Abstract This study presents geophysical data from two passive seismic measurements conducted at two different sites in Antarctica. We analyzed the signals mainly in the frequency domain through the multitaper method to extract some spectral characteristics of the signals that would have been out of reach through the usual FFT approach. The power spectral density of the signals carries information about the processes that generated them, allowing its correlation with their source origin and type, either natural or anthropogenic. We deal with three different source types: calving, wind, and anthropogenic origins. The former is closely related to glacier dynamics, being modulated by the prevailing atmospheric processes. At both locations the wind noise is prevalent, complicating the analysis of other events like calving. We have used data classification, estimation of the source azimuth, and seismic apparent velocity to demonstrate the viability of using geophysical methods to study glacier elastic parameters and dynamics. Moreover, the calving rate can yield a wider and more independent understanding of glacier hydrodynamics and may help to estimate the future response of the polar areas to a changing environment. Antarctica approach them type types origins dynamics prevalent classification azimuth Moreover environment

Abstract Iron ore tailings dams must be constantly monitored for safety purposes. Among the aspects traditionally monitored are geotechnical protocols, such as piezometric levels along the dam. Recently, geophysics, a science that studies, among other things, dynamic processes in the Earth, has contributed to non-invasive monitoring using electro-resistivity methods. Geophysical methods provide a large amount of data in relatively quick samples, but there is little information on the integration of traditional geotechnical and geophysical techniques. Therefore, this work aimed to evaluate the relationship between geophysical data, monitored every 15 days between May 2022 and March 2023, and geotechnical data from an iron ore tailings dam located in the Iron Quadrangle. The geophysical method used was two-dimensional electrical imaging with a Schlumberger array. Analysis of variance and multiple regression allowed us to evaluate the relationship between resistivity values, piezometer level, sampling time, and rainfall. Piezometry data explained the electro-resistivity significantly, while sampling time and rainfall did not significantly explain electro-resistivity. Therefore, the dam's electro-resistivity patterns have not changed significantly over the period, and local rainfall does not imply an immediate response in resistivity. These conclusions can support new directions in decisions about monitoring iron ore tailings dams and may contribute to advances in dam safety in the mining sector. purposes protocols Recently geophysics studies things Earth noninvasive non invasive electroresistivity electro samples techniques Therefore 1 202 2023 Quadrangle twodimensional two dimensional array values level electroresistivity. s period sector 20 2

Abstract The main coal reserves in Brazil are located in the southern region, where the most important coalfield, including the Candiota mine, is found. The mineral exploration and mine planning programs of the companies mining these coal deposits are generally restricted to drilling data and cores, despite the exploratory potential of geophysical methods in coal prospecting. This study aims to investigate the ability of the seismic method known as Multichannel Analysis of Surface Waves (MASW) to identify coal seams in the Candiota area. The MASW method allows obtaining a layer model composed of a low-velocity (blind) layer and/or relatively thin (hidden) layer from the surface wave dispersion curves. The hidden and blind layer problems are pitfalls of the traditional seismic refraction method and the geological settings related to coal seams may encompass both problems. In addition, the Candiota mine has conditions favorable for applying the MASW method due to the shallow depths of the coal seams. The study was based on the analysis of synthetic seismic data generated from a 3-layer conceptual model of the Candiota deposit. The dispersion curves of the fundamental mode of the Rayleigh surface waves were generated and the effects of each of the parameters of the seismic model were evaluated, as well as the relationship between the parameters through objective function tests. A new inversion algorithm capable of obtaining the true model was implemented. The results obtained from the application of the inversion algorithm demonstrated the potential of the MASW method in identifying coal seams from S-wave profiles and proves it to be a powerful tool for coal mineral exploration programs. region coalfield found cores prospecting (MASW area lowvelocity low velocity (blind andor or (hidden addition 3layer 3 deposit evaluated tests implemented Swave S

Abstract This study presents geophysical data from two passive seismic measurements conducted at two different sites in Antarctica. We analyzed the signals mainly in the frequency domain through the multitaper method to extract some spectral characteristics of the signals that would have been out of reach through the usual FFT approach. The power spectral density of the signals carries information about the processes that generated them, allowing its correlation with their source origin and type, either natural or anthropogenic. We deal with three different source types: calving, wind, and anthropogenic origins. The former is closely related to glacier dynamics, being modulated by the prevailing atmospheric processes. At both locations the wind noise is prevalent, complicating the analysis of other events like calving. We have used data classification, estimation of the source azimuth, and seismic apparent velocity to demonstrate the viability of using geophysical methods to study glacier elastic parameters and dynamics. Moreover, the calving rate can yield a wider and more independent understanding of glacier hydrodynamics and may help to estimate the future response of the polar areas to a changing environment. Antarctica approach them type types origins dynamics prevalent classification azimuth Moreover environment

