INTRODUCTION Data are presented showing the variation of compressional wave velocity (Vp) and electrical resistivity with increasing confining pressure for basalt samples from Holes 407,408,409, and 412A. In addition, Vp has been measured on two samples with varying temperatures but constant confining pressure. Knowledge of the seismic properties of the basalts is important for interpretation of seismic refraction lines. Similarly, laboratory measurements of the electrical resistivity are

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... le in understanding the conductivity structure of the crust. The samples were subsequently to be used for thermal conductivity measurements, and a detailed study of their petrology was not made. The site descriptions and sample examination show that the samples from Hole 407 are generally fine-to medium-grained aphyric basalts with rare microphenocrysts of plagioclase in a groundmass of clinopyroxene and plagioclase. There is some alteration to smectitie in all the sections. The three samples from Hole 408 are aphyric sub-variolitic basalt, and are highly vesicular. Thin sections show plagioclase and olivine embedded in glass, with alteration of the glass and olivine to smectite. The one sample from Hole 409 is a highly vesicular aphyric basalt with some microphenocrysts of plagioclase and olivine. The sample from Hole 412A is a medium-grained basalt with phenocrysts of plagioclase, olivine, and clinopyroxene. Phenocrysts are up to 2 mm in diameter, and occupy between 5 and 10 per cent of the rock. METHOD The samples were cylinders, 2.52 cm in diameter, 1.15 to 2.05 cm long after being cut and lapped to give smooth ends. Measurements of the compressional wave velocity employed a pulse-transmission method, and the electrical conductivity measurements used an AC bridge. The stainless steel transducer holders acted as electrodes, thus enabling both parameters to be measured on a sample under identical conditions of confining pressure, pore water pressure, and temperature. All samples were saturated in a seawater solution. The transducers and sample were enclosed in a jacket to prevent contamination of the pore fluid by the confining pressure medium (Plexol oil). A heater coil around the sample allowed temperature control. The pore water pressure was kept at zero for all measurements, apart from those where the temperature was varied. A summary of the results of the measurements is given in Table 1 . Figure 1 shows the effect of increasing confining pressure on the compressional wave velocity. Measurements of veloc-ity were made both when the pressure was being increased and when it was decreased, but only those velocities obtained on the increasing part of the cycle are shown. Fairly close agreement was obtained between the two velocities, though in general the velocities on the decreasing part were slightly lower than on the increasing part. A similar effect has previously been observed by Christensen (1976) on basalts from Leg 35. The velocities obtained are within the range of values previously obtained for DSDP basalts Salisbury and Christensen, 1976) and there is a clear relationship between velocity and density ( Figure 2 ). The regression line for these few samples is given by Vp = 3.80Φ -5.27 km/s where Φ is density. The linear relation obtained by Christensen and Salisbury (1975) for a much more comprehensive suite of samples was Vp = 3.56Φ -4.26 km/s It has been observed ) that velocities increase with basement recovery depth. This relationship, however, is not evident for the six samples from Hole 407, which show a considerable scatter of values over a depth range of 114 meters. COMPRESSIONAL-WAVE VELOCITIES The effect of temperature on Vp was studied on two samples. Only a limited temperature range was used, to reduce the risk of any thermal damage to the specimen. The confining pressure was fixed at 1.5 kbar and the pore water pressure was fixed at 1.0 kbar. The results are shown in Figure 3 . The two samples showed differential velocity gradients of approximately -2.4 and -3.4 × 10-4 °C-1 , values somewhat higher than others previously obtained for mafic rock (e.g., Birch, 1958) . However, it should be noted that because of the need to preserve the sample in good condition for thermal conductivity measurements, no rigorous study of the stability of the thermal effect was conducted. The recycling was fairly rapid; it has been established (Spencer and Nur, 1976 , and work of present authors) that if the sample is left at its highest temperature for some hours, then the velocities on the decreasing part of the cycle may be higher, although the differential velocity gradient would be the same.