Óscar Pueyo Anchuela

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

The Concud Fault is a ~14-km-long active fault that extends close to Teruel, a city with about 35,000 inhabitants in the Iberian Range (NE Spain). It shows evidence of recurrent activity during Late Pleistocene time, posing a significant seismic hazard in an area of moderate-to-low tectonic rates. A geophysical survey was carried out along the mapped trace of the southern branch of the Concud Fault to evaluate the geophysical signature from the fault and the location of paleoseismic trenches. The survey identified a lineation of inverse magnetic dipoles at residual and vertical magnetic gradient, a local increase in apparent conductivity, and interruptions of the underground sediment structure along GPR profiles. The origin of these anomalies is due to lateral contrast between both fault blocks and the geophysical signature of Quaternary materials located above and directly south of the fault. The spatial distribution of anomalies was successfully used to locate suitable trench sites and to map non-exposed segments of the fault. The geophysical anomalies are related to the sedimentological characteristics and permeability differences of the deposits and to deformation related to fault activity. The results illustrate the usefulness of geophysics to detect and map non-exposed faults in areas of moderate-to-low tectonic activity where faults are often covered by recent pediments that obscure geological evidence of the most recent earthquakes. The results also highlight the importance of applying multiple geophysical techniques in defining the location of buried faults.

Factors influencing magnetic susceptibility in the southern Pyrenees

We analyse paramagnetic, ferrimagnetic and frequency-dependent susceptibility in the southern Pyrenees and northern Ebro basin. The analyzed rocks show a wide range of values for the three parameters within the different lithological groups. Sandstones, shales and marls exhibit middle to high values of paramagnetic susceptibility while mudstones usually show low values. However, a general correlation can be established for the different rock types with a wide variability for each group (for example, Eocene marls show average values of paramagnetic susceptibility of 82% but within a range between 12 and 99%, or Flysch materials, with mean values of 47–52% within a range between 15 and 90%). These changes in the paramagnetic contribution to the susceptibility are due to the change in the ferrimagnetic susceptibility. This wide variability is independent of the sedimentological characteristics and can be related to the higher ferrimagnetic contribution to the susceptibility with similar ferrimagnetic mineral phase assemblages. The ferrimagnetic and superparamagnetic contributions, independent of site location with respect to individual macrostructures (thrusts and nappes), show a sharp increase at the occurrence of the macroscopic regional Pyrenean cleavage, probably relating both aspects with changes in pressure-temperature (P-T) conditions.

Integrated approach for sinkhole evaluation and evolution prediction in the Central Ebro Basin (NE Spain)

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