What is the main grammatical and rhetorical role of zilzālahā in 99:1?

Supplementary Practice 25 — Comparative Rhetoric of Sūrat az-Zalzalah and Sūrat al-ʿĀdiyāt

• A cognate accusative highlighting the exceptional shaking
• A circumstantial accusative specifying the earth’s color
• A direct object describing an action upon another body
• The predicate of inna reinforcing a previous noun