4.2.1. Model 1

Model 1 is one single balloon-shaped salt structure from the Hidra High (Figure 10). The salt structure geometry of Model 1 was based on an interpreted seismic section close to a well 1/8-3 on the Hidra High on the North-Eastern flank of the Central Graben (Figure 2).

**Figure 10.** Interpreted present-day geometry of Model 1. Units are coloured by age. Ex situ salt volume is marked by cross-hatching. In situ salt coloured dark purple as defined by age interval (248–300 Ma).

Figure 11 shows the reconstructed geohistory combining litho-switching and mass-editing to enable both upward and later horizontal movement of the salt volume into an overhang. The lithology input parameters are shown in Table 1. The salt movement is initiated along a fault zone and once a relief on the salt surface is established in Triassic time upward movement of salt continuous through Cretaceous time when a vertical salt diapir of more than 5 km height was established. Increasingly differential loading lead to a skewed development of the top salt bulb, bending it over and developing it into a hemisphere asymmetrically placed relative to its now dramatically thinned and broken stem during Paleogene to Cenozoic evolution.



**Figure 11.** Reconstructed geohistory of Model 1, showing the stepwise evolution from a uniform salt layer to the present day salt balloon. The figure is colored based on the lithologies used in the model. The main salt volume protrudes through the Ekofisk and Hod chalks (in purple and blue) and is capped by Cenozoic shales.
