Mortgage rates declined this past week as investors raced to Treasury bonds on concerns over the European debt crisis, Freddie Mac said Thursday. The government-sponsored enterprise released its primary mortgage market survey, which shows the 30-year, fixed-rate mortgage falling to 4%, the lowest reading since Oct. 6 when the rate hit a historic low of 3.94%. The 30-year FRM fell to 4% from 4.1% the prior week and 4.24% from a year earlier, Freddie said. The 15-year FRM hit 3.31%, down from 3.38% last week and 3.63% last year. The 5-year, Treasury-indexed hybrid-adjustable-rate mortgage averaged 2.96%, down from 3.08% last week and 3.39% a year earlier.  The 1-year, Treasury-indexed ARM fell to 2.88% from 2.9% last week and 3.26% a year earlier. Bankrate also reported plunging mortgage rates, noting that the conforming 30-year, FRM fell to 4.23% from 4.33% last week. In addition, the average 15-year FRM dropped to 3.48% while the larger jumbo 30-year FRM dropped to 4.81%. The 5-year ARM dropped to 3.18%, while the 7-year ARM declined to 3.37%. Write to Kerri Panchuk.