Monday, June 1, 2015
HG F3, 13:00 - 13:30

Preconditioning Strategies for Multi-parameter Full Waveform Inversion; Ludovic Métivier (CNRS, France)

Co-Authors: Romain Brossier (University of Grenoble Alpes, France); Stéphane Operto Géoazur (University of Sophia-Antipolis, France); Jean Virieux (University of Grenoble Alpes, France)

Full Waveform Inversion (FWI) is a high-resolution seismic imaging method, based on the minimization of the misfit between observed and synthetic data. FWI is now routinely used in seismic exploration, as a velocity-building method. However, the formalism of FWI allows for the simultaneous reconstruction not only of P- and S-wave velocities, but also for parameters such as density, attenuation and anisotropy. This current limitation is due to trade-offs between parameters, making difficult to decipher between them only from seismic data. We propose to review and analyze the issues related to multi-parameter FWI, and propose a preconditioning strategy trying to mitigate these difficulties.

Monday, June 1, 2015
HG F3, 13:30 - 14:00

Data Assimilation for Source Encoding Strategies in Full-Waveform Seismic Inversion; Christian Boehm (ETH Zurich, Switzerland)

Co-Authors: Andreas Fichtner (ETH Zurich, Switzerland); Alessandro Lechmann (ETH Zurich, Switzerland)

Full-Waveform seismic tomography infers the material properties of the Earth based on the observation of seismograms. Since the costs of solving this inverse problem are roughly proportional to the number of seismic events, source-encoding strategies can reduce the computational effort substantially. We exploit statistical properties of a sample average approximation to gradually incorporate more information into the problem formulation and to update the weights of the encoded sources. This alternates with a Newton-type method based on mini-batch Hessian approximations to update the material model.

Monday, June 1, 2015
HG F3, 14:00 - 14:30

Full Waveform Inversion for the Identifiable Subspace; Drosos Kourounis (Università della Svizzera italiana, Switzerland)

Co-Authors: Olaf Schenk (Università della Svizzera italiana, Switzerland)

Full-waveform inversion (FWI) optimizes subsurface model estimates to derive high-fidelity geological models. A mathematically sound method is described for selecting the part of the geological parameters that is best identifiable from the seismic acquisition geometry. This is combined with either interior-point or sequential quadratic programming methods for performing FWI for the subset of parameters that have been characterized as identifiable. Numerical results are presented on several examples of increased complexity.

Monday, June 1, 2015
HG F3, 14:30 - 15:00

A Data-Comprehensive Seismic Earth Model across the Scales; Michael Afanasiev (ETH Zurich, Switzerland)

Co-Authors: Andreas Fichtner (ETH Zurich, Switzerland); Daniel Peter (ETH Zurich / Università della Svizzera italiana, Switzerland); Korbinian Sager (ETH Zurich, Switzerland); Saulé Zukauskaité (ETH Zurich, Switzerland); Laura Ermet (ETH Zurich, Switzerland)

The Comprehensive Seismic Earth Model (CSEM) is a 3D multi-scale visco-elastic model of Earth's interior. Designed to combat scaling issues in seismic inversion, the CSEM incorporates models generated from a variety of forward problem solvers, on a variety of spatial scales. Approaching global-scale seismic inversion in this manner allows us to exploit the benefits of both high resolution numerical techniques, such as full waveform inversion via the spectral element method, and more classical inversion techniques, such as traveltime tomography, where each may contribute model updates within their specific regimes of validity.

Monday, June 1, 2015
HG F3, 15:30 - 16:00

Data Assimilation in Geodynamical Modelling: Methods and Applications; Alik Ismail-Zadeh (Karlsruhe Institute of Technology, Germany)

Co-Authors:

Present geophysical, geochemical, and geodetic observations together with geological information provide a clue to understanding dynamics of the Earth interior in the past. Assimilation of present observations allows to constrain mantle temperature/composition and flow in the past using dynamical models. Quantitative tools are required to assimilate the data and hence to solve inverse retrospective problems in geodynamics. The basic inversion methods (adjoint and quasi-reversibility) including the methodologies uncertainties and requirements for HPC, and two case studies related to mantle/lithosphere dynamics and to a volcanic lava flow will be presented and discussed.

Monday, June 1, 2015
HG F3, 16:00 - 16:30

Towards Joint Reconstruction of Paleo Mantle-Lithosphere Dynamics Using Data Assimilation; Nicolas Coltice (Université Lyon 1, France)

Co-Authors:

Data assimilation becomes suitable when the observations are sufficient in number and accurate enough, and if the forward model contains sufficient complexity to necessary for predictions. When it comes to reconstructing convection in the Earth's mantle, data assimilation raises questions for both observations and models. I will review inverse methods used so far, for which seismic tomography is central, and present another angle for data assimilation: using tectonic data as the data to match. I will describe preliminaries and present a sequential data assimilation scheme, and a variational data assimilation scheme, both using tectonic information as the data to match.

