Physical properties in Hole 1224 were measured on whole cores, split cores, and discrete samples. The multisensor track (MST) was used to perform nondestructive measurements of GRA bulk density, magnetic susceptibility (MS), compressional wave velocity using the P-wave logger (PWL), and natural gamma radiation (NGR) on whole cores. Discrete sample measurements were made on sediments and hard rock cores. Compressional wave velocity was measured on split cores using the PWS3 contact probe system in the x-direction for soft sediments and in the x-, y- and z- directions for hard rock cubes. Moisture and density properties, such as bulk density, water content, porosity, and grain density, were measured on discrete samples. The thermal conductivity was measured on whole cores for soft sediments and on discrete samples for hard rock cores.
GRA bulk density and magnetic susceptibility were measured every 1.0 cm. NGR was measured every 10 cm.
Three notable zones were identified in the soft sediment acquired from Hole 1224C by MST measurements (Fig. F65). In the first zone, the GRA densities range from 1.5 to 1.8 g/cm3 between 0 and 2 mbsf (Fig. F65A). In the second zone, the GRA densities continuously decrease from 1.8 to 1.5 g/cm3 with increasing depth between 2 and 4.5 mbsf. In the third zone, the GRA densities are relatively constant at 1.5 g/cm3 from 4.5 to 6 mbsf. In the second zone, magnetic susceptibilities remain constant at ~85 (raw meter SI units) (Fig. F65B); however, in the third zone, they rapidly increase from 86 to 125 between 4.5 and 6.0 mbsf. Natural gamma ray intensities rapidly decrease from 115 to 35 counts per second (cps) within 1 mbsf (Fig. F65C); however, they remain constant at 20-30 cps with increasing depth through all three zones. The decrease in bulk density with increasing depth in the second and third zones is difficult to explain.
Moisture and density properties, such as bulk density, water content, porosity, and grain density, were measured on individual samples. Thermal conductivity was measured on split cores for each section. Bulk density and dry density gradually decrease from 1.53 to 1.36 g/cm3 and from 0.8 to 0.5 g/cm3, respectively (Fig. F66; Table T7). Dry densities have similar tendencies to bulk densities, although dry densities are lower than bulk densities. Grain densities range from 2.7 to 2.8 g/cm3 (Fig. F66C). They remain constant at 2.7 g/cm3 between 2.5 and 5.5 mbsf. Porosities gradually increase from 71% to 80% with increasing depth (Fig. F66D). Thermal conductivity remains fairly constant at 0.8 W/(m·K) except for Section 200-1224C-1H-1 (Fig. F67A; Table T8).
PWL velocities remain constant at 1480 m/s between 0 and 1.5 mbsf (Fig. F67B). They slightly increase from 1480 to 1490 m/s between 2.5 and 4.5 mbsf. Between 4.5 and 5 mbsf, they remain constant at 1480 m/s. Below 5 mbsf they range from 1480 to 1500 m/s with increasing depth. PWS velocities were measured on split cores. PWS velocities are ~40 m/s higher than PWL velocities (Fig. F67B; Table T9), although their trends are somewhat similar. This difference can be explained by moisture lost from the split cores during the measurements. PWS velocities remain between 1525 and 1535 m/s except for Section 200-1224C-1H-5, which has a velocity of 1555 m/s. Figure F68 shows the relation of PWL velocity vs. GRA density. As velocity decreases, bulk density increases. This differs from the general relation between bulk density and compressional wave velocity (e.g., Birch, 1960, 1961; Hamilton, 1976).
Most of the physical properties of Hole 1224C show unusual variations with increasing depth. GRA bulk density, PWL velocity, and MS from the MST, and bulk and dry density, porosity, and PWS velocity for individual samples show strong correlations to each other. Birch (1960, 1961) suggested a positive gradient between velocity and density for most silicates. The GRA density vs. velocity relation for Hole 1224C, however, shows a negative gradient (Fig. F68). Bulk and dry density decrease and porosity increases with increasing depth, suggesting that a large amount of water can be absorbed in the zone between 2 and 4.5 mbsf (Fig. F66).
GRA bulk density and MS were measured every 1.0 cm. NGR was measured every 5.0 cm. The GRA bulk density was not measured for cores obtained from depths shallower than 50 mbsf. GRA densities (between 52 and 55 mbsf) range from 2.5 to 3.1 g/cm3 (Fig. F69A). Although MS and natural gamma radiation intensity were measured for all cores, like the GRA data they may have large errors owing to variations in core diameter and gaps between core pieces. MS also shows large variations (Fig. F69B). Natural gamma radiation intensities are very low values, which is typical for basalt (Fig. F69C).
Figure F70 shows the results of bulk and dry densities, grain densities, porosity, and thermal conductivity for Hole 1224D. Bulk and dry densities increase from 2.7 to 2.9 g/cm3 and 2.6 to 2.8 g/cm3, respectively in Core 200-1224D-2R (Fig. F70A). In Core 200-1224D-3R, bulk and dry densities decrease from 2.9 to 2.8 g/cm3 and from 2.8 to 2.7 g/cm3, respectively. In Cores 200-1224D-4R and 5R, they also decrease from 2.85 to 2.8 g/cm3 and from 2.8 to 2.7 g/cm3. Porosities remain at low values and range from 4% to 9%. Grain densities are fairly constant and range from 2.8 to 3.0 g/cm3. Thermal conductivities for Hole 1224D are scattered and range from 1.65 to 1.85 W/(m·K) (Fig. F70C).
