March 11, 2024
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
There was no remarkable activity.
There was no remarkable activity.
There was no remarkable activity.
* In the crust of the Noto region, Ishikawa Prefecture, the number of earthquakes
was increasing since about 2018, and the seismic activity became high since
December 2020, and it became higher since about July 2021. In the series
of the seismic activity, since December 1, 2020 till December 31, 2023,
there were 506 earthquakes with seismic intensity 1 or over observed. Also,
crustal deformation was observed since about December 2020.
On January 1, 2024 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 the period from January 1 at 16 o'clock
to March 8 at 08 o'clock, there were 1,727 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 2 months 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. Compared with the state till December of the last
year, the range of the seismic activity is expanding, and earthquakes are
observed in wider areas at present. From February 1 till March 11 at 08
o'clock, there occurred 173 earthquakes with seismic intensity 1 or over
observed (maximum seismic intensity: number of earthquakes, 4: 3, 3: 14).
Of these the largest scale one is the M5.2 earthquake (maximum seismic
intensity 4) occurring on February 7 at 06:08. After the M7.6 earthquake
on January 1, during about 2 months, the following crustal deformations
considered as the post-seismic deformations are observed: the horizontal
displacements observed in wide areas, in Toyama, Niigata, and Nagano Prefectures
centering on the Noto Peninsula such as the displacement of about 3 cm
in an NW direction at Noto observatory and subsidence in the northern Noto
Peninsula such as about 4 cm observed at Wajima observatory.
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. Comparing the water depth data in this area obtained in the period from January to March 2024 and that in 2008, in the Saruyama-Oki segment and Suzu-Oki segment of the active fault zone in the northern Noto Peninsula, in the seabed southeast side of the fault trace, uplift of about 4 m and about 3 m, respectively, are observed. The possibility that these uplifts are deformations associated with the M7.6 earthquake on January 1, is high and these are estimated to be caused by the activity of the reverse faults dipping southeast.
Comparing the water depth data obtained in February 2024 and that in May 2023, the slope of a seabed valley seated at about 30 km east of the Noto Peninsula collapsed at several points. Of these points the largest collapse occurred about 1.6 km in length and about 1.1 km in width and the slope deepened about 50 m at maximum. This collapse is considered to be caused by the M7.6 earthquake.
Comparing the seabed topography of Toyama Bay investigated in 2024 and that in 2010, it was confirmed that the slope of a seabed valley, about 4 km offshore of Toyama City, collapsed about 3.5 km in NS direction and about 1 km in EW direction, and 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.
Compared to the moment of the M7.6 earthquake on January 1, the seismic activity is decreasing but it still keeps a high state. In the examples of large earthquakes within the continental plate, a large earthquake occurred while the number of earthquakes was gently decreasing: such as the Mid Niigata prefecture Earthquake in 2004 (M6.8), the 2016 Kumamoto Earthquake (M7.3), and the 2018 Hokkaido Eastern Iburi Earthquake (M6.7).
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.
* On February 12, there was an M6.5 earthquake at a depth of approximately 270 km under the ocean area near Ioto Island. The focal mechanism had a tension axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate.
* Since February 26 at about 23 o'clock (JST, hereinafter the same time),
there continues a seismic activity centering on offshore east of Chiba
Prefecture. Till March 11 at 08 o'clock there were 42 earthquakes with
seismic intensity 1 or over observed (maximum seismic intensity: number
of earthquakes, 4: 4, 3: 6), the largest scale earthquake being an M5.3
earthquake occurring on March 1 at 05:43. The focal mechanisms of these
earthquakes showed a reverse fault type with a compression axis generally
in an NNW-SSE direction. These events occurred at the boundary between
the Philippine Sea and the continental plates.
According to the GNSS and tilt data, since about February 26, slight crustal deformations were observed in the Boso Peninsula. The crustal deformations detected by GNSS is about 2 cm at maximum. These phenomena are considered as due to slow slip at the boundary between the Philippine Sea and the continental plates.
In the vicinity of the recent activity, seismic activity associated with slow slip was observed at the frequency once per several years in the past and the recent one is considered as the similar one. Hitherto in 1996, 2002, 2007, 2011, 2014, and 2018, the seismic activity continued for 1 week or several months. Also, in 2007 maximum seismic intensity 5 Lower was observed.
Based on the past seismic activity, the activity will continue, and it is possible that strong shaking as seismic intensity 5 Lower will be observed, so we should pay attention to strong shaking.
