June 19, 2019
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Earthquake Offshore Yamagata Prefecture on June 18, 2019

* On June 18 at 22:22 (JST), there was a magnitude (M) 6.7 (provisional) earthquake at a depth of approximately 15 km, offshore Yamagata prefecture. Maximum seismic intensity 6 Upper was observed in Kaetsu region, Niigata prefecture and some damage was caused.

* This event caused tsunami observed along the coasts of Akita, Yamagata, Niigata, and Ishikawa prefectures, such as that of 0.1 m (preliminary) at Niigata Nishi port (Ports and Harbours Bureau) observatory, Niigata city.

* According to the result (provisional) of GNSS observation, the crustal deformation associated with the event was observed: about 5 cm north-westward movement at Niigatasanpoku observatory, Murakami city, Niigata prefecture.

* After the M6.7 event, the seismic activity continues in the area extending about 20 km length in an NE-SW direction. The maximum earthquake until 19th at 17 o'clock was that of M4.1 (preliminary) which occurred on 19th at 00:57 (JST) with maximum seismic intensity 4.

* The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred within the crust.

* Along the area offshore Hokkaido to Niigata prefecture, i.e. in the eastern margin of the Japan Sea, there have sometimes been large earthquakes. From the point of view of geology, several bands of active faults and active folding zones are formed extending in an N-S direction with width in an E-W direction. The recent seismic activity has occurred in the area adjacent to the source region of the 1964 Niigata Earthquake.

* In the area where strong shaking was felt, it is necessary to be prepared for an earthquake with maximum seismic intensity 6 Upper, for a week or so from the occurrence of the earthquake. Especially in a few days or so, an earthquake of a large magnitude often occurs.

Note: GNSS is a general name of satellite positioning system such as GPS.