January 15, 2024
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* 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 Kano, Shika Town, Hakui County, Ishikawa Prefecture, shaking above seismic intensity 6 Lower was observed in a wide area of the Noto region and damage was caused. 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.
* The recent event caused tsunami observed at the Sea of Japan side of the area extending from Hokkaido to Kyushu, such that of height 1.2 m over (preliminary) observed at Wajima Port observatory (Ports and Harbours Bureau), and of height 0.9m (preliminary) observed at Kanazawa observatory (Ports and Harbours Bureau). In addition, flood due to tsunami was observed in wide areas in the Noto Peninsula from aerial photography and field surveys. In those areas there is an area where tsunami run-up height of 4m over was observed.
* According to the GNSS observation, associated with the recent event, the crustal deformations were observed in wide areas centering on the Noto Peninsula: 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). 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, in wide areas of the north coast of the Noto Peninsula, it was found that there are areas that were landificated due to uplift.
* 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 extends about 150 km in an NE-SW direction. In the seismic activity area, the seismic sources 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 west end of the seismic activity area an M6.1 earthquake occurred on 1st, and near the east end an M6.1 earthquake occurred on 9th. The seismic fault estimated from the focal mechanism of the M7.6 earthquake on January 1, the distribution of the seismic activity, the analysis of GNSS observation, and the analysis of seismic waves and tsunami waveforms is a reverse fault mainly dipping southeast, extending about 150 km or so in an NE-SW direction. The fault slip progressed bilaterally from the origin 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).
* Associated with the M7.6 earthquake on January 1, large accelerations were observed, such as 2,828 gal (synthesis of 3 components) at Kano, Shika Town (K-NET Togi observatory).
* At present the active seismic activity continues. From 1st at 16 o'clock till 15th at 08 o'clock, there occurred 1398 earthquakes with seismic intensity 1 or over observed (maximum seismic intensity: number of earthquakes, 7: 1, 6 Lower: 1, 5 Upper: 7, 5 Lower: 7). The aftershock activity of the recent M7.6 earthquake is similar to those of large earthquakes along the Sea of Japan coast accompanying tsunami, such as the 1983 Central Japan Sea Earthquake (M7.7), the 1993 Offshore Southwest of Hokkaido Earthquake (M7.8).
* Now two weeks have 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 two or three weeks or so, to an earthquake with maximum seismic intensity 5 Upper or over. For an earthquake with maximum seismic intensity 6 Lower or over, the possibility of occurrence has become smaller than the period just after the M7.6 earthquake, there is still a possibility of occurrence. Note that in the cases of large earthquakes along the Sea of Japan coast accompanying tsunami, 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. The range of the seismic activity has expanded compared with the state till December of the last year, and strong shaking has been observed in a wider area than before. Also, in the case of a large earthquake at the ocean bottom, we should pay attention for tsunami.
* 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: of these 67 earthquakes with seismic intensity 3 or over observed. In December 2023, there were 8 earthquakes with seismic intensity 1 or over observed. On May 5, 2023, there was an M6.5 earthquake.
* According to the result of the GNSS observation, since about December 2020 till the occurrence of the M6.5 earthquake, the following crustal deformation had continued: the cumulative displacement of 1 cm over in the horizontal direction and the uplift of 4 cm or so in Suzu City, Ishikawa Prefecture. The GNSS observation and the analysis of the Synthetic Aperture Radar Images by Advanced Land Observing Satellite "the Daichi-2," at the time of the M6.5 event, showed the crustal deformation of maximum 20 cm or so was found at the surrounding area of the epicenter. The deformation in different tendency from the pre-earthquake stage observed at several observatories after the M6.5 event decayed as time passed, and at the end of 2023 it had returned to the tendency in the stage before the M6.5 earthquake.
* The series of seismic activity was mainly in the northeastern part and the northern sea area of the Noto Peninsula. The seismic activity area after January 1 traverses the northern Noto Peninsula in an NE-SW direction, reaches the northeastern sea area off the Noto Peninsula in the northeastern side and reaches the activity area of "the Noto Hanto Earthquake in 2007" in the southwest side. Also, in the northeastern Noto Peninsula the seismic activity is observed in the shallower depth than before.
* According to the result of the GNSS observation, after the M7.6 earthquake on January 1, the crustal deformation considered as an after-slip is observed in the Noto Peninsula and its surroundings.
* On January 6 at 23:20, there was an M4.3 earthquake at a depth of approximately 5 km offshore of the Noto Peninsula, and maximum seismic intensity 6 Lower was observed at Kano, Shika Town. At Kano observing point, Shika Town, seismic intensity larger than those at other surrounding stations was observed: it may be possible that the seismic origin is very near to the station.
* In the ocean offshore west, north and northeast of the Noto Peninsula, several active faults, which are of reverse fault type dipping southeast with strikes generally in an NE-SW direction, are known to exist. The possibility that these active faults are related to the recent earthquake is high.
* Also, in the ocean area from offshore northeast further of the Noto Peninsula to offshore west of Sadoshima Island, several active faults, which are of reverse fault type dipping northwest, are known to exist. The possibility that a part of these active faults is related to the recent earthquake cannot be denied.
* 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 recent activity area 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.