Downhole measurements in Hole 1224F (141°58.7567´W, 27°53.3634´N) were made after completion of RCB coring to a total depth (TD) of 174.5 mbsf. The water depth was 4978 mbrf, and sediment thickness was ~28 m in Hole 1224F. Three wireline tool strings were run: the triple combo, the FMS/DSI, and the WST-3 (see "Downhole Measurements," Fig. F14, and Tables T3, T4, and T5, all in the "Explanatory Notes" chapter). For each logging run, the base of the pipe was initially lowered to 49.9 mbsf. As each run was made uphole, the pipe was pulled from 49.9 to 34.5 mbsf to increase the open hole interval for logging. The Lamont-Doherty Earth Observatory (LDEO) Borehole Research Group wireline heave compensator was used for the three logging runs. Prior to logging, Hole 1224F was reamed and flushed of debris. The drill bit was released in the hole, and then the hole was filled with sepiolite mud. The total time used for hole preparation was ~6 hr. Logging operations began at 0530 hr on 20 January and were completed at 1030 hr on 21 January, using a total of 29 hr of rig time.
The first tool string, the triple combo, is 31.5 m long and includes the Hostile Environment Gamma Ray Sonde (HNGS), Accelerator Porosity Sonde (APS), Hostile Environment Litho-Density Tool (HLDT), the Phasor Dual Induction-Spherically Focused Resistivity Tool (DIT-E), and the LDEO Temperature/Acceleration/Pressure (TAP) tool (see "Downhole Measurements," Fig. F14, and Tables T3, T4, and T5, all in the "Explanatory Notes" chapter). The initial depth of the TAP recording was set to start from 4778 mbrf. The depth recording for the TAP tool from the Schlumberger Minimum Configuration Maxis (MCM) system started at 4578 mbrf. Total rig-up time for this run was 2.25 hr. At 1109 hr on 20 January, the bottom of the triple combo tool string reached the mudline at 4978 mbrf and stopped there for 5 min for TAP tool calibration. Then the tool string (TAP tool only) was logged downhole at a speed of 600 m/hr. After the bottom of the hole was reached, the entire tool string was logged uphole at 275 m/hr from TD to the seafloor. The data are of excellent quality, with the exception of one 5-min interval near 138 mbsf where the hole diameter exceeded 17 in and the density and neutron porosity measurements may be unreliable. A shotpoint log was also acquired over the open-hole interval. Total rig time for this run was 10.5 hr.
The second tool string, FMS/DSI, includes the DSI, Natural Gamma Ray Spectrometry Tool, and FMS tools and has a total length of 33 m. The FMS/DSI tool string was rigged up starting at 1600 hr on 20 January. When the tool string reached a water depth of ~1000 m, a tool power anomaly occurred and the tool string was immediately brought back to the surface. It was determined that the telemetry cartridge was malfunctional, and a new cartridge was installed. The tool string reached TD at 2320 hr. Three passes of this string were run using the DSI in monopole, dipole, and Stoneley-wave recording modes. Switching between recording modes was accomplished while the tool was downhole. Pass 1 was run uphole at 275 m/hr from TD to the hard rock/sediment interface (27.7 mbsf) to record the data-intensive FMS and DSI lower dipole and monopole P-wave and S-wave (P&S) modes. Pass 2 was run uphole from TD in open hole, then through the pipe to the hard rock/sediment interface, with the data-intensive cross-dipole mode enabled. Pass 3 was run uphole from TD to the hard rock/sediment interface, with the Stoneley, the upper dipole, and the P&S monopole recording modes enabled. The frequency band is from 80 to 5 kHz for dipole measurements and low-frequency Stoneley acquisition and from 8 to 30 kHz for monopole acquisition. Excellent FMS and compressional and shear waveform data were collected during these three passes. The washout at 138 mbsf apparent on the triple combo caliper reading is not evident on the two FMS caliper readings. A total of 14 hr of rig time was used for the above three passes.
The third tool string is 7 m long and consists of only the WST-3. This was the first test run of the Schlumberger WST-3 in an ODP hole. The WST-3 run was planned to record the zero-offset vertical seismic profiles with a 5-m depth interval between clamping stations. At each receiver station, the WST-3 was to record 6-10 shots with a 1-ms sample interval, a record length of 10 s, and 45 s between shots. A 4.92-L (300 in3) air gun aboard the JOIDES Resolution was used. To maintain a constant depth below the sea surface, the gun was suspended from a buoy and tethered to the aft port crane. Gun depth was set at 5.5 m below the sea surface to obtain the best downward propagating combination of the source and its phase-inverted surface reflection. When the WST-3 tool was in the drill pipe at a water depth of 1057 m, it was clamped to the pipe to conduct a test. The shot time was supposed to be detected by the blast hydrophone suspended 3 m beneath the gun. However, no source signals from either the blast hydrophone or the WST-3 were detected by the SAT. Subsequently, it was found that the blast hydrophone had a faulty circuit; the air gun had a leakage of air; and the WST-3 telemetry was intermittent. The experiment was therefore terminated. The total rig time for this test was 4.5 hr.
