Earthquake rupture properties of the 2016 Kumamoto earthquake foreshocks (M _j 6.5 and M _j 6.4) revealed by conventional and multiple-aperture InSAR

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• 作者：Tomokazu Kobayashi
• 关键词：Foreshocks ; Kumamoto earthquake ; InSAR ; MAI ; Crustal deformation ; Fault model
• 刊名：Earth, Planets and Space
• 出版年：2017
• 出版时间：December 2017
• 年：2017
• 卷：69
• 期：1
• 全文大小：5989KB
• 刊物类别：Earth Sciences, general; Geology; Geophysics/Geodesy;
• 刊物主题：Earth Sciences, general; Geology; Geophysics/Geodesy;
• 出版者：Springer Berlin Heidelberg
• ISSN：1880-5981
• 卷排序：69

文摘

By applying conventional cross-track InSAR and multiple-aperture InSAR (MAI) techniques with ALOS-2 SAR data to foreshocks of the 2016 Kumamoto earthquake, ground displacement fields in range (line-of-sight) and azimuth components have been successfully mapped. The most concentrated crustal deformation with ground displacement exceeding 15 cm is located on the western side of the Hinagu fault zone. A locally distributed displacement which appears along the strike of the Futagawa fault can be identified in and around Mashiki town, suggesting that a different local fault slip also contributed toward foreshocks. Inverting InSAR, MAI, and GNSS data, distributed slip models are obtained that show almost pure right-lateral fault motion on a plane dipping west by 80° for the Hinagu fault and almost pure normal fault motion on a plane dipping south by 70° for the local fault beneath Mashiki town. The slip on the Hinagu fault reaches around the junction of the Hinagu and Futagawa faults. The slip in the north significantly extends down to around 10 km depth, while in the south the slip is concentrated near the ground surface, perhaps corresponding to the M_j 6.5 and the M_j 6.4 events, respectively. The focal mechanism of the distributed slip model for the Hinagu fault alone shows pure right-lateral motion, which is inconsistent with the seismically estimated mechanism that includes a significant non-double couple component. On the other hand, when taking the contribution of normal fault motion into account, the focal mechanism appears similar to that of the seismic analysis. This result may suggest that local fault motion occurred just beneath Mashiki town, simultaneously with the M_j 6.5 event, thereby increasing the degree of damage to the town.Graphical abstract.