10:45 AM - 12:15 PM
[STT39-P07] Crustal deformation of the 2021 Alaska earthquake estimated from interferometric SAR analysis
Keywords:InSAR, Alaska
The Alaska-Aleutian subduction zone is one of the most seismically active regions, where the Pacific plate subducts beneath the North American plate. An Mw 8.2 earthquake occurred on the plate interface at a depth of 35 km in 2021 (hereafter, the 2021 Alaska earthquake). The crustal deformation caused by this earthquake was estimated by land-based GNSS observation networks but not yet by InSAR. InSAR analysis may enable us to detect small-scale deformations caused by secondary fault movement, landslides, etc. This study, therefore, applied InSAR analysis to the 2021 Alaska earthquake to obtain spatial continuous crustal deformation.
We used PALSAR-2 data on ALOS-2 sattellite. InSAR image showed that the crustal displacement near the epicenter was about 30 cm away in the satellite line-of-sight direction. We compared these displacements estimated from InSAR with those from the GNSS observation networks. However, there was a non-negligible difference of about 7 cm to 16 cm between InSAR and GNSS estimations. This difference may be because the InSAR analysis included long-wavelength errors for various reasons, such as disturbances in the ionosphere. Therefore, we assumed that the crustal deformation estimated by GNSS observations was correct and shifted the InSAR results to match the GNSS observation data.
However, the InSAR correction to match only one GNSS site did not work because the differences between the two data varied at GNSS sites. We used three GNSS stations to estimate the first-order trend surface of the difference and removed it from InSAR estimation. In this way, we successfully obtained the spatially continuous crustal deformation of the 2021 Alaska earthquake from the InSAR analysis. The result indicated that the land near the epicenter moved away from the satellite by about 20 cm in the satellite's line-of-sight direction. There still was no small-scale deformation such as secondary fault movement, landslide, etc. Even with the GNSS-corrected InSAR estimates, there was a difference (about 9 cm~27 cm) from the GNSS observations at Sand Point, Nagai Island, and Charnabula Island. This difference is due to the proximity of the ocean, which is a non-interference area.
We used PALSAR-2 data on ALOS-2 sattellite. InSAR image showed that the crustal displacement near the epicenter was about 30 cm away in the satellite line-of-sight direction. We compared these displacements estimated from InSAR with those from the GNSS observation networks. However, there was a non-negligible difference of about 7 cm to 16 cm between InSAR and GNSS estimations. This difference may be because the InSAR analysis included long-wavelength errors for various reasons, such as disturbances in the ionosphere. Therefore, we assumed that the crustal deformation estimated by GNSS observations was correct and shifted the InSAR results to match the GNSS observation data.
However, the InSAR correction to match only one GNSS site did not work because the differences between the two data varied at GNSS sites. We used three GNSS stations to estimate the first-order trend surface of the difference and removed it from InSAR estimation. In this way, we successfully obtained the spatially continuous crustal deformation of the 2021 Alaska earthquake from the InSAR analysis. The result indicated that the land near the epicenter moved away from the satellite by about 20 cm in the satellite's line-of-sight direction. There still was no small-scale deformation such as secondary fault movement, landslide, etc. Even with the GNSS-corrected InSAR estimates, there was a difference (about 9 cm~27 cm) from the GNSS observations at Sand Point, Nagai Island, and Charnabula Island. This difference is due to the proximity of the ocean, which is a non-interference area.