[S-SS05] Crustal Deformation

[SSS05-08] Preliminary results of sea-floor crustal deformation measured by GNSS-Acoustic technique in Nemuro-Oki, southwestern part of Kuril Trench

*Yusaku Ohta¹, Motoyuki Kido², Chie Honsho¹, Yukiho Kimura¹, Makiko Sato¹, Syuichi Suzuki¹, Ryosuke Azuma¹, Mako Ohzono^3,5, Hiroki Aota³, Hiroaki Takahashi³, Fumiaki Tomita⁴, Takeshi Iinuma⁴, Masanao Shinohara⁵, Ryota Hino¹ (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 2.International Research Institute of Disaster Science, Tohoku University, 3. Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University, 4.Japan Agency for Marine-Earth Science and Technology, 5.Earthquake Research Institute,The University of Tokyo)

Keywords:Sea-floor geodesy, GNSS-A, Nemuro-Oki

The sea-floor geodetic technique including GNSS-Acoustic measurement played an important role to understand the coseismic slip behavior in the 2011 Tohoku-Oki earthquake and revealed that more than 50m coseismic slip occurred at the shallow part of the plate boundary. In order to understand the diversity of earthquakes, it is essential to clarify the factors that determine the large slip at the shallow part of the plate boundary from comparative studies with past huge earthquakes in other regions.
In the Nemuro-Oki of the southwestern part of Kuril Trench, M8 class earthquakes have repeatedly occurred in the Tokachi-Oki and Nemuro-Oki segments. On the other hand, based on the survey of the distribution of tsunami deposits, it has been pointed out that a large slip may have occurred in the shallow part of the plat boundary in the 17^th century, rupturing both of the Tokachi-Oki and Nemuro-Oki segments, and that the slip characteristic is similar with the 2011 Tohoku-Oki earthquake (Ioki and Tanioka, 2016). In contrast, Nemuro-Oki is no sea-floor geodetic network.
Based on these backgrounds, Tohoku University and Hokkaido University have jointly developed a sea-floor geodetic network to estimate the interplate locking at the shallower portion of the subducting plate interface, and installed three GNSS-A stations (G21, G22, and G23) in Nemuro-Oki. The G21 and G22 were installed on the landward slope, and the G23 installed on the incoming Pacific plate. The first observation was carried out in July 2019, and the second in October 2020. Although the obtained results are still tentative because of the only two times observations, the estimated horizontal velocity shows the more than 9cm/year to the northwest direction relative to the Okhotsk plate in both of G21 and G22. This result is expected to suggest that the interplate locking at the shallow part of the subducting plate interface. The modeling of these results will be discussed in detail in the presentation.