P-WAVE LOGGER

INTRODUCTION

The P-wave logger data file contains information generated onboard the JOIDES Resolution by the shipboard physical properties scientists and technicians. The P-wave logger is an automated system used to measure and record the compressional wave velocity (VP) of soft sediments within a plastic core liner. A detailed velocity log can be obtained by combining the data from a sequence of adjacent core sections. These logs can be used to provide detailed cross-correlation between different holes at the same site, or can be used to identify sedimentary structures rapidly (such as slump structures or turbidites). The detailed velocity profiles provided by the logger, when used in conjunction with the density profiles provided by the Gamma Ray Attenuation Porosity Evaluator (GRAPE), can be used to generate synthetic seismograms that can be correlated with seismic profiles.

The P-wave logger can be used on conventional cores obtained by piston- or gravity-driven drilling systems that use any type of cylindrical plastic liners, although it was developed specifically for use with cores obtained with the hydraulic piston corer.

Velocity measurements are automatically taken, with a precision of +/- 1.5 m/sec, at regular intervals throughout the core as the core travels between a pair of ultrasonic transducers, one serving as a transmitter and the other serving as a receiver. The P-wave logger measures the speed of the compressional waves by timing pulses between the two transducers, which are spring loaded and mounted diametrically across the core.

EXPLANATION OF DATA ITEMS

LEG - Number identifying the cruise.

SITE - Number identifying the site. A site is the position of a beacon around which holes are drilled.

HOLE - Letter identifying the hole.

CORE - Number identifying the core. Cores are numbered serially from the top of the hole downward.

CORETYPE - A letter code identifying the drill bit/coring method used to retrieve the core. The coretype codes are:

B - Drill Bit
C - Center Bit
D - Positive Displacement
H - Hydraulic Piston Core
M - Miscellaneous
N - Downhole Mud Motor (Navidrill)
P - Pressure Core Barrel
R - Rotary
S - Side Wall Core
W - Wash Core
X - Extended Core Barrel

SECTION - A core is cut into 1.5 meter long sections that are numbered serially from the top of the core. A core with full recovery will have 7 sections and a core catcher and be approximately 9.8 meters long.

TOP_INTERVAL - Distance in centimeters from the top of the section to the top of the sample interval.

SUB_BOTTOM_DEPTH - Distance in meters from the seafloor to the top of the sample interval.

P-WAVE VELOCITY (cm/s)

SIGNAL STRENGTH - It indicates the quality of observation - if this value is greater than 40, the observed velocity is considered reliable.

TRAVEL TIME

DISPLACEMENT (steps) - This value ranges between 0 and 255, and can be used to calculate the thickness of the core at each sample location using the constants given in Header Record 3. This value is expected to be close to the 'Displacement Zero Calibration' value. It defaults to 255 if the obervation is not reliable.

RUN NUMBER - the run number added by the MST program.