SED - Latest Articles

The model of own seismoelectromagnetic oscillations of LAI system

Mon, 26 Jul 2010 00:00:00 +0200

The model of own seismoelectromagnetic oscillations of LAI system

Solid Earth Discussions, 2, 233-250, 2010

Author(s): M. K. Kachakhidze, Z. A. Kereselidze, and N. K. Kachakhidze

Very low frequency (VLF) electromagnetic radiation (in diapason 1 kHz – 1 MHz) in atmosphere, generated during earthquake preparation period, may be connected with linear size, characterizing incoming earthquake source. In order to argue this hypothesis very simple quasi-electrostatic model is used: local VLF radiation may be the manifestation of own electromagnetic oscillations of concrete seismoactive segments of lithosphere-atmosphere system. This model explains qualitatively well-known precursor effects of earthquakes. At the same time, it will be principally possible to forecast expected earthquake with certain precision if we use this model after diagnosing existed data.

As physical basis of working hypothesis is atmospheric effect of polarization charges occurred in surface layer of the Earth, it is possible to test the below constructed model in medium, where reasons of polarization charge generation may be different from piezoelectric mechanism, for example, due to electrolytic hydration.

A simple method for solving the Bussian equation for electrical conduction in rocks

Tue, 06 Jul 2010 00:00:00 +0200

A simple method for solving the Bussian equation for electrical conduction in rocks

Solid Earth Discussions, 2, 213-231, 2010

Author(s): P. W. J. Glover, T. J. Ransford, and G. Auger

One of the most general and effective models for calculating the complex electrical conductivity and relative dielectric permittivity of rocks saturated with pore fluids is that of Bussian. Unlike most models, it is non-linear and cannot be solved algebraically. Consequently, researchers use reiterating numerical routines to obtain a solution of the equation, and then only for the real part of the solution. Here we present a different approach to the solution that uses conformal mapping in the complex plane, and implements it within Maple. The method is simple and elegant in that it requires, for example, only 3 lines of code in Maple 11 and little programming experience. The approach has been shown to be as precise as using the classical reiterating bisection method for real data implemented in C++ on an ordinary desktop computer to within a probability over 1 in 10⁹. However, the conformal mapping approach is 52 times as fast. We show once more that the Bussian equation breaks down for low fluid conductivities, but recommend it (with the modified Archie's law) for use with rocks saturated with high salinity fluids when the matrix is conductive.

Use of rare earth oxides as tracers to identify sediment source areas for agricultural hillslopes

Thu, 01 Jul 2010 00:00:00 +0200

Use of rare earth oxides as tracers to identify sediment source areas for agricultural hillslopes

Solid Earth Discussions, 2, 195-212, 2010

Author(s): C. Deasy and J. N. Quinton

Understanding sediment sources is essential to enable more effective targeting of in-field mitigation approaches to reduce diffuse pollution from agricultural land. In this paper we report on the application of rare earth element oxides to arable soils at hillslope scale in order to determine sediment source areas and their relative importance, using a non-intrusive method of surface spraying. Runoff, sediments and rare earth elements lost from four arable hillslope lengths at a site in the UK with clay soils were monitored from three rainfall events after tracer application. Measured erosion rates were low, reflecting the typical event conditions occurring at the site, and less than 1% of the applied REO tracers were recovered, which is consistent with the results of comparable studies. Tracer recovery at the base of the hillslope was able to indicate the relative importance of different hillslope sediment source areas, which were found to be consistent between events. The principal source of eroded sediments was the upslope area, implying that the wheel tracks were principally conduits for sediment transport, and not highly active sites of erosion. Mitigation treatments for sediment losses from arable hillslopes should therefore focus on methodologies for trapping mobile sediments within wheel track areas through increasing surface roughness or reducing the connectivity of sediment transport processes.

