Spatio-Temporal Variability of the Earthquake-Generated Ocean Soundscape: Decoupling Source Magnitude from Acoustic Conversion Efficiency

Ocean soundscape analysis frequently relies on time-averaged metrics, treating geophony as a quasi-stationary background component. This approach obscures the stochastic, high-amplitude variability introduced by solid Earth seismicity, which dominates the low-frequency spectrum (<100 Hz) and exerts significant, transient environmental forcing. A fundamental knowledge gap remains regarding the transfer function between seismic ground motion and the resulting hydroacoustic pressure field. While T-phase excitation is known to occur via scattering at rough fluid-solid interfaces, the global scaling relationship between seismic source parameters (magnitude, depth, focal mechanism) and far-field acoustic intensity remains unconstrained. Specifically, it is unknown whether seismic-to-acoustic coupling is a globally constant scalar or a spatially variance function of local boundary conditions.

 

We present a comprehensive, data-driven analysis of the global earthquake soundscape, utilizing ten years (2015–2025) of continuous hydrophone records from the CTBTO International Monitoring System (Pacific, Atlantic, and Indian Oceans). Integrating IRIS seismic catalogs, we analyze over 10,000 events to quantify T-phase energy flux and duration. To isolate source mechanics from propagation effects, we correct for transmission loss using 3D ocean acoustic models and apply backprojection techniques to verify source azimuths. We employ a machine-learning framework to regress acoustic observations against high-resolution geophysical constraints, including Slab 2.0 geometry, slab thermal structure (controlling attenuation), global sediment thickness maps, and seafloor roughness metrics.

 

Our results challenge the assumption of a linear magnitude-loudness relationship. We identify significant spatial heterogeneity in T-phase generation, governed by a "Tectonic Efficiency" factor unique to specific margins. We demonstrate that acoustic amplitude and signal duration are strongly modulated by the incidence angle of P- and S-waves relative to the seafloor slope (conversion efficiency) and the scattering potential of the bathymetric interface. Furthermore, we find that thermal structure and sediment cover significantly damp high-frequency injection into the SOFAR channel at specific subduction zones. By resolving the physics of this coupling, we transform earthquake geophony from noise into a deterministic signal. This framework allows for the inversion of far-field hydroacoustic records to monitor changes in seafloor roughness and near-surface crustal properties, providing a novel remote sensing modality for the ocean floor.