Reflection Matrix Imaging of the Hengill Geothermal Field, Iceland

Imaging the Earth’s subsurface is fundamental to a wide range of geophysical applications, including natural hazard assessment and mitigation, geothermal and mineral exploration, and crustal characterization. However, achieving reliable seismic images in strongly heterogeneous media remains a significant challenge. In such environments, conventional seismic imaging approaches, including tomography and migration, often perform poorly due to the prevalence of multiple scattering and high attenuation, which obscures primary reflections and degrades image quality.

While multiple scattering has traditionally been regarded as a major impediment to seismic imaging, recent advances have demonstrated that this scattered energy can instead be exploited to extract valuable information. One such approach is Reflection Matrix Imaging (RMI). RMI involves using seismic interferometry to construct a reflection matrix that contains the full wavefield response between virtual source–receiver pairs, allowing for the analysis of reflected energy generated by subsurface heterogeneities. From this, the distortions undergone by the incident and reflected waves  can be isolated and compensated for even with a rough estimate of the background seismic velocity. RMI has been shown to enhance imaging in complex geological settings, including volcanic environments, and has also been seen to be effective in 3D imaging applications in fields such as optical microscopy and medical ultrasound.

In this study, RMI is adapted to data from a dense seismic array deployed in the Hengill Geothermal Field, Iceland. The subset of the array considered here comprises 267 stations distributed over a rectangular approximately 5X10km² , with continuous recordings spanning 2.5 months. Reflection matrices are constructed, and the applicability and performance of RMI in this highly heterogeneous geothermal setting are systematically evaluated.