Geoelectrical structures beneath Spitsbergen-Svalbard derived from magnetotelluric imaging

In this thesis a series of geophysical surveys are carried out on the geologically important and remote Svalbard using magnetotelluric imaging, to constrain better the geology particularly defining geothermal resources. Magnetotellurics (MT) relays on natural source time-varying electric and magnetic field data measured at the earth’s surface in order to derive the subsurface resistivity structure. As part of the thesis, broadband MT data are collected in central and northwestern Spitsbergen in the period range between 0.003 - 1000 s from nearly 80 stations distributed along five profiles of 6 - 42 km long. The new MT data have brought significant contributions to extend the existing crustal scale geological knowledge, which mostly inferred from surficial, seismic and gravity studies in the past. From the MT data, we derived 2D and 3D resistivity models for selected areas and enabled to image the structure of the near surface bedrock geology and crustal scale architecture. The 2D and 3D inversion results indicated reasonable agreement with previous geological data, models and well reflected tectonic histories. Within the Central Tertiary Basin a higher frequency of fractures, localized faults and thick intrusive dyke swarms are resolved in the sub-horizontal and less deformed Mesozoic plat- form cover deposits. The tectonic history of the Paleocene-Eocene fold-thrust belt structure in northwest Svalbard is well indicated in the MT data from the Brøgger peninsula as a deformed architecture. The MT data from this section imaged elegantly an interplay between repeated basement-involved fold-thrust structures and successive down-dropped strata along steeply dipping oblique-normal faults that created a horst/ridge and graben/depression systems. MT is sensitive to subsurface geothermal attributes, such as fluid and heat migration zones. In this respect, the new MT data have proposed locations that may favour technologically accessible geothermal potentials

Neuronal calcium imaging signals modeling and analysis

The advent of two-photon calcium imaging in vivo has presented a new arena to detect neuronal action potentials and identify neuron types based on their fluorescence signatures. However, despite the growing popularity, reconstructing spike patterns from the fluorescence traces still remains a major challenge. Also, not much is usually said about how the calcium waveforms corresponding to a spike (calcium kernel) should be estimated. In this thesis, we present a novel approach for calcium kernel estimation from slopes of a fluorescence trace by combining the Savitzky-Golay filter with an iterative algorithm for fitting a nonlinear model (Levenberg-Marquardt). We also present a new method for spike detection, which employs deconvolution and greedy optimization. First we test these methods on synthesized calcium signals, and then we apply them to experimental traces from wild-type and transgenic mice expressing human α- synuclein (model of Parkinson’s disease). We show longer calcium response in the somatosensory cortex neurons of the transgenic mice, read-out both spontaneous and evoked activities as well as follow the hierarchy in fluorescence transient elevation arrivals when mice whiskers were stimulated electrically

The First Magnetotelluric Image of the Lithospheric-Scale Geological Architecture in Central Svalbard, Arctic Norway

Magnetotelluric data, collected from 30 stations on Spitsbergen as part of a reconnaissance geothermal resource assessment along a profile with 0.53-km spacing in 0.0031000-s period range, were used to develop a lithospheric-scale two-dimensional (2D) resistivity model, heretofore unavailable for the region. Inverting the determinant of the impedance tensor in 2D, we found the smoothest model fitting the data within a specified tolerance level. We justified the model by perturbing it, performing sensitivity analysis and re-running the inversion with a different algorithm and starting models. From our final model, we constructed a crustal-scale stratigraphic framework, using it to estimate the depth of major geological features and to locate structural deformations. The 2D resistivity model indicates a shallow low resistive (B100 Vm) Paleozoic Mesozoic sedimentary sequence, varying laterally in thickness (24 km), obstructed by a gently dipping PermianCarboniferous succession (1000 Vm) east of the Billefjorden Fault Zone. Underneath, a (possibly Devonian) basin is imaged as a thick conductive anomaly stretching 15 km downwards. Beneath a deformed PaleozoicMesozoic successions, an uplifted pre-Devonian shallow basement (3000 Vm) is revealed. We estimated a thin lithosphere, in the range of ca. 55100 km thick, that could explain the area’s elevated surface heat flow (ca. 6090 mW/m2 ), consistent with the calculated depth of thermal lithosphere heat-base boundaries for a partially melting mantle. The model indicates a possible replenishment pathway of upward heat transport from the shallow convective mantle to the composite crustal conductive units. This is encouraging for low-enthalpy geothermal development. Human se

Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard

Magnetotelluric (MT) data were recently collected on Brøggerhalvøya, Svalbard, in a 0.003–1000 s period range along a curved WNW–ESE profile. The collected data manifested strong three-dimensional (3D) effects. We modelled the full impedance tensor with tipper and bathymetry included in 3D, and benchmarked the result with determinant data two-dimensional (2D) inversion. The final inversion results indicated striking similarity with known surface bedrock geology and well reflected the tectonic history of the region. The most convincing contribution of the MT data is perhaps the elegantly imaged interplay between repeated basement-involved fold–thrust belt structures and successive down-dropped strata along steeply dipping oblique-normal faults (e.g., the Scheteligfjellet Fault) that created a horst/ridge and graben/depression system. Peculiarly, the MT result suggests that the Paleocene–Eocene fold–thrust belt structures dominate the shallow crustal level, while later normal faults in the area can be traced deeper into the pre-Devonian basement formations strongly affecting fluid and heat migration towards the surface. Near the sub-vertical Scheteligfjellet Fault, the MT model indicates aquifers within the upraised horsts of the pre-Devonian system at 2–5 km depth, sandwiched between the down-faulted resistive (ca. 500–3000 Ωm) Carboniferous and Permian successions. The section west of the Ny-Ålesund settlement has signatures of lateral and subvertical cap-rock sealings, surrounding a steep and deep-seated major fault and aquifer systems. This section of the peninsula therefore requires closer investigation to evaluate the deep geothermal resource prospect

In vivo Stimulus-Induced Vasodilation Occurs without IP3 Receptor Activation and May Precede Astrocytic Calcium Increase

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