11:00 AM - 11:15 AM
[SGD02-07] Detecting inter-seismic displacement velocity field along the Median Tectonic Line (MTL) in Shikoku by InSAR time series analysis
Keywords:Interferometric Synthetic Aperture Radar (InSAR), time series analysis, Median Tectonic Line (MTL), fault, inter-seismic displacement
Japan is located on subduction zone which make complicated crustal deformation. It causes not only inter-plate earthquakes but also intra-prate earthquakes. Median Tectonic Line (MTL) is one of the largest fault zones in Japan which can give rise to earthquakes in the future, running from western Japan to eastern Japan whose total length reaches 1,000 km or longer. As for MTL in Shikoku, it is suggested that the tectonic topographic feature is the most obvious and the displacement velocity of surface is the fastest (Tsutsumi and Goto, 2006). Although some researches who estimated displacement velocity field along the MTL has been published (e.g., Aoki and scholz, 2003), most of them used fixed point observations such as Global Navigation Satellite System (GNSS). It is difficult for such a point observation to detect detailed spatial distribution of displacement velocity because the density of observation network is limited due to several reasons. Thus, we tried to estimate the displacement velocity field due to the fault slip along the MTL by using Interferometric Synthetic Aperture Rader (InSAR).
Synthetic Aperture Rader (SAR) is one of the remote sensing techniques. SAR does not require any equipment on the ground and can observe large extent of the target area. In this research, we used SAR data acquired by “ALOS-2”, which JAXA operates, from 2014/9/26 to 2022/6/24. Path-Frame No. of SAR data we used is “21-2930” (observed by descending satellite), which covers north-eastern Shikoku. We used RINC (ver.0.45) to conduct InSAR analysis to all possible interferometric pairs. It is reported that the displacement due to MTL’s dextral strike-slip is 5~10mm/yr in middle and eastern Shikoku (Okada, 1973), which is difficult to be detectd by traditional two-pass InSAR processing, because InSAR images usually contain delay noises caused by atmosphere. Thus, we apply the Split Spectrum Method (Gomba et al., 2015) to correct the ionospheric noise. After that, we estimated the line-of-sight (LOS) velocity by using LiCSBAS (Morishita, 2020), a software for the InSAR time series analysis based on the SBAS method.
As a result of the InSAR time series analysis on descending frame (with the ionospheric noise correction), we could recognize small LOS velocity changes at the fault line in some part of the MTL. In particular, at Ikeda fault and Chichio fault, LOS velocities (negative value means approaching to the satellite) in northern part of the fault lines was 1~2mm/yr lower than southern part of the fault lines. It indicates that the northern area moves eastward and/or uplift direction relative to the southern part, because the LOS in the descending right-looking configuration changes positively if the surface moves westward and/or downward directions. This may reflect the MTL’s dextral strike-slip. Also, the smooth LOS velocity change at the MTL may reflect the existence of an asperity. We will also show the result of InSAR time series analysis with a neutral atmospheric delay correction in the presentation.
Synthetic Aperture Rader (SAR) is one of the remote sensing techniques. SAR does not require any equipment on the ground and can observe large extent of the target area. In this research, we used SAR data acquired by “ALOS-2”, which JAXA operates, from 2014/9/26 to 2022/6/24. Path-Frame No. of SAR data we used is “21-2930” (observed by descending satellite), which covers north-eastern Shikoku. We used RINC (ver.0.45) to conduct InSAR analysis to all possible interferometric pairs. It is reported that the displacement due to MTL’s dextral strike-slip is 5~10mm/yr in middle and eastern Shikoku (Okada, 1973), which is difficult to be detectd by traditional two-pass InSAR processing, because InSAR images usually contain delay noises caused by atmosphere. Thus, we apply the Split Spectrum Method (Gomba et al., 2015) to correct the ionospheric noise. After that, we estimated the line-of-sight (LOS) velocity by using LiCSBAS (Morishita, 2020), a software for the InSAR time series analysis based on the SBAS method.
As a result of the InSAR time series analysis on descending frame (with the ionospheric noise correction), we could recognize small LOS velocity changes at the fault line in some part of the MTL. In particular, at Ikeda fault and Chichio fault, LOS velocities (negative value means approaching to the satellite) in northern part of the fault lines was 1~2mm/yr lower than southern part of the fault lines. It indicates that the northern area moves eastward and/or uplift direction relative to the southern part, because the LOS in the descending right-looking configuration changes positively if the surface moves westward and/or downward directions. This may reflect the MTL’s dextral strike-slip. Also, the smooth LOS velocity change at the MTL may reflect the existence of an asperity. We will also show the result of InSAR time series analysis with a neutral atmospheric delay correction in the presentation.