Integrated Geostructure-Based Inversion of Complementary Geophysical Data for Improved Site Characterization

Abstract

Summary Reliable characterization of subsurface structure is essential for radioactive waste repository siting, where faults and geological interfaces strongly influence hydraulic behavior, mechanical integrity, and long-term containment. Borehole data provide detailed local information but leave substantial uncertainty between drillholes, motivating the integration of spatially continuous geophysical constraints. We present a joint structure-based inversion framework that directly updates geological structural geometry by combining complementary geophysical data sets within a shared model representation. The approach couples implicit geological modeling with seismic travel-time tomography and electrical resistivity tomography, allowing multiple methods to jointly refine fault geometry and stratigraphic boundaries while preserving method-specific property models. The workflow is tested using a synthetic case study inspired by the Mont Terri Underground Laboratory, where Opalinus Clay is intersected by a major fault zone relevant to repository performance. Starting from initially flat interfaces, the inversion reconstructs the fault geometry using data from two boreholes, enabling evaluation of the acquisition geometry and structural sensitivity. Results show improved geometric recovery and faster convergence compared to single-method inversions, reflecting the complementary coverage of seismic and electrical data. Although demonstrated for the Mont Terri setup, the open-source-driven framework is generic and transferable to other site characterization contexts.

Authors 4

1. A. Balza Morales Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University

2. F M Wagner Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University

3. F. Wellmann Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University

4. H. Maurer

   ETH Zurich · Institute of Geophysics

   Affiliation as printed

   ETH Zürich Institute for Geophysics