Establishment of a Non-Permanent GPS Network to Monitor the Recent NE-SW Deformation in the Granada Basin (Betic Cordillera,Southern Spain)

The Granada Basin (Central Betic Cordillera), one of the most seismically active areas of the Iberian Peninsula, is currently subjected to NW-SE compression and NE-SW extension. The present day extension is accommodated by normal faults with various orientations but particularly with a NW-SE strike. At the surface, these active NW-SE normal faults are mainly concentrated on the NE part of the Basin. In this part we have selected a 15-km long segment where several active normal faults crop out. Using the marine Tortonian rocks as a reference, we have calculated a minimum extensional rate of 0.15-0.30 mm/year. The observed block rotation, the listric geometry of faults at depth and the distribution of seismicity over the whole Basin, indicate that this rate is a minimum value. In the framework of an interdisciplinary research project a non-permanent GPS-network has been established in the central sector of Betic Cordillera to monitor the crustal deformations. The first two observation campaigns were done in 1999 and 2000.     

Alpujarride attribution of the supposed ‘Almagride Complex’ (Betic Internal Zone,Almerı́a Province,Spain)Appartenance Alpujarride du prétendu « Complexe almagride » (Zones internes bétiques,province d'Almeria,Espagne)

The differentiation of units in the Sierra de Almagro has been a source of controversy. There were defined the Almagride and Ballabona–Cucharón complexes, the former considered by several authors as part of a Subbetic metamorphosed and outcropping in a tectonic window. In this study, the units of Ballabona, Almagro and Cucharón are integrated into a single one, that of Tres Pacos, because they correspond to different parts of the same stratigraphic series. This unit is tectonically over the Nevado–Filabride Complex. The existence of the Almagride and Ballabona–Cucharón complexes is discarded and their units form part of the Alpujarride Complex. To cite this article: C. Sanz de Galdeano, F.J. Garc??a Tortosa, C. R. Geoscience 334 (2002) 355–362.     

Seasonal variation of the soil seed bank of grasses in central Argentina as related to grazing and shrub cover

The objectives of this research were to (a) study seasonal variation of the seed bank of grasses in two areas with different grazing history, (b) analyse the effect of the presence of shrubs on the seed bank and (c) study seed viability and dormancy in buried seeds of Piptochaetium napostaense and Stipa tenuis. The seed density of grasses was in general low and showed seasonal variation. Most of the grasses showed maximum seed density in December when seed dispersal occurs. Shrub cover did not show a marked influence in seed accumulation. The relatively high number of damaged seeds suggests that predation may be an important factor in seed bank dynamics in the Caldenal. Seeds of dominant perennial forage grasses showed dormancy that could explain, at least in part, persistence of these species in spite of periodical disturbance.     

System identification of the Vincent Thomas suspension bridge using earthquake records

The Vincent Thomas Bridge in the Los Angeles metropolitan area, is a critical artery for commercial traffic flow in and out of the Los Angeles Harbor, and is at risk in the seismically active Southern California region, particularly because it straddles the Palos Verdes fault zone. A combination of linear and non‐linear system identification techniques is employed to obtain a complete reduced‐order, multi‐input–multi‐output (MIMO) dynamic model of the Vincent Thomas Bridge based on the dynamic response of the structure to the 1987 Whittier and 1994 Northridge earthquakes. Starting with the available acceleration measurements (which consists of 15 accelerometers on the bridge structure and 10 accelerometers at various locations on its base), an efficient least‐squares‐based time‐domain identification procedure is applied to the data set to develop a reduced‐order, equivalent linear, multi‐degree‐of‐freedom model. Although not the main focus of this study, the linear system identification method is also combined with a non‐parametric identification technique, to generate a reduced‐order non‐linear mathematical model suitable for use in subsequent studies to predict, with good fidelity, the total response of the bridge under arbitrary dynamic environments. Results of this study yield measurements of the equivalent linear modal properties (frequencies, mode shapes and non‐proportional damping) as well as quantitative measures of the extent and nature of non‐linear interaction forces arising from strong ground shaking. It is shown that, for the particular subset of observations used in the identification procedure, the apparent non‐linearities in the system restoring forces are quite significant, and they contribute substantially to the improved fidelity of the model. Also shown is the potential of the identification technique under discussion to detect slight changes in the structure's influence coefficients, which may be indicators of damage and degradation in the structure being monitored. Difficulties associated with accurately estimating damping for lightly damped long‐span structures from their earthquake response are discussed. The technical issues raised in this paper indicate the need for added spatial resolution in sensor instrumentation to obtain identified mathematical models of structural systems with the broadest range of validity. Copyright © 2003 John Wiley & Sons, Ltd.     

