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Why do some rift valleys have step-like sides and terraces?

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tectonic basins and rift valleys Escarpments of the Great Rift Valley rising above the plain north of Samburu Game Preserve, central Kenya. Beisa oryxes graze in the foreground.

Rift valleys form when segments of the Earth's crust subside between normal faults due to the extension of the lithosphere. While some rift valleys are bounded by single, steep walls, others feature step-like sides and terraces because the valley edges consist of multiple smaller inner blocks.123

In these areas, each small block drops downward relative to its neighboring outer block, creating a tiered or stepped appearance along the valley margins. This process means that the deepest part of the rift valley is not always located at its center. These structural characteristics are a direct result of the complex faulting that occurs as tectonic plates diverge, causing the crust to fracture and subside in a series of displacements rather than a single, uniform drop.314