Abstract The geotechnical monitoring of tailings dams combined with a suitable application of geophysical electrical methods can improve their structure evaluation, allowing several correlations between direct analyses and the resistivity anomaly pattern. Considering this synergy, twenty-three electrical resistivity sections (ERT) were acquired along the beach, abutments, and central part of a dam, totalizing 10,776 m of dataset. After the interpretation of each ERT section, comparing the anomaly ranges with the water level meters measurements, three resistivity zones were defined: Zones of low resistivity (<64 ohm-m), correlated to regions of high humidity; zones of high resistivity (> 357 ohm-m), interpreted as dry zones, and regions with intermediate resistivity values, located between these limits. The groundwater surface generated from the interpretation of the electrical resistivity dataset and the groundwater surface acquired from the water level gauges were almost coincident. On the right abutment, the conductive anomalies showed remarkable continuity, suggesting a high moisture content in this region with strong gradients (200 mV) directed towards the zone of low resistivity values identified in the sections. The analysis showed a robust correlation of the ERT data with localized physical geotechnical measurements, valuable for monitoring dam integrity, overseeing the structure's response to climate and operational changes, and ultimately mitigating the risks of failure. The results of this study support the adoption of a seasonal 4D electrical resistivity survey as an effective tool to monitor and manage surface and high humidity zones, key indicators of dam integrity throughout the entire structure. evaluation pattern synergy twentythree twenty (ERT beach abutments 10776 10 776 10,77 section measurements defined <64 64 (<6 ohmm, ohmm ohm , ohm-m) > ( 35 limits coincident abutment continuity 200 (20 mV structures s changes failure D 1077 1 77 10,7 <6 6 (< ohm-m 3 20 (2 107 7 10, < 2

Resumen Este trabajo presenta la caracterización geológica-geofísica de una probable ocurrencia de oro en el Gabro Santa Catarina, en la región de São Sepé, estado de Rio Grande do Sul, sur de Brasil. Trabajos anteriores han indicado la presencia de oro en la región en las actuales campañas de prospección geoquímica de sedimentos y sugieren que el área de origen sería el Gabro Santa Catarina. Para investigar sobre esta probable ocurrencia de oro, se realizaron estudios geológicos y estructurales, seguidos de la adquisición de información geofísica utilizando los métodos de resistividad DC e IP, con el arreglo dipolo-dipolo. De estos datos se obtuvieron inversiones 2D las cuales luego fueron interpolados para permitir la visualización tridimensional de la posible mineralización. Interpretaciones basadas en la recopilación de datos geológicos y geofísicos, en asociación con el contexto estructural regional, sugieren que la probable mineralización se originó a partir de la intrusión del Granito São Sepé, cuyos fluidos hidrotermales se alojaron en fracturas durante los eventos tectónicos ocurridos en la región. Los resultados obtenidos en este trabajo permiten delinear una arquitectura de yacimiento factible con el contexto geológico de la región y ayudar a una futura estrategia de perforación dirigida a los objetivos probables identificados.

Abstract This work presents the geological-geophysical characterization of a probable occurrence of gold in Santa Catarina Gabbro, in São Sepé region, Rio Grande do Sul state, southern Brazil. Previous works have indicated the presence of gold in the region in current sediments geochemical prospecting campaigns and suggests that the source area would be the Santa Catarina Gabbro. To investigate over this probable occurrence of gold, geological and structural surveys were conducted, followed by the acquisition of geophysical information using the DC-resistivity and IP methods, with the dipole-dipole array. The geophysical data were processed in 2D inversion and then interpolated to allow the three -dimensional visualization of possible mineralization. Interpretations based on the compilation of geological and geophysical data, in association with the regional structural context, suggest that the probable mineralization were originated from the intrusion of the São Sepé Granite, whose hydrothermal fluids were hosted in fractures during the tectonic events that occurred in the region. The results obtained in this work allow to outline a feasible deposit architecture with the geological context of the region and to assist a future drilling strategy aimed at the identified probable targets.

