On December 6, 2025, a powerful 7.0 magnitude earthquake struck Alaska. While quakes of that size draw attention, earthquakes occur far more often than many people realize. The United States Geological Survey (USGS) estimates that roughly 55 earthquakes happen every day worldwide, adding up to about 20,000 each year. Typically, one earthquake per year reaches a magnitude of 8.0 or higher, while around 15 others fall within the magnitude 7 range on the Richter scale, which measures the amount of energy released. In 2025 alone, an offshore 8.8 earthquake near Russia's Kamchatka Peninsula ranked among the 10 strongest earthquakes ever recorded, according to USGS.

Earthquakes can cause loss of life, destroy buildings and roads, disrupt economies, and leave lasting emotional scars on those affected. Their financial impact is also increasing. A 2023 report from USGS and the Federal Emergency Management Agency (FEMA) found that earthquake damage now costs the United States an estimated $14.7 billion each year. One major reason is that more people are living in regions where seismic activity is common.

Being able to forecast when and where a major earthquake will strike would greatly improve preparedness and reduce harm. Despite decades of research, scientists still cannot predict earthquakes with reliable accuracy.

Understanding the Ground Beneath Our Feet

While timing remains unpredictable, understanding what lies beneath the Earth's surface can significantly improve risk assessments. Kathrin Smetana, Assistant Professor in the Department of Mathematical Sciences at Stevens, explains that underground materials vary widely. "You may have layers of solid rock, or you may have sand or clay," she says. Because seismic waves move differently through each material, the type of subsurface strongly influences how shaking is felt at the surface.

How Scientists Image the Subsurface

To map these underground layers, researchers use a method known as Full Waveform Inversion. This seismic imaging technique helps reconstruct the structure of the subsurface by combining simulations with real earthquake data. Scientists first generate computer-based earthquakes and track how seismic waves travel through the Earth. They then analyze the simulated wave patterns at seismograph locations and compare them with real seismograms, which are graphical records of ground motion from actual earthquakes. After many rounds of refinement, the simulated data begins to closely match real observations, offering a clearer picture of underground conditions.

In practice, researchers begin with an initial estimate of the subsurface in a given area. They repeatedly adjust this model, running new simulations each time, until it aligns with real earthquake measurements.

"You compare the data from your computer simulation with actual data that you got from earthquakes," says Smetana. "This allows you to find out what the subsurface looks like and what effect an earthquake has on the composition of the subsurface -- and that ultimately, helps determine the risk for an earthquake at a certain location."