Mortgage rates posted a sharp decline, with the benchmark conforming 30-year fixed mortgage rate falling to 4.91 percent, according to Bankrate.com's weekly national survey. The average 30-year fixed mortgage has an average of 0.38 discount and origination points.

The average 15-year fixed mortgage dropped to 4.12 percent, and the larger jumbo 30-year fixed rate retreated to 5.46 percent. Adjustable rate mortgages were mostly lower also, with the average 5-year ARM sinking to 3.74 percent and the 7-year ARM pulling back to 4.10 percent.

Mortgage rates fell sharply, pulling back below the 5 percent mark for the first time in nearly two months. While mortgage rates had been lower in three of the past four weeks owing to concerns about Middle East tensions and the potentially negative economic consequences of higher oil prices, it was the unfolding tragedy in Japan that produced this week's movement. Concerns among investors about a potential nuclear meltdown and worries about slower global growth stemming from the devastating earthquake and tsunami in Japan, had investors piling into safe haven U.S. Treasuries, helping to drive mortgage rates lower. Mortgage rates are closely related to yields on long-term government bonds.

The last time mortgage rates were above 6 percent was Nov. 2008. At the time, the average 30-year fixed rate was 6.33 percent, meaning a $200,000 loan would have carried a monthly payment of $1,241.86. With the average rate now 4.91 percent, the monthly payment for the same size loan would be $1,062.67, a difference of $179 per month for anyone refinancing now.

SURVEY RESULTS

30-year fixed: 4.91% - down from 5.04% last week (avg. points: 0.38)

15-year fixed: 4.12% - down from 4.32% last week (avg. points: 0.38)

5/1 ARM: 3.74% - down from 3.88% last week (avg. points: 0.39)