Geomechanical-numerical modeling of the crustal stress state of Germany

The stress state in the earth crust is an important quantity for many scientific and technical questions, e.g., seismic hazard assessment, borehole stability and underground storage. However, the level of knowledge about the recent stress field in Germany is still limited. There are basically two larger data sets available: (1) the World Stress Map (WSM) providing mainly information about the orientation of the maximum horizontal stress (SHmax) as well as the stress regime and (2) a stress magnitude database of Germany providing magnitude information about the individual components of the absolute stress tensor. However, the data are sparse, pointwise and unequally distributed. Therefore, a continuous prediction of the recent crustal stress state of Germany by linear interpolation between these data points is not suitable, in particular due to vertical and lateral inhomogeneities, e.g., mechanical properties, or faults leading to stress variations within in the crust. The presented cumulative dissertation is part of the SpannEnD project that aims to enhance the state of knowledge of the stress field in Germany. This dissertation contains three manuscripts: two dealing with the continuous prediction of the recent crustal stress state of Germany by large scale (1000 x 1250 x 100 km3) geomechanical-numerical models and one with the analysis of slip tendency (TS) of faults in Germany using results of one of these models. The two geomechanical-numerical models contain units describing the present geological conditions, which are parameterized with individual rock properties. Linear elasticity is assumed and the Finite Element Method (FEM) is used to solve the equilibrium of forces. The models enable a continuous prediction of the absolute stress state based on continuum mechanics within the upper lithosphere for the entire area of Germany for the first time. The first model presented in this cumulative dissertation contains seven units: a sedimentary unit, four laterally overlapping units of the upper crust, the lower crust and parts of the lithospheric mantle. It is calibrated against magnitudes of the minimum horizontal stress (Shmin) and compared with orientations of SHmax of the WSM and some additional data. The results show an overall good fit to the orientation of SHmax with a mean of the absolute deviations of 15.6° and a median of 5.6° and to the Shmin magnitudes with a mean of the absolute differences of 3.3 MPa used for calibration. However, the SHmax magnitudes show some larger differences especially too low values within the upper part of the model. The second model is an improved version of the first model with focus on a higher stratigraphic resolution of the sedimentary unit, containing 22 units. In combination with an 18-time higher mesh resolution and an additional calibration with SHmax magnitudes the results show an overall good fit to the magnitudes of all principal stresses (Shmin, SHmax and the vertical stress (SV)) and the WSM orientation data. This is indicated by absolute differences of 0.0 MPa for SV, 4.6 MPa for Shmin and 6.4 MPa for SHmax and by a median of 0.3° and absolute differences of 11.9° for the SHmax orientations within the central part. The third manuscript shows a possible application for the results of a large-scale geomechanical-numerical model. It is a TS analysis of faults for Germany using the results of the first model of this study and three different sets of faults with increasing complexities. The analysis show a good spatial agreement between the calculated TS and earthquakes within the study area. However, the fit between the depth of earthquake occurrence and the highest predicted TS show some discrepancies. In general, the study shows the influence of the fault geometry, the fault orientation in relation to the stress field and the crucial influence of the pore pressure. The results of this cumulative dissertation are a step towards a better understanding of the recent stress field of Germany. By two geomechanical models providing - for the first time the 3D stress tensor - and results, which are in good agreement with different calibration and comparison data sets. However, there are still some local and few general deviations that need to be further investigated, for example, with smaller more complex models, for which the stress field of this study can be used as an initial stress state

The analysis of slip tendency of major tectonic faults in Germany

Seismic hazard during subsurface operations is often related to the reactivation of pre-existing tectonic faults. The analysis of the slip tendency, i.e., the ratio of shear to normal stress acting on the fault plane, allows an assessment of the reactivation potential of faults. We use the total stresses that result from a large-scale 3D geomechanical–numerical model of Germany and adjacent areas to calculate the slip tendency for three 3D fault geometry sets with increasing complexity. This allows us to draw general conclusions about the influence of the fault geometry on the reactivation potential. In general, the fault reactivation potential is higher in Germany for faults that strike NW–SE and NNE–SSW. Due to the prevailing normal stress regime in the geomechanical–numerical model results, faults dipping at an angle of about 60∘ generally show higher slip tendencies in comparison to steeper or shallower dipping faults. Faults implemented with a straight geometry show higher slip tendencies than those represented with a more complex, uneven geometry. Pore pressure has been assumed to be hydrostatic and has been shown to have a major influence on the calculated slip tendencies. Compared to slip tendency values calculated without pore pressure, the consideration of pore pressure leads to an increase in slip tendency of up to 50 %. The qualitative comparison of the slip tendency with the occurrence of seismic events with moment magnitudes M$_w$>3.5 shows areas with an overall good spatial correlation between elevated slip tendencies and seismic activity but also highlights areas where more detailed and diverse fault sets would be beneficial

