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Why do normal faults dip toward a graben?

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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.

A graben is a tectonic depression formed by the extension of the Earth’s crust, which causes a central block of rock to drop downward between two normal faults.12

These faults dip toward the graben because of the mechanics of crustal extension. As the surrounding crustal blocks diverge, the brittle crust fractures, and the central block—the hanging wall—slides down along the fault planes into the resulting gap. Because the hanging wall is the block located above the inclined fault plane, its downward movement relative to the footwall necessitates that the fault planes on either side of the block incline toward the center of the depression. This geometry creates the characteristic trough-like shape of a rift valley, where the central block is effectively "dropped" into the space created by the pulling apart of the lithospheric plates.12345