10:15 AM - 10:30 AM
[SSS10-05] Characteristics of earthquake source parameter and fault rupture propagation for moderate-to large earthquake
Keywords:Dynamic fault rupture, Source process, Scaling law
During an earthquake, a dynamic fault rupture grows from small to large scale and sometimes shows a complex rupture front with a various slip rate. For example, the 2011 Mw 9.1 Tohoku earthquake showed complex rupture propagation (e.g. Ide et al., 2011) in which the rupture firstly propagated to the down-dip direction and then a significant slip occurred at the up-dip of the hypocenter along the Japan trench. The fault rupture of the 2016 Mw 5.1 Gyeongju earthquake was separated into two slip regions at 1.2 s after the initiation, indicating a complex pattern (Uchide & Song, 2018). Yoshida & Kanamori (2023) investigated the source complexity using the radiated energy enhancement factor (REEF; Ye et al., 2018), which evaluates the shape of the moment rate function of the source fault. Consequently, they revealed that the complexity in the fault rupture was not dependent on the magnitude of the earthquake. Although the REEF is useful in evaluating the temporal complexity of the fault rupture as this index evaluates the spatial integral of the moment release, the REEF is not suitable for evaluating the spatial source complexity.
In this study, to investigate the dependency of the spatiotemporal complexity in the source process on the magnitude, we first obtained source processes of Mw-5 class earthquakes around Japan including crustal and plate-boundary earthquakes. For the source process estimation, we utilized the waveform inversion with the radiation-corrected empirical Green’s function (Shibata & Aso, 2025a, BSSA), which is advantageous for the analysis of moderate earthquakes and with the ocean bottom seismometer data. Then, we evaluated the rupture propagation direction using the method of Shibata & Aso (2025b, EPS in review). Shibata & Aso (2025b) introduced the rupture propagation intensity by comparing the slip rate distribution around a reference location before and after the reference time. Because this method does not require the assumption of the rupture front shape, we can apply this method to any source process. In this study, by combining the source processes of six Mw-6 class crustal earthquakes in Japan obtained in Shibata & Aso (2025a), we investigated the complexity of the rupture propagation at various earthquake magnitudes. We found that the large crustal earthquakes had a more complex rupture front than the Haskell-like or circular-crack rupture, and the large crustal earthquakes did not show a biased rupture propagation. In addition, we investigated the scaling law of the source parameter, such as the maximum slip and radiated energy.
In this study, to investigate the dependency of the spatiotemporal complexity in the source process on the magnitude, we first obtained source processes of Mw-5 class earthquakes around Japan including crustal and plate-boundary earthquakes. For the source process estimation, we utilized the waveform inversion with the radiation-corrected empirical Green’s function (Shibata & Aso, 2025a, BSSA), which is advantageous for the analysis of moderate earthquakes and with the ocean bottom seismometer data. Then, we evaluated the rupture propagation direction using the method of Shibata & Aso (2025b, EPS in review). Shibata & Aso (2025b) introduced the rupture propagation intensity by comparing the slip rate distribution around a reference location before and after the reference time. Because this method does not require the assumption of the rupture front shape, we can apply this method to any source process. In this study, by combining the source processes of six Mw-6 class crustal earthquakes in Japan obtained in Shibata & Aso (2025a), we investigated the complexity of the rupture propagation at various earthquake magnitudes. We found that the large crustal earthquakes had a more complex rupture front than the Haskell-like or circular-crack rupture, and the large crustal earthquakes did not show a biased rupture propagation. In addition, we investigated the scaling law of the source parameter, such as the maximum slip and radiated energy.