How do terraces form along the inner rim of a complex crater?

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four impact craters — Meteorite crater Four impact craters of the same size (30 km [20 miles] in diameter) imaged by spacecraft on different solid bodies of the solar system and reproduced at the same scale. They are (clockwise from upper left) Golubkhina crater on Venus, Kepler crater on the Moon, an unnamed crater on Jupiter's moon Ganymede, and an unnamed crater on Mars. The images are oriented such that the craters appear illuminated from the left; the Venusian crater is imaged in radar wavelengths, the others in visible light.

In the formation of a complex crater, the initial parabolic depression is often too large to remain stable. Consequently, the crater undergoes a modification stage, during which the structure collapses.1

Terraces along the inner rim are formed by downward faulting of large blocks of material as the cavity walls collapse toward the center of the impact site. In the case of exceptionally large craters, this process can produce even more extensive, widely spaced, inward-facing faults known as megaterraces, which develop well outside the original excavation cavity.1