Earthquakes cause fires primarily by rupturing gas lines, toppling appliances, and damaging electrical systems, all while simultaneously crippling the water infrastructure firefighters depend on to respond. The shaking itself rarely produces a flame directly. Instead, it creates the conditions for ignition: fractured pipes leak fuel, downed power lines arc, overturned heaters meet combustible material, and broken water mains leave hydrants dry. What makes earthquake-triggered fires so destructive is not just how they start but how they cascade, spreading through neighborhoods that have already lost the ability to fight back.
Broken Gas Lines Are the Single Biggest Ignition Source
Natural gas flows through buried pipelines into homes, businesses, and industrial facilities under continuous pressure. When the ground shakes violently, those pipes can crack, separate at joints, or buckle entirely. The gas that escapes needs only a small spark to ignite, and earthquakes provide plenty of sparks: electrical short circuits in damaged wiring, pilot lights still burning in shifted appliances, or arcing from severed power lines. One risk assessment framework developed for urban gas networks specifically models the probability that earthquake-damaged gas and power infrastructure will interact to produce ignition across different land-use zones in a metropolitan area.1Crises in Oil, Gas and Petrochemical Industries. Explosion and fire following earthquake risk assessment of gas pipelines: a case study in an urban district The scenario is straightforward: a gas pipe cracks underground, gas accumulates in a confined space like a basement or utility room, and an electrical spark or open flame sets it off.
This is not just a theoretical concern. In virtually every major urban earthquake of the past century, ruptured gas mains have been identified as a leading cause of post-earthquake fires. The problem compounds quickly in older cities where gas infrastructure has degraded over decades and where pipe joints were not designed to flex with ground movement. Modern seismic-resistant pipeline joints can absorb some deformation, but vast stretches of older urban gas networks remain vulnerable.
Household Appliances That Become Fire Starters
Inside homes, the most common ignition culprit is surprisingly mundane: the gas water heater. These tall, narrow tanks are top-heavy and often poorly secured. Strong shaking can topple them, snapping the rigid gas supply line. Gas then pours out near the unit’s own pilot light or into a room where any electrical spark can set it off. After the 1992 Big Bear Lake earthquake in California, 11 out of 13 structural fires in the affected area were traced back to gas leaks from displaced water heaters, a rate of roughly 6 fires per 1,000 structures.2Earthquake Spectra. Residential Water Heater Damage and Fires following the Loma Prieta and Big Bear Lake Earthquakes That rate sounds small until you multiply it by a city with hundreds of thousands of buildings.
Water heaters are far from the only household risk. Gas stoves and ovens can shift off their connections. Furnaces in basements can crack their fuel lines. Space heaters, candles, and even fireplaces in active use at the time of a quake can ignite fallen curtains, furniture, or structural debris. The timing of an earthquake matters enormously for fire risk: a quake that strikes during dinner preparation, when stoves are lit and homes are occupied, produces far more ignition opportunities than one that hits at three in the morning when most gas appliances are off and most people are in bed.
Industrial Facilities and the Natech Problem
Some of the most dangerous post-earthquake fires originate not in homes but in refineries, chemical plants, and fuel storage facilities. Researchers have a term for these events: “Natech,” short for natural-hazard-triggered technological accidents. The concept captures something important. When an earthquake damages a facility that processes, stores, or transports flammable or explosive chemicals, the resulting fire or explosion is not simply a natural disaster anymore. It is a technological accident riding on the back of a natural one, and the combined impact on surrounding populations can be far worse than either event alone.3Heliyon. Chemical release risk assessment in earthquake: Natech event scenario
A vivid example came during the 2011 Great East Japan earthquake. At the Cosmo Oil refinery in Chiba, ground shaking buckled the support braces of a liquefied petroleum gas (LPG) tank, causing the tank to collapse entirely. The collapse ruptured connected LPG pipes, and the escaping gas quickly ignited into a major refinery fire that burned for ten days and became one of the most dramatic images of the disaster.4Natural Hazards. Impact of the 11 March 2011, Great East Japan earthquake and tsunami on the chemical industry The fire was not caused by the tsunami that followed the earthquake; the ground shaking alone was enough to destroy critical structural supports.
