Integrated Seismic and Resistivity Imaging Reassesses the Existence of the Qadimah Fault Near the Red Sea Shoreline

We used three geophysical methods (electrical resistivity tomography (ERT), P-wave traveltime tomography from shallow seismic refraction, and seismic reflection imaging) to study the shallow subsurface in the Qadimah area near KAEC and KAUST on the Red Sea coastal plain. The results define four main near-surface units: terrace deposits, fan deposits, Quaternary limestone, and a low-velocity zone (LVZ). The LVZ lines up with low-resistivity areas from ERT. Although these features can look like a fault zone, the reflection sections do not show clear reflector offsets, and there is no surface break along the lineament. We therefore interpret the linear step in the topography as a Quaternary reef/paleo-shoreline (about 7 m above present sea level) that sits near the outcrop of a seaward-dipping salt layer. The anomalies are better explained by salt withdrawal and dissolution than by an active normal fault. In our survey area, the proposed “Qadimah fault” does not continue through the shallow section and does not pose a current surface-rupture hazard to KAEC or KAUST.