Earthquake of Sumatra : did the axis of the Earth tremble ?

Earthquake of Sumatra : did the axis of the Earth tremble ?
Extrait du Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la Recherche.
https://www.obspm.fr/earthquake-of-sumatra-did-the.html
Earthquake of Sumatra : did
the axis of the Earth tremble ?
Date de mise en ligne : mardi 1er février 2005
Observatoire de Paris centre de recherche et enseignement en astronomie et
astrophysique relevant du Ministère de l'Enseignement supérieur et de la
Recherche.
Copyright © Observatoire de Paris centre de recherche et enseignement en astronomie et astrophysique relevant du Ministère de l'Enseignement
Page 1/3 supérieur
Earthquake of Sumatra : did the axis of the Earth tremble ?
The recent earthquake of magnitude 9.3 which took place on December 26, 2004 close to
Sumatra is the second stronger in the world since 1900 and is even stronger than the one
which occurred in Alaska in 1964 (mag 9.2). Could it have a perceptible effect in the rotation
of the Earth ? The expert researchers in Paris Observatory, pertaining to IERS
(International Earth Rotation Service) show that the effect is not discernible.
Figure 1 :
Observations : What can be seen in the observations of
IERS ?
There exist several data bases concerning the major earthquakes in particular the catalogue of U.S. Geological
Survey. From several parameters (magnitude, localization, seismic moment..) characterizing the event one can from
a model make an estimate of the effect of an event in the variations of the rotation of the earth. According to various
calculations made independently from these parameters by R. Gross (JPL), B Chao (NASA) and by C Bizouard
(Paris Observatory), the effect in the movement of the pole should be of a few centimetres in the polhodie and of a
few microseconds of time in the duration of the day, which is not very likely to be detected seen the current precision
of the observations. The Earth rotation Center of the International Earth Rotation Service (IERS) at the Observatory
of Paris has in particular the role of follow-up in quasi-real time of the variations of the earth motion by using the
observations resulting from various space techniques like the GPS, interferometry on extragalactic radio sources as
well as laser telemetry on satellites and the Moon. The fine analyses of the variations observed in the "polhodie"
(see figure 1) did not show a discernible effect.
Copyright © Observatoire de Paris centre de recherche et enseignement en astronomie et astrophysique relevant du Ministère de l'Enseignement
Page 2/3 supérieur
Earthquake of Sumatra : did the axis of the Earth tremble ?
References
•
Chao B.F.and Gross R.S., 1987 : Changes in the Earth.s rotation and low degree gravitational field induced by
earthquakes. Geophys J. Roy.Astron. Soc., 91, 569-596. Smylie D.E. and Manshina L., 1971 : The elasticity
theory of dislocation in real Earth models and changes in the rotation of the Earth, Geophys. J. Roy. Astron.
Soc., 23, 329-354. Soldati G. and Spada G., 1999 : Large earthquakes and Earth rotation : the role of mantle
relaxation. Geophys. Res. Lett., 26 , 911-914. Varga P., 1987 : Influence of the elastic stress accumulation on
the Earth.s polar position. Proc. of the int. Symp. .Figure and dynamics of the Earth, Moon and Planets., Prague,
257-269.
Copyright © Observatoire de Paris centre de recherche et enseignement en astronomie et astrophysique relevant du Ministère de l'Enseignement
Page 3/3 supérieur