careen torbey, bbc news. tech to detect earthquakes is improving. limited. the earthquake that struck central morocco on friday night was the strongest to hit the region since before 1900. now, this magnitude 6.8 quake killed thousands of people and caused widespread damage. but why do earthquakes occur? and was the one in morocco to be expected? well, they happen when the earth's crust, which is its outermost shell, moves. tectonic plates, which are pieces of the earth's crust, don't always move smoothly alongside each other, and sometimes they get stuck. now, when this happens, pressure builds up and when the pressure is eventually released as energy, an earthquake tends to occur. there are several earthquake belts around the world, regions that are prone to earthquake activity. tectonic plate activity can be seen in them, such as the pacific belt, also known as the ring of fire, which is the most deadly, having previously led to earthquakes in chile and alaska. other earthquake belts, according to the us geographic survey, include the alpine eart