Surface waves, specifically Rayleigh waves and Love waves, produce the most dramatic ground movements during an earthquake. These waves travel along the Earth’s surface rather than through its interior, and they carry the energy responsible for the violent shaking that topples buildings, opens fissures, and reshapes landscapes. While all seismic waves contribute to ground motion, surface waves arrive last but hit hardest.
Body Waves vs. Surface Waves
Earthquakes generate four main types of seismic waves, split into two categories. P waves (compressional) and S waves (shear) are body waves that radiate outward from the earthquake’s source and travel through the Earth’s interior. Love waves and Rayleigh waves are surface waves that travel roughly parallel to the ground.
P waves move fastest, reaching speeds of 5 to 7 km/s through typical crust and over 8 km/s in the mantle. They’re the first vibrations to arrive at any given location, which is why they’re called “primary” waves. But they’re also generally smaller in amplitude and higher in frequency than what follows. S waves arrive next, with larger motions. Surface waves arrive last, moving slower but displacing the ground far more violently. This is why earthquake shaking often starts as a subtle rumble and builds to intense jolting.
How Rayleigh Waves Move the Ground
Rayleigh waves force particles at the surface into an elliptical, rolling motion, similar to ocean waves but traveling through solid ground. The motion is retrograde, meaning the particles rotate in the opposite direction from the wave’s travel. This creates a combination of vertical and horizontal displacement that can lift and drop the ground surface in a rolling pattern. The effect is especially destructive to buildings because structures must absorb both up-and-down and back-and-forth forces simultaneously.
How Love Waves Move the Ground
Love waves produce a different kind of destruction. Instead of rolling, they jerk the ground sideways, perpendicular to the direction the wave travels. The motion is purely horizontal, similar to an S wave but confined to the surface. This snapping, side-to-side displacement is particularly damaging to the foundations of buildings and bridges, which aren’t designed to resist rapid lateral forces. Love waves are often the single greatest contributor to structural damage in shallow earthquakes.
Soft Soil Makes Everything Worse
The type of ground beneath your feet dramatically changes how intense the shaking gets. When seismic waves pass from hard bedrock into softer soil or sediment, they slow down and their energy gets compressed into larger motions. This is called site amplification, and the numbers can be striking. Studies of shallow bedrock sites in Japan found that soft soils amplified peak ground acceleration by factors of 3 to 6 compared to underlying rock. One site recorded amplification of over 6 times the bedrock motion.
This is why two neighborhoods in the same city can experience the same earthquake very differently. Areas built on fill, clay, or old lake beds shake far more than areas on solid rock. Basin-shaped geological formations, like those beneath Los Angeles or Salt Lake City, can trap and amplify seismic waves even further, focusing energy into certain areas. The USGS now incorporates 3D simulations of these basin effects into its national hazard models for cities like San Francisco, Seattle, and Portland.
When Shaking Triggers Ground Failure
At high enough intensities, surface waves don’t just shake the ground. They transform it. Two secondary effects account for some of the most dramatic ground movements ever recorded: liquefaction and earthquake-triggered landslides.
Liquefaction happens when strong shaking causes waterlogged, sandy soil to temporarily lose its strength and behave like a liquid. Buildings sink, underground pipes float to the surface, and the ground can spread laterally in a process called lateral spreading. The USGS models indicate that liquefaction is most likely where shaking is strong and the land is flat and wet. A minimum peak ground acceleration of about 0.1 g (one-tenth the force of gravity) is generally needed to trigger it, though the actual threshold depends on local soil conditions and water table depth.
Landslides are more likely where shaking is strong and slopes are steep. During large earthquakes, entire hillsides can collapse, burying roads and communities under millions of tons of debris. Both liquefaction and landslides can move the ground surface by meters in seconds, far exceeding the displacement from the seismic waves alone.
The USGS intensity scale reflects this progression. At intensity levels of VIII and above, structural damage becomes the primary measure of shaking severity. At the highest levels (X and above), the most spectacular ground failures, including visible surface faulting, massive landslides, and widespread liquefaction, become defining features of the event.
Tsunami Waves and Coastal Ground Movement
Seismic waves aren’t the only waves that reshape the ground. Tsunami waves, triggered by undersea earthquakes or landslides, carry enough energy to cause dramatic changes to coastlines. Their longer wavelengths, higher velocities, and ability to cross entire ocean basins with minimal energy loss give them destructive potential that far exceeds typical storm waves.
When a tsunami reaches shore, the primary effects include extensive flooding, powerful wave impacts, severe coastal erosion, and the transport of massive volumes of debris. Research on clifftop boulder deposits along Mediterranean coastlines has confirmed that tsunami waves can move multi-ton boulders from nearshore environments and deposit them on cliff tops tens of meters above sea level. The size and position of these boulders serve as geological evidence that tsunami forcing is the primary mechanism capable of producing such deposits. Impact velocity turns out to be the key factor in determining whether boulders get transported and how far they travel.
In this sense, tsunami waves produce some of the most dramatic ground movements of all, not through shaking, but through the sheer hydraulic force of water moving across land at high speed, stripping sediment, carving new channels, and rearranging the coastline in minutes.