Title: Postdoctoral Researcher
Country/Region: France
Period: 2024/5/7-2024/7/6
Theme: Analyzing slow earthquake catalogs to constrain fault rheology at the ETS zone
Host: Yuji ITOH
Introduction: I completed my PhD at the University of Paris-Saclay, specializing in mechanics, energy, materials, and geoscience. My doctoral thesis focused on investigating granular structures with shear interactions. Currently, I am pursuing a postdoctoral position at the National Scientific Research Center of France, based at the Earth Science Institution in Grenoble. I focus on mechanically modeling the movements of tectonic plates within subduction zones. My aim is to gain a deeper understanding of slow earthquakes by investigating both displacement and tremor phenomena through viscoelastic rheology using the damage propagation and healing effects that occur over time. My research interests encompass the study of micropolar media, granular materials, and complex systems, employing both analytical and numerical approaches such as the discrete element method or finite element method.
Research Report:
Variations in Slow Earthquake Features Along the Nankai Fault: A Comparative
Study Using Observational Data and FEM Modeling
Sina MASSOUMI (Visitor)1, Yuji ITOH (Host)2
1 Earth Science Institute, University of Grenoble, Grenoble, France.
2 Earthquake Research Institute, University of Tokyo, Tokyo, Japan.
Introduction
During my two-month research visit to the Earthquake Research Institute (ERI) in Tokyo, I focused on
studying the along-dip variation of observational features of slow earthquakes. This research aimed to
provide a comparison between the observations in Nankai and a viscoelastic damage rheology of slow
earthquakes (Dansereau et al. (2023)) obtained through my postdoctoral research at ISTerre. The
primary datasets utilized in this study include epicenters and energy of deep low-frequency tremor
reported by Obara et al. (2010) and a slow slip events (SSE) catalog reported by Okada et al. (2022). I
investigated the correlation between locations and occurrence times of tremor and SSE, and analyzed
their variation in the recurrence interval, event frequency and energy in the down-dip direction.
Methodology
The tremor data used in this study were obtained using a clustering method of hourly tremor activity as
described by Obara et al. (2010). This method involves a hybrid analysis using envelope correlation
and amplitude, as detailed by Maeda and Obara (2009). The slow slip events (SSEs) analyzed in this
research by Okada et al. (2022) were identified using global navigation satellite system (GNSS) data,
which detects millimeter-order signals of short-term slow slip events (S-SSEs) and estimates their fault
parameters, and duration.
Results
Our analysis revealed several significant features:
1. Tremor Energy Concentration:
The concentration of tremor energy was observed to occur at certain depths within the Episodic Tremor
and Slip (ETS) zone. This indicates that specific depth ranges are more active or conducive to tremor
generation. In Figure 1 we presented all the tremor events from 2003 to 2019 and we are focusing on
the energy values of each events in the red swath centered at longitude 133.5 and latitude 34.03. The
down-dip variation of cumulative tremor energy is also reported in Figure 2. Considering the down-dip
variation of tremor energy and recurrence interval, we tried to replicate the observational results
through the FEM simulations by applying variable shear strength and healing effects (Figure 3).
Study Using Observational Data and FEM Modeling
Sina MASSOUMI (Visitor)1, Yuji ITOH (Host)2
1 Earth Science Institute, University of Grenoble, Grenoble, France.
2 Earthquake Research Institute, University of Tokyo, Tokyo, Japan.
Introduction
During my two-month research visit to the Earthquake Research Institute (ERI) in Tokyo, I focused on
studying the along-dip variation of observational features of slow earthquakes. This research aimed to
provide a comparison between the observations in Nankai and a viscoelastic damage rheology of slow
earthquakes (Dansereau et al. (2023)) obtained through my postdoctoral research at ISTerre. The
primary datasets utilized in this study include epicenters and energy of deep low-frequency tremor
reported by Obara et al. (2010) and a slow slip events (SSE) catalog reported by Okada et al. (2022). I
investigated the correlation between locations and occurrence times of tremor and SSE, and analyzed
their variation in the recurrence interval, event frequency and energy in the down-dip direction.
Methodology
The tremor data used in this study were obtained using a clustering method of hourly tremor activity as
described by Obara et al. (2010). This method involves a hybrid analysis using envelope correlation
and amplitude, as detailed by Maeda and Obara (2009). The slow slip events (SSEs) analyzed in this
research by Okada et al. (2022) were identified using global navigation satellite system (GNSS) data,
which detects millimeter-order signals of short-term slow slip events (S-SSEs) and estimates their fault
parameters, and duration.
Results
Our analysis revealed several significant features:
1. Tremor Energy Concentration:
The concentration of tremor energy was observed to occur at certain depths within the Episodic Tremor
and Slip (ETS) zone. This indicates that specific depth ranges are more active or conducive to tremor
generation. In Figure 1 we presented all the tremor events from 2003 to 2019 and we are focusing on
the energy values of each events in the red swath centered at longitude 133.5 and latitude 34.03. The
down-dip variation of cumulative tremor energy is also reported in Figure 2. Considering the down-dip
variation of tremor energy and recurrence interval, we tried to replicate the observational results
through the FEM simulations by applying variable shear strength and healing effects (Figure 3).
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Fiscal Year: 2024
Fiscal Year: 2024