Source rupture processes of the foreshock and mainshock in the 2016 Kumamoto earthquake sequence estimated from the kinematic waveform inversion of strong motion data

(Guest post by Kimiyuki Asano)

The 2016 Kumamoto earthquake sequence started on April 14, 2016, with an MW 6.1 foreshock occurring along the northern part of the Hinagu fault central Kyushu, Japan, and the MW 7.0 mainshock occurred just 28 h after the foreshock. A seismic intensity observation station at Mashiki town hall (93051) recorded a seismic intensity of 7 on the Japan Meteorological Agency (JMA) scale during both events, and another station at Nishihara village hall (93048) recorded a seismic intensity of 7 during the mainshock. Asano and Iwata (2016) 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 propagating toward Mashiki town along the northern part of the Hinagu fault. On the other hand, 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 transferred to the Futagawa fault with surface breaks. Most of the sig

Map view of final slip distribution on fault plane of mainshock with aftershocks within 24 h after mainshock. Blue line represents surface projection of source fault plane of foreshock. Triangles represent strong motion stations used in the source inversion analysis.
Map view of final slip distribution on fault plane of mainshock with aftershocks within 24 h after mainshock. Blue line represents surface projection of source fault plane of foreshock. Triangles represent strong motion stations used in the source inversion analysis.

nificant slip occurred on the Futagawa fault. 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 spatial relationship between the rupture areas of the foreshock and mainshock implies a complex fault structure in this region. The central and southern parts of the Hinagu fault were not ruptured during this earthquake sequence.

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