Evaluation of Seismic Activities for September 2024 (2024)

October 9, 2024
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

1 Major Seismic Activities

* On September 24, a magnitude (M) 5.8 earthquake occurred at a depth ofabout 10 km (according to the CMT solution) in the ocean area near TorishimaIsland (near Sumisujima (Smith Rocks) about 100 km north of Torishima Island).The earthquake caused tsunamis in the Izu Islands and along the Pacificcoast from Chiba to Kagoshima Prefectures, including a 0.7 m observed atYaene, Hachijojima Island.

  • Seismic Activities for All of Japan in September 2024 (Magnitude 4.0 or over)

to supplementary reports

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

* On September 24, an M3.7 earthquake occurred at a depth of about 15 km in the central and northern Rumoi Region. This earthquake occurred within the crust.

* On September 26, an M5.7 earthquake occurred offshore of Kushiro at a depth of about 60 km. This earthquake has a focal mechanism with a WNW-ESE compression axis and occurred inside the Pacific Plate.

  • Hokkaido Region
  • Earthquake in the Central and Northern Rumoi Region on September 24
  • Earthquake Offshore of Kushiro on September 26

to supplementary reports

(2) Tohoku Region

There was no remarkable activity.

  • Tohoku Region

to supplementary reports

(3) Kanto-Chubu Region

* Although seismic activity in the focal region of the M7.6 earthquake on January 1 in the Noto region, Ishikawa Prefecture has been decreasing, seismic activity, which has been high since December 2020, is still ongoing. There were 18 earthquakes with seismic intensity 1 or over (maximum seismic intensity: number of earthquakes, 2: 4) from September 1 to September 30. The largest earthquake in September was the M3.7 event (maximum seismic intensity 1) at 00:53 on September 29. Note that there were 18 earthquakes with seismic intensity 1 or over in August.
According to the GNSS observation, following crustal deformations, which were considered to be post-seismic deformation, were observed in 9 months after the M7.6 earthquake on January 1: the horizontal displacements larger than 1 cm were observed in wide areas; in Toyama, Niigata, and Nagano Prefectures centering on the Noto Peninsula such as the displacement of about 5 cm in an NW direction at the Suzu observatory and subsidence in the northern Noto Peninsula such as about 9 cm at the Wajima observatory.
The number of earthquakes in the crust of the Noto region, Ishikawa Prefecture has been increasing since around 2018. The seismic activity became high from December 2020: there was an M5.4 earthquake in June 2022, an M6.5 in May 2023, an M7.6 in January 2024, and an M6.0 in June 2024. In the series of seismic activities, 2,442 earthquakes with seismic intensity 1 or over occurred from December 1, 2020 to September 30, 2024. Crustal deformation has also been observed since December 2020.
Based on the seismic activity and crustal deformation to date, the series of seismic activity from December 2020 is considered to continue for the time being, and there is a possibility of future earthquakes with strong shaking and tsunamis in and around the active area after the M7.6 earthquake.

* On September 24, an M5.8 earthquake occurred at a depth of about 10 km (according to the CMT solution) in the ocean area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km north of Torishima Island). The earthquake caused tsunamis in the Izu Islands and along the Pacific coast from Chiba to Kagoshima Prefectures, including a 0.7 m tsunami observed at Yaene, Hachijojima Island.
Similar to the present event, there have been other earthquakes in the vicinity, including an M5.9 on June 13, 1984, an M6.2 on September 5, 1996, an M5.9 on January 1, 2006, and an M5.9 on May 3, 2015, all of which have generated tsunamis despite being around M6.0 in size.

  • Kanto - Chubu Region
  • Seismic Activity of "the 2024 Noto Peninsula Earthquakes"
  • Table of the Number of "the 2024 Noto Peninsula Earthquakes" by Maximum Seismic Intensity
  • GNSS Observation Data After the 2024 Noto Peninsula Earthquakes (January 1, M7.6) (provisional)
  • GNSS Observation Data After the 2024 Noto Peninsula Earthquakes (January 1, M7.6) (provisional)
  • GNSS Observation Data After the 2024 Noto Peninsula Earthquakes (January 1, M7.6) (provisional) (continued)
  • GNSS Observation Data After the 2024 Noto Peninsula Earthquakes (January 1, M7.6) (provisional) (continued)
  • Earthquake in the Ocean Area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km North of Torishima Island) on September 24, 2024 -Overview-
  • Earthquake in the Ocean Area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km North of Torishima Island) on September 24, 2024 -Seismic Activity-
  • Earthquake in the Ocean Area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km North of Torishima Island) on September 24, 2024 -Seismic Activity- (continued)
  • Earthquake in the Ocean Area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km North of Torishima Island) on September 24, 2024 -Tsunami-
  • Earthquake in the Ocean Area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km North of Torishima Island) on September 24, 2024 -Tsunami- (continued)
  • Earthquake in the Ocean Area near Torishima Island (near Sumisujima (Smith Rocks) about 100 km North of Torishima Island) on September 24, 2024 -Tsunami- (continued)
  • Source Mechanism and Tsunami of the Earthquake in the Ocean Area near Torishima Island on September 24, 2024: Similarity with the 2015 Sumisu Caldera Earthquake and Tsunamis