Shipboard analysis of the logs and core descriptions during ODP Leg 200 clearly shows that Hole 1224F consists of definable alternative layers of fresh and fractured and/or altered basalts (breccia and pillows) that correlate to changes in the measured log properties. The logs run during Leg 200 provided high-quality results and can be used to significantly enhance our understanding of the geological settings and the shallow structure of the upper ocean crust at this strategic ODP site in this Pacific region.
A selection of most of the logs acquired in three runs during Leg 200 are presented in Figures F79, F80, F81, F82, and F83. The interval displayed corresponds to depth in Hole 1224F, from TD (174.5 mbsf) to the base of the pipe (35 mbsf; all in basaltic rocks). The nuclear and sonic logs were also run through the pipe to the seafloor, and repeat passes were made for the FMS/DSI tool string but are not shown. The caliper log from the triple combo run is shown in Figure F79 (Track 1; blue color). The caliper reading changes from 10 to 18 in. However, the measurement of this one-arm caliper is highly nonlinear, and it is directional, generally tracking the major axis of elliptical holes. Two caliper logs from the FMS four pads are also shown in Figure F79 (Track 1; black and red colors) and illustrate two orthogonal dimensions of the borehole as a function of depth. Generally the caliper readings from the FMS tool are much more reliable than the one-arm caliper. The diameter of Hole 1224F varies generally between the bit size (97/8 in) and 11 in from the FMS caliper logs. The apparent "washout" or conduit from 138 to 142 mbsf from the directional caliper reading is not identified on the two FMS calipers. The FMS images show that this vertical fracture has a large opening on the northeast part of the borehole wall. The orientation of the calipers with respect to magnetic north (PAZ1 in Track 3) illustrates a relatively constant position of the logging tool as it was pulled uphole. The tool started rotating only when the top of the tool was in the pipe, and the calipers were closed. This is an indication of a very circular borehole without large breakouts, key slots, or elliptical intervals. Small-scale variations in tool rotation are likely related to localized and minor changes in the shape of the borehole.
Figure F79 (Track 2) shows the hole deviation log. In general, Hole 1224F is nearly vertical, having a slightly increasing deviation below the base of the pipe (35 mbsf) to ~2° off vertical at TD. This low angle of hole deviation does not affect the operation of the logging tools. The overall quality of the log data acquired during Leg 200 is excellent.
The three-component acceleration and magnetic field measurements made with the General Purpose Inclinometer Tool (GPIT) of the FMS/DSI tool string are used usually for depth determination and other postcruise log data processing. Both the magnetic field and the magnetic inclination, which are computed from the GPIT log, show elevated values above 67 mbsf and below 142 mbsf (Fig. F79). The boundary at 142 mbsf coincides with the lower boundary of the conduit detected by the triple combo caliper. Both the magnetic intensity and inclination log data between 67 and 103 mbsf and between 103 and 142 mbsf reveal much less variation than those acquired in the upper and lower parts of the hole. The magnetic inclination between 103 and 142 mbsf exhibits a higher variation than that between 67 and 103 mbsf.
The temperature log is presented in Figure F80 (Track 1). The raw temperature data recorded with the LDEO TAP tool (see "Temperature, Acceleration, and Pressure" in "Tool Measurement Principles and Applications" in "Downhole Measurements" in the "Explanatory Notes" chapter) are of excellent quality. Although the low-resolution mode was used, it was enough to accurately define the depth (136 mbsf) at which the temperature increased abruptly by ~1°C. The temperature log shows that the temperature between 138 and 142 mbsf remains at a constant temperature of 4.6°C. The temperature steeply decreases to 3.7°C within a 3-m interval from 138 to 135 mbsf, and it then gradually decreases to 3.5°C to the seafloor (only shown up to 35 mbsf). On the other hand, the temperature gradually increases to 5.0°C from 142 mbsf to TD. Combined with the analysis of the caliper logs and the drilling conditions, the temperature log indicates that there is a vertical zone of relatively warm fluid at a temperature of 4.6°C. This vertical zone is 4 m high and corresponds to a vertical fracture oriented in a northeastern direction. Drilling might have enlarged the opening of the fracture (conduit) on the borehole wall. The high-precision GPIT also detected an anomaly at ~142 mbsf. Further analysis is needed to conclude if cool seawater is flowing down Hole 1224F and exiting the borehole through this permeable zone and into the surrounding formation.
