142 research outputs found
Improved mapping functions for atmospheric refraction correction in SLR
[1] We present two new mapping functions (MFs) to model the elevation angle dependence of the atmospheric delay for satellite laser ranging (SLR) data analysis. The new MFs were derived from ray tracing through a set of data from 180 radiosonde stations globally distributed, for the year 1999, and are valid for elevation angles above 3degrees. When compared against ray tracing of two independent years of radiosonde data (1997-1998) for the same set of stations, our MFs reveal submillimetre accuracy for elevation angles above 10degrees, representing a significant improvement over other MFs, and is confirmed in improved solutions of LAGEOS and LAGEOS 2 data analysis.info:eu-repo/semantics/publishedVersio
Testing General Relativity with Satellite Laser Ranging: Recent Developments
In this paper the most recent developments in testing General Relativity in
the gravitational field of the Earth with the technique of Satellite Laser
Ranging are presented. In particular, we concentrate our attention on some
gravitoelectric and gravitomagnetic post--Newtonian orbital effects on the
motion of a test body in the external field of a central mass.Comment: Latex2e, 10 pages, no figures, no tables. Paper presented at
COSPAR2002 conference held in Houston, TX, from 10 October 2002 to 19 October
2002. To appear in Advance in Space Research. References added and update
A comparison of robust polynomial fitting, global geopotential model and spectral analysis for regionalâresidual gravity field separation in the Doñana National Park (Spain)
Doñana National Park is a protected area of approximately 500 km2 located on the SW coast of Spain with
singular and interesting ecological and geological features. A gravimetric survey is presented where L&R
gravity metres were used in the gravimetric observations with GPS and high-precision levelling positioning.
Bouguer gravity anomalies were computed and least squares prediction was used for gross-error detection.
Robust polynomial fitting, the recent EGM2008 global geopotential model (complete to degree and order
2159), and spectral analysis were tested for regionalâresidual gravity field separation. A detailed description
of the gravimetric characteristics of the Doñana National Park is presented and the values of residual gravity
anomalies were correlated with geological features, where the use of the EGM2008 global geopotential model
has revealed an interesting tool for regionalâresidual gravity field separation. Finally, the interpretation of the
results is justified by the well-known geological aspects of the park, but some modifications in the boundaries
of the different geological features are needed in order to fit the modelled gravity with the residual gravity
anomalies in the two cross-sections analysed.The studies presented here were part of CICYT (Spanish Research Directorate) research project nos. HID 97-0321 and REN2001-1293. We would like to thank all UPC members participating in these projects and the staff from the Biological Station of Donana (CSIC), Palacio de Donana and Donana National Park. We remain deeply grateful for the fruitful discussion with Dr. Salvany and for the geological review of the manuscript.MartĂn Furones, ĂE.; Nuñez AndrĂ©s, M.; Gili, J.; Anquela JuliĂĄn, AB. (2011). A comparison of robust polynomial fitting, global geopotential model and spectral analysis for regionalâresidual gravity field separation in the Doñana National Park (Spain). Journal of Applied Geophysics. 75(2):327-337. https://doi.org/10.1016/j.jappgeo.2011.06.037S32733775
Reconstruction of the Talkeetna intraoceanic arc of Alaska through thermobarometry
Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): B03204, doi:10.1029/2007JB005208.The Talkeetna arc is one of two intraoceanic arcs where much of the section from the upper mantle through the volcanic carapace is well exposed. We reconstruct the vertical section of the Talkeetna arc by determining the (re)crystallization pressures at various structural levels. The thermobarometry shows that the tonalites and quartz diorites intruded at âŒ5â9 km into a volcanic section estimated from stratigraphy to be 7 km thick. The shallowest, Tazlina and Barnette, gabbros crystallized at âŒ17â24 km; the Klanelneechena Klippe crystallized at âŒ24â26 km; and the base of the arc crystallized at âŒ35 km depth. The arc had a volcanic:plutonic ratio of âŒ1:3â1:4. However, many or most of the felsic plutonic rocks may represent crystallized liquids rather than cumulates so that the liquid:cumulate ratio might be 1:2 or larger. The current 5- to 7-km structural thickness of the plutonic section of the arc is âŒ15â30% of the original 23- to 28-km thickness. The bulk composition of the original Talkeetna arc section was âŒ51â58 wt % SiO2.Funded by NSF EAR-9910899
