2:45 PM - 3:00 PM
[SGL35-05] ESR technique for the assessment of fault activity; an approach from frictional tests using the Asano fault gouge collected by a trenching survey
Keywords:ESR dating, Electron spin resonance, Asano fault, Fault gouge, Assessment of fault activity, Frictional test
The fault gouge sample used for frictional tests is grayish white gouge with a width of ~10mm distributed along the fault plane between granite and Osaka group on the north wall of the Asano fault trench. The grayish white gouge was dried under natural circumstances, ground with an agate mortar and set between a pair of columnar gabbro samples with a diameter of 24.98mm. In shearing, one columnar gabbro was fixed and another was rotated. Frictional tests were carried out at a normal stress of 2 MPa and a slip rate of 1.3 m/s under dry and wet conditions (Tsutsumi et al., 2016). When the total displacement was 30m, the maximum frictional heat temperature attained was estimated as 380 degree C under dry condition and 340 degree C under wet condition. The gouge samples after frictional tests under dry and wet conditions were divided into three parts of 0-9mm (central part), 9-16mm (intermediate part) and 16-25mm (circumference part), and ESR measurements of the three parts were carried out. As a result, a strong FMR (ferrimagnetic resonance) signal formed by frictional heat is detected from all the three parts under dry condition (Fukuchi, 2012), and the FMR signal intensity increases from the central part to the circumference part. Besides, E’ center in quartz and quartet signals in montmorillonite available for ESR dating have been completely reset. On the other hand, a weak FMR signal is detected from the circumference part under wet condition, however the E’ center and quartet signals have been hardly reset. These results mean that the FMR signal intensity is available for the judgement of resetting state of ESR signals. Moreover, as a result of ESR analysis of the fault gouge along a fault (fa-5) located at a depth of about 200m in the Asano fault 300m boring core sample, a similar FMR signal to that obtained from the circumference part under wet condition is detected. This suggests that frictional heat along the Asano fault may have been generated under wet condition.
T. Fukuchi, 2004, Absolute dating of fault movement by ESR (Electron Spin Resonance) technique-Its principle and practice. Fukadaken Library, 63, 45pp.
T. Fukuchi, 2012, ESR Techniques for the Detection of Seismic Frictional Heat. In: Earthquake Research and Analysis: Seismology, Seismotectonics and Earthquake Geology (ed. D'Amico Sebastiano). InTech-Open Access Publisher, 285-308.
A. Tsutsumi et al., 2016, High-velocity frictional properties of the fault core zone material from the Asano fault, a branch fault of the Nojima fault. Abstract of the 123rd Annual Meeting of the Geological Society of Japan, T1-P-7.