Strange seismic attractor?

Different time series were constructed from the data set containing all the seismic events recorded by the Parkfield network between 1969 and 1987. These series were analyzed to determine whether there exists an attractor in the phase space of the dynamical system characterizing seismic activity and to tentatively establish its dimension. The study has yielded ambiguous results. For all the time series analyzed, the dimension of the attractor appears higher than 12 and the correlation function of the seismic time series is undistinguishable from that of a series of random numbers of the same length. The lack of difference between the scaling parameters of two series suggests that, for all practical purposes, the seismic time series cannot be discriminated from a random series.     

Magnetotelluric measurements at Eusebio,an equatorial station

Magnetotelluric measurements in the period range 100–86400 s were conducted at a coastal station under the equatorial electrojet (Eusebio, 3.87°S, 321.58°E). The magnetotelluric data were hand-scaled and analysed to obtain a scalar apparent resistivity profile at Eusebio. The depth of the intermediate conducting layer was found to be in the range 45–75 km and the final conducting layer seems to begin at a depth of about 350 km. Possible effects of the source field equatorial electrojet are discussed and our results are compared with those of an African station under the equatorial electrojet.     

The metamorphic evolution of garnet-cordierite-sillimanite-gneisses of the Gruf-Complex,Eastern Pennine Alps

Metapelitic gneisses occuring as lenses and bands within the migmatites of the Gruf-Complex in the eastern Pennine Alps contain various combinations of the minerals quartz, biotite, cordierite, garnet, sillimanite, plagioclase. K-feldspar, spinel, orthopyroxene, anthophyllite and muscovite. The most common rock type is represented by a darkschistosebiotiterichcordierite-garnet-sillimanite-gneiss. A consistent pressure-temperature range of 3–4 kb and 600–650° C has been calculated for the last metamorphic equilibration from six geological thermobarometers. However, from textural evidence it may be concluded that the rocks were at both higher temperatures and pressures prior to the PT-conditions calculated from thermobarometry. Although the maximum conditions reached are unknown and earlier stages are poorly preserved it is suggested that they coincide with the maximum conditions deduced from rare occurrences of sapphirine granulite in the Gruf-Complex. These are 10 kb and 800° C (Droop and Bucher 1983). Sillimanite+K-feldspar, orthopyroxene+quartz, spinel+quartz and garnet-K-feldspar persisting in rocks with low activity of H₂O are strong evidence for this. The H₂O required to make the observed high degree of equilibration at 3–4 kb and 600–650° C possible was presumably released by crystallizing migmatitic melts present in the quartzo-feldspathic gneisses of the Gruf-Complex. Further evidence comes from the PT-coordinates of the H₂O-saturated muscovite granite solidus which coincides with the high temperature limits of inferred equilibration above and which the rocks must have crossed along the decompression and cooling path during their metamorphic evolution.     

The surface seiches of Lake of Lugano

A computational analysis of the periods and structure of surface seiches of the southern basin of Lake of Lugano and its experimental verification from three simultaneous water gauge recordings, mounted along the shores in Agno, Morcote and Riva S. Vitale, is given. The first five theoretical modes are calculated with a finite element code of the tidal equations; it yields the eigenperiods and co-range and co-tidal lines, which are graphically displayed and discussed in detail. Experimental verification is from recordings taken during February/March 1982. Inspection by eye allows identification of the five lowest order modes, partly including interstation phase shift. Power spectral analysis of three-time series and interstation phase difference and coherence spectra allow identification of higher order modes, probably up to order 13. Agreement between the theoretically predicted and the experimentally determined periods is excellent for all calculated modes. Computational results for the four lowest modes and their structure of the northern basin of Lake of Lugano are also presented and experimentally verified with records taken from an event in August 1979. Agreement is again excellent.     

Electron microprobe dating of monazite substantiates ages of major geological events in the southern Brazilian shield

To obtain the chemical Th^*–Pb isochron ages and surface maps of monazite crystals in igneous and metamorphic rocks from the southern Brazilian Shield, we employ Th–U-total Pb dating by an electron probe microanalyzer. The ages of two Trans-Amazonian metamorphic events are given by a felsic, garnet-bearing granulite from the Santa Maria Chico granulitic complex. The age of the first event, at approximately 2.35 Ga, was obtained by surface mapping in a grain included in garnet. The dating of the second event, 1899±43 Ma, is in agreement with previous data obtained in zircon crystals with sensitive high-resolution ion microprobe. Other determinations belong to the Brasiliano cycle. In the São Gabriel block, an age of 643±129 Ma was obtained on monazite from a staurolite-garnet schist of the Cambaizinho Formation, whereas a staurolite-bearing schist from the Passo Feio complex yielded a 510±68 Ma age. Several units in the Dom Feliciano belt were dated, including the biotite-sillimanite gneisses of the Várzea do Capivarita complex (552±90 Ma), the sillimanite-garnet gneisses of Camboriú complex (565±77 Ma), the Três Figueiras granite (558±57 Ma), and the Plaza Itapema granite (545±55 Ma). The ages presented in this study, obtained through monazite chemical dating, are confirmed through comparison with previous data regarding zircon crystals from the same geological units.     

Seismic behavior of asymmetric RC wall buildings: principles and new deformation‐based design method

The seismic design of multi‐story buildings asymmetric in plan yet regular in elevation and stiffened with ductile RC structural walls is addressed. A realistic modeling of the non‐linear ductile behavior of the RC walls is considered in combination with the characteristics of the dynamic torsional response of asymmetric buildings. Design criteria such as the determination of the system ductility, taking into account the location and ductility demand of the RC walls, the story‐drift demand at the softer (most displaced) edge of the building under the design earthquake, the allowable ductility (ultimate limit state) and the allowable story‐drift (performance goals) are discussed. The definition of an eccentricity of the earthquake‐equivalent lateral force is proposed and used to determine the effective displacement profile of the building yet not the strength distribution under the design earthquake. Furthermore, an appropriate procedure is proposed to calculate the fundamental frequency and the earthquake‐equivalent lateral force. A new deformation‐based seismic design method taking into account the characteristics of the dynamic torsional response, the ductility of the RC walls, the system ductility and the story‐drift at the softer (most displaced) edge of the building is presented and illustrated with an example of seismic design of a multi‐story asymmetric RC wall building. Copyright © 2005 John Wiley & Sons, Ltd.     

The influence of impurities on the dissolution of Ca- and Sr-bearing barite at room temperature

1INTRODUCTION BARITE(BASO4)ISANEXTREMELYINSOLUBLESALT;THISAROUSESPROBLEMSINPETROLEUMINDUSTRYBECAUSE BASO4ISAPARTICULARLYINTRACTABLESCALINGAGENT.BARITE PRECIPITATIONINTHEWELLBOREENVIRONMENTGENERALLYRE QUIRESMECHANICALREMOVAL,WITHCONSIDERABLEASSOCIAT EDEXPE…