Paper:

# Postseismic Uplift Along the Pacific Coast of Tohoku and Kanto Districts Associated with the 2011 off the Pacific Coast of Tohoku Earthquake

## Takeshi Iinuma^{†}

Yokohama Institute for Earth Sciences, Japan Agency for Marine-Earth Science and Technology

3173-25 Showa-machi Kanazawa-ku, Yokohama, Kanagawa 236-0001, Japan

^{†}Corresponding author

The 2011 off the Pacific coast of Tohoku earthquake (M9.0) produced up to 1.2 m subsidence along the Pacific coast in northeastern Japan. Based on Global Positioning System (GPS) observations, continuing postseismic coastal uplift has been detected in the past six years after the main shock. By applying a 3D spherical Earth viscoelastic finite element model using the postseismic seafloor and terrestrial GPS observations as constraints, I demonstrate that this uplift is mainly caused by the postseismic viscoelastic relaxation of the asthenosphere. Although the model was constrained only based on horizontal crustal deformation, the vertical displacements predicted for six years after the 2011 Tohoku earthquake agree reasonably well with the time series of the observed uplift at sites along the Pacific coast including the southern Sanriku coast and Kanto district. I estimated the time at which the cumulative postseismic uplift will fully compensate the coseismic subsidence. The results show that large coseismic coastal subsidence on the southern Sanriku coast will be fully offset by the postseismic uplift within several decades. To the immediate north, the model underpredicts the postseismic uplift and possibly indicates unaccounted postseismic fault creep. Farther south, the postseismic uplift of the coast of the Kanto district has already exceeded the small amount of coseismic subsidence over the past six years, as predicted by the model. To prepare for future earthquakes, especially with respect to the coastal construction at fishery ports, it is important to construct a comprehensive rheological structure model based on geophysical observations including GNSS positioning.

*J. Disaster Res.*, Vol.13, No.3, pp. 496-502, 2018.