RESUMEN Malasia es uno de los países donde cada año se presentan deslizamientos de tierra debido a eventos naturales y actividades humanas. La isla de Penang es el segundo estado más desarrollado de Malasia y el más poblado. Es un estado propenso a deslizamientos de tierra con impactos ambientales devastadores. Por consiguiente, es necesario caracterizar las condiciones roca-suelo cerca de la superficie. Este estudio utiliza información de teledetección a través de técnicas de Radio Frecuencia (FR, del inglés Frequency Ratio) para identificar las áreas propensas a deslizamientos con base en diferentes categorías de factores causales de deslizamientos. Para entender mejor las condiciones y los perfiles hidrodinámicos suelo-roca que causan los deslizamientos de tierra se realizaron tomografías de resistividad eléctrica y de refracción sísmica en una zona del área de estudio que se presume es propensa a estos movimientos. Además, se realizó el modelamiento satelital de la anomalía gravitacional de Bouguer para identificar las variadas anomalías de la gravedad asociadas con los factores que desencadenan los deslizamientos en las unidades litológicas. Los modelos multigeofísicos ofrecen resultados fuertemente correlacionados con los mapas causales teledetectados y el mapa del índice de susceptibilidad de deslizamientos de tierra (LSI, del inglés Landslide Susceptibility Index). La probabilidad de ocurrencia de deslizamientos, de acuerdo con lo sugerido por la curva de información LSI en el área, establece una alta efectividad de predicción de 83.47 %. Con esto, la perspectiva de deslizamientos fue mayor en las secciones elevadas y montañosas, mientras que las secciones menos susceptibles se identificaron en las planicies. Los deslizamientos también podrían desencadenarse, en algunas instancias, en secciones empinadas con cuerpos variados de suelos contractivos y estructuras superficiales. Lo más destacado es que el aprovechamiento del mapa LSI ayudaría a las agencias a prevenir o mitigar los futuros deslizamientos de tierra en el área.

ABSTRACT Malaysia is one of the countries in the world that experiences landslides yearly due to natural events and human activities. Penang Island is Malaysia's second most developed state and the largest by population. It is prone to landslides with devastating environmental impacts. Hence, the need to characterize its near-surface soil-rock conditions. This study uses remotely sensed data, with frequency ratio (FR) analysis, to identify landslide-prone areas based on different categories of landslide causative factors. To further understand the conditions and hydrodynamics of the soil-rock profiles causing landslides, electrical resistivity tomography and seismic refraction tomography were carried out at a landslide-suspected section in the study area. Also, satellite-derived Bouguer gravity anomaly modeling was performed to map the varied gravity anomalies associated with landslide-triggering factors in lithologic units. The multi-geophysical models offer strongly correlated results with the remote sensing causative factor maps and the landslide susceptibility index (LSI) map. The likelihood of landslides occurring in the area, as suggested by the area under curve modeling of LSI data, yielded a high predicted success rate of 83.47%. Hence, prospective landslides were identified in the hilly and elevated sections, while the less susceptible sections were identified on flat reliefs. Landslides may also be triggered, for instance, at steep sections with varied contractive soil bodies and shallow structures. Most importantly, leveraging the LSI map would help the necessary agencies forestall and mitigate future landslide occurrences in the area.

Abstract Geophysical methods are potent tools for geotechnical site characterization in a non-destructive way. They improve the extrapolation of punctual data from direct survey methods, allowing a fast and cost-effective evaluation of large areas. Ground Penetrating Radar (GPR) and DC electrical resistivity (ER) are the most requested methods for geotechnical and geoenvironmental applications. Their use, however, is usually uncoupled, with no sharing of information from one method to another to improve data interpretation. This case study illustrates the development of protocols and scripts in R© programming language for ER and GPR data analysis with Standard Penetration Tests (SPT) data to produce more accurate information on subsurface conditions concerning lithology, water content, and groundwater table (GWT) position. The SPT data were used to associate resistivity ranges with different soil lithologies and GPR pulse velocities for estimating the soil water content. Estimated water content values aided in interpreting ER data and locating the groundwater table. The contacts between layers in the radargrams allowed the refinement of the ER model, rendering 3D volumes for each soil layer in situ. nondestructive non destructive way costeffective cost effective areas (GPR (ER applications use however uncoupled interpretation R (SPT lithology GWT (GWT position model D situ

