Imaging Shallow Deformation Zone Using 2D and 3D Seismic Tomography

Near-surface deformation zones present considerable imaging challenges due to complex structural geometries, heterogeneous lithologies, and elevated ambient noise, particularly in urban and infrastructurerich environments. This study investigates a 30-meter-wide deformation outcrop within the Dammam Dome, Eastern Saudi Arabia, using 2D and 3D seismic tomography techniques complemented by detailed mineralogical analysis. The 2D seismic refraction survey was conducted along a 360-meter profile using a cabled geophone system, while the 3D survey employed a wireless nodal array comprising 108 receivers and 385 shot points. The receivers were deployed along six in-line profiles with 8-meter spacing in both in-line and cross-line directions, and sources were distributed along 11 profiles with 4-meter offsets. Super-virtual refraction interferometry (SVI) was applied to both datasets to enhance signal-to-noise ratios and improve the continuity of first-arrival traveltimes in the challenging field environment. The resulting 2D tomograms revealed a prominent high-velocity anomaly ranging from 1210 to 1650 m/s within the upper 20 meters of the subsurface. A comparable deformation zone was observed in the 3D model, with velocities ranging from 650 to 800 m/s, delineating lateral and vertical heterogeneities consistent with structural deformation. Mineralogical analyses using X-ray diffraction (XRD) and X-ray fluorescence (XRF) confirmed dolomite as the dominant mineral phase, with subordinate gypsum, quartz, and clay minerals. Elevated concentrations of magnesium, calcium, aluminum, and silicon indicate diagenetic mineralization processes, supporting a closed-system interpretation with internally sourced infill. These results collectively suggest a multi-stage deformation model characterized by faulting, brecciation, and mineral sealing. The integration of 2D and 3D seismic tomography with mineralogical data offers a robust approach for imaging shallow deformation zones in carbonate settings. The methodology offers critical insights for geohazard evaluation and subsurface characterization, particularly in tectonically active regions relevant to infrastructure development.