  We analyze the effect of seismic activity on sealevel variations, by
computing the time-dependent vertical crustal movement and geoid change due to
coseismic deformations and postseismic relaxation effects. Seismic activity can
affect both the absolute sealevel, by changing the Earth gravity field and
hence the geoid height, and the relative sealevel, i.e. the radial distance
between seafloor and geoid level. By using comprehensive seismic catalogues we
assess the net effect of seismicity on tidal relative sealevel measurements as
well as on the global oceanic surfaces, and we obtain an estimate of absolute
sealevel variations of seismic origin.
  Our results confirm that, on a global scale, most of the signal is associated
with few giant thrust events, and that RSL estimates obtained using tide-gauge
data can be sensibly affected by the seismic driven sealevel signal.
  The recent measures of sealevel obtained by satellite altimetry show a wide
regional variation of sealevel trends over the oceanic surfaces, with the
largest deviations from the mean trend occurring in tectonically active
regions. While our estimates of average absolute sealevel variations turn out
to be orders of magnitude smaller than the satellite measured variations, we
can still argue that mass redistribution associated with aseismic tectonic
processes may contribute to the observed regional variability of sealevel
variations.
