17:15 〜 18:45
[SSS05-P06] 2023年モロッコ地震で観測されたバリアによる破壊伝播速度の急減速と急加速
キーワード：2023年モロッコ地震、バリアモデル、アスペリティモデル
On September 8, 2023, a reverse fault earthquake of moment magnitude (Mw) 6.8 occurred in southern Morocco. Barrier-induced rupture front disturbances were reported for this large earthquake (Yagi et al., 2024, Seismol. Res. Lett., doi: 10.1785/0220230357). In this presentation, the results of Yagi et al. (2024) will be introduced.
Seismic waveforms, including teleseismic body waves, contain information about the complex seismic source process. Recently, a new method, Potency Density Tensor Inversion (PDTI), has been proposed for reducing the influence of modeling errors. The method incorporates the modeling errors due to uncertainty in the Green's function into the data covariance matrix and the fault geometry information into the model parameters. In Yagi et al. (2024), PDTI was applied to the teleseismic P-waves of the 2023 Morocco earthquake to reveal an irregular seismic source process.
We downloaded 57 components of teleseismic P-waves from the Science Advancement for Geosciences and Earth and Planetary Science (SAGE) and used them in our analysis. The horizontal location of the initial break point was set to the epicenter determined by the Portuguese Institute for Sea and Atmosphere (IPMA), and the depth of the initial break point was set to 25 km, based on a preliminary analysis. The model plane was set to a strike and dip of 255° and 69°, respectively, based on the United States Geological Survey (USGS) CMT solution.
The rupture initiated from the hypocenter propagates to east-northeast direction, then propagates bilaterally, in both up-dip and down-dip directions. The down-dip rupture propagates to 10 km below the hypocenter and is nearly terminated at about 4 s after the origin time (OT). The main up-dip propagating rupture is temporarily suppressed around a point at 19 km depth and 10 km east-northeast of the initial break point (region B) from OT+3 s to OT+4 s. After OT+4 s, the rupture grows into the region B to the left and continues until 6 s. After OT+6 s, no clear events are detected, and rupture is terminated at OT+8 s. It is noteworthy that the main up-dip propagating rupture is temporarily suppressed around region B, and after the rupture propagates surrounding region B, the rupture propagates into region B, where a relatively fast slip-rate is observed. The sensitivity test shows that the irregular rupture propagation associated with region B is reproduced even when the model settings and the data sampling interval are slightly changed.
The irregular rupture propagation suggests that a barrier with high-strength can cause the rupture to be initially suppressed within the barrier region, followed by delayed rupture propagation through the apparent barrier. Since high-frequency seismic motions are excited by irregular changes in rupture propagation, it can be inferred that the perturbation of the rupture front by the barriers increased the damage caused by the strong ground motion.
Seismic waveforms, including teleseismic body waves, contain information about the complex seismic source process. Recently, a new method, Potency Density Tensor Inversion (PDTI), has been proposed for reducing the influence of modeling errors. The method incorporates the modeling errors due to uncertainty in the Green's function into the data covariance matrix and the fault geometry information into the model parameters. In Yagi et al. (2024), PDTI was applied to the teleseismic P-waves of the 2023 Morocco earthquake to reveal an irregular seismic source process.
We downloaded 57 components of teleseismic P-waves from the Science Advancement for Geosciences and Earth and Planetary Science (SAGE) and used them in our analysis. The horizontal location of the initial break point was set to the epicenter determined by the Portuguese Institute for Sea and Atmosphere (IPMA), and the depth of the initial break point was set to 25 km, based on a preliminary analysis. The model plane was set to a strike and dip of 255° and 69°, respectively, based on the United States Geological Survey (USGS) CMT solution.
The rupture initiated from the hypocenter propagates to east-northeast direction, then propagates bilaterally, in both up-dip and down-dip directions. The down-dip rupture propagates to 10 km below the hypocenter and is nearly terminated at about 4 s after the origin time (OT). The main up-dip propagating rupture is temporarily suppressed around a point at 19 km depth and 10 km east-northeast of the initial break point (region B) from OT+3 s to OT+4 s. After OT+4 s, the rupture grows into the region B to the left and continues until 6 s. After OT+6 s, no clear events are detected, and rupture is terminated at OT+8 s. It is noteworthy that the main up-dip propagating rupture is temporarily suppressed around region B, and after the rupture propagates surrounding region B, the rupture propagates into region B, where a relatively fast slip-rate is observed. The sensitivity test shows that the irregular rupture propagation associated with region B is reproduced even when the model settings and the data sampling interval are slightly changed.
The irregular rupture propagation suggests that a barrier with high-strength can cause the rupture to be initially suppressed within the barrier region, followed by delayed rupture propagation through the apparent barrier. Since high-frequency seismic motions are excited by irregular changes in rupture propagation, it can be inferred that the perturbation of the rupture front by the barriers increased the damage caused by the strong ground motion.