July 9, 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 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 11 cm at Nezugaseki (Geospatial Information Authority of Japan), Tsuruoka city, Yamagata prefecture.

* According to the result of GNSS observation, the crustal deformation associated with the event was observed such as about 5 cm north-westward movement at Niigatasanpoku observatory, Murakami city, Niigata prefecture. Also, the image of Interferometry Analysis of SAR data by the Advanced Land Observing Satellite "Daichi-2" showed the crustal deformation on land near the epicenter.

* After the M6.7 event, the seismic activity of the main shock-aftershock sequence continues in the area extending about 20 km length in an NE-SW direction until now. The largest aftershock until July 9 at 17 o'clock was that of M4.2 which occurred on June 19 at 00:57 (JST) with the 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. Based on the distribution of aftershocks and the focal mechanism of the main shock, the source fault was estimated to be the fault plane which dips to ESE direction.

* 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.

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

• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Summary (1)
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Summary (2)
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Seismic Activity (1)
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Seismic Activity (2)
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Seismic Activity (3)
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Seismic Intensity and Acceleration (1)
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Seismic Intensity and Acceleration (2)
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Tsunami
• Earthquake Offshore Yamagata Prefecture on June 18, 2019 – Seismic Activity (as of July 2 at 15:00)
• Result of the Waveform Coherence DD Method
• Observed Data Before and After the Earthquake Offshore Yamagata Prefecture (June 18, M6.7)
• The Earthquake Offshore Yamagata Prefecture (June 18, M6.7) – Result of "Daichi-2" SAR Interferometry Analysis
• The Geology and Active Faults Around the Boundary Between Yamagata and Niigata Prefectures
• Seismic Activity of the Eastern Edge of the Japan Sea and the Recent Earthquake
• The Positional Relation with the Aftershock Activity of the Niigata Earthquake