Visualization and characterization of active normal faults and associated sediments by high-resolution GPR

Abstract

Abstract Ground penetrating radar (GPR) is applied here to visualize sedimentary structures related to recent deformation. Several 200 MHz GPR profiles perpendicular to active normal faults in Spain and Italy were analysed. The El Camp normal fault with associated sedimentary and tectonic patterns in northeastern Spain serves as test site. Faulted alluvial and colluvial sediments of the Pleistocene were studied in a trench for direct comparison with GPR profiles. GPR investigations across buried faults from several localities are compared to these observations in a case study. The hanging walls of these faults form half-grabens or grabens, which are generally characterized by internal asymmetric, concave, displaced reflectors or wedge-like features comparable to sedimentary features in adjacent outcrops. The examples demonstrate that high-resolution GPR profiling provides not only the possibility to trace and map active normal faults but also to visualize the associated sedimentary hanging-wall patterns in the subsurface, such as heterogeneous graben and half-graben structures, including coarse-grained clastic wedges. Quantitative and qualitative GPR evaluation of those wedges yields a certain possibility of estimation of palaeomagnitudes and slip rates on active normal faults. We regard high-resolution GPR as an additional tool in pretrenching palaeoseismological investigations.