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[SSS10-02] Multi-hypocenter rupture propagation validated from realistic multi-cycle earthquake simulation
Keywords:rupture propagation, dynamic source model, multi-hypopocenter, characterized source model, strong motion generation area, rate-and-state friction
Multi-hypocenter modelling of rupture propagation in the kinematic source modelling for strong-motion simulation becomes a widely accepted approach. In this approach, ruptures within SMGA’s propagate from the sub-hypocenters assigned within each SMGA, while in background area rupture propagate from the main hypocenter of the earthquake. Directivity effect strongly depend on location of these sub-hypocenters. E.g., if sub-hypocenter is in the bottom of SMGA, directivity effect at the ground surface (and ground motions respectively) become larger (e.g., Somei et al., 2019). It is naturally to assume that sub-hypocenter should be assigned to a point of first touch of the main rupture, i.e., on the edge of SMGA where the main rupture arrives. However, source inversion of observed waveforms by the characterized (SMGA) model, frequently requires that sub-hypocenters should be assigned to the edges aside to the main rupture arrival, and sometimes even on the opposite side (e.g., Matsushima and Kawase, 2009). In this study, we discuss multi-hypocenter features of the rupture propagation observed in the realistic dynamic rupture models validated by observed data.
Due to a small number of time windows, rupture propagation heterogeneities, estimated from source inversions, may have poor resolution. Realistic dynamic rupture modelling of observed earthquakes is an alternative approach. Source inversions using forward dynamic modelling are frequently used to obtain rupture models. Alternatively, in this study, we use set of spontaneous physically self-consistent rupture models on strike-slip fault, whose rupture process is consistent with the spatio-temporal heterogeneity of previous earthquakes on the same fault, as the result of cycle simulations under the rate-and-state friction law (Galvez et al., 2021). Models are well validated by comparison with: (1) source scaling relations from the seismic inversions, (2) GMPE, and (3) observed fault displacements.
For validated ruptures, we did detail analysis of the animations of the slip-rate snapshots of rupture propagation. One example of this analysis is on the figure below. We found that:
1.Ruptures accelerate in areas of small values of characteristic distance Dc (asperities).
2.Ruptures vanish or may stop on barriers, which are areas of large Dc.
3.Chains of asperities make channels for rupture propagation, these channels guide ruptures aside of the straightforward propagation.
4.As result of (3) above, inside asperities ruptures may propagate not only forward, but also downward, upward, and sometimes even backward.
5.In rare but possible cases rupture may encircle a barrier spot forming “barrier-like asperity” (Oglesby and Archuleta, 1997).
6.Due to rupture refractions and reflections from the ground surface, behind primary rupture there are numerous secondary ruptures propagating chaotically in different directions.
7.Overlapping of secondary ruptures with arrested primary rupture may trigger rupture re-nucleation.
Acknowledgement: This study was based on the 2021 research project “Examination for uncertainty of strong ground motion prediction for inland crustal earthquakes” by The Secretariat of the Nuclear Regulation Authority (NRA), Japan.
References.
Galvez et al. (2021). “Multi-cycle earthquake modeling …”, Bull.Seismol.Soc.Am., doi: 10.1785/0120210104.
Matsushima and Kawase (2009). “Re-evaluation of strong motion and damage …”, J. Struct. Eng., AIJ 55B (3), 537-543.
Oglesby and Archuleta (1997). “A faulting model for the 1992 Petrolia earthquake …”, Journal of Geophysical Research, 102(B6), 11,877-11,897.
Somei et al. (2019). “Near-Source Strong Pulses During …”, Pure Appl. Geophys., doi.org/10.1007/s00024-019-02095-6.
Somerville et al. (1999). “Characterizing crustal earthquake slip models …”, Seismol. Res. Lett. 70, 59–80.
Due to a small number of time windows, rupture propagation heterogeneities, estimated from source inversions, may have poor resolution. Realistic dynamic rupture modelling of observed earthquakes is an alternative approach. Source inversions using forward dynamic modelling are frequently used to obtain rupture models. Alternatively, in this study, we use set of spontaneous physically self-consistent rupture models on strike-slip fault, whose rupture process is consistent with the spatio-temporal heterogeneity of previous earthquakes on the same fault, as the result of cycle simulations under the rate-and-state friction law (Galvez et al., 2021). Models are well validated by comparison with: (1) source scaling relations from the seismic inversions, (2) GMPE, and (3) observed fault displacements.
For validated ruptures, we did detail analysis of the animations of the slip-rate snapshots of rupture propagation. One example of this analysis is on the figure below. We found that:
1.Ruptures accelerate in areas of small values of characteristic distance Dc (asperities).
2.Ruptures vanish or may stop on barriers, which are areas of large Dc.
3.Chains of asperities make channels for rupture propagation, these channels guide ruptures aside of the straightforward propagation.
4.As result of (3) above, inside asperities ruptures may propagate not only forward, but also downward, upward, and sometimes even backward.
5.In rare but possible cases rupture may encircle a barrier spot forming “barrier-like asperity” (Oglesby and Archuleta, 1997).
6.Due to rupture refractions and reflections from the ground surface, behind primary rupture there are numerous secondary ruptures propagating chaotically in different directions.
7.Overlapping of secondary ruptures with arrested primary rupture may trigger rupture re-nucleation.
Acknowledgement: This study was based on the 2021 research project “Examination for uncertainty of strong ground motion prediction for inland crustal earthquakes” by The Secretariat of the Nuclear Regulation Authority (NRA), Japan.
References.
Galvez et al. (2021). “Multi-cycle earthquake modeling …”, Bull.Seismol.Soc.Am., doi: 10.1785/0120210104.
Matsushima and Kawase (2009). “Re-evaluation of strong motion and damage …”, J. Struct. Eng., AIJ 55B (3), 537-543.
Oglesby and Archuleta (1997). “A faulting model for the 1992 Petrolia earthquake …”, Journal of Geophysical Research, 102(B6), 11,877-11,897.
Somei et al. (2019). “Near-Source Strong Pulses During …”, Pure Appl. Geophys., doi.org/10.1007/s00024-019-02095-6.
Somerville et al. (1999). “Characterizing crustal earthquake slip models …”, Seismol. Res. Lett. 70, 59–80.