To compare the attitudes towards common intensive care triage scenarios in New Zealand and Austra... more To compare the attitudes towards common intensive care triage scenarios in New Zealand and Australia and to evaluate Australasian intensive care triage practice. A web-based survey of Australian and New Zealand intensive care doctors measuring demographics, details of recent triage decisions and attitudes towards various triage scenarios. A total of 238 responses were obtained (32.6% response rate). The mean number of triage decisions was 6.3 per clinician per week in New Zealand (95%CI 4.6-8.0) and 8.5 per week in Australia (95% CI 6.6-10.4) (test for difference in means, p=0.08). The mean rate of refusal for the week prior to the survey was 30.8% (95%CI 19.5-42.1) among New Zealand respondents and 25.1% (95% CI 19.7-30.4) among Australian respondents (test for difference in proportions, p=0.35). Australian respondents were more likely than New Zealand respondents to agree that it was appropriate to admit a patient: - with a non-survivable brain injury who may progress to brain dea...
To investigate the extent of current problem gambling in New Zealand, and the risk factors, addic... more To investigate the extent of current problem gambling in New Zealand, and the risk factors, addictive behaviours, and self-rated health status associated with problem gambling. Analysis of the gambling questions from the 2002/03 New Zealand Health Survey, which interviewed 12,529 people aged 15 years and over, and included increased sampling of Maori, Pacific, and Asian people. Approximately 1.2% (95% confidence interval: 1.0-1.5) of the New Zealand adult population were found to be current problem gamblers, representing an estimated 32,800 (26,200-39,400) people. Risk factors for problem gambling included being of Maori or Pacific ethnicity, being aged 25-34 years, living alone, being employed, and being less qualified. Problem gambling was significantly associated with potentially hazardous drinking behaviour, daily cigarette smoking, and worse self-rated health, as measured on several SF-36 health domains. Maori and Pacific peoples were at significantly greater risk of being problem gamblers than other people, particularly among those people who gambled. Associations between gambling problems and health problems and/or risk behaviours suggest compounded problems from comorbidity. This evidence may be useful in informing policy and public health programmes to reduce the harmful impact of problem gambling on individuals and communities, and in addressing the inequalities evident in gambling-related harm.
... 55 4.17 Lomb-Scargle Periodogram for EC20058-5234 (18 Jun 1999) sam-pled at ∆ Ωºººpoints. ...... more ... 55 4.17 Lomb-Scargle Periodogram for EC20058-5234 (18 Jun 1999) sam-pled at ∆ Ωºººpoints. ... in this wide temperature range are pulsators, however, and there seem to be several different classes of pulsat-ing White Dwarfs and hot subdwarfs (Vauclair, Moskalik, Pfeiffer & ...
A sequence of four earthquakes of magnitude 6.0-6.5 struck the South Iceland Seismic Zone (SISZ) ... more A sequence of four earthquakes of magnitude 6.0-6.5 struck the South Iceland Seismic Zone (SISZ) between June 2000 and May 2008, just over one hundred years since a similar sequence of five large earthquakes occurred in the area in 1896. Large earthquakes typically occur in the east-west-trending SISZ as right-lateral strike-slip events on north-south-striking faults. During both the 2000-2008 and 1896 sequences, earthquake activity migrated westward along the SISZ, with the May 2008 earthquake doublet striking only 10 kilometres away from the Hengill triple junction. We have examined stress parameters derived from a large catalog of earthquake focal mechanism data obtained during routine analysis of data recorded by the Icelandic SIL network since 1991. The focal mechanism catalogue for south Iceland contains more than 100,000 events larger than M~-1. Stress inversion using focal mechanism data yields the orientations of the three principal stresses and a measure of the relative magnitude of the intermediate principal stress. We use both a probabilistic (Bayesian) stress estimation algorithm (Arnold and Townend, 2007) and a grid search based inversion scheme adapted to the uncertainty estimates available for each SIL focal mechanism (Lund and Slunga, 1999) to compute the four resolvable stress parameters at different points in space and time. In order to discriminate spatial and temporal variations in stress, we subdivide the focal mechanism catalog on the basis of time and estimate the stress parameters at each epoch at fixed locations. In this presentation we report on spatial and temporal variations in stress during the 1991-2010 period, concentrating on the source areas of the M6+ events. Preliminary results indicate a stress change in the area of the June 17, 2000, earthquake prior to the event, and resolvable spatial stress variations in the aftershock sequences of the June 2000 events.
