February 9, 2024
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
[Summary of the M7.6 Earthquake]
* On January 1 at 16:10 (JST, hereinafter the same time), there was a magnitude (M) 7.6 earthquake at a depth of approximately 15 km in the Noto region, Ishikawa Prefecture. In addition to maximum seismic intensity 7 observed at Wajima City and Shika Town, Ishikawa Prefecture, shakings with seismic intensity 6 Upper and 6 Lower were observed in a wide area of the Noto region and damage was caused. Before and after the M7.6 earthquake, large scale earthquakes occurred, and strong shakings continued for a long time. Also, in Ishikawa Prefecture long-period ground motion class 4 was observed. The focal mechanism showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred within the crust.
[Tsunami Associated with the M7.6 Earthquake]
* The recent event caused tsunami observed at the Sea of Japan side of the area extending from Hokkaido to Kyushu, such that of height 80 cm observed at Kanazawa observatory (Ports and Harbours Bureau), and of height 0.8 m observed at Sakata observatory (Japan Meteorological Agency). In addition, flood due to tsunami was observed in wide areas in the Noto Peninsula from aerial photography and field observations. Also from field surveys, in Noto Town and Suzu City, Ishikawa Prefecture, tsunami flood height of 4 m over was observed and in Joetsu City, Niigata Prefecture, tsunami run-up height of 5 m over was observed.
[Crustal Deformations Associated with the M7.6 Earthquake]
* According to the GNSS observation, associated with the recent event, the crustal deformations were observed in wide areas centering on the Noto Peninsula: such as the displacement of 2.0 m or so in a southwest direction and the uplift of 1.3 m or so at Wajima-2 observatory (GSI). Moreover, crustal deformations in a northwest or north direction were observed not only in the Sea of Japan side, such as Niigata Prefecture, but also in wide areas of Kanto and Chubu regions. Also, the analysis of the Synthetic Aperture Radar Images by Advanced Land Observing Satellite "the Daichi-2" detected the uplift of maximum 4 m or so and the westward displacement of maximum 2 m or so at the western Wajima City, and the uplift of maximum 2 m or so and the westward displacement of maximum 3 m or so at the northern Suzu City. By field survey, a new marine terrace associated with this event was recognized in the northwest coast of the Noto Peninsula. Also, by aerial photography, the analysis of the Synthetic Aperture Radar Images, and field survey, areas landificated due to uplift were found in wide areas of the north coast of the Noto Peninsula.
[Source Fault of the M7.6 Earthquake]
* The range of seismic activity area till December 2023 was a square of about 30 km sides in the northeastern Noto Peninsula. The range just after the M7.6 earthquake on January 1 extended about 150 km in an NE-SW direction. In the seismic activity area, the seismic sources just after the M7.6 earthquake are mainly distributed in the plane dipping southeast, and in the northeast side in the plane dipping northwest. At present there are earthquakes in the almost same range: near the western end of the seismic activity area an M6.1 earthquake occurred on January 1, and near the eastern end an M6.1 earthquake occurred on January 9. The seismic fault estimated from the focal mechanism of the M7.6 earthquake, the distribution of the seismic activity, the analysis of GNSS observation, the Synthetic Aperture Radar Images, and the analysis of seismic waves and tsunami waveforms, is a reverse fault mainly dipping southeast, extending 150 km or so in an NE-SW direction. The fault slip progressed from the origin bilaterally to the northeast and southwest.
* By the analysis of tsunami data, the eastern end of the lift area associated with the M7.6 earthquake is estimated at the northeast of the source area (about 40 km northeast of the Noto Peninsula).
[Seabed Landslide]
* Comparing the seabed topography of Toyama Bay investigated in 2024 and in 2010, it was confirmed that the slope of a seabed valley, about 4 km offshore of Toyama City, collapsed in length of about 500 m and in width of about 80 m, and is deepened maximum 40 m or so. It is possible that the collapse is related to the tsunami observed at Toyama tide station after 3 minutes of the occurrence of the earthquake.
[Ground Surface Deformation Associated with the M7.6 Earthquake]
* Along Wakayama River in the northeastern Noto Peninsula, ground surface deformation accompanying vertical displacement of maximum about 2 m was confirmed for about 4 km length.
[Seismic Activity After the M7.6 Earthquake]
* Compared with the state till December of the last year, the range of the seismic activity is expanding, and strong shakings are observed in wider areas. In the northeastern Noto Peninsula, the seismic activity is observed also at shallower depth than before. From January 1 at 16 o'clock till February 8 at 08 o'clock, there occurred 1,608 earthquakes with seismic intensity 1 or over observed (maximum seismic intensity: number of earthquakes, 7: 1, 6 Lower: 2, 5 Upper: 8, 5 Lower: 7).
* Now 1 month has passed since the M7.6 earthquake occurring on January 1, and the seismic activity is still high compared to the state before the M7.6 earthquake. We should pay attention for one or two weeks or so, to an earthquake with maximum seismic intensity 5 Lower or over. For an earthquake with maximum seismic intensity 5 Upper or 6 Lower or over, a possibility of occurrence is still higher than the normal state. Note that in the cases of large earthquakes along the Sea of Japan coast, the 1964 Niigata Earthquake (M7.5), the 1983 Central Japan Sea Earthquake (M7.7), the 1993 Offshore Southwest of Hokkaido Earthquake (M7.8), large magnitude earthquakes occurred about 1 month after the largest earthquakes. In the case of a large earthquake at the seabed, we should pay attention for tsunami.
[Post-Seismic Deformation After the M7.6 Earthquake]
* According to the result of the GNSS observation, after the M7.6 earthquake on January 1, in wide areas in Toyama and Niigata Prefectures centering on the Noto Peninsula, crustal deformations considered as the post-seismic deformation are observed.
[The Relation with Active Faults]
* In the sea offshore west, north and northeast of the Noto Peninsula, several reverse faults dipping southeast with strikes generally in an NE-SW direction, are recognized as active faults. The possibility that these active faults are related to the recent earthquake is high. Of these faults, at Saruyama-Oki segment where data of seabed topography were obtained, uplift of the seabed topography was observed.
* Further to offshore west of Sadoshima Island, reverse faults mainly dipping northwest are recognized as active faults, and the possibility that a part of these active faults is related to the recent earthquake cannot be denied.
[Seismic Activity Before the M7.6 Earthquake and Crustal Deformation]
* In the crust of the Noto region, Ishikawa Prefecture, where the recent earthquake occurred, the number of earthquakes was increasing since about 2018, then the seismic activity became high since December 2020, and it had become higher since about July 2021. In the series of the seismic activity, from December 1, 2020 till December 31, 2023 there occurred 506 earthquakes with seismic intensity 1 or over observed. Also, the crustal deformation was observed since about December 2020.
[Perspective of Seismic Activity]
* Based on the situation of the seismic activity and the crustal deformation until now, the series of the seismic activity since December 2020 will continue for the time being. Especially in the activity area after the M7.6 earthquake and its surroundings, there is a possibility of generation of an earthquake which causes strong shaking and tsunami.
# :"The 2024 Noto Peninsula Earthquakes" (named by JMA) denotes the series of earthquakes after January 1, 2024 and the series of seismic activity in the Noto region since December 2020.
Note: GNSS is a general name of satellite positioning system such as GPS.