大气电场异常作为地震短临预报标志研究进展

通过对华北地地区进行震前大气电场异常观测研究的较为全面分析和总结,验证和论述了震前大气电场异常的基本特征,用大量的震例证实了在每次较大的近场地震发生前都能观测到该类异常现象,以及当较长一段时间内观测不到该类异常时,近场近期也不会有较大地震发生的可能。     

阿塔卡玛盐湖的综合开发

近年来,智利阿塔卡玛盐湖的开发进展迅速。本文报道了阿塔卡玛盐湖的形成、资源、开发过程、主要技术路线、氯化钾和碳酸锂产品技术经济指标以及阿塔卡玛盐湖的开发前景。     

The Juiz De Fora Granulite Complex of the Central Ribeira Belt, SE Brazil: A Paleoproterozoic Crustal Segment Thrust During the Pan-African Orogeny

The granulites of the Juiz de Fora complex occur within thick basement thrust slices associated with the Pan-African shortening process in the central segment of the Ribeira belt. Five lithological units of the Intermediate tectonic domain of the belt can be identified on the basis of detailed geological mapping: a) orthogranulites, b) orthogneisses; c) kinzigite; d) intrusive garnet charnockite and e) amphibolite facies metasediments of probable Meso to Neoproterozoic age, correlated to the cover of the belt. Petrological data indicate high temperatures and intermediate to low lithostatic pressure conditions for the Paleoproterozoic granulite facies metamorphism. Textures and CO₂-rich fluid inclusions are probably related to an IBC path. Geochemical data do not show relevant compositional change as a result of the granulite metamorphism. Two calc-alkaline suites and tholeiitic to alkaline basic rocks can be related to compressional and extensional settings, respectively. The overall composition of the granulites, the lack of substantial LILE depletion as well as the composition of the fluid inclusion points to granulitization process driven by CO₂-rich fluids. Orthogranulites gave rise to banded gneisses as a result of the Pan-African retrograde metamorphism and intense deformation. The U and Th depletion detected in few rocks is possibly related with the hydrated conditions of the retrograde reactions.     

Constraints on the ore fluids in the Sando Alcalde AuAg epithermal deposit,southwestern Peru: fluid inclusions and stable isotope data

The Sando Alcalde ore deposit (southwestern Peru) has been studied in order to characterize the physicochemical parameters of the ore fluids and to determine the fluid process (mixing or boiling) which involves the precious metal mineralization. Mineralogy, ${\delta }^{18}{\mathrm{O}}_{\mathrm{quartz}}$ isotopic values and fluid inclusion data give arguments in favour of a boiling phenomenon. This conclusion corroborates fluid inclusion studies previously performed in this area on the low-sulphidation epithermal deposits of Arcata, Orcopampa and Apacheta, where boiling has been described as the main factor for ore deposition. To cite this article: A.-S. André-Mayer et al., C. R. Geoscience 337 (2005).     

Seismicity of an andesitic volcano during block-lava effusion: Volcán de Colima, México, November 1998–January 1999

The block-lava effusion at Volcán de Colima, México began on November 20, 1998, after 12 months of seismic activity, and ended about 80 days later. Three types of seismic events were observed during the lava effusion. Volcano—tectonic earthquakes occurred mainly at the very beginning and after the termination of lava effusion. Explosion earthquakes occurred frequently during the period of the maximum rate in lava effusion. The remainder of the seismic signals were associated with pyroclastic flows and rockfalls from the lava dome. These latter signals increased sharply in number at the onset of lava effusion. The rate of occurrence remained high when the lava discharge rate decreased but gradually decreased after the termination of lava effusion. Maximum daily durations of seismic signals are proportional to the daily volumetric output of lava, indicating the dependence of the number of pyroclastic flows on the rate of lava output. A log-log plot of seismic signal duration vs. number of events with this duration displays a linear relationship. The short-period seismic signals can be divided into three categories based on duration: short events with durations less than 100 s; intermediate events with durations between 100 and 250 s; and long events with durations longer than 250 s. We infer that long events correspond to pyroclastic flows with mean deposit volume 2×10⁵ m³, and intermediate events represent pyroclastic flows with mean deposit volume 1×10³ m³.Editorial responsibility: J McPhie     

