@phdthesis{Neuharth2022,
  author    = {Neuharth, Derek},
  title     = {Evolution of divergent and strike-slip boundaries in response to surface processes},
  doi       = {10.25932/publishup-54940},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549403},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xiii, 108},
  year      = {2022},
  abstract  = {Plate tectonics describes the movement of rigid plates at the surface of the Earth as well as their complex deformation at three types of plate boundaries: 1) divergent boundaries such as rift zones and mid-ocean ridges, 2) strike-slip boundaries where plates grind past each other, such as the San Andreas Fault, and 3) convergent boundaries that form large mountain ranges like the Andes. The generally narrow deformation zones that bound the plates exhibit complex strain patterns that evolve through time. During this evolution, plate boundary deformation is driven by tectonic forces arising from Earth's deep interior and from within the lithosphere, but also by surface processes, which erode topographic highs and deposit the resulting sediment into regions of low elevation. Through the combination of these factors, the surface of the Earth evolves in a highly dynamic way with several feedback mechanisms. At divergent boundaries, for example, tensional stresses thin the lithosphere, forcing uplift and subsequent erosion of rift flanks, which creates a sediment source. Meanwhile, the rift center subsides and becomes a topographic low where sediments accumulate. This mass transfer from foot- to hanging wall plays an important role during rifting, as it prolongs the activity of individual normal faults. When rifting continues, continents are eventually split apart, exhuming Earth's mantle and creating new oceanic crust. Because of the complex interplay between deep tectonic forces that shape plate boundaries and mass redistribution at the Earth's surface, it is vital to understand feedbacks between the two domains and how they shape our planet. In this study I aim to provide insight on two primary questions: 1) How do divergent and strike-slip plate boundaries evolve? 2) How is this evolution, on a large temporal scale and a smaller structural scale, affected by the alteration of the surface through erosion and deposition? This is done in three chapters that examine the evolution of divergent and strike-slip plate boundaries using numerical models. Chapter 2 takes a detailed look at the evolution of rift systems using two-dimensional models. Specifically, I extract faults from a range of rift models and correlate them through time to examine how fault networks evolve in space and time. By implementing a two-way coupling between the geodynamic code ASPECT and landscape evolution code FastScape, I investigate how the fault network and rift evolution are influenced by the system's erosional efficiency, which represents many factors like lithology or climate. In Chapter 3, I examine rift evolution from a three-dimensional perspective. In this chapter I study linkage modes for offset rifts to determine when fast-rotating plate-boundary structures known as continental microplates form. Chapter 4 uses the two-way numerical coupling between tectonics and landscape evolution to investigate how a strike-slip boundary responds to large sediment loads, and whether this is sufficient to form an entirely new type of flexural strike-slip basin.},
  language  = {en}
}
@phdthesis{Farkas2022,
  author    = {Farkas, Marton Pal},
  title     = {Hydraulic fracturing in hard rock - numerical studies from laboratory to reservoir scale},
  doi       = {10.25932/publishup-54934},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-549343},
  school      = {Universit{\"a}t Potsdam},
  pages     = {155},
  year      = {2022},
  abstract  = {Hydraulic-driven fractures play a key role in subsurface energy technologies across several scales. By injecting fluid at high hydraulic pressure into rock with intrinsic low permeability, in-situ stress field and fracture development pattern can be characterised as well as rock permeability can be enhanced. Hydraulic fracturing is a commercial standard procedure for enhanced oil and gas production of rock reservoirs with low permeability in petroleum industry. However, in EGS utilization, a major geological concern is the unsolicited generation of earthquakes due to fault reactivation, referred to as induced seismicity, with a magnitude large enough to be felt on the surface or to damage facilities and buildings. Furthermore, reliable interpretation of hydraulic fracturing tests for stress measurement is a great challenge for the energy technologies. Therefore, in this cumulative doctoral thesis the following research questions are investigated. (1): How do hydraulic fractures grow in hard rock at various scales?; (2): Which parameters control hydraulic fracturing and hydro-mechanical coupling?; and (3): How can hydraulic fracturing in hard rock be modelled? In the laboratory scale study, several laboratory hydraulic fracturing experiments are investigated numerically using Irazu2D that were performed on intact cubic Pocheon granite samples from South Korea applying different injection protocols. The goal of the laboratory experiments is to test the concept of cyclic soft stimulation which may enable sustainable permeability enhancement (Publication 1). In the borehole scale study, hydraulic fracturing tests are reported that were performed in boreholes located in central Hungary to determine the in-situ stress for a geological site investigation. At depth of about 540 m, the recorded pressure versus time curves in mica schist with low dip angle foliation show atypical evolution. In order to provide explanation for this observation, a series of discrete element computations using Particle Flow Code 2D are performed (Publication 2). In the reservoir scale study, the hydro-mechanical behaviour of fractured crystalline rock due to one of the five hydraulic stimulations at the Pohang Enhanced Geothermal site in South Korea is studied. Fluid pressure perturbation at faults of several hundred-meter lengths during hydraulic stimulation is simulated using FracMan (Publication 3). The doctoral research shows that the resulting hydraulic