Terremoto fa tremare New York

Pronome diretto L’
Direct object pronoun L’

“Molte persone l’hanno sentito”
(Many people felt it)

In this sentence, the word lo is a direct object pronoun and is taking the place of il terremoto.
Instead of repeating the noun, we use “lo” to avoid repetition and make the sentence more fluent.

Note that the pronouns lo and la can be shortened to l’ when they are followed by a verb that begins with a vowel sound (h, in this case).
Here are some more examples:

– Ho comprato un libro e l’ho finito subito (I bought a book and finished it immediately)
– Conosci Sofia? L’ho vista ieri al supermercato (Do you know Sofia? I saw her yesterday at the supermarket)