Geophysics | Keiichi Ishizu

Inversion Algorithm Determining Sharp Boundaries (Ishizu et al., 2025, Geophysics)

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

Ishizu, K. et al. (2025). Inversion algorithm determining sharp boundaries in electrical resistivity tomography. Geophysics, 90(3), 1-46.

Point 1: Data-driven inversion algorithm capable of reproducing sharp boundaries without excessive reliance on prior information

We have developed a new inversion algorithm that can accurately depict sharp resistivity boundaries. This data-driven approach represents a significant advancement by minimizing reliance on prior assumptions about boundary locations.

Accurately depicting sharp resistivity boundaries is crucial for improving the precision of resource exploration, particularly for metallic deposits. This method can be implemented by incorporating an ABIC search into existing inversion codes, and we hope it will be adopted across many platforms in the future.

Successful 3D Subsurface Mapping of Embedded Massive Sulfides (Ishizu et al., 2024, Geophysics)

Mon, 01 Jan 2024 00:00:00 +0000

Ishizu, K. Kasaya, T., Goto, T. N., Koike, K., Siripunvaraporn, W., Iwamoto, H., … & Ishibashi, J. I. (2024). A marine controlled-source electromagnetic application using towed and seafloor-based receivers capable of mapping seafloor and embedded massive sulfides. Geophysics, 89(3), E87-E99.

Point 1: Successful 3D subsurface mapping of embedded massive sulfides

Conventional marine electromagnetic methods for deep-sea metallic deposit exploration involved towing cables with current transmitters and receivers. While this allowed for mapping massive sulfides on the seafloor (mound-type seafloor massive sulfides), it was difficult to detect anomalies buried beneath the seafloor (embedded seafloor massive sulfides).

In this paper, we developed a system that combines the aforementioned towed system with multiple seafloor-based electric and magnetic field receivers. We demonstrated its effectiveness for simultaneously exploring embedded anomalies through numerical simulations and real-world data. Since embedded seafloor massive sulfides are highly promising as resources but lacked established exploration methods, the development of this technique represents a breakthrough in deep-sea metallic deposit exploration. Applying this method to various hydrothermal fields in the future may lead to more accurate resource assessments.

Successful 3D Subsurface Mapping of Seafloor Massive Sulfides (Ishizu et al., 2022, Geophysics)

Sat, 01 Jan 2022 00:00:00 +0000

Ishizu, K. Siripunvaraporn, W., Goto, T. N., Koike, K., Kasaya, T., & Iwamoto, H. (2022). A cost-effective three-dimensional marine controlled-source electromagnetic survey: exploring seafloor massive sulfides. Geophysics, 87(4), E219–E241.

Point 1: Successful 3D subsurface mapping of seafloor massive sulfides

Point 2 (Most Important): Proposal of a new 3D marine electromagnetic exploration technology that reduces receivers and costs while maintaining performance equivalent to conventional methods

Marine electromagnetic exploration is effective for estimating the 3D subsurface distribution of seafloor massive sulfides. However, existing methods require a large number of receivers to obtain 3D information, leading to high survey costs. In this paper, we proposed a new 3D marine electromagnetic technology that reduces the number of receivers and survey costs while maintaining performance equivalent to conventional methods. The proposed method is very simple, involving the placement of a single line of receivers in the center of the survey track. We first demonstrated the effectiveness of this method using a synthetic model and data. We then applied the proposed method to explore the Ieyama hydrothermal field in the Okinawa Trough and estimated the 3D subsurface distribution of seafloor massive sulfides, successfully identifying areas likely to be deposit bodies.