to supplementary reports

(4) Kinki-Chugoku-Shikoku Region

* On September 20, an M4.7 earthquake occurred at a depth of about 40 km under the Bungosuido Strait. This earthquake has a normal fault-type focal mechanism with an E-W tension axis, and occurred inside the Philippine Sea Plate.

  • Kinki-Chugoku-Shikoku Region
  • Earthquake Under the Bungosuido Strait on September 20

to supplementary reports

(5) Kyushu-Okinawa Region

* On September 14, an M5.7 earthquake occurred offshore southeast of Tanegashima Island. The focal mechanism of this earthquake has an east-west compression axis.

* On September 16, an M5.3 earthquake occurred at a depth of about 20 km under the Hyuganada Sea. The focal mechanism of this earthquake was of a reverse fault type with a compression axis in the WNW-ESE direction, and the earthquake occurred at the boundary between the Philippine Sea and the continental plates. An M7.1 earthquake occurred near the hypocenter of this earthquake on August 8, 2024, and 32 earthquakes of seismic intensity 1 or over were observed from August 8 to September 30 (maximum seismic intensity: number of earthquakes, 6 Lower: 1, 3: 4, 2: 6, 1: 21). Although seismic activity continues, the number of earthquakes has been decreasing over time.
According to GNSS observations, crustal deformation, which is considered to be post-seismic deformation, was observed mainly in the southern Miyazaki Prefecture, including a 3 cm displacement in the southeast direction at the Miyazaki observatory during the two months after the M7.1 earthquake.

  • Kyushu Region
  • Earthquake Offshore Southeast of Tanegashima Island on September 14
  • Earthquake Under the Hyuganada Sea on September 16 (Seismic Activity Since August 8)
  • Earthquake Under the Hyuganada Sea on September 16 (Seismic Activity Since August 8) (continued)
  • GNSS Observation Data After the Earthquake Under the Hyuganada Sea (August 8, M7.1) (provisional)
  • GNSS Observation Data After the Earthquake Under the Hyuganada Sea (August 8, M7.1) (provisional)(continued)
  • Okinawa Region

to supplementary reports

(6) Around the Nankai Trough

* There has been observed no unusual change which indicates that the possibility of occurrence of a great earthquake along the Nankai Trough has relatively risen compared to the normal time.

  • Vertical Movement of GNSS-Based Control Stations - Omaezaki
  • Vertical Movements of GNSS-Based Control Stations - the Kii Peninsula and Around Cape Muroto -

to supplementary reports

Note: GNSS is a general name of a satellite positioning system such as GPS.


October 9, 2024
Earthquake Research Committee

1 Major Seismic Activities

The numbers of earthquakes by magnitude (M) in and around Japan in September2024 are as follows.

  • M4.0 or over: 94 (92 events in August)
  • M5.0 or over: 12 (9 events in August)
  • M6.0 or over: 0 (3 events in August)

(Reference)

  • M4.0 or over: 81 / month (69-104)
  • (Median monthly number from 1998 to 2017, half of the numbers are included in the interval shown in parentheses)
  • M5.0 or over: 10 / month (7-14)
  • (Median monthly number from 1973 to 2017, half of the numbers are included in the interval shown in parentheses)
  • M6.0 or over: 1 / month (0-2)
  • (Median monthly number from 1919 to 2017, half of the numbers are included in the interval shown in parentheses)
  • M6.0 or over: 16 / year (12-21)
  • (Median annual number from 1919 to 2017, half of the numbers are included in the interval shown in parentheses)

The following events for the period from September 2023 until the end ofAugust 2024 have been listed as "Major Seismic Activities" inthe monthly "Evaluation of Seismic Activities."

