MTfit: A Bayesian approach to seismic moment tensor inversion

MTfit is a Python module for Bayesian moment tensor source inversion of earthquake seismic data using polarities, amplitudes or amplitude ratios. It can solve for double couple or full moment tensor solutions, taking into account uncertainties in polarities, take-off angles of the rays from the source to the receiver, and amplitudes. It provides an easily accessible and extendable approach to earthquake source inversion which is particularly useful for local and regional events.The MTfit code was developed as part of a PhD project (Pugh 2015), funded under a Natural Environment Research Council (NERC) studentship at the University of Cambridge, as a CASE award with Schlumberger. Seismometers were borrowed from the NERC SEIS-UK (loan 842)

Securing a sustainable phosphorus future for Australia: implications of global phosphorus scarcity and possible solutions

Food production is fundamentally dependent on inputs of key natural resources, including water, energy and nutrients. Meeting the needs of a growing world population means agricultural fields will need to expand or intensify, either way requiring more fertilisers, including phosphorus (FAO, 2006). Unlike energy and water resources, there is very little discussion, research and policies that addresses long-term availability and accessibility of phosphorus for global food production. Yet the worlds main source of phosphorus phosphate rock is declining in both quantity and quality. Indeed, peak phosphorus is anticipated in the coming decades, after which demand will exceed supp

Automatic Bayesian polarity determination

The polarity of the first motion of a seismic signal from an earthquake is an important constraint in earthquake source inversion. Microseismic events often have low signal-to-noise ratios, which may lead to difficulties estimating the correct first-motion polarities of the arrivals. This paper describes a probabilistic approach to polarity picking that can be both automated and combined with manual picking. This approach includes a quantitative estimate of the uncertainty of the polarity, improving calculation of the polarity probability density function for source inversion. It is sufficiently fast to be incorporated into an automatic processing workflow. When used in source inversion, the results are consistent with those from manual observations. In some cases, they produce a clearer constraint on the range of high-probability source mechanisms, and are better constrained than source mechanisms determined using a uniform probability of an incorrect polarity pick.This work was funded under a Natural Environment Research Council (NERC) studentship as a CASE award with Schlumberger. Seismometers were borrowed from the NERC SEIS-UK (loan 842), who also archive the data.This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1093/gji/ggw146

A Bayesian method for microseismic source inversion

Earthquake source inversion is highly dependent on location determination and velocity models. Uncertainties in both the model parameters and the observations need to be rigorously incorporated into an inversion approach. Here, we show a probabilistic Bayesian method that allows formal inclusion of the uncertainties in the moment tensor inversion. This method allows the combination of different sets of far-field observations, such as P-wave and S-wave polarities and amplitude ratios, into one inversion. Additional observations can be included by deriving a suitable likelihood function from the uncertainties. This inversion produces samples from the source posterior probability distribution, including a best-fitting solution for the source mechanism and associated probability. The inversion can be constrained to the double-couple space or allowed to explore the gamut of moment tensor solutions, allowing volumetric and other non-double-couple components. The posterior probability of the double-couple and full moment tensor source models can be evaluated from the Bayesian evidence, using samples from the likelihood distributions for the two source models, producing an estimate of whether or not a source is double-couple. Such an approach is ideally suited to microseismic studies where there are many sources of uncertainty and it is often difficult to produce reliability estimates of the source mechanism, although this can be true of many other cases. Using full-waveform synthetic seismograms, we also show the effects of noise, location, network distribution and velocity model uncertainty on the source probability density function. The noise has the largest effect on the results, especially as it can affect other parts of the event processing. This uncertainty can lead to erroneous non-double-couple source probability distributions, even when no other uncertainties exist. Although including amplitude ratios can improve the constraint on the source probability distribution, the measurements are often systematically affected by noise, leading to deviation from their noise-free true values and consequently adversely affecting the source probability distribution, especially for the full moment tensor model. As an example of the application of this method, four events from the Krafla volcano in Iceland are inverted, which show clear differentiation between non-double-couple and double-couple sources, reflected in the posterior probability distributions for the source models.NERCThis is the final version of the article. It first appeared from Oxford University Press via https://doi.org/10.1093/gji/ggw186

Temperature effects on mass-scaling exponents in colonial animals: a manipulative test

