ALBERT

Description: There are two types in anomalies of short period geomagnetic variations: one (High cut ΔZ type) is characterised by high attenuation of high frequency components of ΔZ and the other (Directional variation type) by unusual directionality in the variation vector. “High-cut ΔZ type” anomaly is expected to be found in areas where the electrically conducting layer is raised and “Directional variation type” is expected to exist at boundaries between areas having different electrical properties. Reported anomalies of geomagnetic variations in various parts of the world are classified into the above two types and compared with the observations of terrestrial heat flow. Most of “High-cut ΔZ type” anomalies are associated with high heat flow, whereas most of “Directional variation type” anomalies are associated with the boundaries of high and low heat flow areas. Such correlations are interpreted in terms of the temperature distribution in the upper mantle. Typical of “Directional variation type” anomalies are found at continental margins, where the effect of sea water should not be overlooked. It is further shown that, from the view-point of both heat flow and the conductivity anomaly, there are two types in continental margins: normal (Atlantic type) and island arc type (Pacific type) continental margins. Finally, a model that appears reasonable is presented for Central Japan anomaly of which complex nature so far rejected theoretical interpretations: Central Japan anomaly is caused by the superposition of peninsula effect and undulation of high conductive layer under the Philippine Sea coastal area of southwestern Honshu where heat flow is higher in the sea than in the land. Unlike northeastern Honshu, southwestern Honshu is not a typical island arc. © 1970, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.