Quake Risk Maps
Most kinds of earthen walls can be safe without reinforcement if your location is white on the map above.
That is, assuming that if your building is built carefully with conservative plans (more walls than openings), great detailing, and you maintain it well.
In the gray areas? Look into your risk level and types of construction more carefully.
In the black? Well, better get to know an engineer. Just saying.
From 1992 to 1999 International scientists cooperated to develop a worldwide map of seismic risk. Yes, this Global Seismic Hazard Map (or GSHAP) data is now outdated. Better research is done all the time. But no other image shows so clearly the approximate range of risk.
The different levels of seismic hazard shown on GSHAP maps don’t relate to the levels that are critical for earthen buildings. So, using data for more than 100 cities in a 2013 US Army document, we revised the GSHAP.
Really, amateur seismic mapping? Well, it’s a start. Please, volunteer to do a better version using GIS software and/ or better engineering formulas!
Low-rise buildings are damaged most by short length quake vibrations (0.2 seconds long). Don’t worry about the slower 1 second vibrations that destroy skyscrapers.
Reputable earthen engineering guidelines (New Zealand has the closest thing to safe earthen building for dummies) show that unreinforced adobe or rammed earth of a basic strength soil with best detailing on reinforced concrete footings can survive to 0.6 g risk levels. In the light gray areas consider unreinforced earth
- if you are fussy and willing to check everything twice.
- Make sure each and every wall has long enough bracing walls turned sideways to it. (We’re working to make this a simpler process).
In the dark gray areas, always reinforce!
And reinforce correctly.
Earth walls won’t survive the possible quake unless they are reinforced well. New Zealand’s info sets a strength level good to their maximum risk. So if other types of earth walls reach this strength level, using the comparable adobe or rammed earth guidelines is our best guess.
In the black areas extra strength is a good thing. Some kinds of contained earth (improved earthbag) can probably make walls stronger than NZ’s reinforced adobe. But note that the Nepal 2015 quakes left 40 square miles of devastation. And it was only about half of what could be expected.
We’re hoping to develop some model plans for higher risk areas, but the quality of the soil under your footing or lots of other details can influence damage from a quake. If you can, talk it over with a local engineer when you want to build with natural materials in areas that have the highest seismic risk in the world.
Europe, Canada and the US are not included in our seismic risk maps because you can get local seismic risk info online.
If the map above shows your area in anything other than white, google search for or ask a local engineer or professor for a detailed country or region-wide seismic risk map (ask for a Ss peak ground acceleration map).