Browsing by Author "Yanez, Gonzalo"

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    A multiscale inversion algorithm for engineering inspection using GPR data
    (2023) Gutierrez Cid, Sergio Enrique; Menanno, Giovanni; Yanez, Gonzalo
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    An Empirical Correlation between the Residual Gravity Anomaly and the H/V Predominant Period in Urban Areas and Its Dependence on Geology in Andean Forearc Basins
    (2021) Maringue, Jose; Saez, Esteban; Yanez, Gonzalo
    The study of site amplification effects is crucial to assess earthquake hazards that can produce great damage in urban structures. In this context, the gravity and the ambient noise horizontal-to-vertical spectral ratio (H/V) are two of the most used geophysical methods to study the properties of the subsoil, which are essential to estimate seismic amplification. Even though these methods have been used complementarily, a correlation between them has not been thoroughly studied. Understanding this correlation and how it depends on geology could be important to use one method as an estimator of the other and to make a distinction between the seismic and gravimetric basement. In this research, a comparison between the residual gravity anomaly and the H/V predominant period is performed using a long dataset from different projects on sedimentary basins in a group of the most important cities in Chile. To simplify the geological information, a seismic classification is used for soils, which considers the Vs30 and the predominant period of vibration (T0). The results of this comparison show a direct correlation between both parameters, the higher the negative residual gravity anomaly the higher the H/V predominant period. This correlation improves when only soft soils are considered, increasing the R2 value in more than a 50% in all the individual cities with respect to the overall correlation. When all the cities are considered, the R2 value for soft soils increases up to 0.87. These results suggest that the ideal geological background for this correlation is when a soft soil layer overlies a homogeneous bedrock. Heterogeneities in the bedrock and in the soil column add dispersion to the correlation. Additionally, the comparison between the depth to basement inferred by both methods show differences of less than 15% in soft sites; in denser sites, the difference increases up to 30% and the definition of a clear H/V peak is more difficult. In general, the gravimetric basement is deeper than the seismic one. However, gravimetric depths to basement can be under/over-estimated in zones with a heterogeneous soil column.
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    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.
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    Exploration, mapping and characterization of filtration galleries of the Pica Oasis, northern Chile: A contribution to the knowledge of the Pica aquifer
    (2020) Lictevout, Elisabeth; Abellanosa, Carlos; Maass, Constanza; Perez, Nicolas; Yanez, Gonzalo; Veronique, Leonardi
    In arid areas, the efficient management of scarce water resources is key for population survival and development. One of the oldest and greatest ancient water management system in drylands is the filtration gallery. Originated from ancient Persia, they were spread to other regions and cultures, and are found in the oasis of Pica, in the Atacama Desert. A filtration gallery consists of an almost horizontal tunnel dug underground until it reaches a water-bearing zone. It allows to tap and drains out groundwater, and thus a direct contact with groundwater table. With the objective to understand groundwater processes, preserve the water and geoheritage of one of the driest places on Earth and improve land-use planning, the present work explored and studied the filtration galleries, locally called socavones, of the oasis of Pica. Through direct exploration, topographical survey and geo-electrical prospection, 24 socavones were identified, mapped and their main physical features described, showing common traits with filtration galleries described worldwide, but also proper features highlighting their originality. The findings of the geological and hydrogeological studies of the socavones, complemented by physical and chemical analysis, allow to identify new groundwater recharge processes and, thus, to review and complete the hydrogeological model of the local aquifer of Pica. Most socavones are abandoned today, owing to physical and socioeconomic changes. Nevertheless, this study concludes that they can still have a role to play in the groundwater management of this arid area.
