[SMP32-P18] Seismic slipping events recorded in a fault gouge zone: evidence from the Nojima Fault drill holes, SW Japan
Keywords:Fault gouge zone, Nojima Fault, Seismic slipping event
In the present study, we focused on the structural features of the fault gouge zone observed in drill cores acquired from nine holes that were drilled through the Nojima Fault (NF) at different depths from ~260 to 900 m at the Ogura site (Lin and Nishiwaki, 2019). Drilling investigations and structural analyses of drill cores reveal that a ~60 m wide fault damage zone containing a 10–30 cm thick fault gouge zone developed along the Nojima Fault (NF), on which the 1995 Mw 6.9 Kobe (Japan) earthquake occurred. The fault gouge zone was observed at depths of ~260 to 900 m in nine drill holes that intersected the NF. Our findings show that i) the fault gouge zone observed at different depths in the nine drill cores is the principal fault slip zone of the NF, ii) the fault gouge zone can be divided into 11–20 thin layers of different color, and iii) the individually colored layers contain different color breccias of fault gouge that are offset and/or cut by cracks and crack-filled calcite and quartz veinlets. Our results reveal that the fault gouge zone probably records more than 11–20 paleoseismic faulting events along the NF during the late Pleistocene-Holocene.
1) Lin, A., 2008. Fossil Earthquakes: The Formation and Preservation of Pseudotachylytes. Springer, Berlin, 348p (ISBN 978-3-540-74235-7).
2) Lin, A., Nishiwaki, T., 2019. Repeated seismic slipping events recorded in a fault gouge zone: evidence from the Nojima Fault drill holes, SW Japan. Geophys. Res. Lett., doi: 10.1029/2019GL081927.