A small earthquake and a subsequent aftershock lent an element of "surprise" to the overnight hours in a suburb west of Dallas. Authorities reported no serious damage from Saturday's late-night quakes, just cracked walls and pictures being knocked down. The unscathed Dallas-Fort Worth airport, near the epicenter, kept up with normal flight operations. And emergency officials said they had no indications of any injuries. The initial earthquake, measured at a preliminary magnitude of 3.4, struck at 11:05 p.m. Saturday and was centered about 2 miles north of the Dallas suburb of Irving.