Paramètres statistiques de la houle au large de la côte sud-aquitaine

Statistical parameters of waves on the south Aquitaine coast have been determined by comparison of two datasets: in situ local measurements on a short duration and numerical simulation outputs from the WAVEWATCH III model over a period of 6 years and 9 months. Data and simulation results are well correlated in the case of the significant wave height, whereas in the case of the peak periods $(T_{\mathrm{p}})$ and directions $(D_{\mathrm{p}})$, this correlation is lower. This is due respectively to the intrinsic unstable nature of $T_{\mathrm{p}}$ and the narrow distribution of $D_{\mathrm{p}}$. An adjustment of simulation data on measurement is then used to give an evaluation of the wave statistics for the southern fraction of the French Atlantic coast. Eventually, the relationships between the three statistical variables $(H_{\mathrm{s}},T_{\mathrm{p}},D_{\mathrm{p}})$ are analysed in order to determine representative sea states. The classification obtained shows the predominance of swell regimes, distributed on a very narrow angular sector over wind sea regimes. To cite this article: S. Abadie et al., C. R. Geoscience 337 (2005).     

Géométrie et cinématique post-oligocène des failles d'Aix et de la moyenne Durance (Provence,France)

The southern termination of the left-lateral ‘Moyenne Durance’ Fault (FMD) consists in several segments, some being connected to WSW-trending south-verging reverse faults. To the south, the Aix fault is reactivated in a post-Oligocene strike-slip movement showing that these two faults might belong to the same system. This system seems to transfer, in turn, slip to the east-trending, south-verging Trévaresse reverse fault, allowing southward propagation of the Alpine deformation front in western Provence. Fault kinematics analysis shows lateral stress field change between the two faults. Strike-slip stress state is characterized by an average N150°E trending σ1 near the FMD termination, whilst strike-slip and reverse faulting stress states show north-trending ${\sigma }_1$ to the south. To cite this article: P. Guignard et al., C. R. Geoscience 337 (2005).     

Behavior of radium,thorium and uranium in groundwater near the Buena Lagoon in the Coastal Zone of the State of Rio de Janeiro,Brazil

Groundwater found near the head of the Buena Lagoon in the State of Rio de Janeiro, Brazil, has high salinity and low pH values. There is a strong correlation between concentrations of radium and light rare earth elements (LREEs) that suggests the leaching of monazite as a common source. Radium is present predominantly as ²²⁸Ra. The factors responsible for high radium mobility in groundwater seem to be high levels of salinity resulting in the competition for adsorption sites, and low pH values resulting in the limited adsorption of Ra²⁺ on the positively-charged surface of adsorbents. The behavior of uranium and thorium is also influenced by their speciation and low pH conditions. Uranium is present as a positively charged uranyl ion UO₂²⁺ in low pH samples and is very mobile. Similarly, the presence of positively charged Th⁴⁺ and thorium complexes with sulfate result in relatively high thorium concentrations at a low pH range. On the other hand, the mobility of phosphate released by dissolving monazite is probably reduced due to its adsorption and precipitation close to its source.     

Instability of Two Interacting Quasi-Monochromatic Waves in Shallow Water

The nonlinear interactions of waves with a double-peaked power spectrum have been studied in shallow water.The starting point is the prototypical equation for nonlinear unidirectional waves in shallow water,i.e.the Korteweg de Vries equation.By means of a multiple-scale technique two defocusing coupled Nonlinear Schrdinger equations are derived.It is found analytically that plane wave solutions of such a system are unstable for small perturbations,showing that the existence of a new energy exchange mechanism which can influence the behavior of ocean waves in shallow water.