Anne Obermann


Last Name

Obermann

First Name

Anne

ORCID

0000-0001-6933-6301

Organisational unit

03476 - Giardini, Domenico / Giardini, Domenico

Search Results

Publications 1 - 10 of 97
  • Coda-wave decorrelation sensitivity kernels in 2-D elastic media: a numerical approach
    Item type: Journal Article
    Duran, Alejandro; Planès, Thomas; Obermann, Anne (2020)
    Geophysical Journal International
    Probabilistic sensitivity kernels based on the analytical solution of the diffusion and radiative transfer equations have been used to locate tiny changes detected in late arriving coda waves. These analytical kernels accurately describe the sensitivity of coda waves towards velocity changes located at a large distance from the sensors in the acoustic diffusive regime. They are also valid to describe the acoustic waveform distortions (decorrelations) induced by isotropically scattering perturbations. However, in elastic media, there is no analytical solution that describes the complex propagation of wave energy, including mode conversions, polarizations, etc. Here, we derive sensitivity kernels using numerical simulations of wave propagation in heterogeneous media in the acoustic and elastic regimes. We decompose the wavefield into P- and S-wave components at the perturbation location in order to construct separate P to P, S to S, P to S and S to P scattering sensitivity kernels. This allows us to describe the influence of P- and S-wave scattering perturbations separately. We test our approach using acoustic and elastic numerical simulations where localized scattering perturbations are introduced. We validate the numerical sensitivity kernels by comparing them with analytical kernel predictions and with measurements of coda decorrelations on the synthetic data.
  • Noise-based monitoring and imaging of aseismic transient deformation induced by the 2006 Basel reservoir stimulation
    Item type: Journal Article
    Hillers, Gregor; Husen, Stephan; Obermann, Anne; et al. (2015)
    Geophysics
  • Imaging potential geothermal resources in the Hengill volcanic area (Iceland) with active-source seismics recorded by a dense nodal array 
    Item type: Other Conference Item
    Gyger, Lea; Sánchez Sánchez-Pastor, Maria Del Pilar; Maurer, Hansruedi; et al. (2022)
    EGUsphere
    The Hengill area, located a few km west of Reykjavik, is situated on the triple junction of three large geological features: the onshore section of the Mid-Atlantic Ridge, called the Reykjanes Peninsula Oblique Rift, the Western Volcanic Zone and the South Iceland Seismic Zone. This area hosts two large-scale geothermal power plants, Nesjavellir and Hellisheiði. Both are producing electricity and hot water. Hengill is also one of the targets of the Iceland Deep Drilling Project that aims at finding and exploiting supercritical fluids. In summer 2021, a nodal network of 500 5 Hz geophones was deployed in the area over a period of 2 months. It complemented seismic data from a network of broadband stations that were already deployed earlier. In July 2021, a vibroseis experiment was conducted in the area in form of two surveys performed by a fully electrical seismic vibrator truck. The seismic waveforms were recorded by parts of the nodal network. In this study, we focus on the survey conducted along the road leading to the Nesjavellir geothermal power plant, in Mosfellsheiði. The aim of the survey in Mosfellsheiði is to obtain new insights on a low-velocity anomaly as well as on a yet poorly understood seismic cluster that has been detected in the area by previous studies. To study the velocity and attenuation structure of the area, we computed a first arrival travel time tomography and an attenuation profile. Finally, we compared our results with an existing 3D seismic ambient noise tomography Vs model of the area as well as with known local subsurface properties, such as resistivity and mineralogy. The final results of this vibroseis study could be useful for finding new geothermal resources in the Nesjavellir area.
  • Induced micro-seismicity observed during meter-scale hydraulic-fracturing
    Item type: Other Conference Item
    Gischig, Valentin; Doetsch, Joseph; Krietsch, Hannes; et al. (2017)
  • Seismicity at Lusi and the adjacent volcanic complex, Java, Indonesia
    Item type: Journal Article
    Obermann, Anne; Karyono, Karyono; Diehl, Tobias; et al. (2018)
    Marine and Petroleum Geology
  • Full-Waveform based methods for Microseismic Monitoring Operations: An Application to Natural and Induced Seismicity in the Hengill Geothermal Area, Iceland
    Item type: Journal Article
    Rossi, Camilla; Grigoli, Francesco; Cesca, Simone; et al. (2020)
    Advances in Geosciences
    Geothermal systems in the Hengill volcanic area, SW Iceland, started to be exploited for electrical power and heat production since the late 1960s. Today the two largest operating geothermal power plants are located at Nesjavellir and Hellisheiði. This area is a complex tectonic and geothermal site, located at the triple junction between the Reykjanes Peninsula (RP), the Western Volcanic Zone (WVZ), and the South Iceland Seismic Zone (SISZ). The region is seismically highly active with several thousand earthquakes located yearly. The origin of such earthquakes may be either natural or anthropogenic. The analysis of microseismicity can provide useful information on natural active processes in tectonic, geothermal and volcanic environments as well as on physical mechanisms governing induced events. Here, we investigate the microseismicity occurring in Hengill area, using a very dense broadband seismic monitoring network deployed in Hellisheiði since November 2018, and apply sophisticated full-waveform based method for detection and location. Improved locations and first characterization indicate that it is possible to identify different types of microseismic clusters, which are associated with either production/injection or the tectonic setting of the geothermal area.