Radon signals at the Roded site, southern Israel

Tue, 22 Jun 2010 00:00:00 +0200

Radon signals at the Roded site, southern Israel

Solid Earth Discussions, 2, 161-193, 2010

Author(s): G. Steinitz and O. Piatibratova

Temporal variations of radon in the geological environment (upper crust) are frequent and recognized as unique in terms of the signals encountered and for the lack of substantial and generally applicable explanations. The phenomena observed at the Roded site, located in arid southern Israel, emphasize this situation. Monitoring of radon during more than 10 years is carried out in massive meta-diorite of the Precambrian basement block of Roded. Measurement is conducted using an alpha detector at a resolution of 15-min, lowered in a borehole at a depth of 9 m, within a PVC casing to that depth. Systematic temporal variation patterns, manifesting large relative signals are composed of sub-daily (SDR) radon, multi-day (MD) and annual (AR) signals. The overall variation in dominated by the intense SDR signals which occur in some days, and may vary from background levels (5 counts or less) to peak values (attaining >1000 counts) and back to background in an interval of 6 to 12 h. Intervals of up to several tens of days without significant SDR signals interchange with times of intense daily occurrences of such signals. Their occurrence indicates very fast variations of radiation from radon at the point of measurement. The peak times, within the diurnal 24-h cycle of SDR signals occur preferentially in the interval of 14–16 h (UT+2). Spectral analysis indicates: (a) A diurnal periodicity composed of a primary 24-h and a secondary 12-h periodicity, which are attributed to the solar tide constituents S1 and S2. Tidal constituents indicative for gravity tide (O1, M2) are lacking; (b) An annual periodicity. A compound relation among the diurnal and annual periodicity is indicated by: (a) Wavelet (CWT) analysis showing an overall annual structure with a modulation of the S1 and S2 periodicities; (b) FFT analysis using consecutive 21.3-day long time intervals shows that the amplitudes of S1 and S2 vary in an annual pattern, with relatively high values in summer. The phase of S1 and S2 and S3 shows a systematic multi-year variation. Existing frames of reference of geophysical processes cannot explain the highly systematic phenomena. It is suggested that the significant signatures of the periodic phenomena and their modulations are reflecting a direct link with solar radiation tide.

Some possible correlations between electro-magnetic emission and seismic activity during West Bohemia 2008 earthquake swarm

Mon, 12 Apr 2010 00:00:00 +0200

Some possible correlations between electro-magnetic emission and seismic activity during West Bohemia 2008 earthquake swarm

Solid Earth Discussions, 2, 145-160, 2010

Author(s): P. Kolář

There are long time lasting speculations about electro-magnetic emission phenomena (hereafter EME) connected with seismic activity. In the present work we study such relations in West Bohemia region during 2008 earthquake swarm. After brief characterization of the seismic region, we describe recording method and data analysis. We did not observe any direct link between EME and seismic events, however statistical analysis indicates that it could be some increase of EME activity in time 60 to 30 min before an event on periods 17–14 min, some gap in EME activity approximately 2 h after the event and a maximum 4 h after the events (note, that this result qualitatively correspond with observations from other seismic regions). Also global decrease of EME activity with the decay of the swarm activity was observed. However due to incomplete EME data and short time of observation these results must be understand as indication of possible correlation rather than reliable relation.

The mechanics of gravity-driven faulting

Mon, 12 Apr 2010 00:00:00 +0200

The mechanics of gravity-driven faulting

Solid Earth Discussions, 2, 105-144, 2010

Author(s): L. Barrows and V. Barrows

Faulting can result from either of two different mechanisms. These involve fundamentally different energetics. In elastic rebound, locked-in elastic strain energy is transformed into the earthquake (seismic waves plus work done in the fault zone). In force-driven faulting, the forces that create the stress on the fault supply work or energy to the faulting process. Half of this energy is transformed into the earthquake and half goes into an increase in locked-in elastic strain. In elastic rebound the locked-in elastic strain drives slip on the fault. In force-driven faulting it stops slip on the fault.

Tectonic stress is reasonably attributed to gravity acting on topography and the Earth's lateral density variations. This includes the thermal convection that ultimately drives plate tectonics. Mechanical analysis has shown the intensity of the gravitational tectonic stress that is associated with the regional topography and lateral density variations that actually exist is comparable with the stress drops that are commonly associated with tectonic earthquakes; both are in the range of tens of bar to several hundred bar.

The gravity collapse seismic mechanism assumes the fault fails and slips in direct response to the gravitational tectonic stress. Gravity collapse is an example of force-driven faulting. In the simplest case, energy that is released from the gravitational potential of the stress-causing topography and lateral density variations is equally split between the earthquake and the increase in locked-in elastic strain.

The release of gravitational potential energy requires a change in the Earth's density distribution. Gravitational body forces are solely dependent on density so a change in the density distribution requires a change in the body forces. This implies the existence of volumetric body-force displacements. The volumetric body-force displacements are in addition to displacements generated by slip on the fault. They must exist if gravity participates in the energetics of the faulting process.

From the perspective of gravitational tectonics, the gravity collapse mechanism is direct and simple. The related mechanics are more subtle. If gravity is not deliberately and explicitly included in an earthquake model, then gravity is locked out of the energetics of the model. The earthquake model (but not necessarily the physical reality) is then elastic rebound.

