volcanic eruptions is called a seismograph or seismometer.

A seismograph detects and records the vibrations caused by seismic waves as they travel through the Earth. It consists of a mass that is suspended freely; when the ground shakes, the mass moves, and the relative motion between the mass and the ground is recorded. This action produces a seismogram, which is a visual representation of the amplitude and frequency of the seismic waves.

Seismographs are crucial for understanding seismic activity, which can provide insights into the Earth's structure, the locations of fault lines, and the dynamics of tectonic movements. They are essential tools in seismology and are also used for real-time monitoring of events such as earthquakes, allowing for early warning systems to be established in earthquake-prone regions.