Science says earthquakes can make the ground behave like a liquid: Why buildings can sink and here’s what happens beneath your feet

During a powerful earthquake, solid-looking ground can suddenly behave less like a stable foundation and more like a fluid. Buildings may tilt, roads can buckle, buried pipes can rise toward the surface and water mixed with sand can erupt through cracks.

This phenomenon is called soil liquefaction. Despite the name, the ground does not literally melt. Instead, intense shaking can cause loose, water-saturated sediments to lose much of their ability to support weight, temporarily behaving more like a liquid. The process is governed by a combination of pore-water pressure, effective stress and cyclic loading.

Science says earthquake shaking can destroy the strength of soil

To understand liquefaction, imagine a layer of loose sand whose individual grains are surrounded by water. Under normal conditions, the grains press against one another and their contacts help the soil support buildings and other loads.


An earthquake repeatedly shakes those grains. Because the shaking happens rapidly, water trapped between the particles may not have enough time to drain away. Instead, pore-water pressure rises.

As this pressure increases, the force carried directly through contacts between soil particles decreases. This is the basis of effective stress theory, a foundational concept in soil mechanics associated with Karl Terzaghi.


When effective stress becomes extremely small, the soil can lose much of its shear strength. In simplified terms, the grains become temporarily suspended in pressurized water rather than behaving as a stable framework.

What is effective stress theory?

The central relationship can be expressed as σ′ = σ − u, where σ′ represents effective stress, σ is total stress and u is pore-water pressure.

The equation explains why water pressure matters so much. If pore-water pressure rises while the total load remains similar, the effective stress holding the granular structure together decreases.

When earthquake shaking produces sufficiently high pore pressure, the soil's resistance to shearing can collapse.

This is why scientists do not describe liquefaction simply as “wet soil moving.” It is a stress-and-pressure problem involving the interaction between solid particles and pore fluid.

Why loose, waterlogged sand is especially vulnerable

Not every patch of ground can liquefy. The most susceptible materials are generally loose, saturated, granular sediments, particularly sands and silts under favorable conditions.

Young sediments deposited by rivers, beaches, floodplains and artificial fills can be especially vulnerable because their particles may have relatively loose arrangements and groundwater can occupy the spaces between them.

The National Academies explains the process using a simple physical picture: as shaking causes soil grains to lose contact, they can become suspended in water and the soil behaves more like a thick liquid until the particles settle again.

The 1964 Niigata earthquake showed the danger

One of the classic examples occurred during the 1964 Niigata earthquake in Japan. Liquefaction caused major ground failures, including the dramatic tilting and overturning of buildings. The phenomenon demonstrated that even structures that remain structurally intact can become dangerously unstable if the soil underneath them loses its bearing strength.


The U.S. Geological Survey identifies the Niigata earthquake as a major historical example of widespread earthquake-induced liquefaction.

The 1989 Loma Prieta earthquake provided another striking example. In San Francisco's Marina District, artificial fill placed over a former lagoon liquefied, producing subsidence, fractures and horizontal ground movement.

Christchurch revealed how widespread liquefaction can become

The phenomenon was also dramatically visible during the 2010–2011 Christchurch earthquakes in New Zealand.

The February 22, 2011 earthquake triggered extensive liquefaction, particularly in eastern Christchurch. Research found that liquefaction affected nearly 60,000 residential properties and buildings, while widespread ground deformation damaged infrastructure.

Sand and water erupted onto streets and through cracks in the ground, creating what are commonly called sand boils. These eruptions occur because elevated pore-water pressure can force water and sediment upward through fractures or permeable pathways toward the surface.

The ground can move sideways after liquefaction

Liquefaction does not only cause buildings to sink. It can also produce lateral spreading, in which blocks of ground move horizontally, particularly toward a river, shoreline or other free face. This can tear apart roads, bridges and buried utility lines even when the earthquake itself has stopped.

Research following Christchurch showed that lateral spreading was one of the important forms of ground failure associated with liquefaction.

Does the ground stay liquid after the earthquake?

Usually, no.

Liquefaction is generally temporary. Once shaking stops and excess pore-water pressure dissipates, the soil particles can settle back into contact and regain strength. However, the rearrangement can leave the ground permanently densified, settled or deformed.

That creates another hazard: buildings may experience differential settlement, meaning one part of a foundation moves more than another.

So the most accurate description is not that an earthquake turns the Earth itself into water. Rather, under specific geological conditions, a saturated granular soil temporarily loses the particle-to-particle forces that normally make it behave like a solid.

The result can look astonishingly fluid, but the physics begins with something much less visible: water pressure rising between grains of soil.

FAQs

What causes soil liquefaction during an earthquake?

Rapid cyclic shaking can rearrange soil particles and increase pore-water pressure. As pore pressure rises, effective stress falls, reducing the forces between soil grains and potentially causing severe loss of shear strength.

Can buildings sink during liquefaction?

Yes. When supporting soil loses strength or settles unevenly, buildings can tilt, sink or become severely damaged. Buried infrastructure can also be displaced or pushed upward.