Learn Farsi: در اثر زلزله، صخره کاملاً فرو ریخت. - As a result of the earthquake, the cliff completely collapsed.

Not quite. در اثر (dar asar-e) is a preposition meaning "as a result of" or "due to," which sets up the context for the whole action (the cliff collapsing). ناشی از (nâshi az) acts more like an adjective phrase meaning "resulting from" and usually describes a specific noun. For example, you would use ناشی از to say "the destruction resulting from the earthquake" (خرابی ناشی از زلزله).

How does the verb فرو ریخت literally translate?

It literally translates to "poured down." It is a compound verb made from the prefix فرو (down, into) and ریختن (to pour, to spill). When combined as فرو ریختن, it means "to collapse," "to crumble," or "to cave in" — a very visual way to describe a cliff falling apart.

Why does the word کاملاً have that double dash on the final letter?

That is the Arabic tanwin marker, pronounced as "-an". In Farsi, you can add the suffix اً to many Arabic-derived adjectives to turn them into adverbs. Here, the adjective کامل (complete) becomes the adverb کاملاً (completely).

What does the word اثر mean on its own outside of this prepositional phrase?

On its own, اثر (asar) means a "trace," "effect," or "impact," and is also commonly used to mean a "work of art." When used in the set phrase در اثرِ (linked with an ezafe to the next noun), it translates literally as "in the effect of," giving us the everyday meaning "as a result of."