The Niigataken Chuetsu-oki Earthquake in 2007

* On July 16, at 10:13 (JST) there was a M6.8 earthquake at a depth of approximately 10km off-shore of Jo-Chuetsu, Niigata prefecture. This event had maximum seismic intensity 6 Upper in Niigata and Nagano prefectures. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. (see the 171st Evaluation of the Earthquake Research Committee of July 17, "The Niigataken Chuetsu-oki Earthquake in 2007")

* Seismic activity was a main shock-aftershock sequence. The aftershock activity has been declining. The aftershock activity is not so strong compared to other recent damaging earthquakes. The aftershock locations are distributed along a trend about 30km long in a NE-SW direction, and there are 2 planes that dip downwards to the southeast and downwards to the northwest. The largest aftershock as of 14:00 on August 8, was a M5.8 earthquake at 15:37 on July 16, which occurred at a location in the deeper portion of the aftershock distribution dipping downwards to the southeast.

* According to the GPS data, there were crustal movements associated with the main shock, with the largest displacement of approximately 17cm to the northwest on the coast in Kashiwazaki city. From the geological field surveys and leveling results, a maximum uplift of approximately 25cm was observed in the area centered on Cape Kannon, Kashiwazaki city, and a subsidence of approximately 4cm was observed at the Kashiwazaki tidal station. In addition, using Synthetic Aperture Radar data (SAR) from the advanced land observing satellite, "Daichi", crustal movements associated with this earthquake are observed to be consistent with a planar source, and centered in the area on the coast of the Chuetsu region, Niigata prefecture. The various geodetic observations of crustal movements are consistent with each other.

* Associated with this event, small tsunamis were observed centered on the coast in Niigata prefecture, such as 0.3m high waves in Kashiwazaki and Ogi. In addition, a 1m tsunami was observed in Kashiwazaki (Niigata prefecture jurisdiction).

* In the previous Earthquake Research Committee (emergency meeting) evaluation of the earthquake, the source fault was thought to dip downwards to the southeast, judging mainly from the aftershock distribution. Further study showed that there was another aftershock distribution dipping downwards to the northwest. With analysis results from crustal movements, seismic waves of the main shock, and tsunamis, it remains undetermined whether the source fault of the main shock was dipping downwards to the southeast or the northwest.

* In relation to faults in the local area, if the source fault is dipping downwards to the southeast, the earthquake is related to faults offshore of Chuetsu, Niigata prefecture. If the source fault is dipping downwards to the northwest, it may be associated with a fault that is a deeper extension of the Nagaoka-Heiya-Seien Fault Zone.

• The Niigataken Chuetsu-oki Earthquake in 2007
• Relocations of Hypocenters
• Temporal Changes on Cross Sections of the Aftershock Distribution
• Comparison of Aftershock Occurrences
• Crustal Movements Associated with the Niigataken Chuetsu-oki Earthquake in 2007
• Vertical Movements of Leveling from Kashiwazaki City to Izumozaki-cho
• Relative Amounts of Height of the Oyster Habitat Distribution Top (preliminary)
• The Niigataken Chuetsu-oki Earthquake in 2007  Results from Synthetic Aperture Radar Interferometry Analysis
• Tsunamis Associated with the Niigataken Chuetsu-oki Earthquake
• Tsunamis Associated with the Niigataken Chuetsu-oki Earthquake (continued)
• The Niigataken Chuetsu-oki Earthquake in 2007  Source Fault Model Dipping to the Northwest
• Earthquake Source Mechanism and Slip Distribution from Near-field Waveform Data
• Comparisons to the Tide Records
• Relationship between Geological Structures and Aftershock Distribution in the Focal Region
• Interpretation of Aftershock Distribution and Geological Cross Section
• An Interpretation of the Northern Focal Region assuming a Main Fault Plane Dipping Downward to the Southeast

^{Supplementary Information to the Evaluation of the Niigataken Chuetsu-oki Earthquake in 2007 by the Earthquake Research Committee}

August 8, 2007

  "In the previous Earthquake Research Committee (emergency meeting) evaluation of the earthquake, the source fault was thought to dip downwards to the southeast, judging mainly from the aftershock distribution. Further study showed that there was another aftershock distribution dipping downwards to the northwest. With analysis results from the data from crustal movements, seismic waves of the main shock, and tsunamis, it has remained undetermined whether the source fault of the main shock dips downwards to the southeast or the northwest.":
   It is impossible to determine the dip direction of the fault plane from the current results. Further evaluation is being withheld pending the results from a rapid survey supported by a Grant-in-Aid for Scientific Research (Grant-in-Aid for Special Purposes) and Special Coordination Funds for Promoting Science and Technology.

• Comprehensive Study for the Niigataken Chuetsu-oki Earthquake in 2007
• Outline of the Immediate Survey of the Niigataken Chuetsu-oki Earthquake in 2007