Open AccessPore pressure and oceanic crustal seismic structure
Author(s) -
Christensen Nikolas I.
Publication year - 1984
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1984.tb02232.x
Subject(s) - geology , overpressure , pore water pressure , oceanic crust , crust , basalt , shear (geology) , ridge , overburden pressure , hydrostatic pressure , poisson's ratio , seismology , mid ocean ridge , petrology , geophysics , poisson distribution , geotechnical engineering , subduction , mechanics , paleontology , statistics , physics , tectonics , mathematics , thermodynamics
Summary Marine refraction studies during the past decade have found considerable lateral variability in the seismic properties of the upper basaltic regions of the oceanic crust. In many localities, compressional and shear‐wave velocities are quite low at the top of the basalt section and velocities increase rapidly with depth. It is concluded that pore pressure may be at least in part responsible for the low upper crustal velocities and contribute significantly to the lateral variability. This is supported by compressional and shear‐wave velocity measurements as functions of confining pressure and pore pressure for basalt from the Juan de Fuca ridge and dolerite from the Samail ophiolite, Oman. Within the oceanic crust, regions of overpressure and underpressure will possess anomalous velocities, the magnitude of which will depend upon the porosity and the deviation of the pore pressure from hydrostatic. The influence of pore pressure on velocities is expected to diminish with depth and is unlikely to be significant at lower crustal depths where porosity is extremely low. Of significance, Poisson's ratio is shown to be dependent on pore pressure as well as confining pressure. At constant confining pressure, Poisson's ratio increases with increasing pore pressure. Thus, overpressured regions within the upper oceanic crust are likely to have relatively high Poisson's ratios as well as low compressional‐ and shear‐wave velocities.