Candidates for multiple impact craters: popigai and chicxulub as seen by EGM08, a global 5'×5' gravitational model

Tue, 09 Mar 2010 00:00:00 +0100

Candidates for multiple impact craters: popigai and chicxulub as seen by EGM08, a global 5'×5' gravitational model

Solid Earth Discussions, 2, 69-103, 2010

Author(s): J. Klokočník, J. Kostelecký, I. Pešek, P. Novák, C. A. Wagner, and J. Sebera

In 2008 the new Earth Gravitational Model (EGM08) was released. It contains a complete set of spherical harmonic coefficients of the Earth's gravitational potential (Stokes parameters) to degree 2190 and order 2159 that can be used for evaluation of various potential quantities with both the unprecedented accuracy and high spatial resolution. Two such quantities, the gravity anomaly and second-order radial derivative of the disturbing potential, were computed over selected areas with known impact craters. The displays of these derivatives for two such sites clearly show not only the strong circular-like features known to be associated with them but also other symmetrical structures which appear to make them multiple impact sites. At Popigai, Siberia, the secondary circular features fall in a line from the primary in the SE direction. At Chicxulub, Yucatán, there appears to be one secondary crater close to the primary in the NE direction, as well as possibly others in the vicinity of the main crater. Gravity information alone is not proof of the impact craters but it is useful in identifying candidate sites for further study, for future examination by geologists and geophysicists.

The stochastic quantization method and its application to the numerical simulation of volcanic conduit dynamics under random conditions

Thu, 04 Mar 2010 00:00:00 +0100

The stochastic quantization method and its application to the numerical simulation of volcanic conduit dynamics under random conditions

Solid Earth Discussions, 2, 43-67, 2010

Author(s): E. Peruzzo, M. Barsanti, F. Flandoli, and P. Papale

Stochastic Quantization (SQ) is a method for the approximation of a continuous probability distribution with a discrete one. The proposal made in this paper is to apply this technique to reduce the number of numerical simulations for systems with uncertain inputs, when estimates of the output distribution are needed. This question is relevant in volcanology, where realistic simulations are very expensive and uncertainty is always present. We show the results of a benchmark test based on a one-dimensional steady model of magma flow in a volcanic conduit.

Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna

Fri, 19 Feb 2010 00:00:00 +0100

Rheological control on the dynamics of explosive activity in the 2000 summit eruption of Mt. Etna

Solid Earth Discussions, 2, 19-42, 2010

Author(s): D. Giordano, M. Polacci, P. Papale, and L. Caricchi

In the period from January to June 2000 Mt. Etna exhibited an exceptional explosive activity characterised by a succession of 64 Strombolian and fire-fountaining episodes from the summit South-East crater. Textural analysis of the eruptive products reveals that the magma associated with the Strombolian phases had a much larger crystal content >55 vol% with respect to the magma discharged during the fire-fountain phases (~35 vol%). Rheological modelling shows that the crystal-rich magma falls in a region beyond a critical crystal content where the small addition of solid particles causes an exponential increase of the effective magma viscosity. When implemented into the modelling of steady magma ascent dynamics, the large crystal content of the Strombolian eruption phases results in a one order of magnitude decrease of mass flow-rate, and in the onset of conditions where small heterogeneities in the solid fraction carried by the magma translate into highly unsteady eruption dynamics. Therefore, we argue that crystallization on top of the magmatic column during the intermediate phases when magma was not discharged caused the conditions to shift from fire-fountain to Strombolian activity. The numerical simulations also provide a consistent interpretation of the association between fire-fountain activity and emergence of lava flows from the crater flanks.

Some improvements in subbasalt imaging using pre-stack depth migration

Mon, 08 Feb 2010 00:00:00 +0100

Some improvements in subbasalt imaging using pre-stack depth migration

Solid Earth Discussions, 2, 1-17, 2010

Author(s): I. Flecha, R. Carbonell, R. W. Hobbs, and H. Zeyen

Subbasalt imaging can be improved by carefully applying pre-stack depth migration. Pre-stack depth migration requires a detailed velocity model and an accurate traveltime calculation. Ray tracing methods are fast but, often fail in calculating traveltimes in complex models, specially, when they feature high velocity contrasts. Finitte difference solutions of the eikonal are more stable and can produce a traveltime field for the whole model avoiding shadow zones. A synthetic test was carried out to check the performance of a new pre-stack depth migration algorithm in a model that features a high velocity layer surrounded by lower velocities. The results reasonably reproduce the original model. The same scheme was used to process long-offset reflection data from the Faroe Shelf where conventional techniques (stack) were insufficient to assess the structure under a basalt layer. Pre-stack depth migration produced an improved image which recovered the main features in the stacked section and allowed to identify some subbasalt coherent events.

