Bayesian estimation of seismic hazard for two sites in Switzerland

Seismic hazard analysis is based on data and models, which both are imprecise and uncertain. Especially the interpretation of historical information into earthquake parameters, e.g. earthquake size and location, yields ambiguous and imprecise data. Models based on probability distributions have been developed in order to quantify and represent these uncertainties. Nevertheless, the majority of the procedures applied in seismic hazard assessment do not take into account these uncertainties, nor do they show the variance of the results. Therefore, a procedure based on Bayesian statistics was developed to estimate return periods for different ground motion intensities (MSK scale).Bayesian techniques provide a mathematical model to estimate the distribution of random variables in presence of uncertainties. The developed method estimates the probability distribution of the number of occurrences in a Poisson process described by the parameter . The input data are the historical occurrences of intensities for a particular site, represented by a discrete probability distribution for each earthquake. The calculation of these historical occurrences requires a careful preparation of all input parameters, i.e. a modelling of their uncertainties. The obtained results show that the variance of the recurrence rate is smaller in regions with higher seismic activity than in less active regions. It can also be demonstrated that long return periods cannot be estimated with confidence, because the time period of observation is too short. This indicates that the long return periods obtained by seismic source methods only reflects the delineated seismic sources and the chosen earthquake size distribution law.     

Total ozone variations in the tropical belt: An application for quality of ground based measurements

Summary The study of the regime of ozone variations in the huge tropical belt (25° S to 25° N), which are, in general, very small and zonally nearly symmetric, permits to establish a statistical model for estimating the ozone deviations using Total Ozone Mapping Spectrometer (TOMS) data. The equatorial stratospheric winds at 25 and 50hPa and the solar flux at 10.7 cm are used as major predictors and the linear trend was also estimated. The 10m/sec stratospheric wind change is related to1.2% ozone change at the equator, to practically no change in the 8–15° belts and up to 1.4% change with opposite phase over the tropics in spring but nearly zero change in fall. The solar cycle related amplitude is about 1.4% per 100 units of 10.7 cm solar flux. The ozone trends are negative: not significant over the equator and about –2% per decade (significant at 95% level) over the tropics. The latter could have been enforced by the 2 to 4% lower ozone values during 1991–1993, part of which might be related to the effects of the Mt. Pinatubo eruption, but might also be due to the strong QBO. The estimated deviations are verified versus reliable observations and the very good agreement permits applying the model for quantitative quality control of the reported ozone data from previous years. The standard deviation of the difference between observed ozone deviations and those estimated from the model is only 0.9–1.6% for yearly mean, that means instruments used for total ozone observations in the tropical belt should have systematic error of less than 1%. Cases when the discrepancies between the model and reported observations at a given station exceed 2–3% for time interval of 2 or more years should be verified.With 17 Figures     

Objective measures of the information density of satellite data

Summary We propose and objective method whereby the density of Shannon's information associated with the retrieval of a profile of atmospheric variables from satellite-derived infrared radiance measurements may be estimated. The technique is a natural extension of one we previously proposed to estimate the effective data density in a profile. We test the method in a comparison of simulated satellite instruments to show that the method does indeed provide an objective summary of the spatial distribution of each instrument's information content. We propose that further extensions of the method be developed to include other more traditional data sources in a fully three-dimensional scheme. We also note that analogous and compatible methods may be used to diagnose the information content of meteorological analysis and forecast fields relative to the information contained in the covariance, at the appropriate season, of the corresponding climate fields.With 8 Figures     

Crystal-Mush Compaction and the Origin of Pegmatitic Segregation Sheets in a Thick Flood-Basalt Flow in the Mesozoic Hartford Basin, Connecticut

Where the Holyoke flood-basalt flow in the Mesozoic HartfordBasin in Connecticut is thick and contains coarse-grained, horizontalsegregation sheets in its central part, the lower part of theflow is strongly depleted in incompatible elements; where theflow is thin and contains no segregation sheets it is homogeneousthroughout. This chemical variation can be explained only throughcompaction of the partly crystallized basalt. The compositionof the segregation sheets shows that they separated from thebasalt following only 33% crystallization. The segregation sheets,however, are clearly intrusive into the basalt, which must thereforehave already formed a crystal mush with finite strength at thislow degree of crystallinity. The incompatible element concentrationsindicate that the partly crystallized basalt underwent as muchas 28% compaction in the lowest 60 m of the flow. Between 60and 130 m above the base of the flow, the crystal mush becamedilated, and eventually ruptured with formation of the segregationsheets. No segregation sheet has a composition indicating separationafter more than 33% crystallization of the basalt. This is interpretedto indicate that compaction ceased at this stage because ofthe increasing strength of the mush and the increasing densityof the fractionating interstitial liquid KEY WORDS: crystal-mush compaction; segregation shtets; flood basalt; tholeiitie; Connecticut ^*e-mail: philpotts{at}geol.uconn.edu     

Quantification of the effects of secondary matrix on the analysis of sandstone composition, and a petrographic-chemical technique for retrieving original framework grain modes of altered sandstones

