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3 Abstract Gravimetry is an enormously expanding geophysical exploration method during the last decade. Unfortunately the gravity inversion ambiguity problem introduces the necessity to constrain gravity model parameters by other independent data. Overview of gravity data processing and interpretation is presented. All stages of the project lifecycle are discussed with emphasis to the methodological aspects and new challenges introduced by common use of modern digital zero-length spring gravimeters. Special attention is drawn on approaches used in the presented case histories projects. Description of the interpretation stage of the project concentrates on constraining of gravity model parameters with a complex of geophysical and geological data in order to reduce ambiguity of the inversion process in gravimetry. In addition, approaches used for delineation of tectonic structures, an important aspect of the interpretation stage, are described. Three case histories examples are presented to demonstrate methodological aspects of the interpretation of gravity data. They are focused on environmental problems and tectonic structure assessment. The first project represents an attempt to use micro-gravity for determination of internal structure of an undocumented sealed landfill. The second project demonstrates...

To increase measuring accuracy in magnetotellurgic measurements anelectrode can be lowered into a borehole to create constraints forthe inversion. For this method a long cable is need to connect tothe electrode. This creates a new type of problems with parasiticeffects when the cable is placed on a winch made of metal. Toaccount for this, the behavior of the cable while on the winchwas measured. It was considered to be a multilayered multi rowcoil with a resistance of 2,4Ohm. The inductance of the winch wasmeasured for different frequencies and with different amount ofcable on the winch. With this data the physical properties of amultilayered multi row coil was numerically fitted. To explain thefrequency dependency of the inductance two different models wherecreated. Model one described the frequency dependency as randomand fitted the physical properties of the multilayered multi rowcoil once for every frequency. The second model (cftool-model)described the frequency dependency of the coil as a power-functionand fitted this behavior numerically in MATLABs curvefittingtoolbox (cf-tool). Both models predicted an inductance which increased with more cable on the winch and with lowerfrequencies. The models fitted the measured data points well insome areas. But for the measurements made with 135m of cable ofthe winch both models fitted poorly with relative errors of up to43%. This can be because of a systematic error made in how thecable was wound on the winch. To help to improve furthermeasurements the error needed to be within 10% which it overallfails to be. It is uncertain if more data and a better model wouldallow the error to reach tolerable levels or if the dependency ofthe winding of the cable onto the winch is too large.

<p> The first part of my thesis is mainly focused on the effect of grain size distribution on compaction localization in porous sandstone. To identify the microstructural parameters that influence compaction band formation, I conducted a systematic study of mechanical deformation, failure mode and microstructural evolution in Bleurswiller and Boise sandstones, of similar porosity (&sim;25%) and mineralogy but different sorting. Discrete compaction bands were observed to develop over a wide range of pressure in the Bleurswiller sandstone that has a relatively uniform grain size distribution. In contrast, compaction localization was not observed in the poorly sorted Boise sandstone. My results demonstrate that grain size distribution exerts important influence on compaction band development, in agreement with recently published data from Valley of Fire and Buckskin Gulch, as well as numerical studies. </p><p> The second part aimed to improve current knowledge on inelastic behavior, failure mode and brittle-ductile transition in another sedimentary rock, porous carbonates. A micritic Tavel (porosity of &sim;13%) and an allochemical Indiana (&sim;18%) limestones were deformed under compaction in wet and dry conditions. At lower confining pressures, shear localization occurred in brittle faulting regime. Through transitional regime, the deformation switched to cataclastic flow regime at higher confining pressure. Specifically in the cataclastic regime, the (dry and wet) Tavel and dry Indiana failed by distributed cataclastic flow, while in contrast, wet Indiana failed as compaction localization. My results demonstrate that different failure modes and mechanical behaviors under different deformation regimes and water saturation are fundamental prior to any geophysical application in porous carbonates. </p><p> The third part aimed to focus on investigating compaction on quartz aggregate starting at low (MPa) using X-ray diffraction. We report the diffraction peak evolution of quartz with increasing pressures. Through evaluating the unit cell lattice parameters and the volume of the quartz sample, macroscopic stress and strain were resolved. Moreover, we observed quartz peak broadened asymmetrically at low pressure, such extent is more prominent in axial than in radial direction. Our evaluation on peak [101] (highest intensity among peaks) demonstrated that full width at half maximum can be a good proxy for microscopic stress distribution. We observed deviations in the pressure-volume curves at P = &sim;0.4 GPa and speculated that it was the point of which onset of grain crushing and pore collapse occur in quartz. This is on the same order of which onset of grain crushing (commonly known as P*) is observed in sandstones in the rock mechanics literature. This demonstrated that there is potential in estimating grain crushing and pore collapse pressure with our technique.</p>

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