Geophysics and Shallow Faults in Unconsolidated Sediments

Abstract

This paper presents a case study using various geophysical techniques in unconsolidated sediments where shallow faulting is probable and most likely affects ground‐water flow. Wenner and dipole‐dipole resistivity, ground penetrating radar (GPR), and high resolution reflection seismic data are compared with cone penetrometer (CPT) information, existing monitoring well data and models of anticipated fault styles. The results of this study suggest that (1) the CPT study, combined with monitoring well data may suggest that discontinuities in corrrelatable zones indicate that faulting is present; (2) the addition of Wenner and dipole‐dipole data may further suggest that offset zones exist in the shallow subsurface but make it difficult to map specific faults; (3) the high resolution seismic data will image faults to within a few meters of the surface but cannot identify faulting on the scale of our models; (4) offset 100 MHz and 200 MHz common mid‐point (CMP) GPR will image features that may be fault planes and strands similar to the models; and (5) the combination of all the tools in this study, particularly the GPR and seismic, may allow for the mapping of small‐scale, shallow faults in unconsolidated sediments that affect ground‐water flow.

Relating Cone Penetrometer Test Information to Geophysical Data: A Case Study

“…This point has already been empirically demonstrated by Wyatt et al (1996) and Clement et al (1997a,b). Conversely, CPT profiles, like conventional well-logs, provide detailed information that is localized to the immediate vicinity of the borehole.…”

Ground penetrating radar investigations to study active faults in the Norcia Basin (central Italy)

“…In some cases, the GPR technique is considered a powerful tool for the definition of the geometry of sedimentary and tectonic structures and for detection of shallow faults (Bristow and Jol, 2003;Cai et al, 1996;Liner and Liner, 1997;Salvi et al, 2003;Wyatt et al, 1996). Resolution and propagation depth are a function of radar frequency (Davis and Annan, 1989).…”

Geophysical characterization of buried active faults: the Concud Fault (Iberian Chain, NE Spain)

“…Within the downthrown block, the GPR sections showed bending of the lowermost layers, defining a rollover monocline, while the upper layers evidenced a wedge shape open toward the fault, both features being related to active deformation. Comparison of these profiles with the geological relationships observed in the trenches confirms that GPR profiling is valuable for locating buried faults and inferring structural features associated with tectonic activity as shown in other studies (e.g., Wyatt et al 1996;Demanet et al 2001a;Louis et al 2002;Khan et al 2013). The amplitude of the observed magnetic anomalies exceeds what is obtained in the field measurements at the surface and in trenches.…”