Tuesday, April 8, 2008

FEMA Projects A 6.0 Quake On West Valley Fault Could Inflict $2.5 Billion Damage In Salt Lake City-Ogden Metro Area

The 6.0 earthquake that rocked Wells, Nevada in February 2008 has spawned research into the probable impact of a similar quake along Utah's Front Range, particularly in Salt Lake, Davis, and Weber Counties. And both the Salt Lake Tribune and KSL Channel 5 report on April 8th, 2008 that a new analysis of a magnitude 6.0 earthquake on a fault that lies just west of Interstate 215 - the West Valley Fault - provides some sobering projections:

- 16 to 17 people would die in an area from Weber County through Salt Lake County and 9 to 20 would sustain life-threatening injuries.
- Homes and businesses would suffer about $2.5 billion in damage.
- About 1,004 buildings would be unsalvageable, another 11,074 would have extensive damage and 73,979 would show slight or moderate damage.

The Federal Emergency Management Agency (FEMA) and earthquake experts at the University of Utah have sketched out the scenario in the weeks since the 6.0 quake rocked Wells, Nevada and left some buildings in ruins.

Bob Carey, earthquake coordinator for the Utah Department of Homeland Security, will present the findings on April 8th at the Top of Utah's Ready Your Business Conference at the Ogden Marriott. Carey expects that a map he's produced will be a vivid education tool.

Click HERE to view map. The map shows the most widespread damage (light or greater) in Salt Lake City proper, West Valley City, and a strip including Granger-Hunter-Kearns-Magna. However, the are of the valley expected to receive heavy damage is concentrated in the Downtown Salt Lake area, Rose Park, and Glendale. In contrast, the area least likely to sustain noticeable damage is the southwest part of the Salt Lake Valley from West Jordan down to Herriman.

But the reason for this expected pattern is not just geological. It's also structural. The aforementioned areas are the oldest parts of the valley, with the oldest buildings. And a high percentage of the homes and other structures were constructed with unreinforced masonry (URM).

According to the scenario, all but five of the projected 1,004 destroyed buildings would be brick or another type of unreinforced masonry. And all but 259 of the projected 11,074 extensively damaged buildings would be unreinforced masonry, the study estimates. And all of the projected deaths would come in "URM's," as the buildings are called.

And the likelihood of a 6.0 earthquake in the Salt Lake Valley is roughly 20 percent in the next 50 years, or about 1 in 250. But the "good" news, if you can call it such, is that this would not be the "big" one. That's because the West Valley Fault is not the primary fault.

The primary fault is the Wasatch Fault along the east side of the valley, evidence of which is visible particularly as you drive along I-15 through North Salt Lake and Woods Cross. In April 2006, the Deseret Morning News published a five-part analysis of the potential impact of a 7.0 quake along the Wasatch Front. They estimate this quake would cause 6,000 fatalities, 90,000 injuries, and inflict a $40 billion economic hit. And, like the West Valley Fault scenario, the most widespread and severe damage would involve unreinforced masonry structures. The first report is published HERE. Here are the remaining reports:

Unreinforced Masonry, April 17th, 2006
Shaken To Pieces, April 18th, 2006
Neighbors Mobilize, April 19th, 2006
Ready For Big Quake, April 20th, 2006

And, like in the West Valley scenario, the southwest part of the Salt Lake Valley would be directly impacted the least as well.

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