Feedback between deformation and magmatism in the Lloyds River Fault Zone : an example of episodic fault reactivation in an accretionary setting, Newfoundland Appalachians
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Tectonics 25 (2006): TC4004, doi:10.1029/2005TC001789.The Lloyds River Fault Zone is a 10â15 km wide amphibolite-grade shear zone that formed during the Ordovician Taconic Orogeny. It separates ophiolites and arcâback-arc complexes formed in Iapetus from a peri-Laurentian microcontinent (Dashwoods microcontinent). The Lloyds River Fault Zone comprises three high-strain zones, dominantly composed of mylonitic amphibolites, separated by less deformed plutonic rocks. Structural, age and metamorphic data suggest the Lloyds River Fault Zone accommodated sinistral-oblique underthrusting of ophiolites underneath the Dashwoods microcontinent prior to 471 ± 5 Ma at 800°C and 6 kbar. Plutonic rocks within the Lloyds River Fault Zone comprise two suites dated at 464 ± 2 plus 462 ± 2 and 459 ± 3 Ma, respectively. The younger age of the plutons with respect to some of the amphibolites, evidence for magmatic deformation, and the elongate nature of the plutons parallel to the Lloyds River Fault Zone suggest they were emplaced within the fault zone during deformation. Both intrusive episodes triggered renewed deformation at high temperatures (770â750°C), illustrating the positive feedback between deformation and magmatism. Offshoots of the plutons intruded undeformed ophiolitic gabbros outside the Lloyds River Fault Zone. Deformation localized within the intrusive sheets, coeval with static contact metamorphism of the host gabbros, leading to the development of new, small-scale shear zones. This illustrates that channeling of plutons into shear zones and nucleation of shear zones in melt-rich zones may occur simultaneously within the same fault system.This research is funded by a scholarship
from the Faculty of Graduate and Postdoctoral Studies, University of
Ottawa, to C.J.L. and a NSERC grant to C.v.S in his position as Adjunct
Professor at the University of Ottawa
Error sources and data limitations for the prediction ofsurface gravity: a case study using benchmarks
Gravity-based heights require gravity values at levelled benchmarks (BMs), whichsometimes have to be predicted from surrounding observations. We use EGM2008 andthe Australian National Gravity Database (ANGD) as examples of model and terrestrialobserved data respectively to predict gravity at Australian national levelling network(ANLN) BMs. The aim is to quantify errors that may propagate into the predicted BMgravity values and then into gravimetric height corrections (HCs). Our results indicatethat an approximate ±1 arc-minute horizontal position error of the BMs causesmaximum errors in EGM2008 BM gravity of ~ 22 mGal (~55 mm in the HC at ~2200 melevation) and ~18 mGal for ANGD BM gravity because the values are not computed atthe true location of the BM. We use RTM (residual terrain modelling) techniques toshow that ~50% of EGM2008 BM gravity error in a moderately mountainous regioncan be accounted for by signal omission. Non-representative sampling of ANGDgravity in this region may cause errors of up to 50 mGals (~120 mm for the Helmertorthometric correction at ~2200 m elevation). For modelled gravity at BMs to beviable, levelling networks need horizontal BM positions accurate to a few metres, whileRTM techniques can be used to reduce signal omission error. Unrepresentative gravitysampling in mountains can be remedied by denser and more representative re-surveys,and/or gravity can be forward modelled into regions of sparser gravity
Phenomenology of the Lense-Thirring effect in the Solar System
Recent years have seen increasing efforts to directly measure some aspects of
the general relativistic gravitomagnetic interaction in several astronomical
scenarios in the solar system. After briefly overviewing the concept of
gravitomagnetism from a theoretical point of view, we review the performed or
proposed attempts to detect the Lense-Thirring effect affecting the orbital
motions of natural and artificial bodies in the gravitational fields of the
Sun, Earth, Mars and Jupiter. In particular, we will focus on the evaluation of
the impact of several sources of systematic uncertainties of dynamical origin
to realistically elucidate the present and future perspectives in directly
measuring such an elusive relativistic effect.Comment: LaTex, 51 pages, 14 figures, 22 tables. Invited review, to appear in
Astrophysics and Space Science (ApSS). Some uncited references in the text
now correctly quoted. One reference added. A footnote adde
New Insight on the Increasing Seismicity during Tenerife's 2004 Volcanic Reactivation
