ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
Geophysical measurements of a single physical property provide weak constraints on the large-scale porosity structure of the sea-floor. This limitation arises from fundamental principles which may be overcome by examing two independent pieces of information. As an example, electrical resistivity values and seismic compres-sional velocities from the East Pacific Rise at 13°N are simultaneously compared to various combinations of empirical expressions. the best agreement between theory and the data sets is found using either the connected Hashin-Shtrikman bound or, equivalently, Archie's law with a low value of exponent to describe the resistivities, and Wyllie's time-average equation for the seismic velocities. the combination implicitly requires a connected fluid distribution and, hence, a highly permeable crust throughout the uppermost 1 km of sea-floor. Porosities in the surface regions remain poorly constrained. Assuming a fluid temperature below 15°C predicts porosities of at least 20 per cent in the uppermost 50 m, decreasing to less than 1 per cent at depths around 1 km. Permeabilities of around 5 X 10−12m2 are inferred for the surface regions decreasing to 3 × 10−17 m2 at depth.The method described should prove useful in constraining the structure in older sea-floor as more resistivity profiles are gathered along with seismic data.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1994.tb04023.x
