WASHINGTON — Mortgage rates experienced the biggest one-week drop in nearly four years after stock market volatility rattled investors.

According to the latest data released Thursday by Freddie Mac, the 30-year fixed-rate average sank to 4.81 percent with an average 0.4 point. (Points are fees paid to a lender equal to 1 percent of the loan amount.) It was 4.94 percent a week ago and 3.92 percent a year ago. The 30-year fixed rate has fallen to its lowest level in seven weeks.

The 15-year fixed-rate average dropped to 4.24 percent with an average 0.5 point. It was 4.36 percent a week ago and 3.32 percent a year ago. The five-year adjustable rate average fell to 4.09 percent with an average 0.3 point. It was 4.14 percent a week ago and 3.22 percent a year ago.

When the stock market is fitful, investors are inclined to park their money where it is safe, such as in long-term bonds. As demand pushes up bond prices, yields fall, and the yield on the 10-year Treasury has been in a persistent decline. It has receded for six straight days before plateauing at 3.06 percent on Tuesday. Because mortgage rates tend to follow the same path as bond yields, they also tumbled.

“The global rout of stocks has yet to subside – with stocks now down for the year – which caused mortgage rates to slide and approach the bottom of their recent trading range, as investors sought safer assets,” said Aaron Terrazas, senior economist at Zillow. “Despite a slew of strong economic releases over the past few months, especially in the labor market, investors appear to be growing increasingly wary of the global economy’s ability to maintain recent growth and are resetting their expectations accordingly. For now, however, rates remain near their highest levels since 2011 and a December rate increase [by the Federal Reserve] is all but inevitable.”

Home buyers hoping rates will continue to slide are likely to be disappointed. Bankrate.com, which puts out a weekly mortgage rate trend index, found that two-thirds of the experts it surveyed say rates will remain relatively stable in the coming week. Jim Burrington, a mortgage loan officer at Grande Financial, is one who predicts rates will hold steady.

“Mortgage rates are at their lowest point in a month,” Burrington said. “However, it seems like we have reached a temporary floor when it comes to mortgage rates and Treasury yields. Given how much they have dropped in the last week and the fact that there is a lack of data this week and that trading volumes will be light because of the Thanksgiving holiday, I don’t see much of a chance for further improvement.”

Meanwhile, mortgage applications were flat, according to the latest data from the Mortgage Bankers Association. The market composite index – a measure of total loan application volume – declined 0.1 percent from a week earlier. The refinance index fell 5 percent from the previous week to its lowest level since December 2000. The purchase index rose 3 percent.

The refinance share of mortgage activity accounted for 38.5 percent of all applications.

“The recent stock market volatility is likely causing some potential buyers to be more cautious,” said Mike Fratantoni, MBA’s chief economist. “Purchase mortgage applications continued their recent trend of falling slightly below year-ago levels.”