11:00 AM - 11:15 AM
[SSS10-12] Constructing Plausible Rupture Scenario for the Nankai Trough Megathrust Earthquake based on Dynamic Simulation
Keywords:Nankai Trough, Stress Accumulation Rate, Slow Slip, Dynamic Model, Inter Seismic Period, Rupture Scenario
In the Nankai Trough, huge earthquakes of magnitude eight or greater have occurred repeatedly in the past, and a “Nankai Trough megathrust earthquake” is supposed to occur in the future. In particular, the occurrence of the recent M7-class earthquakes (on August 8, 2024, and January 13, 2025) within the assumed source area of the Nankai Trough megathrust earthquake that the Cabinet Office proposed has increased the need to clarify the mechanism of the ‘next Nankai Trough megathrust earthquake.’ However, the source area of such earthquake proposed by the Cabinet Office is not based on physical evidence. Until now, only Hok et al. (2011) have constructed a dynamic rupture model for the Nankai Trough megathrust earthquake. Recently, the spatial distribution of the stress accumulation rate in the Nankai Trough subduction zone has been estimated based on the inversion analysis of geodetic data (e.g., Noda et al., 2021). We developed a dynamic rupture model of the Nankai Trough by considering the stress accumulation rate (Noda et al., 2021) and realistic plate boundary structures (Iwasaki, 2015).
This study aims to construct more physically plausible dynamic rupture scenarios and verify each scenario’s validity. To achieve this goal, we investigate the effects of the initiation point on the rupture and the time length required for stress accumulation until the occurrence of an earthquake in each region of the Nankai Trough. As for setting the friction parameter, we consider the location of various slow slip events (SSE) and slow earthquakes in the deep and shallow regions of the plate boundary (e.g., Obara and Kato, 2016; Takemura et al., 2023; Ozawa et al., 2023). We first examine the effects of starting points of rupture. Our previous results (Tsuda et al., 2024) revealed that the model with the starting point of rupture from offshore of the Kii Peninsula generated a large slip area of up to 7.8 m was observed offshore of Cape Muroto, and fault rupture extended over a vast area from offshore of Tokai to Miyazaki Prefecture. On the other hand, even the model with the starting point of rupture of the asperities of the 1968 Hyuganada-Oki earthquake showed no rupture extension to the area offshore of Miyazaki Prefecture, the large slip areas of up to 8.7 m were generated offshore of Cape Muroto and offshore of the Kii Peninsula.
We model the frictional characteristics of long-term slow slip in the deep part of the plate boundary (Ozawa et al., 2023). The long-term SSE occurring in the region below 24 km follows the frictional law of low-velocity slip weakening and high-velocity slip strengthening (Shibazaki and Iio, 2003). Then, the slip strengthening could be activated at high speeds, such as during fault rupture. Therefore, we give the friction law of slip strengthening to the region below 24 km. In addition, we consider the spatial heterogeneity of the accumulation time length of stress until the occurrence of an earthquake in each region of the Nankai Trough. For example, there has been no fault rupture in the Tokai segment since the 1854 Ansei earthquake. Therefore, we assume the coupling period is 90 years longer than that (100 years) assumed for the other Tonankai and Nankai segments. The dynamic rupture scenarios based on such physical models and the examination of various scenarios will provide more reliable disaster mitigation measures.
This study aims to construct more physically plausible dynamic rupture scenarios and verify each scenario’s validity. To achieve this goal, we investigate the effects of the initiation point on the rupture and the time length required for stress accumulation until the occurrence of an earthquake in each region of the Nankai Trough. As for setting the friction parameter, we consider the location of various slow slip events (SSE) and slow earthquakes in the deep and shallow regions of the plate boundary (e.g., Obara and Kato, 2016; Takemura et al., 2023; Ozawa et al., 2023). We first examine the effects of starting points of rupture. Our previous results (Tsuda et al., 2024) revealed that the model with the starting point of rupture from offshore of the Kii Peninsula generated a large slip area of up to 7.8 m was observed offshore of Cape Muroto, and fault rupture extended over a vast area from offshore of Tokai to Miyazaki Prefecture. On the other hand, even the model with the starting point of rupture of the asperities of the 1968 Hyuganada-Oki earthquake showed no rupture extension to the area offshore of Miyazaki Prefecture, the large slip areas of up to 8.7 m were generated offshore of Cape Muroto and offshore of the Kii Peninsula.
We model the frictional characteristics of long-term slow slip in the deep part of the plate boundary (Ozawa et al., 2023). The long-term SSE occurring in the region below 24 km follows the frictional law of low-velocity slip weakening and high-velocity slip strengthening (Shibazaki and Iio, 2003). Then, the slip strengthening could be activated at high speeds, such as during fault rupture. Therefore, we give the friction law of slip strengthening to the region below 24 km. In addition, we consider the spatial heterogeneity of the accumulation time length of stress until the occurrence of an earthquake in each region of the Nankai Trough. For example, there has been no fault rupture in the Tokai segment since the 1854 Ansei earthquake. Therefore, we assume the coupling period is 90 years longer than that (100 years) assumed for the other Tonankai and Nankai segments. The dynamic rupture scenarios based on such physical models and the examination of various scenarios will provide more reliable disaster mitigation measures.