(Update 1 reflects a corrected statement from Frank Nothaft.) Long-term mortgage rates plummeted in the past week following announcements that the Federal Reserve would begin buying housing-related debt and mortgage-backed securities from the GSEs, according to the Primary Mortgage Market Survey released Thursday by Freddie Mac (FRE). The 30-year fixed mortgage rate fell to 5.53 percent for the week ending Dec. 3, down significantly from last week's average of 5.97 percent and the last year's same-week average of 5.96 percent. The 15-year fixed mortgage rate averaged 5.33 percent, down from 5.74 percent last week. “After Federal Reserve actions to increase liquidity in the mortgage market, interest rates for fixed-rate mortgages took a dive,” said Frank Nothaft, Freddie Mac vice president and chief economist. “This week’s decline was the largest since the week of Nov. 27, 1981, and 30-year [fixed-rate mortgage] rates are now almost a full percentage point lower since the last week in October." Short-term mortgage rates also dropped, though not as severely, according to the survey. Five-year Treasury-indexed hybrid adjustable-rate mortgages (ARMs) averaged 5.77 percent this week, down from 5.86 percent last week. One-year Treasury-indexed ARMs averaged 5.02 percent this week, down from last week when it averaged 5.18 percent. A separate study agreed with the downward trends, although its numbers showed variance. Bankrate.com on Thursday released its own weekly survey, which showed the average 30-year fixed-rate fell 5 basis points, to 5.92 percent. The average 15-year fixed -- a popular option for refinancing, according to Bankrate's weekly mortgage interest rate roundup author Chris Kissell -- dropped 8 basis points, to 5.67 percent. The average jumbo 30-year fixed fell 9 basis points, to 7.46 percent. The survey found that adjustable-rate mortgages also fell significantly. The one-year adjustable-rate mortgage plummeted 21 basis points to 5.96 percent while the 5/1 ARM dropped 13 basis points to 6.14 percent. Both surveys attributed the decreases to the Fed's announcement it will buy up to $500 billion of securitized loans from Federal Home Loan Banks, Freddie Mac, Fannie Mae (FNM) and Ginnie Mae. Following these lowered rates on long-term mortgages, mortgage application volume increased, especially in the refinance sector, suggesting struggling homeowners are refinancing into mortgages with lower rates and more affordable monthly payments. The MBA’s weekly composite index of purchase and refinancing application activity -- released Wednesday -- rose sharply to 857.7 for the week ending Nov. 28, a shortened week due to the Thanksgiving holiday. The rise wasn’t enough to offset a yearly decline in application activity, however, with the MBA report that composite applications remained 21.9 percent below year-ago levels — meaning applications remain weak. Write to Diana Golobay at diana.golobay@housingwire.com. Disclosure: The author held no relevant investment positions when this story was published. Indirect holdings may exist via mutual fund investments. HW reporters and writers follow a strict disclosure policy, the first in the mortgage trade.