The idea is similar to what I did, except the circles are not filled, and there are two instead of one.
It seems that two circles grow from the center and then fade out, one slightly later than the other.
This can be done this way:
- create a circle
- turn off fill and turn on outline
- keyframe the radius (in the Inspector, under Shape->Geometry) so that it starts at 0, then add another keyframe at the place you want it to reach maximum value
- keyframe the opacity: add a keyframe for opacity, near the one where the radius is max, and set it to 100%; then move to where you want it to disappear, and set it to 0
Duplicate the circle, and drag the second one slightly to the right in the timeline. Done.
