TITLE:
Assessment of the Relationship between ESR Signal Intensity and Grain Size Distribution in Shear Zones within the Atotsugawa Fault System, Central Japan
AUTHORS:
Emilia B. Fantong, Akira Takeuchi, Toshio Kamishima, Ryosuke Doke
KEYWORDS:
Active Fault, Shear Zones, ESR Signal Intensity, Grain Size Distribution, Atotsugawa Fault System
JOURNAL NAME:
International Journal of Geosciences,
Vol.5 No.11,
October
22,
2014
ABSTRACT: For the
first time, a relationship between ESR signal intensity and grain size
distribution (sieve technique) in shear zones within the Atotsugawa fault
system have been investigated using fault core rocks. The grain size
distributions were estimated using the sieve technique and microscopic
observations. Stacks of sieves with openings that decrease consecutively in the
order of 4.75 mm, 1.18 mm, 600 μm, 300 μm, 150 μm and 75 μm were chosen for
this study. Grain size distributions analysis revealed that samples further
from the slip plane have larger d50 (average gain size) (0.45 mm at
a distance of 30 - 50 mm from the slip plane) while those close to the slip
plane have smaller d50 values (0.19 mm at a distance of 0 - 10 mm
from the slip plane). This is due to intensive crushing that is always
associated with large displacement during fault activities. However, this
pattern was not respected in all shear zones in that, larger d50 values were instead observed in samples close to the slip plane due to admixture
of fault rocks from different fault activities. Results from ESR analysis
revealed that the relatively finer samples close to the slip plane have low ESR
signals intensity while those further away (coarser) have relatively higher
signal intensity. This tendency however, is not consistence in some of the
shear zones due to a complex network of anatomizing faults. The variation in
grain size distribution within some of the shear zones implies that, a series
of fault events have taken place in the past thus underscoring the need for
further investigation of the possibility of reoccurrence of faults.