Indonesia has experienced a pattern of similar cascading failures. The 2018 Palu earthquake, a magnitude 7.5 event, destroyed fuel depots and small industries and triggered secondary fires from infrastructure collapse, contributing to economic losses exceeding $911 million. Subsequent earthquakes in the Indonesian archipelago disrupted ammonia storage and nickel smelter operations, revealing that the country’s extractive industries remain seismically fragile and often lack standardized rapid-shutdown protocols for high-risk facilities.5PubMed Central. Enhancing geohazard-based natural hazards triggering technological accidents’ preparedness: A policy framework in Indonesian context
Why Earthquake Fires Spread So Fast
A fire that starts after an earthquake faces almost none of the barriers that normally keep urban fires contained. The first and most critical missing barrier is water. Water distribution networks are buried underground, exactly where seismic forces are most intense. Pipes crack, joints separate, and pumping stations lose power. A study on urban water system resilience noted that the Pan-American Health Organization has identified earthquakes as having the most destructive potential of any natural disaster for water networks, in part because the damage is underground and hard to detect or repair quickly.6PubMed Central. Urban water supply systems’ resilience under earthquake scenario The 1906 San Francisco earthquake is the most famous illustration: one minute of shaking destroyed thousands of water pipes, and the resulting shortage of water for firefighting allowed a fire to burn for three days, killing hundreds and causing enormous property damage.
The second missing barrier is access. When buildings partially collapse, the debris spills into streets and blocks the roads that fire trucks need. Research on post-earthquake road blockage has confirmed that accumulated debris can severely impair evacuation and emergency response operations.7Earthquake Engineering & Structural Dynamics. Probabilistic Prediction Model of Debris Extent and Blockage Fragility Estimation for Post‐Earthquake Road Networks A separate study modeling road disruption from building damage underscored that one of the primary consequences of blocked roads is the obstruction of firefighting services specifically.8Reliability Engineering & System Safety. Predicting road blockage due to building damage following earthquakes So even when fire crews are available and hydrants have water, they may not be able to reach the fire.
The third factor is building density and construction type. A study assessing fire-following-earthquake risk at the regional level found that the overall fire risk was shaped by a complex interaction between how densely buildings were packed together and what proportion of them were built with fire-resistant materials.9PubMed Central. Static analysis-based rapid fire-following earthquake risk assessment method using simple building and GIS information Dense neighborhoods of older wood-frame construction are the worst-case scenario: fires jump between closely spaced buildings before anyone can intervene. Neighborhoods with more modern concrete or steel construction, spaced further apart, resist fire spread far more effectively even when individual ignitions occur.
Electrical Systems and Restored Power
Electrical failures during an earthquake create immediate ignition risks through arcing, short circuits, and downed power lines contacting flammable material. But there is a less obvious hazard that comes after the shaking stops: power restoration. When utility crews bring electricity back online to a neighborhood, current flows into buildings that may have sustained hidden damage. Wires inside walls may be frayed, insulation may be compromised, and junction boxes may have been loosened from their mountings. Restoring power to a structurally damaged building can create new ignition points hours or even days after the earthquake itself.
This delayed ignition is one reason post-earthquake fire counts often continue climbing well after the shaking ends. Residents who return home and flip breakers back on, or utility crews re-energizing grid sections without building-by-building inspection, can inadvertently start fires in structures that survived the quake itself but were not safe to re-electrify. The lesson from past earthquakes is that electrical ignition is not a single-moment hazard but an extended one, stretching across the entire recovery period.
Automatic Shutoff Devices and How Well They Work
One of the most practical defenses against post-earthquake gas fires is the automatic seismic shutoff valve. These devices are installed on gas meters or at key points in a gas distribution system and are designed to close when they detect shaking above a certain threshold, cutting fuel supply before a leak can form. Research into these devices has found that the probability they will actually trigger during an earthquake depends heavily on the strength of the shaking. At a peak ground acceleration of about 0.23g (where g is the force of gravity), there is roughly a 50% chance the valve will activate. At 0.31g, that probability climbs to about 90%.10Earthquake Engineering & Structural Dynamics. Probability of actuating a seismic shutoff device
Those numbers reveal both the promise and the limitation. In a strong earthquake close to the epicenter, where ground acceleration is high, the valves work reliably. But in moderate earthquakes or areas farther from the fault rupture, the shaking may be strong enough to damage gas connections without being strong enough to trip the shutoff. This gap is significant because moderate earthquakes are far more common than large ones, and they still break gas lines. Some jurisdictions, including parts of California, require these valves on all new gas meter installations, but vast numbers of older homes remain unequipped. Retrofitting is straightforward and relatively inexpensive, but uptake has been slow outside of mandated areas.
