REACTIVATION OF THE ABU-JIFAN FAULT BORDERING THE RAYN ANTICINES IN EASTERN SAUDI ARABIA: GRAVITY MODELING OF A SEISMOGENIC CRUST

The Abu-Jifan Fault truncates the Rayn anticlines along an 1100 km long margin within the Rayn Microplate in eastern Saudi Arabia. This set of anticlines is comprised of six sub-parallel super-giant anticlines, including the Ghawar uplift. Crust on either side of the fault is seismically active; width of the seismic zone varies from 170 – 220 km. The Ghawar anticline is however seismically intensely active which is supposed to be an outcome of fluid-extraction induced seismicity. Top part of this seismogenic crust is currently intensely deformed in consequence to induced seismicity below the Rayn anticlines and prevailing east-west stress. Here we argue that induced seismicity plays an important role in reactivating the Proterozoic east-west faults in the deeper crust. An integrated geophysical modeling approach is next adopted to derive the deeper geometry of the Abu-Jifan Fault that slices the seismogenic crust south of the Ghawar anticline. Geophysical data sets include: seismic velocity analysis for crust and top- lithosphere, IRIS seismic line interpretation for the Arabian Platform as well as the crustal structure and upper mantle stratigraphy from receiver function analysis and shear-wave splitting studies, conventional seismic interpretation for deep sedimentary layers, isopach map prepared for the major sediment lithologies, and the relevant density information for the major formations deduced from density logs obtained from drill holes in the oil fields. Their combined use is found to be a potentially powerful tool for investigating the deeper fault geometry which is modeled by gravity inversion along a profile in central part of the fault. Gravity modeling suggests that the Abu-Jifan Fault is a deep penetrative strike-slip fault, demarcating a denser crust along its north margin.