EXPLORING SALT TECTONICS IN NORTHERN PAKISTAN USING InSAR AND GEOPHYSICAL TECHNIQUES

Salt tectonics in Northern Pakistan affects the geological structures and the seismology of the area. Salt layers are important in influencing the deformation style of geological structures. The difference in deformation intensity between the Potwar Plateau-Salt Range and the Kohat-Surghar systems is attributed to the presence of a Pre-Cambrian salt layer. Overburden will slide efficiently on the ductile salt detachment and will result in low internal deformation, which is evident in the Potwar Plateau-Salt Range system. On the other hand, the Kohat-Surghar system has high internal deformation. This could be due to the absence or the thinning of the salt layers which causes friction between the overburden and the basement rocks.

Furthermore, north of the Main Boundary Thrust (MBT), where the area is believed to be locked due to the absence of the salt layer, strain could be accumulating and a potentially huge earthquake could occur. This is significant as the area include three major populated cities, which are Islamabad, Peshawar and Rawalpindi with over 4.1 million in population.

The extent of the Pre-Cambrian salt layer is mapped using seismic and ground gravity data. Several 2-D migrated seismic lines crossing the MBT and the Kalabagh fault were obtained. The top of the salt layer can be distinguished easily, as well as the overlying sedimentary sequence. Contrary to the seismic data, the gravity points give a broader picture of the salt layer. A Bouguer anomaly map has been created in ArcGIS using gravity data obtained from Bureau Gravimetrique International. The map shows that the study area has a relatively low gravity anomaly. However, topography and isostatic corrections are currently applied to the measurements in order to reduce the effects of the rugged terrain.

InSAR is used to study the flow of exposed salt and salt domes in the area by measuring the cumulative displacement of the surface. Eight PALSAR images from 2006 to 2009 were obtained and a pair with the highest coherence was picked. Using GAMMA, 2-pass differential interferometric processing with and without unwrapping was done using a 90m resolution DEM. Fringes showing subsidence and uplift are calculated. By combining and integrating these different data sets, this work will improve and further the study of salt tectonics in Pakistan.