Abstract
In order to evaluate the magnetic heterogeneity in volcano, I constructed the magnetic model of the Hakkoda volcanoes from magnetic data with the help of other geophysical and geological information. By removing the effect of volcano, I estimated the amount of anomalies caused by structures underlying the volcano. A temperature gradient map delineates the Hakkoda volcanoes as a high temperature zone more than 100°C/km suggesting the existence of buried heat sources beneath the volcanoes. A north-south trending gravity high in the area expresses a geological basement uplift including intrusions related to Hakkoda volcanic activity. But intrusions can not be separated from the other basement rocks in the gravity map because they are almost same in density. Measurements of rock samples reveal that magnetization is strong and variable in each Hakkoda lava. Construction of a heterogeneously magnetized lava model was based on magnetization measurements. The calculated magnetic anomalies from the heterogeneous lava model correlate well with the observed rather than the homogeneous model. The good correlation indicates that the observed magnetic data include a large effect of the Quaternary lavas. A residual of the observed subtracted the calculated of heterogeneous model shows low amplitude anomalies over the Hakkoda volcanoes. It is not certain that the residual map expresses errors in the terrain correction or structures beneath lavas related to volcanic activities.
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