Gas leak checks, structural damage inspection, aftershock readiness, and when to call a structural engineer — what to do in the hours after an earthquake.
The shaking stops. You get up. Now what?
The period immediately following a significant earthquake is one of the most hazardous intervals in the entire event. Gas leaks ignite. Aftershocks arrive. Damaged structures that appeared intact fail suddenly. Downed power lines are invisible in the dark. People who survived the earthquake are injured or killed in the aftermath by hazards they failed to check for.
A systematic, calm assessment of your situation in the minutes following an earthquake is not overcaution — it is the difference between a bad experience and a catastrophic one.
Household natural gas is odourised with mercaptan — the characteristic "rotten egg" or "sulphur" smell added deliberately to make leaks detectable. If you smell this odour in or around your building after an earthquake:
Do all of the following immediately:
If you do not smell gas but want to check, listen near gas appliances, gas metres, and gas lines for a hissing sound. A hissing sound near a gas line or appliance indicates escaping gas even without the smell being strong enough to detect (the odorant disperses quickly in open or well-ventilated spaces).
This is an important counterintuitive point: do not shut off your gas supply unless you have positive evidence of a leak (smell or sound). In a wide-area earthquake affecting many properties, gas utility teams will be overwhelmed restoring service. Unnecessary shutoffs contribute to service restoration backlogs that may leave you without gas for cooking, heating, and hot water for days or weeks while teams manage thousands of properties.
⚠️ Only shut off your gas main if you smell gas or hear a hissing sound. If you shut it off, do not turn it back on yourself — the utility company must restore service, relight pilot lights, and verify safety before reconnection.
If you evacuated your building during the earthquake or if you are assessing before re-entering after being outside, perform an exterior walk-around before going inside:
Foundation: Look for cracks wider than 6mm (quarter inch), sections that appear displaced or that have moved relative to the building above. Note the direction and location of any cracks.
Walls: A straight vertical wall that is now visibly leaning or bowing is a serious warning sign. Diagonal cracks from the corners of windows or door openings indicate structural movement (as opposed to settlement cracks, which are horizontal or vertical and often pre-existing).
Chimney: Look at the chimney — a partially collapsed or leaning chimney is a common earthquake casualty. Do not enter the building beneath a compromised chimney.
Damage tagging: In the aftermath of a major urban earthquake, structural assessment teams may tag buildings:
These tags are placed by qualified inspectors. Respect them absolutely.
If the exterior check did not reveal obvious hazards, you may enter — but do so cautiously:
Aftershocks are earthquakes that follow a mainshock — the earth's crust continues adjusting after the primary rupture. For a major earthquake (magnitude 7+), aftershocks can continue for weeks, months, or even years.
The general pattern:
Every time you feel shaking after a mainshock, apply DROP, COVER, HOLD ON exactly as for the mainshock. You cannot know in the moment whether a subsequent event is a "small aftershock" or the beginning of another major event.
Buildings that appeared structurally sound after the mainshock may be significantly more vulnerable to aftershocks because of internal damage not visible externally. A building that survived the mainshock with hidden structural damage may fail during a moderately sized aftershock.
This is a primary reason to have structures professionally assessed after any significant earthquake before continued occupation. Structural engineers conduct rapid post-earthquake assessments (RAPID evaluations) in affected areas. Contact your local emergency management office for information on assessment programmes following a major event.
Power lines down after an earthquake may be visible in daylight and invisible in the dark. Treat every downed line as energised.
Safe distance: Maintain at least 10 metres (30 feet) from any downed power line. Do not approach a power line that is:
Do not attempt to remove a downed power line with any object. Only authorised utility workers can safely handle energised lines.
Report downed lines to your electricity utility by phone from a safe distance. If a downed line is creating an immediate danger to life, call emergency services (911 in the US).
Major earthquakes routinely damage underground water mains. After a significant event, expect:
Safe water practices after earthquake:
Before water supply is confirmed safe by authorities, assume all tap water may be contaminated. Use your stored emergency water supply (the recommended minimum is 4 litres per person per day). Follow any boil-water orders issued by the water utility.
Large cracks, pavement collapse, or water erupting from the ground in areas where no pipes should be surface-visible are signs of major main failures. Report them to water utilities.
Chimneys are brick or masonry structures — among the most earthquake-vulnerable construction types. After a significant earthquake, chimneys can sustain damage that is invisible from the ground:
Do not use your fireplace, wood heater, or any appliance that uses a chimney until the chimney has been physically inspected from top to bottom by a chimney professional. A damaged chimney can result in carbon monoxide poisoning or chimney fire.
| Observation | Required Action |
|---|---|
| Any crack in foundation wider than 6mm | Structural engineer inspection before occupancy |
| Visible wall lean or bowing | Vacate and call structural engineer |
| Chimney partial collapse or lean | Do not use fireplace; call chimney professional |
| Door frames racked (doors will not open/close) | Structural engineer assessment |
| Floor feels soft or has obvious sag | Vacate; structural engineer required |
| Cracking at corners of door or window openings | Structural engineer assessment recommended |
| Building is tagged yellow or red | Obey tag — do not enter without authorised inspection |
| Building in soft-storey or URM category | Professional assessment after any significant earthquake |
| Pipes separated from walls | Plumber and potentially structural check |
| Large visible crack in ceiling | Do not stand beneath; assess with structural engineer |
| Situation | Action |
|---|---|
| Smell gas after earthquake | Exit without touching anything, call gas utility from outside |
| No gas smell, want to verify | Listen near appliances and lines for hissing |
| Gas shut off — want to restore | Call utility — do not restore yourself |
| Building has red or yellow tag | Obey the tag; do not enter without authorised inspection |
| Chimney appears damaged | Do not use fireplace until professional inspection |
| Aftershock occurs | Drop, cover, hold on — same as mainshock |
| Downed power line visible | 10 metre minimum distance; call utility |
| Tap water available but safety unknown | Use stored water; follow boil-water advisories |
| Foundation crack found | Structural engineer assessment before continued occupancy |
| Doors won't open after quake | Racking may indicate structural damage — engineer assessment |
| Ceiling sagging or cracked | Do not stand beneath; evacuate and get engineer assessment |
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