17:15 〜 18:30
[SSS08-P03] Inverse analysis of seismic swarm induced by slab-derived fluids
キーワード：間隙水圧、群発地震、誘発地震
Understanding the dehydration behavior from subducting plates and migration of slab-derived fluids is a critical topic in broad geoscience areas to understand catastrophic earthquakes and relevant phenomena. So far, much geophysical research has discovered the overall distribution of fluid around the subduction zone and its vicinity by seismic tomography or electromagnetic analysis. Besides, the geological approach also could estimate the long-term fluid flux from subducting plate by thermodynamic analysis of dehydration reactions (e.g., van Keken et al., 2011) and from solidifying magmatic chambers and dikes (e.g., Amanda et al., 2019; Uno et al., 2017).
Seismic swarms are one of the apparent and interesting phenomena related to slab-derived fluid. They typically show the apparent spatial migration of seismic activity with time, and it has been often interpreted as caused by the fluid migration. Seismic swarm activity in the Yamagata-Fukushima border was activated after the Tohoku-Oki earthquake, and this sequence shows clear upward migration in their hypocenters (Yoshida and Hasegawa, 2018a). Also, various features of seismic activity have been investigated, and it shows very similar characteristics to the injection-induced seismicity.
In research of injection-induced seismicity, the physics between the injection and seismic activity has been investigated. For the seismic risk assessment, the maximum magnitude of injection-induced seismicity can be estimated with the total injection volume by elastic theory (McGarr, 2014). Shapiro et al., (1997) introduced the method to model the pore pressure migration as a diffusion process in a fully saturated poroelastic medium, although it does not always match with the observation based on the fluid flow hydrological model (Mukuhira et al., 2016). This diffusion model has been used to characterize the features of hypocenter migration of seismic swarm (e.g., Shelly et al., 2016; Yoshida & Hasegawa, 2018b,). The optimized value of diffusivity is the proxy of the hydraulic features of the flow path that dehydrated pore pressure went through. However, we have not fully utilized these hydraulic features for a deeper understanding of the pore pressure migration behavior.
In this study, utilizing these theories related to seismic activity and fluid, we conduct inverse analysis on the seismic swarm data from the Yamagata-Fukushima border region. We consequently try to estimate the pore pressure value at the source and the amount of filtration fluid that caused seismic swarm activity. Then, we discuss the validity of our estimates of hydraulic parameters comparing with the values estimated from the geological viewpoint.
Seismic swarms are one of the apparent and interesting phenomena related to slab-derived fluid. They typically show the apparent spatial migration of seismic activity with time, and it has been often interpreted as caused by the fluid migration. Seismic swarm activity in the Yamagata-Fukushima border was activated after the Tohoku-Oki earthquake, and this sequence shows clear upward migration in their hypocenters (Yoshida and Hasegawa, 2018a). Also, various features of seismic activity have been investigated, and it shows very similar characteristics to the injection-induced seismicity.
In research of injection-induced seismicity, the physics between the injection and seismic activity has been investigated. For the seismic risk assessment, the maximum magnitude of injection-induced seismicity can be estimated with the total injection volume by elastic theory (McGarr, 2014). Shapiro et al., (1997) introduced the method to model the pore pressure migration as a diffusion process in a fully saturated poroelastic medium, although it does not always match with the observation based on the fluid flow hydrological model (Mukuhira et al., 2016). This diffusion model has been used to characterize the features of hypocenter migration of seismic swarm (e.g., Shelly et al., 2016; Yoshida & Hasegawa, 2018b,). The optimized value of diffusivity is the proxy of the hydraulic features of the flow path that dehydrated pore pressure went through. However, we have not fully utilized these hydraulic features for a deeper understanding of the pore pressure migration behavior.
In this study, utilizing these theories related to seismic activity and fluid, we conduct inverse analysis on the seismic swarm data from the Yamagata-Fukushima border region. We consequently try to estimate the pore pressure value at the source and the amount of filtration fluid that caused seismic swarm activity. Then, we discuss the validity of our estimates of hydraulic parameters comparing with the values estimated from the geological viewpoint.