How Fire Risk Models Try to Predict the Damage
Because post-earthquake fires are so destructive and so dependent on local conditions, researchers have built models that try to predict where fires are most likely to start and how far they will spread. One approach uses simple, publicly available building data like construction year, occupancy type, number of stories, and total floor area, combined with geographic information systems, to estimate ignition rates and fire-spread patterns at a regional level. A study that applied this method to Pohang City in South Korea developed a cluster-based model for estimating how much area would burn, calibrated against historical fire-following-earthquake data.11Scientific Reports. Static analysis-based rapid fire-following earthquake risk assessment method using simple building and GIS information
These models matter for practical planning. Emergency managers use them to pre-position firefighting resources, identify neighborhoods most vulnerable to fire spread, and plan evacuation routes that account for likely road blockages. The models are also used in building codes and urban planning: if a model shows that a particular district’s fire-following-earthquake risk is driven primarily by the density of older wood-frame buildings, that finding can inform decisions about retrofitting programs, building spacing requirements, or where to invest in fire-resistant construction.
Why Some Earthquakes Produce Firestorms and Others Produce Almost None
Not every earthquake leads to significant fires, and the reasons are worth understanding because they reveal how much of the fire risk is controllable. Several factors combine to determine whether a given earthquake will spark a city-scale conflagration or just a handful of small blazes:
- Time of day: Earthquakes during cooking hours, heating season, or periods of high gas and electricity use produce far more ignition opportunities than those during warm-weather nights when appliances are off.
- Wind conditions: Post-earthquake fires in calm air tend to stay localized. Strong winds can turn isolated fires into fast-moving urban firestorms, as happened in both San Francisco in 1906 and Tokyo in 1923.
- Water system integrity: Cities with earthquake-resilient water networks, including flexible pipe joints, backup pumping capacity, and dedicated firefighting water reservoirs, can suppress fires before they merge and spread.
- Gas infrastructure age: Older cast-iron and unreinforced concrete gas mains are far more brittle than modern polyethylene or welded steel pipes. Cities that have not upgraded their gas networks face disproportionate fire risk.
- Building stock: A city dominated by fire-resistant concrete and steel structures with adequate spacing will see far less fire spread than one packed with older wood-frame buildings, even if the same number of ignitions occur.
- Emergency access: Narrow streets, unreinforced masonry buildings that shed debris across roadways, and bridges or overpasses that collapse all impede the firefighting response that would normally contain small fires before they grow.
This list explains why two earthquakes of similar magnitude can produce wildly different fire outcomes. A magnitude 6.7 quake under a modern city with updated gas lines, automatic shutoff valves, and a resilient water network might produce a dozen small fires that are quickly controlled. The same magnitude under a densely packed older city with aging infrastructure and narrow streets could produce hundreds of ignitions that merge into an uncontrollable urban fire.
What You Can Do About It
If you live in a seismically active area, the most effective single step you can take to reduce post-earthquake fire risk in your own home is securing your water heater. Strapping it to the wall with earthquake straps prevents the toppling that leads to gas line rupture and is required by code in many earthquake-prone regions. Installing a seismic gas shutoff valve on your gas meter adds another layer of protection, automatically cutting fuel supply during strong shaking. Both measures are inexpensive relative to the damage they prevent.
Beyond individual homes, the larger picture involves infrastructure choices that communities and governments make: upgrading brittle gas mains to flexible materials, building dedicated high-pressure firefighting water systems independent of the domestic supply, enforcing building spacing and fire-resistance standards in dense neighborhoods, and keeping emergency access routes clear of structures likely to collapse into the street. The research on fire-following-earthquake risk consistently points to the same finding: the earthquake provides the shaking, but the fire risk is largely a function of how the built environment was designed, maintained, and prepared. Cities that invest in seismic resilience across gas, water, electrical, and transportation systems see dramatically less fire damage than those that treat earthquake and fire as separate problems.
The Overlooked Role of Aftershocks
Most discussions of earthquake-caused fires focus on the initial event, but aftershocks extend the hazard window considerably. A structure that survived the mainshock with minor gas line damage may have a slow leak that goes undetected in the chaos. An aftershock hours or days later can widen that crack, increase the flow rate, and create the conditions for ignition in a building that was not on anyone’s list of damaged properties. Similarly, firefighting water systems that were patched or jury-rigged after the mainshock may fail again during a strong aftershock, leaving crews without water at exactly the moment new fires are starting.
Aftershocks also affect the electrical restoration problem. A building cleared for re-electrification after the mainshock may sustain additional structural movement during an aftershock, damaging wiring that had been intact during the initial inspection. For this reason, seismic engineers generally advise that gas and electrical systems in damaged areas should remain off until the aftershock sequence has substantially decayed, a recommendation that is easy to make in a report and extremely difficult to follow in practice when displaced residents are desperate to return home and restore normal life.