Inner structure of the Puy de Dˆome volcano: cross-comparison of geophysical models (ERT, gravimetry, muon imaging)

International audienceMuon imaging of volcanoes and of geological structures in general is actively being developed by several groups in the world. It has the potential to provide 3-D density distributions with an accuracy of a few percent. At this stage of development, comparisons with established geophysical methods are useful to validate the method. An experiment has been carried out in 2011 and 2012 on a large trachytic dome, the Puy de Dˆome volcano, to perform such a comparison of muon imaging with gravimetric tomography and 2-D electrical resistivity tomography. Here, we present the preliminary results for the last two methods. North-south and east-west resistivity profiles allow us to model the resistivity distribution down to the base of the dome. The modelling of the Bouguer anomaly provides models for the density distribution within the dome that are directly comparable with the results from the muon imaging. Our ultimate goal is to derive a model of the dome using the joint interpretation of all sets of data

Dissecting a Zombie:Joint Analysis of Density and Resistivity Models Reveals Shallow Structure and Possible Sulfide Deposition at Uturuncu Volcano, Bolivia

The recent identification of unrest at multiple volcanoes that have not erupted in over 10 kyr presents an intriguing scientific problem. How can we distinguish between unrest signaling impending eruption after kyr of repose and non-magmatic unrest at a waning volcanic system? After ca. 250 kyr without a known eruption, in recent decades Uturuncu volcano in Bolivia has exhibited multiple signs of unrest, making the classification of this system as “active”, “dormant”, or “extinct” a complex question. Previous work identified anomalous low resistivity zones at <10 km depth with ambiguous interpretations. We investigate subsurface structure at Uturuncu with new gravity data and analysis, and compare these data with existing geophysical data sets. We collected new gravity data on the edifice in November 2018 with 1.5 km spacing, ±15 μGal precision, and ±5 cm positioning precision, improving the resolution of existing gravity data at Uturuncu. This high quality data set permitted both gradient analysis and full 3-D geophysical inversion, revealing a 5 km diameter, positive density anomaly beneath the summit of Uturuncu (1.5–3.5 km depth) and a 20 km diameter arc-shaped negative density anomaly around the volcano (0.5–7.5 depth). These structures often align with resistivity anomalies previously detected beneath Uturuncu, although the relationship is complex, with the two models highlighting different components of a common structure. Based on a joint analysis of the density and resistivity models, we interpret the positive density anomaly as a zone of sulfide deposition with connected brines, and the negative density arc as a surrounding zone of hydrothermal alteration. Based on this analysis we suggest that the unrest at Uturuncu is unlikely to be pre-eruptive. This study shows the value of joint analysis of multiple types of geophysical data in evaluating volcanic subsurface structure at a waning volcanic center

Structure of Alluvial Valleys from 3-D Gravity Inversion: The Low Andarax Valley (Almería, Spain) Test Case

This paper presents a gravimetric study (based on 382 gravimetric stations in an area about 32 km2) of a nearly flat basin: the Low Andarax valley. This alluvial basin, close to its river mouth, is located in the extreme south of the province of Almería and coincides with one of the existing depressions in the Betic Cordillera. The paper presents new methodological work to adapt a published inversion approach (GROWTH method) to the case of an alluvial valley (sedimentary stratification, with density increase downward). The adjusted 3D density model reveals several features in the topography of the discontinuity layers between the calcareous basement (2,700 kg/m3) and two sedimentary layers (2,400 and 2,250 kg/m3). We interpret several low density alignments as corresponding to SE faults striking about N140?145°E. Some detected basement elevations (such as the one, previously known by boreholes, in Viator village) are apparently connected with the fault pattern. The outcomes of this work are: (1) new gravimetric data, (2) new methodological options, and (3) the resulting structural conclusions

Leintz gatzaga landslide: geotechnical analysis and monitorization with terrestial and radar techniques (eoslide project

[ES] La inestabilidad de ladera que afecta a la villa de Leintz Gatzaga (Gipuzkoa) y su entorno ha producido desde hace siglos daños estructurales en viviendas, muros y viales, que van desde moderados a intensos. Esto ha obligado a ejecutar diferentes actuaciones de reparación y consolidación. Se realiza en este trabajo una discusión geológico/geotécnica de los datos disponibles sobre el deslizamiento que afecta a la ladera, así como de los resultados obtenidos a partir de su monitorización con inclinómetros, piezómetros y fisurómetros en los últimos años. Complementariamente, este deslizamiento ha sido elegido como zona test del proyecto EOSLIDE, en el que se han desarrollado e implementado metodologías de vigilancia que combinan técnicas terrestres clásicas con Técnicas Avanzadas de Interferometría Diferencial Radar de Satélite (A-DInSAR), además de utilizar técnicas gravimétricas para la el estudio de estructuras bajo superficie. Se describen las actuaciones realizadas en el marco de este proyecto y los resultados obtenidos.[EN] Leintz Gatzaga village settles on a slope which whose instability has caused the former moderate to severe structural damages for centuries. Different remedial and consolidation solutions have been adopted in order to mitigate the landslide effects. In this work, we analyse and discuss the geological and geotechnical characteristics of the landslide, and the monotorization monitorization results obtained by inclinometers, piezometers and fisurometers in recent years. This landslide has been chosen as a test case to for the EOSLIDE project, which aims is to develop and implement surveillance methodologies combining classic terrestial techniques with Advanced Differential Radar Interferometry (A-DInSAR). Furthermore, gravimetric techniques have been applied in order to study subsoil structures. We describe the procedures and results obtained in within the framework of this project.Este trabajo se ha desarrollado en el marco del proyecto EOSLIDE del MINECO (IPT-2011-1234-310000) de la convocatoria INNPACTO 2011. La investigación de AGC, JFP y JF ha sido también parcialmente sufragada por los proyectos GEOSIR (AYA2010-17448) y AQUARISK (ESP2013-47780-C2-I-R) del MINECO.Peer reviewe

Deslizamiento de leintz gatzaga: instrumentación geotécnica y monitorización del movimiento con técnicas terrestres y espaciales.

La inestabilidad de ladera que afecta a la villa de Leintz Gatzaga (Gipuzkoa) y su entorno ha producido desde hace siglos daños estructurales en viviendas, muros y viales, que van desde moderados a intensos. Esto ha obligado a ejecutar diferentes actuaciones de reparación y consolidación. Se realiza en este trabajo una discusión geológico/geotécnica de los datos disponibles sobre el deslizamiento que afecta a la ladera, así como de los resultados obtenidos a partir de su monitorización con inclinómetros, piezómetros y ?surómetros en lo