* On February 7, there was an M4.1 earthquake at a depth of approximately 5 km in the northern Wakayama Prefecture. The focal mechanism showed a strike-slip fault type with a compression axis in an E-W direction. This event occurred within the crust.
* On February 14, there was an M4.4 earthquake at a depth of approximately 10 km in the southern Kyoto Prefecture. This event occurred within the crust.
* On February 26, there was an M5.1 earthquake at a depth of approximately 45 km under Iyonada Sea (#1). The focal mechanism had a tension axis in an ENE-WSW direction. This event occurred within the Philippine Sea plate.
There was no remarkable activity.
* There has been observed no unusual change which indicates that the possibility of occurrence of a great earthquake along the Nankai Trough has relatively raised compared to the normal time.
* On March 2, there was an M4.3 earthquake at a depth of approximately
15 km in the northern plain region, Miyazaki Prefecture. This event occurred
within the crust.
#1: "the Nanyo region, Ehime Prefecture" was the regional name of the epicenter used in the JMA announcement.
Note: GNSS is a general name of satellite positioning system such as GPS.
March 11, 2024
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude (M) that occurred in Japan and the surrounding area during February 2024.
(Reference)
The following events for the period from February 2023 to late January 2024 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Offshore of Kushiro | M6.0 on February 25, 2023 (Depth of approximately 65 km) |
||
| – Offshore of the Noto Peninsula | M6.5 on May 5, 2023 (Depth of approximately 10 km) |
||
| – Under the Southern Chiba Prefecture | M6.5 on May 5, 2023 (Depth of approximately 10 km) |
||
| – In the Ocean Area near Tokara Islands (Near Kuchinoshima and Nakanoshima Islands) |
M5.1 on May 13, 2023 | ||
| – In the Ocean Area near Niijima and Kozushima Islands | M5.3 on May 22, 2023 (Depth of approximately 10 km) |
||
| – Offshore East of Chiba Prefecture | M6.2 on May 26, 2023 (Depth of approximately 50 km) |
||
| – Offshore of Tomakomai | M6.2 on June 11, 2023 (Depth of approximately 140 km) |
||
| – In the Ocean Area near Torishima Island | Maximum M6.5 October 2 ~ 9, 2023 | ||
| – in Mindanao, the Philippine Islands | Mw7.5 on December 2, 2023 | ||
| – 2024 Noto Peninsula Earthquakes | M7.6 on January 1, 2024 (Depth of approximately 15 km) |
||
There is no supplementary information for Hokkaido region.
– 13 years have passed since the generation of “the 2011 off the
Pacific coast of Tohoku Earthquake” (hereinafter referred to the Tohoku-Oki
Earthquake), and the seismic activity in the aftershock area is approaching
to the state before the Tohoku-Oki Earthquake as a whole, but the number
of earthquakes per year is still larger than that of the era before the
Tohoku-Oki Earthquake, and the seismic activity of the present state will
continue for the time being.
According to the GNSS and the ocean-bottom crustal deformation observation, the crustal deformation considered as the post-seismic deformation is still observed in a wide area of eastern Japan and seabed in the aftershock area. As time has passed, the post-seismic deformation has become small as a whole, but it has not yet returned to the state before the Tohoku-Oki Earthquake.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the area extending from the western Shizuoka to the eastern Aichi Prefectures has been observed from early 2022. This phenomenon is considered to be caused by a long-term slow slip around the Atsumi Peninsula at the deeper part of the boundary between the Philippine Sea and the continental plates.
– According to the GNSS observation, the crustal deformation different from the ordinary trend in the central Shikoku has been observed from about spring 2019. This phenomenon is considered to be caused by a long-term slow slip around the central Shikoku at the deeper part of the boundary between the Philippine Sea and the continental plates. Recently this crustal deformation seems to be decaying.
There is no supplementary information for Kyushu-Okinawa region.
– "There has been observed no unusual change which indicates
that the possibility of occurrence of a great earthquake along the Nankai
Trough has relatively raised compared to the normal time.":
(This evaluation is in agreement with the views presented at the regular
meeting on March 7 of the Assessment Committee for Earthquakes Along the
Nankai Trough (reference below).)
(Reference)
Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, March 7, 2024)
"n the present, there has been observed no unusual change which indicates that the possibility of occurrence of great earthquakes along the Nankai Trough has relatively raised compared to the normal time.. (Excerpted)"
Reference 1
Earthquakes that are described in the "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) have the following features.
Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes: