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One of the benefits of building with Insulated Concrete Forms is the ability to choose what level of seismic protection you prefer for your home or commercial building.  Few other construction technologies allow you the flexibility to build to the highest seismic protection standards, as with ICF.  We can build your structure to any of the top three strengths: Seismic C, Seismic D1, or Seismic D2, D2 being the highest standard in the International Building Code.

Western Washington is known as a "seismically active" area, although the hazard is not believed to be to the degree it is in San Francisco, Los Angeles, and southern California.  We don't know whether there will be a large earthquake in our lifetime, but those who prepare in advance are most assured to be safe.

Scientists at the U.S. Geological Survey, working with colleagues at the UW, gathered various earthquake studies and data done over more than a decade.  The information was used to run 540 quake simulations on a network of computers, over the equivalent of 25 days of computing time, to create what the scientists believe is one of the most sophisticated analyses ever done of a community's seismic hazard. (map, right)  The map, incorporating the site-sampling fieldwork of UW geologist Kathy Troost and many other colleagues, is based on a three-dimensional model of how all the different quakes would shake the region, and is intended to greatly increase the ability to determine how the quake threat varies according to geology, soil type, proximity to a fault and other factors.  For the latest seismogram of the geophone located closest to Seattle, click here.

The Puget Sound basin is at risk from three quake types:  The violent, shallow and so far distantly prehistoric quakes from the likes of the Seattle Fault;  the massive ones produced by the Cascadian Subduction Zone Fault off the coast (the last one was in 1700);  and the deep, generally milder but more frequent ones such as the 2001 Nisqually Quake.

A related analysis also indicates the potential for a destructive tsunami on Lake Washington, based on new data showing a fault cutting across the bottom of Lake Washington from Seward Park to Mercer Island, according to Craig Weaver, senior seismologist for the Geological Survey in Seattle.  He says this appears to be evidence of a large major quake long ago that created a localized tsunami, or seiche, in the lake, and that the size of the rupture on the lake bottom indicates that such a Lake Washington tsunami could be anywhere from 9 to 18 feet high.

The seismic hazard map does factor in the probability of specific events.  The Seattle Fault -- which actually is a series of many faults running east-west from Bremerton across Puget Sound, through Seattle and Redmond into the foothills of the Cascades -- has been estimated to produce a major quake perhaps every 1,000 years.  The Cascadian Subduction Fault, a massive fault off the coast of Washington and Oregon similar to the Sumatran Fault, which produced the 2004 Indian Ocean tsunami, is thought to rupture every 500 years or so.  Scientists have determined that its last major quake was in January 1700.  Deep quakes like the 2001 Nisqually take place maybe every 50 years.

We recommend that in designing your ICF building, your architect or engineer factor in the methods standardized in the International Building Code, and the HUD Prescriptive Method on which it was based.  As a side note, all else being equal a home with a basement is better anchored than one without, so we recommend this.  ICF basements are superior to standard-formed ones, as there is no sense of damp air or that 'basement feel' since ICFs seal and insulate the space.  And they cost about the same as conventional basement wall forming.

In general, Seismic C is the normal strength of new stick-built homes built nationwide.  This is the baseline standard.  Seismic D1 and D2 progressively increase the amount of reinforcing bar, methods of bending and placement, and addition of fittings to enhance strength.  HUD's Prescriptive Method was the first standard for ICF construction to seismic standards, and the International Building Code has now adopted HUD's recommendations.  These methods apply to a basic home of limited size, so larger homes and commercial structures should be engineered -- essentially an adaptation of the prescriptive methods to your project taking into account load calculations and stresses, by a licensed structural engineer.

The level of seismic strength, of course affects costs for materials and labor, but the extent depends on the complexity and size of the project.   We will gladly work with you and your consulting professionals in sorting out the best balance of strength versus cost for your project.


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