Displacement and Velocity Results
3/11/2011 (Mw 9.0), Tohoku-oki, Japan
Francisco Ortega
These simulations are made possible because of the density of GPS stations in Japan (about 1200 GPS stations, or approximately one GPS station every 30 km). The preliminary GPS displacement data that these animations are based on are provided by the ARIA team at JPL and Caltech. All original GEONET RINEX data provided to Calech by the TEOspational Information Authority (GSI) of Japan.
Cumulative displacement of the land in Japan over the first 35 minutes following the start of the Tohoku earthquake
This simulation shows how much the land in Japan moved during the first 35 minutes following the start of the Tohoku earthquake (which itself lasted two minutes).
The arrows show the direction of movement of each GPS station, and the color of the land shows the magnitude of its cumulative displacement.
Two kinds of motions are observed: 1) an immediate permanent deformation in the vicinity of the earthquake (first red star), 2) followed by a more elastic perturbation that travels about 4 km/sec, corresponding to the surface waves generated by the earthquake.
Velocity of the land in Japan over the first 35 minutes following the start of the Tohoku earthquake
This simulation shows the instantaneous velocities of each GPS station, and thus only shows the transient motion caused by the earthquake.
The first waves to propagate from the main shock (located at the large red star) are the body waves (P and S), but they can barely be seen (look for a slight purple perturbation).
These waves are followed by the surface waves (Love and Rayleigh), propagating as two orange-red stripes. Surface waves generate larger velocities at the surface than body waves.
After about 25 minutes, there is a subtle signal from the seismic waves generated by a small aftershock located in northern Japan (location not indicated).
After about 30 minutes, we observe the seismic waves from a 7.9M aftershock (located at the second, small, star), which is the largest aftershock to date. Since this event is 30 times smaller than the mainshock, its P and S waves are too small to be detected by our method of rapid GPS solutions, but our method does register the surface waves. The small patches of color that appear randomly across Japan indicate the noise level of the measurements and are not related to any ground motion.
|