What happened on this byzantine gold coin ?

Hi, everyone, I have just bought a half-gold Byzantine nomisma, and it has some kind of "ripple" on the edge of the emperor's bust (I circled the area). I wonder what might cause this, or could it be a soft strike?

And the gold content of this coin is supposed to be around 50% to 70% (the rest being silver), but its surface luster seems very similar to that of pure gold to me. So I wonder if there is any way to distinguish electrum from pure gold only by sight?

Could anyone share some opinions?

The formation technique for these scyphate coins is believed to have involved striking the top (concave) die obliquely twice, from opposite directions.  That gives opportunity for all kinds of strange effects, though usually on the side with Christ..  Often the lettering out toward the edge of the struck up part of the coin looks kind of smeared.   

I can't say exactly what happened, but it's part of the character of these coins to have imperfections of various kinds due to that unusual process.