Rupture processes of the 2016 Kumamoto earthquake sequence: Causes for extreme ground motions

Kobayashi, Hiroaki; Koketsu, Kazuki

doi:10.1002/2017gl073857

Cited by 45 publications

(62 citation statements)

References 38 publications

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“…6b). Thus, the large slip on the Futagawa fault that was observed by the seismic waveform analyses (Asano and Iwata 2016;Kubo et al 2016;Uchide et al 2016;Yagi et al 2016;Kobayashi et al 2017;Hao et al 2017) as well as in the geodetic data (Himematsu and Furuya 2016) would not be produced, even if the D c and S H values are smaller than those used in this study. If D c is much smaller than 0.1 m in case E, the rupture might transfer to the Futagawa fault.…”

Section: Rupture Processes In An Infinite Mediummentioning

confidence: 84%

“…1). The largest slip was shown to occur at a portion of the Futagawa fault shallower than 12 km by seismic waveform inversion analyses (Asano and Iwata 2016;Kubo et al 2016;Uchide et al 2016;Yagi et al 2016;Kobayashi et al 2017;Hao et al 2017) as well as in the geodetic data (Himematsu and Furuya 2016). These studies reported the maximum slip amount was 4-6 m. The seismic waveform inversion results suggested that the slip of the main shock occurred on the Hinagu fault first and propagated to the Futagawa fault at a depth of 10-15 km at 2-4 s (Asano and Iwata 2016;Kubo et al 2016;Uchide et al 2016;Hao et al 2017).…”

Section: Introductionmentioning

confidence: 94%

“…This slip model can avoid stress singularities around the edge of the fault with the uniform slip distribution. We used the analytical solution because the slip distribution was estimated only for the largest foreshock by waveform inversions initially (Kubo et al 2016;Asano and Iwata 2016), although most recently the slip distribution of foreshock 3 was estimated by Kobayashi et al (2017). The details of the procedure are described in "Appendix 1" section.…”

Section: Static Stress Changes By Foreshocksmentioning

confidence: 99%

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3-D dynamic rupture simulations of the 2016 Kumamoto, Japan, earthquake

Urata

Yoshida

Fukuyama

et al. 2017

Earth Planets Space

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Using 3-D dynamic rupture simulations, we investigated the 2016 M w 7.1 Kumamoto, Japan, earthquake to elucidate why and how the rupture of the main shock propagated successfully, assuming a complicated fault geometry estimated on the basis of the distributions of the aftershocks. The M w 7.1 main shock occurred along the Futagawa and Hinagu faults. Within 28 h before the main shock, three M6-class foreshocks occurred. Their hypocenters were located along the Hinagu and Futagawa faults, and their focal mechanisms were similar to that of the main shock. Therefore, an extensive stress shadow should have been generated on the fault plane of the main shock. First, we estimated the geometry of the fault planes of the three foreshocks as well as that of the main shock based on the temporal evolution of the relocated aftershock hypocenters. We then evaluated the static stress changes on the main shock fault plane that were due to the occurrence of the three foreshocks, assuming elliptical cracks with constant stress drops on the estimated fault planes. The obtained static stress change distribution indicated that Coulomb failure stress change (ΔCFS) was positive just below the hypocenter of the main shock, while the ΔCFS in the shallow region above the hypocenter was negative. Therefore, these foreshocks could encourage the initiation of the main shock rupture and could hinder the propagation of the rupture toward the shallow region. Finally, we conducted 3-D dynamic rupture simulations of the main shock using the initial stress distribution, which was the sum of the static stress changes caused by these foreshocks and the regional stress field. Assuming a slip-weakening law with uniform friction parameters, we computed 3-D dynamic rupture by varying the friction parameters and the values of the principal stresses. We obtained feasible parameter ranges that could reproduce the characteristic features of the main shock rupture revealed by seismic waveform analyses. We also observed that the free surface encouraged the slip evolution of the main shock.

