Radiometric constraints on hydrothermal circulation in cooling granite plutons

Improved precision of radiometric dating of ore deposits can provide information about the thermal history of hydrothermal circulation in cooling plutons. In Jales a Hercynian porphyritic two-mica granite and pre-Ordovician mica schists are cut and intensely altered by the Campo gold-quartz vein. The unaltered granite must be younger than 320 ± 6 Ma, and gives mica Rb-Sr ages of 308.5 ± 2.4 (1) Ma (muscovite) and 294.5 ± 1.1 Ma (biotite). Alteration muscovites from the granite give a weighted mean Rb-Sr age of 308.1 ± 1.5 Ma, and a mean ³⁹Ar-⁴⁰Ar age of 300.7 ± 2.8 Ma. Alteration muscovites from the mica schists give similar ³⁹Ar-⁴⁰Ar ages, averaging 303.0 ± 2.8 Ma. The results suggest that circulation of the Campo mineralising fluids took place no more than 2–4 Ma after the granite cooled through the muscovite Rb-Sr closure temperature, about 500 °C, and that subsequent cooling to biotite closure at about 300 °C took place at less than 14°C/Ma. The mean cooling rate following emplacement was 15 to 25 °C/Ma. The most detailed comparable published data, for the Cornubian ore field, imply much faster cooling rates.     

Comparative sensitivity of harbour and grey seals to several environmental contaminants using in vitro exposure

In this study, we investigated the effects of cadmium chloride (CdCl₂), mercury chloride (HgCl₂), methylmercury chloride (CH₃HgCl), and PCBs on lymphocyte proliferation in phocids. PBMCs isolated from harbour and grey seals were exposed in vitro to varying concentrations of contaminants. A reduction of viability occurred when cells were exposed to 10⁻⁴ M HgCl₂ or CH₃HgCl or to 50 ppm of Aroclor 1254. In both grey and harbour seals, T-lymphocyte proliferation was suppressed when their cells were incubated with 5 × 10⁻⁵ M CdCl₂ or 10⁻⁴ M HgCl₂. An inhibition of proliferation occurred with CH₃HgCl from 10⁻⁶ M in grey seals and from 10⁻⁵ M in harbour seals. In grey seals, Aroclor 1254 reduced lymphocyte proliferation at 15 ppm. In both harbour and grey seals, CH₃HgCl was ten times more immunotoxic that HgCl₂. From IC₅₀, chemicals were ranked in terms of toxicity as followed: CH₃HgCl > CdCl₂ > HgCl₂ > Aroclor 1254.     

Some Insights into Topographic,Elastic and Self-gravitation Interaction in Modelling Ground Deformation and Gravity Changes in Active Volcanic Areas

Surface displacements and gravity changes due to volcanic sources are influenced by medium properties. We investigate topographic, elastic and self-gravitation interaction in order to outline the major factors that are significant in data modelling. While elastic-gravitational models can provide a suitable approximation to problems of volcanic loading in areas where topographic relief is negligible, for prominent volcanoes the rough topography could affect deformation and gravity changes to a greater extent than self-gravitation. This fact requires the selection, depending on local relief, of a suitable model for use in the interpretation of surface precursors of volcanic activity. We use the three-dimensional Indirect Boundary Element Method to examine the effects of topography on deformation and gravity changes in models of magma chamber inflation/deflation. Topography has a significant effect on predicted surface deformation and gravity changes. Both the magnitude and pattern of the geodetic signals are significantly different compared to half-space solutions. Thus, failure to account for topographic effects in areas of prominent relief can bias the estimate of volcanic source parameters, since the magnitude and pattern of deformation and gravity changes depend on such effects.     

Evaluating practical macrophyte control tools on small agricultural waterways in Canterbury,New Zealand

Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2?m?×?2?m). We found intensive hand weeding, weed mat and herbicide spraying to be effective treatments, reducing macrophyte cover to <5%. Hand weeding and weed mat immediately reduced cover, while dieback from herbicide took two months. Weed mat was a novel and effective control mechanism along stream banks. Secondly, we tested the impact of shading on macrophyte growth. Macrophyte growth was enhanced under partially shaded conditions, but with 80% effective shading over the entire channel, cover was reduced to 17%. Once treatments ceased, macrophytes grew back within 3–5 months. Long-term, control methods will require combinations of tools but will need to include optimal shading for the target species.     

Optimization of Seismicity-Based Forecasts

In this paper, the extent to which some improvement can be made in seismicity-based earthquake forecasting methods are examined. Two methods that employ the statistics and locations for past smaller earthquakes to determine the location of future large earthquakes, the pattern informatics (PI) index and the Benioff relative intensity (RI), are employed for both global and regional forecasting. Two approaches for forecast parameter estimation, the TM metric and threshold optimization, are applied to these methods and the results evaluated. Application of the TM metric allows for estimation of both the training and forecast time intervals as well as the minimum magnitude cutoff and spatial discretization. The threshold optimization scheme is employed in order to formulate a binary forecast that maximizes the Pierce’s skill score. The combined application of these techniques is successful in forecasting those large events that occurred in Haiti, Chile, and California in 2010, on both global and regional scales.     

Forecasting the Locations of Future Large Earthquakes: An Analysis and Verification

The objective of this paper is to quantify the use of past seismicity to forecast the locations of future large earthquakes and introduce optimization methods for the model parameters. To achieve this the binary forecast approach is used where the surface of the Earth is divided into l° × l° cells. The cumulative Benioff strain of m ≥ m _c earthquakes that occurred during the training period, ΔT _tr, is used to retrospectively forecast the locations of large target earthquakes with magnitudes ≥m _T during the forecast period, ΔT _for. The success of a forecast is measured in terms of hit rates (fraction of earthquakes forecast) and false alarm rates (fraction of alarms that do not forecast earthquakes). This binary forecast approach is quantified using a receiver operating characteristic diagram and an error diagram. An optimal forecast can be obtained by taking the maximum value of Pierce’s skill score.     

Space- and Time-Dependent Probabilities for Earthquake Fault Systems from Numerical Simulations: Feasibility Study and First Results

In weather forecasting, current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed “model steering”. Here we describe a similar approach that is motivated by analyses of previous forecasts of the Working Group on California Earthquake Probabilities (WGCEP). Our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike-slip fault system in California. By systematically comparing simulation data to observed paleoseismic data, a series of spatial probability density functions (PDFs) can be computed that describe the probable locations of future large earthquakes. We develop this approach and show examples of PDFs associated with magnitude M > 6.5 and M > 7.0 earthquakes in California.     

Towards spatially distributed quantitative assessment of tsunami inundation models

This paper presents a framework and data for spatially distributed assessment of tsunami inundation models. Our associated validation test is based upon the 2004 Indian Ocean tsunami, which affords a uniquely large amount of observational data for events of this kind. Specifically, we use eyewitness accounts to assess onshore flow depths and speeds as well as a detailed inundation survey of Patong City, Thailand to compare modelled and observed inundation. Model predictions matched well the detailed inundation survey as well as altimetry data from the JASON satellite, eyewitness accounts of wave front arrival times and onshore flow speeds. Important buildings and other structures were incorporated into the underlying elevation model and are shown to have a large influence on inundation extent.