U.S. foreclosure actions firmly centered around Sun Belt states in 2009 but activity spread to previously insulated areas, and unemployment became the biggest driving factor, RealtyTrac said on Thursday.

Cities in four Sun Belt states accounted for all top 20 foreclosure rates in 2009 among metropolitan areas with a population of 200,000 or more, the Irvine, Calif.-based real estate data company said.

California accounted for nine of the top 20 metro foreclosure rates, followed by Florida with eight, Nevada with two and Arizona with one, the company said in its Year-End 2009 Metropolitan Foreclosure Market Report.

Outside these states, the highest-ranked was Boise City-Nampa, Idaho, at No. 24 with 4.66 percent of its housing units receiving at least one foreclosure notice in 2009.

"The first wave of foreclosures was driven by home prices that were unsustainable and unbelievably poor lending practices, but now we have a second wave of foreclosures that it is being driven by unemployment," Rick Sharga, senior vice president at RealtyTrac, said in an interview.

"Foreclosures will likely increase in some of the secondary markets that are the most heavily impacted by unemployment," he said.

Unemployment started driving foreclosures in late 2009 and will not crest until the end of 2010, he said.

While unemployment is expected to peak in the first quarter, most believe it will take a long time before actual jobs return, which should prolong a peak in foreclosures.

"Areas like Provo, Utah, Fayetteville, Ark., Portland, Ore., and Rockford, Ill., all posted foreclosure rates above the U.S. average in 2009," James J. Saccacio, chief executive officer of RealtyTrac, said in a statement.

"And markets like Honolulu, Minneapolis and Seattle saw foreclosure activity increase at more than twice the national pace over the past 12 months — although all three of those markets still had 2009 foreclosure rates that were at or below the U.S. average," he said.

Negative equity has also been one of the biggest banes of homeowners, making many unqualified for home loan refinancing and preventing some from selling.

Borrowers in negative equity, meaning they owe more on their mortgage than their home is currently worth, are more prone to defaults and foreclosures.

Las Vegas posted the nation's highest metro foreclosure rate for the year, with more than 12 percent of its housing units receiving a foreclosure notice in 2009 — more than five times the national average.

Las Vegas, however, reported a quarter-over-quarter decline in foreclosure activity in the fourth quarter, as did all other metro areas with foreclosure rates ranking among the top 10.

Filings include notice of default, auction sale or bank repossession.

Banks' government-mandated efforts to rescue millions of distressed homeowners has slowed the flow of foreclosures hitting the market.

Sharga said a third wave of foreclosures should emerge in the second half of 2010. This will be driven by a deluge of interest rate resets on adjustable-rate mortgages and a crest will not be reached until next year, he said.

"In the coming years the housing market should be marginally better, but it will probably take until 2013 to reach a full recovery," he said.