日本語版: 地震のあとの宅地・擻壁・斜面の点検ポイント
On July 28, 2026, a major earthquake measuring a maximum seismic intensity of 7 struck the Kumamoto region of Kyushu, Japan. Our deepest sympathies go out to everyone affected. We sincerely hope that calm and safe days return as soon as possible.
After a major earthquake, attention naturally focuses on building damage. But the ground itself — your yard, retaining walls, and nearby slopes — also changes, and that damage can progress silently through aftershocks and rainfall. This article explains, from the perspective of regenerative civil engineering and landscaping, what to observe on your property after an earthquake.
One thing first: never make the final safety judgment yourself. In Japan, municipalities operate post-disaster emergency risk assessment programs for buildings and residential land. Use them, along with qualified professionals. This article gives you the observational eye to stay away from danger — not to replace expert assessment.
An Earthquake Changes the Ground Below, Not Just the Structures Above
Seismic shaking alters the state of the soil itself. When water-saturated sandy ground is shaken violently, soil particles lose their interlocking structure and the ground behaves like a liquid — the phenomenon known as liquefaction. Valley-fill housing lots, where former valleys were buried with artificial fill, are particularly vulnerable: water naturally collects there, and deformation tends to appear at the boundary between cut ground and fill.
There is also a practical blind spot in conventional structural design: it considers soil mainly in terms of compressive strength, while the movement of water within the soil is rarely accounted for. When water stagnates behind a retaining wall or around a foundation, that trapped water becomes the source of localized liquefaction and of the lateral pressure that pushes walls outward during an earthquake.
Yet there is an encouraging observation as well. Excavations of roughly 800-year-old medieval castle earthworks in Japan have revealed structures of pine piles, interlocked logs, crushed stone and rice straw that survived centuries of earthquakes without liquefying. Structures that preserved pathways for water and air within the soil remained stable across enormous spans of time. How we treat soil and water underfoot determines the lifespan of the land above.
How to Inspect Your Property After an Earthquake
The following steps assume aftershocks have subsided. Do not inspect during ongoing aftershocks or rainfall.
Step 1: Observe the whole site from a distance
Before walking the grounds, view the entire property from a safe location such as the street. Look for three things:
- Any change in the tilt or alignment of buildings, fences and retaining walls
- New steps, ridges or depressions in the ground surface
- Changes in the angle of utility poles, gate posts, sheds — anything that used to stand vertical
Your sense that “something looks different” is the first sensor. Take photographs so you can compare after each aftershock.
Step 2: Read the ground — cracks, settlement, tilting
- New ground cracks, especially those running parallel to the top of a retaining wall or along the shoulder of a slope, may indicate ground movement
- Localized settlement: new gaps between concrete aprons and the soil
- Heaved manholes or drainage boxes: possible signs of liquefaction or ground subsidence
If you find a crack, do not lean over it or straddle it to measure it. Photographs from a distance are enough for documentation.
Step 3: Read the water — puddles, springs, wells
Underground change shows itself first through water. Field engineers read the subsurface the same way.
- Puddles forming in new places — or familiar wet spots suddenly dry — suggest that underground water paths have shifted
- New springs, especially mid-slope or at the base of a retaining wall, deserve careful attention
- Cloudy well water or changed water levels are clues that groundwater veins were affected
These signs do not automatically mean danger, but they are valuable information. Note the date, time and location, and share them when consulting your municipality or a professional — it greatly improves the accuracy of their judgment.
Retaining Walls, Stone Walls and Concrete Block Fences
These deserve the greatest caution, because collapse can occur with a time lag — after an aftershock or rainfall, not only during the main shock.
Before approaching: observe from a distance, top to bottom
Never approach a tilted wall, even on your own property. Binoculars or a smartphone zoom from several meters away are sufficient. Avoid standing on either side a wall could fall toward.