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    From presentation to publication: an 11-year comparison of aesthetic and reconstructive surgery research among Chilean plastic surgeons
    (2021) Tejos, Rodrigo; Navia, Alfonso; Berner, Juan Enrique; Searle, Susana; Yanez, Gonzalo; Dagnino, Bruno; Guerra, Claudio; Cuadra, Alvaro
    Background The transition from a presentation in a scientific conference to publication in an academic journal should be the ideal journey for a research project. This phenomenon is summarized in a conversion rate, which has been previously reported in the literature. The aim of this study was to determine the characteristics and conversion rate of Chilean authors' aesthetic and reconstructive research projects in a nationwide study. Methods Conference abstracts from the two official Chilean plastic surgery meetings released between 2008 and 2018 were analyzed. A bibliographic search of all published articles involving each Chilean plastic surgeon followed. This information was cross-referenced to obtain the conversion rates and time to publication for transferred studies. Fisher's exact test and Mann-Whitney test were used to establish statistical associations. Results Four hundred sixty-eight abstracts were included, and 227 articles were found in our bibliographic search. Of these, 82 were considered to qualify as transferred studies. Aesthetic surgery publications had a higher proportion of prospective design than reconstructive articles (34.6% vs 20.1% (p= 0.02)). Median time to publication was 15 months, with a longer delay for reconstructive articles (19.5 vs 13 (p= 0.035)). The 2008-2016 conversion rate index was 19.2%, which was significantly higher for aesthetic surgery studies (36.4% vs 11.9% (p< 0.001)). Conclusions Despite a smaller proportion of plastic surgery research being focused on aesthetic topics in our sample, they accounted for higher quality study design, shorter time to publication, and higher overall chances of publication following presentations in local meetings. Level of evidence: Not ratable.
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    Geological and geotechnical investigation of the seismic ground response characteristics in some urban and suburban sites in Chile exposed to large seismic threats
    (2022) Maringue, Jose; Mendoza, Laura; Saez, Esteban; Yanez, Gonzalo; Montalva, Gonzalo; Soto, Valeria; Ayala, Felipe; Perez-Estay, Nicolas; Figueroa, Ronny; Sepulveda, Natalia; Galvez, Carlos; Ramirez, Paola; Ovalle, Carlos
    The central area of Chile's Valparaiso Region has been classified as a seismic gap for a major earthquake, which makes it very important to understand the seismic hazard of the zone. Generally, seismic codes consider a qualitative classification of sites to estimate the possible damage in the case of an earthquake scenario. Estimating the values of acceleration could be very important to prevent damages and increase preparedness for these rare events. In this research, a qualitative and quantitative estimation of seismic hazard is performed in the study area (Valparaiso region between Papudo and San Antonio 32 degrees-34 degrees S). This is achieved through an integrated and relatively economical approach which considers the information from Geology, Geophysical experiments (Gravity and seismic methods), and Geotechnical analyses. The results of the geophysical survey and geology information allow dividing the zone into five site types through a new proposal of site classification that depends not only on the V-s30,V- but also on the sites predominant period (T-0), which is an innovation of this work for the Chilean code. The Peak Ground Acceleration (PGA) values in the study zone were estimated using a Ground Motion Predictive Equation developed for the Chilean subduction zone. Additionally, we consider three different seismic scenarios according to the history of events in Central Chile. The results of this quantitative analysis show PGA values up to 0.52 g for the median and 1.2 g for the 84th percentile of the scenarios. Overall, the highest accelerations (PGA) are in zones with low shear wave velocities (< 500 m/s), a long predominant period (> 0.4 s) and where geology establishes the presence of low stiffness soils. The comparison of response spectra from the model against records from 2010 Maule and 1985 Valparaiso earthquakes shows available models tend to overpredict the intensities.
