Ground Magnetic Anomalies in the Tanna Fault and Their Implications.

A blimp-borne survey system was developed to measure the geomagnetic field at low altitude, with a portable proton-precession magnetometer and a portable global positioning system (GPS) installed in a small radio-controlled blimp. The total weight of the instruments was well below the blimp payload of 25kg. The result of the blimp-borne survey which we carried out in the Tanna Basin was compared with that of the ground survey in the same area. It was then confirmed that a magnetic anomaly map could successfully be derived from the blimp survey.

Section: Introductionsupporting

confidence: 55%

“…Also a magnetic low can be recognized in the east of the fault. OKUBO et al (1991) suggested that these high magnetic anomalies are caused by the basaltic lava which is located at the depth of 100m under the Tanna Basin sediments. In the south there is a negative anomaly extending from the west to the east.…”

Section: Introductionmentioning

confidence: 99%

An Attempt of Geomagnetic Field Measurement with a Radio-Controlled Blimp in the Vicinity of the Tanna Fault.

Makino¹,

Okubo²,

Morijiri³

et al. 1991

“…In the meantime, Okubo et al (1991) conducted a magnetic survey across the same fault system, but about 4 km to the north of the AMT profile. Their magnetic model, supported by drilling results, shows a significant magnetic contrast across the fault.…”

Section: Discussionmentioning

confidence: 99%

Audio-Frequency Magnetotelluric Imaging of an Active Strike-Slip Fault.

Ogawa

Uyeshima

Honkura

et al. 1994

A tensor audio-frequency (10,000-1 Hz) magnetotelluric method was used to image the Kita-Izu fault system, a typical active strike-slip fault in Japan. Regional strike direction (N55°E) was first determined after decomposing tensor impedances; this direction is consistent with the strike of geomorphology and also with the strike of the fault. Local anisotropy and site gain were then corrected for each site. Finally, the impedances were inverted using two-dimensional modeling with a smoothness constraint. The model shows (1) that the fault corresponds to a discontinuity of the surface resistive volcanic cover and (2) that there is a significant conductive anomaly (-1 SZm) beneath the valley at 500 m depth from the surface, which may correspond to a fractured zone.

“…Honkura and I §ikara, 1991;Okubo et al, 1991). Such a zone has been interpreted as corresponding to a fractured zone created by repeated displacement of the fault plane, as supported by field evidence (Honkura and I §ikara, 1991).…”

Section: Introductionmentioning

confidence: 76%

“…Brabb and Hanna, 1981;Honkura et al, 1985;I §ikara et al, 1985;Ohshiman et al, 1987;Honkura and I §ikara, 1991;Makino et al, 1991;Okubo et al, 1991;Tuncer et al, 1991a, b). In particular, the examples obtained in the North Anatolian Fault Zone Honkura and I §ikara, 1991) are the most representative ones and the observed anomalies could be interpreted in terms of highly magnetized dike-like bodies lying along the active faults (I §ikara et al, 1985).…”

Section: Introductionmentioning

confidence: 99%

Local Magnetic Anomalies Associated with Active Faults in Beppu Bay, Southwest Japan.

Honkura

Isihara

Shimazaki

et al. 1994

Many examples of local magnetic anomalies in the vicinity of active faults have been reported, although the association of magnetic anomalies with active faults has not been well established. Aiming at studying local magnetic anomalies, we made magnetic surveys in Beppu Bay, Southwest Japan, where many active faults have been found through acoustic sounding. Along individual survey profiles, we found many magnetic anomalies seemingly associated with active faults, but in the contour maps of the geomagnetic total intensity and the shaded relief maps, no clear lineation-like feature could be identified. Profile data could be interpreted in terms of either a model of spatial magnetization variation or a model of magnetic basement undulation. The former model implies the correspondence of a low magnetization zone to a fractured zone, whereas the latter model suggests the depression of magnetic basement.