It's induction, not electric. This happens with all my cast iron pans. Easiest way to see it is to boil a thin layer of water mixed with a little hand dishwashing liquid in it. There are clearly two rings where cavities are formed more easily, thus there are two circles of peaking foam.

Oh neat. I have a thermador star burner gas range that makes a wonderful five point star shape oil pattern on a cast iron using a similar technique. I can produce this effect by applying a very thin sheen of high smoke oil point at high heat.

No idea if that’s better for cooking than concentric rings, but it looks really cool.