Earthquake Hazards Explained: Ground Rupture, Liquefaction, Building Collapse and Infrastructure Failure

What Are Earthquake Hazards?

Earthquake hazards are the potentially damaging physical effects produced by fault movement and seismic shaking. Some occur directly at the fault, while others develop because shaking destabilizes soil, buildings, slopes, utility networks or coastal environments.

The earthquake itself is a geological event. A disaster occurs when that event interacts with vulnerable communities, weak buildings, unstable ground or critical infrastructure.

This distinction is important because earthquake magnitude alone does not determine the scale of destruction. A very large earthquake beneath a remote, sparsely populated region may cause relatively limited losses. A smaller but shallow earthquake beneath a dense city can become catastrophic.

Hazard, exposure and vulnerability

Hazard

The potentially damaging process, such as strong shaking, ground rupture or liquefaction.

Exposure

The people, buildings, roads, utilities and economic assets located in the affected area.

Vulnerability

How likely those people and structures are to be harmed when exposed to the hazard.

Modern earthquake-risk planning therefore considers more than the location of active faults. It also examines soil conditions, building types, population density, emergency access, utility networks and the possibility of several hazards occurring in sequence.

Primary, Secondary and Cascading Earthquake Hazards

Earthquake hazards are often divided into primary and secondary effects. In practice, however, major disasters usually involve a chain of interconnected failures.

For example, intense shaking may rupture a water main and a gas pipeline at the same time. The gas can ignite while the damaged water network leaves firefighters without sufficient pressure. Collapsed roads and bridges may then prevent emergency crews from reaching the fire.

This is known as a cascading disaster: the initial earthquake triggers a sequence of failures that becomes more damaging than any single hazard acting alone.

Ground Shaking: The Starting Point of Most Earthquake Damage

Ground shaking is the most widespread earthquake hazard. It occurs when seismic waves radiating from a rupturing fault travel through the Earth and move the ground beneath buildings, roads and infrastructure.

The severity of shaking at a particular location depends on several factors:

• earthquake magnitude;
• depth of the earthquake;
• distance from the ruptured fault;
• direction in which the rupture propagates;
• duration of fault movement;
• local soil and rock conditions;
• the frequency content of the seismic waves;
• the shape and depth of nearby sedimentary basins.

Strong shaking subjects structures to rapid horizontal and vertical acceleration. Buildings possess mass and inertia, so their foundations move with the ground while upper floors may initially resist that motion. This creates stress within columns, walls, beams and joints.

Long-duration shaking can be especially destructive because structures undergo repeated cycles of deformation. Even when individual movements are not enough to cause immediate collapse, repeated loading can weaken connections, crack concrete and produce cumulative damage.

Magnitude is not the same as shaking intensity

Earthquake magnitude describes the overall size of an earthquake and the energy released by the rupture. Shaking intensity describes how strongly the earthquake is experienced at a specific location.

The same earthquake can therefore produce violent shaking near the fault, moderate shaking farther away and unexpectedly strong shaking in distant areas underlain by soft sediment.

Ground Rupture

Ground rupture occurs when movement along a fault reaches the surface and permanently displaces the land. The rupture may appear as a sharp break, a series of cracks, a broad zone of deformation or a step-like scarp crossing the landscape.

Surface displacement can be horizontal, vertical or a combination of both, depending on the type and geometry of the fault.

• Strike-slip faults primarily move the ground sideways.
• Normal faults generally lower one block relative to another.
• Reverse and thrust faults push one block upward and over another.
• Oblique faults combine horizontal and vertical movement.

What ground rupture can damage

Structures positioned directly across an active rupture zone can be torn apart or displaced even when they are designed to resist strong shaking.

Ground rupture can:

• offset roads and railway lines;
• break pipelines and sewer systems;
• deform canals, levees and drainage systems;
• damage bridge approaches;
• split foundations;
• tilt or rotate structures;
• disrupt agricultural land and irrigation networks.

Flexible pipelines and specially designed fault crossings can accommodate limited displacement, but ordinary rigid structures are poorly suited to survive direct fault movement.

Fault rupture zones are not always narrow

A surface rupture is not necessarily a single clean line. Deformation may be distributed across a broad corridor containing cracks, folds, tilted blocks and smaller subsidiary faults.

This is why earthquake zoning often uses fault-rupture corridors rather than treating the fault as a perfectly precise line on a map.

Liquefaction

Liquefaction is a form of ground failure that occurs when loose, water-saturated sediment temporarily loses strength during earthquake shaking.

