Part 3: Fault Zone Structure, Composition and Physical Properties

Fault zone drilling provides valuable insights into under-standing the dynamics, physical properties, and structure of an active fault. We drilled into the four major active faults in central and western Japan to directly access mechanics, physical properties, and fault rock distributions in and around the fault zones—the Nojima fault (which appeared by the 1995 Hyogo-ken Nanbu Earthquake, M7.2, also called the Kobe Earthquake); the Neodani fault, which appeared by the 1891 Nobi earthquake (M8.0); the Atera fault of which some parts seemed to have been dislocated by the 1586 Tensho earthquake (M7.9); and the Gofukuji Fault, which is said to have activated more than a thousand years ago. We measured in situ stress magnitude and direction in and around a fault zone by hydraulic fracturing and borehole breakout method. Additionally, integrating in situ measure