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

Abstract

The 2016 Kumamoto earthquake sequence started with an M JMA 6.5 foreshock occurring along the northern part of the Hinagu fault, central Kyushu, Japan, and the M JMA 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.

Toward automated directivity estimates in earthquake moment tensor inversion

“…7). However, we emphasize that the Kumamoto earthquake is a relatively large earthquake with complex ruptures across multiple fault segments (Asano & Iwata 2016;Kubo et al 2016;Yagi et al 2016). As a primary estimate, our method well resolves the average behavior of the rupture and provides reasonable and rapid results critical for hazards estimates.…”

“…Preceded by a foreshock (M w 6.0) occurring on the Hinagu fault 28 hr before, the mainshock rupture initiated on the Hinagu fault and propagated north-northeast toward the Futagawa fault (Asano & Iwata 2016;Kubo et al 2016;Yagi et al 2016). The average rupture velocity was around 2.4 km s −1 in the north-northeast direction (Asano & Iwata 2016;Yagi et al 2016). Since the Kumamoto earthquake is a relatively large event, to better satisfy the plane wave assumption, we use stations at a larger distance within 500 km from the epicenter (Fig.…”

Long-term slow slip events along the Nankai trough subduction zone after the 2011 Tohoku earthquake in Japan

“…The reason why we chose the data before April 10, 2016, is that the 2016 Kumamoto earthquakes occurred from April 14, 2016 (e.g., Asano and Iwata 2016), the coseismic and postseismic slips of which contaminated the subsequent GNSS data. The degree n of the polynomial function and the overtone m of the trigonometric functions were estimated from Akaike's information criterion (AIC) (Akaike 1974) (Additional file 1).…”

Source process of the 2016 Kumamoto earthquake (Mj7.3) inferred from kinematic inversion of strong-motion records

“…Several source models of the Mj7.3 of the 2016 Kumamoto earthquake have been proposed on the basis of the Open Access *Correspondence: yoshida@geor.or.jp 1 Geo-Research Institute, 2-1-2 Otemae, Chuo-ku, Osaka 540-0008, Japan Full list of author information is available at the end of the article strong motions (e.g., Asano and Iwata 2016), teleseismic waveforms (Yagi et al 2016), and crustal deformation (e.g., Himematsu and Furuya 2016). Most of these studies based on seismic data assume northwest-dipping fault planes.…”