Using Eigenpattern Analysis to Constrain Seasonal Signals in Southern California

— Earthquake fault systems are now thought to be an example of a complex nonlinear system (Bak, et al., 1987; Rundle and Klein, 1995). The spatial and temporal complexity of this system translates into a similar complexity in the surface expression of the underlying physics, including deformation and seismicity. Here we show that a new pattern dynamic methodology can be used to define a unique, finite set of deformation patterns for the Southern California Integrated GPS Network (SCIGN). Similar in nature to the empirical orthogonal functions historically employed in the analysis of atmospheric and oceanographic phenomena (Preisendorfer, 1988), the method derives the eigenvalues and eigenstates from the diagonalization of the correlation matrix using a Karhunen-Loeve expansion (KLE) (Fukunaga, 1970; Rundle et al., 2000; Tiampo et al., 2002). This KLE technique may be used to determine the important modes in both time and space for the southern California GPS data, modes that potentially include such time-dependent signals as plate velocities, viscoelasticity, and seasonal effects. Here we attempt to characterize several of the seasonal vertical signals on various spatial scales. These, in turn, can be used to better model geophysical signals of interest such as coseismic deformation, viscoelastic effects, and creep, as well as provide data assimilation and model verification for large-scale numerical simulations of southern California.     

Dynamic performance of twin curved cable‐stayed bridges

The dynamic behaviour of two curved cable‐stayed bridges, recently constructed in northern Italy, has been investigated by full‐scale testing and theoretical models. Two different excitation techniques were employed in the dynamic tests: traffic‐induced ambient vibrations and free vibrations. Since the modal behaviour identified from the two types of test are very well correlated and a greater number of normal modes was detected during ambient vibration tests, the validity of the ambient vibration survey is assessed in view of future monitoring. For both bridges, 11 vibration modes were identified in the frequency range of 0ndash;10Hz, being a one‐to‐one correspondence between the observed modes of the two bridges. Successively, the information obtained from the field tests was used to validate and improve 3D finite elements so that the dynamic performance of the two systems were assessed and compared based on both the experimental results and the updated theoretical models. Copyright © 2003 John Wiley & Sons, Ltd.     

Seismic tests on reinforced concrete and steel frames retrofitted with dissipative braces

Seismic tests have been conducted on two 3‐storey structures protected with pressurized fluid‐viscous spring damper devices. One of the structures was a reinforced concrete frame with clay elements in the slabs, while the other one was a steel frame with steel/concrete composite slabs. The spring dampers were installed through K bracing in between the floors. The tests were performed by means of the pseudodynamic method, which allowed the use of large and full‐size specimens, and by implementing a specific compensation strategy for the strain‐rate effect at the devices. The test results allowed the verification of the adequacy of the attachment system as well as the comparison of the behaviour of the unprotected buildings with several protected configurations, showing the benefits of the application of the devices and the characteristics of their performance. The response of the protected structures was always safer than that of the unprotected ones mainly due to a significant increase of equivalent damping. The increase in the damping ratio depends on the level of deformation. Copyright © 2004 John Wiley & Sons, Ltd.     

Bayesian algorithm for the estimation of the dielectric constant from active and passive remotely sensed data

An inversion technique based on the merging of microwave remotely sensed data is applied to ground-based radiometer and scatterometer data acquired for the same area. The purpose of this technique is to retrieve the dielectric constant of bare soils. The algorithm is based on a Bayesian approach and combines prior information on the dielectric constant and surface roughness with observed data, in order to obtain a marginal posterior probability density function. The function describes how the probability is distributed within the range of the dielectric constant values, given the measured values of emissivity and backscattering coefficient. The algorithm allows for the incorporation of all the available sources of information, such as multipolarization and multifrequency data. Several criteria, which have been used to compare the predicted and the observed values, show that for dielectric constant values higher than 10 the best performance is achieved when data with one polarization and one or two frequencies are exploited. For dielectric constant values of less than 10, the configuration with two polarizations produces the best estimates.     

Paleozoic serpentinite-enclosed chromitites from Tehuitzingo (Acatlán Complex, southern Mexico): a petrological and mineralogical study

