A rupture model of the 2011 off the Pacific coast of Tohoku Earthquake

Abstract

The 11 March 2011 Tohoku Earthquake ruptured the interplate boundary off-shore of east Japan, with fault displacements of up to 40 m and a rupture duration of 150-160 s. W-phase inversion indicates a moment of 3.9 × 10 22 N m (M w 9.0) and a centroid time of 71 s. We invert teleseismic P waves and broadband Rayleigh wave observations with high-rate GPS recordings from Japan to characterize the rupture. The resulting rupture model begins with a steady increase of moment rate for the first 80 s, and a rupture speed of 1.5 km/s. Then the rupture expands southwestward at a speed of about 2.5 km/s. The model's primary slip is concentrated updip from the hypocenter, with significant displacement extending to the trench. The seaward location of large slip is consistent with estimates of the tsunami source area from regional and remote tsunami observations. The region with large slip is approximately 150-km wide by 300-km long, which is relatively compact compared with the 200-km wide, 500-km long aftershock region. The model's initial updip rupture expansion and the location of most slip updip of the hypocenter differs from P-wave array back-projections, which map high-frequency radiation along the downdip of the hypocenter, closer to the coast.

Outer trench-slope faulting and the 2011 M w 9.0 off the Pacific coast of Tohoku Earthquake

“…22 N m (J-Mod) to 4.1×10 22 N m (Pmod), compatible with long-period determinations of seismic moment (∼3.9×10 22 N m; Ammon et al, 2011); and have maximum slips of about 40 m, with average slip of about 15 m over the regions of the fault models where slip is well-resolved. Even larger slips at very shallow depth are proposed by other inversions (e.g., Lay et al, 2011c), and the calculations based on these models can be viewed as a conservative estimate for stress changes.…”

“…2. Maps of slip distributions for two finite-faulting models derived from teleseimic P-waves (left) and joint inversion of P waves, Rayleigh waves and continuous GPS observations (right, adapted from Ammon et al, 2011). The P wave inversion model has variable rake of the subfaults, indicated by the small vectors; the joint inversion has uniform rake of 85 • .…”

Spatio-temporal distribution of seismic moment release near the source area of the 2011 Tohoku-Oki earthquake

“…Many source inversion and geodetic modeling results have shown that the primary seismic moment contributions of the 2011 Tohoku mainshock were from the up-dip portion, possibly extending to the trench (Ammon et al, 2011;Iinuma et al, 2011;Lay et al, 2011b;Miyazaki et al, 2011) and that the source area was relatively strongly coupled (Mazzotti et al, 2000;Hashimoto et al, 2009;Loveless and Meade, 2010;Uchida and Matsuzawa, 2011). We thus propose a first scenario to explain the occurrence of the 2011 Tohoku-Oki, and the 2003 Tokachi-Oki, earthquakes.…”

Observation of Core Phase ScS from the Mw 9.0 Tohoku-Oki Earthquake with High-Rate GPS

“…This inference is supported by comparison of the high-rate GPS records with seismic records and synthetic seismograms. (Ammon et al, 2011;Simons et al, 2011;Fig. 1).…”