5:15 PM - 6:45 PM
[U15-P05] Evaluation of favorable to slip of the fault – in the case of the 2024 Noto Peninsula Earthquake
Keywords:the 2024 Noto Peninsula Earthquake, Stress field, Fault
The 2024 Noto Peninsula earthquake (M 7.6) occurred on January 1st, 2024, at a depth of approximately 15 km in the eastern part of Noto Peninsula. The stress field in the Noto Peninsula is estimated as a reverse fault type with the NW-SE compressional direction in the eastern part and a strike-slip fault type with the NW-SE compressional direction in the western part (Terakawa and Matsu'ura, 2009). The presence of high dip angle faults (50-60°) in this area has been inferred from reflection seismic surveys (e.g., Okamura, 2002). Those faults were formed by the extensional stress field during the formation of the Japan Sea. However, those faults are thought to be active as reverse faults (tectonic inversion faults) due to the present compressional stress field. In addition, increased seismic activity has been observed on the Noto Peninsula since 2020, and it has been speculated that fluid supplied from deep underground was involved in this activity (e.g., Nishimura et al., 2023; Yoshida et al., 2023; Okada et al., 2024).
We have previously used the Slip Tendency method (Morris et al., 1996) to evaluate the favorability of faults to slip for large-sized earthquakes that occurred in northeastern Japan. We found that reverse faults with low dip angle are favorable to slip in the eastern margin of the Japan Sea area (Tagami et al., 2024).
In this study, we estimated the stress field around the source region before the 2024 Noto Peninsula earthquake and evaluated the favorability of faults to slip.
Data and Methods
Stress fields were estimated using the stress tensor inversion method (Michael, 1984; 1987). We used the moment tensor solutions (period: 1/1/1997 - 12/31/2023, depth: 0 - 30 km) from F-net (National Research Institute for Earth Science and Disaster Prevention) for the estimation of the stress field. The Slip Tendency method (Morris et al., 1996) was used to evaluate how favorable the fault slip was to the stress field. We also compared the rake angle expected stress field with the actual (model) rake angle using the program of Neves et al. (2009).
Results
1. Stress fields
In the area around the Noto Peninsula, focal mechanisms of reverse fault type are dominant. Based on the distribution and trend of the focal mechanism solutions, we divided the region into west and east by longitude 137°. The stress field in the west area was a reverse fault type with a shape ratio φ(=(σ2-σ3)/(σ1-σ3))=0.32, and maximum horizontal compressional direction (SHmax)=109°. In the east area, stress field was a reverse fault type stress field with φ=0.45, and SHmax=130°.
2. Slip Tendency value (ST) and the rake angle
2-1. Preliminary Estimation Models
The ST of the fault planes in the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) model and “Nihon-kai Earthquake and Tsunami Research Project model” were larger than 0.7, indicating that the fault planes were favorable to slip to the stress field.
Nihon-kai model has a larger dip angle (50-60°) than the MLIT fault model, resulting in smaller ST values for Nihon-kai model. However, these ST are around 0.7, which is considered to be favorable to slip.
2-2. Models based on 2024 Noto Peninsula earthquake data
The ST of the JMA (Japan Meteorological Agency) CMT solutions and F-net MT solutions were approximately 0.7 or larger in both stress fields, indicating that they were favorable to slip in the stress field. The rake differences were also within about 10°.
The ST of the Geospatial Information Authority of Japan (GSI) model, and fault model from Ohta and Yamada (2024 printing) were larger than 0.7, indicating that the faults were favorable to slip to the stress field. The rake angle of Fault 2 in the GSI model exceeds 120°, and the rake angle due to the stress field estimated in this study is similarly large.