The serpentinites and associated chromitite bodies in Tehuitzingo (Acatlán Complex, southern Mexico) are in close relationship with eclogitic rocks enclosed within a metasedimentary sequence, suggesting that the serpentinites, chromitites and eclogitic rocks underwent a common metamorphic history.Primary chromites from the chromitite bodies at Tehuitzingo are of refractory-grade (Al-rich) and have a chemical composition similar to that expected to be found in an ophiolitic environment. The chromite grains in chromitites and serpentinites are systematically altered to ‘ferritchromite’. The alteration trend is usually characterized by a decrease in the Al, Mg and Cr contents coupled by an increase in Fe³⁺ and Fe²⁺.The Tehutizingo chromitites have low Platinum Group Elements (PGE) contents, ranging from 102 to 303 ppb. The chondrite-normalized PGE patterns are characterized by an enrichment in the Ir-subgroup elements (IPGE=Os, Ir, Ru) relative to the Pd-subgroup elements (PPGE=Rh, Pt, Pd). In addition, all chromitite samples display a negative slope from Ru to Pd [(Os+Ir+Ru)/(Pt+Pd)=4.78−14.13]. These patterns, coupled with absolute PGE abundances, are typical of ophiolitic chromitites elsewhere. Moreover, all the analyzed samples exhibit chondrite-normalized PGE patterns similar to those found for non-metamorphosed ophiolitic chromitites. Thus, the PGE distribution patterns found in the Tehuitzingo chromitites have not been significantly affected by any subsequent Paleozoic high-pressure (eclogite facies) metamorphic event.The chondrite-normalized PGE patterns of the enclosing serpentinites also indicate that the PGE distribution in the residual mantle peridotites exposed in Tehuitzingo was unaffected by high-pressure metamorphism, or subsequent hydrothermal alteration since the serpentinites show a similar pattern to that of partially serpentinized peridotites present in mantle sequences of non-metamorphosed ophiolites.Our main conclusion is that the chromitites and serpentinites from Tehuizingo experienced no significant redistribution (or concentration) of PGE during the serpentinization process or the high-pressure metamorphic path, or during subsequent alteration processes. If any PGE mobilization occurred, it was restricted to individual chromitite bodies without changing the bulk-rock PGE composition.Our data suggest that the Tehuitzingo serpentinites and associated chromitites are a fragment of oceanic lithosphere formed in an arc/back-arc environment, and represent an ophiolitic mantle sequence from a supra-subduction zone, the chemical composition of which remained essentially unchanged during the alteration and metamorphic events that affected the Acatlán Complex.     

Web-cam’s potential for collaborative activities in the Earth sciences

We report here our experiences from using easily acquired web-cam components for collaborative ventures in the Earth sciences. We have used a variety of hardware and different software. We demonstrate from various locations in the U.S.A. the feasibility of using web-cam in multitudinous activities, relevant for conducting research and knowledge dissemination. We summarize the quality of the connections from the various combinations of communicating parties. Today, web-cams can be utilized as an economical and viable means of point-to-point communication in the Earth science community. Greater bandwidth is sorely needed for activities such as multi-party conferencing on the present internet network. We propose that web-cam can be readily deployed as a web-service for facilitating collaborative research over the GRID infrastructure, using the middleware Narada-Brokering. Web-cam will play an important role in the emerging field of geoinformatics.     

Wildlife management and land reform in southeastern Zimbabwe: a compatible pairing or a contradiction in terms?

This paper examines the melding of two discourses in southeastern Zimbabwe: land reform and wildlife management. The former seeks to redistribute large, ‘under-utilized’ landholdings to smallholders whilst the latter needs extensive land holdings to be viable. These two discourses are rooted in very different models of development. The land reform exercise emphasizes direct redistribution, equity and land for crops; whilst the wildlife management discourse tends to stress maximizing foreign exchange earnings, encouraging public-private partnerships and trickle down. Yet there has been a recent flurry of interest in the development of ‘wildlife models’ for land reform which would combine the two. This paper investigates whether the competing discourses about land for smallholders and wildlife-based land reform are compatible or can be successfully reconciled. It traces the ways they have come together in Zimbabwe’s southeast lowveld and examines the ‘science’ and politics underlying their melding. Finally it explores the potential implications for rural people’s livelihoods of this development. It concludes that land reform and wildlife management can be reconciled, but probably not in a particularly equitable way: it is more likely to provide an opening for an equitable land reform agenda to be usurped by local and non-local elites with wildlife interests.     

Chemical composition of 15 photometric analogues of the Sun

The results of a spectroscopic analysis of 15 stars that are photometric analogues of the Sun are reported. The effective temperatures and surface gravities in the stellar atmospheres are derived from published photometric indices and the HIPPARCOS parallaxes. The abundances of 33 elements ranging from lithium to europium are analyzed based on high-dispersion spectra taken with the new Coudé echelle spectrometer of the Terskol Observatory in the northern Caucasus. The main parameters of most of the stars agree with the data of an [Fe/H] catalog published in 2001. Our study of the chemical compositions of the sample stars indicates that photometric analogues of the Sun can be divided into three groups according to their elemental abundances: six stars have solar chemical composition, four have abundance excesses, and five have some abundance deficiencies. The sample contains two metal-deficient subgiants (HD 133002 and HD 225239). Our results demonstrate that photometric similarity is not a sufficient criterion to consider a star as solar analogue. When several criteria, including chemical composition, are simultaneously taken into account, only four stars from the sample can be considered true solar analogues: HD 10307, HD 34411, HD 146233 (18 Sco), and HD 186427 (16 Cyg B). These results confirm the previously published suggestion that 18 Sco is the most probable twin of the Sun: essentially all the parameters of the two stars coincide within the errors.