Beyond theoretical wave mechanics: Advancing the geophysical relevance of induced supersonic head waves across solid–liquid interfaces

Solid-liquid interface: Appearing induced supersonic head waves in liquid layers, which presents an elegant theoretical analysis of reflected and refracted bulk waves at the interface between an elastic isotropic substrate and an overlying liquid layer.By employing Helmholtz decomposition together with the spherical and deviatoric decomposition of stress and strain tensors, the study demonstrates that, under a specific angle of incidence, an S-wave can generate a geometric shear-to-compressional (S-P) head wave that subsequently induces a head wave propagating within the liquid layer at an apparent velocity exceeding the bulk wave velocity of the liquid.This contribution expands the theoretical understanding of interface wave phenomena and introduces a potentially important mechanism for wave propagation in coupled solid-liquid media.The study is particularly significant because wave propagation across heterogeneous interfaces remains a fundamental challenge in exploration geophysics, earthquake seismology, underwater acoustics, and geotechnical engineering.The identification of induced supersonic head waves offers a novel perspective for interpreting complex wavefields that are often observed but insufficiently explained using conventional reflection and refraction models.The analytical framework presented by the author may therefore stimulate further investigations into interfaceguided wave phenomena and their implications for subsurface characterization [2].While the theoretical contribution is noteworthy, an important research gap lies in the absence of numerical validation or experimental verification.The predicted occurrence of induced supersonic head waves is based on mathematical analysis under idealized assumptions, including an isotropic elastic substrate and a homogeneous liquid layer.Natural geological environments rarely satisfy these conditions.Most sedimentary basins, offshore environments, and volcanic regions exhibit varying degrees of elastic anisotropy, heterogeneity, attenuation, poroelastic behavior, and rough interface geometries [3].These factors may significantly modify wave generation, energy partitioning, and propagation characteristics.Consequently, future studies integrating finite-element simulations, laboratory ultrasonic experiments, or controlled field observations would substantially strengthen the practical applicability of the proposed theory.Another aspect deserving greater attention is the potential integration of this phenomenon into modern seismic imaging and inversion workflows.Advances in computational geophysics increasingly employ full-waveform inversion, elastic reverse-time migration, and machine learning algorithms to extract subtle wavefield information from complex datasets.If induced supersonic head waves can be reliably detected and distinguished from conventional refracted or interface waves, they may provide complementary constraints for estimating subsurface elastic properties, fluid distributions, and interface geometries.Such applications could improve the resolution of exploration surveys and enhance the interpretation of fluid-bearing formations [4].The findings are particularly relevant to the Philippine setting, where complex tectonic processes, active fault systems, volcanic provinces, and extensive offshore sedimentary basins present persistent challenges for seismic imaging and hazard assessment.The Philippines lies along the Pacific Ring of Fire and is characterized by highly heterogeneous geological structures that influence seismic wave propagation.Improved theoretical understanding