Lattice-Boltzmann Method for Geophysical Plastic Flows

We explore possible applications of the Lattice-Boltzmann Method for the simulation of geophysical flows. This fluid solver, while successful in other fields, is still rarely used for geotechnical applications. We show how the standard method can be modified to represent free-surface realization of mudflows, debris flows, and in general any plastic flow, through the implementation of a Bingham constitutive model. The chapter is completed by an example of a full-scale simulation of a plastic fluid flowing down an inclined channel and depositing on a flat surface. An application is given, where the fluid interacts with a vertical obstacle in the channel.Comment: in W. Wu, R.I. Borja (Edts.) Recent advances in modelling landslides and debris flow, Springer Series in Geomechanics and Geoengineering (2014), ISBN 978-3-319-11052-3, pp. 131-14

How efficient is an integrative approach in archaeological geophysics? Comparative case studies from Neolithic settlements in Thessaly (Central Greece)

The geophysical prospection of Neolithic tells imposes specific challenges due to the preservation and nature of the architectural context and the multiple, usually disturbed, soil strata. Contrary to the usual application of a single method, this paper deals with the advantages of using an integrated geophysical approach through the employment of various methodologies to map the Neolithic cul-tural and environmental landscape of Thessalian tells (magoules) in Central Greece. The success and failure of each method in resolving the various features of the magoules are discussed in detail, and as a whole, they demonstrate the benefits of a manifold geophysical prospection of the sites

Near surface geophysical surveying of Northern Ireland from the air

A recent low-level high resolution airborne geophysical survey of Northern Ireland has provided detailed imagery of ground radioactivity, electrical conductivity and magnetisation. Although airborne geophysics is usually thought of as a regional mapping method, these results are being used widely for near-surface applications - for shallow mineral exploration, geological mapping, environmental management and for research in these fields. Data have been licensed to industry and have prompted significant inward investment in mineral exploration. Together with complementary geochemical datasets, these near-surface geophysical results support environmental monitoring by regulators. They provide a basis for research in other fields, including structural geology, environmental radioactivity, soil science, groundwater management and geostatistics. Some of these applications are described. The project illustrates the value of airborne geophysical data in a range of economic sectors

Error analysis of a continuous-discontinuous Galerkin finite element method for generalized 2D vorticity dynamics

A detailed a priori error estimate is provided for a continuous-discontinuous Galerkin finite element method suitable for two-dimensional geophysical flows. Special attention is given to derive estimates which require only minimal smoothness in the vorticity field

Disordered vortex arrays in a two-dimensional condensate

We suggest a method to create turbulence in a Bose-Einstein condensate. The method consists in, firstly, creating an ordered vortex array, and, secondly, imprinting a phase difference in different regions of the condensate. By solving numerically the two-dimensional Gross-Pitaevskii equation we show that the motion of the resulting positive and negative vortices is disordered.Comment: 14 pages, 18 figures, accepted by Geophysical and Astrophysical Fluid Dynamic

Discontinuities without discontinuity: The Weakly-enforced Slip Method

Tectonic faults are commonly modelled as Volterra or Somigliana dislocations in an elastic medium. Various solution methods exist for this problem. However, the methods used in practice are often limiting, motivated by reasons of computational efficiency rather than geophysical accuracy. A typical geophysical application involves inverse problems for which many different fault configurations need to be examined, each adding to the computational load. In practice, this precludes conventional finite-element methods, which suffer a large computational overhead on account of geometric changes. This paper presents a new non-conforming finite-element method based on weak imposition of the displacement discontinuity. The weak imposition of the discontinuity enables the application of approximation spaces that are independent of the dislocation geometry, thus enabling optimal reuse of computational components. Such reuse of computational components renders finite-element modeling a viable option for inverse problems in geophysical applications. A detailed analysis of the approximation properties of the new formulation is provided. The analysis is supported by numerical experiments in 2D and 3D.Comment: Submitted for publication in CMAM

Method and apparatus for calibrating the ionosphere and application to surveillance of geophysical events

The columnar electron content of the ionosphere between a spacecraft and a receiver is measured in realtime by cross correlating two coherently modulated signals transmitted at different frequencies (L1,L2) from the spacecraft to the receiver using a cross correlator. The time difference of arrival of the modulated signals is proportional to electron content of the ionosphere. A variable delay is adjusted relative to a fixed delay in the respective channels (L1,L2) to produce a maximum at the cross correlator output. The difference in delay required to produce this maximum is a measure of the columnar electron content of the ionosphere. A plurality of monitoring stations and spacecraft (Global Positioning System satellites) are employed to locate any terrestrial event that produces an ionospheric disturbance

Geophysical surveys near Strontian, Highland Region

Reconnaissance VLF-EM and magnetic surveys have bean carried out over Ba- Pb-Zn prospects in an area near Strontian in the Highland Region of Scotland. Rather than attempting to detect the economic minerals directly, which is unlikely to be practicable by geophysical methods, the trials concentrated on exploration for the crush zones and associated Permo-Carboniferous basic dykes which act as hosts to mineralisation. The results are encouraging, with the VLF-EM method proving effective in delineating crush zones while magnetic traverses detected the basic dykes. To the east of Bellsgrove mine a crush zone and dyke extend eastwards along the strike of the Strontian Main Vein; however, to the west of the Whitesmith mine the evidence of a westward extension of the Main Vein is insubstantial. A number of crush zones and associated dykes have been identified in the Corrantee-Whitesmith area. Probable ext_ensions are indicated to a number of known veins in the vicinity of the Fee Donald mine. The rss~llts merit geophysical, geological and possibly geochemical follow-up

Comment on "Spatio-temporal filling of missing points in geophysical data sets" by D. Kondrashov and M. Ghil, Nonlin. Processes Geophys., 13, 151–159, 2006

Kondrashov and Ghil (2006) (KG hereafter) describe a method for imputing missing values in incomplete datasets that can exploit both spatial and temporal covariability to estimate missing values from available values. Temporal covariability has not been exploited as widely as spatial covariability in imputing missing values in geophysical datasets, but, as KG show, doing so can improve estimates of missing values. However, there are several inaccuracies in KG’s paper. Since similar inaccuracies have surfaced in other recent papers, for example, in the literature on paleo-climate reconstructions, I would like to point them out here