–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
– In the Noto Region, Ishikawa Prefecture# M7.6 on January 1, 2024
(Depth of approximately 15 km)
– Offshore of Fukushima Prefecture M5.8 on March 15, 2024
(Depth of approximately 50 km)
– Under Southern Ibaraki Prefecture M5.3 on March 21, 2024
(Depth of approximately 45 km)
– Under the Northern Coast of Iwate Prefecture M6.0 on April 2, 2024
(Depth of approximately 70 km)
– Near Taiwan M7.7 on April 3, 2024
– Offshore East of the Osumi Peninsula M5.1 on April 8, 2024
(Depth of approximately 40 km)
– Under the Bungosuido Strait M6.6 on April 17, 2024
(Depth of approximately 40 km)
– In the Noto Region, Ishikawa Prefecture# M6.0 on June 3, 2024
(Depth of approximately 15 km)
– Under the Hyuganada Sea M7.1 on August 8, 2024
(Depth of approximately 30 km)
– In western Kanagawa Prefecture M5.3 on August 9, 2024
(Depth of approximately 15 km)
– In the northern Ibaraki Prefecture M5.1 on August 19, 2024
(Depth of approximately 10 km)

   # Seismic activity of the 2024 Noto Peninsula Earthquakes

to the text

2 Nationwide Seismic Activities by Region

(1) Hokkaido Region

There is no supplementary information for Hokkaido region.

to the text

(2) Tohoku Region

There is no supplementary information for Tohoku region.

to the text

(3) Kanto-Chubu Region

– According to the GNSS observation, the crustal deformation differentfrom the ordinary trend in the area extending from the western Shizuokato the eastern Aichi Prefectures has been observed since early 2022. Thisphenomenon is considered to be caused by a long-term slow slip around theAtsumi Peninsula at the deeper part of the boundary between the PhilippineSea and the continental plates.

  • Coordinate Time Series (Black Circles) and Calculated Values (Red Lines) of Observing Stations in Tokai Region
  • Long-Term Slow Slip in the Tokai Region Estimated from GNSS Data (Provisional)

to the text

(4) Kinki-Chugoku-Shikoku Region

– According to the GNSS observation, the crustal deformation different from the ordinary trend in the central Shikoku has been observed since 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 plate and the continental plate. This crustal deformation was temporally decaying since fall 2023, but appears to have continued recently.

  • Time Series (Black Points) Representing the Coordinates of the Observatories in the Central Shikoku and Calculated Values (Red Lines) - Time-Dependent Inversion -
  • Long-Term Slow Slip in the Central Shikoku Estimated from GNSS Data (Provisional)

to the text

(5) Kyushu-Okinawa Region

There is no supplementary information for Kyushu-Okinawa region.

to the text

(6) Around the Nankai Trough

– "There has been observed no unusual change which indicates that the possibility of occurrence of a great earthquake along the Nankai Trough has relatively risen compared to the normal time.":
(This evaluation is in agreement with the views presented at the regular meeting on October 7 of the Nankai Trough Earthquake Assessment Committee (reference below).)

(Reference)

Recent Crustal Activity Around the Nankai Trough (Seismological and Volcanological Department, Japan Meteorological Agency, October 7, 2024)
"In 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 risen compared to the normal time. (Excerpted)"

to the text


Reference 1
Earthquakes that are described in the "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) have the following features.

  1. Events of M6.0 or greater, or events that have maximum seismic intensity 4 or greater
  2. Onshore events of M4.5 or greater that have maximum seismic intensity 3 or greater
  3. Events under the ocean areas of M5.0 or greater that have maximum seismic intensity 3 or greater

Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes:

  1. Reference information related to the seismic activity described in the "Evaluation of Seismic Activity"
  2. Recent earthquake activity over the past year related to the events described in "Major Seismic Activity" in the "Evaluation of Seismic Activity"
  3. Seismic activity that has been evaluated, but not included in the "Evaluation of Seismic Activity" because it is within normal bounds and not prominent
  4. A sequence of slow-slip events of estimated M6.0 or greater and accompanying low-frequency earthquakes (tremors)

Evaluation of Seismic Activities for September 2024 (2024)

References

Top Articles
Latest Posts
Recommended Articles
Article information

Author: Jamar Nader

Last Updated:

Views: 6455

Rating: 4.4 / 5 (55 voted)

Reviews: 86% of readers found this page helpful

Author information

Name: Jamar Nader

Birthday: 1995-02-28

Address: Apt. 536 6162 Reichel Greens, Port Zackaryside, CT 22682-9804

Phone: +9958384818317

Job: IT Representative

Hobby: Scrapbooking, Hiking, Hunting, Kite flying, Blacksmithing, Video gaming, Foraging

Introduction: My name is Jamar Nader, I am a fine, shiny, colorful, bright, nice, perfect, curious person who loves writing and wants to share my knowledge and understanding with you.