Abstract The plate interface beneath the Mejillones Peninsula in Northern Chile is characterized by anomalous seismogenic behaviors, with seismic and aseismic slip, and low coupling values. We analyze this zone through the seismicity pattern and a 3‐D tomography model. We identify high V P / V S values within the oceanic crust and in the lower continental crust, which we interpret as hydrated zones rich in fluids. These zones are correlated with the Mejillones fracture zone and with highly permeable lithologies of the lower continental crust, which allow a greater accumulation of fluids at the plate interface beneath the Mejillones Peninsula. Additionally, these areas exhibit a high rate of seismicity and concentrated swarms and repeaters. We propose that the presence of fluids controls the anomalous seismogenic behavior along the plate interface beneath the Mejillones Peninsula.
Abstract Active deformation and landscape evolution in North Chilean forearc involve multiscale tectonic processes, such as crustal thickening causing orogenic‐scale uplift and faulting modulating the mountain‐front landscape. In the Central Depression, faults redirecting Quaternary drainages are poorly understood due to their subtle surface expressions and limited structural data acquisition. To address this, we combined remote‐sensing analysis of high‐resolution DEMs, satellite and UAV imagery, new geomorphic mapping, structural data, and morphometric analysis with available surface age dating to identify and give temporal constraints on previously unmapped faults impacting drainages across this region. Our findings reveal the reactivation of east‐vergent NNW‐SSE reverse to transpressive and NW‐SE strike‐slip faults over approximately 100 km of latitude. Faults movement can be summarized into two main stages (a) A Late Miocene‐Pliocene stage, dominated by east‐vergent reverse faults inverting the Andean piedmont in the northern study area. (b) A Pliocene‐Quaternary stage, characterized by transpressive activity of these east‐vergent faults extending southward, alongside structures of the West Vergent Thrust System. The tectonic evolution of the east‐vergent structures relates to the ongoing deformation of the coastal forearc, encroaching into the Central Depression. Minimum vertical and strike‐slip displacement rates since the Quaternary are 12 m/Ma and 90 m/Ma, respectively, with the potential for higher rates depending on the onset of displacement. Drainage pattern modification, driven by incremental vertical displacement rates, provides insights to qualitatively evaluate individual fault activity rates. Numerous recently detected structures represent previously unknown sources of seismic hazard, requiring further dating of geomorphic markers and high‐resolution monitoring.
Inland-normal faulting is recognised as an important process following large subduction earthquakes. The lack of data limits the understanding of how normal fault reactivation relates to the subduction earthquake cycle. We characterised the palaeoseismology of the Atacama fault system (AFS) in the Chilean subduction zone. Our results showed that upper plate normal faulting earthquakes with Mw 7.0 and recurrence intervals of 35 ± 9 ky generated surface ruptures preserved as fault scarps. The average fault slip rate of 0.07 ± 0.01 m/kyr is three orders of magnitude slower than the convergence velocity, and the recurrence intervals of surface-rupturing earthquakes on the studied faults are much larger than the recurrence of great to giant (Mw > 8.5) subduction earthquakes in the Chilean margin. This demonstrates that the reactivation of an individual fault in the AFS is not always synchronised with this type of subduction earthquake.
INTRODUCTION The nature of reverse faults scarps morphology is controlled by a complex relation between amount of slip, sense of slip, fault geornetry, properties of deformed layer and topography (Phillip et al., 1992). When the fault plane is covered or buried, the morphotectonic features are the most relevant source of data to constrain the geometry and kinematics of faults. Accurate fault geometry determination is extremely relevant to formulate geodynamic and tectonic implications (shortening magnitude and deformation nature) . Thus, the study of morphotectonic features (scarp profile, flexural bending, tension fractures, secondary faults, displaced geomorphic surfaces and slope structures) and its relations (i.e. tension fracture frequency along the slope profile and magnitude of tension fracture opening along the slope profile) make possible to constrain, with relative accuracy, the fault geometry in depth. ln this contribution we present the first results of morphotectonic study of a reverse fault system developed in the inner part of Bolivian Orocline, northern Chilean Coastal Cordillera. This study was based on field observations and geodetic measurements, detailed analysis of 1 m resolution IKONOS images and FEM models.
RESUMEN. El margen continental en las inmediaciones de Antofagasta puede subdividirse en tres dominios morfoestructurales: Cordillera de la Costa, plataforma costera y talud continental. La Cordillera de la Costa se encuentra separada de la plataforma costera por el acantilado costero, de cerca de 1.000 m de altura. En la Cordillera de la Costa, fallas norte-sur limitan una morfologia de bloques alzados y deprimidos, asimetricos. Las fallas mas recientes (cuaternarias). Exhiben indicadores cinematicos de movimientos transcurrentes sinistrales. La plataforma costera, la peninsula de Mejillones y el talud continental corresponden a una zona afectada por extension desde el Mioceno al Reciente. Las estructuras de esta zona consisten en cuencas tectonicas asimetricas limitadas por fallas normales en su margen occidental. Movimientos episodicos a lo largo de estas fallas han acomodado la rotacion de bloques segun un eje horizontal. Esta rotacion marca un colapso asimetrico y progresivo de bloques tectonicos hacia el eje de la fosa oceanica. El inicio del colapso esta marcado por la transgresion marina del Mioceno. La existencia del acantilado costero se explica por una fuerte erosion marina retrocedente, favorecida por el clima arido del norte de Chile. La deformacion extensional se explica por erosion tectonica prolongada, que habria producido, a partir del Mioceno, un colapso de la region de antearco proxima al frente de subduccion. En dicho colapso toma un papel importante la Falla Antofagasta, la cual marca el desacople de gran parte del talud continental. Se concluye que los movimientos transcurrentes cuaternarios en la Cordillera de la Costa solo obedecen a un fenomeno local, no ligado al colapso del margen continental, ni tampoco a la subduccion oblicua. Esto, porque el vector de convergencia apunta hacia el este noreste en la actualidad, y por lo tanto, es incompatible con el sentido sinistral determinado para las fallas. ABSTRACT. Cenozoic tectonic evolution of the active continental margin of Northern Antofagasta, Chile. The active continental margin of Antofagasta, in Northern Chile, can be divided into three morphostructural domains. These are from east to west: Coastal Cordillera, coastal platform and Continental slope. The boundary between the Coastal Cordillera and coastal platform is the coastal scarp ca. 1.000 m high. The origin of this remarkable morphologic feature is the result of strong marine erosion that was enhanced by the extreme aridity of Northern Chile. In the Coastal Cordillera a set of north-south trending faults controls geometry of asymmetric tectonic blocks and basins. The younger faults exhibit kinematic indicators for sinistral transcurrence. The coastal platform, Mejillones Peninsula and continental slope show the effects of an extensional tectonics since the Miocene. In all three main domains, the extensional tectonics has controlled the sedimentation in the finger print of tectonic history of the continental margin. The extensional tectonics is here interpreteted as the result of tectonic erosion that acted under the South American plate during most of the Mesozoic and Cenozoico This tectonic erosion is responsible for the collapse of the Continental margin towards the Chile-Peruvian Trench. It is believed that the start of this massive collapse is contemporaneous with the Miocene marine transgression. An important part in this collapse is taken by the Antofagasta Fault, which is the material fracture feature against which the collapse took place. It is concluded that the youngest transcurrent sinistral displacements along longitudinal faults in the Coastal Cordillera are only local phenomena, and cannot be related to the massive collapse of the Continental margin, nor to the oblique subduction vector, which at present, has an east northeast direction.
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