Earthquakes provide a key means of estimating tectonic stress at seismogenic depths, and thereby ... more Earthquakes provide a key means of estimating tectonic stress at seismogenic depths, and thereby of investigating directly the mechanisms by which faults slip during earthquakes and interact. To date, however, stress estimation algorithms have not provided sufficiently reliable uncertainty estimates to enable the detection of fine temporal or spatial variations in stress. We have developed a probabilistic (Bayesian) technique for estimating tectonic stress directions from routine seismological observations. The Bayesian approach combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationships between the stresses acting on a fault, slip during an earthquake, and the observed seismic waves. We first quantify the constraints on the four determinable stress tensor parameters imposed by a single focal mechanism in terms of a joint probability density function. Next, we formalise the process of estimating stress tensor parameters from a number of such mechanisms by combining the corresponding probability density functions. We explicitly include the limitation that, in general, the two nodal planes of a given focal mechanism cannot be unambiguously distinguished and are invariably subject to measurement error. Our formulation is equivalent to a well-known analytical solution for a single, errorless focal mechanism observation (McKenzie, BSSA, 59, 1969). The new approach has the distinct advantage, however, that including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors, and (4) prior knowledge of the stress field is mathematically tractable, albeit computationally intensive. Our approach is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, including seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations.
We develop a new probabilistic (Bayesian) method for estimating the distribution of focal mechani... more We develop a new probabilistic (Bayesian) method for estimating the distribution of focal mechanism parameters based on seismic wave polarity data. We investigate the use of generalised Matrix Fisher distributions for parameterising focal mechanism uncertainties. The advantages of our approach are that it (1) models the data generation process and incorporates observational errors, particularly those arising from imperfectly known earthquake locations; (2) allows exploration of the entire parameter space; (3) leads to natural point estimates of focal mechanism parameters; (4) allows the inclusion of a priori information about the focal mechanism parameters; and (5) that the resulting posterior probability density function (PDF) can be well approximated by generalised Matrix Fisher distributions. We present here the results of our method in two situations. We first consider the case in which the seismic velocity of the region of interest (described by a velocity model) is presumed to be precisely known, with application to seismic data from the Raukumara Peninsula, New Zealand. We then consider the case in which the velocity model is imperfectly known, with application to data from the Kawerau region, New Zealand. We find that our estimated focal mechanism solutions are for the most part consistent with all available polarity data, and correspond closely to solutions obtained using established methods. Further, the generalised Matrix Fisher distributions we examine provide a good fit to our Bayesian posterior PDF of the focal mechanism parameters. Finally, we demonstrate how informative prior distributions on focal mechanism parameters can be incorporated into our model.
Recent research has developed a group of likelihood-based finite mixture models for a data matrix... more Recent research has developed a group of likelihood-based finite mixture models for a data matrix with ordinal data, establishing likelihood-based multivari-ate methods which applies fuzzy clustering via finite mixtures to the ordered stereotype model. There are many visualisation tools which depict reduction of dimensionality in matrices of ordinal data. This technical report introduces the spaced mosaic plot which is one new graphical tool for ordinal data when the ordinal stereotype model is used. It takes advantage of the fitted score parameters to determine the spacing between two adjacent ordinal categories. We develop a function in R and its documentation is presented. Finally, the description of a spaced mosaic plot is shown.
... RICHARD ARNOLD & LAURIE BAUER ... as a descrip-tion of the relationship betwe... more ... RICHARD ARNOLD & LAURIE BAUER ... as a descrip-tion of the relationship between the number of languages n in a language family, and the rank r of that family in a list ordered by decreasing n. Two datasets are used by Wichmann, one from Ethnologue (Grimes 2000), which ...
Mapping Tectonic Stress Using Earthquakes. [AIP Conference Proceedings 803, 475 (2005)]. Richard ... more Mapping Tectonic Stress Using Earthquakes. [AIP Conference Proceedings 803, 475 (2005)]. Richard Arnold, John Townend, Tony Vignaux. Abstract. An earthquakes occurs when the forces acting on a fault overcome its intrinsic strength and cause it to slip abruptly. ...
