2D resistivity model around the rupture area of the 2011 Tohoku-oki earthquake (Mw 9.0)

Many active volcanoes and various types of seismic activities exist in the southern part of the Northeast Japan subduction zone. One of the geologically most interesting features in this area is the sequential explosive eruptions of a group of volcanoes. The group consists of Mt. Azuma and Mt. Adatara on the volcanic front line, Mt. Bandai west of the volcanic front, and Mt. Numazawa on the back-arc side. A previous petrological study on the eruption products regarded Mt. Numazawa as an anomalous back-arc volcano because its lavas are similar to those of volcanoes on the volcanic front. The reason behind this unique connection was unclear, and hence, this study was intended to understand the deep fluids distribution beneath the area. For this purpose, a 3-D regional electrical resistivity structure was estimated from a series of wide-band magnetotelluric surveys, with 45 observation points deployed from the fore-arc to the back-arc sides. The most important feature of the resistivity structure is a large conductive zone in the central part of the area, spanning from the upper mantle to the lower crust. Interestingly, the lateral elongation of the conductor is oblique to the volcanic front line and consistent with the spatial distribution of the group of volcanoes and the low-frequency earthquake clusters around them. Therefore, the conductor most likely represents a large, elongated magmatic fluid reservoir beneath the volcanoes. Hydrous partial melting might be the cause of the enhanced conductivity. Graphical Abstract

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Geoelectrical evidence of fluid controlling slow and regular earthquakes along a plate interface

Nakamura,

Ichihara,

Goto

et al. 2024

Preprint

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Shallow subducting plate interfaces, as sites of both destructive and “slow” earthquakes, resulting from rapid and slower fault slips, respectively, present a major scientific and disaster mitigation challenge. Although understanding the different slip mechanisms and their spatial relationships is critical, the role of a key factor, pore fluids, is understudied. Here we present clear observational evidence from Hyuga-nada, southwestern Japan, that the pore-fluid distribution correlates with fault rupture behavior. A 3D electrical resistivity model derived from marine magnetotelluric survey data reveals distinct resistive and conductive anomalies along the plate interface that reflect areas of scarce pore fluid and high concentration area of pore fluids sourced from subducting seamounts (Kyushu–Palau Ridge), respectively. The wet area corresponds to the slow slip area whereas dry and the transition areas correspond to areas of fast fault slip. These findings highlight the influence of the pore-fluid distribution on fault processes and underscore its importance in earthquake and tsunami risk assessments.

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2D resistivity model around the rupture area of the 2011 Tohoku-oki earthquake (Mw 9.0)

Cited by 3 publications

References 54 publications

Forearc seismogenesis in a weakly coupled subduction zone influenced by slab mantle fluids

Forearc seismogenesis in a weakly coupled subduction zone influenced by slab mantle fluids

On a large magmatic fluid reservoir oblique to the volcanic front in the southern part of NE Japan revealed by the magnetotelluric survey

Geoelectrical evidence of fluid controlling slow and regular earthquakes along a plate interface

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