Monday, June 1, 2015
HG F3, 16:30 - 17:00

Data Assimilation and Predictive Models in Geomagnetism; Alexandre Fournier (Institut de Physique du Globe de Paris, France)

Co-Authors: Julien Aubert (Institut de Physique du Globe de Paris, France); Lars Nerger (Alfred Wegener Institute, Germany); Sabrina Sanchez (Institut de Physique du Globe de Paris, France)

Assimilating geomagnetic data in numerical models of Earth's core dynamics is a challenging problem, since the information contained in the geomagnetic record is intrinsically restricted to the large scales of the poloidal geomagnetic field at the core-mantle boundary. After a general introduction on terrestrial magnetism and the observation of Earth's magnetic field, I will report more specifically on recent efforts carried out to investigate the feasibility of resorting to three-dimensional, buoyancy-driven, numerical dynamo models for geomagnetic data assimilation practice. For this symposium, I will discuss in particular the computational cost associated with this exercise.

Monday, June 1, 2015
HG F3, 17:00 - 17:30

On Ensemble and Particle Filters for Large-Scale Data Assimilation; Roland Potthast (Deutscher Wetterdienst, Germany)

Co-Authors: Andreas Rhodin (Deutscher Wetterdienst, Germany); Christoph Schraff (Deutscher Wetterdienst, Germany); Hendrik Reich (Deutscher Wetterdienst, Germany)

Ensemble data assimilation techniques are of rapidly growing importance. Ensemble techniques allow to describe and forecast uncertainty of the analysis, but they also improve the assimilation result itself, by allowing estimates of the covariance or, more general, the prior and posterior probability distribution of atmospheric states. In our talk, we will first give a survey about recent activities of the German Meteorological Service DWD. Then, we present recent work on the further development of the ensemble data assimilation towards a particle filter for large-scale atmospheric systems, which keeps the advantages of the LETKF, but overcomes some of its limitations.

Monday, June 1, 2015
HG E22, 13:00 - 13:30

Modeling of Inelastic Strain Induced by CO2 Injection; Victor Vilarrasa (EPFL, Switzerland)

Co-Authors: Lyesse Laloui (EPFL, Switzerland)

Inelastic strain, which is associated to the induced microseismicity observed in CO2 injection sites like Weyburn or In Salah, is likely to occur in CO2 storage sites. Furthermore, CO2 will reach the storage formation at a colder temperature than the rock, which will induce a thermal stress reduction. We model non-isothermal injection of CO2 in a deep saline formation using the fully coupled finite element code CODE_BRIGHT. We find that despite inelastic strain is likely to occur in the cooled region around the injection well, fracture propagation does not extend into the caprock in the normal faulting stress regime simulated in this study.

Monday, June 1, 2015
HG E22, 13:30 - 14:00

CFD Computations of a Cavitation Vortex Rope; Jean Decaix (HES-SO//Valais-Wallis, Switzerland)

Co-Authors: Sebastien Alligné (Power Vision Engineering Sàrl, Switzerland); Andres Müller (EPFL, Switzerland); Cécile Münch (HES-SO//Valais-Wallis, Switzerland); François Avellan (EPFL, Switzerland)

Due to the increase in renewable energies in the electricity market, hydraulic power plants have to run at off-design operating points. For Francis turbines, this leads to the formation of a vortex rope known to promote cavitation surge. If the flow discharge is higher than the nominal one, an axisymmetric cavitation vortex rope develops in the draft tube cone. Such a vortex rope leads to high pressure fluctuations that interact with the entire power plant and limit the range of operating points. To better understand the physics of the phenomenon and to provide input to 1D models, two-phase 3D CFD calculations are performed and compared with experimental data

Monday, June 1, 2015
HG E22, 14:00 - 14:30

Challenges of Simulating Geothermal Reservoir Processes; Julian Mindel (ETH Zurich, Switzerland)

Co-Authors: Thomas Driesner (ETH Zurich, Switzerland)

Future geothermal power production in Switzerland requires circulating water through deep (~ 5km), fractured rock masses at temperatures exceeding 180°C. The extreme conditions massively limit direct, in situ observation and steering of reservoir processes, making numerical simulation a key research and development technology. The biggest challenges are a combination of complex but poorly know geometries (thin, irregular fracture networks in a large rock mass) and strongly coupled, non-linear processes (thermo-hydro-mechanical-chemical interactions). This contribution outlines the goals and challenges of numerical code development in the SCCER-SoE and related initiatives.

