faultblock

A fault block is a large block of Earth's crust that is bounded by faults and has moved relative to adjacent blocks due to tectonic forces. The term is most often used for blocks separated by normal faults in extensional settings, but it also applies to blocks displaced by reverse or strike-slip faults in compressional or transtensional contexts.

Fault blocks form when brittle rocks break along faults under stress. In extension, normal faults accommodate widening of the crust, producing down-dropped blocks called grabens and the higher blocks between them are known as horsts. In compression, reverse or thrust faults can uplift blocks, creating elevated fault-block mountains. In many regions, multiple faults together segment the crust into a mosaic of interconnected blocks.

Typical fault-block landscapes feature elongated ridges and troughs, with sedimentary basins developing in down-dropped blocks. Blocks may tilt toward one side as displacements accumulate, and some blocks expose deeper basement rocks at the surface. The size of fault blocks ranges from local outcrops to extensive regional blocks spanning tens of kilometers.

Examples of fault-block regions include the Basin and Range Province of western North America, where widespread extension creates numerous grabens and horsts; the East African Rift System, which forms a mosaic of fault blocks in an active continental rift; and various fault-block uplifts and basins in Europe and Asia, such as regions within the Alpine and Anatolian contexts.

Fault blocks are fundamental to understanding crustal deformation, regional tectonics, and related hydrogeology and mineral systems, reflecting the balance of tectonic forces and crustal properties that shape regional landscapes.