- [1] M. Kido, Y. Osada, H. Fujimoto, R. Hino, and Y. Ito, “Trench-normal variation in observed seafloor displacements associated with the 2011 Tohoku-Oki earthquake,” Geophys. Res. Lett., Vol.38, L24303, doi:10.1029/2011GL050057, 2011.
- [2] S. Ozawa, T. Nishimura, H. Suito, T. Kobayashi, M. Tobita, and T. Imakiire, “Coseismic and postseismic slip of the 2011 magnitude-9 Tohoku-Oki earthquake,” Nature, Vol.475, pp. 373-376, doi:10.1038/nature10227, 2011.
- [3] M. Sato, T. Ishikawa, N. Ujihara, S. Yoshida, M. Fujita, M. Mochizuki, and A. Asada, “Displacement Above the Hypocenter of the 2011 Tohoku-Oki Earthquake,” Science, Vol.332, p. 1395, doi:10.1126/science.1207401, 2011.
- [4] F. F. Pollitz, R. Bürgmann, and P. Banerjee, “Geodetic slip model of the 2011 M9.0 Tohoku earthquake,” Geophys. Res. Lett., Vol.38, L00G08, doi:10.1029/2011GL048632, 2011.
- [5] M. Simons, S. E. Minson, A. Sladen, F. Ortega, J. Jiang, S. E. Owen, L. Meng, J. Ampuero, S. Wei, R. Chu, D. V. Helmberger, H. Kanamori, E. Hetland, A. W. Moore, and F. H. Webb, “The 2011 Magnitude 9.0 Tohoku-Oki Earthquake: Mosaicking the Megathrust from Seconds to Centuries,” Science, Vol.332, pp. 1421-1425, doi:10.1126/science.1206731, 2011.
- [6] T. Iinuma, R. Hino, M. Kido, D. Inazu, Y. Osada, Y. Ito, M. Ohzono, H. Tsushima, S. Suzuki, H. Fujimoto, and S. Miura, “Coseismic slip distribution of the 2011 off the Pacific coast of Tohoku earthquake (M9.0) refined by means of seafloor geodetic data,” J. Geophys. Res., Vol.117, B07409, doi:10.1029/2012JB009186, 2012.
- [7] T. Kato, “Crustal movements in the tohoku district, Japan, during the period 1900-1975, and their tectonic implications,” Tectonophysics, Vol.60, pp. 141-167, doi:10.1016/0040-1951(79)90156-2, 1979.
- [8] T. Kato, “Secular and earthquake-related vertical crustal movement in Japan as deduced from tidal records (1951–1981),” Tectonophysics, Vol.97, pp. 183-200, doi:10.1016/0040-1951(83)90147-6, 1983.
- [9] G. S. El-Fiky and T. Kato, “Interplate coupling in the Tohoku district, Japan, deduced from geodetic data inversion,” J. Geophys. Res., Vol.104, pp. 20361-20377, doi:10.1029/1999JB900202, 1999.
- [10] Y. Suwa, S. Miura, A. Hasegawa, T. Sato, and K. Tachibana, “Interplate coupling beneath NE Japan inferred from three-dimensional displacement field,” J. Geophys. Res., Vol.111, B04402, doi:10.1029/2004JB003203, 2006.
- [11] K. M. Johnson, J. Fukuda, and P. Segall, “Challenging the rate-state asperity model: Afterslip following the 2011 M9 Tohoku-oki, Japan, earthquake,” Geophys. Res. Lett., Vol.39, L20302, doi:10.1029/2012GL052901, 2012.
- [12] S. Ozawa, T. Nishimura, H. Munekane, H. Suito, T. Kobayashi, M. Tobita, and T. Imakiire, “Preceding, coseismic, and postseismic slips of the 2011 Tohoku earthquake, Japan,” J. Geophys. Res., Vol.117, B07404, doi:10.1029/2011JB009120, 2012.
- [13] T. Nishimura, “Pre-, Co-, and Post-Seismic Deformation of the 2011 Tohoku-Oki Earthquake and its Implication to a Paradox in Short-Term and Long-Term Deformation,” J. Disaster Res., Vol.9, pp. 294-302, doi:10.20965/jdr.2014.p0294, 2014.
- [14] F. Silverii, D. Cheloni, N. D’Agostino, G. Selvaggi, and E. Boschi, “Post-seismic slip of the 2011 Tohoku-Oki earthquake from GPS observations: implications for depth-dependent properties of subduction megathrusts,” Geophys. J. Int., Vol.198, pp. 580-596, doi:10.1093/gji/ggu149, 2014.
- [15] T. Sun, K. Wang, T. Iinuma, R. Hino, J. He, H. Fujimoto, M. Kido, Y. Osada, S. Miura, Y. Ohta, and Y. Hu, “Prevalence of viscoelastic relaxation after the 2011 Tohoku-oki earthquake,” Nature, Vol.514, pp. 84-87, doi:10.1038/nature13778, 2014.
- [16] T. Iinuma, R. Hino, M. Kido, Y. Osada, D. Inazu, Y. Ito, S. Suzuki, Y. Ohta, and H. Fujimoto, “Investigation on the Postseismic Deformation Associated with the 2011 Tohoku Earthquake Based on Terrestrial and Seafloor Geodetic Observations: To Evaluate the Further Seismic Hazard Potential on the Plate Interface Beneath the Northeastern Japanese Islands,” In C. Rizos and P. Willis (Eds.), “IAG 150 Years,” Int. Assoc. Geod. Symp., Vol.143, pp. 459-466, Springer, Cham, doi:10.1007/1345_2015_162, 2015.
