The 1946 magnitude 6.1 earthquake in the Valais: site-effects as contributor to the damage

The January 25, 1946 earthquake in the central Valais region in southwest Switzerland was the strongest for the last 150 years. It reached an epicentral intensity Io of VIII in the area of Sierre. The Swiss Earthquake Catalogue (ECOS 2002) assigns a moment magnitude of Mw = 6.1 to the event. Assessment of recordings from European stations resulted in a moment magnitude of 5.8 (Bernardi et al. 2005). The earthquake caused moderate to high damage within a circle of about a 25 kilometer radius. Slight damage occurred up to a distance of 200 kilometers from the epicenter. The goal of this study was to reconstruct the damage field and consider its possible site-effects. We used an approach combining historical research with seismo-/geological investigation including a large number of experiments measuring the fundamental frequency of resonance and the shear-wave velocities of the sedimentary layers, using the characteristics of ambient vibration. This kind of research is relevant, since a huge alpine valley characterizes the Valais region, showing ground conditions that make site-effects likely for earthquakes. While we searched for damage in an unlimited area, our investigation of site-effects was limited to the Rhone valley and to Sion and Sierre in the central Valais region in particular.     

Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography,Virttaankangas, southwest Finland

A novel high-resolution (2–4 m source and receiver spacing) reflection and refraction seismic survey was carried out for aquifer characterization and to confirm the existing depositional model of the interlobate esker of Virttaankangas, which is part of the Säkylänharju-Virttaankangas glaciofluvial esker-chain complex in southwest Finland. The interlobate esker complex hosting the managed aquifer recharge (MAR) plant is the source of the entire water supply for the city of Turku and its surrounding municipalities. An accurate delineation of the aquifer is therefore critical for long-term MAR planning and sustainable use of the esker resources. Moreover, an additional target was to resolve the poorly known stratigraphy of the 70–100-m-thick glacial deposits overlying a zone of fractured bedrock. Bedrock surface as well as fracture zones were confirmed through combined reflection seismic and refraction tomography results and further validated against existing borehole information. The high-resolution seismic data proved successful in accurately delineating the esker cores and revealing complex stratigraphy from fan lobes to kettle holes, providing valuable information for potential new pumping wells. This study illustrates the potential of geophysical methods for fast and cost-effective esker studies, in particular the digital-based landstreamer and its combination with geophone-based wireless recorders, where the cover sediments are reasonably thick.

     

Encounters of the Sun with nearby stars in the past and future

The relative space motions of the Sun and nearby stars are considered. The coordinates and velocities of the stars are taken from the Catalogue of Nearby Stars by Gliese and Jahreiss (1991). The minimum space separation between the Sun and every star as well as the corresponding moment of time are calculated by two ways. Firstly, the straight line motions are considered. Secondly, the effect of the Galaxy potential is taken into account. The Galaxy model proposed by Kutuzov and Ossipkov (1989) is used. Twenty five stars approaching the Sun closer than two parsecs are selected. The effects of the uncertainties in the observational data are studied. The influence of the encounters to the Oort cloud is discussed.     

The High Resolution Spectrograph for Spectrum UV

The Spectrum-UV mission, a general purpose ultraviolet observatory equipped with a 170-cm aperture telescope for imaging and spectroscopy in the 912 to 3600 Å range, will be launched in a seven days, high elliptical orbit in the late '90s by a Proton booster. The German contribution to the focal plane instrument complex is described: HIRDES, a High Resolution Double Echelle Spectrograph.     

Regionally representative selection of soil samples for an environmental specimen bank with particular reference to loess soils

Digital evalutation of a series of correlative geo-specific maps in different scales and subsequent multivariate data processing in the form of entropy and neighbourhood analyses are the basis of a comparative selection of soil samples for the environmental specimen bank of the Federal Republic of Germany. By means of regionalisation algorithms, partly developed for, or specifically adapted to the present purpose, the optimum location of sampling points was determined and the result corroborated on large-scale maps or by visual inspection, respectively. In addition an index of representativity was defined, grouping soil taxa in terms of acreage and spatial autocorrelation.Once the spatial structure of the soil associations in an area to be sampled is thus determined variogram analysis, in the second step, contributes to definitely select the most appropriate specimens on the basis of a representative sampling grid and with respect to relevant properties, for instance cation or anion exchange capacities and biodegradability potential.     

RbSr isotope systematics at amphibolite facies conditions,Uppsala Region,Eastern Sweden

On the basis of U-Pb, Rb-Sr and K-Ar isotope analyses of Proterozoic rocks and minerals, a chronology has been established for the tectonic, intrusive and metamorphic evolution of the Svecokarelian orogeny 1750–1950 Ma ago in the Uppsala Region, Eastern Sweden. It is suggested that when synkinematic granitoids intruded the orogenic belt, at a stage of general subsidence and at medium metamorphic conditions (600°C and 3.5–4 kbar), the U-Pb isotope system in zircons closed earlier than the Rb-Sr whole-rock system. The zircon age (1886 Ma) reflects the intrusion and crystallization of the rock melt and the Rb-Sr whole-rock age (1830 Ma) the time when the temperature had decreased below the threshold for ⁸⁷Sr migration. The Rb-Sr whole rock age (1898 Ma) determined for metaandesites and metadacites reflects a recrystallization related to the intrusion of the granitoids. On the contrary, the more silicic metarhyodacitic volcanic rocks have a Rb-Sr whole rock age (1830 Ma) reflecting the cessation of the synkinematic metamorphism. The difference in the way the Rb-Sr isotope system responds in subsilicic or silicic metavolcanics is probably dependent on the amount of radiogenic ⁸⁷Sr and on the fixation of ⁸⁷Sr in Ca-rich minerals. Subsequent, late-kinematic, low amphibolite facies metamorphism has not altered the Rb-Sr ages of the granitoids and the recrystallized metavolcanics.     

Spatial dispersion of Faraday rotation and its connexion with mode coupling

It is shown that the lack of linear polarization in the microwave radiation of solar bursts (reported in a earlier paper) may be explained by spatial dispersion of Faraday rotation. The maximum source diameter s without noticeable destruction of linear polarization is determined by the electron density and the magnetic field strength in the volume, where the linear polarization is generated. In the case where linear polarization is produced by the radiation source, s is smaller than only 20 km. In the other case where linear polarization is produced by mode coupling in a quasi-transverse magnetic field in the corona, the s-values are found to range from 10 to 6000 km, which is still much smaller than the generally adopted sizes of microwave burst sources. The second case has been investigated for several models of magnetic fields.     

Analysis and interpretation of soft X-ray photographs of coronal active regions taken with Fresnel zone plates

Soft X-ray photographs of the Sun taken at O vii 21.6 Å and in a spectral band ranging from 13.2 to 22.1 Å have been analysed in order to establish spatially resolved maps of temperature and emission measure for several active regions in the corona. The photographs were taken on 11 March, 1971, and on 2 March, 1972, with Fresnel zone plate cameras which were flown on ESRO and NRL sounding rockets.In Part I of this paper we first deal with those aspects of the instrumentation which are important for setting up a suitable image analysis procedure. We discuss the characteristics of the wavelength dependent image formation by zone plates combined with absorption filters. Results of the calibration of the X-ray film are given. Then we describe a specific iterative data reduction procedure and finally present the resulting maps of temperature and emission measure for a selected active region. In Part II corresponding results for further active regions will be given and discussed.