Geophysics is a quantitative natural science that uses physics-based tools to study Earth processes and structures. With highly precise tools, we can reveal things that are far too subtle to observe ourselves. Satellite measurements of gravity can show mass changes as an ice sheet shrinks or as groundwater is depleted during a drought. The laser light in a fiber optic cable on the seafloor can be used to detect offshore earthquakes—or the songs of passing whales. The navigation satellite signal reaching a GPS receiver can tell us how much water vapor is in the atmosphere overhead. The possibilities are expanding all the time.

This means that geophysics is a broad field with many applications and subdisciplines. Two large disciplines with long histories are seismology and geodesy.

Seismology

Seismology is the scientific study of earthquakes and their environmental effects, such as tsunamis and landslides. Seismologists aim to understand where and why earthquakes occur where they do. One of the main pieces of evidence for plate tectonics was the observation that earthquakes tend to occur on plate boundaries where plates move relative to one another. Another aspect of seismology is the study of how the elastic waves generated by earthquakes travel through the Earth. Seismic data has provided evidence of the Earth’s structure, like the fact that the Earth has a solid inner core and a liquid outer core. But it can also tell us about much smaller features, like the bedrock layers below a town, the conditions at the base of a glacier, or changing groundwater levels.

Geodesy

Geodesy is the science of extremely accurate measurements of Earth’s shape, gravity, and orientation—everything from the coordinate system that underlies all navigation and positioning to detecting the warning signs of a volcanic eruption. The tools of geodesy let us measure moving tectonic plates, rising sea level, shrinking glaciers, soil erosion after a wildfire, or groundwater overuse during a drought. They can also be used for emerging applications like autonomous vehicles and precision agriculture.

Instruments that measure very precise positions using GPS satellites (or multiple satellite networks, more generally termed GNSS for “Global Navigation Satellite System”) are among those tools. There are also satellites that can measure tiny surface changes, like InSAR (Interferometric Synthetic Aperture Radar) satellites. And lidar devices on the ground or in the air use lasers to generate 3D imagery that also quantifies small changes over time. These are just some of the technologies that geodesists use to study our dynamic planet.

Go deeper

This section of our website is meant to help you learn more about all these techniques and applications of geophysics. Use the links below to learn more—either by starting with specific hazards or applications of geophysical tools, or by diving straight into a specific technology.