1)
What is the meaning of "Ro'ah Hisro'a'ah"?
1.
Rashi: It is an expression of breakage, like "Tero'em b'Shevet Barzel" (Tehilim 2:9).
2.
Malbim: This is the first stage of the breakage of the land. First there will be crevices due to the earthquakes.
2)
What is the meaning of "Por Hisporerah"?
1.
Rashi: It is an expression of crumbs.
2.
Radak: Also this is an expression of breakage, like "Atah Porarta v'Azecha Yam" (Tehilim 74:13). It is doubled to strengthen the great affliction that will be then on the entire land.
3.
Malbim: This is the second stage of the breakage of the land. It will crumble into fine pieces. Finally, "Hismotetah" - it will totally falter and be uprooted from its place.