Figure 12: The variation in bulk resistivity downhole derived from logging in Hole 504B, the crustal velocity structure at the site, and the lithostratigraphy. The crustal velocity model is based on a Layer 3 velocity of 6.5km/sac derived from sonobuoy studies around Hole 504B (vertical bar) and a linear regression of the shallow crustal velocity gradient determined from travel-time and amplitude modeling of the borehole seismic experiment (thick solid line). For comparison, the thin grey line shows the sonic velocity log and the dashed line shows the sonobuoy velocity model. The change in the vertical velocity gradient that defines the seismic layer 2/3 boundary at 1.2+/-0.2km sub-basement, occurs within the sheeted-dyke section, about 660m above the base of the hole. At least the upper 400-800m of seismic layer 3 consists of dolerites and metadolerites rather than gabbro. [Detrick et al., 1993]

Retun to the 2003 Fall AGU Poster

THIRD PARTY BOREHOLE SEISMIC EXPERIMENTS DURING THE OCEAN DRILLING PROGRAM

Created on December 10, 2003 by Tom Bolmer