Control estructural y geometría de fallas activas, asociadas a erosión por subducción y su potencial peligrosidad entre los 32°–33° S, Valparaíso, Chile
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Fecha
2023
Autores
Facultad/escuela
Idioma
es
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Editor
Universidad Andrés Bello
Nombre de Curso
Licencia CC
Licencia CC
Resumen
La evolución geodinámica entre los 32°- 33°S se relaciona con los procesos de erosión por
subducción del ridge de Juan Fernández, determinando las morfoestructuras del margen. El
progresivo avance de montes submarinos bajo la corteza continental, desde hace unos 10 Ma,
determinó la formación de la cuenca de Valparaíso, extendida ampliamente en el talud y limitada
hacia el este por una angosta plataforma. A lo largo de la costa, se evidencian alzamientos
diferenciales e importante retroceso de acantilados situados al NE de Caleta Horcón. El fallamiento
activo consiste predominantemente de estructuras normales NE, NW y NS. Sin embargo, aún se
desconoce el control estructural y geometría de fallas a esta latitud. Estudios previos evidencian
una estructura de rumbo N75°E/45°W y salto de 60 cm, asociado a un paleo terremoto
tsunamigénico, identificado en el límite entre el miembro inferior y superior de la Formación
Horcón, incrementando la vulnerabilidad de la zona. Considerando lo anterior, este estudio intenta
comprender y precisar el control estructural asociado al área de estudio a través de un modelo de
esfuerzos que representa el comportamiento de fallas siguiendo patrones de Riedel. A lo largo del
acantilado costero se identificaron al menos 3 orientaciones predominantes de fallas normales con
componente en el rumbo. El dominio NE representa la falla maestra con movimiento dextral. Las
fallas NW se presentan como fracturas de tipo R y T. Adicionalmente, mediante tomografía sísmica,
se identificó una estructura subsuperficial de rumbo NE, correlacionable con la estructura principal.
De este modo, la geometría de las fallas es consistente con la aplicación del modelo de Riedel. El
retroceso del acantilado y caída de bloques, si bien está afectado por el clima y el oleaje, se
encuentra principalmente controlado por el fallamiento activo, evidenciándose con mayor
intensidad en los acantilados situados entre el sector sur de Playa Larga y NE de Caleta Horcón,
determinando una elevada peligrosidad para las construcciones existentes en el área.
The geodynamic evolution between 32°- 33°S is related to the processes of erosion by subduction of the Juan Fernández ridge, determining the morphostructures of the margin. The progressive advance of seamounts under the continental crust, since about 10 Ma ago, limits the formation of the Valparaíso basin, which extended extensively on the slope and limited to the east by a narrow shelf. Along the coast, differentials uplift and important retreats of cliffs located to the NE of Caleta Horcón are evident. The active faults consist predominantly of NE, NW, and NS normal structures. However, the structural control and fault geometry at this latitude is still unknown. Previous studies show a structure with a N75°E/45°W strike and a 60 cm of displacement, associated with a tsunamigenic paleoearthquake, identified at the limit between the lower and upper member of the Horcón Formation, increasing the vulnerability of the area. Considering the above, this study tries to understand and specify the structural control associated with the study area through a stress model that represents the behavior of failures following Riedel patterns. Along the coastal cliff, at least 3 predominant orientations of normal faults with strike components were identified. The NE domain represents the master fault with dextral movement. The NW faults appear as R and T type fractures. In addition, a subsurface structure trending NE was identified by means of seismic tomography. Thus, the geometry of the faults is consistent with the application of the Riedel model. The retreat of the cliff and the fall of blocks, although it is affected by the weather and the waves, is mainly controlled by the active faulting, showing more intensity in the cliffs located between the southern sector of Playa Larga and NE of Caleta Horcón determining highly dangerous situation for existing buildings in the area
The geodynamic evolution between 32°- 33°S is related to the processes of erosion by subduction of the Juan Fernández ridge, determining the morphostructures of the margin. The progressive advance of seamounts under the continental crust, since about 10 Ma ago, limits the formation of the Valparaíso basin, which extended extensively on the slope and limited to the east by a narrow shelf. Along the coast, differentials uplift and important retreats of cliffs located to the NE of Caleta Horcón are evident. The active faults consist predominantly of NE, NW, and NS normal structures. However, the structural control and fault geometry at this latitude is still unknown. Previous studies show a structure with a N75°E/45°W strike and a 60 cm of displacement, associated with a tsunamigenic paleoearthquake, identified at the limit between the lower and upper member of the Horcón Formation, increasing the vulnerability of the area. Considering the above, this study tries to understand and specify the structural control associated with the study area through a stress model that represents the behavior of failures following Riedel patterns. Along the coastal cliff, at least 3 predominant orientations of normal faults with strike components were identified. The NE domain represents the master fault with dextral movement. The NW faults appear as R and T type fractures. In addition, a subsurface structure trending NE was identified by means of seismic tomography. Thus, the geometry of the faults is consistent with the application of the Riedel model. The retreat of the cliff and the fall of blocks, although it is affected by the weather and the waves, is mainly controlled by the active faulting, showing more intensity in the cliffs located between the southern sector of Playa Larga and NE of Caleta Horcón determining highly dangerous situation for existing buildings in the area
Notas
Tesis (Geólogo)
Palabras clave
Zonas de Fallas (Geología), Análisis Estructural (Ingeniería), Riesgo Geológico, Chile, Región de Valparaíso