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Earth, Planets and Space
Fig. 4 | Earth, Planets and Space

Fig. 4

From: Two independent signals detected by ocean bottom electromagnetometers during a non-eruptive volcanic event: Ogasawara Island arc volcano, Nishinoshima

Fig. 4

a Time variation of the residual total magnetic force of each OBEM site to CBI magnetic observatory. Yellow shade indicates Period A. b Same as a, but the data are filtered to reduce the shorter period fluctuations and linear trends. NS06–CBI is omitted in the plot because the NS06 data show a jump. The circles with error bars indicate the average and standard deviation of the data after Period A. Stars are the values predicted by the best fit point-source demagnetization model. c The total magnetic force anomaly distribution (colored contour lines) on the seafloor predicted using the best fit demagnetization source. Note that the contour lines are not drawn at an equal interval but are shown for the values, 0, ± 0.1, ± 0.2, ± 0.5, ± 1, ± 2, ± 5, ± 10, ± 20, ± 50, and ± 100 nT. Crosses with labels denote the site location and their color except for NS06 indicates the observed total magnetic force change. The white circle denotes the horizontal location of the best fit dipole moment, whose radius corresponds to that of the equivalent demagnetization sphere (1.1 km). The background gray shade is the bathymetry map. The black line indicates the island coast

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