Discussions
The 2024 Noto Peninsula earthquake and related fault groups all showed large ST values and tended to favorable to slip to the stress field prior to the 2024 Noto Peninsula earthquake. In the west area, the fault strike and the SHmax are oblique, so that even faults with high dip angle are favorable to slip. This characteristic of the Noto Peninsula area is different from the tendency of high-angle faults in the eastern margin of the Japan Sea (Tagami et al., 2024). The Noto Peninsula earthquake is considered to be an earthquake caused by the interlocking rupture of multiple faults. Although it is necessary to consider other factors such as the slip history of each fault, the Noto Peninsula earthquake was/is considered to have occurred under conditions that are natural for interlocking rupture or delayed rupture as an aftershock (e.g., the 2016 Kaikoura earthquake: Matsuno et al., 2022).
We have previously used the Slip Tendency method (Morris et al., 1996) to evaluate the favorability of faults to slip for large-sized earthquakes that occurred in northeastern Japan. We found that reverse faults with low dip angle are favorable to slip in the eastern margin of the Japan Sea area (Tagami et al., 2024).
In this study, we estimated the stress field around the source region before the 2024 Noto Peninsula earthquake and evaluated the favorability of faults to slip.
Data and Methods
Stress fields were estimated using the stress tensor inversion method (Michael, 1984; 1987). We used the moment tensor solutions (period: 1/1/1997 - 12/31/2023, depth: 0 - 30 km) from F-net (National Research Institute for Earth Science and Disaster Prevention) for the estimation of the stress field. The Slip Tendency method (Morris et al., 1996) was used to evaluate how favorable the fault slip was to the stress field. We also compared the rake angle expected stress field with the actual (model) rake angle using the program of Neves et al. (2009).
Results
1. Stress fields
In the area around the Noto Peninsula, focal mechanisms of reverse fault type are dominant. Based on the distribution and trend of the focal mechanism solutions, we divided the region into west and east by longitude 137°. The stress field in the west area was a reverse fault type with a shape ratio φ(=(σ2-σ3)/(σ1-σ3))=0.32, and maximum horizontal compressional direction (SHmax)=109°. In the east area, stress field was a reverse fault type stress field with φ=0.45, and SHmax=130°.
2. Slip Tendency value (ST) and the rake angle
2-1. Preliminary Estimation Models
The ST of the fault planes in the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) model and “Nihon-kai Earthquake and Tsunami Research Project model” were larger than 0.7, indicating that the fault planes were favorable to slip to the stress field.
Nihon-kai model has a larger dip angle (50-60°) than the MLIT fault model, resulting in smaller ST values for Nihon-kai model. However, these ST are around 0.7, which is considered to be favorable to slip.
2-2. Models based on 2024 Noto Peninsula earthquake data
The ST of the JMA (Japan Meteorological Agency) CMT solutions and F-net MT solutions were approximately 0.7 or larger in both stress fields, indicating that they were favorable to slip in the stress field. The rake differences were also within about 10°.
The ST of the Geospatial Information Authority of Japan (GSI) model, and fault model from Ohta and Yamada (2024 printing) were larger than 0.7, indicating that the faults were favorable to slip to the stress field. The rake angle of Fault 2 in the GSI model exceeds 120°, and the rake angle due to the stress field estimated in this study is similarly large.
Discussions
The 2024 Noto Peninsula earthquake and related fault groups all showed large ST values and tended to favorable to slip to the stress field prior to the 2024 Noto Peninsula earthquake. In the west area, the fault strike and the SHmax are oblique, so that even faults with high dip angle are favorable to slip. This characteristic of the Noto Peninsula area is different from the tendency of high-angle faults in the eastern margin of the Japan Sea (Tagami et al., 2024). The Noto Peninsula earthquake is considered to be an earthquake caused by the interlocking rupture of multiple faults. Although it is necessary to consider other factors such as the slip history of each fault, the Noto Peninsula earthquake was/is considered to have occurred under conditions that are natural for interlocking rupture or delayed rupture as an aftershock (e.g., the 2016 Kaikoura earthquake: Matsuno et al., 2022).