2D characterization of near-surface V P/V S: surface-wave dispersion inversion versus refraction tomography

International audienceThe joint study of pressure (P-) and shear (S-) wave velocities (Vp and Vs ), as well as their ratio (Vp /Vs), has been used for many years at large scales but remains marginal in near-surface applications. For these applications, and are generally retrieved with seismic refraction tomography combining P and SH (shear-horizontal) waves, thus requiring two separate acquisitions. Surface-wave prospecting methods are proposed here as an alternative to SH-wave tomography in order to retrieve pseudo-2D Vs sections from typical P-wave shot gathers and assess the applicability of combined P-wave refraction tomography and surface-wave dispersion analysis to estimate Vp/Vs ratio. We carried out a simultaneous P- and surface-wave survey on a well-characterized granite-micaschists contact at Ploemeur hydrological observatory (France), supplemented with an SH-wave acquisition along the same line in order to compare Vs results obtained from SH-wave refraction tomography and surface-wave profiling. Travel-time tomography was performed with P- and SH- wave first arrivals observed along the line to retrieve Vtomo p and Vtomo s models. Windowing and stacking techniques were then used to extract evenly spaced dispersion data from P-wave shot gathers along the line. Successive 1D Monte Carlo inversions of these dispersion data were performed using fixed Vp values extracted from Vtomo p the model and no lateral constraints between two adjacent 1D inversions. The resulting 1D Vsw s models were then assembled to create a pseudo-2D Vsw s section, which appears to be correctly matching the general features observed on the section. If the pseudo-section is characterized by strong velocity incertainties in the deepest layers, it provides a more detailed description of the lateral variations in the shallow layers. Theoretical dispersion curves were also computed along the line with both and models. While the dispersion curves computed from models provide results consistent with the coherent maxima observed on dispersion images, dispersion curves computed from models are generally not fitting the observed propagation modes at low frequency. Surface-wave analysis could therefore improve models both in terms of reliability and ability to describe lateral variations. Finally, we were able to compute / sections from both and models. The two sections present similar features, but the section obtained from shows a higher lateral resolution and is consistent with the features observed on electrical resistivity tomography, thus validating our approach for retrieving Vp/Vs ratio from combined P-wave tomography and surface-wave profiling

Chromosomal assignment of four genes encoding Na/H exchanger isoforms in human and rat.

The plasma membrane Na/H exchanger plays an essential role in regulating intracellular pH and Na+ concentration and has been implicated in several pathophysiological conditions, including essential hypertension and congenital secretory diarrhea. Four isoforms of the Na/H exchanger encoded by separate genes have recently been identified by cDNA cloning. To map their locations in the human and rat genomes, rat isoform-specific cDNA probes were hybridized to Southern filters containing panels of somatic cell hybrids that segregate either human or rat chromosomes. The rat Nhe1 gene was assigned to Chromosome (Chr)5, extending the homology with human chromosome 1p that has previously been shown to contain the human NHE1 gene. The genes encoding the NHE-2 and NHE-4 isoforms were syntenic in the two species and assigned to rat Chr 9 and human Chr 2. A single Nhe3 gene was detected in rat and assigned to Chr 1. In contrast, although evidence to date has suggested a single human NHE3 gene on Chr 5, two NHE3 genes, NHE3A and NHE3B, were identified and assigned to Chrs 10 and 5, respectively. Interestingly, rat Chr 1 has recently been found to carry a gene controlling systolic blood pressure upon sodium loading in stroke-prone, spontaneously hypertensive rats. Thus, this and other evidence implicates rat Nhe3 as a possible candidate gene in this disease process.Journal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe