Hydrothermal circulation at the Cleft-Vance overlapping spreading center : results of a magnetometric resistivity survey

We report on a magnetometric resistivity sounding carried out in the overlapping spreading center between the Cleft and Vance segments of the Juan de Fuca Ridge. The data collected reveal a strong three dimensionality in the crustal electrical resistivity structure on wavelengths of a few kilometers. Areas of reduced crustal electrical resistivities, with values approaching that of seawater, are seen beneath the neovolcanic zones of both active spreading centers. We interpret these reduced resistivities as evidence of active hydrothermal circulation within the uppermost 1 km of hot, young oceanic crust

Subsurface characterization using time-domain electromagnetics at the Texas A&M University Brazos River Hydrologic Field Site, Burleson County, Texas

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to [email protected], referencing the URI of the item.Includes bibliographical references: p. 99-102.Issued also on microfiche from Lange Micrographics.A transient controlled-source electromagnetic (TDEM) survey has been performed at the Texas A&M University Hydrogeological Test Site adjacent to the Brazos River in Burleson County, Texas. A I-D regularized inversion of the data shows that the surficial clays appear as zones of low electrical resistivity to depths of about 6m and the sandy unconsolidated alluvial unit which constitutes the main aquifer for subsurface transport of groundwater is apparent as a resistive zone at the depths between 6-20m. Inversion results also show that the TDEM data is sensitive to the lateral heterogeneity in geology at the site. Analysis of collected TDEM data indicates that it is not influenced by the aluminum pipeline present at the research site. The TDEM survey was conducted as part of a larger, interdisciplinary effort by agricultural engineers, environmental geochemists and geophysicists to characterize nonpoint-source containinant transport at the test site