Why some buildings collapse in an earthquake while others stay standing
The twin earthquakes that struck Venezuela on 24 June 2026, collapsing buildings across northern Venezuela, from Yaracuy state to Caracas, have revived a question that follows every major quake: why do some buildings fall while others nearby remain standing?
The remains of a collapsed building in Catia La Mar following the earthquakes that struck Venezuela on 24 June 2026. ( Photo: RatUnderground/Wikimedia Commons, CC BY-SA 4.0.)
Much of the answer lies underground. Two earthquake experts at NGI explain that the size of a quake is only half the story. The ground a building stands on, and whether it was designed for that ground, often decides whether it survives.
The Venezuela sequence was a so-called doublet: a magnitude 7.2 shock, followed only 39 seconds later by a larger magnitude 7.5, both well west of the capital. The damage was strikingly uneven. Some tall buildings in the city’s sediment-filled districts collapsed, while others nearby came through.
Brian Carlton, lead engineer and earthquake expert at NGI, and Jörgen Johansson, principal engineer in geohazards and dynamics at NGI, both study how the ground behaves when it shakes. A building’s fate, they say, is rarely sealed by the earthquake alone.
“It is the combination of how hard the ground shakes, what that ground is made of, and how well the structure was built for it,” Carlton says.
Both stress that they are describing the general mechanisms at work in any earthquake, not diagnosing why particular buildings in Caracas fell, which would require site-specific investigation. The same questions have followed the earthquakes in Peru in July and in Colombia and Indonesia in August.
“Most building damage is manmade. We have known how to design for earthquake shaking for a long time,” says Johansson.
However, some buildings, especially older ones, may have been built before modern seismic design requirements were implemented in the specific country.
“The date of implementation varies from country to country, and the earliest standards were born of disaster: Italy issued the world’s first seismic design regulations after the 1908 Messina earthquake, and Japan adopted the first national seismic code in 1924, following the Great Kantō earthquake,” says Johansson.
The collapsed General Hospital in Mexico City following the 1985 earthquake. The disaster demonstrated how local ground conditions can greatly influence earthquake damage. Photo: USGS/Wikimedia Commons, public domain. ( Photo: USGS/Wikimedia Commons, public domain)
When the ground amplifies the shaking
The most important geotechnical mechanism is resonance.
“Caracas sits in a deep basin filled with soft sediments, and when seismic waves pass from hard rock into that soft ground, the soil can amplify the shaking, in places by several times,” Carlton explains.
Both the ground and a building have a natural period, the rhythm at which each tends to sway:
“A tall building has a longer natural period than a short one. When the period of the soil matches the period of the building, the two reinforce each other and the shaking multiplies,” says Carlton.
Johansson offers an everyday comparison: “Think of pushing a child on a swing. If you push in time with the swing’s own rhythm, each small push builds on the last and the child soars higher and higher. Push at random, and nothing much happens,” he says.
This mechanism helps explain why damage often clusters in the deepest, softest districts, where the ground sways slowly enough to match the sway of tall high-rises, while shorter buildings and those on firmer ground are largely spared.
Carlton points to two well-studied precedents.
“In Caracas in 1967, buildings of a certain height on a certain thickness of soft soil failed far more than others,” he explains. The 1985 Mexico City earthquake showed the same effect. The defence is knowledge.
“A site investigation reveals the thickness of the soil and its natural period, so engineers can deliberately give a new building a different period from the ground beneath it and/or improve the ground to make it stiffer and stronger. Where resonance cannot be avoided, the building must be built stronger to absorb the heavier vibration,” says Johansson. Such structural reinforcement requirements are specified in engineering design standards like the Eurocode.
When firm-seeming ground turns to liquid
A second major mechanism that can bring buildings down is liquefaction.
“In loose, sandy, water-saturated ground, violent shaking raises the water pressure between the sand grains until the sand loses its strength entirely. The sand behaves like a very dense liquid. Buildings on top can settle, tilt, or collapse, and on sloping or waterfront ground, the liquefied layer can slide sideways, tearing foundations and buried pipes apart, and manholes may pop out of the ground,” says Carlton.
A third danger appears when the fault ruptures all the way to the surface and shifts the ground by several metres. Almost no structure can survive that. Carlton points to a stadium in California as an example of how engineers can design for it.
“California Memorial Stadium at Berkeley was built right across a known fault whose seismic hazard was not understood at the time. During a later retrofit, it was rebuilt as separate sections that can slide past each other without tearing apart,” says Carlton.
Collapse is often a human failure
Modern engineering can already design buildings to withstand enormous earthquakes. In Japan, Carlton notes, the skyscrapers of Tokyo withstood the 2011 Tohoku earthquake, magnitude 9.0 and one of the most powerful ever recorded, with minimal damage, because they were built for it. While the ground shaking was not very strong, its frequency was close to the vibration frequencies of the tall buildings, and it therefore caused them to sway for several minutes.
When buildings do fall, the cause is often human rather than natural.
“Almost every country has an adequate building code. The problem is that often, it isn’t followed either during design or construction,” says Carlton.
There can be several reasons why building codes are not consistently met. Compliance can be costly, oversight is not always complete, and older buildings may predate the current rules. Whether any of this played a role in Caracas is a question only site-specific investigation can answer. After the 2010 Haiti earthquake, which struck close beneath the capital, destruction was widespread because buildings had not been raised to the standards seen in countries like Japan or the United States.
Apartment buildings tilted after the ground beneath them liquefied during the 1964 Niigata earthquake in Japan. Photo: USGS/Wikimedia Commons, public domain. ( Photo: USGS/Wikimedia Commons, public domain)
Built right, a building can ride out the largest quakes
The reassuring corollary is that a properly designed building can survive even the most violent shaking.
“It may be a horrible experience for the people inside, because it will vibrate or swing a lot, but the building will at least not fall on them,” says Johansson. Another important aspect of seismic safety is to fasten furniture to walls and floors so that it cannot fall on people.
To understand why buildings are not always damaged, Johansson suggests keeping seismic shaking in perspective.
“The magnitude is like the size of a bomb, but the bomb could be one kilometre away or a thousand kilometres away,” he notes.
What truly matters for a structure is the shaking it actually experiences, which depends as much on the distance from the source as it does on the magnitude itself. Depth matters too. A shallow quake directly beneath a city can shake it far harder than a deeper one of the same magnitude, because the energy has less distance to travel before it reaches the surface. Peru saw both within weeks: a magnitude 5.5 quake near Huancayo in July collapsed hundreds of homes, while a magnitude 6.7 quake some 100 kilometres beneath southern Peru in August left only scattered damage.
None of these geotechnical principles mentioned above are new discoveries. The mechanisms that bring buildings down in an earthquake have been understood for decades, and the underlying insight, that what a building stands on matters as much as how it is built, is far older still. What the 2026 Venezuela twin earthquakes show, once again, is how much the ground beneath a building matters. Even so, engineers do not know everything. Structures were damaged in Japan in 2011 as well, and that is why the research goes on.
“There was an earthquake in India in the 1800s, and the houses built on rock survived while the ones on soft ground collapsed. Even 200 years ago, people understood how important the soil is,” Carlton concludes.
