[2oral301-13] T1.［トピック］変成岩とテクトニクス

[T1-O-7] Naturally injected short-lived fluid flow in a single fracture related to seismic events in the middle crust.

*Diana Mindaleva¹, Masaoki Uno¹, Noriyoshi Tsuchiya¹ (1. Tohoku University)

キーワード：Short-lived fluid flow, Crustal fracturing, Voluminous fluid flow, Fluid-rock reaction zone

Short-lived fluid flow in the crust modifies hydrological properties and controls on the earthquake triggering. However, there are limited numerical constraints on the fluid volumes that can be rapidly transported. Comprehension of the timescales of fluid infiltration and the permeability evolution from geological samples is essential to estimating the fluid flux during crustal fracturing and its relation to seismic activities. This study focuses on fluid flow through a single fracture and scales its results to a series of low-magnitude fracturing events, such as tremors and low-frequency earthquakes, providing insights into fracturing and fluid-rock interactions in the lower–middle crust. Specifically, we analyse unique geological and geochemical evidence preserved in amphibolite-facies fluid-rock reaction zones to approximate the duration of fluid infiltration and time-integrated fluid fluxes and then determine the generated seismic moment and magnitude. This study is based on evidence of rapid fluid infiltration (~10 h) related to crustal fracturing and permeability evolution from low- to highly-permeable rocks (~10⁻⁹–10⁻⁸ m²). We estimate both through and perpendicular time-integrated fluid fluxes to a given fracture and the overall fluid-rock reaction zone. We present an advanced methodology for calculating the fluid volume via coupled reactive-transport modelling and thermodynamic analyses, focusing on Si alteration processes within reaction zones. In this study, we use two independent methods for constraining magnitude, which are based on fluid volumes and single fracture geometry. We compare the estimated values with the results provided by fluid injection experiments. Our finding reveals that the transportation of voluminous fluid volumes through a fracture (10¹ to 10⁴ m³) may be related to short seismic/aseismic events such as tremors and LFEs, as suggested from duration (~10 h) and cumulative magnitude, representing the maximum values as 2.0–3.8. In addition, we define the lower limit of the magnitude for a single fluid-driven seismic event as –0.6 to 0.2. However, a single fracture remains possible to transfer voluminous fluid flow and could be a key control on the generation of seismic activity above the tremor and slow slip events source regions in the lower–middle crust.