10:00 〜 10:15
[SSS06-05] Extracting rupture-mode preferences of crustal earthquakes in Japan
★Invited Papers
キーワード：経験的グリーン関数、波形インバージョン、破壊モード
Fault rupture has a complex variety in space-time. While the slip inversion results or back-projected images mainly reveal the spatial complexities, the radiated energy enhancement factor (Ye et al., 2018) can express the temporal complexity of the moment rate function. As a spatio-temporal rupture characteristic, the rupture directivity has also been investigated from small magnitude (e.g. Boatwright 2007) to large magnitude (e.g. Ruiz et al., 2016). While the rupture directivity generally represents a macroscopic spatio-temporal characteristic over the entire fault, we focus on the subfault-scale spatio-temporal characteristic, which is called a rupture mode in fracture mechanics. Specifically, we investigated the relationship between the slip direction and the rupture propagations at each subfault, based on the waveform inversion results.
To study subfault-scale natures, we analyzed several M6-class crustal earthquakes in Japan using the waveform inversion with the radiation-corrected empirical Green’s functions (EGF; Shibata et al., 2022), which enable us to estimate slip directions by synthesizing the EGF waveforms for any focal mechanisms. Then, we introduced rupture-mode intensity to evaluate the rupture-mode preferences by comparing the rupture propagation direction with the slip direction. Since the rupture-mode intensity was extracted at each subfault and each reference time, we can statistically discuss the characteristic of the rupture propagation. As a result, we confirmed that the rupture preferentially propagated parallel (mode II) or perpendicular (mode III) to the slip direction in the subfault scale, which is consistent with fracture mechanics. In addition, the characteristic of rupture-mode selection in the early stage was similar to that in the entire rupture, implying that most rupture characteristics are determined at the early stage. In addition, we discussed the effect of the difference in the grid interval for the rupture-mode intensity and the effect of the fault edge.
To study subfault-scale natures, we analyzed several M6-class crustal earthquakes in Japan using the waveform inversion with the radiation-corrected empirical Green’s functions (EGF; Shibata et al., 2022), which enable us to estimate slip directions by synthesizing the EGF waveforms for any focal mechanisms. Then, we introduced rupture-mode intensity to evaluate the rupture-mode preferences by comparing the rupture propagation direction with the slip direction. Since the rupture-mode intensity was extracted at each subfault and each reference time, we can statistically discuss the characteristic of the rupture propagation. As a result, we confirmed that the rupture preferentially propagated parallel (mode II) or perpendicular (mode III) to the slip direction in the subfault scale, which is consistent with fracture mechanics. In addition, the characteristic of rupture-mode selection in the early stage was similar to that in the entire rupture, implying that most rupture characteristics are determined at the early stage. In addition, we discussed the effect of the difference in the grid interval for the rupture-mode intensity and the effect of the fault edge.