In the aftermath of the crisis in Japan, interest rates have fallen significantly across a wide range of markets, driving mortgage rates lower across the country.Mortgage giant Freddie Mac says the average interest rate for 30-year fixed-rate mortgages over the past week was just 4.76 percent, down 12 basis points from the previous week.Also, rates for 15-year loans fell from 4.15 percent to just 3.97 percent – the first time that rate had dipped below 4 percent since December. The interest charged for the adjustable-rate and hybrid loan products tracked by the report also fell.”With the crisis in Japan, investors rushed to buy the security of U.S. Treasury bonds , which lowered its yields and other interest rates as well. This allowed fixed mortgage rates to drift lower this week,” said Frank Nothaft, vice president and chief economist, Freddie Mac.The changes could make a significant difference for some of those looking at Houston homes for sale. Back on February 10, 30-year mortgage rates averaged 5.05 percent. Basing estimates on the February median price for local single-family homes – $151,900 – the current rate would save buyers more than $9,600 over the length of the loan.?