Abstract The characterization of unsaturated soils using hydromechanical methods is an essential requirement in soil science. However, current laboratory techniques used to obtain soil water retention and unsaturated hydraulic conductivity curves are time-consuming. To address this issue, a method based on indirect measures (electrical resistivity/electrical conductivity) was developed to quantitatively characterize soils. A novel unsaturated semi-empirical hydrogeophysical model of soils was developed by incorporating the hydrodynamic, geophysical, and petrophysical characteristics of soils. The model assumes that the parameters influencing the variation in the volumetric water content with matric suction and electrical resistivity are the same. The electrical resistivity characteristic curve (ERCC) defines a function that correlates environmental variables, electrical resistivity, soil water status, matric suction, hydraulic and petrophysical parameters, and fluid electrical resistivity. Model validation confirmed that the proposed approach can estimate the soil water retention curve (SWRC) via the indirect measures, and the results agreed with the experimental data. This indicates that it is possible to determine the SWRC and unsaturated hydraulic conductivity function of soil using the described approach. science However timeconsuming. timeconsuming time consuming. consuming time-consuming issue resistivityelectrical semiempirical semi empirical hydrodynamic geophysical same ERCC (ERCC variables status (SWRC data

RESUMEN En este trabajo se utilizan redes neuronales como una ventajosa herramienta para estimar parámetros petrofísicos de la columna estratigráfica atravesada por varios pozos. Los parámetros porosidad, volúmenes minerales y saturación de agua e hidrocarburos, se obtienen a partir de registros geofísicos de pozo básicos (rayos gamma, resistividad profunda, densidad volumétrica y tiempo de tránsito) y se infieren para otras zonas de la misma área geológica, en los que no se cuenta con este cuadro de información. Este análisis se realizó en secuencias siliciclásticas areno-arcillosas atravesadas por varios pozos perforados para alcanzar un yacimiento de hidrocarburos de baja permeabilidad. Se presentan estimaciones con modelos empíricos para enfrentarlas con las obtenidos con las redes neuronales de forma que se califique la actuación de la alternativa inteligente. Las leyes que rigen la dinámica de los parámetros, así como los detalles del contexto geológico quedan inmersos en los pesos de la red y la consistencia fenomenológica está definida a través de la congruencia de las entradas para conseguir las salidas elegidas. Se muestra la forma en la que el modelo neuronal habilita la propagación confiable de valores de propiedad y se convierte en un ventajoso auxiliar en el estudio de contextos geológicos muy complejos o escasamente parametrizados en los que las condiciones para la aplicación de correlaciones y métodos empíricos, así como el tiempo que se invierte en los procesos de ajuste y contextualización de registros, menguan la calidad y cantidad del conocimiento que se obtiene sobre el medio.

ABSTRACT In this work neural networks are used as an advantageous tool to estimate petrophysical parameters of the stratigraphic column traversed by several wells. The parameters porosity, mineral volumes, and water and hydrocarbon saturation are obtained from basic geophysical well logging (gamma rays, deep resistivity, volumetric density and transit time) and are inferred for other sites, in the same geological area, where they are not measured, so this information matrix is not available. This analysis was performed on sand-clay siliciclastic sequences traversed by several wells drilled to reach a low-permeability hydrocarbon reservoir. Estimates with empirical models are presented to compare them with those obtained with neural networks in order to qualify the performance of the intelligent alternative. The laws that govern the dynamics of the parameters as well as the details of the geological context are immersed in the weights of the network and the phenomenological consistency is defined through the congruence of the inputs to achieve the chosen outputs. The way in which the neural model enables the reliable propagation of property values is shown and becomes an advantageous auxiliary in the study of very complex or poorly parameterized geological contexts in which the conditions for the application of correlations and empirical methods as well as how the time invested in the processes of adjustment and contextualization of records, decreases the quality and quantity of knowledge obtained about the environment.

