Yosuke TAGUCHI, Norimichi MASHIKO, Akira YAMAZAKI and Toshiaki MISHIMA
Abstract
To monitor volcanic activity of Izu-Oshima volcano, Kakioka Magnetic Observatory has conducted continuous geomagnetic total intensity observations since March 2007 at two observation points, located about 40 m apart and about 400 m north of Miharayama crater. The amplitude of the annual variation in the observed geomagnetic total intensity was about 20-30 nT compared with that at a reference point. In addition, variation patterns at the two observation points were different. The causes of these variations are considered to reflect the influence of magnetized rocks around the magnetometer sites; thus, these variations are considered noise in the volcanic activity monitoring data. We investigated the characteristics of these geomagnetic variations by decomposing them into several components. We found that most of the variations in the residual component of geomagnetic total intensity consisted of irregular variations with a period of several months. Moreover, the variations were affected by precipitation and their sense was opposite at the two observation points. We suggest that the irregular variations with a period of several months can be reduced by averaging the data of the two observation points
Received 20 December 2012; received in revised from 5 August 2013; accepted 6 August 2013
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