Outline This Web Appendix contains technical details of for the paper 'Capture-Recapture esti... more Outline This Web Appendix contains technical details of for the paper 'Capture-Recapture estimation using finite mixtures of arbitrary dimension' by R. Arnold, Y. Hayakawa and P. Yip (Biometrics ...) Appendix A contains technical details of the implemen-tation of the various MCMC moves in the reversible jump sampler. Appendix B contains a brief description of the one and two-dimensional degenerate normal distributions used as priors for β and γ. The results of model fitting for the standard Cottontail Rabbit dataset are given in Appendix C. Appendix D contains the AT&T software relibaility dataset analysed by Basu (1998). A. Implementation of RJMCMC In this Appendix we present details of the implementation of RJMCMC for each of three models: M h , M t[f]h and M th . In each case we consider the full hierarchical generation of the observed capture matrix X, the priors required for the specification of the model, and details of the RJMCMC estimation.
Journal of Geophysical Research: Solid Earth, 2015
ABSTRACT Automatic shear wave picking and shear wave splitting measurement tools (MFAST) are comb... more ABSTRACT Automatic shear wave picking and shear wave splitting measurement tools (MFAST) are combined to build a near-real time application for monitoring local stress around volcanoes. We use an adapted version of Diehl et al. [2009] on seismograms provided by the New Zealand GeoNet network and having an origin time and location based only on P picks. The best automatic picks are processed by MFAST, which computes the corresponding shear wave fast direction ϕ , and splitting delay time δt, interpreted respectively as the principal direction of stress underneath the station and the amount of anisotropy integrated along the wave ray-path. We applied our system to nine years of local earthquakes recorded at seven stations around Ruapehu volcano, New Zealand. Results are compared against MFAST measurements from manual S picks when available and show less than 10° difference for 90% of ϕ measurements and less than 0.05 s difference for 95% of δt measurements. Shear wave splitting from automatic S arrival times are slightly more consistent than those from manual arrival times. At some stations, two populations of delay times occur, which depend upon computed initial polarization. This may be caused in part by cycle skipping, an artefact usually associated with monochromatic signals. However spatial consistency in the behavior suggests a physical cause as well, such as focal mechanisms varying with earthquake source location or a spatially-varying near-source anisotropic region. The numbers of events in each population group vary over time, possibly related to activity at Ruapehu volcano.
To compare the attitudes towards common intensive care triage scenarios in New Zealand and Austra... more To compare the attitudes towards common intensive care triage scenarios in New Zealand and Australia and to evaluate Australasian intensive care triage practice. A web-based survey of Australian and New Zealand intensive care doctors measuring demographics, details of recent triage decisions and attitudes towards various triage scenarios. A total of 238 responses were obtained (32.6% response rate). The mean number of triage decisions was 6.3 per clinician per week in New Zealand (95%CI 4.6-8.0) and 8.5 per week in Australia (95% CI 6.6-10.4) (test for difference in means, p=0.08). The mean rate of refusal for the week prior to the survey was 30.8% (95%CI 19.5-42.1) among New Zealand respondents and 25.1% (95% CI 19.7-30.4) among Australian respondents (test for difference in proportions, p=0.35). Australian respondents were more likely than New Zealand respondents to agree that it was appropriate to admit a patient: - with a non-survivable brain injury who may progress to brain dea...
To investigate the extent of current problem gambling in New Zealand, and the risk factors, addic... more To investigate the extent of current problem gambling in New Zealand, and the risk factors, addictive behaviours, and self-rated health status associated with problem gambling. Analysis of the gambling questions from the 2002/03 New Zealand Health Survey, which interviewed 12,529 people aged 15 years and over, and included increased sampling of Maori, Pacific, and Asian people. Approximately 1.2% (95% confidence interval: 1.0-1.5) of the New Zealand adult population were found to be current problem gamblers, representing an estimated 32,800 (26,200-39,400) people. Risk factors for problem gambling included being of Maori or Pacific ethnicity, being aged 25-34 years, living alone, being employed, and being less qualified. Problem gambling was significantly associated with potentially hazardous drinking behaviour, daily cigarette smoking, and worse self-rated health, as measured on several SF-36 health domains. Maori and Pacific peoples were at significantly greater risk of being problem gamblers than other people, particularly among those people who gambled. Associations between gambling problems and health problems and/or risk behaviours suggest compounded problems from comorbidity. This evidence may be useful in informing policy and public health programmes to reduce the harmful impact of problem gambling on individuals and communities, and in addressing the inequalities evident in gambling-related harm.
