3:30 PM - 3:50 PM
[O09-05] Earthquake activity in the Noto Peninsula during 2020-2024 deduced from geodetic observations
★Invited Papers
Keywords:Earthquake activity, Noto Peninsula, Crustal deformation, GNSS
The M7.6 Noto Peninsula earthquake occurred at 16:10 on January 1, 2024 is one of the largest shallow crustal earthquakes in the Japan Islands arc. Active seismic swarm activity had been occurred in the northeastern Noto Peninsula for about three years before this earthquake, and the largest earthquake in the swarm activity occurred on New Year's Day, 2024, amid a series of large earthquakes, including a M6.5 earthquake (maximum intensity: 6+) on May 5, 2023. In this presentation, we will introduce our hypothesis on the series of seismic activity and its mechanism, focusing on the crustal deformation observation by GNSS.
This earthquake probably ruptured active faults extending in a northeast-southwest direction off the northern coast of the Noto Peninsula. This active fault dipping southeastward moved in the reverse-type fault such that the land mass of the Noto Peninsula overrides the land mass on the Sea of Japan side. The crustal deformation associated with the earthquake was observed by GNSS. The horizontal motion in the westward direction reached to 2 m mainly in the northern part of the Noto Peninsula, and the vertical motion shows uplift up to 2 m on the northern coast of the Noto Peninsula. Furthermore, analysis of synthetic aperture radar images indicates that the uplift reached a maximum of about 4 m in the coastal area of the western part of Wajima City. The uplift along the northern coast of the Noto Peninsula is concordant with the current elevation and distribution of marine terraces, suggesting that similar earthquakes have occurred repeatedly in the past.
Prior to the great earthquake on New Year's Day, 2024, seismic activity had increased in the northeastern Noto Peninsula since December 2020. At the same time as the seismic activity increased, anomalous crustal deformation with a different trend from the previous one, such as uplift, was observed at GNSS stations in the northeastern Noto Peninsula. Therefore, in cooperation with Kanazawa University, the Disaster Prevention Research Institute of Kyoto University installed temporary GNSS stations near the epicentral area in September 2021. In addition, with data provided by SOFTBANK Corp. from its original reference point (GNSS station), we could clarify the unsteady crustal deformation in the Noto Peninsula.
The author's hypothesis regarding the mechanism of the seismic activity is as follows. In the northeastern Noto Peninsula, there was a mantle-derived deep fluid-rich region in the lower crust. Fluid flow from this region rose to a depth of ~16 km in December 2020, accompanied by seismic activity. The volume of the upwelled fluid is thought to be as large as 30 million m3. This fluid migrated and diffused through the southeast-trending fault zone, mainly causing slow slip at depths greater than 15 km and triggering intense earthquake swarms at depths shallower than 15 km. Furthermore, Active faults have accumulated stress over the past millennium in the vicinity of numerous earthquakes, and the fluid welling is likely to be the final trigger for its rupture, resulting in the M7.6 earthquake.
Acknowledgments: The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science". We are also grateful to GSI for providing GNSS data.
This earthquake probably ruptured active faults extending in a northeast-southwest direction off the northern coast of the Noto Peninsula. This active fault dipping southeastward moved in the reverse-type fault such that the land mass of the Noto Peninsula overrides the land mass on the Sea of Japan side. The crustal deformation associated with the earthquake was observed by GNSS. The horizontal motion in the westward direction reached to 2 m mainly in the northern part of the Noto Peninsula, and the vertical motion shows uplift up to 2 m on the northern coast of the Noto Peninsula. Furthermore, analysis of synthetic aperture radar images indicates that the uplift reached a maximum of about 4 m in the coastal area of the western part of Wajima City. The uplift along the northern coast of the Noto Peninsula is concordant with the current elevation and distribution of marine terraces, suggesting that similar earthquakes have occurred repeatedly in the past.
Prior to the great earthquake on New Year's Day, 2024, seismic activity had increased in the northeastern Noto Peninsula since December 2020. At the same time as the seismic activity increased, anomalous crustal deformation with a different trend from the previous one, such as uplift, was observed at GNSS stations in the northeastern Noto Peninsula. Therefore, in cooperation with Kanazawa University, the Disaster Prevention Research Institute of Kyoto University installed temporary GNSS stations near the epicentral area in September 2021. In addition, with data provided by SOFTBANK Corp. from its original reference point (GNSS station), we could clarify the unsteady crustal deformation in the Noto Peninsula.
The author's hypothesis regarding the mechanism of the seismic activity is as follows. In the northeastern Noto Peninsula, there was a mantle-derived deep fluid-rich region in the lower crust. Fluid flow from this region rose to a depth of ~16 km in December 2020, accompanied by seismic activity. The volume of the upwelled fluid is thought to be as large as 30 million m3. This fluid migrated and diffused through the southeast-trending fault zone, mainly causing slow slip at depths greater than 15 km and triggering intense earthquake swarms at depths shallower than 15 km. Furthermore, Active faults have accumulated stress over the past millennium in the vicinity of numerous earthquakes, and the fluid welling is likely to be the final trigger for its rupture, resulting in the M7.6 earthquake.
Acknowledgments: The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science". We are also grateful to GSI for providing GNSS data.