The great (M(w)=9.3) Valdivia earthquake of May 21-22, 1960, was assoc
iated with ground deformation over a distance of over 800 km parallel
to the Peru-Chile trench. Downwarping by as much as 2.3 m affected a b
elt averaging a width of 100 km which was bordered by a major upwarped
zone in the west, where uplift locally attained 5.7 m, and a minor up
warped zone in the east. The deformation has been explained by thin vi
scous sheet models or by dislocation models involving predominantly di
p-slip movement on thrust faults. We show that it can be modeled by el
astic buckling of the overriding South American plate without the need
to invoke specific fault geometries. The proposed buckling mechanism
accounts for both zones of upwarping and for the exceptionally rapid u
plift experienced by Mocha Island to the west. Moreover, elastic relax
ation provides a simple explanation for the postseismic recovery repor
ted by observers at several sites. It is also consistent with the resu
lts obtained by C-14 dating of fossil shorelines within and outside th
e area affected by the 1960 events, which show that central and northe
rn Chile has undergone little uplift during the last 30,000 years desp
ite convergence between the South American and Nazca plates at over 90
mm/yr, although the presence of numerous older shorelines shows that
coastal uplift was very active earlier in the Cenozoic.