Contrǒle des concentrations d'aluminium dissous dans les eaux des sources thermales

We analized about 100 hot springs of different regions in France for dissolved Al. In an area where the chemical composition of the springs for major elements is about the same and the emergence temperatures are different, we usually observe correlations between dissolved Al and temperature. This correlation is positive in the case of high pH hot springs (Pyrénées). On the contrary, the correlation is negative for the CO₂ rich waters of the Massif Central (Vichy). We also observe intermediate patterns, where Al concentrations are roughly independant of the temperature.Using a set of consistant values of thermodynamical data for ions and minerals of Al, we find that the observed correlations between Al and temperature are related to the solubility of a mineral which is generally kaolinite.     

Acquisition des ions alcalino-terreux par les eaux thermales carbogazeuses

Nous présentons différents arguments tendantàmontrer qu'une proportion importante deséléments alcalinoterreux présents dans les sources thermominérales du Massif Central français est acquise en subsurface lors de la remontée de l'eau. Au cours de ces réactions subsuperficielles, le rapport Na/K est peu modifié. Les hautes teneurs en Ca²⁺ et Mg²⁺ de ces eaux ne constituent pas un argument suffisant pour rejeter l'information fournie par le géothermomètre Na/K.Nous montronségalement que l'utilisation des rapports isotopiques du strontium comme indicateur d'origine doite?tre menée avec précautions.     

Oxygen and hydrogen isotopes in the volcano-sedimentary complex of Huelva (Iberian Pyrite Belt): example of water circulation through a volcano-sedimentary sequence

The minerals of basic and acidic rocks from the volcano-sedimentary sequence in the Huelva area, Spain, Iberian Pyrite Belt, display an extendedδ¹⁸O enrichment. Quartzδ¹⁸O values from quartz-keratophyres vary from +10.5 to +17.0 and feldsparδ¹⁸O values from +14.4 to +16.0. For the spilite or spilitized doleritesδ¹⁸O values vary from +9.9 to +13.4 for feldspar, from +6.4 to +9.8 for chlorite, from +3.7 to +4.3 for ilmenite and from +13.6 to +14.0 for quartz, but pyroxene exhibits magmatic values, from +5.3 to +6.1 with an exception at +7.5. The chloriteδD values vary from −34 to −43‰.This is attributed to hydrothermal alteration with seawater enriched inδ¹⁸O by circulation through sediments.The temperatures of interaction determined from isotopic fractionations between minerals range from 400° to 520°C.CalculatedδD andδ¹⁸O values for water in equilibrium with the minerals at isotopic temperatures range from −16 to +5 and from +8.3 to +12.8, respectively.A model of circulation of seawater through a pile of sedimentary rocks and then through basaltic rocks is proposed to explain the high¹⁸O compositions of the rocks from the Huelva District. Water/rock mass ratios calculated from this model range between 0.3 and 0.7 for the determined range of temperatures.     

Towards a microzonation of the Greater Beirut area: an instrumental approach combining earthquake and ambient vibration recordings

Lebanon is situated on the 1000 km long Levant transform fault that separates the Arabic from the African tectonic plates. In Lebanon, the Levant fault splits up into a set of ramifications that had, in the past, generated major destructive earthquakes causing a lot of destruction and thousands of casualties. The most devastating one was the 551 A.D. offshore earthquake that destroyed Beirut, the capital of Lebanon. This paper presents a site effect study in Beirut, aimed at proposing a framework for future microzonation works in the city. It includes two complementary parts. A 6-month, temporary seismological experiment was first conducted to estimate the site response at 10 sites sampling the main geological units of Beirut on the basis of local and regional earthquake recordings. This spatially sparse information was then complemented by a large number (615) of microtremor measurements covering the Beirut municipality and part of its suburbs with a 400 m dense grid. The recordings were analysed with the standard site-to-reference and horizontal-to-vertical spectral ratio methods for earthquake recordings, and the horizontal-to-vertical ratio for ambient noise recordings. Significant ground motion amplification effects (up to a factor of 8) are found in a few areas corresponding to recent deposits. The consistency between results from earthquake and microtremor recordings allows proposing a map of the resonance frequencies within the city and its suburbs, with frequencies ranging from 0.5 to 5 Hz for the deepest deposits, and 5–10 Hz for shallow areas. Finally, the results are discussed and a way to combine the results obtained from the temporary stations to the great number of recordings coming from the permanent Lebanese network is proposed.     

