7.1 magnitude - At that shallow a depth could we be looking at magma movements which may reactivate the nearby volcano?
There are two very active volcanoes on the island of Kyushu: Mt. Aso almost in the center of the island and Sakurajima across Kagoshima Bay from the city of Kagoshima in southern Kyushu. These earthquakes could mean either Mt. Aso or Sakurajima could be on the verge of a very active eruption phase, and very large eruptions are common along the Ring of Fire, which the Japanese home islands are part of.