- [17] S. Yamagiwa, S. Miyazaki, K. Hirahara, and Y. Fukahata, “Afterslip and viscoelastic relaxation following the 2011 Tohoku-oki earthquake (Mw9.0) inferred from inland GPS and seafloor GPS/Acoustic data,” Geophys. Res. Lett., Vol.42, pp. 66-73, doi:10.1002/2014GL061735, 2015.
- [18] T. Iinuma, R. Hino, N. Uchida, W. Nakamura, M. Kido, Y. Osada, and S. Miura, “Seafloor observations indicate spatial separation of coseismic and postseismic slips in the 2011 Tohoku earthquake,” Nature Communications, Vol.7, 13506, doi:10.1038/ncomms13506, 2016.
- [19] H. Nakagawa, T. Toyofuku, K. Kotani, B. Miyahara, C. Iwashita, S. Kawamoto, Y. Hatanaka, H. Munekane, M. Ishimoto and T. Yutsudo, N. Ishikura, and Y. Sugawara, “Development and Validation of GEONET New Analysis Strategy (Version 4),” J. Geogr. Surv. Inst., Vol.118, pp. 1-8, 2009 (in Japanese).
- [20] S. Watanabe, M. Sato, M. Fujita, T. Ishikawa, Y. Yokota, N. Ujihara, and A. Asada, “Evidence of viscoelastic deformation following the 2011 Tohoku-Oki earthquake revealed from seafloor geodetic observation,” Geophys. Res. Lett., Vol.41, pp. 5789-5796, doi:10.1002/2014GL061134, 2014.
- [21] F. F. Pollitz, “Gravitational viscoelastic postseismic relaxation on a layered spherical Earth,” J. Geophys. Res., Vol.102, pp. 17921-17941, doi:10.1029/97JB01277, 1997.
- [22] N. Hatakeyama, N. Uchida, T. Matsuzawa, and W. Nakamura, “Emergence and disappearance of interplate repeating earthquakes following the 2011 M9.0 Tohoku-oki earthquake: Slip behavior transition between seismic and aseismic depending on the loading rate,” J. Geophys. Res. Solid Earth, Vol.122, pp. 5160-5180, doi:10.1002/2016JB013914, 2017.
- [23] T. Sun and K. Wang, “Viscoelastic relaxation following subduction earthquakes and its effects on afterslip determination,” J. Geophys. Res. Solid Earth, Vol.120, pp. 1329-1344, doi:10.1002/2014JB011707, 2015.
- [24] N. Uchida and T. Matsuzawa, “Pre- and postseismic slow slip surrounding the 2011 Tohoku-oki earthquake rupture,” Earth Planet. Sci. Lett., Vol.374, pp. 81-91, doi:10.1016/j.epsl.2013.05.021, 2013.
- [25] C. Goetze and B. Evans, “Stress and temperature in the bending lithosphere as constrained by experimental rock mechanics,” Geophys. J. R. Astr. Soc., Vol.59, pp. 463-478, doi:10.1111/j.1365-246X.1979.tb02567.x, 1979.
- [26] S. H. Kirby, “Rheology of the lithosphere,” Rev. Geophys., Vol.21, pp. 1458-1487, doi:10.1029/RG021i006p01458, 1983.
- [27] Kahoku-Shimpo, “Reworking due to uplifting after the bulk-up at Ayukawa port,” Kahoku-Shimpo, 2016 (in Japanese). http://www.kahoku.co.jp/tohokunews/201612/20161213_11017.html [accessed July 18, 2017]
- [28] K. Kawaguchi, S. Kaneko, T. Nishida, and T. Komine, “Construction of the DONET real-time seafloor observatory for earthquakes and tsunami monitoring,” in P. Favali et al. (Eds.), “Seafloor Observatories,” Springer Praxis Books, pp. 211-228, doi:10.1007/978-3-642-11374-1_10, 2015.
- [29] Y. Kaneda, K. Kawaguchi, E. Araki, H. Matsumoto, T. Nakamura, S. Kamiya, K. Ariyoshi, T. Hori, T. Baba, and N. Takahashi, “Development and application of an advanced ocean floor network system for megathrust earthquakes and tsunamis,” in P. Favali et al. (Eds.), “Seafloor Observatories,” Springer Praxis Books, pp. 643-662, doi:10.1007/978-3-642-11374-1_25, 2015.
- [30] Y. Yokota, T. Ishikawa, S. Watanabe, T. Tashiro, and A. Asada, “Seafloor geodetic constraints on interplate coupling of the Nankai Trough megathrust zone,” Nature, Vol.534, pp. 374-377, doi:10.1038/nature17632, 2016.
- [31] R. Agata, T. Ichimura, K. Hirahara, M. Hyodo, T. Hori, C. Hashimoto, and M. Hori, “Numerical Verification Criteria for Coseismic and Postseismic Crustal Deformation Analysis with Large-scale High-fidelity Model,” Proc. Comput. Sci., Vol.51, pp. 1534-1544, doi:10.1016/j.procs.2015.05.344, 2015.
- [32] T. Ichimura, R. Agata, T. Hori, K. Hirahara, C. Hashimoto, M. Hori, and Y. Fukahata, “An elastic/viscoelastic finite element analysis method for crustal deformation using a 3-D island-scale high-fidelity model,” Geophys. J. Int., Vol.206, pp. 114-129, doi:10.1093/gji/ggw123, 2016.
- [33] P. Wessel and W. H. F. Smith, “New, improved version of Generic Mapping Tools released,” Trans. Am. Geophys. Union, Vol.79, p. 579, doi:10.1029/98EO00426, 1998.