Abstract The inherent structural complexity of fractured aquifers, which controls the groundwater accumulation and flow in restricted zones, can lead to a high number of non-productive tube wells. The combined analysis of geomorphological features and indirect investigations like geophysics methods allows the identification of favorable targets for groundwater exploitation. This paper deals with regional and local structural surveys coupled with electrical resistivity tomography data in order to identify favorable targets for groundwater exploitation for urban consumption in a fractured granite located in Caçapava do Sul city, southern Brazil. The structural control is manifested in the regional landforms and clearly conditions the orientation of main drainages. Based on this structural control, four parallel electrical resistivity tomography lines were performed in an area of interest for groundwater exploitation, followed by the generation of 2D inversion models and pseudo 3D models. The contact between the very thin superficial soil and the underlying granite massif determines the existence of a regional free aquifer and the probable recharge of the fractured aquifer. In the 2D inversion models, abrupt variations of resistivity related to locally recognized vertical fractures in the field occur, although they do not show lateral continuity (out of plane). The analysis of the geophysical maps from 40 meters depth allows the recognition of three alignments of low resistivity (around 500 Ωm) within a granite context where high values predominate (above 15000 Ωm). These alignments show a triple fracture intersection pattern also recognized in satellite images, which are highly favorable for groundwater accumulation and exploitation.

Resumen La complejidad estructural inherente a los acuíferos fracturados, que controla la acumulación y el flujo de agua subterránea en zonas restringidas, puede dar lugar a un elevado número de pozos tubulares no productivos. El análisis combinado de las características geomorfológicas y las investigaciones indirectas, como los métodos geofísicos, permite identificar objetivos favorables para la explotación de aguas subterráneas. Este trabajo trata de los estudios estructurales regionales y locales acoplados con datos de tomografía de resistividad eléctrica con el fin de identificar objetivos favorables para la explotación de aguas subterráneas para el consumo urbano en un granito fracturado situado en la ciudad de Caçapava do Sul, en el sur de Brasil. El control estructural se manifiesta en las formas del terreno regional y condiciona claramente la orientación de los drenajes principales. Basándose en este control estructural, se realizaron cuatro líneas paralelas de tomografía de resistividad eléctrica en una zona de interés para la explotación de aguas subterráneas, seguidas de la generación de modelos de inversión 2D y de modelos pseudo 3D. El contacto entre el suelo superficial muy fino y el macizo granítico subyacente determina la existencia de un acuífero libre regional y la probable recarga del acuífero fracturado. En los modelos de inversión 2D se producen variaciones bruscas de resistividad relacionadas con las fracturas verticales localmente reconocidas en el yacimiento, aunque no muestran continuidad lateral (fuera del plano). El análisis de los mapas geofísicos a partir de 40 metros de profundidad permite reconocer tres alineaciones de baja resistividad (alrededor de 500 Ωm) dentro de un contexto granítico donde predominan los valores altos (por encima de 15000 Ωm). Estas alineaciones muestran un patrón de triple intersección de fracturas reconocido también en las imágenes de satélite, que son altamente favorables para la acumulación y explotación de aguas subterráneas.

Abstract Geophysical methods provide important information in the exploration of geothermal resources. In this study, we search for clues in the shallow resistivity structure of the presence of a known geo-thermal reservoir (Los Humeros, Mexico). We interpret about 410 vertical electric soundings (VES) and 230 transient electromagnetic (TEM) soundings, giving information usually down to depths of 1 km, although in some sites they reached 2 km. The vertical structure of the resistivity generally consists of a resistive-conductive-resistive sequence. The most important feature is the conductive unit, known as the clay-cap, associated with hydrothermal alteration clays overlying the geothermal reservoir. This unit suffers from a widespread equivalence problem, where its resistivity and thickness cannot be determined independently. However, well temperatures and associated alteration clays help to constrain this problem. In the shallow resistive unit we found several zones where its resistivity showed abnormally low values, which could represent recharge zones where fractured rock permits the infiltration of meteoric water to reservoir depths. The conductive clay-cap not only occurs over the geothermal reservoir, but has a regional presence. However, over the reservoir this electric unit has a larger conductance and its top is shallower. The few locations where the resistivity soundings reached depths of the geothermal reservoir with well-resolved estimates give a mean resistivity of 118 ohm'm, with no statistical difference between the producing and non-producing zones. This resistivity value falls within the range found in other geothermal zones in the world.

