Shallow Anatomy of the San Ramón Fault (Chile) Constrained by Geophysical Methods: Implications for its Role in the Andean Deformation

Abstract

The San Ramón Fault (SRF) runs for 30 km along the western flank of the Andes in front of the city of Santiago, Chile (33.5°S). Geological studies have highlighted the SRF role in the Neogene uplift of the Andes at this latitude, but the fault geometry at depth is not well constrained. Here we infer the structure of the sedimentary cover and bedrock up to a depth of 500 m along the SRF by integrating gravimetric, electrical resistivity, seismic, and magnetic methods. In a section crossing the central segment of the SRF, lateral variations in P wave velocity models indicate that the sedimentary cover is more deformed close to SRF scarps, while coincident low‐density and low‐resistivity zones suggest that the presence of two depocenters in the sedimentary cover below the SRF scarps. Gravimetric profiles distributed along the entire trace of the SRF show the same configuration of two depocenters, but the geometry of these depocenters is complex and varies along strike. Our findings suggest that the bedrock and sediments deformation along the SRF exhibit a complex geometry, which can be explained by the interplay of reverse and strike‐slip movements during the late Cenozoic. Based on our results, the distribution of crustal seismicity and shortening rates interpreted across the Andes, we estimated that SRF deformation represents 5–20% of the whole Andean shortening for the last 4 Ma. Using empirical length scales for crustal seismicity, this deformation pattern is consistent with a maximum earthquake magnitude in the range of 6.0–6.5 Mw.

High-Resolution Deformation Monitoring from DInSAR: Implications for Geohazards and Ground Stability in the Metropolitan Area of Santiago, Chile

“…Based on gravity measurements constrained by geological observations at wells, it has been possible to estimate the thickness of the sedimentary cover as being in the range of 100-400 m with an irregular morphology [3]. The role of the eastern deformation front, whose westernmost branch correspond to the San Ramon Fault System (SRFS), has been a source of large scientific debate in terms of its relevance as a seismic hazard source [7][8][9][10]65]; maximum seismic events and recurrence times are among the most relevant unresolved questions. Finally, the basin water table is controlled by surface topography (tilted to the west), asymmetric basin (shallowing to the west), the overexploitation of the water resource, and the limited recharge due to a prolonged drought [66].…”

“…The contact between the basin and the Andean Cordillera is formed by reverse faulting (San Ramon Fault). Previous geological/geophysical studies in the Santiago Metropolitan Area aimed at evaluating geohazards have focused on geology and hydrogeology [2][3][4], seismic potential and microzoning [5,6], and tectonics [7][8][9][10]. Despite advancement in the knowledge and assessment of geohazards in the Santiago basin, few studies have been carried out to analyze the ground surface stability and deformation of the whole basin.…”

El rol de la exploración geofísica en acuíferos profundos en ambientes semiurbanos y rurales en cuencas de ante arco Andino, caso de estudio en acuífero del río Ñuble, Valle Central de Chile

“…La profundidad de la cuenca decae en sentido W, en dirección de la Cordillera de la Costa, sin embargo, en dirección del piedemonte andino se observan profundidades del orden de 700-1.000 m a distancias inferiores de 5 km entre ellas. Esta morfología de basamento aledaño a la Cordillera Principal, podría estar indicando la presencia de un contacto por falla inversa con la cordillera, tal cual ha sido identificado en la zona central de Chile (p. ej.. Yáñez et al, 2020). Las profundidades al basamento constreñidas en este caso por datos geoeléctricos deben considerarse como una profundidad máxima ya que es posible que la parte superficial del basamento se encuentre potencialmente infiltrado por soluciones provenientes del acuífero, reduciendo su resistividad a valores comparables a las observadas en la cuenca sedimentaria.…”

Reconstruction of Fault Architecture in the Natural Thermal Spring Area of Daruvar Hydrothermal System Using Surface Geophysical Investigations (Croatia)

“…Based on the research objectives and the geological and hydrogeological settings of the study area, different geophysical approaches can be applied. For the exploration of geothermal resources [21][22][23][24][25][26], they can be used to: (i) assess the distribution of lithologies, (ii) reconstruct the geometry of the aquifer, and (iii) reconstruct the geometry of faults and their damage zones. Among them, electrical resistivity tomography (ERT) and seismic methods can provide a detailed 3D local scale reconstruction of the subsurface.…”