Automatically updated every morning 8 a.m. (click on image to show full size). Temporal resolution is one day. Estimated from 15-s data, thus frequency resolution is 0.011574 mHz. Although this resolution is not optimum for detection of the 0S0-mode (0.81699 mHz), the use of a Hanning window warrants enough amplitude response to make the signal visible.
|A long-time series' periodogram,
five days of 30-s data. The earthquake has not excited the
"balloon" mode 0S0 to any efficient
degree. The signal strength is 100 times less compared to
Tohoku 2011-03-12, cf. below.
|Free oscillations from Maule
(2010) and Sendai (2011) in comparison
(click for larger image)from four days of 60s band-pass filtered gravity residuals, 2010-02-28-- and 2011-03-12--, respectively.
|The decay of Free
oscillations over time
(click for larger image)after Sendai main shock 2011-03-11 05:46 UT
Link to a wide version, 0 to 5 mHz
The 2011-03-11 UT 05:46 Tohoku Mw9.0 earthquake near Sendai, Japan
From 72h Superconducting gravimetry, 1-s data, at Onsala Space Observatory
Appearance of 0T3, a toroidal oscillation, is due to earth rotation, more specifically Coriolis acceleration.
On a non-rotating earthm a toroidal mode would only have horizontal motion. The Coriolos effect
induces a small fraction of acceleration into the vertical, where the gravimeter can sense it.
The annotation of the 0S0 mode is misplaced in this plot, should be at 0.817 mHz, sorry!
Hans-Georg Scherneck, March 17, 2011