Geodetic evidence for mobilization of evaporites during the 1997 Strophades (W Hellanic Arc) Mw6.5 earthquake

Analysis of repeated GPS campaigns revealed that a station in the Strophades islets, a structural high in the Ionian Sea originating from post-Lower Pliocene compression-associated evaporite diapirism, recorded 12 cm horizontal slip and 10 cm uplift, the latter confirmed also by coastal data. This surface deformation can be assigned to the 1997 Mw 6.5 earthquake, reflects non-elastic response of a major surface salt dome to seismic shortening of the crystalline basement and is structurally similar to the deformation of the nearby island of Cephalonia during the 1953 Mw 7.3 earthquakes; for the latter, the long-term deformation of the Strophades isles had been presented as a model. The 1997 Strophades crustal deformation probably represents the first known case of the geodetically recorded response of a salt dome to an earthquake, and a case of an unusual earthquake cycle.