DSpace Angular :: Browsing by Author "Cembrano, Jose"

Browsing by Author "Cembrano, Jose"

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Along-strike architectural variability of an exhumed crustal-scale seismogenic fault (Bolfin Fault Zone, Atacama Fault System, Chile)
(2022) Masoch, Simone; Fondriest, Michele; Gomila, Rodrigo; Jensen, Erik; Mitchell, Thomas M.; Cembrano, Jose; Pennacchioni, Giorgio; Di Toro, Giulio
Fault zone architecture and its internal structural variability play a pivotal role in earthquake mechanics, by controlling, for instance, the nucleation, propagation and arrest of individual seismic ruptures and the evolution in space and time of foreshock and aftershock seismic sequences. Nevertheless, the along-strike architectural variability of crustal-scale seismogenic sources over regional distances is still poorly investigated. Here, we describe the architectural variability of the >40-km-long exhumed, seismogenic Bolfin Fault Zone (BFZ) of the intra-arc Atacama Fault System (Northern Chile). The BFZ cuts through plutonic rocks of the Mesozoic Coastal Cordillera and was seismically active at 5-7 km depth and <= 300 degrees C in a fluid-rich environment. The BFZ in-cludes multiple altered fault core strands, consisting of chlorite-rich cataclasites-ultracataclasites and pseudo-tachylytes, surrounded by chlorite-rich protobreccias to protocataclasites over a zone up to 60-m-thick. These fault rocks are embedded within a low-strain damage zone, up to 150-m-thick, which includes strongly altered volumes of dilatational hydrothermal breccias and clusters of epidote-rich fault-vein networks at the linkage of the BFZ with subsidiary faults. The strong hydrothermal alteration of rocks along both the fault core and the damage zone attests to an extensive percolation of fluids across all the elements of the structural network during the activity of the entire fault zone. In particular, we interpret the epidote-rich fault-vein networks and associated breccias as an exhumed example of upper-crustal fluid-driven earthquake swarms, similar to the presently active intra-arc Liquin similar to e-Ofqui Fault System (Southern Andean Volcanic Zone, Chile).
Complex Crustal Deformation Controlled by the 3D Geometry of the Chile Subduction Zone
(2023) Herrera, Marco T.; Crempien, Jorge G. F.; Cembrano, Jose
The Chilean subduction zone hosts Mw > 8 earthquakes, which could trigger earthquakes on crustal faults located along the plate margin. Using synthetic earthquakes from a quasidynamic boundary element method model, we obtain traction fields and perform a slip tendency analysis to obtain synthetic faults, which we compare with existing potentially seismogenic crustal faults. With our results, we find geometric patterns of the highest slip tendency planes with deformations induced by synthetic subduction events, such that north of the rupture area of each event, correlate with normal N20(degrees)W-50(degrees)W/N60(degrees)SW fault planes, and to the south, correlate with normal N30(degrees)E-80(degrees)E/N60(degrees)NW faults planes. These observations agree with observed fault traces in central and northern Chile, and past observations of crustal fault reactivation.
Decoding the state of stress and fluid pathways along the Andean Southern Volcanic Zone
(2023) Perez-Estay, Nicolas; Ruz-Ginouves, Javiera; Perez-Flores, Pamela; Sielfeld, Gerd; Roquer, Tomas; Cembrano, Jose
Decoding means decrypting a hidden message. Here, the encrypted messages are the state of stress, fluid pathways, and volcano tectonic processes occurring in volcanoes of the Andean Southern Volcanic Zone (SVZ). To decode these messages, we use earthquake focal mechanisms, fault slip data, and a Monte Carlo simulation that predicts potential pathways for magmatic and hydrothermal fluids. From this analysis, we propose that SVZ volcanoes have three end-member stress patterns: (i) Stress-A, a strike-slip regime coupled with the regional far-field tectonic stress; (ii) Stress-B, an extensional regime that may be promoted by volcanic edifice loading and upward pressure due to magma inflation occurring within the upper brittle-crust; and (iii) Stress-C, a local and transient fluid-driven stress rotated similar to 90 degrees from Stress-A. Notoriously, Stress-C pattern was observed in most volcanoes with historical eruptions. We propose that volcanoes presenting Stress-B are attractive geothermal targets, while Stress-C could be used as a predicting signal for impending eruptions.