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    High-Resolution Deformation Monitoring from DInSAR: Implications for Geohazards and Ground Stability in the Metropolitan Area of Santiago, Chile
    (2022) Orellana, Felipe; Moreno, Marcos; Yanez, Gonzalo
    Large urban areas are vulnerable to various geological hazards and anthropogenic activities that affect ground stability-a key factor in structural performance, such as buildings and infrastructure, in an inherently expanding context. Time series data from synthetic aperture radar (SAR) satellites make it possible to identify small rates of motion over large areas of the Earth's surface with high spatial resolution, which is key to detecting high-deformation areas. Santiago de Chile's metropolitan region comprises a large Andean foothills basin in one of the most seismically active subduction zones worldwide. The Santiago basin and its surroundings are prone to megathrust and shallow crustal earthquakes, landslides, and constant anthropogenic effects, such as the overexploitation of groundwater and land use modification, all of which constantly affect the ground stability. Here, we recorded ground deformations in the Santiago basin using a multi-temporal differential interferometric synthetic aperture radar (DInSAR) from Sentinel 1, obtaining high-resolution ground motion rates between 2018 and 2021. GNSS stations show a constant regional uplift in the metropolitan area (similar to 10 mm/year); meanwhile, DInSAR allows for the identification of areas with anomalous local subsistence (rates < -15 mm/year) and mountain sectors with landslides with unprecedented detail. Ground deformation patterns vary depending on factors such as soil type, basin geometry, and soil/soil heterogeneities. Thus, the areas with high subsidence rates are concentrated in sectors with fine sedimentary cover and a depressing shallow water table as well as in cropping areas with excess water withdrawal. There is no evidence of detectable movement on the San Ramon Fault (the major quaternary fault in the metropolitan area) over the observational period. Our results highlight the mechanical control of the sediment characteristics of the basin and the impact of anthropogenic processes on ground stability. These results are essential to assess the stability of the Santiago basin and contribute to future infrastructure development and hazard management in highly populated areas.
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    Integration of Near-Surface Complementary Geophysical Techniques for the Study of Ancient Archaeological Areas in the Atacama Desert (Pampa Iluga, Northern Chile)
    (2023) Gallegos-Poch, Fernanda; Viguier, Benoit; Menanno, Giovanni; Mandakovic, Valentina; Yanez, Gonzalo; Gutierrez, Sergio; Lizarde, Catalina; Araya, Jaime Vargas; Lopez-Contreras, Camila; Mendez-Quiros, Pablo; Maldonado, Antonio; Uribe, Mauricio
    Near-surface geophysical techniques are useful for the characterization of archaeological areas because of their ability to rapidly cover wide extensions and obtain high-resolution data to identify the location for archaeological excavations. However, in hyperarid environments usual geophysical techniques may fail to obtain the expected results due to the dry near surface. This study proposes an integration of ground penetrating radar (GPR) and electromagnetic induction (EMI) techniques, to elucidate the origin of thousands of aligned circular features located at the Iluga archaeological area emplaced on one of the driest places on Earth (Pampa del Tamarugal, Atacama Desert). The GPR was useful to recognize alluvial deposits, sandy aeolian filling in pre-existing holes and roots right underneath circular features. Magnetic susceptibility data derived from the EMI in-phase component, usually considered a complementary result, were useful to identify fireplaces in the vicinity of the alignments. These geophysical findings were verified with an archaeological excavation. It has been found that circular features resulted from an extensive deforestation process in the Pampa del Tamarugal, consisting in the extraction of both trunk and roots of algarrobos (Prosopis chilensis) or tamarugos (Prosopis tamarugo), likely for recent charcoal production. The proposed methodology delivers promising results for archaeological and shallow geological studies in hyperarid and dry environments.
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    Multi-station automatic classification of seismic signatures from the Lascar volcano database
    (2023) Salazar, Pablo; Yupanqui, Franz; Meneses, Claudio; Layana, Susana; Yanez, Gonzalo
    This study was aimed to build a multi-station automatic classification system for volcanic seismic signatures such as hybrid, long period, tremor, tectonic, and volcano-tectonic events. This system was based on a probabilistic model made using transfer learning, which has, as the main tool, a pre-trained convolutional network named AlexNet. We designed five experiments using different datasets with data that were real, synthetic, two different combinations of these (combined 1 and combined 2), and a balanced subset without synthetic data. The experiment presented the highest scores when a process of data augmentation was introduced into processing sequence. Thus, the lack of real data in some classes (imbalance) dramatically affected the quality of the results, because the learning step (training) was overfitted to the more numerous classes. To test the model stability with variable inputs, we implemented a k-fold cross-validation procedure. Under this approach, the results reached high predictive performance, considering that only the percentage of recognition of the tectonic events (TC) class was partially affected. The results obtained showed the performance of the probabilistic model, reaching high scores over different test datasets. The most valuable benefit of using this technique was that the use of volcano seismic signals from multiple stations provided a more generalizable model which, in the near future, can be extended to multi-volcano database systems. The impact of this work is significant in the evaluation of hazard and risk by monitoring the dynamic evolution of volcanic centers, which is crucial for understanding the stages in a volcano's eruptive cycle.
