Matsushiro earthquake swarm

The Matsushiro earthquake swarm (Japanese: 松代群発地震[1]) was an earthquake swarm that occurred near Matsushiro, a suburb of Nagano, to the northwest of Tokyo in 1965.

The Matsushiro swarm lasted from 1965 to 1967 and generated about 1 million earthquakes.

[2] The total sum of energy from all the tremors was approximately equivalent to an M6.4 earthquake.

[3][4] This swarm had the peculiarity to be sited just under a seismological observatory installed in 1947 in a decommissioned military tunnel.

[5] The phenomenon was clearly identified as linked to a magma uplift, perhaps initiated by the 1964 Niigata earthquake which happened one year before.