Small-displacement linear surface ruptures of the 2016 Kumamoto earthquake sequence detected by ALOS-2 SAR interferometry

Satoshi Fujiwara,Yasuaki Kakiage,Yu Morishita,Hiroyuki Nakai,Haruka Ueshiba,Tomokazu Kobayashi,Hiroshi Yarai,Yuji Miura,Takayuki Nakano,Basara Miyahara,Hiroshi Une

doi:10.1186/s40623-016-0534-x

Satoshi Fujiwara, Yasuaki Kakiage + Show 9 more

Open Access

https://doi.org/10.1186/s40623-016-0534-x

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Abstract

We constructed and analyzed the ground surface displacement associated with the 2016 Kumamoto earthquake sequence using satellite radar interferometry images of the Advanced Land Observing Satellite 2. The radar interferogram generally shows elastic deformation caused by the main earthquakes, but many other linear discontinuities showing displacement are also found. Approximately 230 lineaments are identified, some of which coincide with the positions of known active faults, such as the main earthquake faults belonging to the Futagawa and Hinagu fault zones and other minor faults; however, there are much fewer known active faults than lineaments. In each area, the lineaments have a similar direction and displacement to each other; therefore, they can be divided into several groups based on location and major features. Since the direction of the lineaments coincides with that of known active faults or their conjugate faults, the cause of the lineaments must be related to the tectonic stress field of this region. The lineaments are classified into the following two categories: (1) main earthquake faults and their branched subfaults and (2) secondary faults that are not directly related to the main earthquake but whose slip was probably triggered by the main earthquake or aftershocks.

Highlights

The 2016 Kumamoto earthquake sequence in Japan caused large crustal deformation, and exposed faults have been identified by ground surveys (Geological Survey of Japan 2016; Goto et al 2016; Kumahara et al 2016; Shirahama et al 2016) and aerial photographs (Nakano et al 2016)
Because the displacements of each lineament are not related to their baseline and these lineaments were not found in the interferograms taken before and after the Kumamoto earthquake sequence, as well as the fact that accuracy of the DEM was 5 m (GSI 2014), the DEM error was small enough to not affect the lineaments
General features of linear surface ruptures We found approximately 230 linear surface ruptures, for example in the somma of Aso volcano, along the Futagawa and Hinagu fault zones, and even in Kumamoto city center

Summary

Introduction

The 2016 Kumamoto earthquake sequence in Japan caused large crustal deformation, and exposed faults have been identified by ground surveys (Geological Survey of Japan 2016; Goto et al 2016; Kumahara et al 2016; Shirahama et al 2016) and aerial photographs (Nakano et al 2016). ALOS-2 has three main advantages for observation of this earthquake sequence. L-band SAR interferometry (InSAR) is advantageous for detecting ground displacements, even in vegetated areas, due to its high coherence, compared with C- or X-band microwaves (Kobayashi et al 2011). This capability enables us to capture the entire crustal deformation, even in vegetated mountainous areas. The second advantage is a right-and-left looking observation capability.

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