Although the soil does not literally melt, it can begin to behave more like a dense fluid than a stable foundation material. Buildings may sink or tilt, roads can buckle, buried structures may rise and riverbanks can spread sideways.

How earthquake liquefaction develops

Loose sand and silt contain grains separated by small pore spaces. When those pore spaces are filled with groundwater, strong shaking can cause the grains to rearrange.

The shaking increases pressure in the water between the grains. If the water cannot escape quickly enough, it begins to support more of the overlying load. Contact between the grains weakens, reducing the soil’s ability to support buildings and infrastructure.

1. Loose sediment is saturated with groundwater.
2. Earthquake shaking rearranges the soil grains.
3. Pore-water pressure rises.
4. Effective stress between the grains falls.
5. The sediment temporarily loses strength and stiffness.

Where liquefaction is most likely

Liquefaction is particularly likely in:

• river floodplains;
• deltas and estuaries;
• coastal plains;
• young lake deposits;
• reclaimed waterfront land;
• artificial fill;
• areas with shallow groundwater;
• loose sand deposited by rivers or waves.

Dense soil, well-cemented sediment and solid bedrock are generally less susceptible, although local conditions can vary over short distances.

Effects of liquefaction

Foundation settlement

Buildings may settle unevenly as the soil beneath them loses strength. This can produce tilted walls, cracked foundations and severe structural distortion.

Lateral spreading

Gently sloping ground or riverbanks may move horizontally toward an open channel, shoreline or depression. Even modest lateral movement can rupture bridges, roads and buried pipelines.

Sand boils

Pressurized water and sediment can erupt through cracks at the surface, producing small cones or patches of sand known as sand boils or sand blows.

Flotation of buried structures

Underground tanks, pipelines, manholes and other lightweight structures can rise toward the surface when the surrounding soil loses strength.

Loss of bearing capacity

Soil that previously supported a building, embankment or bridge pier may no longer carry the same load, causing sudden settlement or failure.

Can liquefaction be reduced?

Engineers can reduce liquefaction risk by densifying loose soil, improving drainage, lowering groundwater, mixing soil with stabilizing materials or transferring structural loads to deeper, stronger layers through piles.

The most effective approach depends on the soil type, groundwater conditions, structure and expected level of shaking.

Soil Amplification

Seismic waves do not produce the same level of shaking everywhere. Local geology can amplify, prolong or concentrate ground motion, making some neighborhoods experience significantly stronger shaking than nearby areas.

This phenomenon is commonly called site amplification or soil amplification.

Why soft soil can increase earthquake shaking

Seismic waves generally travel faster through hard rock than through loose sediment. When waves enter softer material, their velocity decreases. To transmit the seismic energy, the amplitude of the ground motion may increase.

Thick layers of clay, sand, gravel or artificial fill can therefore shake more strongly than nearby bedrock.

Sedimentary basin effects

Many major cities occupy valleys, coastal plains or sediment-filled basins. Seismic waves can become trapped within these basins, reflect from their edges and continue reverberating after the strongest direct waves have passed.

Basin geometry can also focus energy into particular areas. As a result, earthquake damage may form concentrated zones that do not correspond simply to distance from the epicenter.

Resonance between soil and buildings

Every soil layer and structure has natural vibration frequencies. Damage may become more severe when the dominant frequency of the ground motion approaches the natural frequency of a building.

Low-rise, mid-rise and high-rise buildings respond differently to different wave frequencies. A shaking pattern that strongly affects a tall building may have less effect on a short, stiff structure, and vice versa.

Why microzonation matters

Broad regional hazard maps are useful, but local soil conditions can change from one neighborhood to the next. Seismic microzonation divides cities into smaller zones based on expected shaking, soil response, liquefaction potential and slope instability.

This information can guide building codes, land-use planning, emergency preparation and the placement of hospitals, bridges and other critical facilities.

Building Collapse During Earthquakes

Building collapse is one of the principal causes of earthquake deaths and serious injuries. People are often harmed not by the moving ground itself, but by collapsing roofs, walls, floors, facades and unsecured structural components.

Whether a building survives depends on much more than its age or height. Design, materials, construction quality, maintenance, foundation conditions and the character of the shaking all matter.

Why buildings fail during earthquakes

Common causes include:

• insufficient lateral strength;
• poorly reinforced columns and joints;
• weak connections between roofs, walls and foundations;
• heavy roofs or upper floors;
• irregular floor plans;
• open ground floors with inadequate support;
• poor-quality concrete or masonry;
• corrosion, deterioration or unauthorized alterations;
• foundation settlement or liquefaction;
• construction that does not follow seismic codes.

