Prof. Hans-Peter Bunge

Ausbildung

• Abitur, 1984, Clausthals-Zellerfeld
• Vordiplom Geologie, 1987, Eberhard-Karls Universität Tübingen
• Vordiplom Physik, 1988, Eberhard-Karls Universität Tübingen
• Ph.D. Geophysics, Fall 1996, University of California, Berkeley
  Thesis title: Global Mantle Convection Models
  Thesis advisor: Mark Richards

• Research Assistant, 1986-88, Structural Geology
  Eberhard-Karls Universität Tübingen
• Research Assistant, January 1989 - May 1989, Mining Geology
  Council for Mineral Technology (MINTEK), Johannesburg, South Africa
• Graduate Research Assistant, 1990-1996, Geophysics
  Los Alamos National Laboratory and UC Berkeley
• European Union post doctoral scholar, 1997-1998
  Invited to the Institut de Physique du Globe, Paris
• Visiting Professor, June - July 1999
  Laboratoire des Sciences de la Terre, Ecole Normale Superieure de Lyon
• Assistant Professor, 1998 - 2003
  Department of Geosciences, Princeton University
• Professor and Chair of Geophysics, since 2003
  Department of Earth and Environmental Sciences, Ludwig-Maximilians University Munich

Mitgliedschaft in Akademien

• Member of the Bavarian Academy of Sciences (BAdW)
• Member of the Academia Europaea

Mitgliedschaft in Standesorganisationen

• Member American Geophysical Union (AGU)
• Member European Geophysciences Union (EGU)
• Member German Geophysical Society (DGG)

Ausgewählte Service-Tätigkeiten

• Reviewer for NSF, DFG, ERC and other funding agencies (since 1993)
• Member National Center for Supercomputer Applications (NCSA) resource allocation committee (2000-2003)
• External advisor of the Los Alamos National Laboratory (LANL) Institute of Geophysics and Planetary Physics (IGPP) (since 2001)
• Member of the scientifc advisory board of the Geoforschungszentrum (GFZ) (2004-2007)
• Associate and Guest Editor for various journals
• Editorial Board Member – Proceedings of the Royal Society A (since 2018)
• President EGU Geodynamics Division (2007-2009)
• Coordinator of DFG Schwerpunktprogramm (SPP) 1375 'SAMPLE' on South Atlantic Margin Processes (2008-2016)
• ESA appointed lecturer in Geophysics to European Astronauts since 2010
• Board of Trustees, Universitaet der Bundeswehr Muenchen (2016-2024)
• Head, Commission of Geodesy and Glaciology, Bavarian Academy of Sciences (BAdW)
  charged with directing geophysical and geodetic research of the BAdW
• Resource Allocation Board Member, Leibniz Rechenzentrum (LRZ) Munich
  German National Supercomputing Center (Tier-1 Supercomputer)
• Permanent Secretary (speaker for the president of the BAdW) of t

• Fulbright Scholar, 1989-1990
• Student Fellow "Studienstiftung des deutschen Volkes", (top 0.1% German students)
  1985-1991
• PhD Fellow "Studienstiftung des deutschen Volkes", (top 0.1% German PhD students)
  1991-1996
• Fellow of the University of California, Institute of Geophysics and Planetary Physics
  since 1996
• Bernard Friedman award in Applied Mathematics
  Department of Mathematics, UC Berkeley, 1997
• Computerworld Honors Program, Smithsonian Institution, 2001
• LMU Research Professor for Geophysics (Bundesexzellenzinitiative)
• Member of the LMU Center of Advanced Studies since 2010

• Scientific Advisor for American Museum of Natural History (New York)
  Gottesman Hall of Planet Earth ‘Deep Earth’ scientific display,(2000-current)

The seismic signature of our planet is an essential reference for geodynamic models. Over the past few decades, seismological studies have revealed distinct physical structures in Earth’s mantle that entail a plethora of geophysical implications. While seismology provides data and models of the present-day state of Earth, the exact nature and evolution of the mantle can only be investigated in a dynamic flow model. Understanding the link between seismology and geodynamics in a quantitative manner thus is one of our main areas of research. To bridge the gap between geophysical hypotheses and seismic observations, we follow a multidisciplinary approach:

1. Mantle circulation is simulated at high resolution to predict the present-day mantle temperature field.
2. Thermodynamic models of mantle mineralogy are used to convert temperatures to seismic velocities or vice versa. This ensures a physically consistent seismic representation of the geodynamic model, which is a prerequisite to
3. Predict synthetic seismic data on a global scale, foremost full-waveform seismograms from numerical 3-D wave propagation simulations.
4. Synthetic data can be compared to seismic observations, which allows for an explicit testing of the geodynamic mantle circulation model. Alternatively, it is possible to compare geodynamic models directly to 3D-images of the mantle obtained by seismic tomography. Such comparisons are only meaningful if the limited resolution of seismic tomography and the associated uncertainties are accounted for. In our studies, this is done by so-called "tomographic filtering" of the geodynamic mantle structures. This way, we can look at our models with the same “lense” that seismic tomography uses to probe the real Earth.

In the context of our seismic forward modelling, our further interests in the research area between seismology and geodynamics include the role of phase transitions for global mantle flow and their effect on seismic data, normal mode constraints on mantle properties, as well as the prediction of seismic body-wave traveltime residuals in our geodynamic models with ray-theory and finite-frequency sensitivity kernels.

Many surface processes, including motions of the Earth’s tectonic plates, can be related to underlying mantle circulation. Geological manifestations that are evidence of this, can be found across the Earth’s surface, such as the Andean mountain range in South America and the elevated topography of the African continent. In turn, these surface features have an impact on mantle convection, modulating and organizing its convective planform.

It is possible to reconstruct plate motions based on observations of the ocean floor’s age, its magnetization and the occurrence of fracture zones. An accurate representation of these observations is essential to study plate tectonics and mantle dynamics. An outstanding characteristic of past plate motions is the record of rapid (on the order of a few million years) temporal plate motion variations. These changes occur on short time scales relative to the time it takes for the large-scale structure associated with mantle buoyancy to evolve. Past and present-day plate motions are increasingly well mapped. They allow geodynamicists to connect structures in the mantle to the history of subduction and to link plate tectonics to mass motion driven by mantle convection. A difficulty arises from the superposition of sublithospheric and shallow plate-boundary forces. This hinders our interpretation of plate motions solely in terms of forces related to mantle convection or lithosphere dynamics. In particular, our efforts in this context focus on (i) simulating the impact of the mantle time-evolving buoyancy field on plate motions; and (ii) exploring the dynamics of mantle and lithosphere interactions by using the record of plate motions as a reference to validate parameter choices in numerical simulations.

It is well known that plate tectonics is intrinsically linked with large-scale convective forces in the mantle. However, geologic observations also document the occurrence of significant vertical surface motions that cannot be explained by eustatic sea level changes or isostatic considerations alone. Flow in the underlying mantle is the likely cause that governs these surface deflections. This is known as "dynamic topography".

Important observations that allow us to understand mantle-flow-induced dynamic topography and its temporal evolution can be found in the geologic record, specifically the distribution of sediments. Continent scale sediment distributions are characterized by unconformities (absence of a stratigraphic unit) owing to non-deposition or erosion of sedimentary layers. These surfaces, also known as hiatal surfaces, can be mapped through geological times for geodynamic purposes. This allows us to get proxies for paleotopography. The latter relate to changes in the vertical motion of the lithosphere at interregional scales. Other techniques that yield valuable constraints on various timescales are, for example, GPS measurements, drainage analysis, mapping of paleosurfaces, thermochronology and more (for a comprehensive overview, see Hoggard et al. 2020, Observational estimates of dynamic topography through space and time).

Estimates of time-dependent dynamic topography provide a new and powerful class of geodynamically relevant observations, which we compile for comparison with next-generation Earth models.

By definition, mantle circulation leads to a redistribution of masses. It thus has a dominant influence on the internal density structure of the Earth. The associated gravity field provides a valuable data set to constrain properties of the Earth’s interior. Moreover, modern satellite missions, like e.g. GRACE, GOCE and GRACE-FO, are capable of providing global data coverage and highly accurate measurements of the Earth’s present-day gravitational structure.

