Abstract
The Atotsugawa fault system is one of the best-known active faults in Japan. However, revealing the interseismic velocity field in and around the Atotsugawa fault system with high spatial resolution is challenging because of dense vegetation, steep topography, and heavy snowfall in winter. To overcome these difficulties, we combined ALOS/PALSAR data and GNSS data from our original stations in addition to the nationwide station network (GEONET). First, we removed the height-dependent phase change in each interferogram using a digital elevation model. Next, we removed the long-wavelength phase trend using the GNSS velocity field. Finally, we applied an InSAR time-series analysis, known as small baseline subset analysis (SBAS), to all the corrected interferograms. The resultant mean velocity field shows a remarkable phase gradient around the Atostugawa fault system. We found a sharp velocity gradient across the Ushikubi fault, a major strand of the Atotsugawa faults system, rather than the main trace of the Atotsugawa fault. Using InSAR, we found that the interseismic deformation inside the strain concentration zone is spatially heterogeneous and different from what we expect from the fault traces.
Highlights
It is well known that the interseismic strain rate of the Japan arc is non-uniform
We focus on the velocity field of this area before the 2011 Tohoku–Oki earthquake (Mw 9.0), with the goal of characterizing a more detailed interseismic velocity field in and around the Atotsugawa fault system by combining L-band interferometric synthetic aperture radar (InSAR) and GNSS data
With much higher spatial resolution of InSAR, we revealed the internal structure of the Atotsugawa fault system and the role of the Ushikubi fault
Summary
It is well known that the interseismic strain rate of the Japan arc is non-uniform. For example, Sagiya et al (2000) found a long-stretching strain concentration zone called the Niigata–Kobe tectonic zone (NKTZ) using GNSS data (Fig. 1). Interseismic deformation fields provide ways to understand the subsurface rheological heterogeneities beneath the Japan arc To detect such a strain concentration at much higher spatial resolution, interferometric synthetic aperture radar (InSAR) analysis is a very powerful tool, which measures two-dimensional distributions of range changes between the surface and satellite (e.g., Massonnet et al 1993). Interseismic velocity fields become detectable using InSAR time-series analysis (Ferretti et al 2001; Berardino et al 2002; Schmidt and Bürgmann 2003) and/ or by stacking many interferograms (e.g., Fialko 2006; Hammond et al 2012). In these previous studies, the satellite images acquired with short-wavelength radio wave (C- or X-band) were used for urban and/or semiarid areas. High temporal resolution of GNSS is suitable for removing the effect
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