Short answers, pulled from the story.
A fault is a planar fracture in rock volumes where significant displacement has occurred due to the immense pressures of plate tectonics. These features are the primary architects of the Earth's surface topography and the source of the most destructive natural disasters.
Friction and rock rigidity prevent the two sides of a fault from gliding past each other easily, creating regions of higher friction called asperities where movement stops and stress builds up. When the accumulated strain energy exceeds the strength threshold of the rock, the fault ruptures, releasing the stored energy in part as seismic waves that form an earthquake.
The hanging wall occurs above the fault plane, while the footwall occurs below it, a distinction that is critical for distinguishing different dip-slip fault types such as reverse faults and normal faults. In a reverse fault, the hanging wall displaces upward, while in a normal fault, the hanging wall displaces downward.
Strike-slip faults, also known as wrench faults, have a surface that is usually near vertical, with the footwall moving laterally either left or right with very little vertical motion. Those with left-lateral motion are known as sinistral faults, and those with right-lateral motion as dextral faults, each defined by the direction of movement of the ground as would be seen by an observer on the opposite side of the fault.
Geologists assess a fault's age by studying soil features seen in shallow excavations and geomorphology seen in aerial photographs, using subsurface clues such as shears and their relationships to carbonate nodules, eroded clay, and iron oxide mineralization to distinguish active from inactive faults. In California, for example, new building construction has been prohibited directly on or near faults that have moved within the Holocene Epoch, the last 11,700 years of the Earth's geological history.
Many ore deposits lie on or are associated with faults because the fractured rock associated with fault zones allows for magma ascent or the circulation of mineral-bearing fluids. Intersections of near-vertical faults are often locations of significant ore deposits, such as the northern Chile's Domeyko Fault with deposits at Chuquicamata, Collahuasi, El Abra, El Salvador, La Escondida, and Potrerillos.