Monday, June 1, 2015
HG E22, 14:30 - 15:00

A New Volcanic Hydrothermal System in Java; the Lusi Mud Eruption and Aftermath; Stephen Miller (University of Neuchatel, Switzerland)

Co-Authors: Maïté Faubert (University of Neuchatel, Switzerland); Reza Sohrabi (University of Neuchatel, Switzerland)

In 2006 a magnitude 6.3 earthquake occurred in Yogyakarta on the island of Java. This relatively shallow earthquake resulted in 20,000 deaths and widespread destruction of the city. About 48 hours later, in the town of Sidoarjo about 250 km from the earthquake epicentre, mud began to spill out onto the surface and Lusi was born. Eruption rates peaked at 180,000 cubic meters of mud per day, and continues today as a vigorous geyser system, with geochemistry studies showing that is a geologic rarity of a newborn tectonic-scale hydrothermal system linked to the nearby volcano complex. We are modelling this system to gain insight of its workings and the possible exploitation of geothermal energy.

Monday, June 1, 2015
HG E22, 15:30 - 16:00

Modeling 3D THM Processes in Geothermics with Continuum Mechanics; Gunnar Jansen (University of Neuchatel, Switzerland)

Co-Authors: Reza Sohrabi (University of Neuchatel, Switzerland); Boris Galvan (University of Neuchatel, Switzerland); Stephen A. Miller (University of Neuchatel, Switzerland)

The geothermal community is challenged by the Energy Strategy 2050 goal to uncover the potential of renewable energy resources in Switzerland. To this end we implement a novel finite element based simulation tool for rock and fluid physics. It efficiently couples the dominant processes in the subsurface, such as fracture nucleation and growth using continuum mechanics, anisotropic multiphase fluid flow and heat transfer to provide a deeper understanding. We aim at state of the art performance by using massively parallel tools and modern accelerator techniques. We present first results from 3D fully coupled THM-simulations and evaluate the performance from a series of benchmark simulations.

Monday, June 1, 2015
HG E22, 16:00 - 16:30

Prediction of Elastostatic Friction for Rock-Like Surfaces with FEM; Alessandro Rigazzi (Università della Svizzera italiana, Switzerland)

Co-Authors: Rolf Krause (Università della Svizzera italiana, Switzerland)

We present the results of our recent work, in which we apply the Finite Element Method to study the frictional forces resulting from the elastostatic interactions of surface asperities. To do this, we generate several self-affine rough surfaces that are statistically similar to rock surfaces. Such surfaces are used as rigid obstacles onto which an elastic smooth cube is pushed and sheared to measure the maximal resistance opposed by the asperities. The contact problem gives rise to a huge nonsmooth system of equations. We solve this system with a solver based on our nonsmooth multigrid algorithm of optimal complexity for which we investigate scaling properties.

Monday, June 1, 2015
HG E22, 16:30 - 17:00

Modeling Induced Seismic Hazard During Geothermal Reservoir Creation; Joseph Doetsch (ETH Zurich, Switzerland)

Co-Authors: Valentin Gischig (ETH Zurich, Switzerland); Dimitrios Karvounis (ETH Zurich, Switzerland); Stefan Wiemer (ETH Zurich, Switzerland)

To enable the large-scale exploitation of deep geothermal energy for electricity generation in Switzerland, solutions must be found for two fundamental and coupled problems: (1) How to create an efficient heat exchanger in the hot underground that can produce energy for decades and (2) at the same time keeping the risk posed by induced earthquakes to acceptable levels' Numerical simulations of different complexity and physical detail are currently being developed for an Advanced Traffic Light System (ATLS) to predict the risk of in induces earthquakes in real-time. This contribution presents developments of the induced seismicity prediction codes towards high performance computing.

Monday, June 1, 2015
HG E22, 17:00 - 17:30

Silt Erosion Simulation Using Finite Volume Particle Method; Ebrahim Jahanbakhsh (EPFL, Switzerland)

Co-Authors:

Silt erosion is a destructive phenomenon that may occur in hydropower plants. This work presents a new erosion prediction model in which, fluid flow and solid deformation equations are discretized by Finite Volume Particle Method (FVPM), and silt contact forces are calculated according to Hertz contact theory. FVPM is a meshless method which includes many of the desirable features of the mesh-based finite volume method. To obtain a more accurate and robust model, a new FVPM formulation is presented in which particle interaction integrals are evaluated exactly and efficiently. To validate the new silt erosion model, 2D and 3D erosion cases are simulated and compared with experimental data.