4:00 PM - 4:15 PM
[SSS31-21] Electrical resistivity survey of subsurface structure of an active fault
- A case study of the Gomura fault in Kyotango, Kyoto -
Keywords:active fault, Magnetotellurics, Gomura fault
Clear electrical conductivity variation is expected to be identifiable in the vicinity of an active fault as a result of enriched and interconnected fluid (meteoric waters and/or groundwater) in fractures and/or uneven fluid distribution across the fault because of impeded cross-fault fluid flow (e.g., Ritter et al., 2005). The electrical conductivity distribution can provide a new image of the subsurface structure of an active fault.
A clear surface earthquake fault appeared associated with the 1927 Kita-Tango Earthquake in the Tango Peninsula of the northwestern part of Kinki district, Japan. This fault is named the Gomura fault and is one of the fault segments of the Yamada fault system.
We made an audio-frequency magnetotelluric (AMT) survey at twelve stations along a transection across the Gomura fault and obtained two-dimensional resistivity model (GMR model) along the line. The model is characterized by four conductive regions.
(1) Shallow sub-horizontal conductive layer (C1) between 160m and 300m in depth.
(2) Deep sub-horizontal conductive layer (C2) between 750m and 1200m in depth.
These layers are located to the east of a surface trace of the Gomura fault.
(3) Sub-vertical conductive zone (C3) beneath a surface trace of the Gomura fault.
(4) Weak and local conductive zone (C4) beneath a surface trace of the Go-seihou fault.
In this presentation, first we show MT responses for some typical resistivity structures which are expected to exist beneath an active fault, second explain some features of the GMR model, and finally interpret the GMR model with referring to the 1,300m-long borehole data.