Weekly unemployment claims fell to their lowest mark since February 2008, the Labor Department said Thursday. Claims fell by 5,000 to a seasonally adjusted 348,000, the lowest in four years, and the less volatile four-week average of applications fell to 355,000, also a four-year low. Applications have steadily declined since last fall, when hiring began picking up. From December to February this year, the economy added about 245,000 jobs a month, pushing the unemployment rate down to 8.3 percent, its lowest point in three years. The economy grew at 3 percent in the final quarter of last year, more than double the 1.7 percent of the previous quarter.