Earth Planets Space, Vol. 63 (No. 7), pp. 693-696, 2011
Charles J. Ammon1, Thorne Lay2, Hiroo Kanamori3, and Michael Cleveland1
1The Pennsylvania State University, University Park, Pennsylvania 16802, USA
2University of California Santa Cruz, Santa Cruz, California 95064, USA
3California Institute of Technology, Pasadena, California 91125, USA
(Received April 7, 2011; Revised May 13, 2011; Accepted May 18, 2011; Online published September 27, 2011)
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 × 1022 N m (Mw 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 up-dip 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.
Key words: Great earthquakes, earthquake rupture processes, broadband seismology.