... 55 4.17 Lomb-Scargle Periodogram for EC20058-5234 (18 Jun 1999) sam-pled at ∆ Ωºººpoints. ...... more ... 55 4.17 Lomb-Scargle Periodogram for EC20058-5234 (18 Jun 1999) sam-pled at ∆ Ωºººpoints. ... in this wide temperature range are pulsators, however, and there seem to be several different classes of pulsat-ing White Dwarfs and hot subdwarfs (Vauclair, Moskalik, Pfeiffer & ...
A sequence of four earthquakes of magnitude 6.0-6.5 struck the South Iceland Seismic Zone (SISZ) ... more A sequence of four earthquakes of magnitude 6.0-6.5 struck the South Iceland Seismic Zone (SISZ) between June 2000 and May 2008, just over one hundred years since a similar sequence of five large earthquakes occurred in the area in 1896. Large earthquakes typically occur in the east-west-trending SISZ as right-lateral strike-slip events on north-south-striking faults. During both the 2000-2008 and 1896 sequences, earthquake activity migrated westward along the SISZ, with the May 2008 earthquake doublet striking only 10 kilometres away from the Hengill triple junction. We have examined stress parameters derived from a large catalog of earthquake focal mechanism data obtained during routine analysis of data recorded by the Icelandic SIL network since 1991. The focal mechanism catalogue for south Iceland contains more than 100,000 events larger than M~-1. Stress inversion using focal mechanism data yields the orientations of the three principal stresses and a measure of the relative magnitude of the intermediate principal stress. We use both a probabilistic (Bayesian) stress estimation algorithm (Arnold and Townend, 2007) and a grid search based inversion scheme adapted to the uncertainty estimates available for each SIL focal mechanism (Lund and Slunga, 1999) to compute the four resolvable stress parameters at different points in space and time. In order to discriminate spatial and temporal variations in stress, we subdivide the focal mechanism catalog on the basis of time and estimate the stress parameters at each epoch at fixed locations. In this presentation we report on spatial and temporal variations in stress during the 1991-2010 period, concentrating on the source areas of the M6+ events. Preliminary results indicate a stress change in the area of the June 17, 2000, earthquake prior to the event, and resolvable spatial stress variations in the aftershock sequences of the June 2000 events.
Earthquakes provide a key means of estimating tectonic stress at seismogenic depths, and thereby ... more Earthquakes provide a key means of estimating tectonic stress at seismogenic depths, and thereby of investigating directly the mechanisms by which faults slip during earthquakes and interact. To date, however, stress estimation algorithms have not provided sufficiently reliable uncertainty estimates to enable the detection of fine temporal or spatial variations in stress. We have developed a probabilistic (Bayesian) technique for estimating tectonic stress directions from routine seismological observations. The Bayesian approach combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationships between the stresses acting on a fault, slip during an earthquake, and the observed seismic waves. We first quantify the constraints on the four determinable stress tensor parameters imposed by a single focal mechanism in terms of a joint probability density function. Next, we formalise the process of estimating stress tensor parameters from a number of such mechanisms by combining the corresponding probability density functions. We explicitly include the limitation that, in general, the two nodal planes of a given focal mechanism cannot be unambiguously distinguished and are invariably subject to measurement error. Our formulation is equivalent to a well-known analytical solution for a single, errorless focal mechanism observation (McKenzie, BSSA, 59, 1969). The new approach has the distinct advantage, however, that including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors, and (4) prior knowledge of the stress field is mathematically tractable, albeit computationally intensive. Our approach is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, including seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations.
We develop a new probabilistic (Bayesian) method for estimating the distribution of focal mechani... more We develop a new probabilistic (Bayesian) method for estimating the distribution of focal mechanism parameters based on seismic wave polarity data. We investigate the use of generalised Matrix Fisher distributions for parameterising focal mechanism uncertainties. The advantages of our approach are that it (1) models the data generation process and incorporates observational errors, particularly those arising from imperfectly known earthquake locations; (2) allows exploration of the entire parameter space; (3) leads to natural point estimates of focal mechanism parameters; (4) allows the inclusion of a priori information about the focal mechanism parameters; and (5) that the resulting posterior probability density function (PDF) can be well approximated by generalised Matrix Fisher distributions. We present here the results of our method in two situations. We first consider the case in which the seismic velocity of the region of interest (described by a velocity model) is presumed to be precisely known, with application to seismic data from the Raukumara Peninsula, New Zealand. We then consider the case in which the velocity model is imperfectly known, with application to data from the Kawerau region, New Zealand. We find that our estimated focal mechanism solutions are for the most part consistent with all available polarity data, and correspond closely to solutions obtained using established methods. Further, the generalised Matrix Fisher distributions we examine provide a good fit to our Bayesian posterior PDF of the focal mechanism parameters. Finally, we demonstrate how informative prior distributions on focal mechanism parameters can be incorporated into our model.
