1:45 PM - 2:00 PM
[HCG20-01] Collecting and Organizing Earthquake Data for Modeling Earthquake and Fault Activity
Keywords:Geological Disposal, Earthquake and Fault Activity, Assessment Model, Damage Zone, Microearthquakes, Source Process
[Background and Objectives]
Among the issues to be considered in the safety assessment and safety regulations of the geological disposal project for HLW, a technical issue in relation to earthquake and fault activity is the modeling of the extent of the impact of the fracture zone and damage zone around a fault when a new fault occurs or a geological fault becomes active again, i.e., the presentation of the setting method, concept, and scientific basis. It is estimated that when a fault is formed, it will become a new route for groundwater migration, and that the amount of displacement and the characteristics of the fault surface are not uniform. However, in the model considered in the safety assessment, the fault displacement and the properties of the fault plane are treated as uniform, and it has not been possible to confirm whether this model is valid.
Detailed information on fault fracture zones, which is necessary information for modeling, has been obtained through geological outcrop surveys. Furthermore, for the damage zone believed to be distributed outside of it, Kaneori (2001) presented a relationship between the "width of the process zone and the length of the fault" based on outcrop surveys. On the other hand, there are no research cases that take an overview of the entire fault.
For the solving this problem, we will attempt to model the entire fault using earthquake data. In the field of geotechnical engineering, techniques have been established to understand the development of rock fractures based on microearthquake observations. The area where aftershocks, including microearthquakes, occur after an earthquake is thought to indicate the extent of the damage zone. The fault model in the "Analysis results of earthquake source process" published by the JMA may be useful reference information for inferring the amount of fault displacement and the characteristics of the fault surface.
Therefore, with a view to reflecting this in the assessment model, a trial effort was undertaken to collect and organize information and data relating to earthquake and fault data published by the JMA, as well as analytical models of earthquake source processes.
[Details]
As a trial, three earthquakes were selected from the JMA's "Analysis results of earthquake source processes" website. When selecting earthquakes, we assumed that geological disposal would occur in the inland or coastal areas, and that the epicenters were shallower than 15 km. To evaluate the impact of a single earthquake or fault activity, we selected seismic activity that was isolated in time and space.
For the earthquakes, data on the "JMA Unified Processing Hypocenter Elements" was collected, and digitized and organized as 3D aftershock zones. The organized data was used to organize spatiotemporal information, such as the range and shape of the aftershock zone, the spatial magnitude distribution of aftershocks within the zone, and time-series changes in the frequency of aftershock occurrence.
[Results]
As a result, we were able to express the range and shape of the aftershock zone according to the scale of fault activity as 3D information, which will serve as a reference when modeling.
In the future, we will expand data collection and organization, organize the relationship between the fault scale and the shape and size of the aftershock zone, and the relationship with the fault displacement.
[References]
Kaneori, Applied Geology, Vol. 41, pp. 323-332, 2001.
[Acknowledgments]
This study was partly funded by the METI, Japan, as part of its R&D supporting program titled “Establishment of Technology for Comprehensive Evaluation of the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste” (grant no. JPJ007597; fiscal year 2024).
Among the issues to be considered in the safety assessment and safety regulations of the geological disposal project for HLW, a technical issue in relation to earthquake and fault activity is the modeling of the extent of the impact of the fracture zone and damage zone around a fault when a new fault occurs or a geological fault becomes active again, i.e., the presentation of the setting method, concept, and scientific basis. It is estimated that when a fault is formed, it will become a new route for groundwater migration, and that the amount of displacement and the characteristics of the fault surface are not uniform. However, in the model considered in the safety assessment, the fault displacement and the properties of the fault plane are treated as uniform, and it has not been possible to confirm whether this model is valid.
Detailed information on fault fracture zones, which is necessary information for modeling, has been obtained through geological outcrop surveys. Furthermore, for the damage zone believed to be distributed outside of it, Kaneori (2001) presented a relationship between the "width of the process zone and the length of the fault" based on outcrop surveys. On the other hand, there are no research cases that take an overview of the entire fault.
For the solving this problem, we will attempt to model the entire fault using earthquake data. In the field of geotechnical engineering, techniques have been established to understand the development of rock fractures based on microearthquake observations. The area where aftershocks, including microearthquakes, occur after an earthquake is thought to indicate the extent of the damage zone. The fault model in the "Analysis results of earthquake source process" published by the JMA may be useful reference information for inferring the amount of fault displacement and the characteristics of the fault surface.
Therefore, with a view to reflecting this in the assessment model, a trial effort was undertaken to collect and organize information and data relating to earthquake and fault data published by the JMA, as well as analytical models of earthquake source processes.
[Details]
As a trial, three earthquakes were selected from the JMA's "Analysis results of earthquake source processes" website. When selecting earthquakes, we assumed that geological disposal would occur in the inland or coastal areas, and that the epicenters were shallower than 15 km. To evaluate the impact of a single earthquake or fault activity, we selected seismic activity that was isolated in time and space.
For the earthquakes, data on the "JMA Unified Processing Hypocenter Elements" was collected, and digitized and organized as 3D aftershock zones. The organized data was used to organize spatiotemporal information, such as the range and shape of the aftershock zone, the spatial magnitude distribution of aftershocks within the zone, and time-series changes in the frequency of aftershock occurrence.
[Results]
As a result, we were able to express the range and shape of the aftershock zone according to the scale of fault activity as 3D information, which will serve as a reference when modeling.
In the future, we will expand data collection and organization, organize the relationship between the fault scale and the shape and size of the aftershock zone, and the relationship with the fault displacement.
[References]
Kaneori, Applied Geology, Vol. 41, pp. 323-332, 2001.
[Acknowledgments]
This study was partly funded by the METI, Japan, as part of its R&D supporting program titled “Establishment of Technology for Comprehensive Evaluation of the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste” (grant no. JPJ007597; fiscal year 2024).