I did some tests and to get that effect you need to use a
Jiggle Deformer insted of motionBlur.
Create a cube a make it the same way as the pic.
Then select the points selected on the pic and Create a Jiggle Deformer, whitch i under Deformation.
Set the attributes on that to 0.000 on everything except
the Jiggle Weight, set that to something like 0.700.
Just use the lambert I've postet.
You can see the result here: