Abstract
The 2016 Kumamoto earthquake sequence started with an MJMA 6.5 foreshock occurring along the northern part of the Hinagu fault, central Kyushu, Japan, and the MJMA 7.3 mainshock occurred just 28 h after the foreshock. We analyzed the source rupture processes of the foreshock and mainshock by using the kinematic waveform inversion technique on strong motion data. The foreshock was characterized by right-lateral strike-slip occurring on a nearly vertical fault plane along the northern part of the Hinagu fault, and it had two large-slip areas: one near the hypocenter and another at a shallow depth. The rupture of the mainshock started from the deep portion of a northwest-dipping fault plane along the northern part of the Hinagu fault, then continued to transfer to the Futagawa fault. Most of the significant slip occurred on the Futagawa fault, and the shallow portion of the Hinagu fault also had a relatively large slip. The slip amount on the shallowest subfaults along the Futagawa fault was approximately 1–4 m, which is consistent with the emergence of surface breaks associated with this earthquake. Right-lateral strike-slip dominated on the fault segment along the Hinagu fault, but normal-slip components were estimated to make a significant contribution on the fault segment along the Futagawa fault. The large fault-parallel displacements recorded at two near-fault strong motion stations coincided with the spatiotemporal pattern of the fault slip history during the mainshock. The spatial relationship between the rupture areas of the foreshock and mainshock implies a complex fault structure in this region.
Highlights
The 2016 Kumamoto earthquake sequence started with an MJMA 6.5 earthquake at a shallow depth in Kumamoto Prefecture, which is in the central part of Kyushu Island, southwest Japan, at 21:26 Japan Standard Time (JST) on April 14, 2016 (12:26 UTC on April 14, 2016)
This paper focuses on the source rupture processes of the two significant events during the 2016 Kumamoto earthquake sequence based on kinematic waveform inversion analyses using strong motion data
The source rupture processes of the foreshock and mainshock in the 2016 Kumamoto earthquake sequence were estimated by kinematic waveform inversion of strong motion data
Summary
The 2016 Kumamoto earthquake sequence started with an MJMA 6.5 earthquake at a shallow depth in Kumamoto Prefecture, which is in the central part of Kyushu Island, southwest Japan, at 21:26 Japan Standard Time (JST) on April 14, 2016 (12:26 UTC on April 14, 2016). Another station at Nishihara village hall (93048, blue triangle in Fig. 1a) recorded a seismic intensity of 7 during the mainshock These two near-fault stations belong to the seismic intensity information network deployed by the Kumamoto prefectural government, and their observed records were released via the JMA. This earthquake sequence occurred along the Futagawa fault zone and the northern part of the Hinagu fault zone in central Kyushu. The crustal deformation and surface rupture along the Futagawa–Hinagu fault system were identified by multiple-aperture interferometry (MAI) analysis using ALOS-2/PALSAR-2 data (Yarai et al 2016) These observational results imply that the fault rupture is associated with the Futagawa fault and northern part of the Hinagu fault
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