downthrown

Downthrown refers to a geological term describing the relative movement of rock blocks along a fault line. Specifically, in a downthrown block, the rock has moved downwards compared to the adjacent block. This movement is a result of tensional forces in the Earth's crust, which pull the crust apart, leading to the formation of faults.

When a fault occurs, the rock mass on either side of the fault plane can shift. If one side moves vertically relative to the other, it creates a displacement. The downthrown block is the side that has moved down. This contrasts with an upthrown block, which is the side that has moved up. The difference in elevation between these two blocks creates a scarp or cliff-like feature at the fault line.

Faults where downthrown blocks are present are commonly found in areas of extensional tectonics, such as rift valleys and basin and range provinces. These geological structures are crucial for understanding the formation of mountains, valleys, and sedimentary basins. The study of downthrown blocks helps geologists reconstruct past tectonic activity and predict future seismic events.