How Earthquakes Affect Buildings
- Craig Kaiser
- Oct 31
- 5 min read
Earthquakes are natural disasters that occur when two plates of the earth's crust suddenly shift and release energy. They can also be caused by human activity (referred to as 'Induced Earthquakes'). This sudden release of energy creates seismic waves that cause the ground to shake violently, resulting in damage to buildings, infrastructure and human lives. In this article, we will discuss how earthquakes affect buildings and what factors contribute to their vulnerability.
How Do Earthquakes Affect Buildings?
The intense forces exerted by seismic waves from earthquakes can manifest in several types of damage, ranging from cosmetic cracks to complete structural collapse. Earthquakes can cause a variety of damages to buildings, including:
1) Structural Failures
Buildings collapse during earthquakes because the shaking ground transmits forces the structure cannot withstand. This often results from poor design, inadequate materials, or weak foundations. Specific factors include structural weaknesses, building resonance with seismic waves, and liquefaction, which destabilizes foundations. The most severe damage involves the failure of primary load-bearing elements. A common example is a "soft-story" collapse, occurring in buildings with a large, open ground floor (like apartment buildings with parking garages or storefronts with large windows). The lack of interior walls makes the first floor less rigid, causing it to pancake under lateral stress. Another critical failure is pancaking, where connections between floors and columns fail, stacking the floors on top of one another.
2)Non-Structural Damage
Even if a building's frame remains intact, non-structural components can pose significant risks. Façades, plaster walls, ceilings, and large glass windows can break apart and fall, injuring people both inside and outside. Heavy fixtures, shelving units, and mechanical equipment can topple over. Broken gas lines can lead to fires, and ruptured water pipes can cause extensive flooding, compounding the initial disaster.
3) Foundation Damage
The ground itself can fail during an earthquake. Soil liquefaction is a phenomenon where saturated, sandy soil types temporarily lose their strength and behave like a liquid. Buildings on such soil can tilt, sink, or collapse as their foundations lose support. Earthquakes can also cause permanent ground displacement, creating cracks and fissures that can tear a building's foundation apart.
What Makes a Building Vulnerable to Earthquake Damage?
Not all buildings respond to an earthquake in the same way. Several factors determine a structure's ability to withstand seismic forces, like the building materials, structural design, soil type, and building age.
Building Materials: The materials used in construction play a huge role. Unreinforced masonry, such as brick or concrete block, is notoriously brittle and performs poorly during earthquakes. These materials can crumble under lateral stress. In contrast, materials with more ductility, like steel and reinforced concrete, can bend and deform without breaking, absorbing seismic energy more effectively.
Structural Design: A building's shape and layout are critical. Symmetrical, simple, and regular shapes tend to perform better than complex, irregular ones. Structures with large overhangs or significant variations in stiffness between floors are more susceptible to damage. The quality of the connections between beams, columns, and foundations is also paramount.
Location and Soil Type: Proximity to an active fault line is the most obvious risk factor. However, local soil conditions can amplify ground shaking. Buildings constructed on soft, loose soil will experience much stronger vibrations than those built on solid bedrock, even if they are the same distance from the earthquake's epicenter. As a result, building damage from earthquakes tends to be greater in areas with soft soils.
Age and Building Codes: Older buildings constructed before the implementation of modern seismic codes are significantly more vulnerable. These codes are regularly updated based on new research and lessons learned from past earthquakes, meaning newer buildings are generally much safer.
Buildings are considered safe during earthquakes if they are modern, well-designed, and constructed with strong, flexible materials like steel or reinforced concrete. Newer structures benefit from updated seismic codes, and those built on solid bedrock offer greater stability. In contrast, older buildings, particularly those made of unreinforced masonry, are at a higher risk of collapse.
How Do Buildings Handle Earthquakes?
Buildings handle earthquakes through specialized design and technology. These methods absorb, dissipate, or redirect seismic energy. Techniques include base isolation systems that decouple the building from its foundation, damping devices like pendulums or hydraulic pistons that absorb vibrations, and reinforced structures with flexible frames and bracing that allow safe movement.
Building Technologies for Earthquake Resistance
One of the most effective technologies is base isolation. The building is decoupled from its foundation using flexible bearings or pads made of rubber and steel. When the ground shakes, the isolators absorb most of the motion, allowing the structure above to remain relatively still. It's like putting the building on roller skates to let the ground move underneath it.
Dampers and energy dissipation is another technology used to mitigate the effects of earthquakes on buildings. Similar to the shock absorbers in a car, dampers can be installed within a building's frame. These devices, which often consist of pistons filled with oil or viscous fluid, absorb seismic energy and reduce the magnitude of vibrations. Another approach is using tuned mass dampers- massive pendulums or weights, often located at the top of a skyscraper, that are designed to swing in opposition to the building's sway, effectively canceling out the motion.
Building reinforcement and ductile design is another technique used to mitigate the effects of earthquake damage on buildings. Modern design focuses on creating a ductile structural system. This involves using steel frames that can bend without breaking and special reinforced concrete that includes carefully placed steel bars (rebar) to prevent concrete from shattering under tension. Special moment-resisting frames are designed with flexible connections that allow the building to sway safely.
How Strong Does an Earthquake Have to be to Destroy Buildings?
There is not one magnitude above which property damage can occur from an earthquake because there are other variables that play a role in the level of damage that an earthquake can cause. However, according to the U.S. Geological Survey (USGS), damage does not usually occur until the earthquake magnitude reaches somewhere above a 4 or 5.
How to Check Earthquake Risk
You can assess earthquake risk using tools like the FEMA National Risk Index or state-specific resources such as the USGS Earthquake Hazards Program and California Geological Survey's EQ Zapp application. These tools provide detailed hazard maps showing fault zones, liquefaction, and landslide risks for specific addresses, while the USGS website offers broader information on national earthquake hazards.
Another tool you can use to evaluate earthquake risks is LandApp. You can use our Earthquake Risk Heatmaps on our mobile app to view the highest and lowest-risk regions for earthquakes, with red indicating the highest risk and white indicating the lowest risk:
You can check your property's risk for earthquakes by getting a free LandApp Property Report. By assigning a risk score on a scale of 0 to 100, LandApp shows you how likely it is for you to experience an earthquake so that you can plan effectively and create a greater piece of mind:
