Upper trigram
☳
Thunder · Zhen
Arousal and shock.
FamilyEldest son
ElementWood
Hexagram 54 of 64
☳☱ The Marrying Maiden
Entering a situation from a weak position.
Lower trigram
☱
Lake · Dui
Joy and openness.
FamilyYoungest daughter
ElementMetal
The image
Thunder above, Lake below.
Thunder over Lake: arousal and shock meeting joy and openness.
That combination is the whole meaning of hexagram 54. Nothing about it is arbitrary — change either trigram and you get a different hexagram with a different reading, which is why the 64 form a system rather than a list.