Soft-story collapse

A soft-story building has one level that is significantly weaker or more flexible than the floors above it. This often occurs where the ground floor contains open parking, large shop windows or few internal walls.

During strong shaking, deformation becomes concentrated in the weak level. Columns can fail, allowing the upper floors to drop or tilt.

Pancake collapse

Pancake collapse occurs when vertical supports fail and floors fall onto one another. It can happen when columns lack adequate reinforcement, connections fail or a structure cannot carry redistributed loads after part of the building is damaged.

Unreinforced masonry failure

Brick, stone and concrete-block walls are strong under compression but weak when subjected to lateral forces. Without reinforcement and secure connections, walls may separate from floors and roofs or collapse outward into streets.

Adobe and earthen construction

Traditional adobe buildings can be highly vulnerable when walls are heavy, brittle and poorly connected. Seismic reinforcement, lighter roofs and stronger wall-to-roof connections can substantially improve performance.

Reinforced-concrete failure

Reinforced concrete can perform well when correctly designed and constructed. Failures occur when reinforcement is inadequate, columns are too weak, joints are poorly detailed or concrete quality is low.

Short-column effects, inadequate confinement and weak first floors can produce rapid structural failure.

Nonstructural hazards inside buildings

A building does not have to collapse to become dangerous. Falling ceilings, glass, shelves, lighting fixtures, pipes, equipment and facade elements can cause serious injuries.

Hospitals, laboratories, factories and data centers may remain structurally intact but become unusable when internal systems and equipment are damaged.

Infrastructure Failure

Earthquakes can disrupt the interconnected systems that keep modern communities functioning. Damage to one network can rapidly spread into transportation, health care, communications, water supply, energy distribution and emergency response.

Infrastructure failure often determines how quickly a region can rescue survivors and recover after the shaking stops.

Roads and highways

Roads can be damaged by surface rupture, settlement, liquefaction, embankment failure and collapsed overpasses. Cracked pavement may be relatively easy to repair, while displaced bridges and unstable slopes can isolate entire communities.

Bridges

Bridges are vulnerable to strong ground motion, foundation movement and displacement between adjoining spans. Older bridges may lack adequate restraints to prevent decks from moving off their supports.

Bridge foundations near rivers and coastlines may also be affected by liquefaction, lateral spreading and scour.

Railways and transit systems

Railway tracks can buckle, shift or become misaligned. Tunnels, platforms, elevated lines and electrical systems may also be damaged, preventing workers and emergency supplies from moving through a city.

Airports and ports

Runways built on reclaimed land can settle or crack. Port facilities are especially vulnerable because docks, cranes and fuel systems are often constructed on loose, water-saturated sediment.

Damage to ports can delay the arrival of heavy equipment, food, fuel and reconstruction materials.

Water and wastewater systems

Buried pipes may rupture where the ground settles, spreads laterally or crosses a fault. Loss of water pressure can interrupt drinking-water supplies, sanitation and firefighting.

Wastewater failures can release sewage into streets, rivers or coastal waters, creating additional public-health risks.

Gas and fuel networks

Broken gas mains, storage tanks and fuel pipelines can leak flammable material. Automatic shutoff valves, flexible joints and segmented networks can reduce the risk, but extensive ground deformation may overwhelm even well-designed systems.

Electricity

Power plants, substations, transformers, transmission lines and local distribution networks can all be damaged. Extended power outages affect hospitals, water pumping, refrigeration, communications and emergency coordination.

Telecommunications

Cell towers, fiber-optic cables, switching centers and backup generators may fail. Even when physical systems remain intact, networks can become overloaded by sudden demand.

Hospitals and emergency services

Hospitals may suffer structural damage, loss of power, water interruption or failure of medical equipment. Roads blocked by debris can delay ambulances, firefighters and search-and-rescue teams.

Infrastructure interdependence

Modern infrastructure systems rely on one another. Water utilities need electricity for pumps. Telecommunications require power and fuel for backup generators. Hospitals depend on roads, communications, electricity, water and supply chains.

Fire Following Earthquakes

Fire following earthquakes can become one of the most destructive urban consequences of strong seismic shaking. Numerous fires may start simultaneously while damaged roads, water systems and communication networks weaken the emergency response.

How earthquakes start fires

Common ignition sources include:

• ruptured natural-gas lines;
• damaged electrical wiring and transformers;
• overturned stoves and heating equipment;
• broken fuel pipelines;
• industrial chemical releases;
• damaged storage tanks;
• sparks from collapsing structures or electrical equipment.

