Japan Geoscience Union Meeting 2023

Presentation information

[E] Oral

S (Solid Earth Sciences ) » S-EM Earth's Electromagnetism

[S-EM14] Electric, magnetic and electromagnetic survey technologies and scientific achievements

Tue. May 23, 2023 3:30 PM - 4:45 PM 103 (International Conference Hall, Makuhari Messe)

convener:Kiyoshi Baba(Earthquake Research Institute, The University of Tokyo), Tada-nori Goto(Graduate School of Science, University of Hyogo), Yuguo Li(Ocean University of China), Wiebke Heise(GNS Science, PO Box 30368, Lower Hutt, New Zealand), Chairperson:Yuguo Li(Ocean University of China), Keiichi Ishizu(University of Hyogo)

4:30 PM - 4:45 PM

[SEM14-10] Application of EM-ACROSS to investigate underground structures of the Kusatsu-Shirane Volcano, Japan

*Keiichi Ishizu1, Yasuo Ogawa2, Kuo Hsuan Tseng2, Sohei Serita2, Takahiro Kunitomo6, Takuto Minami4, Hiroshi Ichihara3, Grant Caldwell5, Wiebke Heise5, Ted Bertrand5 (1.University of Hyogo, 2.Tokyo Institute of Technology, Japan, 3.Nagoya University, 4.Kobe University, 5.GNS Science, 6.Ontake Science Lab)

Keywords:resistivity, electromagnetic exploration, CSEM

We have constructed a controlled source electromagnetic transmission system called ElectroMagnetic-Accurately Controlled, Routinely Operated, Signal System (EM-ACROSS). The basic idea of EM-ACROSS is to enable long stacking times by repeatedly transmitting a precisely controlled signal. As a result of long-time stacking, a high signal-to-noise ratio can be achieved. High-precision signal control of the transmitter is conducted by synchronizing with a 10 MHz GPS signal. In addition to the basic concept, our EM-ACROSS has the following feature: two dipole antennae simultaneously transmit independent sets of signal time series consisting of eight sinusoids. The two sets are slightly different in frequency and can be recorded by the receiver without interference. This allows efficient data acquisition without turning off single dipole transmission. Our EM-ACROSS was applied to an investigation of the Kusatsu-Shirane Volcano, Japan. Phreatic eruptions frequently occur at the Yugama crater of the Volcano. A 0.5 km north-south dipole and a 1.0 km east-west dipole were placed at about 3 km from the Yugama crater. The current values were about 5 A for the north-south dipole and 3 A for the east-west dipole. Eight receivers were placed around the Yugama crater to record the electromagnetic fields from the transmitters. The processed electromagnetic data with a stacking period of 1 week showed a high signal-to-noise ratio even at receiving points 3 km apart from the transmitter.