Effects of topography and basins on seismic wave amplification: the Northern Chile coastal cliff and intramountainous basins
(2021) Garcia-Perez, Tiaren; Ferreira, Ana M. G.; Yanez, Gonzalo; Iturrieta, Pablo; Cembrano, Jose
During earthquakes, structural damage is often related to soil conditions. Following the 2014 April 1 M-w 8.1 Iquique earthquake in Northern Chile, damage to infrastructure was reported in the cities of Iquique and Alto Hospicio. In this study, we investigate the causes of site amplification in the region by numerically analysing the effects of topography and basins on observed waveforms in the frequency range 0.1-3.5 Hz using the spectral element method. We show that topography produces changes in the amplitude of the seismic waves (amplification factors up to 2.2 in the frequency range 0.1-3.5 Hz) recorded by stations located in steep areas such as the ca. 1-km-high coastal scarp, a remarkable geomorphological feature that runs north-south, that is parallel to the coast and the trench. The modelling also shows that secondary waves probably related to reflections from the coastal scarp propagate inland and offshore, augmenting the duration of the ground motion and the energy of the waveforms by up to a factor of three. Additionally, we find that, as expected, basins have a considerable effect on ground motion amplification at stations located within basins and in the surrounding areas. This can be attributed to the generation of multiple reflected waves in the basins, which increase both the amplitude and the duration of the ground motion, with an amplification factor of up to 3.9 for frequencies between 1.0 and 2.0 Hz. Comparisons between real and synthetic seismic waveforms accounting for the effects of topography and of basins show a good agreement in the frequency range between 0.1 and 0.5 Hz. However, for higher frequencies, the fit progressively deteriorates, especially for stations located in or near to areas of steep topography, basin areas, or sites with superficial soft sediments. The poor data misfit at high frequencies is most likely due to the effects of shallow, small-scale 3-D velocity heterogeneity, which is not yet resolved in seismic images of our study region.
Fluid flow migration, rock stress and deformation due to a crustal fault slip in a geothermal system: A poro-elasto-plastic perspective
(2023) Saez-Leiva, Felipe; Hurtado, Daniel E.; Gerbault, Muriel; Ruz-Ginouves, Javiera; Iturrieta, Pablo; Cembrano, Jose
Geothermal systems are commonly genetically and spatially associated with volcanic complexes, which in turn, are located nearby crustal fault systems. Faults can alter fluid flow in their surroundings, potentially acting as barriers or conduits for fluids, depending on their architecture and slip-rate. However, this fundamental control on fluid migration is still poorly constrained. Most previous modeling efforts on volcanic and hydrothermal processes consider either only fluid flow in their formulations, or only a mechanical approach, and seldom a full, monolithic coupling between both. In this work, we present a poro-elasto-plastic Finite Element Method (FEM) to address the first-order, time-dependent control that a strike-slip crustal fault exerts on a nearby geothermal reservoir. For the model setting, we selected the Planchon-Peteroa geothermal system in the Southern Andes Volcanic Zone (SAVZ), for which the geometry and kinematics of a potentially seismogenic fault and fluid reservoir is constrained from previous geological and geophysical studies. We assess the emergence and diffusion of fluid pressure domains due to fault slip, as well as the development of tensile/dilational and compressive/contractional domains in the fault' surroundings. Mean stress and volumetric strain magnitudes in these domains range between +/- 1 [MPa] and +/- 10-4 [-], respectively. Our results show the appearance of negative and positive fluid pressure domains in these dilational and contractional regions, respectively. We also investigate the spatial and temporal evolution of such domains resulting from changes in fault permeability and shear modulus, fluid viscosity, and rock rheology. These variations in fluid pressure alter the trajectory of the reservoir fluids, increasing migration to the eastern half of the fault, reaching a maximum fluid flux of 8 to 70 times the stationary flux. Pressure-driven fluid diffusion over time causes fluid flow to return to the stationary state between weeks to months after fault slip. These results suggest that the mechanism that exerts a first-order control is similar to a suction pump, whose duration heavily depends on fault permeability and fluid viscosity. We also show how a von Mises plasticity criterion locally enhances fluid flow. The transient process analyzed in this work highlights the importance of addressing the solid-fluid coupling in numerical models for volcano-tectonic studies.(c) 2023 Elsevier B.V. All rights reserved.
