1:45 PM - 3:15 PM
[SSS06-P15] Screening method based on energy balance to generate earthquake scenarios on the Median Tectonic Line
Dynamic rupture simulations have been used to construct anticipated earthquake scenarios and to evaluate the possibility of occurrence of multi-segment earthquakes. Unfortunately, computational load for the dynamic rupture simulations is very high to perform parameter searches due to uncertainty of the friction parameters and stress field. In this study, we propose a screening method to pick up possible parameter sets where earthquake magnitude can be large before running dynamic rupture simulations, using energy-based method by Noda et al. (2021, JGR). Noda et al. (2021) suggested that positive residual energy, ER, is a necessary condition for earthquake generation. ER is defined as the strain energy released by the fault slip minus the energy dissipated on the fault, and it can be obtained from static slip distribution and the assumed friction law. To investigate the applicability of the method, we examined the Median Tectonic Line active fault zone (MTL) in Shikoku, southwest Japan, comparing ER with dynamic rupture simulations.
First, we investigated whether the sign of ER is consistent with results of dynamic rupture simulations done by MEXT & AIST (2021) and Kase & Urata (2021, SSJ). In the calculation of ER, stress drop and friction laws are assumed to be the same as those used in the dynamic rupture simulations. Static slip distribution is calculated by using analytical solution for triangular dislocation (Nikkhoo & Walter, 2015, GJI) for the fault segments where the rupture propagated in the dynamic rupture simulations. We examined 48 cases with the various values of stress drop and friction coefficients and various rupture initiation location. ER for the fault segments where the dynamic rupture propagated was positive in almost all the cases; thus, the prediction by the energy-based method was consistent with the results of dynamic rupture simulations.
Next, for parameters where dynamic rupture propagated only in a part of MTL, we evaluated ER including fault segments where dynamic rupture did not propagate in addition to the segments where dynamic rupture propagated. As expected from Noda et al. (2021), both cases with positive and negative ER were observed. In the cases with negative ER, energy-based method can predict the maximum slip area for each parameter set. Unfortunately, the number of these cases were not many. For the parameter sets with positive ER, possibility of the occurrence of the large multi-segment earthquakes remains. In the majority of such cases, static slip was almost zero in the segment adjacent to the segment where the dynamic rupture terminated; thus the additionally included region did not affect ER for whole slip region.
Then, we investigated the dependency between slip area and earthquake moment, M0, obtained from static slip. In some cases, M0 did not increase with slip area; therefore, the maximum earthquake magnitude can be estimated.
We successfully estimated the maximum earthquake magnitude and/or fault segments which cannot break simultaneously by using ER and M0 for 8 cases each: one-third of the examined cases in total. This method would be useful for picking up possible parameter sets where earthquake magnitude can be large before running dynamic rupture simulations.
Acknowledgments: This research was funded by Research Project for Long-term Evaluation Methods of Multi-segment Earthquakes from Active Fault Zones in FY2022 by MEXT.
First, we investigated whether the sign of ER is consistent with results of dynamic rupture simulations done by MEXT & AIST (2021) and Kase & Urata (2021, SSJ). In the calculation of ER, stress drop and friction laws are assumed to be the same as those used in the dynamic rupture simulations. Static slip distribution is calculated by using analytical solution for triangular dislocation (Nikkhoo & Walter, 2015, GJI) for the fault segments where the rupture propagated in the dynamic rupture simulations. We examined 48 cases with the various values of stress drop and friction coefficients and various rupture initiation location. ER for the fault segments where the dynamic rupture propagated was positive in almost all the cases; thus, the prediction by the energy-based method was consistent with the results of dynamic rupture simulations.
Next, for parameters where dynamic rupture propagated only in a part of MTL, we evaluated ER including fault segments where dynamic rupture did not propagate in addition to the segments where dynamic rupture propagated. As expected from Noda et al. (2021), both cases with positive and negative ER were observed. In the cases with negative ER, energy-based method can predict the maximum slip area for each parameter set. Unfortunately, the number of these cases were not many. For the parameter sets with positive ER, possibility of the occurrence of the large multi-segment earthquakes remains. In the majority of such cases, static slip was almost zero in the segment adjacent to the segment where the dynamic rupture terminated; thus the additionally included region did not affect ER for whole slip region.
Then, we investigated the dependency between slip area and earthquake moment, M0, obtained from static slip. In some cases, M0 did not increase with slip area; therefore, the maximum earthquake magnitude can be estimated.
We successfully estimated the maximum earthquake magnitude and/or fault segments which cannot break simultaneously by using ER and M0 for 8 cases each: one-third of the examined cases in total. This method would be useful for picking up possible parameter sets where earthquake magnitude can be large before running dynamic rupture simulations.
Acknowledgments: This research was funded by Research Project for Long-term Evaluation Methods of Multi-segment Earthquakes from Active Fault Zones in FY2022 by MEXT.