1992 Lincoln Cent off-center question.

This is a 1992 Lincoln Cent off-center strike, but why is the MD zinc instead of copper? I know very little, obviously, about off-center strikes, but this puzzles me. Thanks
Jim
When a man who is honestly mistaken hears the truth, he will either quit being mistaken or cease to be honest....Abraham Lincoln
Patriotism is supporting your country all the time, and your government when it deserves it.....Mark Twain
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Comments
The copper plated 'split' from the zinc planchet
due to striking pressure outward.
A fairly common occurrence on some off center
and broadstruck cents.
What @FredWeinberg said.
Interesting effect.
@FredWeinberg .... Thanks for the explanation. Cheers, RickO
You can see that effect on the reverse of my off center as well.
Thanks to all, but especially @FredWeinberg and @TurtleCat. I just had never seen that effect before. Of course, I am not a collector of these type error strikes, so a learning post.
Jim
When a man who is honestly mistaken hears the truth, he will either quit being mistaken or cease to be honest....Abraham Lincoln
Patriotism is supporting your country all the time, and your government when it deserves it.....Mark Twain