Do all earthquakes cause tsunamis?

No, all earthquakes do not cause tsunamis. There are four conditions necessary for an earthquake to cause a tsunami:

• The earthquake must occur beneath the ocean or cause material to slide in the ocean.
• The earthquake must be strong, at least magnitude 6.5.
• The earthquake must rupture the Earth’s surface and it must occur at shallow depth – less than 70km below the surface of the Earth.
• The earthquake must cause vertical movement of the sea floor (up to several metres).