The crustal stress field of Germany: a refined prediction

Information about the absolute stress state in the upper crust plays a crucial role in the planning and execution of, e.g., directional drilling, stimulation and exploitation of geothermal and hydrocarbon reservoirs. Since many of these applications are related to sediments, we present a refined geomechanical–numerical model for Germany with focus on sedimentary basins, able to predict the complete 3D stress tensor. The lateral resolution of the model is 2.5 km, the vertical resolution about 250 m. Our model contains 22 units with focus on the sedimentary layers parameterized with individual rock properties. The model results show an overall good fit with magnitude data of the minimum (S$_{hmin}$) and maximum horizontal stress (SS$_{Hmax}$) that are used for the model calibration. The mean of the absolute stress differences between these calibration data and the model results is 4.6 MPa for Shmin and 6.4 MPa for SS$_{Hmax}$. In addition, our predicted stress field shows good agreement to several supplementary in-situ data from the North German Basin, the Upper Rhine Graben and the Molasse Basin

Strongly coupled chameleon fields: possible test with a neutron Lloyd's mirror interferometer

The consideration is presented of possible neutron Lloyd's mirror interferometer experiment to search for strongly coupled chameleon fields. The chameleon scalar fields were proposed to explain the early and late time acceleration of expansion of the Universe. They may produce short-range interaction between particles and matter. This interaction causes phase shift of neutron waves in the interferometer. Estimates of sensitivity are performed.Comment: 11 p, 3 fig; the title is changed, extended feasibility consideration: expected intensity and systematic effect

Axion-like-particle search with high-intensity lasers

We study ALP-photon-conversion within strong inhomogeneous electromagnetic fields as provided by contemporary high-intensity laser systems. We observe that probe photons traversing the focal spot of a superposition of Gaussian beams of a single high-intensity laser at fundamental and frequency-doubled mode can experience a frequency shift due to their intermittent propagation as axion-like-particles. This process is strongly peaked for resonant masses on the order of the involved laser frequencies. Purely laser-based experiments in optical setups are sensitive to ALPs in the $\mathrm{eV}$ mass range and can thus complement ALP searches at dipole magnets.Comment: 25 pages, 2 figure

Cosmological Tests of Gravity

Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. We review recent developments in modified gravity theories, focusing on higher dimensional approaches and chameleon/f(R) theories. We classify these models in terms of the screening mechanisms that enable such theories to approach general relativity on small scales (and thus satisfy solar system constraints). We describe general features of the modified Friedman equation in such theories. The second half of this review describes experimental tests of gravity in light of the new theoretical approaches. We summarize the high precision tests of gravity on laboratory and solar system scales. We describe in some detail tests on astrophysical scales ranging from ~kpc (galaxy scales) to ~Gpc (large-scale structure). These tests rely on the growth and inter-relationship of perturbations in the metric potentials, density and velocity fields which can be measured using gravitational lensing, galaxy cluster abundances, galaxy clustering and the Integrated Sachs-Wolfe effect. A robust way to interpret observations is by constraining effective parameters, such as the ratio of the two metric potentials. Currently tests of gravity on astrophysical scales are in the early stages --- we summarize these tests and discuss the interesting prospects for new tests in the coming decade.Comment: Invited review for Annals of Physics; 58 pages, 8 figures

Probing new physics with long-lived charged particles produced by atmospheric and astrophysical neutrinos

As suggested by some extensions of the Standard Model of particle physics, dark matter may be a super-weakly interacting lightest stable particle, while the next-to-lightest particle (NLP) is charged and meta-stable. One could test such a possibility with neutrino telescopes, by detecting the charged NLPs produced in high-energy neutrino collisions with Earth matter. We study the production of charged NLPs by both atmospheric and astrophysical neutrinos; only the latter, which is largely uncertain and has not been detected yet, was the focus of previous studies. We compute the resulting fluxes of the charged NLPs, compare those of different origins, and analyze the dependence on the underlying particle physics setup. We point out that even if the astrophysical neutrino flux is very small, atmospheric neutrinos, especially those from the prompt decay of charmed mesons, may provide a detectable flux of NLP pairs at neutrino telescopes such as IceCube. We also comment on the flux of charged NLPs expected from proton-nucleon collisions, and show that, for theoretically motivated and phenomenologically viable models, it is typically sub-dominant and below detectable rates.Comment: 27 pages, 6 figures; accepted for publication in JCA