The continued and dramatic fall of mortgage rates this week led to a flood of refinance requests on Zillow Mortgage Marketplace, accounting for more than half of all requests. Refi requests are up 230 percent in the first half of December, compared with the first half of November.

The weekly average rates for 30-year fixed mortgages declined to 5.15 percent, down from 5.34 percent the week prior, according to the Zillow Mortgage Rate Monitor, compiled by leading real estate Web site Zillow.com(R). Rates for 15-year fixed mortgages decreased to 5.00 percent, down from 5.16 percent and 5-1 adjustable rate mortgages increased slightly to 5.94 percent from 5.93 percent.

Rates for 30-year fixed mortgages remained fairly steady on Monday evening with the average rate on Zillow Mortgage Marketplace at 4.98 percent.

At a state level, the 30-year fixed mortgage rate in Tennessee had the biggest decrease, falling from 5.40 percent to 5.09 percent. Rates on 30-year fixed mortgages were lowest in the states of Georgia (5.07%) and Tennessee (5.09%), while Illinois (5.27%) and New York (5.25%) had the highest rates.