The Niigataken Chuetsu-oki Earthquake in 2007⁺

* On July 16, at 10:13 (JST) there was a M6.8 (preliminary) earthquake at a depth of approximately 15km off-shore of Jo-Chuetsu, Niigata prefecture. This event had maximum seismic intensity 6 Upper in Niigata and Nagano prefectures, and caused damage. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred at shallow depth within the crust. Seismic activity has been a main shock - aftershock sequence. The largest aftershock as of 10:00 on July 17, was a M5.8 (preliminary) earthquake that occurred at 15:37 on July 16, with maximum seismic intensity 6 Lower.

* Associated with this event, small tsunamis were observed centered on the coast in Niigata prefecture, such as waves of 0.2 to 0.3m high in Kashiwazaki and Ogi.

* The earthquake caused large ground accelerations of over 1,000 gal observed at the Ikeura station in Nishiyama-cho, Kashiwazaki city.

* According to the GPS data, there were large crustal movements associated with the mainshock in the area close to the event, with the largest displacement of approximately 16cm to the northwest, on the coast in Kashiwazaki city.

* From the focal mechanism of the main shock and the aftershock distribution, it is thought that the source is a reverse fault in a NE-SW direction, dipping to the southeast. That corresponds to the fault model estimated from the seismic wave data. In addition, from the focal process analysis of the main shock and the aftershock distribution, it is thought that the rupture propagated from the northeast to the southwest.

* There is an active structure along the eastern margin of the Japan Sea, called a strain concentration zone. It is thought that this event is related to a part of that active zone. The Nagaoka-Heiya-Seien Fault Zone is a reverse fault dipping to the west located about 10km east of this event. However, this is inconsistent with the estimated fault model, and thus the fault zone is thought not to have been active during this earthquake.

* Although the 2004 Niigata Chuetsu Earthquake occurred to the east of the recent event, it is thought that the 2004 earthquake did not trigger the recent event.

* Aftershock activity of this event is not that strong compared to other recent damaging earthquakes. There is a possibility that aftershocks might cause shaking with intensity 5 Upper, or 6 Lower in some areas, within the next week. It is estimated that there is about a 30 percent chance of occurrence for M5.5 or greater aftershocks (with seismic intensity 6 Lower in some areas) within the 3 days from 11:00 on July 17.

    + Japan Meteorological Agency named this earthquake the Niigataken Chuetsu-oki Earthquake in 2007.

• The Niigataken Chuetsu-oki Earthquake in 2007 (Aftershock activity)
• Moment Tensor Analyses for the Main Shock and the Largest Aftershock Using Broadband Seismographs
• Tsunami Records Associated with the Niigataken Chuetsu-oki Earthquake in 2007
• Maximum Ground Velocity Values at Significant Observation Stations
• Distance Attenuation
• Horizontal Displacement Vectors Associated with the Niigataken Chuetsu-oki Earthquake in 2007
• Crustal Movements Associated with the Niigataken Chuetsu-oki Earthquake in 2007 (1)
• Comparison of Hypocenters from the Integrated List and Redetermined with a Three-Dimensional Velocity Model
• Source Process of the Niigataken Chuetsu-oki Earthquake in 2007
• Seismic Activity along the Eastern Margin of the Japan Sea
• Geological Structure in the Area from Mid-southern Niigata Prefecture to the Ocean Area South of Sado
• Static Stress Effect on the Niigataken Chuetsu-oki Earthquake in 2007 on July 16
• Comparison of Numbers of Aftershocks (M4.0 or greater)
• Comparison of Aftershock Occurrences
• Changes of the Aftershock Activity for Earthquakes (M6.5 or greater) Occurring Onshore and near the Coast (shallower than 30km deep)
• Forecast of Aftershocks of the Niigataken Chuetsu-oki Earthquake in 2007
• Aftershock Activity of the Niigataken Chuetsu-oki Earthquake in 2007 (Probability of Aftershock Occurrence)