Trans-crustal magma plumbing system of Kirishima Volcanic Complex as inferred from dense broadband magnetotelluric observations

Abstract To investigate the magma plumbing system of the Kirishima Volcanic Complex (KVC), we conducted a broadband magnetotelluric (MT) survey over an expanded area of approximately 60 × 60 km, including the region around Shinmoe-dake volcano, which recently experienced magmatic eruptions in 2011, 2018, and 2025. Three-dimensional inversion of the MT data reveals a detailed resistivity structure extending to upper mantle depths. A large low-resistivity zone (C1) is interpreted as a long-lived trans-crustal magmatic system, whereas an adjacent high-resistivity zone (R1) is interpreted as solidified magma associated with past caldera-forming eruptions. The geodetically inferred pressure source associated with the recent eruptions of Shinmoe-dake is situated at the boundary between C1 and R1 and is interpreted as a small, temporary magma pocket. The craters of three active volcanoes (Iwo-yama, Shinmoe-dake, and Ohachi) are located above the edges of C1, and deep low-frequency earthquakes (DLFEs) occur at its eastern edge. Notably, the spatial alignment of the DLFE cluster, pressure source, and Shinmoe-dake crater is approximately linear and follows the margin of C1, suggesting that magma preferentially ascends along the edge of C1. Furthermore, the nearly simultaneous onset of DLFEs, pressure source inflation, and shallow seismicity—with time lags of only a few days—indicates the presence of an established and efficient magma ascent pathway along the edge of C1. The large volume of C1 (> 3000 km 3 ) and its structural characteristics imply a relatively high potential for large-scale eruptions to occur over short timescales in the future. These findings provide a new framework for understanding the long-term magmatic evolution and eruption potential of the KVC. Graphical abstract