High-resolution aeromagnetic survey in the Fukui plain, central Japan

Authors: Shigeo Okuma, Masahiko Makino and Tadashi Nakatsuka

Abstract: We have conducted a helicopter-borne high-resolution aeromagnetic survey in the Fukui Plain, central Japan, to better understand concealed faults associated with the 1948 Fukui earthquake (M7.3) which brought disastrous damage to this area. The survey was flown with a Cesium Vapour magnetometer and a differential GPS along E-W flight lines at an altitude of 150 m above terrain and spaced 300 m apart. The compiled total intensity map of IGRF residuals shows the following interesting magnetic features: 1) a broad magnetic high area occupies the western half of the
plain; consisting of several large-amplitude dipole magnetic anomalies and small-amplitude regional magnetic highs; 2) a small-amplitude magnetic high extends SW-NE from eastern Harue to downtown Maruoka, implying a local uplift of the basement; 3) a sharp eastern border of the broad magnetic high area corresponds well to the inferred trace of the concealed Fukui earthquake fault; 4) a low-amplitude magnetic high extends along the inferred Fukui eastern earthquake fault; 5) One of distinctive magnetic anomalies in the broad magnetic high area lies at the western part of the Awara hot spring, implying an intrusive body related to the hot spring; and 6) magnetic lows are dominant in coastal and offshore areas of the Japan Sea, suggesting the existence of reversely magnetized volcanic rocks in these areas.
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