Breakdown of Al parecer, el bombazo arruinó la fiesta anoche.
la fiesta
the party
anoche
last night
arruinar
to ruin
el bombazo
the bombshell (news)
Questions & Answers about Al parecer, el bombazo arruinó la fiesta anoche.
The current lesson is about por cierto and a propósito. Could I use one of them here instead of al parecer?
You could, but it would change the meaning entirely. Al parecer is an epistemic marker meaning "apparently"—it shows you are sharing something you deduce but aren't entirely sure of. If you used por cierto or a propósito (by the way), you would be abruptly changing the subject to drop this gossip about the party as a digression.
Does bombazo mean a literal explosion here?
It could in a news report, but in social contexts, it is usually figurative. A bombazo is a "bombshell"—a shocking piece of news or a massive surprise. It is formed by adding the suffix -azo (which indicates a blow, strike, or something huge) to bomba (bomb).
Why is al parecer used instead of just saying aparentemente?
Both mean "apparently" and are completely interchangeable in this context. Al parecer is simply a very common fixed phrase in Spanish, built from al and the infinitive parecer, functioning exactly like an adverb to express probability.
Why is arruinó in the preterite here rather than the imperfect?