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.All data and code necessary to reproduce this paper, its analyses, tables and figures can be obtained on GitHub https://github.com/dbarneche/MTRBrEs (Barneche et al. 2016a, doi: 10.5281/zenodo.159736)Body size and temperature are fundamental drivers of ecological processes because they determine metabolic rates at the individual level. Whether these drivers act independently on individual‐level metabolic rates remains uncertain. Most studies of intraspecific scaling of unitary organisms must rely on preexisting differences in size to examine its relationship with metabolic rate, thereby potentially confounding size‐correlated traits (e.g., age, nutrition) with size, which can affect metabolic rate. Here, we use a size manipulation approach to test whether metabolic mass scaling and temperature dependence interact in four species (two phyla) of colonial marine invertebrates. Size manipulation in colonial organisms allows tests of how ecological processes (e.g., predation) affect individual physiology and consequently population‐ and community‐level energy flux. Body mass and temperature interacted in two species, with one species exhibiting decreased and the other increased mass‐scaling exponents with increasing temperature. The allometric scaling of metabolic rate that we observe in three species contrasts with the isometric scaling of ingestion rates observed in some colonial marine invertebrates. Thus, we suggest that the often observed competitive superiority of colonial over unitary organisms may arise because the difference between energy intake and expenditure increases more strongly with size in colonial organisms.Australian Research Counci

Review of the National Packaging Covenant

The NSW Nature Conservation Council, with funding from the NSW Department of Environment and Conservation, commissioned the Institute for Sustainable Futures at the University of Technology, Sydney, to carry out an independent review of the National Packaging Covenant and the National Environmental Protection Measure for Used Packaging Materials (the Covenant systema), in December 2003. This review was intended to evaluate the Covenant system's effectiveness in achieving both its stated objectives and broader environmental and social outcomes, including reduction in generation of packaging waste, specifically reduction in virgin materials used in packaging and a reduction in packaging material disposed to landfill. The National Packaging Covenant (NPC) is a voluntary agreement between industry, the Commonwealth Government, most State Governments and some local governments, to reduce packaging waste. It is supported by a regulatory measure, the National Environmental Protection Measure (NEPM), designed to encourage brand owners to sign the NPC. The NPC came into effect in August 1999 and is due to finish in July 2004. It is currently the subject of three separate reviews, including this one. The principle of a cooperative regulatory framework supported by a regulatory safety net is an appealing one, so there is a strong desire on the part of industry and some government agencies to provide the maximum possible opportunity for the NPC to demonstrate that it has provided benefits. This review has determined that the Covenant system is not an effective instrument for reducing the generation of packaging waste and therefore an alternative policy framework will be needed to achieve this goal. The evaluation is briefly summarised for each of the criteria

Revolution in acute ischaemic stroke care: a practical guide to mechanical thrombectomy

Rapid, safe and effective arterial recanalisation to restore blood flow and improve functional outcome remains the primary goal of hyperacute ischaemic stroke management. The benefit of intravenous thrombolysis with recombinant tissue-type plasminogen activator for patients with severe stroke due to large artery occlusion is limited; early recanalisation is generally less than 30% for carotid, proximal middle cerebral artery or basilar artery occlusion. Since November 2014, nine positive randomised controlled trials of mechanical thrombectomy for large vessel occlusion in the anterior circulation have led to a revolution in the care of patients with acute ischaemic stroke. Its efficacy is unmatched by any previous therapy in stroke medicine, with a number needed to treat of less than 3 for improved functional outcome. With effectiveness shown beyond any reasonable doubt, the key challenge now is how to implement accessible, safe and effective mechanical thrombectomy services. This review aims to provide neurologists and other stroke physicians with a summary of the evidence base, a discussion of practical aspects of delivering the treatment and future challenges. We aim to give guidance on some of the areas not clearly described in the clinical trials (based on evidence where available, but if not, on our own experience and practice) and highlight areas of uncertainty requiring further research

Effects of participation in and connectedness to the LGBT community on substance use involvement of sexual minority young people

© 2018 Elsevier Ltd Introduction: Research shows disproportionate levels of substance use among sexual minority young people. A range of reasons for these disparities have been suggested, including connectedness to and participation in the LGBT community. Little is known about how these constructs are related to substance use involvement in sexual minority (sub)groups or how these relationships are affected by other factors. Methods: 1266 young sexual minority Australians completed a cross-sectional online survey. Multiple regressions were conducted to assess associations between connectedness to and participation in the LGBT community on substance use involvement, before and after controlling for other factors such as substance use motives, psychological distress, wellbeing, resilience, minority stress, and age. Results/conclusion: Most participants identified as homosexual (57%, n = 726) and male (54%, n = 683). In the overall sample, participation in and connectedness the LGBT community were significantly associated with increased substance use involvement before (F(2,1263) = 35.930, p ≤ 0.001, R 2 = 0.052) and after controlling for other variables (F(8,1095) = 33.538, p ≤ 0.001, R 2 = 0.191), with meaningfully higher effect sizes for participation than for connectedness. After controlling for other variables, connectedness only remained significant for homosexuals. Effect sizes for participation were higher for females than males, and bisexuals than homosexuals. However, participation in the LGBT Community was not associated with substance use in participants identifying with a non-binary gender identity. In conclusion, substance use involvement was associated with participation in the LGBT community, but connectedness to the LGBT community only had a weak association with substance use involvement in the homosexual subgroup