neotectonic activity of the granada basin · n e o t e k t o n i k g e o r i s i k e n andreas...
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N e o t e k t o n i k
G e o r i s i k e n
Andreas RudersdorfB.Sc.
working at his M.Sc. thesison the Nigüelas Fault Zone, Spain
Jochen HürtgenB.Sc.
working at his M.Sc. thesison the Padul Fault Zone, Spain
PRELIMINARY RESULTS
The 3-week �eld work for this study has just been completed in the end of April 2011 and the evaluation and processing of recorded data is still in progress. Therefore, we present preliminary results.
During our �eld work, we have found several obvious evidences which suggest geo-logically recent fault activity in the PNFZ: - triangular facets, - deeply incised channels, - faultward dipping layers, - faults in both colluvial wedges and alluvial fans.
We could con�rm the observations from Alfaro et al. (2001),who have stated that the scarp is exhumed due to erosion and not due to fault activity. Focussing on col-luvial wedges and alluvial fans in front of the PNFZ, we documented several pro�les of faults. We found active and fossilized faults in the sediments (see also Ham-douni et al. (2008)).
Fig. 5 shows a photograph of the outcrop with inter-preted faults in the sediments and a sketch with the simpli�ed geometry and certain marker horizons. Based on these horizons, we can determine the o�set of the larger faults. It varies between a few cm and 1.8 m. Some of the faults are traceable up to the surface and build small scarps in the topo-logy. A GPR pro�le upon the outcrop surface (Fig. 6) supports our inter-pretation.
REFERENCES
Alfaro, P., J. Galindo-Zaldívar, A. Jabaloy, A.C. López-Garrido & C. Sanz de Galdeano, (2001). Evidence for the activity and paleoseismicity of the Padul fault (Betic Cordillera, southern Spain). Acta Geologica Hispanica 36 (3-4), 283-295.
Azañón, J.M., J. Galindo-Zaldívar, V. García-Dueñas and A. Jabaloy (2002). Alpine tectonics II. Betic Cordillera and Balearic Islands. In: W. Gibbons and T. Moreno (eds.),The Geology of Spain 16, 401-416.
Galindo-Zaldívar, J., A.J. Gil, M.J. Borque, F. González-Lodeiro, A. Jabaloy, C. Marín-Lechado, P. Ruano, C. Sanz de Galdeano (2003). Active faulting in the internal zones of the central Betic Cordilleras (SE, Spain). Jorunal of Geodynamics 36, 239-250.
Hamdouni, R., Irigaray, C., Fernández, T., Chacón, J., Keller, E.A. (2008). Assessment of relative active tectonics, southwest border of the Sierra Nevada (southern Spain). Geomorphology 96, 150-173.
Reicherter, K.R. (2001). Paleoseismologic advances in the Granada basin (Betic Cordilleras, southern Spain). Acta Geologica Hispanica 36 (3-4), 267-281.
LASER DISTANCE MEASUREMENTS
Laser distance measurements have been done with the compact range�nder LTI TruPulse 360 (Fig. 3 & 4).
Measured features: - slope- horizontal &
vertical distance- inclination- azimuth
Aims: - scarp undulation &
geometry- interfault relation-
ship
Measured features:
Aims:
compact range�nder LTI TruPulse 360 (
Measured features:
Aims:
Fig. 3: LTI TruePulse 360Source: csdsinc.com
Fig. 5: Outcrop of an incised channel in the alluvial and colluvial fan in the north of Marchena. A: Photograph of the colluvial sediments and existing faults. B: Sketch of the same outcrop with a few traceable layers.
THE PADUL-NIGÜELAS FAULT ZONE
The Granada Basin is a seismically active intramontane basin in the Betic Cordillera of Andalucía, Southern Spain. Earthquakes have been documented both in the
historic and the instrumental record (Reicherter (2001) among others). Situated in an extensive regime, normal faults delimit basins of Neogene and Quaternary ages (Fig. 1). They usually show a sedimentary succession from Tortonian ages (11.6 - 7.2 Ma BP) on (Azañón et al., 2002).
The PNFZ (Fig. 2) deli-mits the Granada Basin in the south-western part.
Due to the carbonate lithology of the base-ment, active faults in this region are com-monly preserved as escarpments.
Fig. 1: Geological Map of the southern Iberian region (after Reicherter & Peters,
2005).
Fig. 2: Geological Map of the Padul-Nigüelas Fault Zone, simpli�ed and composed from Sanz de Galdeano, et al. (1975) and González Donoso, et al. (1978).
GROUND-PENETRATING RADAR
We used a 270 MHz antenna to record the raw data, which have to be interpreted by various �ltering and cor-rection tools. According to subsurface conditions the penetration depth varies between 5 and 10 m with high-resolution data.
Aims:- support outcrop data- infer subsurface geometry- trace faults & strata in
non-outcropping areas
Fig. 4: llustration of a laser distance measurement on an
exhumed scarp near Nigüelas
Aims:
The 3-week �eld work for this study has just been completed in the end of April 2011 and the evaluation and processing of recorded data is still in progress Therefore, we The 3-week �eld work for this study has just been completed in the end of April 2011
Aims:- support outcrop data- infer subsurface geometry- trace faults & strata in
non-outcropping areas
Fig. 6: GPR pro�le on the upper surface of the outcrop (Fig. 5). The pro�le is not topographically corrected and a velocity of 0.1 m/ns is assumed for the time-depth conversion. Black lines: interpreted faults.
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2 km10
Alluvium, Peat Sand, Silt, Conglomerate, Calcarenite Limestone, calcitic Dolomite
Dolomitic Carbonate
Quartzite, Micaschist
Micaschist
PaleozoicQuaternary Neogene Triassic (middle-upper)
Triassic (lower)Inferred Normal Fault
Thrust Fault
Normal Fault
PADUL
DÚRCAL
Fig. 5
NIGÜELAS
HÜRTGEN, J., A. RUDERSDORF, C. GRÜTZNER, K. REICHERTERNeotectonics and Natural Hazards, RWTH Aachen University
NEOTECTONIC ACTIVITY OF THE GRANADA BASIN