Slip history of the 2016 M_w 7.0 Kumamoto earthquake: Intraplate rupture in complex tectonic environment

Abstract

Rupture history of the 2016 Mw 7.0 Kumamoto earthquake is constrained by using the waveforms of strong motion observations, teleseismic broadband body waves, and long‐period surface waves. Its fault geometry is modeled with Hinagu (orienting 205° and dipping 73°) and Futagawa (orienting 235° and dipping 60°), two segments. The result reconciles the difference between moment tensor solutions and the surface fault trace. It reveals a complex rupture process that initiated on the Hinagu segment in dextral motion, propagated northeastward unilaterally, and after 15 s ceased near Aso volcano with normal fault motion. The average slip, rise time, and slip rate are 1.8 m, 2.0 s, and 1.2 m/s, respectively. The rupture broke through an ~30° fault intersection without notable delay, which can be a result of dynamic “unclamping.” The northeast boundary of the largest asperity might mark the bottom of the seismogenic zone, which becomes shallower gradually near Aso volcano.

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

“…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.…”

“…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). Then, the large slip occurred on the Futagawa fault at a depth of 4-12 km for 6-10 s, and on the shallower region of the Futagawa fault later than 8 s (Asano and Iwata 2016;Kubo et al 2016;Uchide et al 2016;Hao et al 2017). Yagi et al (2016) and Hao et al (2017) reported from the waveform inversion that the observed moment rate function was 6.3 × 10 18 Nm/s at maximum at 8-9 s and became zero at 15-18 s. Field investigations showed that the main shock produced surface ruptures along the Hinagu and Futagawa fault zones, and the maximum slip (larger than 2 m) was observed in the Futagawa segment (Lin et al 2016;Shirahama et al 2016).…”

“…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). Then, the large slip occurred on the Futagawa fault at a depth of 4-12 km for 6-10 s, and on the shallower region of the Futagawa fault later than 8 s (Asano and Iwata 2016;Kubo et al 2016;Uchide et al 2016;Hao et al 2017).…”

“…Then, the large slip occurred on the Futagawa fault at a depth of 4-12 km for 6-10 s, and on the shallower region of the Futagawa fault later than 8 s (Asano and Iwata 2016;Kubo et al 2016;Uchide et al 2016;Hao et al 2017). Yagi et al (2016) and Hao et al (2017) reported from the waveform inversion that the observed moment rate function was 6.3 × 10 18 Nm/s at maximum at 8-9 s and became zero at 15-18 s. Field investigations showed that the main shock produced surface ruptures along the Hinagu and Futagawa fault zones, and the maximum slip (larger than 2 m) was observed in the Futagawa segment (Lin et al 2016;Shirahama et al 2016).…”

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

“…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.…”