Possible large near-trench slip during the 2011 M w 9.0 off the Pacific coast of Tohoku Earthquake

Abstract

The 11 March 2011 off the Pacific coast of Tohoku (M w 9.0) Earthquake ruptured a 200 km wide megathrust fault, with average displacements of ∼15-20 m. Early estimates of the co-seismic slip distribution using seismic, geodetic and tsunami observations vary significantly in the placement of slip, particularly in the vicinity of the trench. All methods have difficulty resolving the up-dip extent of rupture; onshore geodetic inversions have limited sensitivity to slip far offshore, seismic inversions have instabilities in seismic moment estimation as subfault segments get very shallow, and tsunami inversions average over the total region of ocean bottom uplift. Seismic wave estimates depend strongly on the velocity structure used in the model, which affects both seismic moment estimation and inferred mapping to slip. We explore these ideas using a least-squares inversion of teleseismic P-waves that yields surprisingly large fault displacements (up to ∼60 m) at shallow depth under a protrusion of the upper plate into the trench. This model provides good prediction of GPS static displacements on Honshu. We emphasize the importance of poorly-constrained rigidity variations with depth for estimating fault displacement near the trench. The possibility of large slip at very shallow depth holds implications for up-dip strain accumulation and tsunamigenic earthquake potential of megathrusts elsewhere.

Effects of Earth's layered structure, gravity and curvature on coseismic deformation

“…The fault inversion work has been done by many scientists (e.g. Iinuma et al 2011;Lay et al 2011;Pollitz et al 2011). Such as, Pollitz et al (2011) inverted the slip model using on-land GPS and offshore GPS data based on spherical model.…”

Analysis of the Far-Field Co-seismic and Post-seismic Responses Caused by the 2011 M W 9.0 Tohoku-Oki Earthquake

“…Based on these data, the co-seismic dislocation of the 9.0 earthquake can be obtained by several different inversion methods (see, for example, HAYES 2011;SIMONS et al 2011;LAY et al 2011; KOPER et al Spatial distribution of the co-seismic displacements caused by the 9.0 Tohoku-Oki earthquake (KIDO et al 2011;IINUMA et al 2012). The green arrows represent the seabed surface co-seismic displacements, the blue arrows are the near-field surface co-seismic displacements on the Japanese Island (GEONET), and the red arrows show the far-field co-seismic displacements (WANG et al 2011;ZHAO et al 2012;HWANG et al 2012).…”

The quest for wisdom: lessons from 17 tsunamis, 2004–2014

“…This model, in clear violation of scaling laws, was confirmed, in the range u = 33-69 m, by a multitude of independent studies, using inversion of seismic, geodetic and tsunami data (e.g. [31][32][33][34] featuring a seismic moment 5-12 times greater than the Tohoku event [37]. Note, however, that the geodetic data available in 1960 make it impossible to distinguish post-seismic from coseismic slips, and hence direct comparison with the 2011 earthquake may not be warranted.…”