[S-EM16] Geomagnetism, paleomagnetism, and rock magnetism

[SEM16-04] Anomalies Magnetic Susceptibility in the Atera fault and their causes

*Yasuhiro Sugitani¹, Tada-nori Goto¹, Kenji Hagiya¹, Nagi Yamashita¹, Riki Kondo¹ (1.University of Hyogo)

Keywords:Magnetic Susceptibillity, active fault, XRD

It has been reported that active faults and fracture zones have found higher magnetic susceptibility than the surrounding areas [Yoshimura and Ohno, 2012]. Such magnetic anomalies are caused from magnetic minerals generated by fault friction, and their magnetic susceptibility is proportional to the frictional energy applied to the slip surface, as shown by laboratory experiments in [Tanikawa et al., 2007] using rock samples from the Chelungp fault in Taiwan. However, previous ground-surface studies on the fault trace have only measured at intervals of a few meters. Drilled samples are well studied, but the magnetic susceptibility of surroundings of the drill holes are rarely discussed. In this study, we investigated high-density measurements at the outcrop of the Atera fault in Gifu, the one of largest active fault in Japan. We carried out the magnetic susceptibility measurements at intervals of about 10 cm, and we also estimated the mineral compositions and quantities of the rock samples from the outcrop surface using X-ray diffraction (XRD). In the fault core, the black gouge zones showed high magnetic susceptibility and increasing of magnetic minerals. Note that the highest magnetic susceptibility was obtained along a black gouge which seems to not be related to fault slips. Our survey suggest that the causes of high magnetic susceptibility are not only the slip friction, but also the alteration caused by hydrothermal fluid from deep interiors.