Starting in April 2004, unusual seismic activity was observed in the interior
of the island of Tenerife (Canary Islands, Spain) with much evidence pointing
to a reawakening of volcanic activity. This seismicity is now analyzed with
techniques unprecedented in previous studies of this crisis. The 200
earthquakes located onshore during 2004 and 2005 have been classified by
cross-correlation, resulting in a small number of significant families. The
application of a relative location algorithm (hypoDD) revealed important
features about the spatial distribution of the earthquakes. The seismic
catalogue has been enhanced with more than 800 additional events, detected only
by the closest seismic station. These events were assigned to families by
correlation and as a consequence their hypocentral location and magnitude were
estimated by comparing them to the earthquakes of each family. The new
catalogue obtained by these methods identifies two major seismogenic zones, one
to the northwest and the other to the southwest of the Teide-Pico Viejo complex
and having a separation of at least 10 km between them. These regions alternate
their activity starting in January 2004, i.e., three months earlier than
previously thought. We propose a simple model based on the results of this work
which will also concur with all previous geophysical and geochemical studies of
the 2004 crisis. The model proposes a single magma intrusion affecting the
central part of the island with lateral dikes driven by the rifts to the
northwest and southwest.Comment: 20 pages, 15 figure
Effects of crystallographic anisotropy on fracture development and acoustic emission in quartz
Transgranular microcracking is fundamental for the initiation and propagation of all fractures in rocks. The geometry of these microcracks is primarily controlled by the interaction of the imposed stress field with the mineral elastic properties. However, the effects of anisotropic elastic properties of minerals on brittle fracture are not well understood. This study examines the effects of elastic anisotropy of quartz on the geometry of brittle fracture and related acoustic emissions (AE) developed during indentation experiments on single crystals at ambient pressure and temperature. A Hertzian cone crack developed during blunt indentation of a single crystal of flawless Brazilian quartz parallel to the c axis shows geometric deviation away from predictions based on the isotropic case, consistent with trigonal symmetry. The visible cone crack penetration depth varies from 3 to 5 mm and apical angle from 53 to 40. Electron backscatter diffraction (EBSD) mapping of the crack tip shows that fracturing initiates along a ~40 ÎŒm wide process zone, comprising damage along overlapping en echelon high-index crystallographic planes, shown by discrete bands of reduced electron backscatter pattern (EBSP) quality (band contrast).Coalescence of these surfaces results in a stepped fracture morphology. Monitoring of AE during indentation reveals that the elastic anisotropy of quartz has a significant effect on AE location and focal mechanisms. Ninety-four AE events were recorded during indentation and show an increasing frequency with increasing load. They correspond to the development of subsidiary concentric cracks peripheral to the main cone crack. The strong and complex anisotropy in seismic velocity (~28% Vp, ~43% Vs with trigonal symmetry) resulted in inaccurate and high uncertainty in AE locations using Geiger location routine with an isotropic velocity model. This problem was overcome by using a relative (master event) location algorithm that only requires a priori knowledge of the velocity structure within the source volume. The AE location results correlate reasonably well to the extent of the observed cone crack. Decomposition of AE source mechanisms of the Geiger relocated events shows dominantly end-member behavior between tensile and compressive vector dipole events, with some double-couple-dominated events and no purely tensile or compressive events. The same events located by the master event algorithm yield greater percentage of vector dipole components and no double-couple events, indicating that AE source mechanism solutions can depend on AE location accuracy, and therefore, relocation routine that is utilized. Calculations show that the crystallographic anisotropy of quartz causes apparent deviation of the moment tensors away from double-couple and pure tensile/compressive sources consistent with the observations. Preliminary modeling of calcite anisotropy shows a response distinct from quartz, indicating that the effects of anisotropy on interpreting AE are complex and require detailed further study
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