The focus or hypocenter, is the “birthplace” of the seismic event. When tectonic stress exceeds the friction holding a fault together, the rock fractures at this specific point. This rupture then propagates along the fault line. The focus is measured by its three-dimensional coordinates (latitude, longitude and depth). Understanding the focus depth is essential for disaster management; for instance, subduction zone earthquakes often have very deep foci, whereas transform fault quakes, like those on the San Andreas Fault, usually have shallow foci, making them much more dangerous to human infrastructure.