Two Earthquakes Strike Northern Tochigi on Oct. 26, 2025, in Quick Succession

Just after noon on October 26, 2025, two earthquakes with epicenters in northern Tochigi Prefecture occurred in quick succession. The first earthquake registered a magnitude (M) of 4.7 and a maximum seismic intensity of 4, causing widespread shaking primarily across the Kanto region.

According to the Japan Meteorological Agency (JMA), the first earthquake struck around 12:04 PM on the same day. Its epicenter was in northern Tochigi Prefecture, at a very shallow depth of approximately 10 km, and its magnitude was estimated at M4.7. This earthquake recorded a seismic intensity of 4 in Nakasai, Ashio-machi, Nikko City, Tochigi Prefecture, and Tsudo, Ashio-machi, Nikko City. Additionally, seismic intensities of 1 to 3 were observed in various locations including Ashikaga City, Tochigi City, Sano City, Kanuma City, Takanezawa Town in Tochigi Prefecture; Maebashi City, Kiryu City, Numata City, Tatebayashi City, Shibukawa City, Oura Town in Gunma Prefecture; Saitama City, Gyoda City, Konosu City, Kuki City in Saitama Prefecture; Adachi Ward in Tokyo; and Yokohama City in Kanagawa Prefecture. Reports indicated that shaking was felt not only across a wide area of the Kanto region but also in parts of the Tohoku and Chubu regions.

Just three minutes later, around 12:07 PM, another earthquake with a magnitude of M3.7 struck, this time with an epicenter in southern Tochigi Prefecture. This quake also occurred at a shallow depth of approximately 10 km and registered a seismic intensity of 3 in Nikko City.

The area from northern Tochigi Prefecture to the border with Gunma Prefecture, where the epicenters were located, is known for frequent micro-earthquakes. Some voices are raising concerns about future activity, given the presence of an active fault south of the M4.7 earthquake's epicenter, and the proximity of Mount Kusatsu-Shirane, Lake Chuzenji, and Mount Nantai. Personal accounts from those who experienced the shaking described it as a "sudden, 'Doon!!'-type earthquake" and "quite strong shaking even in Tokyo."

The JMA has stated that there is no concern for a tsunami from this series of earthquakes. However, due to the shallow depth and consecutive occurrence of the quakes, continued vigilance regarding future aftershock activity and earthquake information is advised.

The context

For non-Japanese readers, understanding certain terms and geographical references is crucial:

  • Magnitude (M): A measure of the energy released at the source of an earthquake. It is a single number for each earthquake.
  • Seismic Intensity (Shindo 震度): The Japan Meteorological Agency (JMA) seismic intensity scale measures the degree of ground motion at a specific location. It ranges from 0 to 7, with 7 being the strongest. It is distinct from magnitude, as a single earthquake can have different seismic intensities in various places depending on distance from the epicenter, ground conditions, etc. A seismic intensity of 4 is considered strong enough to startle most people, cause hanging objects to swing considerably, and possibly move unstable items.
  • Kanto Region: This is the largest plain in Japan and encompasses the Tokyo metropolitan area and several surrounding prefectures, including Tochigi, Gunma, Saitama, Chiba, Kanagawa, and Ibaraki.
  • Tochigi Prefecture: A prefecture located in the northern part of the Kanto region, north of Tokyo. Its northern areas are mountainous and known for volcanic activity and hot springs.
  • Active Fault: A fault that is likely to be a source of another earthquake sometime in the future. Their presence near an epicenter can be a concern for seismic activity.
  • Mount Kusatsu-Shirane, Lake Chuzenji, Mount Nantai: These are prominent geographical features in the region. Mount Kusatsu-Shirane is an active volcano on the border of Gunma and Nagano prefectures, known for its volcanic lakes. Lake Chuzenji and Mount Nantai are iconic natural landmarks in Nikko City, Tochigi Prefecture.

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