[S-CG45] Science of slow-to-fast earthquakes

[SCG45-P39] How can InSAR contribute to understanding slow-slip transients? The 2018 slow slip event in the Boso Peninsula, Japan

Taiki Takabe¹、*Yosuke Aoki¹、Jiaqing Wang^1,2 (1.Earthquake Research Institute, University of Tokyo、2.The First Monitoring and Application Center, China Earthquake Administration)

キーワード：Slow earthquake, GNSS, InSAR

In the last few decades, Geodetic observations such as with the Global Navigation Satellite System (GNSS) have detected Slow Slip Events (SSEs) in subduction zones. However, the limitation of its spatial coverage does not allow us to obtain the slip distribution of SSEs with the greatest spatial resolution. This study includes Synthetic Aperture Radar Interferometry (InSAR) images to complement this limitation by taking the SSE off the Boso Peninsula, central Japan, in June 2018 as an example. We employed images taken between 2017 and 2019 from the ALOS-2/PALSAR-2 descending orbit. Because the duration of the SSE is only about two weeks, much shorter than the average recurrence time of the SAR image acquisition of a few months, we tried to image the total displacement field during the SSE rather than trying to investigate its temporal evolution. We corrected ionospheric and tropospheric disturbances and the postseismic deformation of the 11 March 2011 MW 9.0 Tohoku-oki earthquake. This postseismic deformation was corrected with the GNSS data. The correct InSAR image shows that the SSE generated a shortening of the line of sight (LOS) by up to 40 mm on the east coast of the central Boso Peninsula. The LOS changes are lower inland. This observation is consistent with GNSS observations. The slip distribution estimated from both the InSAR and GNSS observations was then compared with that estimated only from the GNSS data. The slip estimated from the GNSS data alone has a peak at a depth of about 10 km, while the slip estimated from InSAR and GNSS data has two peaks at depths of 10 km and 20 km. This finding is attributed to the increase in the data, thereby improving the resolution of the slip distribution. The obtained slip distribution from both InSAR and GNSS data suggests that seismic swarms associated with this SSE are located on the downdip extension of the slip at around a depth of 20 km, which is newly found in this study.