Final answer:
An older machine that detects seismic waves is known as a seismograph. These devices provide essential data for understanding Earth's structure by measuring seismic waves generated by natural events like earthquakes or human activities such as underground nuclear tests.
Step-by-step explanation:
An older machine that detects seismic waves is known as a seismograph. Seismographs are devices that measure the arrival times of earthquakes with precision, comparing the arrival times of S- and P-waves, which travel through the Earth at different speeds. These instruments play a crucial role in geophysical studies by providing data to help understand the Earth's interior and structure.
Geophones, similar to seismographs, are used in seismic surveys which help geologists and scientists in map out the Earth's subsurface by converting ground movement into voltage. Modern monitoring equipment, including seismographs and geophones, enables the detection and analysis of seismic waves generated by natural events like earthquakes or human activities such as underground nuclear tests.
Seismic waves provide valuable information because as they travel through different materials within the Earth, their velocity changes, thus helping to construct a model of Earth's interior, consisting of several layers with distinct compositions.