Earthquakes have collectively the tendency to displace the pole of rotation of the earth towards a preferred direction (~140 ¿E). This trend, which is still unexplained on quantitative grounds, has been revealed by computations of earthquake-induced inertia variations on both a secular and a decade time-scale. Purpose of this letter is to show that the above trend results from the combined effects of the geographical distribution of hypocenters and of the prevailing dip-slip nature of large earthquakes in this century. Our findings are based on the static dislocation theory and on simple geometrical arguments.¿ 1997 American Geophysical Union