You can also put the Blur effect on the effects track, which is between track 1 and track 2 by default. Every clip above the effects track will be effected, in case you add video tracks.
Another option is to produce a video with one blur, then use that as the source to put another blur on it.
Gateway DX4380, AMD A8-5500 Quad Core 3.2GHz with ATI Radeon HD 7560D; 16GB RAM; 1 TB SATA 7200 RPM; Windows 8 Pro 64-bit; PDR11, PDVD12.