DRILLING MEASUREMENT OF NMR CHARACTERISTIC OF EARTHQUAKE AND INTERPRETATION THEREOF

摘要

PURPOSE: To determine the magnetic characteristics of a stratum accurately and reliably by mounting an RF antenna on the outside of a metallic structure of a stratum detector in parallel with a boring axis and the elongated volume of a static field in an adjacent stratum. CONSTITUTION: A stratum detector 13 connected with a unit 7 on the ground surface through a wire line 8 is inserted into a bore 10. The stratum detector 13 comprises a surface 14 touching the bore wall tightly, and a retractable arm 15 which presses the body of the stratum detector 13 against the bore wall thus pressing the surface 14 against the wall surface. The stratum detector 13 further comprises an antenna 18 interposed between a magnet array 17 and the surface 14. The magnet array 17 generates a static field over the entire region surrounding the stratum detector 13. The antenna 18 generates an oscillatory magnetic field B1 which is focused in a stratum 12 and is superposed on a static field in the stratum 12 facing the surface 14. The stratum detector 13 magnetically tilts the nuclear spin of particles in the stratum 12 and carries out measurement by detecting the precessions of tilted particles in a uniform magnetic field.