Mesoscale fractures control the scale dependences of seismic velocity and fluid flow in subduction zones

IF 2.7 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Tectonophysics Pub Date : 2024-12-17 DOI:10.1016/j.tecto.2024.230606
Yuya Akamatsu, Hanaya Okuda, Manami Kitamura, Michiyo Sawai
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引用次数: 0

Abstract

Natural geological systems contain porosity structures of various scales that play different roles in geophysical properties, fluid flow, and geodynamics. To understand seismic activity associated with high pore-fluid pressure and fluid migration in subduction zones, it is necessary to explore the scale dependence of geophysical properties such as seismic velocity and permeability. Here, we compare laboratory-measured ultrasonic velocity measured on core samples from the Susaki area in the Shimanto accretionary complex, SW Japan, with sonic velocity measured by borehole logging experiments. Results show that P-wave velocity decreases from the laboratory (∼6 km/s) to the borehole scales (∼5 km/s). This scale-variant effect can be explained by a differential effective medium model whereby mesoscale porosity that is undetectable at the ultrasonic wavelength is introduced into the matrix phase with microscale porosity. Assuming typical apertures for micro- and mesoscale fractures, we estimate that the effective permeability can increase to 10−12–10−11 m2 with increasing in the mesoscale porosity and decreasing P-wave velocity down to 4–5 km/s. These results indicate that seismic velocity anomalies and related seismic activity are associated with the presence of mesoscale fractures in subduction zones.
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来源期刊
Tectonophysics
Tectonophysics 地学-地球化学与地球物理
CiteScore
4.90
自引率
6.90%
发文量
300
审稿时长
6 months
期刊介绍: The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods
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