  • Modeling Coupled Hydro-Mechanical Processes During Hydraulic Stimulation at the Bedretto Underground Laboratory
    Item type: Conference Paper
    Clasen Repollés, Victor; Jiang, Danyang; Rinaldi, Antonio Pio; et al. (2024)
    58th U.S. Rock Mechanics/Geomechanics Symposium
    In the framework of Enhanced Geothermal Systems (EGS), hydraulic stimulations play an important role in increasing the permeability of the host rock, facilitating more efficient heat extraction. However, these stimulations unavoidably induce reactivation of faults and earthquakes. The induced seismicity serves as proxy for the enhanced fracture network's spatial extent, but at the same time could pose a risk to nearby populations if the earthquakes' magnitude is large. To address this challenge, understanding the coupled physical processes generating fault reactivation and seismicity is crucial, and the development of forecasting tools could help mitigating the risk. Numerous numerical simulators capable of modeling complex coupled processes exist, yet their computational demands hinder their application in real-time induced seismicity forecasting. In this work, we present the development of two distinct categories of models: the first category encompasses a simplified hybrid hydromechanical model tailored for real-time applications, while the second category comprises a more detailed 3D numerical model designed to advance the fundamental understanding of the physical processes at play. By applying these models to reproduce a hydraulic stimulation at the Bedretto Underground Laboratory, we demonstrate that we can simulate first-order observations (e.g. pressure changes, seismicity rate, strain) without introducing excessive complexity.
  • Insights into the dynamics of the Nirano Mud Volcano through seismic characterization of drumbeat signals and V/H analysis
    Item type: Journal Article
    Antunes, Verónica; Planès, Thomas; Obermann, Anne; et al. (2022)
    Journal of Volcanology and Geothermal Research
    Mud volcanoes are rapidly-evolving geological phenomena characterized by the surface expulsion of sediments and fluids from over-pressurized underlying reservoirs. We investigate the Nirano Mud Volcano, Northern Italy, with seismic methods to better understand the dynamic evolution of the system and shed light on its subsurface structure. Our study allowed to detect and characterize three different types of high-frequency drumbeat signals that are present in the most active part of the mud volcano plumbing system. With a back-projection method based on the cross-correlation envelope of signals recorded at different station pairs, we can determine the source location of the drumbeats. These coincide with the location of V/H (vertical-to-horizontal) amplitude peaks obtained from an ambient vibration profile and resistivity anomalies identified in a previous study. We observe that the drumbeats are P-wave dominated signals, with characteristics similar to those found in magmatic settings, i.e. LPs (long-period signals). We suggest that such tremors originate from the migration of mud and gas inside the mud volcanic conduits. The source location, waveform and frequency content of the drumbeats evolve over time. We found that drumbeat occurrence is directly linked with morphological changes at surface.
  • Fault sealing and caprock integrity for CO2 storage: an in-situ injection experiment
    Item type: Working Paper
    Zappone, Alba; Rinaldi, Antonio Pio; Grab, Melchior; et al. (2020)
    Solid Earth Discussions
    The success of geological carbon storage depends on the assurance of a permanent confinement of the injected CO2 in the storage formation at depth. One of the critical elements of the safekeeping of CO2 is the sealing capacity of the caprock overlying the storage formation, despite faults and/or fractures, which may occur in it. In this work, we present an ongoing injection experiment performed in a fault hosted in clay at the Mont Terri underground rock laboratory (NW Switzerland). The experiment aims at improving our understanding on the main physical and chemical mechanisms controlling i) the migration of CO2 through a fault damage zone, ii) the interaction of the CO2 with the neighbouring intact rock, and iii) the impact of the injection on the transmissivity in the fault. To this end, we inject a CO2-saturated saline water in the top of a 3 m think fault in the Opalinus Clay, a clay formation that is a good analogue of common caprock for CO2 storage at depth. The mobility of the CO2 within the fault is studied at decameter scale, by using a comprehensive monitoring system. Our experiment aims to the closing of the knowledge gap between laboratory and reservoir scales. Therefore, an important aspect of the experiment is the decameter scale and the prolonged duration of observations over many months. We collect observations and data from a wide range of monitoring systems, such as a seismic network, pressure temperature and electrical conductivity sensors, fiber optics, extensometers, and an in situ mass spectrometer for dissolved gas monitoring. The observations are complemented by laboratory data on collected fluids and rock samples. Here we show the details of the experimental concept and installed instrumentation, as well as the first results of the preliminary characterization. Analysis of borehole logging allow identifying potential hydraulic transmissive structures within the fault zone. A preliminary analysis of the injection tests helped estimating the transmissivity of such structures within the fault zone, as well as the pressure required to mechanically open such features. The preliminary tests did not record any induced microseismic events. Active seismic tomography enabled a sharp imaging the fault zone. Weniger anzeigen
Publications 1 - 10 of 97