Most studies of sandstone provenance involve modal analysis of framework grains using techniques that exclude the fine-grained breakdown products of labile mineral grains and rock fragments, usually termed secondary matrix or pseudomatrix. However, the data presented here demonstrate that, when the proportion of pseudomatrix in a sandstone exceeds 10%, standard petrographic analysis can lead to incorrect provenance interpretation. Petrographic schemes for provenance analysis such as QFL and QFR should not therefore be applied to sandstones containing more than 10% secondary matrix. Pseudomatrix is commonly abundant in sandstones, and this is therefore a problem for provenance analysis. The difficulty can be alleviated by the use of whole-rock chemistry in addition to petrographic analysis. Combination of chemical and point-count data permits the construction of normative compositions that approximate original framework grain compositions. Provenance analysis is also complicated in many cases by fundamental compositional alteration during weathering and transport. Many sandstones, particularly shallow marine deposits, have undergone vigorous reworking, which may destroy unstable mineral grains and rock fragments. In such cases it may not be possible to retrieve provenance information by either petrographic or chemical means. Because of this, pseudomatrix-rich sandstones should be routinely included in chemical-petrological provenance analysis. Because of the many factors, both pre- and post-depositional, that operate to increase the compositional maturity of sandstones, petrologic studies must include a complete inventory of matrix proportions, grain size and sorting parameters, and an assessment of depositional setting.     

Revised chemical models of ζ Oph based on HST data

Hubble Space Telescope observations by Savage, Cardelli and Sofia (1992) and Cardelliet al. (1993) have led to improved gas phase abundances for many elements in the diffuse cloud towards the star Oph. Most remarkably, it was found that oxygen is much more strongly depleted than previousCopernicus observations indicated. As a consequence, chemical models of the Oph cloud are severely affected by the drop in the observed oxygen abundance by almost a factor of two; some previous model calculations for the Oph cloud failed to reproduce-even approximately-the observed high CO column density. The model calculations for the Oph cloud developed by Wagenblast (1992) in which the abundance of all observed neutral molecules could be reproduced have been revised and it is found that oxygen and nitrogen hydrides are required to be formed efficiently on the surface of grains; further, there are indications for a high cosmic ray ionization rate of the order 10^–16 s^–1.     

The GEM project: An international collaboration to survey galactic radiation emission

The GEM (Galactic Emission Mapping) project is an international collaboration established with the aim of surveying the full sky at long wavelengths with a multi-frequency radio telescope. A total of 745 hours of observation at 408 MHz were completed from an Equatorial site in Colombia. The observations cover the celestial band 0 ^h <<24 ^h , and –24° 22<<+35° 37. Preliminary results of this partial survey will be discussed. A review of the instrumental setup and a 10° resolution sky map at 408 MHz is presented.Presented by S. Torres at the UN/ESA Workshop on Basic Space Sciences: From Small Telescopes to Space Missions, Colombo, Sri Lanka 11–14 January 1996     

Propagation of solar cosmic rays: Diffusion versus focused diffusion

This paper is designed to bring to the attention the fact that the effect of focusing of solar energetic particles is always essential as compared with scattering, no matter how small the value of the mean free path may be. That is why, an ordinary (focusing-free) diffusion approach can not be applied to the solar cosmic ray transport. In the case of high-energy solar particles, the focused diffusion is demonstrated to lead to a power law decay of energetic particle intensity much like an ordinary diffusion. However, the power law index of the decay is renormalized by the focusing.     

Whistler observations of the quiet time plasmasphere-ionosphere coupling fluxes at low latitude

Observations of whistlers during quiet times made at low-latitude ground station Nainital (geomag. lat. 19 1 N) are used to deduce plasmasphere-ionosphere coupling fluxes. The whistler data from 3 magnetically quiet days are presented that show a smooth decrease in dispersion with time. This decrease in dispersion is interpreted in terms of a corresponding decrease in electron content of tubes of ionization. The electron densities, electron tube contents (10¹⁶ el/m²-tube) and coupling fluxes (10 el m^–1 s^–2) are computed by means of an accurate curve fitting method developed by Tarcsai (1975) and are in good agreement with the results reported by other workers.     

Coherent eddies and turbulence in vegetation canopies: The mixing-layer analogy

This paper argues that the active turbulence and coherent motions near the top of a vegetation canopy are patterned on a plane mixing layer, because of instabilities associated with the characteristic strong inflection in the mean velocity profile. Mixing-layer turbulence, formed around the inflectional mean velocity profile which develops between two coflowing streams of different velocities, differs in several ways from turbulence in a surface layer. Through these differences, the mixing-layer analogy provides an explanation for many of the observed distinctive features of canopy turbulence. These include: (a) ratios between components of the Reynolds stress tensor; (b) the ratio K _H/K _M of the eddy diffusivities for heat and momentum; (c) the relative roles of ejections and sweeps; (d) the behaviour of the turbulent energy balance, particularly the major role of turbulent transport; and (e) the behaviour of the turbulent length scales of the active coherent motions (the dominant eddies responsible for vertical transfer near the top of the canopy). It is predicted that these length scales are controlled by the shear length scale % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamitamaaBa% aaleaacaWGtbaabeaakiabg2da9iaadwfacaGGOaGaamiAaiaacMca% caGGVaGabmyvayaafaGaaiikaiaadIgacaGGPaaaaa!3FD0!\[L_S = U(h)/U'(h)\] (where h is canopy height, U(z) is mean velocity as a function of height z, and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmyvayaafa% Gaeyypa0JaaeizaiaadwfacaGGVaGaaeizaiaadQhaaaa!3C32!\[U' = {\rm{d}}U/{\rm{d}}z\]). In particular, the streamwise spacing of the dominant canopy eddies is _x = mL _s, with m = 8.1. These predictions are tested against many sets of field and wind-tunnel data. We propose a picture of canopy turbulence in which eddies associated with inflectional instabilities are modulated by larger-scale, inactive turbulence, which is quasi-horizontal on the scale of the canopy.