Resumen Los métodos geofísicos dan información importante en la exploración de recursos geotérmicos. En este trabajo buscamos pistas de la presencia de un yacimiento geotérmico conocido (Los Humeros, México) en la estructura somera de la resistividad eléctrica. Interpretamos cerca de 410 sondeos eléctricos verticales (SEV) y 230 sondeos electromagnéticos transitorios (TEM) que dan información de la resistividad eléctrica hasta profundidades de 1 km, alcanzándose en algunos sitios hasta 2 km. La estructura vertical de la resistividad generalmente consiste de una secuencia resistivo-conductor-resistivo. El rasgo más importante es la unidad conductora, conocida como el casquete de arcillas, asociado con arcillas de alteración hidrotermal arriba del yacimiento geotérmico. Esta unidad sufre de un problema de equivalencia, donde no se pueden determinar por separado su resistividad de su espesor. Sin embargo, las temperaturas de los pozos y las arcillas de alteración asociadas ayudan a constreñir este problema. En varias zonas de la unidad resistiva somera encontramos resistividades bajas que podrían representar zonas de recarga donde roca fracturada permite la infiltración de agua meteórica. El casquete de arcillas no solo se presenta sobre el yacimiento, sino que tiene una presencia regional. Sin embargo, sobre el reservorio esta unidad tiene una mayor conductancia y su cima está más somera. Los pocos lugares donde los sondeos eléctricos alcanzaron profundidades del yacimiento con resistividades bien resueltas dan una resistividad media de 118 ohm■m, sin poder diferenciar estadísticamente las zonas productoras de las no productoras. Esta resistividad está dentro del rango de valores encontrados en otras zonas geotérmicas del mundo.

A new methodology is proposed for the preliminary assessment of coal blend quality, which combines gamma-ray spectrometry and magnetic susceptibility measurements. This methodology does not replace the conventional methods of assessing coal quality, but can help to control the quality of the coal blending process, as well as reduce the amount of proximate analysis required and the determinations of calorific value and total sulphur. The methodology includes five steps. First, both geophysical measurements are made with handheld equipment. The samples with magnetic susceptibility < 1 x 10-3 SI are then separated. From these samples, those with total gamma intensity < 20 nGy/h are separated. These samples have a higher calorific value and lower ash and moisture content. To separate the samples of better quality and with lower total sulphur content, in step four the samples with total gamma intensity > 20 nGy/h are separated from those with magnetic susceptibility < 1 x 10-3 SI. This last group includes samples that will cause less total sulphur-related environmental pollution. In the final step, the quality of both radioactive sample groups is corroborated from the calorific value measurement and ash, moisture, and total sulphur contents in at least 10% of all coal blend samples from both groups. In this study, more than 1000 samples were analysed with this new methodology, and the results are remarkably similar to the ASTM classification of the Sabinas Basin coals.

ABSTRACT The hydric resource coming from groundwater has a strategic nature at global scale, within a context of overpopulation and over exploitation of the resource and climate change. Chile doesn’t scape to it, where climate models predict a drought for most of the country, including partially, the agriculture region of the Central Valley between Santiago and Puerto Montt. The adaption process to global climatic change demands the exploration new sources of supply of this resource, being strategic the one coming from aquifers. To date in Chile, the knowledge of these resources is limited to depths below 200 m in each aquifer. However, in the Central Valley between Santiago and Chiloé, the geophysical evidences allow to infer the existence of a thick volcano-sedimentary basin growing in thickness southward well above 500 m, with good potential for occurrence of large groundwater resources. The characterization of deep aquifers, 200-1,000 m of depth, demands to have an affordable, non-invasive, and reliable, exploration tool able to be applied in semi-urban and rural environments, where the water resource need is higher. The geophysical methodologies meet these characteristics and have been applied in Chile and elsewhere as a tool for groundwater resources exploration. However, its application have not been described in Andean environments, of large population and/or agro-industrial activity. In consequence, the present work raises a methodological strategy for the characterization of groundwater resources, in particular for the detection of deep aquifers. We propose the application of a combination of complementary geophysical techniques, including electrical, electromagnetic, and gravimetric methods (to determine the aquifer geometry) along with complementary techniques, like magnetometry, to reduce interpretation ambiguity and, constrained by hydrogeological information and petrophysics of rocks and sediments of the basin and basement. Complementary, we include an analysis of the potential effects of cultural noise and its effects on geophysical observations, given the focus of exploration in semi-urban and rural places. With the aim to validate the proposed methodology we use as a case study the aquifer of Ñuble river, in the Ñuble region, Chile. This aquifer properly represents an Andean forearc environment in rural and semi-urban condition, and potentially hosting a deep seated aquifer. The results allow the characterization of an aquifer with hydrogeological potential between 50 and 300-500 depth, overlying a sedimentary basin of more than 1,000 m thickness. The application of the proposed methodology for the exploration of groundwater resources will provide, in consequence, the recognition of a vital relevance resource for the sustainability of Chile during the following decades.

