Focus: earthquake originates from certain point underground.
Epicenter: the nearest point from the focus on the ground.
Focal depth: distance from focus to epicenter.

According to the focal depth, the earthquake is classified into: shallow-focus earthquake (0-60km); intermedite-focus earthquake (60-300km); deep-focus earthquake (300-720km). Most of earthquakes belong to shallow-focus earthquake (20-60km).
Seismic area: the scope that indicates the earthquake spreads around epipcenter of the ground.