Characteristics of crushed rocks observed in drilled cores in landslide bodies located in accretionary complexes

• Crushed rocks of landslide and fault origin can be distinguished by planar fabrics.
• Crushed rocks of landslide have a random fabric while fault rocks exhibit fabrics.
• A random fabric of landslide crushed rocks is formed under low confining pressure.
• Faults with a planar fabric are produced under high confining pressure.
• Determination of a landslide body can be achieved by describing the crushed structure.

The recent development of high-quality boring, which uses foam surfactants, has made it possible to examine the detailed geological constitution and structure of landslide bodies. However, geological information related to landslides has not been obtained appropriately even from undisturbed high-quality drilled cores. Moreover, it has been difficult to distinguish between rocks crushed by landslide movement and the fault breccia in accretionary complexes. We examined the detailed geology of high-quality drilled cores of landslide bodies on the Shimanto Belt and the Chichibu Belt. The fault breccia near the landslide bodies was found to exhibit planar fabrics while the crushed breccias in the landslide bodies showed a random fabric. We discovered that classifying the degree of crushing and inspecting the planar fabrics of rocks are effective in the geological determination of landslide bodies.