INVESTIGADORES
ORTS Dario Leandro
congresos y reuniones científicas
Título:
Analysis of neotectonic of the El Maitén range, (in North Patagonian Argentina), Used geophysical methods.
Autor/es:
LINCE KLINGER, F; ORTS, D.L.; GIMENEZ, M.; FOLGUERA, A.; MARTINEZ, P.
Lugar:
Hawaii
Reunión:
Conferencia; Near-Surface Asia Pacific Conference, Waikoloa, Hawaii, 7-10 July 2015; 2015
Institución organizadora:
Society of Exploration Geophysicists
Resumen:
A high-resolution superficial geophysical study was carried out in a region of the retroarc of the Patagonian Andes located on the western slope of the Sierra de El Maitén (Figure). This structure is characterized by an imbricated west-vergence fault system developed in the orogenic front area of the North Patagonian Andes that uplifts Oligocene volcanic rocks (Ventana Formation) affecting Miocene to Quaternary sediments. Even though, neotectonic fault scarps are affecting Quaternary deposits in the foothills of this range, no direct observation of slip in Quaternary strata was determined. The main objective of this study was to determine geometry of recognized neotectonic structures, characterizing them by variations in magnetic susceptibility, density and p-wave velocities. A magnetic survey was carried out throughout the area depicted in (Figure), together with profiles of seismic, micro-gravimetric and GPS determinations perpendicular to the trace of the neotectonic fault scarp. The magnetic field intensity values were corrected by diurnal variations, using magnetic recordings from the base station located in the zone north of the study area. Magnetic anomalies were calculated discounting the 2011 IGRF (International Geomagnetic Reference Field 2011) for the data date acquisition, from the magnetic field intensity map. The topographic coordinates in each station were obtained with the post-processing DGPS calculation, with an uncertainty of ±0.1 m. The gravity readings were corrected by tide and instrumental drift. Afterwards, were corrected in reference to the fundamental value of the Miguelete station (located in Buenos Aires province) 97960.03 mGal and the theoretical gravity was calculated according to the ellipsoid IGSN 71 (International Gravity Standardization Net 1971) (Morelli et al. 1974) to be compared with the anomalies from existing databases. Classic formulas were used to calculate the gravity Bouguer anomaly considering an average rock density of 2,200 kg/cm3.The topographic effect was calculated using a density of 2,200 kg/cm3 in accordance with the values determined for the study region. According to the methodology implemented by Spector and Grant (1970) for magnetic data interpretation, low frequencies related to the first section of the power spectrum were filtered, keeping the high frequencies as a residual effect. The initial velocity model was built from interpretation of travel time curves. A misfit function is calculated, consisting of the squared difference between the observed and computed travel times. The velocity Model is adjusted until the misfit is minimized (RMS 0.567839 ms). Inversion was performed using from 3 to 6 nodes for each cell and 10 iterations. Results of the inversion are shown in Figure. The combined application of different geophysical methods has allowed the characterization of the bedrock geometry and the determination of neotectonic displacements along faults. The potential field model, and its integration with a seismic profile shows the accurate geometry of this neotectonic zone, which is crucial for seismogenic hazard analysis, virtually absent, in this populated area of northern Patagonia of high economic importance with several towns dispersed through the area of young tectonic activity.