PWS velocity was measured on individual cubic samples. PWS velocities range from 4200 to 6500 m/s (Fig. F71A). Compressional wave velocity anisotropy for each sample is ~2%-10%. PWS velocities have a sinusoidal depth variation. They decrease between ~27 and 35 mbsf, increase between 35 and 45 mbsf, and decrease again between 45 and 52 mbsf. This sinusoidal depth variation is also identified for Hole 1224F (Fig. F71C). A similar variation is also seen in the gamma radiation intensity measurements in the triple combo logging tool (Fig. F87) (see "Core, Physical Properties, Logging, and Seismic Correlation").
As shown in Figure F72, PWS velocities have positive and negative gradients with bulk densities and porosities, respectively. PWS velocities increase with increasing bulk density, except for two samples. Samples A and B have large anisotropy (Fig. F72A). The velocity of sample B is 4650 m/s for the y-direction and 5100 m/s for the x-direction. PWS velocities decrease with increasing porosity (Fig. F72B). Samples A and B agree with this trend. The porosity of sample B is nearly 9%, and the velocity is low. In contrast to sample B, sample A has medium porosity at 5.6%. The minimum porosity at 3.7% corresponds to a reasonably high velocity of 6000 m/s, which is considered to be representative of unaltered aphyric basalt.
In Holes 1224E (Fig. F73) and 1224F (Fig. F74), GRA bulk density and MS were measured every 1.0 cm and NGR was measured every 10 cm.
GRA densities are fairly constant at 1.5 g/cm3 at 8-9 mbsf and 1.65 g/cm3 between 17 and 27 mbsf. This interval corresponds to the soft sediment above basaltic basement (Fig. F73A). Between 27 and 60 mbsf, they remain constant at 2.8 g/cm3 (Figs. F73A, F74A), and below 70 mbsf they are 2.7 g/cm3 (Fig. F74A). Magnetic susceptibilities are ~50 between 5 and 27 mbsf (Fig. F74B). Between 27 and 60 mbsf, they average ~6000-7000 (Figs. F73B, F74B). Between 60 and 140 mbsf, they decrease and remain constant at a low value (Fig. F74B). They rapidly increase, however, below 140 mbsf. Natural gamma radiation intensities decrease between 8 and 9 mbsf, and below 18 mbsf, they remain at fairly constant low values (Figs. F73C, F74C).
Moisture and density properties, such as bulk, dry, and grain densities, water content, and porosity, were measured on individual samples. Bulk densities, grain densities, and porosities are in good agreement between Holes 1224E and 1224F (Figs. F75A, F76A). According to the bulk densities, porosities, and PWS compressional velocities, we divided the combined results into seven depth zones (Fig. F71D): (1) 30-38 mbsf, (2) 38-41 mbsf, (3) 41-61 mbsf, (4) 61-100 mbsf, (5) 100-138 mbsf, (6) 138-147 mbsf, and (7) deeper than 147 mbsf. Porosities for these depth zones are (1) 5%, (2) 10%-15%, (3) 5%, (4) 5%-10%, (5) 5%-10%, (6) 10%-15%, and (7) 5%. The thermal conductivities are constant over the depth range.
PWS velocity was measured on discrete cubic samples. Between 25 and 60 mbsf, PWS velocity on core from Holes 1224E and 1224F has a similar trend to that of Hole 1224D (Fig. F71). PWS velocities have a strong depth dependence. We use the same zoning for compressional velocity as for porosities. Compressional velocities, including seismic velocity anisotropy, in the seven depth zones are (1) 5500-6000 m/s, (2) 4200-5500 m/s, (3) 5000-6000 m/s, (4) 4500-5000 m/s, (5) 4700-6000 m/s, (6) 4000-4700 m/s, and (7) 5500 m/s. Zones 1 through 3 may be characterized as rather uniform basalt flow zones with a thin low velocity (fractured) layer. Zone 4 is characterized by a slightly low velocity zone. Velocities of zone 5 are higher than velocities for zones 4 and 6. Zone 6 is highly fractured, characterized by the lowest velocities. Zone 7 corresponds to more uniform basalt layers.
Figures F77 and F78 are for Holes 1224E and 1224F, respectively. They show P-wave velocity vs. bulk density and P-wave velocity vs. porosity. P-wave velocities are scattered with increasing bulk density. In general, P-wave velocity has a positive correlation with increasing bulk density (e.g., Birch 1960, 1961). P-wave velocity vs. porosity, however, has a good inverse correlation, as P-wave velocity decreases with increasing porosity. These two relations imply that compressional velocities are less sensitive to bulk density than they are to porosity. Large porosities may be associated with more fractures. If this is true, zones 2 and 6 are intensively fractured.