Recent research has developed a group of likelihood-based finite mixture models for a data matrix... more Recent research has developed a group of likelihood-based finite mixture models for a data matrix with ordinal data, establishing likelihood-based multivari-ate methods which applies fuzzy clustering via finite mixtures to the ordered stereotype model. There are many visualisation tools which depict reduction of dimensionality in matrices of ordinal data. This technical report introduces the spaced mosaic plot which is one new graphical tool for ordinal data when the ordinal stereotype model is used. It takes advantage of the fitted score parameters to determine the spacing between two adjacent ordinal categories. We develop a function in R and its documentation is presented. Finally, the description of a spaced mosaic plot is shown.
... RICHARD ARNOLD & LAURIE BAUER ... as a descrip-tion of the relationship betwe... more ... RICHARD ARNOLD & LAURIE BAUER ... as a descrip-tion of the relationship between the number of languages n in a language family, and the rank r of that family in a list ordered by decreasing n. Two datasets are used by Wichmann, one from Ethnologue (Grimes 2000), which ...
Mapping Tectonic Stress Using Earthquakes. [AIP Conference Proceedings 803, 475 (2005)]. Richard ... more Mapping Tectonic Stress Using Earthquakes. [AIP Conference Proceedings 803, 475 (2005)]. Richard Arnold, John Townend, Tony Vignaux. Abstract. An earthquakes occurs when the forces acting on a fault overcome its intrinsic strength and cause it to slip abruptly. ...
Outline This Web Appendix contains technical details of for the paper 'Capture-Recapture esti... more Outline This Web Appendix contains technical details of for the paper 'Capture-Recapture estimation using finite mixtures of arbitrary dimension' by R. Arnold, Y. Hayakawa and P. Yip (Biometrics ...) Appendix A contains technical details of the implemen-tation of the various MCMC moves in the reversible jump sampler. Appendix B contains a brief description of the one and two-dimensional degenerate normal distributions used as priors for β and γ. The results of model fitting for the standard Cottontail Rabbit dataset are given in Appendix C. Appendix D contains the AT&T software relibaility dataset analysed by Basu (1998). A. Implementation of RJMCMC In this Appendix we present details of the implementation of RJMCMC for each of three models: M h , M t[f]h and M th . In each case we consider the full hierarchical generation of the observed capture matrix X, the priors required for the specification of the model, and details of the RJMCMC estimation.
Journal of Geophysical Research: Solid Earth, 2015
ABSTRACT Automatic shear wave picking and shear wave splitting measurement tools (MFAST) are comb... more ABSTRACT Automatic shear wave picking and shear wave splitting measurement tools (MFAST) are combined to build a near-real time application for monitoring local stress around volcanoes. We use an adapted version of Diehl et al. [2009] on seismograms provided by the New Zealand GeoNet network and having an origin time and location based only on P picks. The best automatic picks are processed by MFAST, which computes the corresponding shear wave fast direction ϕ , and splitting delay time δt, interpreted respectively as the principal direction of stress underneath the station and the amount of anisotropy integrated along the wave ray-path. We applied our system to nine years of local earthquakes recorded at seven stations around Ruapehu volcano, New Zealand. Results are compared against MFAST measurements from manual S picks when available and show less than 10° difference for 90% of ϕ measurements and less than 0.05 s difference for 95% of δt measurements. Shear wave splitting from automatic S arrival times are slightly more consistent than those from manual arrival times. At some stations, two populations of delay times occur, which depend upon computed initial polarization. This may be caused in part by cycle skipping, an artefact usually associated with monochromatic signals. However spatial consistency in the behavior suggests a physical cause as well, such as focal mechanisms varying with earthquake source location or a spatially-varying near-source anisotropic region. The numbers of events in each population group vary over time, possibly related to activity at Ruapehu volcano.
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