A thrust fault increases the thickness of the crust as it moves toward a continental interior in a mountain belt; yet the crust beyond the mountain front stays the same thickness. Isostasy would suggest that the area at the mountain front, where the thrust emerges, should over time.

subside

Explanation:

Isostasy is a geographical term which describes the condition of gravitational equilibrium that exists within the Earth's crust and mantle, there by, making the crust stays above a heights that relies on its physical attributes, such as thickness and density.

In Isostasy, its occurrence process involves principles of buoyancy in which an Earth crust apply stress on the less stronger mantle, such that for over a geological time moves laterally in a way that the load is contained by height adjustments.

Hence, Isostasy would suggest that the area at the mountain front, where the thrust emerges, should SUBSIDE over time.

there are 28 days in feb.