Index properties measurements were made at a resolution of one sample for every two sections in the cores from all Site 1123 holes. Index properties were determined by a gravimetric method (see "Physical Properties" in the "Explanatory Notes" chapter). Values of index properties (void ratio, porosity, water content, bulk density, and grain density) are presented in Table T20 (also in ASCII format). The properties measured from Holes 1123B and 1123C show gradual downhole changes to 540 mbsf (Fig. F38). Decreasing bulk density between 540 and 550 mbsf corresponds to a debris-flow deposit (see "Lithostratigraphy"). Over this same interval, the porosity increases from 40% to 60%. Below 550 mbsf, wet-bulk density increases from 1.4 to 2.2 g/cm3, and porosity decreases from 75% to 30% downhole. The index properties at Site 1123 reflect the effects of an increasing overburden.
The shipboard physical properties program at Site 1123 included nondestructive measurements of bulk density, magnetic susceptibility, and natural gamma-ray activity on whole sections of all cores using the MST (Figs. F39, F40). Magnetic susceptibility was measured at 4-cm intervals and at high sensitivity (4-s measurement time) in all Site 1123 holes. Low magnetic susceptibility values above 450 mbsf and below 590 mbsf in Hole 1123C are associated with a higher carbonate content (see "Organic Geochemistry"). Magnetic susceptibility increases below 451 mbsf, the boundary between lithostratigraphic Units II and III, and then decreases below the debris-flow deposits to the bottom of the hole. Natural gamma radiation was measured with a 15-s count every 14 cm in all Site 1123 holes. Natural gamma radiation values range from 0 to 30 counts/s. High values of natural gamma radiation indicate a relative high abundance of clay minerals. The low natural gamma radiation observed at Site 1123 indicates less clay-rich sediment than at previous Leg 181 sites. High natural gamma radiation values below 451 mbsf in Hole 1123C correlate with high magnetic susceptibility. Natural gamma radiation data from APC cores in Hole 1123A show cyclic variations above 70 mbsf, which reflect changes in mineral composition between carbonate-rich and clay-rich sediment layers. Below 70 mbsf, sediments are dominated by carbonate. The high natural gamma radiation peaks in the upper part of the section (<70 mbsf) are similar in value to those in lithostratigraphic Unit III. The high natural gamma radiation values in the upper part of the section may reflect the presence of tephra layers.
The GRAPE bulk density measurements were made at 4-cm intervals at all Site 1123 holes. A comparison of GRAPE density with the wet-bulk density determined from discrete samples shows general agreement, although GRAPE density values are generally higher than bulk density values obtained by index properties measurements in the upper portion of the cores (APC cores) (Fig. F41). The GRAPE density values increase generally with increasing burial depth. The decrease in GRAPE density at 160 mbsf coincides with the switch from APC to XCB coring. The XCB cores tend to be biscuit-like solid chunks of core material separated by layers of ground sediment. Voids between the biscuit-like core material and the core liner may cause the GRAPE density values to be lower than the actual values.
The P-wave velocity measurements (PWL) were made at 4-cm intervals at all Site 1123 holes. PWL measurements were only collected from APC cores. High values of P-wave velocity from Hole 1123A are associated with tephra layers. The highest P-wave velocity values are seen around 50 and 60 mbsf, where tephra layers are abundant. The peak around 50 mbsf probably occurs in carbonate-rich tephra-bearing sediments and is different from the peak around 60 mbsf, which occurs in clay-rich tephra-bearing sediments. Consistently high P-wave velocity values indicate sediment with high carbonate content and tephra layers, while clay-rich tephra-bearing layers show scattered peaks of increased P-wave velocity. In general, calcareous sediments have higher P-wave velocities than clay-rich sediment.
Measurements of shear strength, using a mechanical vane, were made on split cores from all Site 1123 holes (Fig. F42). Samples were generally taken in the fine-grained sediments at a resolution of one per section. No measurements were made on XCB cores. Shear strength values range from 5 to 130 kPa. There is a general increase in shear strength downhole. The highest shear strength values occurred above 130 mbsf in Hole 1123A and above 140 mbsf in Hole 1123B.
Compressional-wave velocity (P-wave velocity) was measured parallel to the core axis on split cores from Hole 1123A using the DSV (Digital Sound Velocimeter). Sediments were more tightly compacted below 65 mbsf in Hole 1123A, and, therefore, the Hamilton frame velocimeter was used to measure sound propagation perpendicular to the long axis of the core below this depth. P-wave velocity measured from the DSV in Hole 1123A correlates well with the data from the P-wave logger on the MST. However, P-wave velocity values are higher from the Hamilton velocimeter measurement than from the DSV measurement. This may result from the fact that the pressure was applied to the discrete sample when lowering the transducers of the Hamilton Velocimeter onto the half core in the liner and may have caused the sediment samples to become more dense during the actual P-wave velocity measurement. The P-wave velocity was also taken by the Hamilton velocimeter from XCB cores recovered from Holes 1123B and 1123C. A sharp peak in P-wave velocity from 1800 to 2250 m/s occurring around 550 mbsf is associated with a lithified block of limestone contained in the debris-flow unit. The P-wave velocity values of this peak are similar to those measured from limestone in lithostratigraphic Unit IV. This limestone block also produces distinctive responses in the magnetic susceptibility and natural gamma radiation records.