Continuous depth profile of the rock strength in the Nankai accretionary prism based on drilling performance
Yohei Hamada1,2, Manami Kitamura3,4, Yasuhiro Yamada5
1Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 200 Monobe-otsu, Nankoku, Kochi, 783-8502, Japan. yhamada@jamstec.go.jp.
Abstract:
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.
More Related Videos
15:11Surgical Fixation of Sternal Fractures: Preoperative Planning and a Safe Surgical Technique Using Locked Titanium Plates and Depth Limited Drilling
Published on: January 5, 2015
10:36Stress Distribution During Cold Compression of Rocks and Mineral Aggregates Using Synchrotron-based X-Ray Diffraction
Published on: May 20, 2018
Related Concept Videos
Relative Strengths of Conjugate Acid-Base Pairs
Acid and Bases: Ka, pKa, and Relative Strengths
Acid/Base Strengths and Dissociation Constants
Acid Strength and Molecular Structure
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
Strength of Cement
For compressive strength tests, ASTM C 109-05 standards prescribe a cement-sand mix ratio of 1:2.75 and a water/cement ratio of 0.485 for making 2-inch cubes. These cubes are mixed, cast, and cured in saturated lime water at 23°C until testing. Flexural strength testing, outlined in...
Relation Between Tensile Strength and Compressive Strength of Concrete
