Earthquake-origin expansion of the Earth inferred from a spherical-Earth elastic dislocation theory

In this paper, we propose an approach to compute the coseismic Earth's volume change based on a spherical-Earth elastic dislocation theory. We present a general expression of the Earth's volume change for three typical dislocations: the shear, tensile and explosion sources. We conduct a case study for the 2004 Sumatra earthquake (M w 9.3), the 2010 Chile earthquake (M w 8.8), the 2011 Tohoku-Oki earthquake (M w 9.0) and the 2013 Okhotsk Sea earthquake (M w 8.3). The results show that mega-thrust earthquakes make the Earth expand and earthquakes along a normal fault make the Earth contract. We compare the volume changes computed for finite fault models and a point source of the 2011 Tohoku-Oki earthquake (M w 9.0). The big difference of the results indicates that the coseismic changes in the Earth's volume (or the mean radius) are strongly dependent on the earthquakes' focal mechanism, especially the depth and the dip angle. Then we estimate the cumulative volume changes by historical earthquakes (M w 7.0) since 1960, and obtain an Earth mean radius expanding rate about 0.011 mm yr -1 .