Falla Lago Fagnano, sección occidental

A fault line is a fracture in the Earth's crust where blocks of rock have moved relative to each other. Faults can be centimeters to thousands of kilometers long. Active faults are those that have moved in the geologically recent past and are likely to generate future earthquakes.

There are three main fault types: normal faults occur where the crust is being pulled apart (extensional); reverse (thrust) faults occur where the crust is being compressed; and strike-slip faults occur where blocks slide horizontally past each other. The San Andreas Fault is a famous strike-slip fault.

Active faults are identified through geological mapping, satellite imagery (InSAR), GPS measurements, trenching studies that reveal past ruptures in sediment layers, microseismicity monitoring, and historical earthquake records. A fault is typically considered active if it has moved within the last 10,000-100,000 years.

Fault creep is the slow, continuous movement along a fault without generating significant earthquakes. Some sections of faults like the San Andreas undergo aseismic creep at 1-3 cm per year, while locked sections accumulate stress that is released in larger earthquakes. Creeping sections are generally considered less hazardous.

Yes, earthquakes can trigger events on nearby faults through static stress transfer (changing stress on adjacent faults) or dynamic triggering (seismic waves from the first earthquake inducing slip). The 1992 Landers earthquake in California triggered increased seismicity on faults hundreds of kilometers away.