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    Rheological, petrophysical and geometrical constraints of a subduction channel from a numerical model perspective: Insights from La Cabana Paleozoic peridotites, Coastal Cordillera of south-central Chile
    (2022) Sanhueza, Jorge; Yanez, Gonzalo; Barra, Fernando; Maringue, Jose; Figueroa, Ronny; Saez, Esteban
    The emplacement of ultramafic blocks in accretionary complexes poses a geodynamic problem due to their negative buoyancy. In this study, we explore plausible emplacement scenarios for peridotite bodies in the Coastal Cordillera of south-central Chile by combining geophysical observations, numerical modeling and available petrological data for ultramafic blocks exhumed along the subduction channel. The La Cabana massif is the largest serpentinized peridotite complex yet recognized in the Coastal Cordillera, however, its size and petrophysical characteristics remain unknown. The geophysical measurements were performed to determine the size of this body, involving magnetic airborne surveys and electrical resistivity tomography. Inversion data show that the largest ultramafic block in La Cabana is 3 km long, 1.5 km wide and at least 1.2 km deep. This result constrains the characteristics of the block transported by the subduction channel. In the second step, we developed a numerical model for the subduction channel assuming a viscous rheology. In this modeling effort we search for tectonic scenarios that provide adequate conditions for the exhumation of the ultramafic body in La Cabana. These scenarios included a combination of key parameters, subduction angle dip and velocity, subduction channel geometry, rheology and density contrast. Scenarios compatible with the exhumation of La Cabana body type includes channel viscosity range of 10(19-20) Pa s, fast exhumation rates at mantle depths (10-20 mm/yr; >30-40 km), steep subduction angles (30 degrees-60 degrees), subduction channel widths of 3-5 km, density contrast between -200 and -400 kg/m(3) and a body diameter of 1.5 km which is consistent with our geophysical inversions. On the contrary, slow exhumation rates (similar to 1 mm/yr), low subduction angles (15 degrees), high-density contrasts (-400 to -600 kg/m(3)) and bodies larger than 1.5 km wide, are not viable exhumation scenarios. The methodology developed provided insights to infer ancient subduction channel geometries and rheologies that include peridotite.
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    Ridge Subduction: Unraveling the Consequences Linked to a Slab Window Development Beneath South America at the Chile Triple Junction
    (2023) Sanhueza, Jorge; Yanez, Gonzalo; Buck, W. Roger; Vargas, Jaime Araya; Veloso, Eugenio
    The subduction of an active spreading center generates a clear signature in the temporal evolution of subduction zones. It disrupts the typical arc-type magmatism and intraplate seismicity, enhances the emplacement of backarc plateau lava and profoundly change the tectonics and topographic relief. These distinct observations are commonly linked to a slab window opening and mantle upwelling. The Chile Triple Junction provides the ideal setup to study the mid-ocean ridge subduction process where both sides of the spreading center continue to subduct. Here, we use 2-D numerical petrological-thermomechanical modeling to focus on transient geodynamic processes caused by mid-ocean ridge subduction. Model results show slab separation along the ridge axis with the opening of a slab window. During the opening, partial melts from the spreading center migrate toward the subcontinental mantle and high temperatures in the forearc are predicted. The temporal evolution of the modeled temperature is consistent with observed heat flow data, and with magmatism and high-temperature metamorphism recorded in Chilean forearc rocks. Such migrated partial melts might explain the low viscosity inferred and low seismic velocity anomalies imaged in the slab window beneath South America, and the common geochemical signature of the Chile Ridge, the Taitao Ophiolite and the backarc magmatism. Following slab separation, our models suggest forearc uplift and changes in the stress regime, processes which are consistent with deformation records. Summarizing, our model of the geodynamic evolution of the Chile Ridge subduction provides a consistent framework that explains diverse records of magmatism, metamorphism, deformation and mantle physical properties.