The spontaneous potential (SP) log is also shown in Track 2. Although the SP log has been traditionally used to estimate the alternating layers of permeable and impermeable zones, there is no direct relationship between the values of porosity and permeability and the magnitude of the SP deflection. Further analysis will be needed to explain the SP data in Hole 1224F.
Electrical resistivity measurements and images were recorded during the first and second logging runs. The deep induction resistivity (IDPH), medium induction resistivity (IMPH), spherically focused log (SFLU), and formation images (FMS) were obtained in Hole 1224F during Leg 200.
Three independent measurements of electrical resistivity were recorded with the DIT-E, which includes the SFLU array. The deep induction resistivity log (ILD) and the SFLU are shown in Figure F80 (Tracks 3 and 4, respectively). Compared with the resistivity measurements in the oceanic crust in ODP Hole 395A (Shipboard Scientific Party, 1998), the galvanic measurements (SFLU) give readings in the similar range of resistivity for basalts, whereas inductive measurements (IDPH and IMPH) may provide generally lower values, although following closely the same overall profile. This difference is the result of the nature of inductive measurements, where circular current loops are generated in the plane orthogonal to the borehole axis. When used in a vertical hole such as Hole 1224F, the induction tool records the horizontal component of the formation resistivity. In a layered formation, inductive measurements are consequently expected to read lower values than galvanic ones.
The highest values of resistivity correspond to the presence of thin and massive flows at 37, 45, 75, 130, and 155 mbsf, for example. In sections where resistivity values are >100-200 
m, the induction measurements may be erroneous because the secondary magnetic field induced by current loops into the rock is not large enough to be picked by the receiving coils. Such erratic measurements are illustrated in the IDPH (ILD) profile at 38, 92, and 95 mbsf in Figure F80 (Track 3).
The shallow-reaching, centimeter-scale FMS images both lithologic contacts and millimeter-scale fractures (Fig. F81). The FMS images show considerably greater resolution of the relative conductivity changes over the interval, and they reflect formation characteristics that are not apparent at the broad scale of the other logs. The alternatively layered structure of fresh and fractured basalts is probably seen on the continuous-image FMS records. For illustration purposes, Figure F81 shows a 5-m interval of the high-quality FMS images from the entire interval of Hole 1224F acquired during FMS/DSI Pass 1. Conductive features are imaged with darker color, whereas resistive features are indicated by lighter color. In this figure, for example, sheeted lava flows are between 81.5 and 81.8 mbsf, between 82.6 and 82.8 mbsf, and between 84.4 and 84.6 mbsf.
The FMS record provides continuous structural images of the borehole wall penetrated by Hole 1224F. Above 67 mbsf, the FMS images reveal relatively "smooth" basalts with fewer fractures and fine structures. Core recovery was good (~50%) throughout this interval of massive basalts. Below 67 mbsf and above ~103 mbsf, the FMS images show highly fractured intervals interbedded with sheeted layers 10 cm to 0.5 m thick that have high electrical resistivity values. FMS images between 100 and 142 mbsf show large blocks of electrically resistive fragments against large blocks that are highly conductive and have fewer fractures than the intervals above, which may indicate that this interval mainly consists of less fractured pillow basalts. Below 142 mbsf, rocks become electrically more resistive.
