5:15 PM - 6:30 PM
[SSS10-P08] Fault activity recorded in kink bands in the fault jog of the Neodani Fault
Keywords:kink bands, fault jog, Neodani Fault
Neodani Fault, which is located in the northwestern part of Gifu prefecture, central Japan, is basically a left-lateral fault, and shows the vertical displacement at Neomidori, Motosu City. This area is in the compressional fault jog between two faults, and kink bands are developed in shale matrix mélange of the Jurassic Mino accretional complex in this fault jog. These kink band is expected to record old and underground fault activity in the fault jog of the Neodani Fault. The authors studied occurrence, structure, sense of shear, relationship with veins and microstructure to clarify old and underground fault activity in the fault jog of the Neodani Fault.
Well foliated shale matrix mélange is distributed in the study area, and the attitude of foliation concentrates a strike of EW dipping 90. Thirty-one kink bands were measured their attitude. The numbers of left-lateral and right-lateral kink bands are 29 and 2, respectively. The characteristics of kink bands are depending on their sense of shear. Kink planes, which are coincident with fold axial planes, concentrate to N 30 W 80 W in left-lateral kink bands and NS 80 W in right-lateral ones. Fold axes of both types of kink bands trend to be vertical. Folding angle is very small in left-lateral kink bands and large in right-lateral ones. Only right-lateral kink bands include en echelon veins.
Left-lateral kink bands exhibit microstructures of a bending of foliation and open cracks, and displacement of quartz veins along the foliation. These indicate kink folding and layer parallel slip. Thin section observation and powder X-ray diffraction analysis clarify that veins in right-lateral kink bands include quartz, potassium feldspar, chlorite and ankerite.
Left-lateral and right-lateral kink bands are not a conjugate set, because the relationship between their attitudes and sense of shear shows an impossible arrangement of paleo-stress direction and their characteristics are different each other. Left-lateral kink bands are expected to be deformed under the near-surface condition related to the recent activity of the Neodani Fault, because kink planes are almost parallel to the fault plane of the Neodani Fault and kink folding involves not only foliation but also open cracks. Right-lateral kink bands are assumed to be deformed under the higher temperature and deeper condition because these include quartz and chlorite in veins.
Under the assumption that kink planes of the left-lateral kink bands are not accompanied with slip along the kink planes, the total amount of displacement can be calculated from the left-lateral kink bands. In the length of 5.91 m along the foliation, total amount of displacement is calculated to be 0.35 m from the left-lateral kink bands. Under the assumption that deformation in the whole area of the fault jog occurs at same ratio, total amount of displacement is assumed to be 26 m. Although this is smaller than 2 km of the total amount of displacement at Kinbara area (Muramatsu et al., 2002), fault displacement is allocated in not only fault planes but also kink bands in the fault jog.
Reference: Muramatsu et al. (2002) The Nobi earthquake and the Neodani Fault system
Well foliated shale matrix mélange is distributed in the study area, and the attitude of foliation concentrates a strike of EW dipping 90. Thirty-one kink bands were measured their attitude. The numbers of left-lateral and right-lateral kink bands are 29 and 2, respectively. The characteristics of kink bands are depending on their sense of shear. Kink planes, which are coincident with fold axial planes, concentrate to N 30 W 80 W in left-lateral kink bands and NS 80 W in right-lateral ones. Fold axes of both types of kink bands trend to be vertical. Folding angle is very small in left-lateral kink bands and large in right-lateral ones. Only right-lateral kink bands include en echelon veins.
Left-lateral kink bands exhibit microstructures of a bending of foliation and open cracks, and displacement of quartz veins along the foliation. These indicate kink folding and layer parallel slip. Thin section observation and powder X-ray diffraction analysis clarify that veins in right-lateral kink bands include quartz, potassium feldspar, chlorite and ankerite.
Left-lateral and right-lateral kink bands are not a conjugate set, because the relationship between their attitudes and sense of shear shows an impossible arrangement of paleo-stress direction and their characteristics are different each other. Left-lateral kink bands are expected to be deformed under the near-surface condition related to the recent activity of the Neodani Fault, because kink planes are almost parallel to the fault plane of the Neodani Fault and kink folding involves not only foliation but also open cracks. Right-lateral kink bands are assumed to be deformed under the higher temperature and deeper condition because these include quartz and chlorite in veins.
Under the assumption that kink planes of the left-lateral kink bands are not accompanied with slip along the kink planes, the total amount of displacement can be calculated from the left-lateral kink bands. In the length of 5.91 m along the foliation, total amount of displacement is calculated to be 0.35 m from the left-lateral kink bands. Under the assumption that deformation in the whole area of the fault jog occurs at same ratio, total amount of displacement is assumed to be 26 m. Although this is smaller than 2 km of the total amount of displacement at Kinbara area (Muramatsu et al., 2002), fault displacement is allocated in not only fault planes but also kink bands in the fault jog.
Reference: Muramatsu et al. (2002) The Nobi earthquake and the Neodani Fault system