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    Selective reactivation of inherited fault zones driven by stress field changes: Insights from structural and paleostress analysis of the Pocuro Fault Zone, Southern Central Andes (32.8 degrees S)
    (PERGAMON-ELSEVIER SCIENCE LTD, 2022) Taucare, Matias; Roquer, Tomas; Heuser, Gert; Perez-Estay, Nicolas; Arancibia, Gloria; Yanez, Gonzalo; Viguier, Benoit; Figueroa, Ronny; Morataa, Diego; Daniele, Linda
    This study aims to explain the selective reactivation of normal faults during the Andean orogeny at the Southern Central Andes western flank. We conducted a structural mapping and paleostress field reconstruction in the regional-scale Pocuro Fault Zone (PFZ) at 32.8 degrees S. Results reveal that the architecture of the PFZ results from at least two deformation phases, each revealing an individual progressive and gradual evolution. The earliest deformation phase is recorded by two similar to NS-striking normal faults involving a 5 km wide damage zone characterized by quartz-laumontite and calcite veins that were developed under an extensional regime with a WNW-ESE-trending sigma 3-axis. The latest deformation phase is recorded by one NS-striking reverse-dextral fault with goethite-hematite syn-tectonic precipitation and two NW-striking reverse-sinistral faults. Reverse faults were developed under a compressional/transpressional regime characterised by an ENE-WSW-trending sigma 1-axis with a sigma 2-/sigma 3-axis permutation. From a geophysical data reassessment, we inferred that observed faults in the surface within the PFZ are regional-scale deep-seated structures. Considering previous geochronological data, we correlated the earliest and latest phases with the Abanico Basin extension (middle Eocene-early Miocene) and its subsequent inversion (Miocene). Given the neotectonic evidence (geomorphic markers and deformation of unconsolidated deposits), the latter phase likely remains active. Quartz-laumontite cementation of the fault core's cataclastic material promotes mechanical strengthening leading to negative feedback for the reactivation of inherited normal faults as reverse ones. Conversely, the concentration of fractures in the damage zone between the normal faults promotes mechanical weakening resulting in a preferential area for the propagation of reverse fault during the compressive/transpressional phase.
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    The Piuquencillo fault system: a long-lived, Andean-transverse fault system and its relationship with magmatic and hydrothermal activity
    (2021) Piquer, Jose; Rivera, Orlando; Yanez, Gonzalo; Oyarzun, Nicolas
    Lithospheric-scale fault systems control the large-scale permeability in the Earth's crust and lithospheric mantle, and its proper recognition is fundamental to understand the geometry and distribution of mineral deposits, volcanic and plutonic complexes and geothermal systems. However, their manifestations at the current surface can be very subtle, as in many cases they are oriented oblique to the current continental margin and to the axis of the magmatic arc; be partially obliterated by younger, arc-parallel faults; and also be covered by volcanic and sedimentary deposits, through which the fault might propagate vertically.
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    Towards linking slab window geodynamics with the geophysical and geochemical signature of the upper mantle
    (2023) Sanhueza, Jorge; Yanez, Gonzalo; Buck, W. Roger; Sawant, Amol Dayanand; Vargas, Jaime Araya; Lloyd, Andrew J.
    Slab windows have clear consequences for surface observations that are the manifestations of asthenospheric upwelling and uppermost mantle temperature anomalies. In this contribution we link geophysical and geochemical observations from modern slab windows to the asthenospheric flow, temperature field and extent of melting using different geometries. We use an analytical solution for the slab window geometry and implement this solution in 3D steady-state thermomechanical models to calculate the temperature and velocity field. Our results show that upwelling (>1 cm/yr) and temperature anomalies (>1400 C-degrees) are controlled by the ratio between the half-spreading rate and velocity of the overriding plate. The extent of melting depends on both the ratio of these velocities and ridge obliquity while flow patterns are controlled only by ridge obliquity. Finally, we construct ternary diagrams to estimate the efficiency of matrix/melt upwelling and maximum mean mantle temperatures based on plate kinematics and ridge obliquity. This novel approach was used to investigate the slab windows in Antarctica, South America and western North America.