[SSS08-P05] Gravity survey and subsurface structure across the Aomoriwan-Seigan Fault Zone, Northeast Japan
Keywords:Gravity survey, Bouguer gravity anomaly, Aomoriwan-Seigan fault zone, Seismic reflection survey, CSAMT survey
Gravity survey was conducted with a SCINTREX CG-5 gravimeter from May 25 to June 1, 2017. The length of the gravity survey line was about 7.6 km along the Amida river from the coastline of the Yomogita village to the entrance to a route up Mt. Okura-dake. The standard interval of gravity station is 200 m. Around the active fault trace of the Aomoriwan west fault, we changed the interval of gravity stations into 100 m. To obtain the altitudes of the gravity stations, we also conducted GNSS (Global Navigation Satellite System) survey in the eastern side of the survey line and leveling in the mountainside. The total number of gravity stations in this survey was 60. We applied standard procedures of gravity correction to obtain the Bouguer gravity anomalies. The SPECG1988 (GSJ gravity survey group, 1989) method was applied for terrain correction.
In the result of Bouguer gravity anomaly, we cannot identify the significant gradient change around the surface trace of the Aomoriwan west fault. However, the gradient of Bouguer gravity anomaly was changed at the point where 2 km west from the surface trace. It is supposed that the gradient change reflects a density structure dislocated by the deeper extension of the Aomoriwan west fault.
In this study area, seismic reflection survey, CSAMT survey, and gravity survey (this study) were conducted along the same exploration line. We compared these explorations and estimated the subsurface structure of the Aomoriwan west fault (Aomoriwan-Seigan fault zone).
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