Seismic cycle controlled by subduction geometry: novel 3-D quasi-dynamic model of Central Chile megathrust
(2024) Herrera, Marco T.; Crempien, Jorge G. F.; Cembrano, Jose; Moreno, Marcos
Subduction earthquakes show complex spatial and temporal rupture patterns, exhibiting events of varied sizes, which rupture distinct or overlapping fault segments. Elucidating first-order controlling conditions of rupture segmentation and return periods of large earthquakes is therefore critical for seismic and tsunami hazard estimations. The Chilean subduction zone frequently hosts several M-w > 8 earthquakes, with heterogeneous recurrence rates and locations. Here, we implement 3-D quasi-dynamic rate and state frictional models to investigate the role of plate interface geometry on the distribution of interseismic coupling and coseismic ruptures in Central Chile. First, we develop synthetic-parametric models that show how dip and strike variations may increase the probabilities to produce partial seismic barriers, which tend to avoid the production of large earthquake ruptures and modulate rupture lengths. Then, we simulate the subduction seismic cycle processes on Central Chile (25(degrees)S-38(degrees)S), imposing depth-dependent frictional properties on a realistic non-planar 3-D subduction interface geometry. Similar to results obtained for synthetic-parametric models, after 5000 yr of simulation, regions with abrupt dip or strike changes increase the probabilities of stopping coseismic propagation of simulated M-w 8.0-9.0 earthquakes. Our simulated earthquake sequences on the Central Chile subduction zone delimit rupture areas that match geometrical interface features and historical earthquakes, results that point to the crucial role of fault interface geometry on seismic cycle segmentation along strike.
Structural Evolution of a Crustal-Scale Seismogenic Fault in a Magmatic Arc: The Bolfin Fault Zone (Atacama Fault System)
(2021) Masoch, Simone; Gomila, Rodrigo; Fondriest, Michele; Jensen, Erik; Mitchell, Thomas; Pennacchioni, Giorgio; Cembrano, Jose; Di Toro, Giulio
How major crustal-scale seismogenic faults nucleate and evolve in crystalline basements represents a long-standing, but poorly understood, issue in structural geology and fault mechanics. Here, we address the spatio-temporal evolution of the Bolfin Fault Zone (BFZ), a >40-km-long exhumed seismogenic splay fault of the 1000-km-long strike-slip Atacama Fault System. The BFZ has a sinuous fault trace across the Mesozoic magmatic arc of the Coastal Cordillera (Northern Chile) and formed during the oblique subduction of the Aluk plate beneath the South American plate. Seismic faulting occurred at 5-7 km depth and <= 300 degrees C in a fluid-rich environment as recorded by extensive propylitic alteration and epidote-chlorite veining. Ancient (125-118 Ma) seismicity is attested by the widespread occurrence of pseudotachylytes. Field geologic surveys indicate nucleation of the BFZ on precursory geometrical anisotropies represented by magmatic foliation of plutons (northern and central segments) and andesitic dyke swarms (southern segment) within the heterogeneous crystalline basement. Seismic faulting exploited the segments of precursory anisotropies that were optimal to favorably oriented with respect to the long-term far-stress field associated with the oblique ancient subduction. The large-scale sinuous geometry of the BFZ resulted from the hard linkage of these anisotropy-pinned segments during fault growth.
Tectonic setting, structures, and Au-Cu mineralization age of the Indiana deposit: An example of ore deposit formation controlled by Andean transverse faults, Atacama region, Chile
(2024) Reinoso, Felipe; Marquardt, Martin; Cembrano, Jose; Perez-Flores, Pamela; Diaz-Alvarado, Juan; Folguera, Andres
The Indiana Deposit corresponds to a Cu-Au (Mo-Co) fault-vein deposit located in the Central Andes Coastal Cordillera Belt (similar to 27 degrees S). It is hosted by strongly altered volcanic and intrusive rocks located between the NNE-striking central and principal branches of the Atacama Fault System (AFS) in northern Chile. The Indiana Deposit is part of a 10 km-long and 5 km-wide mine district that includes the Iron-Copper bearing Cerro Negro Norte (CNN) deposits and the Cu-Au Galleguillos vein system, termed the CNN-Indiana District in this study. The district provides insights into the mid-Cretaceous structural and lithological control of iron, copper and gold mineralization in northern Chile.Mineralization in the Indiana Deposit is spatially and temporally related to NW- and ENE-striking fault-vein systems, which are kinematically unrelated to the AFS. Three main mineralized ENE-striking, hundred-meter-long structures have been identified in Indiana. Structural and kinematic data suggest that mineral precipitation took place at dilation zones (e.g. extensional jogs, transtensional fault terminations) generating steeply-plunging ore shoots, and reactivating pre-existing structures (NW fault-vein system).Sinistral transtensional kinematics observed in ENE-striking fault-vein structures postdate the activity of the margin-parallel Atacama fault system, which has for long been regarded as accommodating the strike-slip component of plate convergence during the Jurassic to middle Cretaceous neglecting the role of Andean Transverse Faults (ATF), such as the ones recognized in this study. Sinistral transtension along ENE-striking faults gave rise to a local NE-striking maximum principal stress, different from that arising from displacement along the main margin-parallel faults, which in turn is consistent with far field stresses at that time.The CNN-Indiana district evolved from an early Ca-Na high temperature system related to Iron-bearing deposits to a brittle mineralized fault-vein copper-gold-bearing quartz-sericite (k-feldspar-calcite) corridor associated with a lower temperature environment along the Costal belt.Re-Os ages yielded 109-108 Ma obtained along the mineralized ENE-striking structures in Indiana Deposit and are slightly younger than those obtained from similar deposits associated with deformation along the AFS, which is consistent with our field observations indicating that at least part of the strike slip displacement on transverse faults hosting mineralization outlasts that of the AFS.