Unfortunately, a direct determination of the Earth’s interior density structure, relying solely on gravity data, is impossible. Nevertheless, in combination with seismic tomography, gravity signals provide a powerful tool to constrain the radial viscosity structure of the mantle. To this end, so-called "geoid kernels" are well known. They represent the gravitational response of a unit density anomaly at a certain depth level, including effects from flow-induced dynamic topography. The kernels are highly sensitive to the viscosity stratification inside the Earth’s mantle. Exploiting this sensitivity, one can show that the observed gravity field can only be explained with a viscosity profile that includes a low-viscosity channel in the upper mantle, the so-called "asthenosphere".

This method has one main drawback: The viscosity profile cannot be determined uniquely. To overcome this ambiguity, one has to turn to time-dependent Earth models. This naturally motivates the development of mantle circulation models.

From the very beginning in 2003, the Munich Geodynamics group has been actively involved in a number of HPC- and IT-related projects. Thus, there naturally is a close cooperation with the GeoComputing group. Joint work includes research on stereoscopic visualization (GeoWall), data storage and management, as well as numerical and parallelization techniques and the design of compute clusters for capacity computing. Current efforts are focused on the realization of a software framework for extreme scale Earth Mantle simulations. The framework is able to fully exploit the power of next-generation exascale (i.e. reaching 1018 floating point operations per second) supercomputers. First exciting results have been achieved in the project TerraNeo, supported by the Priority Program 1648 "Software for Exascale Computing" (SPPEXA) of the German Research Foundation (DFG). Using a massively parallel multigrid method, based on the hierarchical hybrid grids (HHG) paradigm and implemented in the open source framework Hybrid Tetrahedral Grids (HyTeG), computations with an unprecedented resolution of the Earth’s Mantle are possible. The computational grids subdivide the entire mantle into domains of about 1 km3 volume (compare this to the volume of the mantle of about 9.06x1012 km3). As a consequence, a large system with over a trillion (1012) degrees of freedom gets solved at each time step of a simulation. This demonstrates why mantle convection is regarded as a so-called grand challenge problem. The success of the TerraNeo project is based on a long-term collaborative effort between the groups of Geophysics (LMU Munich), Numerical Mathematics (Prof. Barbara Wohlmuth, TU Munich), and System Simulation (Prof. Ulrich Rüde, FAU Erlangen-Nürnberg).

In order to test software and perform mid-scale geophysical simulations in a routine manner, the GeoComputing group operates an excellent computational infrastructure. At its very center is the Munich Tectonic High-Performance Simulator (TETHYS). Hence a lot of capacity computing can be done in-house. For capability computing, i.e. extremely demanding simulations, we are granted access to high-end supercomputing facilities by the Leibniz Supercomputing Centre (LRZ), especially its flagship supercomputer SuperMUC-NG. Altogether, this ensures that scientific progress in our group is supported by world-leading expertise in the development and application of computational resources.

Going back in time allows us to take these problems into account by performing so-called geodynamic inversions. Such inversions determine the "optimal" initial condition that evolves into the known (best-estimate) present-day state of the mantle. Another term for this type of modelling is data assimilation (originally developed for weather forecasting in meteorology). It makes it possible to formally link the physics of the mantle flow system with the available observational data. Most important, this allows for explicit predictions of the past history of mantle flow. These predictions can then be tested against independent observations gleaned from the geologic record.

In that regard, an important research area in our group involves the development of the theory for reconstructing mantle flow through this novel data-driven geodynamic modelling approach. A powerful technique that we concentrate on in the Munich Geodynamics group is the geodynamic adjoint method. Our group has derived so-called adjoint equations of mantle flow restoration for incompressible (Bunge et al. 2003; Horbach et al. 2014), compressible (Ghelichkhan & Bunge 2016) and thermochemical mantle flow (Ghelichkhan & Bunge 2018). These studies demonstrate that the evolution of the mantle can successfully be predicted from a past flow state in a dynamic model. Such "mantle flow retrodictions" thus provide natural links between many different fields in the geosciences.

Technical questions that are addressed in our research revolve around the different aspects of the geodynamic inverse problem. The explicit linkage of models and observations poses a number of practical questions: from the physical description in terms of equations, to compiling suitable data sets and the propagation of errors in geodynamic models. Our goal is the development of next-generation Earth models that are readily usable for quantitative interpretations in different geoscientific disciplines.