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Pore pressure plays a key role in the generation of earthquakes in subduction zones. However, quantitative constraints for its determination are quite limited. Here, we estimate the subsurface pore pressure by analyzing the transient upwelling flow of drilling mud from borehole C0023A of the International Ocean Discovery Program (IODP) Expedition 370, in the Nankai Trough off Cape Muroto. This upward flow provided the first direct evidence of an overpressured aquifer in the underthrust sediments off Cape Muroto. To estimate the pre-drilling pore pressure in the overpressured aquifer around a depth of 950–1, 050 m below sea floor, we examined the measured porosities of core samples retrieved from nearby IODP wells; we then proceeded to explain the observed time evolution of the flow rate of the upwelling flow by modeling various sized aquifers through solving a radial diffusion equation. It was observed that for a permeability of 10⁻¹³ m², the aquifer possessed an initial excess pore pressure of ∼5–10 MPa above the hydrostatic pressure, with a lateral dimension of several hundred meters and thickness of several tens of meters. The overpressure estimates from the porosity-depth profile at Site C0023 differ from those at other drill sites in the region, suggesting the possible existence of multiple overpressured aquifers with a patchy distribution in the underthrust sediments of the Nankai Trough. As pore pressure is relevant in maintaining fault stability, the overpressured aquifers may be the source of slow earthquakes that have been observed around the drilling site.

This article is devoted to introduce a new class of nonassociative algebras with involution including the class of structurable algebras., QC 20110505

The Metal Mining Agency of Japan was established in 1963 to secure the stable supply of minerals through the promotion of exploration activities in Japan. Its scope has been expanded to include overseas exploration, information services in relation to mineral exploration, domestic mine pollution prevention activities and research into exploration technology and mine-related pollution prevention. The level of overseas exploration now far exceeds the amount being conducted domestically and information services have been expanded from the compilation of geological data in support of exploration activities, to the compilation and exchange of information related to mineral development overall. Environmental programmes include the provision of on-site expert assistance, compiling information on abandoned mines and participating in international environmental activities., The Metal Mining Agency of Japan was established in 1963 to secure the stable supply of minerals through the promotion of exploration activities in Japan. Its scope has been expanded to include overseas exploration, information services in relation to mineral exploration, domestic mine pollution prevention activities and research into exploration technology and mine-related pollution prevention. The level of overseas exploration now far exceeds the amount being conducted domestically and information services have been expanded from the compilation of geological data in support of exploration activities, to the compilation and exchange of information related to mineral development overall. Environmental programmes include the provision of on-site expert assistance, compiling information on abandoned mines and participating in international environmental activities.