The interplay of a fault zone and a volcanic reservoir from 3D elasto-plastic models: Rheological conditions for mutual trigger based on a field case from the Andean Southern Volcanic Zone
(2021) Ruz Ginouves, Javiera; Gerbault, Muriel; Cembrano, Jose; Iturrieta, Pablo; Saez Leiva, Felipe; Novoa, Camila; Hassani, Riad
The Southern Andes margin hosts active and fossil volcanic, geothermal, and mineralized systems documenting intense geofluid migration through the crust. Fluid flow is also spatially associated with crustal faults that accommodate the bulk deformation arising from oblique plate convergence. Although recognized, the precise local mechanical interaction between faults and crustal reservoirs is yet to be better understood. Here we present 3D numerical models of a magmatic reservoir and a fault zone set about 4 km apart, inspired by the Tatara-San Pedro volcanic complex in the Southern Volcanic Zone (similar to 36 degrees S), which displays a geothermal field and a margin-parallel dextral active fault zone constrained by published magnetotelluric profiles and crustal seismicity respectively. We investigate elasto-plastic deformation and stress patterns in the intermediate bedrock space between the reservoir and the fault zone and test how shear stress, volumetric strain, and plastic strain develop. We also test the potential of enabling brittle failure of their counterpart by imposing either (1) a strike-slip displacement along the fault zone, or (2) a magmatic overpressure at the cavity walls. Parametric tests of Young's modulus and frictional strength provide the conditions for macro-scale brittle failure and show the development of diffuse domains of dilational strain of the order of 10(-5) -10(-3) in the intervening bedrock. This dilation is a proxy to the opening of voids or volumetric cracking in the bedrock, which tends to increase porosity and permeability allowing over-pressurized geoflu ids to migrate within these domains. Our results show that a minimum of 60 m of fault displacement is required to trigger brittle failure of an upper crustal cavity if the bedrock is stiff, whereas, for a more compliant bedrock, more than 100 m of localized slip motion is required. This implies that it is rather the accumulated effect of repeated crustal fault displacement that potentially favors fluid pathways upwards, rather than a single seismic event. On the other hand, a minimum of 7.5 MPa of fluid overpressure is required for a mid-crustal cavity (15 km depth) to trigger brittle failure of the fault zone. This threshold overpressure increases up to 50 MPa when the cavity is shallower (6 km depth). Our results show that in general, shallow reservoirs must be very dose to fault zones (less than 1-2 km apart) to reactivate them. The models show that localized strike-slip tectonics and magma intrusions build a dilational stress field at the scale of several kilometers, that promotes fluid pathways to the surface. Further combining this interaction with the regional transpressional stress field may explain observations of transient fluid pathways on seemingly independent timescales along the Andean margin. (C) 2021 Elsevier B.V. All rights reserved.
The orientation of intra-arc crustal fault systems influences the copper budget of magmatic-hydrothermal fluids
(2024) Tardani, Daniele; Tassara, Santiago; Sanchez-Alfaro, Pablo; Reich, Martin; Perez-Flores, Pamela; Robidoux, Philippe; Contreras, Claudio; Pinti, Daniele L.; Cembrano, Jose; Ague, Jay. J.
Some of the largest magmatic-hydrothermal copper ore deposits and deposit clusters are associated with arc-oblique fault systems. Whether this structural context impacts the geochemistry of hydrothermal fluids, including their copper contents, remains unknown. Here, we investigate the copper concentration and helium isotope signature of geothermal fluids as modern analogs of hydrothermal ore deposits in the Andes of central-southern Chile. We show that fault systems broadly parallel to the regional stress field facilitate the early release of fluids from deep primitive magmas. By contrast, fault systems oblique to the regional stress field prevent the early escape of fluids and promote magmatic enrichment in copper, volatiles, and ligands, enhancing the potential to form copper deposits. We conclude that the orientation of fault systems actively influences the copper budget of ascending hydrothermal fluids, explaining the contrasting distribution of metals along distinct structures often observed in porphyry-epithermal systems and other types of magmatic-hydrothermal deposits.

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