It is the buildings that kill
Seismologists often say that earthquakes do not kill people, buildings do. Ground shaking itself is rarely lethal in the open; the danger comes from structures that cannot withstand the forces and collapse on their occupants. Whether a building survives depends on how it was designed, what it is made of, and the ground it stands on.
This is why two buildings side by side can meet very different fates in the same quake. One built to modern seismic standards may sway and survive, while an older or poorly built neighbor crumbles. Understanding these differences is the foundation of earthquake-resistant engineering.
How shaking attacks a structure
Earthquakes shake the ground back and forth, mostly in horizontal directions. Most buildings are designed primarily to carry vertical loads, their own weight and gravity, so the sudden sideways forces of a quake are what they struggle with. These lateral forces can crack walls, snap columns, and tear a structure apart if it lacks the strength and flexibility to resist them.
Brittle materials are especially vulnerable. Unreinforced masonry and poorly built concrete crack and shatter under lateral stress because they cannot bend. A dangerous failure mode is the soft story, where a ground floor with large open spaces, such as parking or shopfronts, is too weak to resist sideways motion and collapses, bringing the floors above down with it.
What makes a building earthquake-resistant
Good seismic design lets a building move with the earthquake rather than rigidly resisting it. Engineers add ductility so structural elements can bend and absorb energy without breaking, and they create continuous load paths so forces flow safely down to the foundation. Reinforced concrete, steel framing, and cross-bracing all help a structure flex and stay standing.
Advanced techniques go further. Base isolation places a building on flexible bearings that decouple it from the shaking ground, while damping systems act like shock absorbers to soak up energy. These methods, used in hospitals, bridges, and skyscrapers in seismic zones, can keep a building fully functional even after a strong quake.
Soil, codes, and retrofitting
The ground beneath a building matters enormously. Solid bedrock transmits less damaging motion, while soft, water-saturated soils can amplify shaking or even liquefy, losing strength so that buildings sink or topple. Site conditions are therefore a critical part of any seismic assessment. Widespread liquefaction was a defining feature of the 2011 Christchurch earthquake, where it buried entire suburbs in silt and left thousands of homes unrepairable.
Modern building codes encode hard-won lessons from past disasters, and countries that enforce them rigorously, such as Japan and Chile, see far fewer collapses. For older buildings, seismic retrofitting, adding braces, reinforcing walls, or strengthening soft stories, can dramatically improve survival. The gap between well-enforced codes and their absence is often the difference between a scare and a catastrophe.