Publicaciones

Gravity derived depth to basement in Santiago Basin, Chile: implications for its geological evolution, hydrogeology, low enthalpy geothermal, soil characterization and geo-hazards

Investigadores

Gonzalo Yáñez

Journal

Andean Geology

Línea de investigación

Amenazas por procesos de tierra sólida

Institución

Pontificia Universidad Católica de Chile

Disciplina

Ciencias de la Tierra

afiliacion

  1. Gonzalo Yáñez, Departamento de Estructuras y Geotecnia, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago, Chile.
  2. Mauricio Muñoz, Andean Geothermal Center of Excellence, Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Correo 21, Santiago, Chile.
  3. Valentina Flores-Aqueveque, Andean Geothermal Center of Excellence, Departamento de Geología, Universidad de Chile, Plaza Ercilla 803, Casilla 13518, Correo 21, Santiago, Chile.
  4. Andrés Bosch, Escuela de Ingeniería, Pontificia Universidad Católica de Chile, Vicuña Mackenna 4860, Macul, Santiago, Chile.

Abstract

A recording of 1,115 gravimetric stations, the review of 368 wells, and the petrophysics measurements of 106 samples from representative outcrops have been used for a comprehensive geological/geophysical study of Santiago Basin. 2.5D and 3D gravimetric modeling, constrained by regional geology, soil and bedrock densities, edge-basin outcrops, depth (minimum) to basement from wells, and detailed modeling of heterogeneous bedrock and mid-crustal blocks, provided a well-constrained depth to basement model. Model results indicate the presence of a relatively shallow basin with an average of 250 m depth, and three sub basins with depth in excess of 500 m, but comprising less than 30% of the basin surface. From erosion rates in central Chile we estimate a basin infill lasting between 10 to 20 Ma. Basement topography/geomorphology, undercover a structural pattern dominated by NE and NW-trending structures that can be traced out of the basin, westwards in the Coastal Cordillera and eastwards in the Main Cordillera, with second order relevance of NS structures in the eastern border of the basin. This observation, further supported by natural crustal seismicity and basement-derived-magnetic signatures, suggests that the basin origin is mainly controlled by inherited old structures oblique to the margin. Active seismicity along these traverse NE and NW structures suggest that permanent deformation, and associated seismic hazard in the basin is mostly concentrated along these structures. The dynamic response of soils, in terms of the natural resonance frequency, shows that the basement-to-sedimentary/infilling-impedance-ratio is proportional to the amplitude of the resonance peak. On the other hand, the expected correlation between fundamental frequency and depth to basement is only partially supported by the empirical evidence. The difference between a greater gravimetric depth-to-basement compared to lesser seismic depth-to-basement, is attributed to changes in mechanical stiffness with depth compaction with minor effects in bulk density. Finally low enthalpy geothermal resources of the Santiago Basin is analyzed considering depth to bedrock, water table estimates and simple Darcy’s-temperature coupled flow modeling. Results show that high groundwater temperature is restricted to deeper parts of southern sub-basin, which improves direct uses of geothermal energy for heating purposes.

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