Sonic data were recorded using the DSI during the second logging run with three separate passes of the tool through the open-hole interval. In total, five different modes of the DSI were enabled (see "Acoustic Velocity" in "Tool Measurement Principles and Applications" in "Downhole Measurements" in the "Explanatory Notes" chapter) and allowed for acquisition of both compressional and shear waveforms using different acoustic sources. Both high-frequency compressional and shear and dipole shear modes produced excellent quality sonic waveforms. Preliminary data processing for compressional and shear traveltimes was completed on the drill ship using Slowness-Time-Coherence analysis software on the MCM acquisition system (Kimball and Marzetta, 1984). The preliminary results of the compressional wave velocity profile from the monopole source (VPMP) are shown in Figure F82 (Track 3). The shear wave velocity profiles from the monopole source and the lower dipole are shown in Track 4 (black = monopole and red = lower dipole). The VPMP and dipole shear VS are raw data converted from the traveltime records. The shear wave velocity data from the monopole that are shown have been edited for the values that are out of the instruments' range. Both the compressional and shear wave velocity data show five logging units: above 45 mbsf (I), 45-63 mbsf (II), 63-103 mbsf (III), 103-142 mbsf (IV), and below 142 mbsf (V). The velocity measurements in the two units above 45 mbsf and from 103 to 142 mbsf have larger variations than the other units. Logging Unit III (63-103 mbsf) has a higher variation than logging Unit II (45-63 mbsf). The average compressional wave velocity is ~4.5, ~5.5, ~5.0, ~4.6, and ~5.4 km/s for the five units from the top to the bottom of the hole, respectively. The average shear wave velocity is ~2.5, ~3.1, ~2.8, ~2.6, and ~3.2 km/s for the five units from the top to the bottom of the hole, respectively. These estimates will be further refined by postcruise studies. Postcruise processing must also be applied to the dipole data to account for dispersion effects. The sonic data from the cross-dipole and the low-frequency Stoneley modes will be further processed postcruise.
The bulk density (RHOB) of the formation was measured using the HLDT and is displayed in Figure F82 (Track 1). Density values range from 1.25 to ~3.0 g/cm3, and the log shows rapid changes as a function of depth. Low density values are probably related to fractures filled with seawater. The average density value is ~2.0, ~2.8, ~2.6, ~2.5, and ~2.9 g/cm3 for the five logging units from the top to the bottom of the hole, respectively. The differences in RHOB between logging Units II, III, and IV are mainly due to density variations in rocks. The variations increase from logging Units II to IV. Typical values for basalt with no fractures measured on core samples are ~2.95 g/cm3, which are different from the in situ large-scale measurements, especially in breccia and highly fractured rocks. However, the density log readings in Unit V approach typical values.
The APS was used to record the neutron porosity log (NPHI) and is shown in Figure F82 (Track 2). NPHI ranges from 5% to 80%. High values correspond to borehole washouts or fractures and generally correlate with low peaks in the density log. NPHI also exhibits the same overall trends as indicated by density, velocity, and other logs. The average porosity value is ~40%, ~5%, ~15%, ~30%, and ~5% for the five logging units from the top to the bottom of the hole, respectively. The porosity log also shows a transition zone between 95 and 103 mbsf, which is apparent in the velocity logs.
The spectral gamma ray logs (Fig. F83) were measured using the HNGS tool (see "Natural Radioactivity" in "Tool Measurement Principles and Applications" in "Downhole Measurements" in the "Explanatory Notes" chapter). The total spectral gamma ray (HSGR; Track 1; black) varies between 2 and 30 gAPI in Hole 1224F. The HSGR, the computed gamma ray (HCGR; Track 1; red), and the potassium content (POTA) also show a strong correlation in the pillow basalts and flows, indicating that most of the natural radioactivity is caused by the potassium rather than the thorium or uranium decay series. Potassium is enriched in oceanic basalts during low-temperature oxidative alteration, thus, HSGR and POTA logs are good indicators of alteration. In the vicinity of the zone of relatively warm fluid between 138 and 142 mbsf, all the natural radioactive elements show elevated values.
Based on shipboard preliminary log analysis at this site during Leg 200, we conclude that Hole 1224F consists of five distinct logging units: above 45 mbsf (I), 45-63 mbsf (II), 63-103 mbsf (III), 103-142 mbsf (IV), and below 142 mbsf (V). These layered formations can be distinguished using the continuous electrical resistivity, density, sonic, neutron porosity, magnetic field, and possibly spectral gamma ray logs, as presented by the analysis above. The existence of a relatively warm zone or large-scale fracture between 138 and 142 mbsf was detected by all the log tools including the temperature tool. In addition, the temperature tool reveals that the relatively "warm" fluid had a temperature of 4.6°C at the time of the logging. The vicinity of this zone is much more highly altered than other rocks penetrated by the hole, which is indicated by the gamma ray logs. Because of the relative position of the tools located in the tool strings, some tools can resolve the top logged intervals like gamma ray, porosity, density, and sonic logs. On the other hand, the resistivity tools and FMS placed at the bottom of the tool string can resolve the formation properties near the bottom of the hole. The values of the magnetic fields measured by the GPIT cannot be used for tool orientation near the bottom of the pipe (~35 mbsf) because of the large field produced by the pipe. In the logged intervals where all the tools overlapped, they provide consistent information to support the layered structural units based on these geophysical properties.
