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Postseismic Deformation Associated With the 2011 Tohoku-oki Earthquake (M9.0) Based on 5 Years of Terrestrial and Seafloor Geodetic Observations

Event Type: 
Seminar
Event Date: 
14 Mar 2017
Venue: 
ASE Conference Room 2 (N2-01C-77)
Speaker: 
Takeshi Iinuma
About the speaker: 

Dr Takeshi Iinuma is a scientist at Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology (JAMSTEC). His field of expertise is in geodesy and solid Earth physics. Takeshi was born in 1977 in Tokyo, and in 2005 he obtained his PhD in geophysics from the University of Tokyo.

His dissertation, under the supervision of Prof Teruyuki Kato, was titled Application of the Inversion Methods of Stress and Constitutive Relation to the Japanese Islands. He was a Postdoctoral Fellow at the Research Center for Predictions of Earthquakes and Volcanic Eruptions, Tohoku University between 2006 and 2011, after which he became an Assistant Professor at the International Research Institute of Disaster Science, Tohoku University.

About the event: 

Sun et al. [2014, nature] revealed that the viscoelastic relaxation is dominant source of the postseismic deformation since immediately after the M9 Tohoku-oki earthquake in 2011 based on about 1 year of the terrestrial and seafloor geodetic observations. However, the distribution of the seafloor geodetic observation sites is too limited around the main rupture area of the M9 main shock to grasp the overall spatio-temporal pattern of the postseismic deformation. Thus, we have been performing GPS/acoustic (GPS/A) observations on a network that includes 20 new stations installed in 2012 that broadly distribute off the Pacific coast of Tohoku district [Kido et al., 2015, IAGS]. We estimated a horizontal seafloor displacement rate at each site with the estimation error of the rates is averagely ~3 cm/yr. The calculated displacement rates at the sites southern portion (36~37°N) show high trenchward displacement rates (5~15 cm/year), which can be interpreted as the effect of postseismic slip. Moreover, we also found out that highest trenchward movement have been occurring off Fukushima Prefecture near the trench, while seaward displacements at the terrestrial sites are not so large. It suggests that the postseismic slip has been occurring at the shallow portion on the plate interface. High landward displacement rates (~10 cm/year) that observed above the main rupture area definitely prove the occurrence of the viscoelastic relaxation, but the rate decreases with approaching to the trench. Large seaward displacement rates (~10 cm/year) at terrestrial observation sites and small trenchward motion (