Separate lead isotope analyses of leachate and residue rock fractions: implications for metal source tracing in ore deposit studies

Separate lead isotope analyses of leachate and residue fractions are applied to a broad spectrum of rocks commonly investigated in metallogenic studies. Resulting data highlight a systematic behavior of leachate and residue fractions with respect to lead isotope compositions, which essentially depends on the mineralogical composition of the rock. Granitoid and high-grade metamorphic rocks have residue compositions virtually identical to common lead. In contrast, low-grade metasedimentary rocks may have residue compositions swamped by radiogenic lead of leach-resistant zircons. Mafic magmatic rocks have residues that are often more radiogenic than leachates, depending on the ratio of leach-refractory zircons to common lead in the residual fraction of these rocks. Separate leachate and residue analyses of source rocks provide two lead isotope end members whose mixture may represent lead with the appropriate ore fluid composition. Our leaching experiments indicate that hot acid solutions (and by inference hydrothermal fluids) preferentially leach radiogenic lead from medium- to high-grade metamorphic and granitoid rocks, whereas they preferentially leach common lead from low-grade metasedimentary and mafic magmatic rocks. The method presented in this study provides a reliable alternative to other methods (i.e., age-correction of bulk-rock compositions) for the determination of the common lead signature of felsic to intermediate magmatic rocks. This may be preferable to age-corrected bulk-rock analyses, where ages to apply for corrections of bulk-rock data are not known or where moderately to highly altered rocks must be used. Case studies of orogenic gold and MVT districts of Peru (Pataz and San Vicente, respectively) show that separate leachate and residue lead isotope analyses carried out systematically on whole rocks allow a more thorough evaluation of metal source reservoirs than does the standard method of age-corrected or uncorrected bulk-rock analyses.     

Computational study of tetrahedral Al–Si and octahedral Al–Mg ordering in phengite

 As part of a wider study of the nature and origins of cation order–disorder in micas, a variety of computational techniques have been used to investigate the nature of tetrahedral and octahedral ordering in phengite, K₂ ^[6](Al₃Mg)^[4](Si₇Al)O₂₀(OH)₄. Values of the atomic exchange interaction parameters J _n used to model the energies of order–disorder were calculated. Both tetrahedral Al–Si and octahedral Al–Mg ordering were studied and hence three types of interaction parameter were necessary: for T–T, O–O and T–O interactions (where T denotes tetrahedral sites and O denotes octahedral sites). Values for the T–T and O–O interactions were taken from results on other systems, whilst we calculated new values for the T–O interactions. We have demonstrated that modelling the octahedral and tetrahedral sheets alone and independently produces different results from modelling a whole T–O–T layer, hence justifying the inclusion of the T–O interactions. Simulations of a whole T–O–T layer of phengite indicated the presence of short-range order, but no long-range order was observed. Received: 8 August 2002 / Accepted: 14 February 2003 Acknowledgements The authors are grateful to EPSRC (EJP) and the Royal Society (CIS) for financial support. Monte Carlo simulations were performed on the Mineral Physics Group's Beowulf cluster and the University of Cambridge's High Performance Computing Facility.     

Validation of Landslide Susceptibility Maps; Examples and Applications from a Case Study in Northern Spain

A procedure for validating landslide susceptibility maps wasapplied in a study area in northern Spain and the results obtained compared. Validationwas used to carry out sensitivity analysis for individual variables and combinationsof variables. The validity of different map-making methods was tested, as well as theutility of different types of Favourability Functions. The results obtained show thatvalidation is essential to determine the predictive value of susceptibility maps. Italso helps to better select the most suitable function and significant variables, thus improving the efficiency of the mapping process. Validation based on a temporal strategy makes it possible to derive hazard maps from susceptibility maps.     

The Influence of Geomorphologic Heritage on Present Nival Erosion: Peñalara, Spain

This article examines how snow plays a role in current erosive processes in a high mountain area (1800—2400 m a.s.l.) known as Peñalara, located in Spain's Central Range (40°50' N; 3°58' W). The hypothesis maintains that snow becomes an important erosive factor when it accumulates over sedimentary or weathered materials, therefore geomorphological heritage is a key factor in nival erosion. To test this hypothesis, the authors identified the landforms in the study area and determined their relative ages by weathering and lichenometry ( Rizocarpon geographicum ag. ), differentiating between preglacial, glacial (Recent Pleistocene) and postglacial (Holocene) forms. The information was used to plot a reticulate pattern of observation sites for the study area. Snow depth and the movement of selected blocks at each site were recorded from October 1991 to June 1995. The relationship between late-lying snowpatches, geomorphological heritage and current erosive processes was determined. Between 1800 and 2000 m a.s.l., there is an indirect relationship between snowpatches and predominant processes (stream incision and gelifluction) on terminal moraines. Between 2000 and 2200 m, direct action is present where there are late-laying snowpatches on lateral moraines and some glacial steps. Between 2200 and 2400 m, gelifraction and gravity processes are also in direct relation to snowpatches.