Earth Planets Space, Vol. 64 (No. 12), pp. 1077-1091, 2012
Geospatial Information Authority of Japan, 1 Kitasato, Tsukuba, Ibaraki 305-0811, Japan
(Received December 22, 2011; Revised June 1, 2012; Accepted July 25, 2012; Online published January 28, 2013)
GPS kinematic time series are analyzed to estimate slip distributions for the Mw 9.0 2011 off the Pacific coast of
Tohoku Earthquake sequence. Empirical orthogonal function (EOF) analysis is employed to enhance the signal-to-noise ratio of the original time series.
The coseismic, and subsequent postseismic, deformations of the foreshock can be described by a single mode, suggesting
that the extent of the source for both events must be similar. The total moment magnitude of the afterslip following the foreshock is estimated
to be Mw 7.1 with a decay time of 0.63 days. The magnitude of the afterslip was larger for its duration than was anticipated
by the scaling law for a typical slow earthquake, although two previous earthquakes in adjacent regions showed the same tendency as that
in the present case. The pattern of slip of the mainshock and the subsequent afterslips and aftershocks indicates
that each slip occurs in a region adjacent to that of the previous slips in a complementary manner. Finally, in the course of
the EOF analysis, the modes representing the thermal expansion of the GPS pillars are clearly identified.
Key words: Kinematic GPS, EOF, coseismic slip, afterslip.