Particle size distributions by laser diffraction – Part 1: Sensitivity of granular matter strength to analytical operating procedures

Mon, 21 Dec 2009 00:00:00 +0100

Particle size distributions by laser diffraction – Part 1: Sensitivity of granular matter strength to analytical operating procedures

Solid Earth Discussions, 1, 93-141, 2009

Author(s): F. Storti and F. Balsamo

We tested laser diffraction particle size analysis in poorly coherent carbonate platform cataclastic breccias and unfaulted quartz-rich eolian sands, representing low- and high-strength granular materials, respectively. We used two different instruments with different sample dispersion and pumping systems and several wet and dry analytical procedures that included different pump speeds, measure precision tests with and without sample ultrasonication, and different dispersant liquids. Results of our work indicate that high strength material is not strongly affected by analytical operating procedures, whereas low strength material is very sensitive to the pump speed, ultrasonication intensity, and measurement run time. To reduce such a data variability, we propose a workflow for analytical tests preliminary to the set up of the most appropriate SOP.

The Gregoriev Ice Cap length changes derived by 2-D ice flow line model for harmonic climate histories

Wed, 02 Dec 2009 00:00:00 +0100

The Gregoriev Ice Cap length changes derived by 2-D ice flow line model for harmonic climate histories

Solid Earth Discussions, 1, 55-91, 2009

Author(s): Y. V. Konovalov and O. V. Nagornov

Different ice thickness distributions along the flow line and the flow line length changes of the Gregoriev Ice Cap, Terskey Ala-Tau, Central Asia, were obtained for some surface mass balance histories which can be considered as possible surface mass balances in the future. The ice cap modeling was performed by solving of steady state hydrodynamic equations in the case of low Reynolds number in the form of the mechanical equilibrium equation in terms of stress deviator components coupled with the continuity equation for incompressible fluid. The numerical solution was obtained by the finite difference method. A compound approximation of the ice surface boundary condition based on the extending of the mechanical equilibrium equation to ice surface points was applied. The approximation is considered as a way to overcome the problem of diagnostic equations numerical solution stability in the full model.

The basal sliding can arise in the glacier tongue at certain climatic conditions and was introduced both through linear and through non-linear friction laws.

A possible glacier length history, that corresponds to the regional climate changes derived from the tree-rings data, was obtained by the model.

The correlations between the glacier length changes and annual air temperature histories were investigated within the simplified equation introduced by J. Oerlemans in the form of linear dependence of annual air temperature versus glacier length and time derivative of the length. The parameters of the dependence were derived from modeled glacier length histories that correspond to harmonic climate histories. The parameters variations were investigated for different periodicities of harmonic climate histories and appropriate dependences are presented in the paper. The results of the modeling are in a good agreement with the J. Oerlemans climatic model.

The Eons of Chaos and Hades

Tue, 24 Nov 2009 00:00:00 +0100

The Eons of Chaos and Hades

Solid Earth Discussions, 1, 47-53, 2009

Author(s): C. Goldblatt, K. J. Zahnle, N. H. Sleep, and E. G. Nisbet

We propose the Chaotian Eon to demarcate geologic time from the origin of the Solar System to the Moon-forming impact on Earth. This separates the solar system wide processes of planet formation from the subsequent divergent evolution of the inner planets. We further propose the division of the Hadean Eon into eras and periods and naming the proto-Earth Tellus.

Earth's surface heat flux

Tue, 24 Nov 2009 00:00:00 +0100

Earth's surface heat flux

Solid Earth Discussions, 1, 1-45, 2009

Author(s): J. H. Davies and D. R. Davies

We present a revised estimate of Earth's surface heat flux that is based upon a heat flow data-set with 38 347 measurements, which is 55% more than used in previous estimates. Our methodology, like others, accounts for hydrothermal circulation in young oceanic crust by utilising a half-space cooling approximation. For the rest of Earth's surface, we estimate the average heat flow for different geologic domains as defined by global digital geology maps; and then produce the global estimate by multiplying it by the total global area of that geologic domain. The averaging is done on a polygon set which results from an intersection of a 1 degree equal area grid with the original geology polygons; this minimises the adverse influence of clustering. These operations and estimates are derived accurately using methodologies from Geographical Information Science. We consider the virtually un-sampled Antarctica separately and also make a small correction for hot-spots in young oceanic lithosphere. A range of analyses is presented. These, combined with statistical estimates of the error, provide a measure of robustness. Our final preferred estimate is 47±2 TW, which is greater than previous estimates.