fracturing geometry will depend "locally", i.e. at the length scale of representative elementary volume (REV) and below that (sub-REV), on the geometry and strength of natural fractures, and "globally", i.e. at super-REV domain volume, on far-field stresses. Regarding hydro-mechanical coupling, it is suggested to define separate coupling relationship for intact rock mass and natural fractures. Furthermore, the relative importance of parameters affecting the magnitude of formation breakdown pressure, a parameter characterising hydro-mechanical coupling, is defined. It can be also concluded that there is a clear gap between the capacity of the simulation software and the complexity of the studied problems. Therefore, the computational time of the simulation of complex hydraulic fracture geometries must be reduced while maintaining high fidelity simulation results. This can be achieved either by extending the computational resources via parallelization techniques or using time scaling techniques. The ongoing development of used numerical models focuses on tackling these methodological challenges.},
  language  = {en}
}
@phdthesis{Dannberg2016,
  author    = {Dannberg, Juliane},
  title     = {Dynamics of mantle plumes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-91024},
  school      = {Universit{\"a}t Potsdam},
  pages     = {162},
  year      = {2016},
  abstract  = {Mantle plumes are a link between different scales in the Earth's mantle: They are an important part of large-scale mantle convection, transporting material and heat from the core-mantle boundary to the surface, but also affect processes on a smaller scale, such as melt generation and transport and surface magmatism. When they reach the base of the lithosphere, they cause massive magmatism associated with the generation of large igneous provinces, and they can be related to mass extinction events (Wignall, 2001) and continental breakup (White and McKenzie, 1989). Thus, mantle plumes have been the subject of many previous numerical modelling studies (e.g. Farnetani and Richards, 1995; d'Acremont et al., 2003; Lin and van Keken, 2005; Sobolev et al., 2011; Ballmer et al., 2013). However, complex mechanisms, such as the development and implications of chemical heterogeneities in plumes, their interaction with mid-ocean ridges and global mantle flow, and melt ascent from the source region to the surface are still not very well understood; and disagreements between observations and the predictions of classical plume models have led to a challenge of the plume concept in general (Czamanske et al., 1998; Anderson, 2000; Foulger, 2011). Hence, there is a need for more sophisticated models that can explain the underlying physics, assess which properties and processes are important, explain how they cause the observations visible at the Earth's surface and provide a link between the different scales. In this work, integrated plume models are developed that investigate the effect of dense recycled oceanic crust on the development of mantle plumes, plume-ridge interaction under the influence of global mantle flow and melting and melt migration in form of two-phase flow. The presented analysis of these models leads to a new, updated picture of mantle plumes: Models considering a realistic depth-dependent density of recycled oceanic crust and peridotitic mantle material show that plumes with excess temperatures of up to 300 K can transport up to 15\% of recycled oceanic crust through the whole mantle. However, due to the high density of recycled crust, plumes can only advance to the base of the lithosphere directly if they have high excess temperatures, high plume volumes and the lowermost mantle is subadiabatic, or plumes rise from the top or edges of thermo-chemical piles. They might only cause minor surface uplift, and instead of the classical head-tail structure, these low-buoyancy plumes are predicted to be broad features in the lower mantle with much less pronounced plume heads. They can form a variety of shapes and regimes, including primary plumes directly advancing to the base of the lithosphere, stagnating plumes, secondary plumes rising from the core-mantle boundary or a pool of eclogitic material in the upper mantle and failing plumes. In the upper mantle, plumes are tilted and deflected by global mantle flow, and the shape, size and stability of the melting region is influenced by the distance from nearby plate boundaries, the speed of the overlying plate and the movement of the plume tail arriving from the lower mantle. Furthermore, the structure of the lithosphere controls where hot material is accumulated and melt is generated. In addition to melting in the plume tail at the plume arrival position, hot plume material flows upwards towards opening rifts, towards mid-ocean ridges and towards other regions of thinner lithosphere, where it produces additional melt due to decompression. This leads to the generation of either broad ridges of thickened magmatic crust or the separation into multiple thinner lines of sea mount chains at the surface. Once melt is generated within the plume, it influences its dynamics, lowering the viscosity and density, and while it rises the melt volume is increased up to 20\% due to decompression. Melt has the tendency to accumulate at the top of the plume head, forming diapirs and initiating small-scale convection when the plume reaches the base of the lithosphere. Together with the introduced unstable, high-density material produced by freezing of melt, this provides an efficient mechanism to thin the lithosphere above plume heads. In summary, this thesis shows that mantle plumes are more complex than previously considered, and linking the scales and coupling the physics of different processes occurring in mantle plumes can provide insights into how mantle plumes are influenced by chemical heterogeneities, interact with the lithosphere and global mantle flow, and are affected by melting and melt migration. Including these complexities in geodynamic models shows that plumes can also have broad plume tails, might produce only negligible surface uplift, can generate one or several volcanic island chains in interaction with a mid-ocean ridge, and can magmatically thin the lithosphere.},
  language  = {en}
}