What to look for
- Bulging: outward swelling of the wall face signals rising earth or water pressure behind it
- Fresh cracks: cracks with clean, white fracture surfaces are likely new, unlike old weathered ones
- Weep holes: continuous flow, muddy discharge, or complete blockage with water pooling behind the wall all indicate changed water conditions in the backfill
For stone walls, check from a distance whether individual stones have loosened or soil is spilling from the joints.
Emergency repairs you should NOT attempt
- Do not try to brace a tilted wall yourself with ropes or props — the work itself is the most dangerous moment
- Do not seal cracks or weep holes with cement or soil; blocking the water’s escape route can raise pressure behind the wall
- Do not begin clean-up work above or below a retaining wall before it has been assessed
After the Shaking, Treat Every Slope as a Different Slope
A slope that endured strong shaking may look unchanged, yet fine cracks and loosening inside the soil mean it is no longer the same slope. When rain follows, water penetrates those cracks rapidly, and landslide risk rises well above normal. In summer, heavy rain and typhoon season overlap with the aftershock period — a combination that deserves respect.
Known warning signs of slope failure include:
- Small stones trickling down the slope
- New springs emerging mid-slope
- Streams or ditches suddenly turning muddy — or suddenly running dry
- Rumbling sounds from the ground or mountainside
If you notice any of these, stay away from the slope and follow your municipality’s evacuation information immediately. Remember that the absence of warning signs is not a guarantee of safety: base evacuation decisions on hazard maps and official information.
The Traditional Idea of Letting a Structure “Release” the Shaking
Finally, a perspective worth knowing when thinking about recovery and future building. To be clear: no construction method can be guaranteed safe against earthquakes. What follows is a difference in design philosophy, not a promise.
In traditional Japanese ishibadate construction, columns simply rest on foundation stones — they are not fixed to the ground. The timber frame, joined with penetrating tie beams, is designed to move slightly in the horizontal direction, releasing seismic energy rather than resisting it head-on. Temples and shrines built this way have stood for over a thousand years.
The same philosophy appears in traditional earthworks. The medieval castle embankments mentioned earlier — piles, interlocked logs, crushed stone and straw — do not fight the shaking with rigidity. They distribute forces through interlocking structures while preserving pathways for water and air in the soil. Stones that shift slightly re-seat themselves; roots and fungal networks bind the structure more firmly with each passing year.
Modern and traditional methods are not enemies. But knowing that an alternative philosophy — “allow movement and release the force” — has existed for centuries, and that it always treated water and air in the soil as essential, widens the options when recovery decisions must be made.
Frequently Asked Questions
Q. When should I inspect my property after an earthquake?
Wait until aftershocks have subsided and inspect during daylight in dry weather. Never inspect during ongoing aftershocks or rain. Start by observing the whole site from a safe distance, and never approach tilted walls or ground cracks.
Q. What should I do if I find a crack in my retaining wall?
Photograph it from a distance and request an assessment from your municipality’s post-disaster risk assessment program or a qualified professional. Do not seal cracks or weep holes with cement, as blocking drainage can increase pressure behind the wall.
Q. Which properties are most prone to liquefaction?
Water-saturated sandy ground is most vulnerable, particularly reclaimed land and valley-fill housing lots where former valleys were buried. Heaved manholes and sand boils on the ground surface are typical signs of liquefaction.
Q. Is it dangerous if puddles in my yard changed position after an earthquake?
Not necessarily dangerous by itself, but it is a clue that underground water paths have shifted. Record the date and location, and report it when consulting professionals, especially if new springs appear near slopes or retaining walls.
Summary
- Earthquakes change underground water flow. Record changes in puddles, springs and wells as information from below
- Inspect only when aftershocks and rain have passed, starting from a distance; photograph cracks and tilting without approaching
- Check retaining walls for bulging, fresh cracks and weep-hole changes — and never attempt DIY bracing or sealing
- A shaken slope is more vulnerable to rain. Know the warning signs, but base evacuation on official information
- Leave final risk judgments to municipal post-disaster assessment programs and qualified professionals
We pray for the earliest possible recovery of the affected areas. As people who work with soil, we hope that quietly sharing reliable knowledge can be of some help.