Abstract
We have quantified the effects of a water mass redistribution associated with the propagation of a tsunami wave on the Earths pole path and on the Length-Of-Day (LOD) and applied our modeling results to the tsunami following the 2004 giant Sumatra earthquake. We compared the result of our simulations on the instantaneous rotational axis variations with the preliminary instrumental evidence on the pole path perturbation (which has not been confirmed) registered just after the occurrence of the earthquake. The detected perturbation in the pole path showed a step-like discontinuity that cannot be attributed to the effect of a seismic dislocation. Our results show that the tsunami induced instantaneous rotational pole perturbation is indeed characterized by a step-like discontinuity compatible with the observations but its magnitude is almost one hundred times smaller than the detected one. The LOD variation induced by the water mass redistribution turns out to be not significant because the total effect is smaller than current measurements uncertainties.
Highlights
Due to the action of various internal geophysical processes the Earth rotates about an axis not aligned with its figure axis; this induces the Planet to wobble as it rotates
This work is aimed at studying the perturbation to the instantaneous rotational pole due to a transient phenomenon that, to our knowledge, has not been still investigated, i.e. the transient water mass redistribution associated with the propagation of a tsunami wave
The pole path variations turn out to have the same temporal dependence of the step-like signal observed by Bianco et al (2005a,b), but their magnitude is too small to explain the observed data, besides the LOD variations turn out to be smaller than the uncertainty in the measurements
Summary
Due to the action of various internal geophysical processes the Earth rotates about an axis not aligned with its figure axis; this induces the Planet to wobble as it rotates. The resulting effect obtained from such an excitation is a shift of the mean pole of rotation while the instantaneous rotational pole describes a continuous curve with a sudden change in the curvature radius at the time t=0 when the perturbation is «turned on» (Lambeck, 1980) Such an effect on the Earth rotation has never been observed, not even in recent earthquakes (i.e. the 26th December 2004 Sumatra earthquake) (Gross and Chao, 2006), with the exception of a preliminary observation by Bianco et al (2005a,b) who evidenced a step-like discontinuity in the pole path instead of the expected change in curvature radius in correspondence of the Sumatra earthquake. The pole path variations turn out to have the same temporal dependence of the step-like signal observed by Bianco et al (2005a,b), but their magnitude is too small to explain the observed data, besides the LOD variations turn out to be smaller than the uncertainty in the measurements
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