地球内部过程 Earthquake Epicenter震中 and focus震源: When an earthquake occurs, seismic waves travel in all directions from the focus, the region where the earthquake's energy originates. The foci焦距、震源 of most earthquakes are concentrated in the earth's crust which is about 50 km thick under continents. Earthquakes are classified according to focal depths a)0-60 km are shallow, b)60-300 km are intermediate and c)deep earthquakes may reach depths of 700 km. The epicenter of an earthquake is the point on the earth's surface directly above the focus 环境迪顶学 minoucntalocelogu ,率地球内部过程 Earthquake Epicenter震中 and Focus震源: When an earthquake occurs, seismic waves travel in all directions from the focus, the region where the earthquake's energy originates. The foci焦距、震源 of most earthquakes are concentrated in the earth's crust, which is about 50 km thick under continents. Earthquakes are classified according to focal depths a) 0-60 km are shallow, b) 60-300 km are intermediate, and c) deep earthquakes may reach depths of 700 km. The epicenter of an earthquake is the point on the earth's surface directly above the focus.