PHYSICAL MODELING OF OVERBURDEN DEFORMATION AROUND SALT DIAPIRS

Salt diapirs produce highly complex deformation patterns in the surrou nding overburden which are difficult to image seismically or model num erically. To further the understanding of deformation around salt stru ctures we have used physical models with brittle granular overburdens, and simulated sedimentation accompanying diapiric rise. Rigid linear indenters produce a crestal horst above the indentor with two flanking graben. Large amounts of indentation produce predominantly reverse fa ults along the margins of the diapir and extensional faults over the c rest. In contrast hemispherical indenters produced inward-dipping conc entric reverse faults. Forefully intruded polymer diapirs produce a na rrow crestal graben above the diapir crest. Downbuilt polymer diapirs produce extensional faults on the flanks of the diapirs which offset t he diapir walls. No clear secondary rim synclines were developed as po lymer is withdrawn evenly from the whole of the polymer layer across t he model. Strong and anisotropic layered overburden were simulated usi ng cohesive clay and mica respectively. Detachments were formed along mica layers which suppressed faults with large throws. Cohesive layer deformation began with tensile fractures, permitting rotation of fract ured rafts around the sides of the diapir. These progressively slip of f the crest and create large gaps in the stratigraphy.