Anatomy of a Reactivated Hydraulic Fracture: An Integrated In Situ Study of Aseismic Slip, Source Mechanisms, and Model Validation

Hydraulic fracturing in naturally fractured rock is often governed by the reactivation of pre-existing discontinuities. To investigate the interplay between seismic and aseismic processes during reactivation, we conducted a multi-scale in situ experiment at the Kamioka Underground Laboratory, Japan. Our integrated analysis combines three key datasets: (1) a “ground truth” 3D fracture geometry mapped from recovered, resin-impregnated cores; (2) a high-resolution relocated acoustic emission (AE) catalog; and (3) quantitative source mechanisms derived from Bayesian moment tensor inversion. The results reveal extensive aseismic fracture opening, with the resin-filled area substantially exceeding the region delineated by AE hypocenters. These findings suggest that relying solely on induced seismicity may significantly underestimate the hydraulically affected volume. Moment tensor analysis shows predominantly mixed-mode AE source mechanisms, providing quantitative confirmation of the “hydroshearing” process—a mechanism characterized by a combination of shear slip and tensile opening. By comparing these observations with a calibrated planar 3D numerical model, we demonstrate the predictive capability of continuum-based models for first-order predictions, while also highlighting their limitations in capturing local-scale complexities. This dataset contains the processed data supporting the findings of the publication. Please see the README.txt file for a detailed description of the files and data format.