According to the Japanese Meteorological Agency, a magnitude 6.0 earthquake struck off the coast of the Ibaraki prefecture, with shaking felt in Tokyo.
Japan is a country with a long history of disastrous earthquakes and tsunamis. Sitting above the collision zone of four tectonic plates, the continuous movements of the plates accumulate a lot of energy, released from time to time as an earthquake. If the earthquake happens beneath the sea, the sudden shift of the ocean floor causes the displacement of a large volume of water, with waves rolling towards the nearest coastline. The risk of a major event striking during the Olympics is small but cannot be ruled out entirely.
