Thermal Conductivity Measurements of Deep Sea Rock and Sediment Core Samples
Thermal conductivity, thermal diffusivity and specific heat are properties that span and are applicable to multiple scientific and industrial disciplines. An interesting example of research being performed to determine thermal conductivity, thermal diffusivity and specific heat using one of the Hot Disk products, the TPS 1500, comes from the Japan Trench Fast Drilling Project (JFAST). This incredibly ambitious and groundbreaking project was created to further understanding around the cause of the massive Tohoku earthquake and subsequent tsunami that devastated the Japanese coast in March of 2011. Subduction zones where one tectonic plate is sliding beneath another are responsible for the largest earthquakes produced; the Tohoku earthquake was triggered off of the eastern coast of Japan where the pacific plate is sliding under the north american plate (Figure 1). The magnitude (9.0 Mw), and the fact that the plates and subsequently the seafloor shifted 50 meters during the Tohoku earthquake shocked experts, as this resulted in the tsunami being much larger than predicted.
Figure 1. Diagram illustrating the two tectonic plates (Pacific and North American) that meet off of the Eastern Japanese coast where the Tohoku earthquake and subsequent tsunami originated in March, 2011.1
The goal of JFAST was to drill into the seafloor and collect rock samples and temperature readings from above, at, and below the interface between the pacific and north american plates to try to understand why such a large shift had occurred. The research vessel Chikyu drilled 845m into the seafloor off of the east coast of Japan to accomplish this (Figure 2). Determining the physical properties of the rocks in that zone and understanding the frictional stress that the fault is subjected to is crucial to understanding how the earthquake and tsunami occurred. The amount of heat created during the 50 meter movement of the plates against each other was such that there was still a residual temperature anomaly of 0.31°C detected by probes placed in the bore hole over a year after the quake. Ascertaining thermal properties such as thermal conductivity and thermal diffusivity of the rocks enables scientists to fully interpret this anomaly.
Figure 2. Map indicating the JFAST drill site along the Japan Trench in relation to the Japanese coast and the subduction zone.2
Research performed by Lin et al. (2014) determined the thermal conductivity, thermal diffusivity and specific heat of four core samples obtained from varying depths of the bore hole. The samples were from 177, 697, 802, and 845 meters below the seafloor respectively. The thermal conductivity equipment used was the Hot Disk TPS 1500, which has a thermal conductivity range of 0.005 to 20 W/mK. The hot disk probe was sandwiched in between two pieces of each sample to attain the results (Figure 3a). The TPS 1500 can also use a single sided sensor, the TPS-S, where only one piece of a sample is required (Figure 3b).
Figure 3. Diagram from Lin et al. (2014) illustrating the sample set up used to ascertain thermal conductivity, diffusivity and specific heat using the TPS 1500.
Figure 4. GIF indicating how a single sided sensor can be used to perform the same test.
Lin et al. (2014) took advantage of the ability of the Hot Disk TPS 1500 to test both bulk and directional (axial and radial) thermal conductivity and diffusivity. They ran all samples in both measurement modes to determine if anisotropy was present. Bulk measurement results obtained are summarized in Table 1, and directional (axial and radial) results are summarized in Table 2. Comparison of results by the team indicated anisotropy was less than 5%.
Table 1. Results of thermal conductivity, thermal diffusivity and specific heat bulk measurement testing performed by Lin et al. (2014) using the Hot Disk TPS 1500 on four samples collected by JFAST. MBSF is metres below sea floor.
Table 2. Results of thermal conductivity (TC) and thermal diffusivity (TD) anisotropic measurement testing performed by Lin et al.(2014) using the Hot Disk TPS 1500 on four samples collected by JFAST. MBSF is metres below sea floor.
Radial TD 10-7
Axial TD 10<-7
What is interesting about this project is that it not only illustrates the direct use of the Hot Disk TPS 1500, but it also highlights the incredible applications that data obtained by the Hot Disk TPS thermal conductivity instruments have the potential to be a part of. Once Lin et al. (2014) had concluded thermal testing on their four samples, they turned to scientific literature and identified an equation used to quantify the relationship between thermal conductivity and thermal diffusivity in sediments that fit their data. Once that equation was selected, they were able to apply it to determine the thermal diffusivity of multiple initial samples whose thermal conductivity had been calculated previously in the JFAST expedition. This meant that the team was able to calculate the thermal diffusivities for the entire depth of the bore hole. This data is incredibly important to quantify the temperature anomaly left by the 2011 earthquake, and will be used to further research on data collected during the JFAST expedition and understanding thermal processes in subduction zones.
Learn More About Hot Disk Transient Plane Source (TPS)
The Hot Disk Transient Plane Source (TPS) technique allows for precise thermal conductivity measurement of a huge array of materials ranging in thermal conductivity from 0.005 to 1800 W/m∙K . TPS is capable of measuring bulk and directional thermal properties of solids, liquids, pastes and powders.
Lin, W., Fulton, P.M., Harris, R.N., Tadai, O., Matsubayashi, O, Tanikawa, W., and Kinoshita, M. 2014. Thermal conductivities, thermal diffusivities, and volumetric heat capacities of core samples obtained from the Japan Trench Fast Drilling Project (JFAST). Earth, Planets and Space. 66:48. Available from: http://link.springer.com/article/10.1186%2F1880-5981-66-48
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