Earthquake Risk : New Revised Data from USGS

The US Geological Survey organization – a government department that few of us think about, but which employs over 10,000 people in over 400 locations – has now revised its earlier 2008 earthquake risk projections.

The new projection shows heightened risk in some of the American Redoubt states, but some parts of the country have their risk downgraded, so overall, there is probably no significant change in national overall earthquake risk.

The areas of changed risk do not necessarily mean there have been changes in the underlying geological structures that cause earthquakes in those regions.  More commonly, it means that in the six years since the 2008 risk projections were published, there have been improvements in the data obtained and the understanding of earthquake causes, allowing for an improved projection of likely future earthquakes.

When you’re planning your retreat location, earthquake risk is of course a small factor to consider – both in general terms from the perspective of ‘might there be an earthquake here’ and in specific terms – are there potential risk factors immediately around your retreat location if a large earthquake were to occur.  It would be useful to check local records to see the potential risk for liquefaction in your area, and also to consider things such as if you’re downstream from a major dam that might break, if there is a bridge or other vital connection that could be destroyed and cutting you off from ‘the rest of the world’, etc.

The risk is also from smaller dams and structures failing – what say you have a small dam yourself as part of a micro-hydro power station.  Or a water tower.  And so on.

Also, of course, you should be sure to ensure that your retreat is built to fully comply with best earthquake resistant building practices, and that everything stored within it be reasonably secured so as not to be at risk in the event of a foreseeably strong earthquake (ie, don’t have glass jars of produce unsecured on an open top shelf of racking!).

Here’s a map showing which areas have had their risk increased and which areas have had their risk decreased (for one of several different earthquake measurement factors).

The sixteen states deemed at highest risk of a significant earthquake are (alphabetically) Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington, and Wyoming.

The full study covers nearly 250 pages and is a 113MB download from the USGS website.  The key summary information can also be found on the USGS site.