Controlled-Source Electromagnetic Survey in Volcanic Areas (Ishizu et al., 2025, GJI)

Wed, 01 Jan 2025 00:00:00 +0000

Ishizu, K. et al. (2025). Controlled-source electromagnetic survey in a volcanic area: relationship between stacking time and signal-to-noise ratio and comparison with magnetotelluric data. Geophysical Journal International, 240(2), 1107-1121.

Point 1: Significant improvement in S/N ratio achieved using EM-ACROSS

Point 2: Detection of a vapor layer undetected by conventional MT surveys

Magnetotelluric (MT) methods, which use natural electromagnetic signals, have primarily been used for structural investigation and monitoring of volcanic bodies. However, their application was limited by unstable signal sources and artificial noise, which reduced the signal-to-noise (S/N) ratio.

In this paper, we demonstrate that a significant improvement in the S/N ratio is possible by using EM-ACROSS, a high-precision controlled-source method, combined with long-duration measurements. This result suggests that high S/N ratio electromagnetic exploration data can be obtained even in areas where MT investigation was previously difficult due to noise levels.

Furthermore, MT methods often struggle to detect thin high-resistivity layers because horizontal electric fields dominate. By using a controlled source, we can excite vertical currents, enabling the detection of vapor layers (thin high-resistivity bodies) that can cause phreatic eruptions. This research introduces a new observation method to the field and represents a significant breakthrough in electromagnetic exploration.

Volcano | Keiichi Ishizu

Controlled-Source Electromagnetic Survey in Volcanic Areas (Ishizu et al., 2025, GJI)

Point 1: Significant improvement in S/N ratio achieved using EM-ACROSS

Point 2: Detection of a vapor layer undetected by conventional MT surveys