Work

Anisotropic properties of fracture zone in sandstone inferred from seismic moment tensors of acoustic emissions

Year: 2025

Type: article

Abstract: • Cracks formed during the semi-circular bend test of sandstone produce anisotropic properties of the fracture zone. • Anisotropy is retrieved from non-double-couple moment tensors of observed acoustic emissions. • The orientation of anisotropy axes is aligned with the stress axes in the rock. • Neglecting anisotropy of the fracture zone leads to biased estimation of the orientation and tensility of cracks. We present an inversion for elastic anisotropy parameters of rocks using a large set of accurate moment tensors (MTs) derived from acoustic emissions (AEs). This method is demonstrated using AEs observed in a sandstone sample during a semi-circular bend test. We inverted 539 highly accurate MTs of AEs and retrieved both the orientation of anisotropy axes and nine elastic parameters defining the orthorhombic anisotropy within the fracture zone that developed in the sample during the test. The anisotropy results from the presence of aligned cracks in the fracture zone and the background transverse isotropy of the sandstone specimen. The observed anisotropy is moderate, with strengths of 18%, 14% and 21% for the P, S1 and S2 waves, respectively. We show that neglecting this anisotropy introduces a significant bias when estimating crack orientation and tensility from MTs. When anisotropy effects are accounted for by recalculating moment tensors into source tensors, the scatter in crack orientations is reduced, and the slope angle, which characterizes crack tensility, is systematically increased by approximately 10°. Our results confirm that the presented anisotropy inversion method is a powerful and robust tool, capable of analyzing anisotropy in rocks, even in cases of low anisotropy symmetry.

Source: Ultrasonics

DOI: 10.1016/j.ultras.2025.107832

Authors: Václav Vavryčuk, Matěj Petružálek, Tomáš Lokajíček

Institutions: Czech Academy of Sciences, Czech Academy of Sciences, Institute of Geophysics, Czech Academy of Sciences, Institute of Rock Structure and Mechanics

Language: English

Topic: Rock Mechanics and Modeling

Subfield: Mechanics of Materials

Field: Engineering

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $3,680

Funders: Grantová Agentura České Republiky, Akademie Věd České Republiky