Investigating gravitational grabens related to lateral spreading and evaporite dissolution subsidence by means of detailed mapping, trenching, and electrical resistivity tomography (Spanish Pyrenees)

Abstract

The active lateral spread of the Peracalç Range (Spanish Pyrenees) has developed on a Cretaceous limestone sequence around 250 m thick, underlain by tectonically thickened (~2.5 km) Triassic halite-bearing evaporites and clays. Outward expansion of the Triassic sequence by ductile deformation and probably halokinesis toward the debuttressed and unloaded front of the range has been accommodated in the overlying cap rock through the development of a striking horst and graben morphostructure. Fault scarps show anomalously high height to length ratios (aspect ratio; H max /L) compared to the values reported for tectonic faults. This retrogressive gravitational deformation has aborted a paleodrainage, expressed as wind gaps, hanging valleys, and defeated streams. The signifi cant vertical displacement component in this rock spread is attributed to subsidence caused by interstratal evaporite dissolution, as supported by the dissolution-induced collapse and graben structures mapped at the foot of the range. To our knowledge, the rock spread of Peracalç, covering around 4.5 km 2 and with a minimum volume of 0.9 km 3 , is the largest documented landslide of the Pyrenees. The excavation of trenches and the acquisition of electrical resistivity tomography profi les provided information on the thickness and subsurface structure of the graben fi lls, the age of the lateral spread (older than 45 ka), an unexpected episodic kinematic behavior of the gravitational faults, and the timing of deformation events, including slumping of lake deposits.

Evaluation of the SBAS InSAR Service of the European Space Agency’s Geohazard Exploitation Platform (GEP)

“…This slope movement appears to involve large blocks of Jurasic limestone that move over the underlying Triassic materials (evaporites, marls, and dolomites) (Figure 12). Similar examples are described in the Betics, Iberian Chain, and Pyrenees [46][47][48].…”

Evaluation of trenching, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) for sinkhole characterization

“…The trenches were excavated with a backhoe. We followed the classical procedure applied to the study of active faults (McCalpin, 2009a), and gravitational ground deformations like landslides , Gutiérrez et al, 2012b), sackung (e.g. McCalpin and Hart, 2003Gutiérrez et al, 2008d), surface ruptures related to interstratal dissolution of evaporites (Gutiérrez et al, 2012a;Carbonel et al, 2013), and sinkholes .…”

Can flexural-slip faults related to evaporite dissolution generate hazardous earthquakes? The case of the Grand Hogback monocline of west-central Colorado

“…This approach may provide practical data on (1) the deformation style, kinematics, and deformation history of hazardous surface-rupturing structures (e.g., slip rate, creeping versus episodic displacement, most recent event); (2) controlling factors; and (3) parameters that may help to differentiate between tectonic and nontectonic faults-a rele vant issue, from the seismic-hazard perspective, with a still poorly developed scientifi c basis (Hanson et al, 1999). Recent trenching studies on active normal faults related to interstratal dissolution of salt-bearing evaporites conducted in the Iberian Chain and the Pyrenees, Spain (Gutiérrez et al, 2012a(Gutiérrez et al, , 2012bCarbonel et al, 2013), and in the Paradox Basin, Utah (Guerrero et al, 2012), indicate episodic displacement on these gravitational structures, and slip rate and displacement-per-event values significantly larger than those expectable for tectonic faults.…”