Titov O.,Geoscience Australia
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010
The gravitational attraction of the Galactic Centre leads to the centrifugal acceleration of the Solar system barycentre. It results in secular aberration drift which displaces the position of the distant radio sources. The effect should be accounted for in high-precision astrometric reductions as well as by the corresponding update of the International Celestial Reference System definition. © 2010 Commonwealth of Australia as represented by Geoscience Australia. Journal compilation © 2010 RAS.
Leonard M.,Geoscience Australia
Bulletin of the Seismological Society of America | Year: 2010
In this paper, I propose the scaling relation W = C 1L β (where [β ≈ 2/3) to describe the scaling of rupture width with rupture length. I also propose a new displacement relation D̄ = C 2√A, where A is the area (LW). By substituting these equations into the definition of seismic moment (M 0 =μDLW), I have developed a series of self-consistent equations that describe the scaling between seismic moment, rupture area, length, width, and average displacement. In addition to β, the equations have only two variables, C 1 and C 2, which have been estimated empirically for different tectonic settings. The relations predict linear log-log relationships, the slope of which depends only on β. These new scaling relations, unlike previous relations, are self-consistent, in that they enable moment, rupture length, width, area, and displacement to be estimated from each other and with these estimates all being consistent with the definition of seismic moment. I interpret C 1 as depending on the size at which a rupture transitions from having a constant aspect ratio to following a power law and C 1 as depending on the displacement per unit area of fault rupture and so static stress drop. It is likely that these variables differ between tectonic environments; this might explain much of the scatter in the empirical data. I suggest that these relations apply to all faults. For small earthquakes (M < ~5)β=1, in which case L 3 fault scaling applies. For larger (M > ~5) earthquakes β 2=3, so L 2.5 applies. For dip-slip earthquakes this scaling applies up to the largest events. For very large (M >~7.2) strike-slip earthquakes, which are fault widthlimited, β = 0 and assuming D ∞ √A, then L 1.5 scaling applies. In all cases, M 0 ∞ A 1.5 fault scaling applies.
Minty B.R.S.,Geoscience Australia
Geophysics | Year: 2011
Many countries have significant coverage of publicly funded airborne magnetic and gamma-ray spectrometric surveys that are available to explorers as precompetitive information to encourage exploration. However, individual surveys are generally small, and after decades of data acquisition, explorers are faced with the problem of how to effectively combine the individual surveys into coherent regional compilations. The Australian government's response was to fly a baseline survey over the whole of Australia at approximately 75-km flight line spacing. This has enabled all of Australia's public-domain magnetic and gamma-ray spectrometric surveys to be leveled to common datums using new techniques facilitated by the baseline control provided by the new traverses. This adds significant value to these data, as they can now be used for the interpretation of regional-scale features and for direct comparison of geophysical signatures from different parts of the continent. Also, quantitative modeling and analysis of the data can now be carried out over much larger areas. © 2011 Society of Exploration Geophysicists.
Byrne M.,University of Sydney |
Przeslawski R.,Geoscience Australia
Integrative and Comparative Biology | Year: 2013
Benthic marine invertebrates live in a multistressor world where stressor levels are, and will continue to be, exacerbated by global warming and increased atmospheric carbon dioxide. These changes are causing the oceans to warm, decrease in pH, become hypercapnic, and to become less saturated in carbonate minerals. These stressors have strong impacts on biological processes, but little is known about their combined effects on the development of marine invertebrates. Increasing temperature has a stimulatory effect on development, whereas hypercapnia can depress developmental processes. The pH, pCO 2, and CaCO3 of seawater change simultaneously with temperature, challenging our ability to predict future outcomes for marine biota. The need to consider both warming and acidification is reflected in the recent increase in cross-factorial studies of the effects of these stressors on development of marine invertebrates. The outcomes and trends in these studies are synthesized here. Based on this compilation, significant additive or antagonistic effects of warming and acidification of the ocean are common (16 of 20 species studied), and synergistic negative effects also are reported. Fertilization can be robust to near-future warming and acidification, depending on the male-female mating pair. Although larvae and juveniles of some species tolerate near-future levels of warming and acidification (+2C/pH 7.8), projected far-future conditions (ca. 4C/pH 7.6) are widely deleterious, with a reduction in the size and survival of larvae. It appears that larvae that calcify are sensitive both to warming and acidification, whereas those that do not calcify are more sensitive to warming. Different sensitivities of life-history stages and species have implications for persistence and community function in a changing ocean. Some species are more resilient than others and may be potential "winners" in the climate-change stakes. As the ocean will change more gradually over coming decades than in "future shock" perturbation investigations, it is likely that some species, particularly those with short generation times, may be able to tolerate near-future oceanic change through acclimatization and/or adaption. © 2013 The Author. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved.
Wilford J.,Geoscience Australia
Geoderma | Year: 2012
Weathering intensity largely controls the degree to which primary minerals are altered to secondary components including clay minerals and oxides. As weathering intensity increases there are changes in the hydrological, geochemical and geophysical characteristics of the regolith. Thus, once calibrated, weathering intensity can be used to predict a range of regolith properties. A weathering intensity index (WII) over the Australian continent has been developed at a 100. m resolution using regression models based on airborne gamma-ray spectrometry imagery and the Shuttle Radar Topography Mission (SRTM) elevation data. Airborne gamma-ray spectrometry measures the concentration of three radioelements - potassium (K), thorium (Th) and uranium (U) at the Earth's surface. The total gamma-ray flux (dose) is also calculated based on the weighted additions of the three radioelements. Regolith accounts for over 85% of the Australian land area and has a major influence in determining the composition of surface materials and in controlling hydrological and geomorphological processes. The weathering intensity prediction is based on the integration of two regression models. The first uses relief over landscapes with low gamma-ray emissions and the second incorporates radioelement distributions and relief. The application of a stepwise forward multiple regression for the second model generated a weathering intensity index equation of: WII = 6.751 + - 0.851 * K + - 1.319 * Relief + 2.682 * Th/K + - 2.590 * Dose. The WII has been developed for erosional landscapes but also has the potential to inform on deposition processes and materials. The WII correlates well with site based geochemical indices and existing regolith mapping. Interpretation of the WII from regional to local scales and its application in providing more reliable and spatially explicit information on regolith properties are described. © 2012.