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Section: Rupture Processes In An Infinite Mediummentioning

confidence: 84%

Section: Introductionmentioning

confidence: 94%

Section: Static Stress Changes By Foreshocksmentioning

confidence: 99%

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3-D dynamic rupture simulations of the 2016 Kumamoto, Japan, earthquake

Urata

Yoshida

Fukuyama

et al. 2017

Earth Planets Space

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“…1), and two aftershocks with M JMA magnitude 4.9 and 4.8. The mainshock itself was omitted from the analysis as it has rather complex earthquake source rupture process that was studied in detail in other studies (e.g., Asano and Iwata 2016;Kubo et al 2016;Kobayashi et al 2017). …”

Section: Application To the 2016 Kumamoto Sequencementioning

confidence: 99%

“…The normal faulting was dominant especially in the northeast part of the rupture zone (e.g., Toda et al 2016). Finite source models for the mainshock were inverted from strong motion records (e.g., Asano and Iwata 2016;Kubo et al 2016;Hao et al 2017;Kobayashi et al 2017;Yoshida et al 2017). The inferred models suggest that the M JMA 7.3 event started near the intersection of the Futagawa and Hinagu faults by right-lateral strike-slip movement; then, the rupture propagated to the NE along the Futagawa fault as strike-slip with a normal faulting component.…”

Section: Introductionmentioning

confidence: 99%

Bayesian inference and interpretation of centroid moment tensors of the 2016 Kumamoto earthquake sequence, Kyushu, Japan

Hallo

Asano

Gallovič

2017

Earth Planets Space

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On April 16, 2016, Kumamoto prefecture in Kyushu region, Japan, was devastated by a shallow M JMA 7.3 earthquake. The series of foreshocks started by M JMA 6.5 foreshock 28 h before the mainshock. They have originated in Hinagu fault zone intersecting the mainshock Futagawa fault zone; hence, the tectonic background for this earthquake sequence is rather complex. Here we infer centroid moment tensors (CMTs) for 11 events with M JMA between 4.8 and 6.5, using strong motion records of the K-NET, KiK-net and F-net networks. We use upgraded Bayesian full-waveform inversion code ISOLA-ObsPy, which takes into account uncertainty of the velocity model. Such an approach allows us to reliably assess uncertainty of the CMT parameters including the centroid position. The solutions show significant systematic spatial and temporal variations throughout the sequence. Foreshocks are right-lateral steeply dipping strike-slip events connected to the NE-SW shear zone. Those located close to the intersection of the Hinagu and Futagawa fault zones are dipping slightly to ESE, while those in the southern area are dipping to WNW. Contrarily, aftershocks are mostly normal dip-slip events, being related to the N-S extensional tectonic regime. Most of the deviatoric moment tensors contain only minor CLVD component, which can be attributed to the velocity model uncertainty. Nevertheless, two of the CMTs involve a significant CLVD component, which may reflect complex rupture process. Decomposition of those moment tensors into two pure shear moment tensors suggests combined right-lateral strike-slip and normal dip-slip mechanisms, consistent with the tectonic settings of the intersection of the Hinagu and Futagawa fault zones.

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Stress rotations due to the M6.5 foreshock and M7.3 main shock in the 2016 Kumamoto, SW Japan, earthquake sequence

Yoshida

Hasegawa

Saito

et al. 2016

Geophysical Research Letters

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A shallow M7.3 event with a M6.5 foreshock occurred along the Futagawa‐Hinagu fault zone in Kyushu, SW Japan. We investigated the spatiotemporal variation of the stress orientations in and around the source area of this 2016 Kumamoto earthquake sequence by inverting 1218 focal mechanisms. The results show that the σ3 axis in the vicinity of the fault plane significantly rotated counterclockwise after the M6.5 foreshock and rotated clockwise after the M7.3 main shock in the Hinagu fault segment. This observation indicates that a significant portion of the shear stress was released both by the M6.5 foreshock and M7.3 main shock. It is estimated that the stress release by the M6.5 foreshock occurred in the shallower part of the Hinagu fault segment, which brought the stress concentration in its deeper part. This might have caused the M7.3 main shock rupture mainly along the deeper part of the Hinagu fault segment after 28 h.

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Rupture processes of the 2016 Kumamoto earthquake sequence: Causes for extreme ground motions

Cited by 45 publications

References 38 publications

3-D dynamic rupture simulations of the 2016 Kumamoto, Japan, earthquake

3-D dynamic rupture simulations of the 2016 Kumamoto, Japan, earthquake

Bayesian inference and interpretation of centroid moment tensors of the 2016 Kumamoto earthquake sequence, Kyushu, Japan

Stress rotations due to the M6.5 foreshock and M7.3 main shock in the 2016 Kumamoto, SW Japan, earthquake sequence

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