TY - JOUR
T1 - Continuous depth profile of the rock strength in the Nankai accretionary prism based on drilling performance parameters
AU - Hamada, Yohei
AU - Kitamura, Manami
AU - Yamada, Yasuhiro
AU - Sanada, Yoshinori
AU - Sugihara, Takamitsu
AU - Saito, Saneatsu
AU - Moe, Kyaw
AU - Hirose, Takehiro
N1 - Funding Information:
We are grateful to Dr. W. Tanikawa for his repeated help with the numerical calculations. We greatly appreciate the advice given by Dr. Hiroko Kitajima in designing the calculations. This study is supported by JSPS KAKENHI grant 16H04064, 15H05717, and a grant-in-aid for Fellows of the Japan Society for the Promotion of Science (JSPS) 14J06074.
Publisher Copyright:
© 2018 The Author(s).
PY - 2018/12/1
Y1 - 2018/12/1
N2 - A new method for evaluating the in situ rock strength beneath the seafloor is proposed and applied to the Nankai Trough accretionary prism. The depth-continuous in situ rock strength is a critical parameter for numerous studies in earth science, particularly for seismology and tectonics at plate convergence zones; yet, measurements are limited owing to a lack of drilled cores. Here, we propose a new indicator of strength, the equivalent strength (EST), which is determined only by drilling performance parameters such as drill string rotational torque, bit depth, and string rotational speed. A continuous depth profile of EST was drawn from 0 to 3000 m below the seafloor (mbsf) across the forearc basin and accretionary prism in the Nankai Trough. The EST did not show a significant increase around the forearc basin-accretionary prism boundary, but it did show a clear increase within the prism, ca. below 1500 mbsf. This result may indicate that even the shallow accretionary prism has been strengthened by horizontal compression derived from plate subduction. The EST is a potential parameter to continuously evaluate the in situ rock strength during drilling, and its accuracy of the absolute value can be improved by combining with laboratory drilling experiments.
AB - A new method for evaluating the in situ rock strength beneath the seafloor is proposed and applied to the Nankai Trough accretionary prism. The depth-continuous in situ rock strength is a critical parameter for numerous studies in earth science, particularly for seismology and tectonics at plate convergence zones; yet, measurements are limited owing to a lack of drilled cores. Here, we propose a new indicator of strength, the equivalent strength (EST), which is determined only by drilling performance parameters such as drill string rotational torque, bit depth, and string rotational speed. A continuous depth profile of EST was drawn from 0 to 3000 m below the seafloor (mbsf) across the forearc basin and accretionary prism in the Nankai Trough. The EST did not show a significant increase around the forearc basin-accretionary prism boundary, but it did show a clear increase within the prism, ca. below 1500 mbsf. This result may indicate that even the shallow accretionary prism has been strengthened by horizontal compression derived from plate subduction. The EST is a potential parameter to continuously evaluate the in situ rock strength during drilling, and its accuracy of the absolute value can be improved by combining with laboratory drilling experiments.
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U2 - 10.1038/s41598-018-20870-8
DO - 10.1038/s41598-018-20870-8
M3 - Article
C2 - 29445141
AN - SCOPUS:85042122964
VL - 8
JO - Scientific Reports
JF - Scientific Reports
SN - 2045-2322
IS - 1
M1 - 2622
ER -