This means that the distributions of earthquakes at divergent boundaries are at shallow depths, where the crust is been pulled apart. The earthquakes happen at shallow depths because the normal faulting occurs near the sea floor, as a result of the tension. The normal faults are the cause of the earthquakes at these divergent boundaries.
The seafloor sees the most intense tectonic activity in the world, meaning that at the sites of mid-ocean ridges the frequency of earthquakes is very high. An example of a mid-ocean ridge is the Mid-Atlantic ridge; there the seafloor is spreading at a rate of about 3cm per year. The frequency of earthquakes at a mid-ocean ridge will depend on how much tension is happening at that point. The more tension means the more seafloor spreading, resulting in a higher frequency of earthquakes at a particular mid-ocean ridge.
Four major oceans make up most of the water in the world, The Atlantic (north & south), The Pacific, The Antarctic and The Indian Ocean. Within the basins of these oceans earthquakes can happen without been caused at Mid-ocean ridges or a Subduction Zones.
When the earth's crust is under tensional forces the crust will become much thinner than normal, if there is no fault. This means that the crust becomes weaker as it is thinner than normal. This can happen to the oceanic crust in the ocean basins, but will only cause an earthquake with a hot spot. A hot spot is an abnormal hot rising area of the mantle that supplies the lava for volcanoes. If at the same time a hot spot is directly below a thinned crust then the magma in the hot spot may hold too much pressure to be held by the thinner weakened crust. If this is the case then the magma can penetrate the lithosphere, and eventually erupt on the surface. The action of the magma forcing its way up can trigger earthquakes as it breaks through the crust. When its breaks through the crust at the sea bed eventually a volcanic island will be formed in the middle of the ocean.