Observation of earthquake ground motion due to aftershocks of the 2016 Kumamoto earthquake in damaged areas

Yamanaka, Hiroaki; Chimoto, Kosuke; Tsuno, Seiji; Yamada, Nobuyuki

doi:10.1186/s40623-016-0574-2

Cited by 21 publications

(12 citation statements)

References 6 publications

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“…This may be because the stress shadow effect was slightly overestimated and the rupture delayed in the stress shadow zone. We did not focus on the reproduction of the observed seismograms in this study because we assumed uniform P-and S-wave velocities in the simulations, but this assumption was too simple to reproduce the near-fault site effect mentioned in the observations (Yamanaka et al 2016). In addition, the element size (0.5 km 2 ) might be too large to represent the surface movement by the fault.…”

Section: Discussionmentioning

confidence: 99%

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: Discussionmentioning

confidence: 99%

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

Urata

Yoshida

Fukuyama

et al. 2017

Earth Planets Space

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“…b Black triangles show the locations of temporary observation sites deployed in Mashiki (S1-S8). Gray triangles indicate the temporary aftershock observation stations deployed by Yamanaka et al (2016) in the same area (MK01, MK02, MK05 and MK09) and a white triangle shows the location of seismic intensity meter deployed by JMA. Gray squares show the locations of the seismic intensity observation station inside Mashiki town office (MTO) and the KiK-net strong-motion observation station KMMH16 (same location as the Hi-net station N.MSIH) operated during both the largest foreshock and the mainshock.…”

Section: Introductionmentioning

confidence: 99%

“…1b). Figure 1b also shows the locations of aftershock observation stations deployed by Yamanaka et al (2016) (gray triangles: MK01, MK02, MK05 and MK09) and a seismic intensity station deployed by JMA (white triangle) just after the mainshock. Our aftershock observation sites were installed in the heavily damaged zones, while the existing temporary aftershock stations were located outside of this zone.…”

Section: Introductionmentioning

confidence: 99%

Subsurface velocity structure and site amplification characteristics in Mashiki Town, Kumamoto Prefecture, Japan, inferred from microtremor and aftershock recordings of the 2016 Kumamoto earthquakes

Hayashida

Yamada

et al. 2018

Earth Planets Space

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In order to investigate the seismic velocity structure in the region of concentrated severe damage during the 2016 Kumamoto earthquake sequence, we conducted continuous seismic observations in the central area of Mashiki Town, Kumamoto Prefecture. During 4 days of observations at eight temporary sites, 2 months after the mainshock, recordings from 30 aftershocks (1.7 ≤ M j ≤ 4.3, 1.9 km ≤ depth ≤ 13.5 km) were obtained. The aftershock data showed that site amplifications at approximately 1 Hz are dominant in a zone where almost no buildings were damaged along the Akitsu riverside, whereas site amplifications at higher than 3 Hz are observed in the heavily damaged zones. Our data also showed that the peak acceleration and velocity amplitudes, as well as seismic intensities for the small events in the less damaged zone, are clearly larger than those in the damaged zones, implying that the damage distribution is inconsistent with site response based on linear site amplifications. The estimated phase velocities of Rayleigh waves using the aftershock and microtremor data show dispersive characteristics in the lower frequency range (0.26 ≤ f ≤ 1.27 Hz), but the values are substantially smaller than those derived from the P-S logging model at the nearest KiK-net strong-motion observation station KMMH16. The derived microtremor horizontal-to-vertical spectral ratios and earthquake radial-to-vertical (R/V) spectral ratios show common distinct peaks at around 0.4 Hz, which are possibly related to the response of deep sedimentary layers beneath the area. The refined velocity structure model that better accounts for both the phase velocity and common dominant peak indicates that the values of S wave velocity (Vs) above the bedrock layer (Vs = 2700 m/s) are smaller than those inferred from the logging model and the depth to the bedrock layer could be much deeper (about 600 m) in comparison with the logging model (234 m). The derived R/V spectral ratio at station KMMH16 also shows a distinct peak at 0.4 Hz, suggesting that there is no large difference of deep sedimentary structure between the observation area and station KMMH16. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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“…Hata et al (2016) also try to reproduce strong ground motion, especially near the Shinkansen (bullet train system in Japan) track, with special reference to site effects. Yamanaka et al (2016) conduct dense observation of aftershocks in heavily damaged areas and find local amplification effects in Mashiki, Nishihara and Kumamoto, but not in Minami-Aso. Chimoto et al (2016) conduct array analysis in Mashiki and Nishihara and obtain the S-wave velocity structure, which they consider controls site amplification.…”

Section: Open Accessmentioning

confidence: 99%