Earth Planets Space, Vol. 63 (No. 7), pp. 535-539, 2011
Zacharie Duputel1, Luis Rivera1, Hiroo Kanamori2, Gavin P. Hayes3,4, Barry Hirshorn5, and Stuart Weinstein5
1IPGS-EOST, CNRS/Universitéde Strasbourg, UMR 7516, Strasbourg, France
2Seismological Laboratory, Caltech, Pasadena, USA
3U.S. Geological Survey, National Earthquake Information Center, USA
4Synergetics Inc., Fort Collins, Colorado, USA
5NOAA, NWS, Pacific Tsunami Warning Center, Hawaii, USA
(Received April 8, 2011; Revised May 19, 2011; Accepted May 24, 2011; Online published September 27, 2011)
The real time W phase source inversion algorithm was independently running at three organizations (USGS, PTWC and IPGS) at the time of the 2011 off the Pacific coast of Tohoku Earthquake. Valuable results for tsunami warning purposes were obtained 20 min after the event origin time. Within the next hour, as more data became available, the W phase solutions improved, and converged to a common result (Mw ≈ 9.0, dip ≈ 14°). A post-mortem W phase analysis using data selection based on pre-event noise confirmed the Mw = 9.0 result and yielded a best double couple given by (strike/dip/rake = 196°/12°/85°). We also ran the algorithm with increasingly longer periods (T ≈ 1500 sec) to test for the possibility of additional slow slip. The seismic moment remained stable, confirming the prior results.
Key words: Tsunamis, surface waves and free oscillations, wave propagation, Early Warning.