Borehole water and hydrologic model around the Nojima fault, SW Japan

The active fault drilling at Nojima Hirabayashi after the 1995 Hyogoken-nanbu (Kobe) earthquake (M_JMA = 7.2) provides us with a unique opportunity to investigate subsurface fault structure and the in-situ properties of fault and fluid. The borehole intersected the fault gouge of the Nojima fault at a depth interval of 623 m to 625 m. The lithology is mostly Cretaceous granodiorite with some porphyry dikes.The fault core is highly permeable due to fracturing. The borehole water was sampled in 1996 and 2000 from the depth interval between 630 and 650 m, just below the fault core. The chemical and isotopic compositions were analyzed. Carbon and oxygen isotope ratios of carbonates from the fault core were analyzed to estimate the origin of fluid.The following conclusions were obtained. (1) The ionic and isotopic compositions of borehole water did not change from 1996 to 2000. They are mostly derived from local ground water as mentioned by Sato and Takahashi [Sato, T., Takahashi, M., 2000. Chemical and isotopic compositions of groundwater obtained from the Hirabayashi well. Geological Survey of Japan Interim Report No. EQ/00/1, 187–192.]. (2) Geochemical speciation revealed that the borehole water was derived from a relatively deep reservoir, which may be situated at a depth of 3 to 4 km where the temperature is about 80–90 °C. (3) The shallower part of the Nojima fault (shallower than the reservoir depth) has not been healed from the hydrological viewpoints 5 years after the event, in contrast to the rapid healing detected by S wave splitting [Tadokoro, K., Ando, M., 2002. Evidence for rapid fault healing derived from temporal changes in S wave splitting, Geophys. Res. Lett., 29, 10.1029/2001GL013644.]. (4) Precipitation of calcite from the present borehole water since drilling supports the idea of precipitation of some calcite in coseismic hydraulic fractures in the fault core [Boullier, A-M., Fujimoto, K., Ohtani, T., Roman-Ross, G., Lewin, E., Ito, H., Pezard, P., Ildefonse, B., 2004. Textural evidence for recent co-seismic circulation of fluids in the Nojima fault zone, Awaji Island, Japan., Tectonophysics, 378, 165–181.]. (5) Carbon and oxygen isotope ratios of calcite indicated that the meteoric water flux had been localized at the fault core. (6) A difference in the carbon isotope ratio between the footwall and the hanging wall suggests that the fault has been acted as a hydrologic barrier, although the permeability along the fault is still high.     

A 12,000-Year Pollen Record from Lake Maliq, Albania

Pollen data from Lake Maliq, the first from Albania, contribute new information to the discussion of the vegetational, hydrological, and climatological history of the Balkans since 12,000 yr B.P. During late-glacial time, a perennial lake expanded at Maliq. It was surrounded by a complex vegetation association composed of steppe and mixed forest elements. The highly diverse forest flora suggest that late-glacial forest refugia were more developed here at middle altitude, rather than at higher altitude as previously suggested. The forest developed after 9800 yr B.P., while the water level remained high in the Korçë basin until 5000 yr B.P. Different environmental conditions, characterized by lower available moisture and warmer winters, progressively took place after this date. Human activity in the Korçë basin ca. 4500 yr B.P. was coeval with conditions characterized by an increase in winter temperatures and a decrease in summer moisture.     

Site effect assessment using KiK-net data: part 2—site amplification prediction equation based on f<Subscript>0</Subscript> and Vsz

This paper presents empirical correlations between amplification factors and simple site parameters derived from a large subset of the KiK-net data. The amplification factor is estimated from the ratios between the surface and down-hole horizontal response spectra, corrected for the varying depths and impedance of the down-hole sites (Cadet et al. in Site effect assessment using KiK-net data—part 1—a simple correction procedure for surface/downhole spectral ratios, 2011). Several site parameters are selected on the basis of their simplicity and availability at relatively low cost. They are the shallow time-average velocities V_SZ, with z equal to 5, 10, 20 and 30 m, and the fundamental frequency f₀. The amplification factors are then correlated with each of the individual site parameters; four other “twin-parameter”—couples (f₀, V_SZ)—are also considered and the correlation with amplification factors is performed through a normalization of the frequencies by each site fundamental frequency. The quality of the correlations is given by a misfit compared with the original data variance. The largest variance reduction is obtained with twin-parameter characterizations, out of which the couple (f₀, V_S30) proves to provide the lower misfit. The performance of single parameter correlations is relatively lower; however, the best single parameter proves to be the fundamental frequency, which provides smaller misfit than the Vsz parameters. A comparison is also performed with the amplification factors recommended in European regulations, showing that it is possible right now to significantly improve both the site characterization criteria and the associated amplification factors, for use in building codes and microzonation studies.