P-Wave Velocity Bayonet/Caliper Gantry (PWB/PWC)

Overview

P-wave velocity is the distance traveled by a compressional P-wave through a medium per unit of time, expressed in meters per second. P-wave velocity is dependent on the composition, mechanical properties, porosity, bulk density, fabric, and temperature of the material, which in turn are functions of consolidation and lithification, state of stress, and degree of fracturing. The P-wave gantry has a set of piezoelectric transducers that allow the velocity to be determined in the X-, Y-, and Z-directions split-core sections. For discrete samples, the velocity can be measured along each of the available axes separately using the PWC.

Note: The bayonet component of the instrument is not in continuous operation and is available by request.

Instrument Make and Model

Custom-built system.

Estimated Measurement Time

Sample Measurement: up to 20 samples/hour

Quantity of Sample Material

1–3 cm, recommended sample thickness

Principles & Analytical Capabilities

The P-wave bayonets (PWB) measure the velocity along the core (z-direction) and across the split-core face (y-direction). PWB data are acquired by transmitting a 500 kHz P-wave pulse across undisturbed split-core sections using pairs of piezoelectric transducers mounted in bayonets that are inserted into soft sediment (y- and z-directions). The distance between the pulser and receiver is fixed, and the traveltime is measured. Calibration is performed with a split liner half filled with pure water, using a known velocity of 1485 m/s at 22°C. The bayonets do not work on consolidated sediment, basalt, or discrete samples.

The P-wave caliper (PWC) measures the velocity perpendicular to the split-core face (x-direction). For discrete sample cubes, the velocity is measured along each of the three axes separately using the PWC. Mini-cores are measured along the axis of the cylinder using the PWC. PWC data are acquired by transmitting a 500 kHz P-wave pulse across a section half (x-direction) or across the faces of a cylinder or cube-shaped sub-sample (x, y, or z-direction). The distance between transducers is measured with a laser rangefinder. A series of acrylic cylinders of varying thicknesses are used to calibrate the PWC systems. The regression of traveltime versus travel distance yields the P-wave velocity of the standard material, which should be within 2750 ± 20 m/s.

The custom velocity gantry IMS software automatically picks the P-wave first arrival and the user has the option to manually pick the first arrival. Traveltime is determined by first arrival of the P-wave signal at a precision of 50 ns. Results are corrected for system propagation delay, and liner thickness and material velocity if applicable.

Data Generated

Data components:

P-Wave Bayonet (PWB)

P-wave velocity y|z (m/s): velocity of pressure wave through sample in the noted axis.
Caliper separation (mm): displacement between the faces of the transducers in contact with the sample, associated with the velocity observation in the specified axis.
Sonic traveltime (µs): traveltime of the sonic wave from transducer to transducer through the sample, associated with the velocity observation in the specified axis.

P-Wave Caliper (PWC)

P-wave velocity x|y|z (m/s): velocity of pressure wave through sample in the noted axis.
Caliper separation (mm): displacement between the faces of the transducers in contact with the sample, associated with the velocity observation in the specified axis.
Sonic traveltime (µs): traveltime of the sonic wave from transducer to transducer through the sample, associated with the velocity observation in the specified axis.

Data files:

P-Wave Bayonet (PWB)

Results, z-axis (CSV): tabular data of PWB along the z-axis
Results, y-axis (CSV): tabular data of PWB along the y-axis

P-Wave Caliper (PWC)

Results (CSV): tabular data of PWC

Raw files:

P-Wave Bayonet (PWB)

Waveform, z-axis (LVM): Data file of transducer signal waveform along the z-axis
Waveform, y-axis (LVM): Data file of transducer signal waveform along the y-axis

P-Wave Caliper (PWC)

Waveform (LVM): Data file of transducer signal waveform

Data Example

Graph of P-wave velocity data (PWB = p-wave bayonet, PWC = p-wave caliper) from Hole U1436 of IODP Expedition 350 in the Izu-Bonin-Mariana Rear Arc. — P-wave velocity data (PWB = p-wave bayonet, PWC = p-wave caliper) from Hole U1436 of IODP Expedition 350 in the Izu-Bonin-Mariana Rear Arc. ^{1, 2}

Procedures & Manuals

References

¹Tamura, Y., Busby, C. J., Blum, P., Guèrin, G., Andrews, G. D. M., Barker, A. K., Berger, J. L. R., Bongiolo, E. M., Bordiga, M., DeBari, S. M., Gill, J. B., Hamelin, C., Jia, J., John, E. H., Jonas, A. S., Jutzeler, M., Kars, M. A. C., Kita, Z. A., Konrad, K., … Yang, A. Y. (2015). IODP Expedition 350 P-wave velocity bayonet (section) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.7502219

²Tamura, Y., Busby, C. J., Blum, P., Guèrin, G., Andrews, G. D. M., Barker, A. K., Berger, J. L. R., Bongiolo, E. M., Bordiga, M., DeBari, S. M., Gill, J. B., Hamelin, C., Jia, J., John, E. H., Jonas, A. S., Jutzeler, M., Kars, M. A. C., Kita, Z. A., Konrad, K., … Yang, A. Y. (2015). IODP Expedition 350 P-wave velocity caliper (section/discrete) [Data set]. https://doi.org/10.5281/zenodo.7502223