Browsing by Author "Jensen, E."
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- ItemDevelopment of a self-similar strike-slip duplex system in the Atacama Fault system, Chile(PERGAMON-ELSEVIER SCIENCE LTD, 2011) Jensen, E.; Cembrano, J.; Faulkner, D.; Veloso, E.; Arancibia, G.Fault development models are crucial to predict geometry and distribution of fractures at all scales. We present here structures related to the development of the Bolfin Fault in the Atacama Fault System (AFS), covering a range of scales of 7 orders of magnitude. The AFS is a 1000 km-long trench-parallel fault system located in the Andean Forearc. The Boffin Fault is a first-order fault of the Caleta Coloso Duplex, has a trend similar to 170 degrees and length >45 km. It cuts mainly meta-diorites and exhibits a 100-200 m thick core of subvertical bands of altered fractured host rock and of foliated cataclasites. This foliation is made up of several trend-parallel cm-thick shear bands, composed of plagioclase fragments (>0.1 mm) surrounded by epidote.
- ItemEfficacy and safety of ticagrelor for long-term secondary prevention of atherothrombotic events in relation to renal function: insights from the PEGASUS-TIMI. 54 trial(2016) Magnani, G.; Storey, R.; Steg, G.; Bhatt, D.; Kuder, J.; Im, K.; Aylward, P.; Ardissino, D.; Isaza, D.; Corbalán Herreros, Ramón; Dellborg, D.; Medina, F.; Braunwald, E.; Sabatine, M.; Bonaca, M.; Jensen, E.
- ItemFrictional Melting in Hydrothermal Fluid-Rich Faults: Field and Experimental Evidence From the Bolfin Fault Zone (Chile)(2021) Gomila, R.; Fondriest, M.; Jensen, E.; Spagnuolo, E.; Masoch, S.; Mitchell, T. M.; Magnarini, G.; Bistacchi, A.; Mittempergher, S.; Faulkner, D.; Cembrano, J.; Di Toro, G.Tectonic pseudotachylytes are thought to be unique to certain water-deficient seismogenic environments and their presence is considered to be rare in the geological record. Here, we present field and experimental evidence that frictional melting can occur in hydrothermal fluid-rich faults hosted in the continental crust. Pseudotachylytes were found in the >40 km-long Bolfin Fault Zone of the Atacama Fault System, within two ca. 1 m-thick (ultra)cataclastic strands hosted in a damage-zone made of chlorite-epidote-rich hydrothermally altered tonalite. This alteration state indicates that hydrothermal fluids were active during the fault development. Pseudotachylytes, characterized by presenting amygdales, cut and are cut by chlorite-, epidote- and calcite-bearing veins. In turn, crosscutting relationship with the hydrothermal veins indicates pseudotachylytes were formed during this period of fluid activity. Rotary shear experiments conducted on bare surfaces of hydrothermally altered rocks at seismic slip velocities (3 m s(-1)) resulted in the production of vesiculated pseudotachylytes both at dry and water-pressurized conditions, with melt lubrication as the primary mechanism for fault dynamic weakening. The presented evidence challenges the common hypothesis that pseudotachylytes are limited to fluid-deficient environments, and gives insights into the ancient seismic activity of the system. Both field observations and experimental evidence, indicate that pseudotachylytes may easily be produced in hydrothermal environments, and could be a common co-seismic fault product. Consequently, melt lubrication could be considered one of the most efficient seismic dynamic weakening mechanisms in crystalline basement rocks of the continental crust.
- ItemNature and tectonic significance of co-seismic structures associated with the Mw 8.8 Maule earthquake, central-southern Chile forearc(PERGAMON-ELSEVIER SCIENCE LTD, 2011) Arriagada, C.; Arancibia, G.; Cembrano, J.; Martinez, F.; Carrizo, D.; Van Sint Jan, M.; Saez, E.; Gonzalez, G.; Rebolledo, S.; Sepulveda, S. A.; Contreras Reyes, E.; Jensen, E.; Yanez, G.The Mw 8.8 Maule earthquake on February 27, 2010 affected the central-southern Chilean forearc of the Central Andes. Here we show the results of field investigations of surface deformation associated with this major earthquake. Observations were carried out within three weeks after the seismic event, mostly in the central and northern part of the forearc overlying the rupture zone. We provide a detailed field record of co-seismic surface deformation and examine its implications on active Andean tectonics. Surface rupture consisted primarily of extensional cracks, push-up structures, fissures with minor lateral displacements and a few but impressive extensional geometries similar to those observed in analogical modeling of rift systems. A major group of NW-WNW striking fractures representing co-seismic extensional deformation is found at all localities. These appear to be spatially correlated to long-lived basement fault zones. The NW-striking normal focal mechanism of the Mw 6.9 aftershock occurred on March 11 demonstrates that the basement faults were reactivated by the Mw 8.8 Maule earthquake. The co-seismic surface ruptures show patterns of distributed deformation similar to those observed in mapped basement-involved structures. We propose that co-seismic reactivation of basement structures play a fundamental role in stress release in the upper plate during large subduction earthquakes. The fundamental mechanism that promotes stress relaxation is largely driven by elastic rebound of the upper plate located right above the main rupture zone. (C) 2011 Elsevier Ltd. All rights reserved.
- ItemScaling of fault damage zones with displacement and the implications for fault growth processes(AMER GEOPHYSICAL UNION, 2011) Faulkner, D. R.; Mitchell, T. M.; Jensen, E.; Cembrano, J.Knowledge of the spatial extent of damage surrounding fault zones is important for understanding crustal fluid flow and also for understanding the physical processes and mechanics by which fault zones develop with slip. There are few data available on the scaling of the fault damage zone with fault displacement, and of those that exist, deriving scaling relationships is hampered by comparing faults that run through different lithologies, have formed at different crustal depths or tectonic regimes (e. g., normal versus strike-slip movement). We describe new data on the microfracture damage zone width from small displacement fault zones within the Atacama fault zone in northern Chile that formed at similar to 6 km depth within a dioritic protolith. The microfracture damage zone is shown by an alteration halo surrounding the faults in which the density of the microfractures is much greater than background levels in the undeformed protolith. The data show that damage zone width increases with fault displacement and there appears to be a zero intercept to this relationship, meaning that at zero displacement, there is no microfracture damage zone. This is supported by field observations at fault tips that show a tapering out of fault damage zones. These data, combined with data from the literature, indicate that this same relationship might hold for much larger displacement faults. There is also a distinct asymmetry to the fracture damage. Several processes for the development of the observed scaling are discussed. The widely accepted theory of a process zone predicts that fault damage zone width increases with fault length and thus should always be largest at a propagating fault tip where displacement is lowest. This prediction is opposite to that seen in the current data set, leading to suggestion that other processes, such as damage zone growth with increasing displacement due to geometric irregularities or coseismic damage formation might better explain the spatial extent of damage surrounding even low-displacement faults.
- ItemSelf-similar length-displacement scaling achieved by scale-dependent growth processes : Evidence from the Atacama Fault System(2020) Stanton Yonge, A.; Cembrano, José; Griffith, W. A.; Jensen, E.; Mitchell, T. M.