Why post-earthquake fires are difficult to control

Firefighters may face many emergencies at once. Streets can be blocked by debris, bridges may be unusable and telephone networks may fail.

At the same time, ruptured water mains may reduce hydrant pressure. Strong winds can then carry flames between closely spaced buildings, particularly where combustible construction is common.

Urban conflagration

When individual fires merge and spread across a large area, they can create an urban conflagration. The risk is influenced by building density, construction materials, weather, road access and the availability of water.

Reducing the risk of earthquake fires

• automatic gas shutoff systems;
• flexible utility connections;
• segmented gas and water networks;
• seismically secured fuel tanks;
• redundant emergency-water supplies;
• fire-resistant building materials;
• rapid inspection of damaged electrical and gas systems;
• community emergency-response planning.

Related Earthquake Hazards: Tsunamis, Landslides and Rockfalls

Earthquakes can also trigger destructive processes beyond the fault zone. These hazards are covered in dedicated guides to avoid repeating the same material here.

Why Do Similar Earthquakes Cause Different Levels of Damage?

Earthquake magnitude is only one part of the damage equation. Two earthquakes with similar magnitudes may have completely different consequences because of their depth, location, rupture direction, local geology and the vulnerability of the affected communities.

Earthquake depth

Shallow earthquakes usually produce stronger surface shaking near the rupture than deeper earthquakes of comparable magnitude because seismic waves travel a shorter distance before reaching the surface.

Distance from the fault

Shaking generally decreases with distance, although local soil conditions and basin effects can produce pockets of unexpectedly strong motion farther away.

Rupture direction

A rupture can direct seismic energy toward certain areas. This effect, known as rupture directivity, may produce strong pulses of motion in the direction of fault propagation.

Duration of shaking

Larger ruptures can continue for a long time, repeatedly loading structures and increasing the likelihood of fatigue, cumulative damage and liquefaction.

Local geology

Soft sediment, reclaimed land and deep sedimentary basins can amplify shaking. Loose, saturated soil may liquefy, while steep slopes may fail.

Construction quality

Buildings designed and maintained according to modern seismic standards generally perform better than brittle, poorly reinforced or illegally modified structures.

Population density

A moderate earthquake beneath a dense urban area can affect far more people and structures than a stronger event in a remote region.

Time of day

Exposure changes throughout the day. Residential buildings may be full at night, while schools, workplaces and transportation systems may be crowded during daytime hours.

Preparedness and emergency response

Early warning, public education, emergency planning, redundant utilities and trained rescue teams can reduce casualties and improve recovery.

How Earthquake Risk Can Be Reduced

Earthquakes cannot be prevented, but their consequences can be reduced. The most effective strategies combine geological mapping, land-use planning, seismic engineering, infrastructure resilience and public preparation.

Seismic building codes

Building codes establish minimum requirements for structural strength, ductility, foundations and connections. Their effectiveness depends on accurate hazard maps, regular updates, skilled construction and consistent enforcement.

Retrofitting older buildings

Existing structures can be strengthened by adding shear walls, bracing, reinforced connections, column jackets, foundation anchors or other structural elements.

Retrofitting is especially important for unreinforced masonry buildings, soft-story structures, schools, hospitals and emergency facilities.

Ductile construction

Ductile structures are designed to deform without suddenly collapsing. Controlled deformation allows the structure to absorb and dissipate seismic energy.

Base isolation

Base-isolation systems place flexible bearings or sliding mechanisms between a building and its foundation. These systems reduce the amount of ground motion transferred into the structure.

Energy-dissipation devices

Dampers and other energy-dissipation devices absorb part of the earthquake’s energy, reducing structural movement and stress.

Ground improvement

Liquefaction-prone soil can be densified, drained, mixed with stabilizing material or bypassed using deep foundations.

Fault-rupture zoning

Restricting critical construction directly across active fault traces reduces exposure to permanent ground displacement.

Resilient infrastructure

Flexible pipelines, bridge restrainers, redundant transport routes, backup water sources and distributed power systems can limit cascading failures.

Securing nonstructural elements

Shelves, water heaters, ceiling panels, equipment, laboratory materials and heavy furniture should be anchored so they do not fall or move during shaking.

Planning for recovery

Communities need more than immediate emergency response. Recovery planning should address temporary housing, debris removal, business interruption, medical care, utility restoration and reconstruction.

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Frequently Asked Questions About Earthquake Hazards