Analysis of surface settlements on the atoll of Mururoa

Geodesic surveys have revealed that all the land testing ares of Mururoa have suffered settlement as a result of underground testing. Parts of the rim of Mururoa, initially only about 1 ~ 2 m above sea level, are now submerged. This settlement is considered by the Commissariat à 1' Energie Atomique (CEA) to be a consequence of the compaction of carbonates (from surface to a depth of 120 m), when surface layers of carbonates were thrown into ballistic flight and fell back to impact and compact the underlying formations. An alternative mechanism of settlement will be discussed. This involves shear deformation of the carbonates, associated with irreversible lateral movement of the submerged atoll flanks. A variety of arguments are presented to support the shearing mechanism, including results of numerical simulations involving the propagation of a stress pulse in yielding carbonate layers. The analysis suggests a connection between the settlements and the stability of atoll flanks.