RESUMEN El recurso hídrico proveniente de aguas subterráneas presenta un carácter estratégico a escala global, en un contexto de sobrepoblación, sobreexplotación y cambio climático. Chile no escapa a esto, pues los modelos climáticos predicen sequía para gran parte del país, incluyendo parcialmente la región agrícola del valle central entre Santiago y Puerto Montt. El proceso de adaptación al cambio climático global exige explorar nuevas fuentes de abastecimiento de este recurso, lo que vuelve estratégico aquel proveniente de acuíferos. A la fecha en Chile, el conocimiento de este recurso generalmente se ha limitado a profundidades inferiores a 200 m. Sin embargo, en el valle central de Chile, entre Santiago y Chiloé, las evidencias geofísicas permiten inferir la existencia de una cuenca con una gruesa secuencia volcanosedimentaria que incrementa su potencia en dirección sur por sobre 500 m, con muy buen potencial para la existencia de acuíferos profundos. El conocimiento del recurso hídrico a 200-1.000 m de profundidad exige disponer de una herramienta de exploración económica, no invasiva y confiable, que pueda ser aplicada de manera eficiente, particularmente en ambientes semiurbanos y rurales, en donde la necesidad de este recurso es mayor. Las metodologías geofísicas reúnen estas características y han sido utilizadas en Chile y en muchos otros países como herramienta de exploración de aguas subterráneas. No obstante, su aplicación no ha sido descrita para ambientes andinos de gran concentración poblacional y/o actividad agroindustrial. En consecuencia, el presente trabajo plantea una estrategia metodológica para la caracterización de recursos de aguas subterráneas, y especialmente para su detección a grandes profundidades. Se propone aplicar una combinación de técnicas geofísicas mediante métodos eléctricos, electromagnéticos y gravimétricos (para la identificación de la geometría acuífera) junto con técnicas complementarias, como magnetometría (para acotar la ambigüedad de la interpretación geofísica), constreñido por información hidrogeológica y propiedades físicas de la cuenca y sus rocas. Además, se incluye un análisis de las potenciales fuentes de ruido cultural y sus efectos en las observaciones geofísicas de carácter electromagnético, dado el foco de exploración en zonas semiurbanas y rurales. A fin de validar la metodología propuesta, se utiliza como caso de estudio el acuífero del río Ñuble, en la región homónima, Chile. Este acuífero representa en forma apropiada un ambiente andino de antearco en condiciones rurales y semiurbanas y potencialmente hospeda un acuífero profundo. Los resultados obtenidos han permitido caracterizar al acuífero con potencial hidrogeológico entre los 50 y 300/500 m de profundidad, y como parte de una cuenca sedimentaria de más de 1.000 m de espesor. La aplicación de la metodología de exploración de aguas subterráneas propuesta permitirá, en consecuencia, reconocer un recurso de vital importancia para la sustentabilidad de Chile en las próximas décadas.

Abstract Knowledge of the physical properties of rock masses is fundamental for the economics and safety of mining projects. The determination of these properties in rock samples in the laboratory requires time, expensive equipment and qualified personnel, which considerably increases the information's cost. Indirect methods were developed to obtain properties related to rock masses, which have been shown to be a viable alternative to traditional procedures. The determination of the compressional mechanical wave velocity (Vp) and subsequent correlation with lithological mechanical properties are indirectly obtained. This study’s objective was to obtain correlations between Vp and the resistance to uniaxial compression, UCS (Unconfined Compressive Strength), as well as the density and porosity of the siltstone and sandstone lithologies present in the coalfield of Candiota, located in the southern region of Rio Grande do Sul, Brazil. The Vp records were obtained in laboratory samples, using ultrasonic velocity sensors, and in-situ by geophysical well logging (directly in boreholes). The results indicate the possibility of using Vp to determine the physical parameters of the investigated lithologies. In the specific case of the correlations between Vp and Unconfined Compressive Strength, determination coefficients R2 above 0.70 were obtained, indicating sufficiently high reliability for using this information (e.g. in roof support projects). The correlation between Vp and density was also high.